What Are the Results of EPA's Risk Assessment for This Waste When Managed in an Industrial Subtitle D Landfill? Our risk assessment results for the industrial landfill scenario, summarized below in Table III± 31, suggest that the only constituent of concern that required modeling (arsenic) does not pose a substantial present or potential hazard to human health and the environment. We found no arsenic cancer risk in excess of 1E± 08 at the 95th percentile for either adult or child exposure scenarios. Therefore, we believe that this waste when managed in industrial Subtitle D landfills clearly does not warrant listing. For a more complete description of this analysis, see `` Risk Assessment for the Listing Determinations for Inorganic Chemical Manufacturing Wastes'' in the docket for this proposal.

TABLE III± 31.Ð RISK RESULTS FOR FILTERS WITHOUT CHROMIUM AND LEADÐ INDUSTRIAL SUBTITLE D LANDFILL SCENARIO Percentile Arsenic Adult cancer risk Child cancer risk 90th ....................... 1E± 09 8E± 10 95th ....................... 5E± 09 4E± 09 What Are the Results of EPA's Risk Assessment for This Waste When Managed in Municipal Subtitle D Landfills?

Our risk assessment results for the municipal landfill scenario, summarized below in Table III± 32, suggest that the three constituents of concern (antimony, arsenic, and cadmium) do not pose a substantial present or potential hazard to human health and the environment. The hazard quotients, for both the adult and child exposure scenarios, of antimony are less than 0.01 at the 95th percentile, and of cadmium, are less than 0.001 at the 95th percentile. We found no arsenic cancer risk in excess of 1E± 08 at the 95th percentile for either adult or child exposure scenarios. Therefore, we believe that this waste when managed in municipal Subtitle D landfills does not warrant listing. For a more complete description of this analysis, see `` Risk Assessment for the Listing Determinations for Inorganic Chemical Manufacturing Wastes'' in the docket for this proposal.

TABLE III± 32. RISK RESULTS FOR FILTERS WITHOUT CHROMIUM AND LEAD MUNICIPAL SUBTITLE D LANDFILL SCENARIO Percentile Antimony Arsenic Cadmium Adult HQ Child HQ Adult cancer risk Child cancer risk Adult HQ Child HQ 90th .............................................................................................. 5E± 04 1E± 03 5E± 10 4E± 10 3E± 05 6E± 05 95th .............................................................................................. 2E± 03 4E± 03 5E± 09 4E± 09 1E± 04 3E± 04 (5) Wastewaters with chromium that are not recycled back to the process.

How Is This Waste Managed and How Is It Characterized?

Two facilities report generating this wastewater and characterize it as hazardous (D002 and D007). One facility generates 11 MT per year of this wastewater from its on site laboratory testings of the electrolyte in the electrolytic cells, the excess caustic from the hydrogen purification step, and the wastewater from the production of sodium chlorate crystals. The facility stores the wastewater on site in closed tanks before sending it off site to a hazardous waste facility for treatment and disposal. The other facility generates 26,725 MT per year of this wastewater from acid washing filters and anodes to remove buildup of trace metals on the surface. The facility combines the wastewaters with the wastewaters from its titanium dioxide production process and treats the commingled wastewaters in tanks. The treated wastewater is then discharged to on site surface impoundments.

VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00056 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55739 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules What Is EPA's Listing Rationale for This Waste?

One facility identifies the waste as hazardous and manages it in accordance with Subtitle C regulations. We believe that applicable Subtitle C regulations adequately protect against mismanagement, and we did not investigate it further. For the other facility, in Hamilton, Mississippi, we evaluated its combined wastewaters and solids as described above in the `` process sludges with chromium or lead'' category. Today's proposal separately addresses the titanium dioxide wastes that are commingled with this sodium chlorate waste. We propose not to list these wastes. (6) Other wastewaters that do not contain chromium or lead and are not recycled.

How Is This Waste Managed?

There are other wastewaters generated from several points of the process, including process condensate, cooling waters, and ion exchange wastewater. Four facilities reported generating these wastewaters. Two facilities generate process condensates from condensing water vapor from their crystalizers, steam jets, or pad water evaporator. Both facilities store their process condensates in closed tanks. One facility neutralizes the condensate prior to discharging it to an NPDES permitted outfall. The other facility does not treat the condensate, but tests to ensure it meets its State Pollutant Discharge Elimination System permit prior to discharge to a river. One facility generates wastewater from regeneration of the ion exchange unit that is used for purification of the brine. The wastewater is collected in a tank for pH neutralization before it is discharged to a POTW. One facility generates wastewater from cooling tower blowdown, chemical storage tank scrubber pad, hydrogen scrubber pad, and water demineralization area. These wastewaters are piped to its on site NPDES facility to be processed and discharged.

What Is EPA's Listing Rationale for This Waste?

We propose not to list these wastewaters as hazardous. We evaluated these wastewaters that are stored and treated in tanks or in a NPDES permitted facility. We found that these wastewaters do not pose risks warranting regulation during treatment because there are no exposure pathways of concern. The wastewater treatment tanks and the wastewater treatment facility provide sufficient structural integrity and have secondary containment areas to minimize potential releases to groundwater. We are unlikely to find potential air releases from these tanks or the permitted facility as neither volatile contaminants nor airborne particulates are likely to be present in these wastewaters.

12. Sodium Dichromate a. Summary. We have evaluated the wastes, waste management practices, and potential risk exposure pathways associated with the sodium dichromate production processes and propose not to list any wastes from this industry as hazardous wastes under Subtitle C of RCRA. These wastes do not meet the criteria listed under 40 CFR 261.11( a)( 3) for listing a waste as hazardous. They do not pose a substantial present or potential threat to human health or the environment. We have identified no risks of concern associated with the current management of these wastes. Note that certain wastes from this sector are exempt mineral processing wastes which are not within the scope of today's listing proposal. b. Description of the sodium dichromate industry. Two facilities in the United States produce sodium dichromate; one in North Carolina and one in Texas. Both facilities sell their product on the open market in addition to using the material as a feedstock for various manufacturing processes onsite The majority of sodium dichromate is used as a feedstock for the production of chromic acid. It is also used in a wide variety of other uses. For more detailed information concerning this industry, see `` Sodium Dichromate Listing Background Document for the Inorganic Chemical Listing Determination'' in the docket for today's proposal. The two sodium dichromate production facilities use somewhat different manufacturing processes and generate somewhat different wastes. Both facilities use imported chromite ore as their primary feedstock. They dry and grind the ore and feed it into a roasting kiln or hearth with other materials such as soda ash, lime, and sodium hydroxide. The facilities roast, then quench and leach the ore with water, producing sodium chromate solution and solid ore residues. Both facilities return the ore residues to the manufacturing process for further roasting and leaching. The facilities purify the resulting sodium chromate solution product stream by adjusting its pH, treating it with sodium carbonate, and, at the Texas facility, sodium dichromate, and filtering out the resulting solid impurities. The two facilities' processes diverge significantly at this point. At the Texas facility, the sodium chromate solution is either crystallized and sold or processed electrolytically to convert the sodium chromate to sodium dichromate. The electrolytic cell system also produces sodium hydroxide solution which, the facility reports, they sell. The North Carolina facility converts the sodium chromate solution to sodium dichromate through acidification, and the sodium dichromate is then partially evaporated. The acidification process also produces sodium sulfate and lower purity sodium sulfate `` saltcake, '' both of which the facility sells. The sodium dichromate is then either used in liquid form or further evaporated to produce a crystalline product. c. How does the Bevill Exclusion apply to wastes from the sodium dichromate manufacturing processes? The sodium dichromate manufacturing facilities produce two types of residuals which are eligible for the Bevill exemption once disposed: beneficiation wastes (See 40 CFR 261.4( b)( 7)( i)) and mineral processing wastes referred to as treated residue from roasting/ leaching of chromium ore (see 40 CFR 261.4( b)( 7)( ii)( N)). Under the Bevill exemption, any wastes generated from beneficiation of ores, such as crushing, mixing, and milling, are Bevill exempt. Both facilities beneficiate ore by drying and grinding chromite ore and mixing the ore with other ingredients prior to placement in the roasting kiln and generate air pollution control dusts from these processes. However, the residuals from these processes, which would be Bevill exempt, are not disposed of but rather captured and returned to the process from which they originated for chromium recovery. In terms of when beneficiation stops and mineral processing starts, EPA determined in 1989 that the roasting/ leaching of chromium ore to produce sodium chromate is mineral processing rather than beneficiation. 54 FR 36592 (September 1, 1989) stated:

`` A specific exception to the above categorization system applies when the roasting/ leaching sequence produces a final or intermediate product that does not undergo further beneficiation or processing steps (e. g., the leach liquor serves as an input to inorganic chemical manufacturing). In this type of situation, the Agency believes that the operation is most appropriately considered a processing, rather than a beneficiation, operation. In the context of this rulemaking, one candidate Bevill waste (roast/ leach ore residue from primary chrome ore processing) is affected by this distinction; EPA believes that this material is clearly a waste from VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00057 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55740 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules processing, rather than beneficiation, of an ore or mineral. ''

The wastes generated after mineral processing begins are not Bevill exempt unless and until they become treated residue from the roasting/ leaching of chromium ore as specified in 40 CFR 261.4( b)( 7)( ii)( N). The wastes eligible for the exclusion, once they are treated, are referred to later in this preamble and associated background documents as spent post leach, spent postneutralization ore residue, and waste heat boiler washout. These wastes are generated from roasting and leaching (including precipitation and filtration to remove the resulting impurities) of chromite ore. Both facilities generate these wastes, treat them in on site treatment systems, and dispose of them in on site surface impoundments. Note that in the January 23, 1990 Federal Register, EPA stated that the Bevill exemption applies to `` only those solids which are entrained in the slurry as it leaves the treatment facility and which settle out in disposal impoundments. '' Wastes generated following the roasting/ leaching processes to produce sodium chromate for sodium dichromate production are not Bevill exempt because they are not from the roasting/ leaching of chromite ore. Wastes generated at these facilities that are not Bevill exempt include sodium chromate evaporation unit wastewaters (Texas facility), sodium dichromate evaporation unit wastewaters (Texas facility), caustic filter sludge (Texas facility), and salt cake drier scrubber wastewater (North Carolina facility). As described below, both facilities in the sodium dichromate manufacturing industry commingle wastes during the treatment process, ultimately producing a commingled treatment residue which is a mixture of Bevill exempt wastes and wastes which do not qualify for the Bevill exemption. In general, the majority of these mixtures consist of Bevill exempt wastes. Mixing Bevill exempt wastes with non hazardous wastes does not affect the regulatory status of the Bevill wastes, but it also does not conversely extend Bevill exempt status to the non hazardous wastes in the mixture (see 63 FR 28595). Therefore, in this rulemaking we have addressed that portion of the treatment residue mixture which derives from wastes which do not qualify for the Bevill exemption. In addition, in general, if any of the non Bevill wastes exhibit a characteristic and is mixed with the Bevill wastes, the entire mixture may become subject to Subtitle C based on the Bevill mixture rule (See 40 CFR 261.3( a)( 2)). d. What kinds of wastes are generated by these processes? Table III± 33 below briefly lists the facility reported residuals from the sodium dichromate manufacturing industry, total industry residual volumes generated in 1998, RCRA hazard codes, and residual management practices.

TABLE III± 33.Ð SODIUM DICHROMATE PRODUCTION RESIDUALS Waste category 1998 volumes (MT) Reported waste codes Sequential management practices North Carolina Facility Residuals commingled in spent ore residue treatment unit 1 : Spent post neutralization ore residue (Bevill exempt after treatment). 146,937 ............ D007 ................. Sent on site to tank based spent ore residue treatment unit with NPDES permitted discharge. Spent post leach ore residue (Bevill exempt after treatment). 25,930 .............. D007 ................. Sent on site to tank based spent ore residue treatment unit with NPDES permitted discharge. Saltcake drier scrubber wastewater ................... 13,851 .............. D007 ................. Sent on site to tank based spent ore residue treatment unit with NPDES permitted discharge. Waste heat boiler washout (Bevill exempt after treatment). 70 ..................... D007 ................. Sent on site to tank based spent ore residue treatment unit with NPDES permitted discharge. Residuals disposed of on site: Reduced chromium treatment residues commingled Bevill exempt and non exempt residues 129,503 ............ None ................. Sent to on site industrial Subtitle D disposal unit.

Commingled treated wastewaters (commingled Bevill exempt and non exempt residues). 920,161 ............ None ................. Passed through sand filters then discharged directly under NPDES permit or sent to on site industrial Subtitle D disposal unit. Residuals disposed of off site: Chromium contaminated filters, membranes, and other plant waste. 67 ..................... D007 ................. Stored in on site roll off bin before off site treatment and landfill disposal at Subtitle C facility. Spent sand filter sands (commingled Bevill exempt and non exempt residues). 21.7 (1997) ....... None ................. Stored in on site drums or roll off bins before disposal in off site industrial Subtitle D landfill.

Texas Facility Residuals commingled in spent ore residue treatment unit: Spent post neutralization ore residue (Bevill exempt after treatment). 60,000 .............. D007 ................. Sent to on site, covered, tank based, spent ore residue treatment unit with NPDES permitted discharge Caustic filter sludge ............................................ 80 ..................... D002 ................. Sent to on site, covered, tank based, spent ore residue treatment unit with NPDES permitted discharge Residuals commingled in wastewater treatment unit 2 : Sodium dichromate evaporation unit wastewater ~2,500 ............... None ................. Sent to on site, tank based wastewater treatment unit with NPDES permitted discharge. Sodium chromate evaporation unit wastewater ~300 .................. None ................. Sent to on site, tank based wastewater treatment unit with NPDES permitted discharge.

VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00058 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55741 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules TABLE III± 33.Ð SODIUM DICHROMATE PRODUCTION RESIDUALSÐ Continued Waste category 1998 volumes (MT) Reported waste codes Sequential management practices Residuals disposed of on site: Reduced chromium treatment residues from spent ore residue treatment unit (commingled Bevill exempt and non exempt residues). 60,000 .............. None ................. Sent to on site industrial Subtitle D, double lined surface impoundment for dewatering and disposal Impoundment has NPDES permitted outflow Reduced chromium treatment residues from wastewater treatment unit (commingled Bevill exempt and non exempt residues). ~30,000 (1999) None ................. Sent to on site industrial Subtitle D, double lined surface impoundment for dewatering and disposal Impoundment has NPDES permitted outflow Commingled treated wastewaters (commingled Bevill exempt and non exempt residues). 186,515 ............ None ................. Sent to on site industrial Subtitle D surface impoundment filtered through sand filters, then discharged directly under NPDES permit. Residuals disposed of off site: Process filters and membranes, baghouse bags, chromium contaminated empty containers and other plant wastes. 24 ..................... D007 ................. Stored in on site roll off box before treatment and landfill disposal at Subtitle C facility.

Spent sand filter sands (commingled Bevill exempt and non exempt wastes). ~2 MT once every two years. None ................. Placed in on site non hazardous soil waste bin and then disposed of in off site industrial Subtitle D landfill.

1 Remediation well water, cooling tower blowdown, and stormwater are also treated in this unit. These materials are beyond the scope of this listing determination. 2 Stormwater and remediation well water are also treated in this unit. Contaminated media are not within the scope of this listing determination.

In addition to these wastes, the sodium dichromate manufacturers produce residuals which are either piped back to the production process or sold for use in other manufacturing processes. Air pollution control devices capture materials that are returned to their units of origin or to other manufacturing process units. At the North Carolina facility, ore residue washwaters and calcium carbonate residuals are returned to the production process for chromium recovery. Chromium bearing solution from the saltcake purification process is directly reused in the roasted ore quench, leach and filter process. At the Texas facility, chromium containing residuals from scrubbers on the hearth and on the sodium chromate and dichromate evaporation/ crystallization units are reused in the hearth kiln and quench tank units. Because these materials are reused in production units in ways that present low potential for release, and because we evaluated process wastes generated after the secondary material is reinserted into the process, we do not believe that these materials present significant risk. The North Carolina facility also produces for sale sodium sulfate `` saltcake'' and purified sodium sulfate anhydrous from the sodium dichromate production process. The Texas facility sells hydroxide solution from their sodium dichromate production process. We found no information indicating that the facilities which purchase these materials burn them for energy recovery or incorporate them into products that are used on the land (use constituting disposal). Since these processes are outside the scope of the consent decree we did not evaluate any of these materials further. We did however, evaluate some residuals produced onsite at the North Carolina and Texas facilities during the preparation of the materials that are sold. See the discussions in the sections below of salt cake drier scrubber water and caustic filter sludge. Finally, the North Carolina facility produces some off specification product, which it reinserts into the sodium dichromate manufacturing process. Off specification product, when reinserted without reclamation into the process from where it originated, is not a solid waste. See the `` Sodium Dichromate Listing Background Document for the Inorganic Chemical Listing Determination'' for more details on these residuals. e. Waste characterization and Agency evaluation. Chromium is the primary constituent of concern in the wastes from both facilities. Chromium occurs in several production wastes at high levels, in some cases exceeding the TC level (5.0 mg/ L) in TCLP leachate samples. These wastes are coded as hazardous (D007). Both facilities treat some of their D007 wastes on site and send other D007 wastes off site for treatment and disposal at permitted Subtitle C hazardous waste facilities. Various other wastes which fall below D007 regulatory levels are either treated on site or sent off site for disposal. No other constituents of concern were reported to be present in the wastes at levels of concern. We propose not to list any of the wastes from the sodium dichromate manufacturing industry. Many wastes from this industry are Bevill exempt once treated, and therefore not within the scope of the consent decree requirements. Other wastes are characteristically hazardous and are managed at permitted Subtitle C facilities off site. Some wastes did not exhibit constituents at levels of concern for purposes of a listing given the nature of their management and disposal. The main constituent of concern, chromium, is treated on site for many of the wastes. Several wastes from each of the facilities are disposed of in a treated form, rather than an as generated form. In general, we focused our evaluation on the treated form of wastes because it is ultimately only the treated wastes which are disposed. The sections below describe how wastes are generated and managed at the two sodium dichromate manufacturing facilities, each with its own production process, and our rationale for proposing not to list the wastes. We solicit comments on the proposed listing decisions described below. (1) North Carolina Facility. (a) Residuals Commingled in Spent Ore Residue Treatment Unit. The North Carolina facility commingles and treats several characteristic wastes from sodium dichromate manufacturing in an on site, tank based treatment unit at the North Carolina facility. These four sodium dichromate manufacturing wastes are: ÐWaste heat boiler washout, which are accumulated solids from the internal VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00059 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55742 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules components of the roasting kiln waste heat boilers (Bevill exempt after treatment) ÐSpent post leach ore residue (Bevill exempt after treatment) ÐSpent post neutralization ore residue (Bevill exempt after treatment) ÐSaltcake drier scrubber wastewater We consider the saltcake drier scrubber wastewater to be a wastestream associated with the production of sodium sulfate at the North Carolina facility, rather than a sodium dichromate manufacturing waste. Nevertheless, we chose to exercise our discretion to evaluate the risk posed by the treated and untreated form of this residue. As explained below, we did not find risks warranting listing. All four wastes catalogued above go directly from their points of generation to the on site spent ore residue treatment unit without intervening storage. The facility treats non contact cooling tower blowdown, remediation well water, and stormwater in the treatment unit as well. The four manufacturing wastes comprise approximately 60± 65% by volume of the wastes entering the treatment unit. The entire treatment process takes place in a series of tanks with secondary containment. Treatment consists of conversion of hexavalent chromium in the wastes to trivalent chromium with pickle liquor (ferrous chloride reducing agent). Trivalent chromium is a generally less toxic and less soluble form of chromium. Wastes containing a high percentage of solids (waste heat boiler washout, spent post leach ore residue, and spent post neutralization ore residue) are also neutralized with lime slurry in order to increase precipitation of trivalent chromium compounds out of solution. The treatment sludge is then thickened in a series of clarifier tanks. Limestone is added to the thickened sludge to further stabilize chromium and other metals. All of the tanks in the treatment train have secondary containment and some are covered. Treated wastewaters, after passing through sand filters, discharge from the treatment unit under an NPDES permit or travel with the treated solid residues to the on site industrial Subtitle D disposal unit (see section III. F. 12. e( 1)( b) ii below regarding the commingled treated wastewaters). The Bevill exemption applies to the waste heat boiler washout, spent postleach ore residue, and spent postneutralization ore residue only after the wastes are treated. We evaluated the potential for releases from the treatment tanks. We assumed that the tanks were intact structures with minimal potential for releases to groundwater. We do not anticipate significant air releases because the wastes do not contain volatile constituents and have high moisture content. Also, some of the tanks have covers which further reduce the possibility of air releases. We are proposing not to list any of these four wastestreams undergoing treatment in this tank system. (b) Residuals Disposed of On Site. (i) Commingled reduced chromium treatment residues. The reduced chromium sludge from the on site spent ore residue treatment unit is slurried and conveyed directly from the treatment unit to one of two on site industrial Subtitle D disposal units (former limestone quarries). Of the several treatment residues contributing to the final commingled treatment residue, only one falls within the scope of today's listing proposal; residue from treatment of saltcake drier scrubber wastewater (we believe this is not within scope of the consent decree but are evaluating it in this rule making). Residues from the treatment of waste heat boiler washout, spent post leach ore residue, and spent postneutralization ore residue are Bevill exempt mineral processing wastes beyond the scope of today's listing proposal (see Section III. F. 12( c)). Stormwater and remediation well water are contaminated media whose treatment residues we also consider to be beyond the scope of the consent decree (see section III. B of today's proposal). Therefore, we do not consider the risks posed by these treatment residues. According to information the facility submitted in their RCRA Section 3007 Survey response, the only potential constituent of concern in the untreated saltcake drier scrubber wastewater is chromium, detected at a level of 6 mg/ L. Therefore, chromium is the only constituent we considered when assessing the level of risk from saltcake drier scrubber wastewater treatment residues. Of the total mass of chromium found in the commingled reduced chromium treatment residues, the saltcake drier scrubber wastewater contributes approximately 0.001%. This estimate is based on calculations using information the North Carolina facility provided to us on chromium contents and tonnages of waste exiting the spent ore residue treatment unit. Both the information and the calculations are further detailed in the `` Sodium Dichromate Listing Background Document for the Inorganic Chemical Listing Determination. '' We found the treatment residues from saltcake drier scrubber solution to pose no significant risks to groundwater. After treatment for hexavalent chromium, the commingled reduced chromium treatment residues from 1998 showed weekly TCLP analysis levels of leachable chromium in the range of 0.01± 1.00 mg/ L for composite samples and <0.01± 0.76 mg/ L for grab samples. Assuming that the saltcake drier scrubber wastewater's percent contribution to total chromium in the commingled residues is equal to its percent contribution to total chromium leaching from the commingled residues (0.001%), the saltcake scrubber solution was responsible for TCLP leaching levels of 1´10 ´7 to 1´10 ´5 mg/ L for composite samples and <3´10 ´7 to 2.28´10 ´5 mg/ L for grab samples. The HBL for ingestion of hexavalent chromium is 0.047 mg/ L and 23 mg/ L for trivalent chromium. The AWQC for hexavalent chromium is 0.011 mg/ L and 0.74 mg/ L for trivalent chromium. Even at a maximum leaching level of 1´10 ´5 mg/ L, the leachable chromium contribution of the saltcake drier scrubber wastewater indicates a very low level of risk to groundwater. The treated wastes are disposed in an uncovered disposal unit that resembles a surface impoundment. However, given the inorganic, nonvolatile nature of the treated wastes, we do not believe they pose a risk through airborne pathways. Given the low level of chromium leaching attributable to the one treatment residue within the scope of today's listing proposal and the lack of volatile constituents of concern, we propose not to list residues deriving from the treatment of saltcake drier scrubber wastewater. (ii) Commingled treated wastewaters. The spent ore residue treatment unit described in the sections above has clarifier units which discharge a wastewater stream to tank based sand filters. After passing through sand filters, the treated wastewaters discharge through an NPDES permitted outfall. These wastewaters are a mixture of nonBevill exempt and Bevill exempt treatment residues, and other treatment residues beyond the scope of the consent decree. The solids suspended in the wastewaters are a mixture of Bevill exempt and non Bevill exempt treatment residues. The liquid portion, the majority of this wastestream, is a mixture of non Bevill exempt residues, some of which are within the scope of this listing determination, and some of which derive from treatment of contaminated media and are therefore not with the scope of this listing determination. We did not find any VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00060 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55743 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules 42 http:// www. epa. gov/ enviro/ index_java. html. 43 As described in Section III. E. 3, we used engineering judgment to screen out constituents with concentrations within a factor of two of the HBL. significant potential for releases from the tanks. (We assess spent filter media from the sand filters separately in section III. F. 12. e( 1)( c) ii below.) We concluded that the NPDES discharge is exempt from RCRA regulation. A portion of the commingled treated wastewaters remains with the commingled reduced chromium treatment residues discharged for disposal to the facility's on site industrial Subtitle D disposal units. The facility also adds water to this mixture from either the nearby Northeast Cape Fear River or the quarry in order to help slurry and convey the residues to the disposal units. The liquids which separate from the settled treatment residues in the facility's disposal units are not Bevill exempt wastes (see Section III. F. 12. c). Because these liquids derive from the same treatment unit from which the NPDES discharged wastewaters discussed above derive, we are assuming their chemical composition is very similar to that of the wastewaters discharged under the facility's NPDES permit. We used NPDES permit discharge data, available to the public from the EPA's Envirofacts database, 42 as a surrogate for characterization of this wastewater (see discussion of SPLP filtrate in Section III. E. 3). The exposure pathway of concern is the groundwater underlying the facility's disposal units and consumption of the groundwater as drinking water. According to the North Carolina facility's NPDES permit, the facility is allowed to discharge 0.31 pounds per day of hexavalent chromium to the Northeast Cape Fear River. Given the amount of treated wastewater reported to be discharged in 1998 and using the permit loading as an upperbound value, we estimate that the facility produced an NPDES effluent with an average hexavalent chromium concentration of 0.056 mg/ L. This concentration is less than twice the HBL for hexavalent chromium (0.047 mg/ L). 43 However, according to NPDES compliance monitoring data for the facility, no hexavalent chromium was detected in the facility's NPDES effluent in 1998. Therefore, it is likely that the actual concentration of hexavalent chromium in the facility's commingled treated wastewaters is less than the concentration the facility is permitted to release. According to the North Carolina facility's NPDES permit, the facility is also permitted to discharge 2.72 pounds of combined hexavalent and trivalent chromium per day. Making the conservative assumption that all 2.72 pounds of chromium are trivalent chromium and given the amount of treated wastewater discharged in 1998, we estimated that the facility produced an NPDES effluent with an average chromium concentration of 0.49 mg/ L, which is less than 23 mg/ L, the HBL for trivalent chromium. Actual reported levels of total chromium release were well below the permit limit. Given that the levels of chromium present in the on site disposal unit liquids are less than or within a factor of two of the HBLs, we do not believe they pose a risk to human health or the environment through groundwater underlying the disposal unit that supports listing these wastewaters as a hazardous waste. (c) Residuals Disposed of Off Site. (i) Chromium contaminated filters, membranes, and other plant wastes. This waste category from the North Carolina facility includes spent filters, membranes, and various other plant wastes which exceed the TC level for chromium. The wastes are stored in a closed roll off bin on site before being sent off site to a permitted Subtitle C facility for treatment and disposal in a landfill. We feel that applicable Subtitle C regulations adequately prevent mismanagement and therefore propose not to list these wastes. (ii) Spent sand filter sands. The North Carolina facility generates waste sand material from the spent ore residue treatment unit sand filters which filter treated wastewaters prior to their NPDES permitted discharge. The purpose of the sand filters is to remove any residual solids which the treatment unit clarifiers fail to remove upstream in the treatment process. Since the clarifiers capture the majority of the solids, the sand filters capture smaller amounts of treatment residue. The most recent disposal of sand from the filters took place in 1997. The facility stores the spent sand in closed drums or rolloff bins on site before disposing of them in an off site industrial Subtitle D solid waste landfill. According to information submitted to EPA by the North Carolina facility, this residue does not exhibit any constituent above the TC level according to TCLP leachate analysis. The only detected constituent of potential concern was chromium, at a level of 0.2 mg/ L. Residue from treatment of saltcake drier scrubber wastewater is the only residue contributing to the chromium levels in the spent sand filters which also falls within the scope of today's listing proposal. All other wastes are either Bevill exempt wastes or treatment residues from contaminated media or non contact cooling water, none of which falls within the scope of the consent decree. As discussed in section III. F. 12. e( 1)( b), the saltcake drier scrubber solution contributes approximately 0.001% of the total chromium exiting the spent ore residue treatment unit. Assuming that a waste's percent contribution to total chromium exiting the treatment unit is equal to its percent contribution to total chromium leaching from waste exiting the unit, the figures above indicate a TCLP leaching level of 2´10 ´6 mg/ L due to the contributions of the saltcake drier scrubber wastewater. The HBL for hexavalent chromium is 0.047 mg/ L and 23 mg/ L for trivalent chromium. The AWQC for hexavalent chromium is 0.011 mg/ L and 0.74 mg/ L for trivalent chromium. At a level of 2´10 ´6 mg/ L, the leachable chromium contribution of the saltcake drier scrubber wastewater presents a very low level of risk. The waste is inorganic in nature and therefore we do not expect it to contain volatile constituents of concern. In addition, the waste is stored before disposal in a closed container. We do not believe, therefore, that this waste poses a risk via airborne pathways. Given the low level of risk posed by the saltcake drier scrubber wastewater treatment residue contribution to leachable chromium levels in the spent sand filters and its nonvolatile nature, we propose not to list this waste. (2) Texas Facility. (a) Residuals Commingled in On Site Treatment Units. At the Texas facility, commingling and treatment of four untreated wastes takes place in two different on site, tank based treatment units. The treatment residues from the two treatment units are then codisposed in an on site, Subtitle D treatment surface impoundment. The first treatment unit, the spent ore residue treatment unit, treats the following two sodium dichromate manufacturing wastestreams: Ðspent post neutralization ore residue (Bevill exempt after treatment) Ðcaustic filter sludge from filtration of sodium hydroxide We consider caustic filter sludge to be a wastestream associated with the production of sodium hydroxide rather than a sodium dichromate manufacturing waste. Nevertheless, we chose to exercise our discretion to VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00061 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55744 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules evaluate the risk posed by the treated and untreated forms of this residue. The spent ore residue treatment unit treatment tanks have both secondary containment and covers. Treatment consists of converting the hexavalent chromium in the units to trivalent chromium. Trivalent chromium is typically a less soluble and less toxic form of chromium. Ore residue wastes are not Bevill exempt and therefore beyond the scope of the consent decree until treatment occurs. Therefore, we have evaluated the potential for releases from these treatment tanks. We assume the tanks are intact structures with minimal potential for releases to groundwater. We believe the covers on the tanks reduce the potential for air releases. Also, the wastes do not contain volatile constituents. The second treatment unit, the wastewater treatment unit, treats the following two sodium dichromate manufacturing wastestreams: Ðsodium chromate evaporation unit wastewaters Ðsodium dichromate evaporation unit wastewaters The wastewater treatment unit also treats remediation well water and stormwater, two types of contaminated media which are outside the scope of the consent decree. The two wastewaters within the scope of the consent decree make up approximately 9% of the total volume of the wastes entering the treatment unit. The facility converts hexavalent chromium to less toxic trivalent chromium during this treatment process. The tanks do not have covers. We evaluated the tanks for potential releases to the environment. We assumed the tank structures were intact and therefore posed minimal potential for releases to groundwater. Since the wastewaters contain no volatile constituents, we found no significant potential for air releases. We are proposing not to list the wastes in these treatment tanks. The facility disposes the treatment materials from the two tank systems described above in an on site surface impoundment. We describe that surface impoundment in the next section. (b) Residuals Disposed of On Site. (i) Commingled reduced chromium treatment residues. The treatment residues from the two treatment tank systems described in the section above are piped directly to the facility's onsite double lined, Subtitle D surface impoundment for co disposal and dewatering. Of the several treatment residues contributing to the mass of reduced chromium treatment residue disposed of in the Subtitle D surface impoundment at the Texas facility, only three fall within the scope of today's listing proposal: residue from treatment of caustic filter sludge, residue from treatment of sodium chromate evaporation unit wastewaters, and residue from treatment of sodium dichromate evaporation unit wastewaters. Residues from the treatment of post neutralization spent ore residue are Bevill exempt mineral processing wastes beyond the scope of today's listing proposal (see section III. F. 12. c). Stormwater and remediation well water are contaminated media whose treatment residues we also consider to be beyond the scope of the consent decree (see section III. B). Therefore, we do not consider the risks posed by these residues. According to information the facility submitted in their RCRA Section 3007 Survey response, the only potential constituent of concern in the untreated sodium dichromate evaporation unit wastewater, sodium dichromate evaporation unit wastewaters, and the caustic filter sludge is chromium, measured at a level of 0.5 mg/ L, 0.5 mg/ L and 20 mg/ kg, respectively. Therefore, chromium is the only constituent we considered when assessing the level of risk from sodium dichromate evaporation unit wastewater, sodium chromate evaporation unit wastewater, and caustic filter sludge treatment residues. Of the total chromium contributed to the co disposed reduced chromium treatment residue by all incoming wastes, the sodium dichromate evaporation unit wastewater, sodium chromate evaporation unit wastewater, and the caustic filter sludge contribute 5´10 ±5 percent by weight. This estimate is based on calculations using information the Texas facility provided to us on chromium contents and tonnages of wastes entering the spent ore residue treatment unit and the wastewater treatment unit on site. Both the information and the calculations are described further in the `` Sodium Dichromate Listing Background Document for the Inorganic Chemical Listing Determination. '' The facility did not provide us with TCLP, SPLP, or total constituent analyses for the co disposed reduced chromium treatment residues. However, the facility did report to us that reduced chromium treatment residues do not exceed the TC level of 5.0 mg/ L according to TCLP analysis. In addition, the facility reported that for the time period between October 1, 1998 and December 31, 1998, weekly samples of reduced chromium treatment residues from the spent ore residue treatment unit analyzed with a facility modified version of the TCLP ranged between 0.16 and 1.75 mg/ L chromium (see `` Sodium Dichromate Listing Background Document for the Inorganic Chemical Listing Determination'' for details). Therefore, conservatively assuming a maximum TCLP chromium leaching level of 4.9 mg/ L and assuming that the percent contribution by the three wastes to total chromium entering the treatment units is equal to their percent contribution to total chromium leaching from treatment residues exiting the treatment units, the caustic filter sludge, sodium chromate evaporation unit wastewaters, and sodium dichromate evaporation unit wastewaters were responsible for TCLP chromium leaching levels of 2.45´10 ±6 mg/ L. The HBL for hexavalent chromium is 0.047 mg/ L and 23 mg/ L for trivalent chromium. The AWQC for hexavalent chromium is 0.011 mg/ L and 0.74 mg/ L for trivalent chromium. At a leaching level of 2.45´10 ±6 mg/ L, the leachable chromium contribution of the caustic filter sludge, sodium chromate evaporation unit wastewaters, and the sodium dichromate evaporation unit wastewaters indicates a very low level of risk to groundwater from potential releases from the surface impoundment. The waste is metallic and inorganic in nature and therefore we do not expect it to contain volatile constituents of concern. We do not believe, therefore, that this waste poses a risk via airborne pathways. Given the low level of chromium leachate deriving from the three treatment residues within the scope of today's listing proposal and placed into the surface impoundments, we propose not to list residues deriving from the treatment of caustic filter sludge, sodium chromate evaporation unit wastewater, and sodium dichromate evaporation unit wastewater. (ii) Commingled treated wastewaters. Treated wastewaters commingled with the commingled reduced chromium treatment residues separate from these solid residues in the Texas facility's surface impoundment disposal unit. These liquids are not Bevill exempt wastes (see Section III. F. 12.3). The solids suspended in the wastewaters are a mixture of Bevill exempt and nonBevill exempt treatment residues. The liquid portion, the majority of this wastestream, is a mixture of non Bevill exempt residues, some of which are within the scope of this listing determination, and some of which derive from treatment of contaminated VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00062 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55745 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules 44 http:// www. epa. gov/ enviro/ index_java. html media and are therefore not within the scope of this listing determination. The commingled treated wastewaters discharge from the surface impoundment through an NPDESpermitted outfall after passing through sand filters to remove residual solids (see discussion below in Section III. F. 12. e( 2)( c)( ii). We therefore assume that the chemical composition of the treated wastewaters in the surface impoundment is very similar to that of the NPDES permitted discharge. We used NPDES permit discharge data, available to the public from the EPA's Envirofacts database, 44 as a surrogate for characterization of this wastewater (see discussion of SPLP filtrate in Section III. E. 3). The exposure pathway of concern is the groundwater underlying the facility's disposal units and consumption of the groundwater as drinking water. According to the Texas facility's 1998 NPDES monitoring data, the facility discharged an average of 0.018 pounds of hexavalent chromium each day through their internal NPDES outfall. Given the amount of treated wastewater the facility reported as discharge from the surface impoundment in 1998, we estimate that the facility produced an NPDES effluent with an average hexavalent chromium concentration of 0.016 mg/ L. This concentration is less than the HBL for hexavalent chromium (0.047 mg/ L). According to the Texas facility's NPDES monitoring data for 1998, the facility released an average of 0.46 pounds of combined hexavalent and trivalent chromium per day. Making the conservative assumption that all 0.46 pounds of chromium are trivalent chromium and given the amount of treated wastewater discharged in 1998, we estimated that the facility produced an NPDES effluent with an average chromium concentration of 0.41 mg/ L, which is less than 23 mg/ L, the HBL for trivalent chromium. Wastes in the surface impoundment dewater and the resulting wastewaters pass out of the surface impoundment and through tank based sand filters. From the sand filters, the treated wastewaters then discharge through an NPDES permitted outfall. These wastewaters are a mixture of non Bevill exempt and Bevill exempt treatment residues, and other treatment residues beyond the scope of the consent decree. We did not find any significant potential for releases from the sand filter tanks. (We assess spent filter media from the sand filters separately in Section III. F. 12. e( 2)( c)( ii) We concluded that the NPDES discharge is exempt from RCRA regulation. (c) Residuals Disposed of Off Site. (i) Process filters and membranes, baghouse bags, chromium contaminated empty containers, and other plant wastes. The Texas facility reports in their RCRA Section 3007 Survey response that process filters and membranes and baghouse bags from their facility exceed the TC level for chromium and are coded D007. The facility also reports that they produce empty containers and other plant wastes contaminated with chromium which are also coded D007. The facility stores these hazardous wastes in a closed rolloff bin on site before sending them off site to a permitted Subtitle C hazardous waste facility for treatment and landfill disposal. These wastes are sufficiently managed under current RCRA Subtitle C regulations and therefore we propose not to list these wastes. (ii) Spent sand filter sands. The Texas facility generates waste sand material from the sand filters which filter treated wastewaters prior to their NPDES permitted discharge from the facility's on site surface impoundment. The purpose of the sand filters is to remove any residual solids which fail to settle in the surface impoundment. Since the majority of the solids settle in the surface impoundment, the sand filters captures smaller amounts of reduced chromium treatment residue. Approximately 2 MT of spent sand filter sand is disposed of every two years. The facility stores the spent sand in nonhazardous soil bins on site before disposing of it at an off site Subtitle D industrial landfill. According to the Texas facility, this residue does not exhibit any constituent above the TC level according to TCLP leachate analysis. Residues from treatment of caustic filter sludge, sodium chromate evaporation unit wastewaters, and sodium dichromate evaporation unit wastewaters are the only residues contributing to the potential constituent of concern levels in the spent sand filters which also fall within the scope of today's listing proposal. All other wastes are either Bevill exempt wastes or treatment residues from contaminated media, neither of which falls within the scope of the consent decree. Chromium was the only potential constituent of concern detected in the sodium chromate evaporation unit wastewaters, sodium dichromate evaporation unit wastewaters and the caustic filter sludge, and is therefore the only potential constituent of concern we considered in the spent sand filter sands. As discussed in the section on commingled reduced chromium treatment residues, the residues contribute 5´10 ±5 percent of the total chromium mass entering the spent ore residue treatment unit. Assuming a maximum TCLP chromium leaching level of 4.9 mg/ L, and assuming that the percent contribution to total chromium by the three wastes entering the treatment units is equal to their percent contribution to total chromium leaching from treatment residues exiting the treatment units, the caustic filter sludge, sodium chromate evaporation wastewaters, and sodium dichromate evaporation unit wastewaters were responsible for TCLP chromium leaching levels of 2.4´10 ±6 mg/ L. The HBL for hexavalent chromium is 0.047 mg/ L and 23 mg/ L for trivalent chromium. The AWQC for hexavalent chromium is 0.011 mg/ L and 0.74 mg/ L for trivalent chromium. At a level of 2.4´10 ±6 mg/ L, the leachable chromium contribution of the sodium dichromate evaporation unit wastewater, the sodium chromate evaporation wastewaters, and the caustic filter sludge presents a very low level of risk. The waste is metallic and inorganic in nature, and therefore we do not expect it to contain volatile constituents of concern. We do not believe, therefore, that this waste poses a risk via airborne pathways. Given the low level of risk posed by the contribution of constituents in the spent filter sands attributable to caustic filter sludge, sodium chromate evaporation unit wastewaters, and sodium dichromate evaporation unit wastewater treatment residue, the absence of volatile constituents of concern, and the relatively small volume of the total waste, we propose not to list this waste.

13. Sodium Phosphate From Wet Process Phosphoric Acid a. Summary. We propose not to list any wastes from the production of sodium phosphate from wet process phosphoric acid as hazardous under subtitle C of RCRA. Many of these secondary materials are piped back into the production process; other wastes are discharged to a permitted publiclyowned treatment works (POTW). Other materials are sent to Subtitle D industrial landfills. After an analysis of waste management practices and potential exposure pathways, we conclude that there are no risk pathways of concern. These wastes do not meet the criteria set out at 40 CFR 261.11( a)( 3) for listing as hazardous. b. Description of the sodium phosphate industry. Sodium phosphate is the more general chemical name for VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00063 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55746 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules 45 In this preamble, we often refer to sodium phosphate produced for the food industry as `` food grade. '' The Food and Drug Administration (FDA), Department of Health and Human Services, refers to the various sodium phosphates used in the food industry as `` substances generally recognized as safe'' (GRAS). The FDA states that: `` This substance is generally recognized as safe when used as in accordance with good manufacturing practice. '' (See, for example, 21 CFR 182.1778, 182.6290, 182.6778, and 182.8778.) In deciding whether a food additive should be approved, the FDA considers the composition and properties of the substance, the amount likely to be consumed, its probable long term effects and various safety factors. a wide variety of salts produced from the neutralization of phosphoric acid. Some of the salts produced by the facilities in this industry are monosodium dihydrogen phosphate (H2NaPO4), disodium monohydrogen phosphate (HNa2PO4), trisodium phosphate (Na3PO4), sodium hexametaphosphate (Na4P 4O12), and sodium tripolyphosphate (Na5P3O10). The various phosphate salts produced are used for a wide variety of purposes, ranging from a water soluble solid acid and pH buffer for acidic cleaners to products manufactured for the food industry 45 . Sodium phosphate is produced from wet process phosphoric acid by two manufacturing companies at four locations in the United States. For more detailed information concerning this industry, see `` Sodium Phosphate Listing Background Document for the Inorganic Chemical Listing Determination'' in the docket for today's proposal. The processes for monosodium dihydrogen phosphate, disodium monohydrogen phosphate, and trisodium phosphate are similar except for the ratio of phosphoric acid to soda ash at the reactor stage and the type, size and construction of the crystallizing and drying equipment. The raw materials are water, phosphoric acid, soda ash, and caustic. The purified phosphoric acid is manufactured elsewhere through the wet acid purification method and is food grade. The process starts with a reaction between phosphoric acid, soda ash, and caustic. The solution is used to make the monosodium dihydrogen phosphate, which passes through a polishing filter before shipment to customers. The sodium to phosphorus ratio of the solution is adjusted with caustic to make disodium monohydrogen phosphate and trisodium phosphate. These solutions are filtered and then crystallized. The crystals from each process pass through dryers. The finished product is packaged or shipped in bulk. Sodium hexametaphosphate and sodium tripolyphosphate are also produced from food grade phosphoric acid and soda ash. Both processes start with a reaction between phosphoric acid and soda ash. For the sodium hexametaphosphate process, the product is fed to a furnace which melts the mix and converts it to sodium hexametaphosphate. For the sodium tripolyphosphate process, the reaction discharge is dried and heat treated in a converter to convert it to sodium tripolyphosphate. In both processes, the product is cooled, sized, stored, and packaged for shipment. c. What kinds of wastes are generated by these processes? A brief description of the waste categories, how they are generated, their volumes across the industry, and how they are managed is presented in Table III± 34:

TABLE III± 34.Ð SODIUM PHOSPHATE PRODUCTION WASTES Waste category 1998 Volume (MT) Source Management practices Filter press cakes .................................... 120 ................... Product polishing ................................... Recycled or Subtitle D landfill. Mix area filters ......................................... 0.009 ................ Product polishing ................................... Subtitle D landfill. Dust collector filter bags .......................... 2.1 .................... Drying and grinding processes .............. Subtitle D landfill. Scrubber waters and effluents ................ 32 ..................... Process vapor scrubbers ....................... POTW or recycled. Product dust collected ............................. Not reported ..... Drying and grinding processes .............. Recycled or Subtitle D landfill. Off specification product .......................... 771 ................... Off specification grinding or customer returns. Recycled or Subtitle D landfill.

For those scenarios where secondary materials (filter press cakes, product dust, off specification product, and scrubber water) are piped back to the production process, we could identify no potential route for significant exposure prior to reuse. In addition, we evaluated all wastes generated after reinsertion of these materials into the process and we do not believe that these secondary materials present significant threats. Also, off specification product, when reinserted without reclamation into the process from where it originated, is not a solid waste. For those scenarios where wastes are discharged via the facility's common sewage line to permitted publiclyowned treatment works (POTWs), these wastes are excluded from RCRA (40 CFR 261.4( a)( 1)( ii)). For those scenarios where wastes are sent to industrial subtitle D landfills, we performed a risk assessment to help us determine whether these risks warranted listing. d. Agency evaluation. (1) Filter press cake and mix area filters. How Was This Waste Characterized?

We collected two samples of this residual at one facility. Based on our assessment of the raw materials and production processes used across the industry, we believe these samples are representative of the range of waste characteristics at the other three sodium phosphate production facilities. Constituents detected above their HBLs are summarized in Table III± 35.

TABLE III± 35.Ð CHARACTERIZATION OF FILTER PRESS CAKES FROM SODIUM PHOSPHATE PRODUCTION Parameter Total (mg/ kg) TCLP (mg/ l) SPLP (mg/ l) HBL (mg/ l)

Primary filter press cake (Sample RCH± 1± SP± 01): Antimony ................................................................................................................... 0.5 <0.5 0.0298 0.006 Thallium .................................................................................................................... <2 <2 0.0055 0.001 VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00064 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55747 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules TABLE III± 35.Ð CHARACTERIZATION OF FILTER PRESS CAKES FROM SODIUM PHOSPHATE PRODUCTIONÐ Continued Parameter Total (mg/ kg) TCLP (mg/ l) SPLP (mg/ l) HBL (mg/ l)

Tray filter cake (Sample RCH± 1± SP± 02): Antimony ................................................................................................................... <0.5 <0.5 <0.025 0.006 Thallium .................................................................................................................... <2 <2 0.0079 0.001 What Management Scenarios Were Assessed and How Was the Risk Assessment Established? These wastes go to industrial subtitle D landfills and we therefore determined that we would model the scenario of offsite disposal in an industrial D landfill. We assessed the off site landfill scenario using the hydrogeologic properties associated with the geographic areas where the landfills reported in the survey are located. We gave the SPLP results primary consideration as there is no reported management in municipal landfills (where the TCLP results would be relevant). Based on the sampling results summarized above, we decided that modeling was necessary for two constituents of concern: antimony and thallium. For antimony, we used onehalf of the detection limit as a model input for sample RCH± 1± SP± 02. We used the probabilistic approach for an off site industrial Subtitle D landfill described in section III. E of today's proposal.

What Is EPA's Listing Rationale for This Waste? From the results of the risk assessment, summarized below in Table III± 36, neither antimony nor thallium (the constituents of concern) pose a substantial present or potential hazard to human health and the environment. The hazard quotients for both constituents, for both the adult and child exposure scenarios, are less than 0.008 at the 95th percentile. As a matter of policy, EPA generally does not consider listing wastes with predicted hazard quotients of less than 1.0. We see no special concerns warranting an exception to this policy. Therefore, we believe that these wastes do not warrant listing. For the mix area filters, the location of these filters indicates that any contaminants found would be similar to those of the filter press cake. Given that our evaluation of the much larger volume filter press cake yielded no significant risk, we are also proposing not to list the very small volume mix area filters. For a more complete description of these analyses, see `` Risk Assessment for the Listing Determinations for Inorganic Chemical Manufacturing Wastes'' in the docket for this proposed rulemaking.

TABLE III± 36.Ð PROBABILISTIC RISK RESULTS FOR FILTER PRESS CAKES Percentile Antimony Thallium Adult HQ Child HQ Adult HQ Child HQ Industrial landfill: 90th ........... 0.001 0.003 0.002 0.003 95th ........... 0.004 0.008 0.004 0.008 (2) Dust collector filter bags.

How Was This Waste Characterized?

We collected one sample of this residual. Based on our assessment of the raw materials and production processes used across the industry, we believe this sample is representative of similar wastes at the other three sodium phosphate production facilities. The waste constituents detected at levels above their HBLs are summarized in Table III± 37:

TABLE III± 37.Ð CHARACTERIZATION OF DUST COLLECTOR FILTER BAG FROM SODIUM PHOSPHATE PRODUCTION [Sample RCH± 1± SP± 03]

Parameter Total (mg/ kg) TCLP (mg/ l) SPLP (mg/ l) HBL (mg/ l)

Antimony 48.8 <0.5 0.309 0.006 Arsenic .. <0.5 <0.5 0.0064 0.0007 What Management Scenarios Were Assessed and How Was the Risk Assessment Established?

Industry reported that this waste is managed in off site industrial D landfills. We assessed this scenario. Antimony and arsenic are the constituents of concern. Because the volume of this waste is relatively small, we first used the de minimis waste quantity screening analysis (described in section III. E. 3) to screen the potential risk to groundwater associated with landfilling this waste. We found that the SPLP data for arsenic screens out because the waste volume is insufficient to release arsenic at levels of concern. For a more complete description of this analysis, see `` Risk Assessment for the Listing Determinations for Inorganic Chemical Manufacturing Wastes'' in the docket for this proposed rulemaking. The detected SPLP levels for antimony did not screen out using the de minimis volume analysis. We conducted full groundwater modeling for the industrial landfill scenario for this constituent. We assessed the off site landfill scenario using the probabilistic approach for off site landfills described in section III. E.

What Is EPA's Listing Rationale for This Waste? From the results of the risk assessment, summarized below in Table III± 38, antimony (the constituent of concern) does not pose a substantial present or potential hazard to human health and the environment. The hazard quotients for antimony, for both the adult and child exposure scenarios, are less than 0.007 at the 95th percentile. As a matter of policy, EPA generally does not consider listing wastes with predicted hazard quotients of less than 1.0. We see no special concerns warranting an exception to this policy. Therefore, we believe that this waste does not warrant listing. For a more complete description of this analysis, see `` Risk Assessment for the Listing Determinations for Inorganic Chemical Manufacturing Wastes'' in the docket for this proposed rulemaking.

TABLE III± 38.Ð PROBABILISTIC RISK RESULTS FOR DUST COLLECTOR BAGS Percentile Antimony Adult HQ Child HQ Industrial landfill: 90th ............................ 0.001 0.002 95th ............................ 0.003 0.003 (3) Scrubber waters and effluents. We did not evaluate scenarios where these secondary materials are piped back into the production process because there is no potential for exposure. For those scenarios where wastes are managed in a tank, the impervious nature of the construction materials (concrete,

VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00065 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55748 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules fiberglass, or steel) of tanks are unlikely to result in releases to groundwater in all but the most catastrophic scenarios. We also are not concerned with potential air releases from these tanks as neither volatile contaminants nor airborne particulates are likely to be present in these aqueous wastes. For those scenarios where wastes are discharged via the facility's common sewage line to POTWs, these wastes are excluded from RCRA (40 CFR 261.4( a)( 1)( ii)). Furthermore, these discharges are regulated by the Clean Water Act pretreatment standards. They do not warrant listing. We propose not to list this waste. (4) Product dust collected. All collected dust that can be recycled is recycled back into the production process. Due to production constraints, some portion of this collected product dust cannot be recycled back to the process and is instead sent to an industrial Subtitle D landfill. However, this landfilled product is still food grade product. Because this `` waste'' is, in fact, food grade product, we believe it unlikely that it contains any constituent exceeding health based limits based on ingestion. Therefore, we propose not to list this waste. (5) Off specification product. Much of this material is reused in the production process with no potential for exposure. However, because of production constraints, they cannot always work all of this material back into the process, and it must be disposed in an industrial subtitle D landfill. In all cases, product is rejected by a customer because of physical property problemsÐ i. e., particle sizeÐ rather than chemical problems or contaminants. Because this `` waste'' is, in fact, food grade product, we believe it unlikely that it contains any constituent exceeding health based limits based on ingestion. Therefore, we propose not to list this waste.

14. Titanium Dioxide a. Summary. We evaluated wastes from the production of titanium dioxide and propose to list one waste and not to list all of the others. Certain wastes from titanium dioxide production are exempt mineral processing wastes and were not assessed as part of today's listing determination because they are outside the scope of the consent decree. We are proposing to list nonwastewaters from the chloride ilmenite process (unless otherwise exempted). K178 Nonwastewaters from the production of titanium dioxide by the chloride ilmenite process. (T) [This listing does not apply to chloride process waste solids from titanium tetrachloride production exempt under section 261.4( b)( 7)] We propose not to list the remainder of the wastes generated by this sector. We do not believe these wastes pose threats to human health or the environment that warrant listing. We have not identified risks of concern associated with the current management of these wastes that support a listing determination. Our findings, however, do not change the applicability of existing standards and regulations, such as the hazardous waste characteristics, to these wastes and this industry. b. Description of the titanium dioxide industry. There are nine facilities producing titanium dioxide. There are three distinct processes currently in use: the chloride process, the sulfate process, and the chloride ilmenite process. Six facilities use the chloride process. Two of these six facilities also produce titanium dioxide via the sulfate process. Three separate facilities use only the chloride ilmenite process. Chloride Process. In the chloride process, rutile or high grade ilmenite is converted to titanium tetrachloride (TiCl4). The conversion takes place in a chlorinator in the presence of chlorine gas with petroleum coke added as a reductant. All U. S. producers of TiCl4 use fluidized bed chlorinators. Vent gases from the chlorinator are scrubbed prior to venting to the atmosphere. Nonvolatile metal chlorides and unreacted coke and ore solids are removed from the gaseous product stream. The facilities also generate waste acid, which they mingle with coke and ore solids before treatment. Vent gases from the chlorinator are scrubbed prior to venting to the atmosphere. The volatile TiCl4 and other volatile metal compounds such as vanadium oxychloride, exit the chlorinator as overhead vapor. The gaseous product stream is purified to separate the titanium tetrachloride from other metal chloride impurities using processes such as partial condensation and chemical treatment. Finally, vanadium compounds, which have boiling points close to that of TiCl4, are removed from the titanium tetrachloride by complexing with mineral oil and reducing with hydrogen sulfide, or by complexing with copper. The purified TiCl4 is then oxidized to TiO2, driving off chlorine gas, which is recycled to the chlorinator. The pure TiO2 is slurried and sent to the finishing process which includes milling, addition of inorganic and organic surface treatments, and/ or spray drying of the product TiO2. The product can be sold as a packaged dry solid or a water based slurry. Sulfate Process. In the sulfate process, ilmenite ore or slag with high TiO2 content is digested with sulfuric acid, forming a porous cake; this cake is further dissolved by dilute acid to form titanyl sulfate (TiOSO4). Iron may be added to the digestion process to ensure that iron impurities remain in the ferrous (Fe 2¶ ) state so that the eventual TiO2 product can be easily washed. The titanyl sulfate solution is then clarified, yielding a waste sulfate digestion sludge, and then concentrated through vacuum evaporation. The filtered titanyl sulfate solution is vacuum evaporated a second time and hydrolyzed to precipitate hydrated titania (TiO( OH) 2).

The titania hydrate is then filtered and washed, yielding filtrate waste and wastewater, respectively, before being calcined at 1,000°C to produce the TiO2 product. Chloride Ilmenite Process. In the chloride ilmenite process, ilmenite ore is converted to titanium tetrachloride. As in the chloride process, the chlorideilmenite process takes place in a chlorinator in which the ore is chlorinated in the presence of coke as a reducing agent. Vent gases from the chlorinator are scrubbed prior to venting to the atmosphere. Non volatile metal chlorides and unreacted coke and ore solids are removed from the gaseous product stream. The gaseous product stream then is purified further to separate the titanium tetrachloride from other volatile metal chloride impurities, including ferric chloride (FeCl3) which is present in higher concentrations than the chloride process due to the high iron content in the ore. The separation is done via condensation and chemical treatment. The process for converting the purified TiCl4 product stream to TiO2 is similar to that used in the chloride process, as described above. c. What kind of wastes are generated by these processes?. The wastes generated by the titanium dioxide sector are described in overview below, organized by process. Additional detail on these wastes is provided in the background document for this sector. The wastes generated by the chloride process include: ÐCommingled wastewaters, including process and non process wastewaters from chlorinator coke and ore solids recovery, reaction and chemical tank storage scrubbers, product finishing operations, wastewater treatment and chlorinator solids decantation, and on site landfill leachate. ÐChloride process waste solids from titanium tetrachloride production (exempt as mineral processing wastes, see 40 CFR 261.4( b)( 7)).

VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00066 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55749 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules ÐWastewater treatment sludges generated by facilities that have chloride only processes (exempt mineral processing wastes at those facilities with no contribution of solids from oxidation and finishing) ÐWaste sands from finishing (milling) of the titanium dioxide product and scouring of oxidation process units. ÐVanadium wastes generated in the purification process. The wastes generated by the sulfate process (used at two plants that also use the chloride process) include: ÐPrimary and secondary gypsum, which is produced when the waste sulfuric acid generated from the filtering of titanium dioxide hydrate solution is neutralized with calcium carbonate. ÐDigestion sludge from the clarification of the titanyl sulfate liquor that is produced during the acid digester step. ÐWastewaters from the sulfuric acid digestion scrubber which removes acidic components and entrained solids from reaction gases, evaporator condensate from the precipitation unit, the calciner scrubber, the sulfate waste sludge settling pond supernatant, and the primary and secondary gypsum precipitation units. These wastewaters are commingled with wastewaters from the chloride process. ÐWastewater treatment sludges. These wastewater treatment sludges are generated from commingled chloride process and sulfate process wastewaters by facilities that have both processes. The wastewater treatment consists of elementary neutralization and precipitation or filtration. ÐAcids from intermediate titanium product filtration/ bleaching units and product calciner overhead scrubbers. ÐProduct milling sand from finishing operations. The wastes generated by the chlorideilmenite process include: ÐCoke and ore solids (exempt as mineral processing wastes, see 40 CFR 261.4( b)( 7)) that are not consumed by the chlorination process. These solids are conveyed through the process as part of various wastestreams. ÐWaste acid (metal chloride) solution, usually called ferric or iron chloride, that is separated from the gaseous titanium tetrachloride product stream and acidified. ÐProcess and non process wastewaters from reaction and oxidation scrubbers, reactant and treatment chemical storage scrubbers, product finishing, HCl storage vent scrubber, oxidation unit tank and equipment vents, supernatant or filtrate from coke and ore solids management and wastewater treatment disposal impoundments. The wastewaters are commingled prior to being introduced into the wastewater treatment system. ÐOther spent scrubber waters from the reaction fume disposal system. The wastewaters are pretreated and are subsequently commingled with other wastewaters prior to being introduced to the wastewater treatment system. ÐNon exempt non wastewaters, including the portion of wastewater treatment solids derived from the neutralization of process and nonprocess wastewaters from oxidation and finishing, and solids from ferric chloride filtration. ÐHCl from the reaction scrubber. ÐAdditive feeder vent filter solids generated in the oxidation process. ÐVanadium waste generated in the purification process. ÐOff specification titanium dioxide product. ÐRail car product washout wastewater. ÐWaste sand removed from a reactor purge stream (coke and ore solids) Table III± 39, below, summarizes our information about the wastes generated rom the production of titanium dioxide.

TABLE III± 39.Ð TITANIUM DIOXIDE WASTES Waste category Number of generators 1998 volumes (MT) Reported hazard codes Management practices Commingled chloride process wastewaters .. 4 7,614,358 ......... D002, D007 ...... Neutralization, solids settling, NPDES discharge Chloride process solids (Bevill exempt) ........ 6 1,200,000 ......... none ................. On site impoundments, on site Subtitle D landfills. Waste sands from oxidation, milling and scouring. 3 9,485 ................ none ................. On site industrial Subtitle D landfill; off site industrial Subtitle D landfill. Gypsum from sulfate process ........................ 2 46 69,500 ........... none ................. On site waste pile storage; on site industrial Subtitle D landfill; sold for various uses. Digestion scrubber water ............................... 2 2,000,333 ......... Neutralization in dedicated impoundment; commingled with other wastewaters. Digestion sludge from sulfate process .......... 2 41,494 .............. D002 ................. Unlined impoundment, dewatering, on site industrial Subtitle D landfill. Commingled wastewaters from the chloride and sulfate process. 2 16,184,031 ....... none ................. Neutralization, solids settling in unlined surface impoundments, NPDES discharge. Wastewater treatment sludges from commingled chloride and sulfate process (partially Bevill exempt). 2 159,121 ............ none ................. Dewatering, on site industrial Subtitle D landfill.

Waste acid (ferric chloride) from chloride ilmenite process. 3 1,883,000 ......... D002, D007, D008. On site hazardous waste underground injection reuse as raw material in sodium chloride production; storage in tanks and unlined impoundment prior to sale as water and wastewater treatment reagent. Chloride ilmenite process solids (Bevill exempt 3 not reported ...... none ................. On site dewatering; on site Subtitle D industrial landfill; on site unlined impoundment; various reuses. Non exempt nonwastewaters from the chloride ilmenite process. 3 14,600 .............. none ................. On site dewatering; on site Subtitle D industrial landfill; on site unlined impoundment; various reuses. HCl from reaction scrubber, chloride ilmenite process. 3 not reported ...... D002 ................. On site wastewater treatment, on site reuse.

Commingled wastewaters from the chlorideilmenite process. 3 13,556,000 ....... none ................. On site neutralization, solids settling, NPDES discharge.

VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00067 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55750 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules 47 All sulfate process waste solids and liquids are non exempt mineral processing wastes (see 55 FR 2322, January 23, 1990). 55 FR 2392 noted that all sulfate process waste solids and wastewaters from the production of titanium dioxide do not meet the high volume/ low hazard criteria established in the September 1, 1989 Bevill rule and therefore were not eligible for continued coverage under the Bevill exclusion (see 54 FR 36592). TABLE III± 39.Ð TITANIUM DIOXIDE WASTESÐ Continued Waste category Number of generators 1998 volumes (MT) Reported hazard codes Management practices Additive vent filter solids from chloride ilmenite process. 1 < 1 .................... none ................. Off site Subtitle D industrial landfill.

Vanadium waste from the chloride ilmenite and chloride process. 4 not reported ...... none ................. Returned to reaction area for TiCl 4 recovery remaining vanadium wastes are incorporated in solids streams. Off spec titanium dioxide product .................. 2 563 ................... none ................. Off site Subtitle D industrial landfill. Railcar/ trailer product washout ...................... 1 <10,000 ............ none ................. On site storage in unlined surface impoundment on site wastewater treatment.

46 Additional volumes are used as products.

The manufacturers also produce materials that are reused in other processes that are outside the scope of the consent decree. With one exception described below, we did not evaluate these materials, or wastes generated during co product production for the purposes of today's listing determinations, because they were outside the scope of the consent decree. One facility produces sulfur from the treatment of off gases. Because the offgas is produced from a production unit rather than a waste management unit and is conveyed to its destination via piping, the gas is not a solid waste. RCRA Section 1004( 27) excludes noncontained gases from the definition of solid waste and thus they cannot be considered a hazardous waste. (See 54 FR 50973) Because this gas is not a solid waste when produced, we did not evaluate it further for purposes of listing. d. What wastes from these processes are exempt mineral processing wastes? In July of 1988, the U. S. Court of Appeals, for the D. C. Circuit in Environmental Defense Fund v. EPA (EDF II), 852 F. 2d 1316 (D. C. Cir. 1988), cert. denied, 489 U. S. 1011( 1989), ordered EPA to restrict the scope of the Bevill mining waste exclusion, as it applied to mineral processing wastes. In response, EPA promulgated rules on September 1, 1989 (54 FR 36592) and on January 23, 1990 (55 FR 2322), issued a Report to Congress on Wastes from Mineral Processing on July 31, 1990, and published a regulatory determination published on June 13, 1991 (56 FR 27300). The list of Bevill exempt wastes is set out at 40 CFR 261.4( b)( 7). We relied on these Bevill rulemakings to determine the Bevill status of waste streams in the titanium dioxide sector. The production of titanium dioxide results in the generation of 2 categories of exempt waste: beneficiation wastes and exempt mineral processing wastes. These categories are described below. The industry reported a number of wastes generated from the storage and handling of various raw materials which are exempt because they are associated with beneficiation. Solid wastes from the extraction/ beneficiation of ores and minerals are Bevill exempt solid wastes (see 51 FR 24496, July 3, 1986 and 54 FR 36592, September 1, 1989). These wastes are described in the background document for this sector. We have not assessed these wastes because they are exempt under 40 CFR 261.4( b)( 7). The only relevant mineral processing waste exemption consists of `` chloride process waste solids from titanium tetrachloride production'' (see 40 CFR 261.4( b)( 7)( ii)( S)). The consent decree mandating today's proposal states in paragraph 1. g that Bevill exempt wastes are not within the scope of the consent decree as it applies to the inorganic chemical listing determinations, and specifically that `` chloride process waste solids'' need not be assessed within the titanium dioxide sector. Titanium tetrachloride production occurs in both the chloride and chloride ilmenite processes. 47 The chloride process waste solids are generated during the chlorination reaction of the titanium ore in the reducing presence of coke at elevated temperatures, and are generated from both the chloride process and the chloride ilmenite process. The majority of these solids are removed from the reaction area as a mass and are quenched, neutralized, settled and disposed as exempt materials. Additional solids from the reactor are carried overhead with the TiCl4 product gas stream and are subsequently removed in various scrubbing units. Although EPA has not previously discussed these solids, we believe that they also fall within the exemption. While they are removed from the product stream and various other wastes at points other than where the majority of the solids are separated from the TiCl4 gas stream, they are similarly composed of unreacted ore and coke solids from the chlorination reactor. They fit within the plain language of the exemption. Solids also are generated from the oxidation and finishing stages of titanium dioxide production. These solids are non exempt solid wastes (not covered by the exemption). Most titanium dioxide producers commingle wastewaters from titanium tetrachloride production with wastewaters from oxidation and finishing. To the extent that the resultant sludges contain nonexempt solids, we have assessed that portion of those solids. Due to process variations, each facility using the chloride or chlorideilmenite process generates its exempt solids in slightly different ways. The general principles that we used to determine the Bevill status of these wastes include the following:

ÐExtraction and beneficiation ends just before chlorination occurs. Wastes generated prior to this point are Bevill exempt, outside the scope of the consent decree and therefore not addressed in this rulemaking. The chlorinator marks the beginning of mineral processing because the ore undergoes a physical/ chemical change (see 54 FR 36619, September 1, 1989). 54 FR 36621 further notes, `` Likewise, EPA considered titanium tetrachloride produced during the titanium chloride [sic] process to be a saleable product; any further processing subsequent to its production is considered to be chemical manufacturing. '' ÐMineral processing ends when titanium dioxide is produced in the oxidation unit. Further steps are chemical manufacturing. The Agency defines the beginning of oxidation as the beginning of chemical manufacturing because the facility is using a saleable mineral product, titanium tetrachloride, to produce titanium dioxide (see 54 FR 366211).

VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00068 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55751 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules 48 `` If EPA finds that this exemption is not protective of human health and the environment and if an examination of titanium tetrachloride waste management shows any continuing or new problems, the Agency will reconsider this subtitle D determination for chloride process waste solids from titanium tetrachloride production. '' 56 FR 273000, June 13, 1991. ÐThe mineral processing exemption only covers solids from the production of titanium tetrachloride. These solids, therefore, are outside of the consent decree. At least six streams of solid bearing material leave the chlorination reaction area. The status of these streams is as follows: (1) Titanium tetrachloride going on for further production. All wastes formed during further processing of this gaseous product stream are chemical manufacturing wastes that are outside the scope of the Bevill exemption. (2) Solids removed from the gaseous titanium tetrachloride stream. These solids are associated with the production of titanium tetrachloride. These solids are typically slurried to impoundments for storage or disposal and are Bevill exempt (with one exception described below). (3) Waste acids. In 1990 and 1998 rulemakings for LDR Phase IV (see 63 FR 28601), EPA took the position that the waste acids do not meet the high volume, lowtoxicity test and thus are not exempt mineral processing wastes. (4) Gases going to scrubbers. Offgases from the chlorinators pass through various air pollution control systems which generate scrubber waters. In 1998, EPA stated that scrubber waters and sludges from scrubber waters were not Bevill exempt. However, as a result of the information collection activities associated with today's proposal, it is now clear to EPA that gases from the chlorinator contain some solids from the chlorinator. We are interpreting the exemption today to cover these particles when they drop out of scrubber waters to form sludges. (Gas streams and wastewaters are not Bevill exempt, even when they are carrying solid particles from chlorinator.) (5) Solids purged from the reactor. A purge stream from the reactor may be taken to reduce silica levels in the reactor. This stream is Bevill exempt. (6) Recovered solids from the reaction area. Housekeeping results in the collection of coke and ore solids from the vicinity of the reaction area. These wastes are Bevill exempt. In one case, the facility conducts some processing of their ferric chloride waste acid (which is subsequently sold as a water and wastewater reagent), and generates a solids stream. We consider the processing that this facility conducts to be either an ancillary process or chemical manufacturing, and thus the subsequent solids stream is not generated from mineral processing and therefore is not exempt.

What Is The Status of the Mineral Processing Exemption for `` Chloride Waste Solids From Titanium Tetrachloride Production'? As part of our waste characterization of the titanium dioxide sector, we conducted analyses for chlorinated dibenzo p dioxins (CDDs) and dibenzop furans (CDFs). We were concerned that these compounds might be present in the wastes as a result of the chlorination step which occurs in the presence of coke, and in fact we found measurable levels of these compounds in wastes from the chloride and chloride ilmenite processes. These data are presented in the Titanium Dioxide Listing Background Document and associated analytical data reports in the docket for today's notice. As explained in this background document, we believe that these compounds are formed in the chlorinator, and are predominantly associated with the exempt mineral processing solids (additional details regarding this conclusion are provided in the referenced background document). These compounds were not assessed, however, as part of the rulemakings which established the mineral processing exemptions, and so these results could present new issues for these wastes if such compounds were found to pose unacceptable risks. During the development of the mineral processing exemption, EPA anticipated certain conditions might suggest the appropriateness of re opening these exemptions. 48 We are considering whether we should re assess the status of these wastes as exempt mineral processing wastes. Any reassessment of these wastes would involve a separate analysis and opportunity for notice and comment.

How Did EPA Assess Mixtures of Exempt and Non Exempt Wastes From the Production of Titanium Dioxide? There are a number of wastes from the titanium dioxide sector that remain partially within the scope of the consent decree because they are composed of both exempt and non exempt solids. Because they are not `` 100 percent exempt'' in composition, we have assessed their potential impacts on the environment, and attempted to isolate the risks associated with the nonexempt solids and wastewaters. Any assessment of the CDD and CDF loading in exempt wastes will involve a separate analysis and opportunity for notice and comment. Finally, we are assessing one nonexempt waste generated at the Delaware facility, non exempt non wastewaters from the chloride ilmenite process, which contains some CDDs and CDFs at levels exceeding our initial screening criteria. We did not, as part of today's listing determination, conduct sufficient risk assessment to fully evaluate the potential for risks. See section III. F. 14. e( 10) below.

5. Agency Evaluation (1) Commingled wastewaters from the chloride process, including wastewaters from coke and ore recovery, scrubber water, finishing wastewaters and sludge supernatants.

How Many Facilities Generate This Waste Category and How Is It Managed? Four facilities generated commingled wastewaters from the chloride process. (As will be discussed further in III. F. 14. e( 7), two additional facilities generate the same wastewaters and commingle them with wastewaters from the sulfate process.) Three of the four `` chloride only'' facilities treat their wastewaters in surface impoundmentbased treatment systems; the fourth facility uses a tank based wastewater treatment system. Each of the impoundment systems include unlined units. These large volume wastes are generated in excess of 29 million metric tons per year. These wastewaters are not Bevill exempt (but convey exempt solids into the wastewater treatment system where those solids are removed to form sludges that are comprised of exempt solids and non exempt solids, depending on the specific piping of the plants). Many facilities commingle waste hydrochloric acids (generated as scrubber water) with their combined wastewaters. Three other facilities, however, return waste acids on site or sell the acids for reuse. Because these materials have no exposure route of concern, we did not further evaluate risk scenarios associated with reuse of this material.

What Management Scenarios Were Assessed? For this rulemaking, we determined that the surface impoundment scenario poses a more significant potential risk than the tank scenario, and thus assessed the groundwater pathway for surface impoundments. We assessed potential groundwater releases to both surface water and drinking water wells. We concluded that the air pathway does not present significant risks for these wastes because the wastes do not contain volatile organics or other constituents that pose risk due to air releases.

How Was This Waste Category Characterized? One of the four facilities, located in Hamilton, Mississippi, was selected for sampling and analysis. This facility's VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00069 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55752 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules 49 This facility also commingles wastewaters from sodium clorate production, which account for approximately 1.7 percent of the total 4aste volume. 50 U. S. EPA RCRA Facility Assessment of Kerr McGee Chemical Corporation; Hamilton, MS. June 16, 1995. waste is representative of the four chloride only facilities. The sample was collected at the inlet to this facility's surface impoundment train. 49 This sample contained a high level of solids, reflecting the facility's practice of managing all waste solids (including Bevill exempt solids) and process wastewaters in the same units which serve as settling ponds. To isolate the impact of the wastewater on the environment from that of the sludge, we conducted the SPLP on the waste matrix, and separately analyzed the filtrate and the leachate generated from the leaching step. We are proposing to use the filtrate analysis as representative of the wastewater portion of the commingled waste matrix (see III. E. 2 and 3 for further discussion on the use of SPLP filtrate). The analytical results for the constituents found to be present in the filtrate at levels exceeding HBLs and/ or AWQC are presented below in Table III± 40 (the Titanium Dioxide Listing Background Document contains the full set of analytical results).

TABLE III± 40.Ð CHARACTERIZATION OF COMMINGLED WASTEWATERS FROM CHLORIDE PROCESS, TITANIUM DIOXIDE Constituent of concern Detected levels in Sample KM± SI± 01 (mg/ L) HBL AWQC Total SPLP Filtrate Antimony .......................................................................................................................................... <0.05 0.044 0.006 0.014 Arsenic ............................................................................................................................................. 0.04 0.001 0.0007 0.000018 Manganese ...................................................................................................................................... 25.9 0.46 0.73 0.05 Molybdenum .................................................................................................................................... 0.53 0.23 0.078 NA Thallium ........................................................................................................................................... 0.086 1 <0.005 0.001 0.0017 1 Thallium is identified as a potential constituent of concern because it was detected in the totals analysis at levels exceeding the HBL and AWQC, and the SPLP filtrate analysis detection limit was too high to confirm that mobile levels of thallium do not exceed these standards. One half the detection limit was used as input to the risk assessment (see III. E. 3).

How Was the Groundwater to Surface Water Risk Assessment Established? We assumed that surface impoundments present greater risks to the environment than tanks. Therefore we focused on the 3 facilities that manage wastewaters in impoundments. We selected the sampled facility for modeling because (1) its management practices (i. e., treatment in surface impoundments) are representative of 3 of the 4 chloride only facilities, (2) the analytical data for this waste were obtained from this site, and (3) its setting is similar to the other 2 facilities that use surface impoundments. The facility selected for modeling is bounded on two sides by a river, tributary creeks, and swamps. The RCRA Facility Assessment 50 for this site provides maps showing distances to these potential receptors and groundwater flow directions in the vicinity of the surface impoundments and plant wide flow directions, with the overall flow being toward the river. We calculated infiltration rates for the unlined impoundment, and divided this flow rate into the flow rate of the river to determine potential concentrations of the five metals of concern in the river as a result of recharge with contaminated groundwater. The results of this screening (see `` Risk Assessment Support to the Inorganic Chemical Industry Listing: Background Information Document'') demonstrate that concentrations of the constituents of concern are likely to be well below risk thresholds for both human health and aquatic life in surface water.

How Was the Groundwater Ingestion Risk Assessment Established?

We were able to collect specific information regarding the physical setting of the modeled facility, and thus used primarily site specific data as input to the risk assessment. We chose this site for modeling because the amount of available information best supported our data requirements for modeling and because we believe this facility is representative of other generators of this waste category in terms of hydrogeological setting and waste characterization. Based on information presented in the RFA for the facility of concern, as well as from the U. S. Geological Survey Groundwater Site Inventory, there are groundwater wells north of the plant. The RFA also indicates that groundwater flow direction in the localized vicinity of the surface impoundments is to the northwest. We modeled the potential impact of the unlined portion of the surface impoundment train on drinking water wells located within 2,000± 5,000 feet (based on well locations and the closest facility property lines). The resultant concentrations are presented below in Table III± 41.

TABLE III± 41.Ð GROUNDWATER PATHWAY RISK ASSESSMENT RESULTS FOR COMMINGLED WASTEWATERS FROM CHLORIDE PROCESS, TITANIUM DIOXIDE Constituent of concern Risk or hazard quotient 90th% 95th%

Adult Child Adult Child Antimony HQ ................................................................................................................... 0. 1 0.2 0.2 0.5 Arsenic cancer risk .......................................................................................................... 2E± 08 2E± 08 8E± 08 6E± 08 Molybdenum HQ .............................................................................................................. 0.03 0.07 0.06 0.1 VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00070 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55753 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules 51 This waste volume includes the non exempt sulfate solids generated at one of the 2 facilities that commingle wastes from the chloride and sulfate processes. 52 The sodium chlorate wastewaters account for only 1.7% of the total volume of managed wastewater, and for only 4.4% of the solids generated. The predominant potential constituent of concern in the sodium chlorate solids is chromium; analytical data for the commingled solids (KM± SI± 04) show that the SPLP concentration is <0.05 mg/ L and not of concern. See section III. F. 11 for further discussion of this facility's sludge. TABLE III± 41.Ð GROUNDWATER PATHWAY RISK ASSESSMENT RESULTS FOR COMMINGLED WASTEWATERS FROM CHLORIDE PROCESS, TITANIUM DIOXIDEÐ Continued Constituent of concern Risk or hazard quotient 90th% 95th%

Adult Child Adult Child Thallium HQ ..................................................................................................................... 0.02 0.03 0.03 0.07 What Is EPA's Listing Rationale for This Waste?

We propose not to list commingled wastewaters from the production of titanium dioxide via the chloride process. The results of our risk assessment show that this waste category does not pose significant risk to human health and the environment. Our assessment of the air and surface water exposure pathways shows no risk of concern. Our assessment of the groundwater exposure pathway similarly shows no risk of concern for the constituents of concern. (2) Chloride process solids (Bevill exempt). Six facilities generate waste solids from the chloride process. As previously discussed, the Agency determined at 56 FR 27312 (June 13, 1991) that chloride process waste solids from titanium tetrachloride production are Bevill exempt mineral processing wastes (40 CFR 261.4( b)( 7)( ii)( S)). Five of the six facilities generate their solids in surface impoundments; the sixth, located in Louisiana, uses tank based settling to segregate the solids from their wastewaters. All six facilities dispose of their solids in their surface impoundments or on site landfills. Approximately 1.2 million MT of this waste was generated in 1998. 51 The waste solids at each of these sites contains contributions from Bevill exempt solids ranging from 100% to 40%, as discussed further below. At the two facilities located in Georgia and Louisiana, coke and ore solids are generated as entirely segregated wastes that are not commingled with nonexempt solids; these exempt wastes are clearly outside the scope of the consent decree dictating today's proposal and have not been assessed further. At three other facilities, the facilities conduct some commingling of their wastewaters, resulting in small potential contributions of non exempt solids to their waste solids. Two of these facilities, both located in Ohio, commingle wastewaters from oxidation and finishing (i. e., generated after the production of titanium tetrachloride and therefore potentially bearing nonexempt solids) with the wastewaters from titanium tetrachloride production that bear exempt solids. Neither facility reported any solids in their oxidation and finishing wastewaters, although data from similar wastewaters from the chloride ilmenite process indicate that very low levels of solids can be present in similar wastewaters. (We assess solids from the chloride ilmenite process in section III. F. 14. e( 10) of this proposal.) At the third facility (located in Mississippi), which operates a slightly different process, there were no reported wastewaters or solids from oxidation and finishing. Note that the wastewaters bearing the exempt solids at this facility are commingled with comparatively small volumes of wastewaters from sodium chlorate production (described in section III. F. 11 of today's proposal). 52 We believe that the contribution of any non exempt solids to the volume of exempt solids from these three facilities would be very small. Thus, we have chosen not to attribute any risks to the nonexempt portion of these commingled solids. Two of the six facilities generating chloride process waste solids also operate sulfate based titanium dioxide production lines. These plants are sited in Georgia and Maryland. Wastewaters from the chloride process and sulfate processes are commingled and results in commingled wastewater treatment solids that are partially composed of exempt solids. The non exempt wastewater treatment solids are described separately in section III. F. 14. e( 8). They contain significant volumes of non exempt solids (> 35%). (3) Various sands from oxidation, milling and scouring.

How Many Facilities Generate This Waste Category and How Is It Managed?

Two facilities using the chloride process reported disposal of 250 MT of milling sand in off site and dedicated on site Subtitle D landfills. One facility also reported landfilling over 2,300 MT of scouring sand. One facility reported 6,935 MT/ yr of waste oxidation sand that is managed in an on site industrial Subtitle D landfill. All of these sands are similar and are associated with titanium dioxide finishing operations. All of these sands are produced after the beginning of chemical manufacturing and therefore are not exempt.

What Management Scenarios Were Assessed?

We assessed the off site industrial landfill scenario for milling sand and a dedicated on site landfill for scouring sand, reflecting the types of management reported for these wastes. We assessed the groundwater ingestion pathway for these landfills. The on site landfill scenario for scouring sand screened out when we compared the SPLP results for this waste directly to the HBLs.

How Was This Waste Category Characterized?

We collected samples of both the milling sand and the scouring sand. We conducted total, TCLP and SPLP analyses on the waste matrix. We used the SPLP results (rather than the TCLP) to assess potential releases to groundwater because there is no contact with municipal landfill leachate in the reported management practices, and no indication that other practices are likely. The SPLP analytical results of concern for the milling sand are presented below in Table III± 42.

VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00071 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55754 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules 53 Additional volumes are used as products.

54 See `` Update of the Hazardous Waste Groundwater Task Force'', April 1998. Maryland Department of the Environment. RCRA Operation and Maintenance Inspection of SCM Chemicals (now Millennium Inorganic Chemicals, Inc.); Hawkins Point Plant; Baltimore, MD. October 1994. TABLE III± 42.Ð CHARACTERIZATION OF MILLING SAND FROM TITANIUM DIOXIDE PRODUCTION Constituent of concern Detected SPLP levels in KP± SO± 05 (mg/ L) HBL (mg/ L)

Antimony ....................... 0.024 0006 How Was the Groundwater Ingestion Risk Assessment Established?

As described in Section III. D. 4. we used our standard distance to well assumptions for an off site landfill, and assumed hydrogeologic conditions would be comparable to those for the reported off site landfill. As shown in Table III± 43, the resultant risks were calculated.

TABLE III± 43.Ð GROUNDWATER PATHWAY RISK ASSESSMENT RESULTS FOR MILLING SAND FROM TITANIUM DIOXIDE PRODUCTION Antimony HQ Percentile Adult risk Child risk 90th ....................................... 0.003 0.006 95th ....................................... 0.008 0.02 What is EPA's Listing Rationale for This Waste?

We propose not to list this waste because the modeled and screening risk for antimony, the sole constituent of concern, is well below a hazard quotient of unity. (4) Gypsum from the sulfate process.

How Many Facilities Generate This Waste Category and How Is It Managed?

The Maryland and Georgia facilities generate this waste. Both sites pipe their acid directly to their gypsum plants where it is neutralized to form gypsum. We found no significant potential for release of this acid waste prior to its treatment in the gypsum plant. The two facilities reported production of 69,500 MT/ yr of gypsum that is landfilled. 53 We chose to look further at this material because it is disposed of in a landfill and used in a manner constituting disposal (i. e., as fertilizer), and because the generators conduct on site land placement (piles). Specifically, the Georgia facility places their gypsum in piles prior to sale for use in agricultural chemicals, cement, chemical products, and wall board. The Maryland facility generates primary and secondary gypsum, both of which are also placed in piles prior to use in wall board manufacture or disposal in an on site landfill. As described above, the gypsum is not an exempt mineral processing waste because this sulfate process wastestream did not meet the high volume/ low toxicity criteria noted in 54 FR 36592 (September 1, 1989).

What Management Scenarios Were Assessed?

We assessed each of the reported management scenarios that involve land placement: agricultural chemicals, cement, piles and landfills. We evaluated potential releases to both air and groundwater. Samples were collected at both facilities, and included both primary and secondary gypsum samples at the Maryland site. The management scenarios were assessed using the appropriate sample for the type of gypsum reported for that scenario. All pathways screened out except for the landfill scenario at the Maryland site. For the Maryland landfill we found constituent concentrations at levels of potential concern for the groundwater and surface water pathways. The primary gypsum contained lower levels of leachable metals than the secondary gypsum; we focused our modeling efforts on the higher volume secondary gypsum as it was more likely to show risk when modeled and the management scenarios are identical (they are placed in the same on site industrial landfill). The screening results are discussed further in the `` Titanium Dioxide Listing Background Document for the Inorganic Chemical Listing Determination, '' available in the docket for today's notice.

We assessed the landfill scenario for potential impacts to both surface water and drinking water wells. The facility selected for modeling is bounded to the north and east by the Patapsco River, which is an estuary. The expected groundwater flow, while not characterized definitively, is expected to be eastward, toward the river. 54 How Was This Waste Category Characterized?

We collected three samples of this waste for analysis. We conducted total, TCLP and SPLP analyses on the waste matrices. We used the SPLP results (rather than TCLP) to assess potential releases to groundwater and surface water because there is no contact with municipal landfill leachate in the reported management practices. We used total results to assess potential air releases, and this pathway screened out. The SPLP analytical results for the secondary gypsum that we used to assess groundwater releases from landfilling are presented below in Table III± 44.

TABLE III± 44.Ð CHARACTERIZATION OF SECONDARY GYPSUM FROM SULFATE PROCESS, TITANIUM DIOXIDE Constituent of concern Detected SPLP levels in MI± SO± 03 (mg/ L) HBL (mg/ L) AWQC (mg/ L)

Antimony .................................................................................................................................................. 0.055 0.006 0.014 Arsenic ..................................................................................................................................................... <0.0035 0.0007 0.000018 Manganese .............................................................................................................................................. 3.1 0.73 0.05 VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00072 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55755 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules How Was the Groundwater to Surface Water Risk Assessment Established? We calculated infiltration rates for the unlined landfill, and divided this flow rate into the flow rate of the river to determine potential concentrations of the three metals of concern (see Table III± 44) in the river as a result of recharge with contaminated groundwater. The results of this screening (available in the Risk Assessment Background Document) demonstrate that concentrations of the constituents of concern are expected to be well below risk thresholds for human health and aquatic life in surface water.

How Was the Groundwater Ingestion Risk Assessment Established?

While we are not aware of any actual drinking water wells in the vicinity of the Maryland facility, we were unable to determine definitively that there are not private wells in use in the residential area to the south of the facility, or that potentially contaminated groundwater would not reach this neighborhood. We thus decided to model potential exposure at this neighborhood. We modeled the potential impact of the unlined landfill on drinking water wells located within 2,500± 5,000 feet (based on distances to the nearest residential area). The resultant risks were calculated and are summarized in Table III± 45.

TABLE III± 45.Ð GROUNDWATER PATHWAY RISK ASSESSMENT RESULTS FOR SECONDARY GYPSUM FROM SULFATE PROCESS, TITANIUM DIOXIDE Antimony HQ ArsenicÐ cancer risk Manganese HQ Adult risk Child risk Adult risk Child risk Adult risk Child risk 90th .................................................................................. 0.23 0.49 6. E± 07 4. E± 07 0.1 0.2 95th .................................................................................. 0.35 0.75 1. E± 06 1. E± 06 0.1 0.3 What is EPA's Listing Rationale for This Waste? We propose not to list gypsum from the sulfate process. The results of our risk assessment demonstrate that there is no significant risk associated with this material, and that it does not warrant control as a listed hazardous waste. At the 95th percentile, the risks for antimony (HQ= 0.75) and arsenic (1E ´6 ), approach levels at which EPA considers listing wastes (HQ= 1.0 and cancer risk> 10 ´6 , respectively). We believe that our modeled exposure scenario, while plausible, contains a number of conservative assumptions that likely overstate these marginal risks. In particular, our assumptions regarding groundwater flow direction (i. e., that a contaminated plume from the landfill would flow to the south toward the nearest residences, rather than due west toward the river) and the use of groundwater for drinking water at these residences (records indicate this community uses public water) may overstate actual risks. (5) Digestion scrubber water from the sulfate process.

How Many Facilities Generate This Waste Category and How Is It Managed?

The Maryland and Georgia facilities reported generation of digestion scrubber water from the sulfate process. The Maryland facility manages this wastewater in a dedicated surface impoundment after neutralization. The other facility commingles this wastewater with other wastewaters from their chloride and sulfate processes. As described above, the gypsum is not an exempt mineral processing waste because this sulfate process wastestream did not meet the high volume/ low toxicity criteria noted in 54 FR 36592 (September 1, 1989). (See 40 CFR 261.4( b)( 7)( ii).)

What Management Scenarios Were Assessed?

We assessed the waste in its commingled form as managed by the Maryland facility, as described below in section III. F. 14. e( 7). We also modeled the dedicated surface impoundment scenario using the physical parameters describing the dedicated Georgia impoundment. This impoundment is placed directly on the banks of a river, and thus we were primarily concerned with potential releases to surface water. We did not model a drinking water well scenario because there are no constituents of concern in this wastewater at levels exceeding HBLs.

How Was This Waste Category Characterized?

We collected one sample of this waste for analysis. We conducted total analyses (leaching was not conducted given the low levels of percent solids in this waste), which are summarized below in Table III± 46 for the constituents of potential concern.

TABLE III± 46.Ð CHARACTERIZATION OF DIGESTION SCRUBBER WATER FROM SULFATE PROCESS, TITANIUM DIOXIDE Constituent of concern Detected levels in MI± WW± 03 (mg/ L) HBL (mg/ L) AWQC (mg/ L)

Aluminum ................................................................................................................................................. 0.58 16 0.087 Manganese .............................................................................................................................................. 0.58 0.73 0.05 Mercury .................................................................................................................................................... 0.0032 0.005 0.000050 How Was the Groundwater to Surface Water Risk Assessment Established?

We calculated infiltration rates for the unlined surface impoundment, and divided this flow rate into the flow rate of the river to determine potential concentrations of the three metals of concern (see Table III± 46) in the river as a result of recharge with contaminated groundwater. The results of this screening (available in the Risk Assessment Background Document) demonstrate that concentrations of the constituents of concern are likely to be VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00073 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55756 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules well below risk thresholds for human health and aquatic life in surface water.

What is EPA's Listing Rationale for This Waste?

We propose not to list digestion scrubber water from the production of titanium dioxide via the sulfate process. The results of our risk assessment show that this waste category does not warrant listing as a hazardous waste. (6) Sulfate process digestion sludges.

How Many Facilities Generate This Waste Category and How Is It Managed?

The Maryland and Georgia facilities generate this sludge. The Georgia facility manages it in a dedicated surface impoundment and the Maryland facility places it in an on site landfill. As described above, the waste is not an exempt mineral processing waste because this sulfate process wastestream did not meet the high volume/ low toxicity criteria noted in 54 FR 36592 (September 1, 1989). (See 40 CFR 261.4( b)( 7)( ii).)

What Management Scenarios Were Assessed? We assessed both management scenarios using the respective samples collected at each facility. The surface impoundment scenario screened out; the levels of constituents in the wastewater were below HBLs and AWQC. We modeled the landfill scenario for potential releases to both groundwater drinking wells and surface water.

How Was This Waste Category Characterized?

We collected one sample of this waste for analysis at the Maryland facility. We conducted total, TCLP, and SPLP analyses. We used the SPLP results as inputs to the on site landfill, which are summarized below in Table III± 47 for the constituents of potential concern.

TABLE III± 47.Ð CHARACTERIZATION OF DIGESTION SLUDGE FROM SULFATE PROCESS, TITANIUM DIOXIDE Constituent of concern Detected SPLP Levels in MI± SO± 02 (mg/ L) HBL (mg/ L) AWQC (mg/ L)

Aluminum ................................................................................................................................................. 2.0 16 0.087 Antimony .................................................................................................................................................. 0.023 0.006 0.014 Copper ..................................................................................................................................................... 0.37 1.3 0.0031 Iron ........................................................................................................................................................... 12.0 5 1 Lead ......................................................................................................................................................... 1 0.004 0.015 0.0025 Manganese .............................................................................................................................................. 0.36 0.73 0.05 Vanadium ................................................................................................................................................. 0.42 0.14 Zinc .......................................................................................................................................................... 0.30 4.7 0.12 1 Results are less than the typical laboratory reporting limit, but are greater than the calculated instrument detection limits.

How Was the Groundwater to Surface Water Risk Assessment Established?

We calculated infiltration rates for the landfill, and divided this flow rate into the flow rate of the river to determine potential concentrations of the three metals of concern (see preceding table) in the river as a result of recharge with contaminated groundwater. Note that this is the same Maryland landfill described elsewhere in III. F. 14. e( 4) and (8). The results of this screening (available in the Risk Assessment Background Document) demonstrate that concentrations of the constituents of concern are likely to be well below risk thresholds for human health and aquatic life in surface water.

How Was the Groundwater Ingestion Risk Assessment Established? See the comparable discussion for the gypsum (III. F. 14. e( 4)). The groundwater ingestion scenario was assessed for antimony and vanadium because the detected SPLP concentrations exceeded their respective HBLs. We did not assess the iron HBL exceedence because the HBL is at or above the solubility limit in ground water under most conditions. The resultant risks were calculated and are summarized in Table III± 48.

TABLE III± 48.Ð GROUNDWATER PATHWAY RISK ASSESSMENT RESULTS FOR DIGESTION SLUDGE FROM SULFATE PROCESS, TITANIUM DIOXIDE Antimony HQ Vanadium HQ Adult risk Child risk Adult risk Child risk 90th .................................................................................................................................. 0.13 0.27 0.02 0.03 95th .................................................................................................................................. 0.18 0.39 0.03 0.07 What Is EPA's Listing Rationale for This Waste?

We propose not to list this waste. The results of our risk assessment modeling show that this waste does not contain mobile metals that are likely to pose risk to human health and the environment due to transport through the subsurface. (7) Commingled wastewaters from the chloride and sulfate process. How Many Facilities Generate This Waste Category and How Is It Managed? The Maryland and Georgia facilities generate this waste category. Both facilities neutralized their commingled wastewaters and manage them in surface impoundments prior to NPDES discharge (but convey exempt solids into the wastewater treatment system where those solids are removed to form sludges that are comprised of exempt solids and non exempt solids, depending on the specific piping of the plants).

What Management Scenarios Were Assessed?

We collected samples at both facilities at the influent to their surface impoundment trains. We screened the VerDate 11< MAY> 2000 20: 03 Sep 13, 2000 Jkt 190000 PO 00000 Frm 00074 Fmt 4701 Sfmt 4702 E:\ FR\ FM\ 14SEP2. SGM pfrm12 PsN: 14SEP2 55757 Federal Register / Vol. 65, No. 179 / Thursday, September 14, 2000 / Proposed Rules 55 Although wastes from calcining are generally treated as Bevill exempt extraction/ beneficiation wastes, wastes from titanium dioxide calcination are post mineral processing, chemical manufacturing wastes. The Agency noted at 54 FR 36619, `` As discussed in the April NPRM, the Agency considers any operations following the initial [mineral] processing operation to be [mineral] processing operations, regardless of whether the activity was included on the list of RTC beneficiation activities or has traditionally been considered beneficiation. '' Therefore, since mineral processing ends and chemical manufacturing starts at the beginning of oxidation, and the calcining step occurs after oxidation, all wastes generated from the calcining step are non exempt wastes. risk at both facilities using the analytical data describing their respective wastes. We concluded that the Georgia facility was not a modeling candidate because none of the constituents detected in its waste exceeded our health based levels or the ambient water quality criteria. At the Maryland facility, we modeled the surface impoundment scenario using the physical parameters describing their unlined impoundment. We assessed both the surface water and drinking water well scenario.

How Was This Waste Category Characterized?