1 BACKGROUND INFORMATION 4 Water Quality Concerns 4 Beneficial Uses Affected 4 Slough Hydrology and Segmentation 4 Available Monitoring Data 5 DISSOLVED OXYGEN 8 Water Quality Criteria 8 Monitoring 8 Modeling 9 Loading Capacity Defined 10 Allocations 12 Implementation Strategy 14 Airport storm water permit 14 Designated Management Agencies 15 Industrial storm water permits 16 New discharges 16 EUTROPHICATION ( PH AND NUTRIENTS) 16 Water Quality Criteria 16 Monitoring 17 Modeling 21 Loading Capacity and Margin of Safety Defined 22 Allocations 23 Implementation Strategy 24 BACTERIA 26 Water Quality Criteria 26 Monitoring 27 Data Analysis 27 Margin of Safety 29 Loading Capacity Defined 29 2 Allocations 30 Implementation Strategy 30 TOXICS 31 Water Quality Criteria 31 Pb Monitoring 33 Instream data 33 Loading Capacity and Margin of Safety Defined 35 Allocations 36 Implementation Strategy 39 Industrial permittee requirements 40 Environmental Cleanup Sites 40 Designated Management Agencies 41 Organics Monitoring 41 Fish tissue sampling 41 Loading Capacity Defined 42 Allocations 43 Implementation Strategy 44 Industrial Storm water permits 45 Environmental Cleanup Sites 45 Designated Management Agencies 45 REFERENCES 46 TEMPERATURE ANALYSIS 49 Water Quality Criteria 49 Monitoring 49 Modeling 49 CONVERSION FACTORS 51 3 Columbia Slough TMDLs WQ Concerns at a Glance:

Water Quality Limited? Yes Segment # 22P COLSO, mouth to Fairview Lake Water Quality Standards: Willamette Basin, OAR 340 41 442, OAR 340 41 445 Parameters with Season Water Quality Limited: Bacteria  annual pH  spring through fall dissolved oxygen ( cool water aquatic life)  annual chlorophyll a  spring through fall phosphorus spring through fall temperature  spring through fall Pb  water column DDE, DDT  fish tissue PCBs fish tissue 2,3,7,8 TCDD  fish tissue dieldrin  fish tissue ( preventative TMDL) Uses Affected: Salmonid fish rearing, resident fish and aquatic life, wildlife and hunting, fishing, boating, water contact recreation, aesthetic quality Known Sources: Industrial discharges, combined sewer overflows, groundwater, urban storm water, landfill leachate, airport de icing, clean up sites Suspected Sources: Sediments, agricultural runoff, failing septage fields, air deposition Water quality in the Columbia Slough is affected in a complex manner by sources such as combined sewer overflow events, groundwater, landfill leachate, airport de icing fluids, urban runoff, past practices and industrial runoff, as well as conventional National Permit Discharge Elimination System ( NPDES) point sources. The Total Maximum Daily Load ( TMDL) strategy will be to identify the loading capacity of the Slough for the pollutants of concern and implement a water quality management plan ( WQMP) to control the identified sources and achieve the TMDLs. The WQMP will incorporate load allocations and waste load allocations, water level management and implementation of storm water Best Management Practices ( BMPs). The TMDL will utilize a phased approach through which the effectiveness of controls will be assessed with a monitoring program and additional controls required if waste loads, loads and TMDLs are not being achieved. The controls will be implemented via Memorandums Of Agreement ( MOAs) with the designated management agencies ( DMAs). For most of the Municipal Separate Storm Sewer System ( MS4) permit holders the permit incorporates the agreements in the MOAs as a permit condition. Requirements for urban storm water control for Multnomah County, however, will be implemented via revisions to their MS4 permits since their permit does not incorporate the TMDL requirements of the MOA. 4 BACKGROUND INFORMATION The Columbia Slough is a 19 mile long complex of narrow and shallow channels located on the southern floodplain of the Columbia River between Fairview Lake and the Willamette River. The Slough was originally a series of wetlands and marshes; it is now a highly managed water system with dikes and pumps to provide watershed drainage and flood control for the lowlands surrounding it. The management of the Slough can have a significant impact on the water quality and uses supported by the Slough. The Slough drains approximately 40,000 acres of land. Many kinds of land use are found within the watershed including heavy and light industries, residential areas, vegetable farming and the Portland International Airport. The Slough also serves as one of the City's largest open space and wildlife habitat areas.

Water Quality Concerns The Columbia Slough, from the mouth to Fairview Lake, has been placed on DEQ's 1994/ 1996 303( d) list for multiple parameters. The Slough is water quality limited for chlorophyll a, pH and phosphorus from spring through fall, because of algal growth. This algal growth affects the aesthetic quality of the Slough and may affect such beneficial uses as fishing and boating. The dissolved oxygen criteria for cool water aquatic life is violated throughout the year; diurnal swings in dissolved oxygen during the summer months are most likely the result of algal growth, while winter violations are likely due to storm water runoff, including de icing fluid. These dissolved oxygen criteria violations may prevent the Slough from supporting salmonid fish rearing as well as resident fish and aquatic life. Elevated bacteria levels through all seasons impact the water contact recreation use ( swimming). In the spring through fall, high temperatures are also a concern, affecting salmonid fish rearing. The Slough is water quality limited for DDE, DDT, PCBs and dioxin due to elevated levels found in fish tissue, impairing the use of the Slough for fishing. The State of Oregon Health Division and the City of Portland have issued recommendations against eating fish from the Slough due to contamination by PCBs, DDE and DDT. Review of data also indicates that dieldrin is present in fish tissue at elevated levels. The Slough is water quality limited for lead ( Pb) because of levels above the fresh water chronic criteria for the protection of aquatic life.

Beneficial Uses Affected The affected beneficial uses for the Columbia Slough, as identified in Oregon Administrative Rules, include salmonid fish rearing, resident fish and aquatic life, fishing, hunting, boating, water contact recreation and aesthetic quality.

Slough Hydrology and Segmentation The Slough has been divided into five reaches ( Figure 1, CH2MHill, 1995), based primarily on hydraulic characteristics. The reaches of the Slough are generally shallow with variable widths. 5 The Lower Slough ( Reach 1) extends from the Willamette River to the Multnomah County Drainage District Pump Station No. 1 at NE 13th Avenue ( MCDD1) and includes the North Slough. The Lower Slough is tidally influenced, so the water quality in the Lower Slough is heavily influenced by that in the Willamette River. At MCDD1 there is a dike that physically separates the Lower and Middle Sloughs. Potential sources of pollutants to Reach 1 include sediments, combined sewer overflow events, groundwater, storm water, leachate from St. Johns landfill, industrial discharges, and water from Reach 2 and the Willamette River. The Middle Slough ( Reach 2) extends from MCDD1 to a cross levee ( mid dike) which has slide gates that can hydraulically isolate flows between the Middle and Upper Sloughs. About half the annual flow in the Middle Slough is due to groundwater. Potential sources of pollutants to Reach 2 include sediments, groundwater, storm water, illicit discharges, and contamination from the NuWay Oil Site and water from Reach 3. The Upper Slough ( Reach 3) extends from the mid dike to the outlet of Fairview Lake. The Upper Slough receives considerably less groundwater than the Middle Slough. West of Four Corners, the Slough is subject to reversal of flows due to the operations of the Multnomah County Drainage District Pump Station No. 4 ( MCDD4) located on Marine Drive. MCDD4 discharges directly to the Columbia River. The arm of the Slough to MCDD4 often has little or no flow exchange with other portions of the reach. During the summer it is basically a stagnant waterbody. The Middle and Upper Slough are not driven by tidal influences or affected by CSO discharges. The system hydraulics are influenced by the MCDD pump stations and inflow of groundwater. Potential sources of pollutants include sediments, groundwater, storm water, industrial discharges and water from Reach 4. Fairview Lake ( Reach 4) is a shallow lake that covers about 105 acres. The lake is not considered part of the Slough, but contributes to the flow of the Slough. During the summer months, however, flow from Fairview Lake to the Upper Slough is negligible compared to the flow from groundwater ( CH2MHill, Part 2, 1995). The flow from Reach 5 ( Fairview Lake drainage basin, not pictured) includes the tributaries of Fairview Lake, which are composed of Fairview Creek, Osborn Creek, and No Name Creek. This reach is not part of the Slough, but it discharges to Fairview Lake.

Available Monitoring Data The Columbia Slough has been monitored sporadically. Metropolitan Service District ( METRO) has been conducting water quality monitoring near St. John's landfill in the Lower Slough since the 1970' s. Portland State University ( PSU) conducted water quality monitoring in 1992 1994 for dissolved oxygen ( DO), temperature and pH. The City of Portland Bureau of Environmental Services ( BES) has conducted monitoring in the Slough since 1992, including hydrolab data for pH, temperature and DO. Additional water quality monitoring has been conducted by the City of Gresham and the US Environmental Protection Agency ( EPA). Toxics data for the Columbia Slough includes water column data, fish tissue data and sediment data. Toxics for which the Slough is routinely monitored include the following metals: cadmium, chromium, copper, nickel and lead. Most of the fish tissue data available for the Columbia Slough was collected as part of the Screening Level Risk Assessment done on Slough sediments as part of the Sediment Remediation Project. As part of this study, fish and crayfish were collected during the summer of 1994 at 10 different locations in the Columbia Slough, and tested 6 for 110 different chemicals. Historical fish tissue data was collected by DEQ as part of a larger investigation of the Lower Willamette River. The following sections discuss the results of monitoring of the Slough, and the allocations and strategies developed to attain water quality standards for each 303( d) list parameter. 7 Figure 1: Columbia Slough 8 DISSOLVED OXYGEN Water Quality Criteria Dissolved oxygen ( DO) is important for maintaining a healthy and balanced distribution of aquatic life. Salmonid species are the most sensitive beneficial use affected by dissolved oxygen concentration. For waterbodies, such as the Columbia Slough, identified by the Department of Environmental Quality ( DEQ) as providing cool water aquatic life, the dissolved oxygen must not be less than 6.5 mg/ L. When DEQ determines that adequate information exists, the dissolved oxygen may not fall below 6.5 mg/ L as a 30 day mean minimum, 5.0 mg/ L as a seven day minimum mean, and may not fall below 4.0 mg/ L as an absolute minimum ( OAR 340  41 445).

Monitoring Synoptic water quality data show DO criteria violations throughout the Slough. During winter, DO criteria violations occur frequently and the DO concentrations are the lowest in the Lower Slough and the main stem of the Middle Slough. During the winters of 1990  1994 there were frequent exceedances of the DO criteria at reaches 2A and 1B ( CH2MHill, Part 1, 1995). A severe DO depletion problem was recorded in February 1995 in the Middle and Lower Slough. DO in the Lower Slough was recorded as zero for almost two days. This severe oxygen depletion occurred after a severe winter storm hit Portland on February 12th, 1995. Significant snow and ice accumulation lasted until February 15th or 16th. Portland International Airport ( PDX) used de icing and anti icing chemicals ( ethylene glycol and urea) with high BOD ( biochemical oxygen demand) values during this time period. The severe oxygen depletion appears to be a result of the de icing activities ( Wells 1995). The dissolved oxygen sag in the Lower Slough, at the St. John's landfill bridge ( SJB), is presented graphically in Figure 2:

February 95, DO sag site SJB 0 2 4 6 8 10 12 15 Feb 16 Feb 17 Feb 18 Feb 19 Feb 20 Feb 21 Feb 22 Feb 23 Feb Date DO mg/ L Figure 2: February 95 Dissolved Oxygen Lower Slough 9 Another incident of dissolved oxygen depression occurred during February 1996. The DO was below 4 mg/ L for almost 10 days at the North Denver Bridge ( NDB) in the Lower Slough. This DO drop occurred after about 8 days of freezing weather. At MCDD1 ( main stem, Middle Slough) DO concentrations were below 4 mg/ L for about 3 days. No impacts of depressed dissolved oxygen were seen above the airport's discharge at NE 92 ND , NE 158 Th., nor at MCDD4 ( main stem, Upper Slough) ( Wells, 1996). This data suggest de icing and anti icing loads dominate the BOD load to the Slough, resulting in oxygen standard violations with anoxic conditions. There are limited DO data available for Reaches 2B, 2C and 2D during the winter months. Data from Reach 3 did not indicate any water quality problems related to DO ( CH2MHill, Part 1, 1995). Summer violations of the DO criteria occur much less frequently than winter violations and may be due to stagnant water and algal processes. Because the DO criteria violations which occur in the summer appear to be caused by algal processes, they are addressed in the eutrophication section. The following discussions of modeling efforts, loading capacity and implementation strategy only address the winter dissolved oxygen criteria violations.

Modeling A water quality model has been used to estimate the effects of winter weather and wet weather loads, particularly from Combined Sewer Overflows ( CSOs) and storm water. The water quality and hydrodynamics model is an adaptation of the Corps of Engineers' model CE QUAL W2 ( Corps of Engineers, 1986, 1990; Cole and Buchak, 1994). Event based pollutant loads from storm water were estimated, including de icing loads from PDX. Model calibration is described in Wells, 1995.

Modeling conclusions:   The major components affecting DO in Reach 1 are upstream discharges from Reach 2, storm water, CSOs and sediment oxygen demands.   De icing materials from PDX contribute to severe oxygen depletion in the Middle and Lower Slough in the late fall and winter.   De icing loads from PDX will have to be reduced significantly to meet dissolved oxygen criteria in the Slough ( Wells, October 1996).   Flood events in the Willamette and/ or Columbia River worsen the oxygen depression because they stagnate the water in the Lower Slough ( Wells, October 1996).

Monitoring data has indicated that low DO levels in the Slough are of concern primarily in the winter months. Because of this, the loading capacity and allocations will be defined for the wet weather BOD loads only. Data analysis and modeling has demonstrated that de icing and anti icing activities at PDX are the dominant source of BOD to the Slough. Anoxic conditions are observed in the Slough when de icing and anti icing loads are coupled with stagnant water conditions. Model calibration by Wells ( 1995) indicates that the BOD load from urban runoff is less than 1/ 2 the concentration reported in the municipal separate storm sewer ( MS4) permits. The implementation strategy will require the DMAs to refine estimates of the BOD load to the Slough and the effect on water quality. The strategy will also require PDX to reduce the de icing and anti icing load. 10 Loading Capacity Defined The ambient DO criteria concentration is used to determine the loading capacity ( LC) of the Slough for BOD materials. The LC is expressed as an ultimate biochemical oxygen demand. The BOD LC is dependent on the deoxygenation ( Kd) and aeration ( Ka) rate. The resulting load allocations are for the winter months of November through March. Allocations are not defined for BOD loads during the summer months. Analysis of data provided by Union Carbide and PDX resulted in a range of possible Kd values for the Slough. Values for Ka were calculated using the Banks and Herrera formula using wind speed and waterbody depth. See Appendix B for a detailed description of this analysis. Once the appropriate Ka and Kd values were chosen, a dissolved oxygen balance ( Streeter Phelps equation) was used to determine a range of ultimate BOD ( Lo) that would result in the attainment of the DO criteria of 6.5, 5.0 and 4.0 mg/ L DO. The Streeter Phelps equation is given as :

( ) ( ) [ ] ( ) ( )] [ ] D K K K K t K t L C C K t d a d d a o s a =

     +     exp exp exp 0 Where: D = DO deficit ( mg/ L) Lo = instream BOD ( BOD ultimate) ( mg/ L) Kd = decay rate (/ day) Cs = DO at saturation ( mg/ L) Ka = aeration rate (/ day) Co = DO initial ( mg/ L) t = time ( days)

( Thomann et al, 1987)

The Streeter Phelps equation contains several assumptions; there is one dominant source of BOD, DO of a stream is unaffected by nitrification and algal respiration, replacement of oxygen is affected by reaeration and not by algal photosynthesis, there are steady state conditions along the river channel. During the winter months, when de icing influences water quality, algal photosynthesis processes will be negligible. PDX has stopped using urea in its de icing operations, so nitrification is not a significant BOD load. In response to comments from PDX, the oxygen analysis was expanded to include dispersion. Dispersion acts to spread the plug of high strength BOD out as it moves down the Slough. By adding dispersion it was no longer assumed that the discharge was continuous or that steady state conditions exist. The de icing discharge was assumed to occur for 1 day per event. Dispersion is represented by the following equation ( Chapra, 1997):

E U B H gHS x = 0 011 2 2 .

where: Ex = longitudinal dispersion coefficient ( m2/ s) U = velocity ( m/ s) B = width ( m) H = depth ( m) 11 g = acceleration due to gravity ( m/ s2) s = channel slope ( dimension less)

A one dimensional dissolved oxygen model was used ( LTI, July, 1997) to represent the influence of dispersion on the Streeter Phelps model predictions. The model divided the Columbia Slough into a one dimensional series of completely mixed reactors of constant volume. The model solves two differential mass balance equations; one each for BOD and DO. Conditions in the Lower Slough appear critical because this is where the BOD plug can stagnate when the Willamette flows are high. The BOD calculations simulated conditions as measured in the field when the anoxic DO levels were recorded; temperatures were near 8 ° C. The five day BOD ( BOD5 ) limits should be expressed in the terms that they would be measured at the laboratory, at standard temperature of 20 ° C. The laboratory measure, and TMDL, will be presented as BOD5. The conversion is made in a two step process that is consistent with how the samples would be handled. First the BOD sample is taken from the field to the laboratory and allowed to equilibrate to 20 ° C which increases the decay rate and is represented as: k k T T =   20 20   ( Tchobanoglous et al, 1985). By rearrangement, k k T T 20 20 =     . The temperature adjustment factor (  ) is 1.102. The calculations to determine   are contained in Appendix B.

The BODu is then converted to BOD5 by the following equation: BODt = BODu( 1 e kt) Where: t= time, 5 days k = the decay rate, at 20 ° C ( Tchobanoglous et al, 1985)

The loading capacity was calculated using the following equation: LC = ( Q)( BOD5)( conversion factor) Where: Q = river flow in cubic meters/ second ( m3/ sec) BOD5 = calculated BOD5 in mg/ L conversion factor = to convert from m3/ sec and mg/ L to kg/ day A portion of the loading capacity is set aside as the margin of safety ( MOS). The margin of safety accounts for the uncertainty about the relationship between pollutant loads and water quality of the receiving water. A baseflow of 1.98 m3/ sec ( groundwater flow only) and storm flows are used to calculate the loading capacity. The storm flows range from 2.83 11.33 m3/ sec, approximating the range of flows achieved by pumping at MCDD1. The results of this analysis are summarized in Table 1. 12 Table 1: BOD5 Loading Capacity The DO water quality criteria has three tiers to recognize that the effect of reduced DO on fish and aquatic life is dependent on how low the DO gets as well as the duration and frequency of the low DO. Since the sources are non steady state pulse loads from runoff, the LC is identified for three specific conditions; an hourly maximum BOD load based on achieving the minimum DO criteria ( 4.0 mg/ L), an event daily average maximum based on achieving the 7 day mean minimum DO criteria ( 5.0 mg/ L), and a long term continuous average based on achieving the 30 day mean minimum DO criteria ( 6.5 mg/ L).

Allocations The TMDL is a matrix of flows and associated average, daily average maximum and hourly maximum BOD5. The LC is distributed between the dominant sources of oxygen demanding material, which include PDX de icing and urban runoff. The background ( BKG) BOD5 concentration is set to 2.5 mg/ L ( Appendix B). The WLA for CSOs is zero ( except for a one in five year winter storm and one in ten year summer storm). A margin of safety ( MOS) is set at 20% of the total BOD5 load at each flow for each DO criteria ( Appendix B). The distribution between airport and urban runoff is based on a percent reduction equivalent to the relative contribution to the observed DO deficit. Modeling results from Wells ( 1995, EWR 2 95) were used to estimate the contributions. The modeling used measured discharge, DO, temperature and limited instream BOD. Storm water and de icing BOD loads were adjusted to fit the measured data. This calibration effort indicated that de icing and anti icing loads contribute 3.8 lb. of BOD load for every 1 pound of urban storm water BOD. The waste load allocations incorporate the ratio of 3.8 lb/ 1 lb de icing and anti icing load removed to urban storm water removed. The loading capacity is therefore defined as:

LC = QCbkg + QCmos + QCsw + QC de icing where: Flow, m3/ sec DO criteria ( mg/ L) LC ( BODu, mg/ L) LC ( BOD5, mg/ L) LC ( kg/ day) MOS ( kg/ day) LC and MOS to meet 4.0 mg/ L DO criteria 2.83 4 48 24 5947 1189 5.66 4 64 33 16108 3222 8.5 4 61 31 22842 4568 11.33 4 69 35 34583 6917 LC and MOS to meet 5 mg/ L DO criteria 2.83 5 41 21 5170 1034 5.66 5 56 28 13893 2779 8.5 5 53 27 19920 3984 11.33 5 60 31 30262 6052 LC and MOS to meet 6.5 mg/ L DO criteria 2.83 6.5 32 16 4004 801 5.66 6.5 42 22 10571 2114 8.5 6.5 41 21 15537 3107 11.33 6.5 48 24 23782 4756 13 C sw( WLA) = Cso( 1  ) or the concentration of the storm water in the waste load allocation is equal to the initial storm water concentration times the reduction needed and: C de icing( WLA)= C de icingo( 1  b), b= 3.8 or the de icing waste load allocation is a function of the initial de icing concentration, the reduction needed and the ratio between storm water and de icing runoff.

The final formula is: LC = QCbkg + QC mos + Q( Cso( 1  )) + Q( C de icingo( 1  b))

The constant   represents the % urban storm water reduction necessary to achieve the BOD loading capacity. This reduction was calculated by iteration. The allocation for the airport is divided between the Port of Portland ( PDX) and the Oregon Air National Guard ( ANG). By analysis of the de icing use estimates provided to DEQ by the Port and the Air National Guard, it was determined that the Port contributes about 89% of the de icing load. The Port therefore receives 89% of the total airport waste load allocation ( WLA). The Oregon Air National Guard receives 11% of the total airport allocation. This is represented mathematically as:

PDX = total airport LA x 0.89 ANG = total airport LA x 0.11 From application of SIMPTM ( Simplified Particulate Transport Model) the City of Portland predicted a 150% increase in the storm water pollutant loading over current loads to the Columbia Slough ( BES, 1989). SIMPTM is a continuous storm water quality program that can simulate the accumulation and washoff of total solids or particulates plus up to six different pollutants. Current storm water loads are given 2/ 3 of the BOD5 allocation and future growth receives 1/ 3 of the allocation. The storm water allocation includes storm water from two sources: industrial facilities that are required to have general industrial storm water permits, and urban runoff from areas in the Slough watershed that are managed by the designated management agencies. To estimate the area covered by the industrial permits, a review of general storm water permits in DEQ was conducted. The area covered by these permits was calculated. By assuming that 100% of the facilities that need industrial permits are covered in these files, the area was calculated to be 997 acres. Using an adaptation of the simple method ( EPA 1992), the annual load of BOD5 from industrial permitted sites can be calculated:

Area x Annual Rainfall x Runoff Coefficient x Pollutant Concentration = Annual Pollutant Load area = 997 acres runoff coefficient = 0.681 annual rainfall = 34.4 inches2 pollutant concentration = 68 mg/ L BOD3 1 Table 3 13, Part 2, City of Portland MS4 permit application, industrial land use runoff coefficient. 2 Table 3 12, Part 2, City of Portland MS4 permit application, storm event statistics. 3 Table 3 14, Part 2, City of Portland MS4 permit application, water quality pollutant concentrations utilized for land use pollutant loading model, industrial land use. 14 Using this equation, a value of 358, 342 lb/ year of BOD5 is obtained for permitted industrial sites. To estimate the BOD5 load from the area managed by the designated management agencies ( DMAs) ( under MS4 permits), the BOD5 load from the MS4 areas is used. An estimate of the total annual BOD5 load from the area covered by the Portland MS4 permit is contained in Appendix C of the City of Portland MS4 application. Using the values for runoff coefficients and pollutant concentrations for the subbasins that drain to the Slough, an annual BOD5 load of 655,274 lb/ yr is calculated. The Gresham MS4 report ( Gresham 1996) estimated the annual BOD5 load to the Slough as 115, 246, lb/ yr. The total annual BOD5 load from the areas managed by the DMAs ( under the MS4 permits) is 770,520 lb/ yr. The industrial load of 358,342 lb/ yr is approximately 46.5% of the total urban load. The industrial sites are allocated 46.5% of the annual storm water BOD5 allocation, after the allocation for future growth is set aside. This is represented mathematically as: Future growth WLA = total urban storm water WLA x 0.333 DMA WLA = total urban storm water WLA x 0.6667 x 0.535 Industrial storm water WLA = total urban storm water WLA x 0.6667 x 0.465 BKG = 2.5 mg/ L x 1.98 m3/ sec x conversion factor = 428 kg/ day The allocation for PDX includes several co permittees. The BOD5 allocations are summarized in Table 2. Differences in the margin of safety ( MOS) between Table 1 and Table 2 are due to rounding.

Table 2: BOD5 Waste Load Allocations Implementation Strategy Airport storm water permit PDX ( and co permittees) will be required to conduct additional instream and source load monitoring and modeling to refine estimates of the rates and loads used to generate the LC. Based on these efforts, the LC and WLA may change. The water quality monitoring is a joint effort with the City of Portland and the City of Gresham. PDX will be required to develop and implement pollution control measures designed to achieve the WLA. The schedule to meet the WLA depends on the control option PDX selects. Option 1 is treatment and discharge from PDX to the Columbia River. Option 2 is treatment and discharge to the Columbia Slough. The specific Flow ( m3/ sec) BKG Future Growth DMA Industrial SW PDX ANG MOS TMDL WLA to achieve 4.0 mg/ L DO criteria, BOD5, kg/ day 2.83 428 188 201 175 3342 413 1200 5947 5.66 428 869 931 809 8752 1082 3237 16108 8.50 428 1585 1702 1479 11641 1439 4568 22842 11.33 428 2435 2608 2267 17679 2185 6981 34583 WLA to achieve 5.0 mg/ L DO criteria, BOD5, kg/ day 2.83 428 187 200 174 2801 346 1034 5170 5.66 428 854 914 795 7225 893 2784 13893 8.50 428 1553 1664 1446 9645 1192 3992 19920 11.33 428 2361 2529 2198 14825 1832 6089 30262 WLA to achieve 6.5 mg/ L, DO criteria, BOD5, kg/ day 2.83 428 183 198 172 1978 244 801 4004 5.66 428 822 889 773 4935 610 2114 10571 8.50 428 1500 1607 1396 6652 822 3132 15537 11.33 428 2251 2411 2095 10504 1298 4795 23782 15 timetable and requirements will be contained in an individual NPDES permit. The following schedule assumes that DEQ will issue the permit by summer 1998. Under the permit PDX will be required to: 1. Implement, during the winters of 1998/ 1999 and 1999/ 2000, a monitoring program for a series of de icing events. The monitoring will include an approved Quality Assurance/ Quality Control plan. The monitoring will provide synoptic data sets of loads and instream response throughout the period of the de icing event and the instream advection of the de icing pulse to the Willamette River. Synoptic monitoring will include: temperature, BOD5, dissolved oxygen, pH, stream flow, pumping rates at MCDD1, and Lower Columbia Slough stage. De icing load monitoring will include BOD5, dissolved oxygen and discharge. 2. By October 2000 provide DEQ with a final report describing model calibration efforts. The report will present the basis for the selection of rates and coefficients used in model calibration, a description of how the rates were derived and the precision of calibration. 3. By October 2000 identify the final TMDL BOD allocations to be achieved with implementation of controls. 4. Option 1: By winter 2003/ 2004 construct the treatment facilities and implement BMPs necessary to meet the final BOD allocations. Demonstrate compliance with the WLA or: 5. Option 2: By winter 2004/ 2005 conduct pilot testing of treatment facilities and implement BMPs. By winter 2005/ 2006 demonstrate compliance with the WLA.

Designated Management Agencies The DMAs will conduct monitoring of storm water BOD5 loads and the instream response to those loads. Previous monitoring under the MS4 permits has measured BOD5 levels from urban runoff that do not correlate with the few instream BOD5 samples taken during storm events. The discrepancy between loads and instream concentration is likely due to processes such as deposition and decay during the transport to the receiving water. The monitoring data will be used to calibrate a dynamic water quality model to simulate the Slough's response to storm water and deicing fluid. The DMA WLA will not be included as an effluent limit. Achievement of the WLA will be through implementation of BMPs. Municipal discharges will be required to implement BMPs and demonstrate that the BMPs achieve the WLAs established. The DMAs will be required, through MOAs, to: 1. Provide DEQ with a description of the program designed to reduce BOD5 loads to the Slough. 2. Implement a program of BMPs that will reduce overall BOD5 load to achieve the DMA WLAs. 3. Implement coordinated monitoring to define storm water loads to the Slough and the influence of storm water BOD5 on receiving water quality. 4. Implement monitoring to demonstrate compliance with BOD5 WLA targets. Instream monitoring will include grab samples of BOD5 and DO and continuous hydrolab monitoring. 5. Implement water quality management plans as developed as part of the Lower Willamette Subbasin plan ( projected completion spring 1999).

Table 3: BOD Control Strategy 16 Reach Control Strategy Responsible DMA 1 1,2,3,4, City of Portland, PDX 2 1,2,3,4 City of Portland, PDX 3 1,2,3,4 City of Portland, City of Gresham 4 1,2 City of Fairview, Multnomah County 5 1 5 1 5 1,2 5 1,2,4 City of Fairview, City of Wood Village, City of Gresham, Multnomah County Oregon Department of Agriculture Oregon Department of Transportation Industrial storm water permits DEQ anticipates implementing storm water permits through application of BMPs. When storm water permits are renewed, a basin specific general storm water permit will be developed by DEQ to address BOD5 loads as well as other 303( d) parameters. The permit will include monitoring and BMP requirements to reduce the BOD5 load to the Slough. The WLA for industrial storm water will not be incorporated into NPDES industrial storm water permits as individual effluent limits.

New discharges Future growth and development will either have to demonstrate that adequate reserve capacity exists in the TMDL or trade effluent with the City of Portland, PDX or other DMA.

Eutrophication ( pH and nutrients)

Water Quality Criteria Eutrophication is the increased primary productivity that occurs in an aquatic system as a result of nutrient input. Nutrients increase primary production and photosynthesis rates. The pH of water can be directly influenced by photosynthesis. Plant growth increases pH during the day as plants utilize carbon dioxide in the water during photosynthesis. At night, plants respire and produce carbon dioxide which decreases pH. pH outside the range in which the species evolved may result in both direct and indirect toxic effects. The water quality standard states that " pH values shall not fall outside the ranges identified in paragraphs ( A), ( B), and ( C) of this subsection. ( A) Columbia River: 7.0  8.5; ( B) All other basin waters ( except Cascade lakes): 6.5  8.5; ( C) Cascade lakes above 3,000 feet altitude: pH values shall not fall outside the range of 6.0 to 8.5." ( OAR 340 41 445 ( 2) ( d)) Photosynthesis may also cause diurnal swings in the dissolved oxygen levels. The dissolved oxygen criteria are discussed in the dissolved oxygen TMDL. Elevated nutrient levels also generate nuisance conditions due to algal growth. Chlorophyll a is an indirect measurement of algal biomass. Oregon rules ( OAR 41 150( 1)( b) cite an action level for average chlorophyll a concentrations of 15 ug/ L ( 3 month average based on a minimum of 3 samples) to control growth of nuisance phytoplankton. When the action level is exceeded, DEQ will conduct studies to describe the water quality problem and develop a proposed control strategy. 17 DEQ has established interim targets of 0.1 mg/ L total phosphorus ( TP) and 0.02 mg/ L ortho phosphate ( O PO4). These values are based on EPA guidelines ( EPA Quality Criteria for Water, EPA, 1986) and Best Professional Judgment of DEQ staff. The CE QUAL W2 model has been calibrated to evaluate the influence of nutrient loads and hydraulics on water quality.

Monitoring Continuous pH data on the Slough demonstrate large swings in pH on a diurnal basis in the summer ( CH2MHill, Part 1, 1995). Values above 8.5 have occurred in the spring to fall. During the summer, reaches 1A and 2B frequently had pH levels above 8.5. Similar diurnal patterns between pH and DO suggest that eutrophication is the cause of the violations, as DO is produced by photosynthesis. Total phosphorus concentrations greater than the 0.1 mg/ L guideline occur throughout the Slough, throughout the year. ( CH2MHill, Part 1, 1995) Sections of Reach 2 and Reach 1 showed frequent exceedance of the dissolved ortho phosphate guideline. Exceedance of the nitrate guideline was found throughout the Slough during all seasons ( CH2MHill, Part 1, 1995). During the summer, spring and fall, the Columbia Slough also exceeds the action level for chlorophyll a, although the fall averages are often skewed due to high chlorophyll a values in the summer . Winter chlorophyll a values are generally low ( CH2MHill, Part 1, 1995). The following graphs demonstrate this exceedance, at sites in the Lower and Upper Slough, respectively ( 1993 1997 grab data).

SJB, chlorophyll a 3 month average 0.000 5.000 10.000 15.000 20.000 25.000 30.000 35.000 40.000 45.000 50.000 55.000 60.000 65.000 70.000 75.000 1/ 0 2/ 19 4/ 9 5/ 29 7/ 18 9/ 6 10/ 26 12/ 15 day chlorophyll a, ug/ L Figure 3: Site SJB chlorophyll a 3 month average 18 US 1, chlorophyll a 3 month average 0.000 5.000 10.000 15.000 20.000 25.000 30.000 1/ 0 2/ 19 4/ 9 5/ 29 7/ 18 9/ 6 10/ 26 12/ 15 day chlorophyll a, ug/ L Figure 4: Site US 1, chlorophyll a 3 month average Despite elevated average chlorophyll a values, summer chlorophyll a values have decreased recently ( since 1992), although not to the action level. The following table shows data for July  September, when available.

Table 4: Summer Chlorophyll a values Site Year SJB ( RM 2.9) US 1 ( RM 8.7) 1992 53.6 35.9 1993 NA NA 1994 NA NA 1995 7.68 3.13 1996 30.43 18.75 1997 32.0 19.08 Improvements in pH variation have been observed in the summer of 1996 in the Slough. At St. John's Landfill Bridge ( site SJB, main channel, Lower Slough, Reach 1) there has been significant improvement in pH since 1992, as seen in the following graphs generated from continuous Hydrolab data: 19 pH fre qu e ncy , S JB , 1 9 92 6 .5 7 7 .5 8 8 .5 9 9 .5 0% 10% 20% 3 0 % 40% 50% 60% 70% 80% 90% 10 0%

freq u en c y p H Figure 5: pH July   September 92 pH frequency, SJB, 1996 6.5 7 7.5 8 8.5 9 9.5 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

frequency pH Figure 6: pH July   September 1996 At site MCDD1, summer 1996 pH levels were within the criteria, for data recorded when the hydrolab was properly calibrated. Additional pH data is contained in Appendix C, although data for summer 1993 and 1994 is limited. Dissolved orthophosphate values in both the Upper and Lower Slough were approximately 0.02 mg/ L, or at the guideline level ( summer 1996 grab data). Examination of data from summer 1992 at sites SJB and MCDD1 did not indicate any violations of the 4 mg/ L instantaneous minimum dissolved oxygen criterion ( see Appendix C for data). Samples taken from a location near the outlet of Fairview Lake ( Reach 3), showed frequent and long term oxygen depressions in the summer. The data presented below is from sampling site US 8, located at Fairview Lake outlet in the main channel in Reach 3. However, flow from Fairview Lake is limited by summer operations designed to keep the water level high in the Lake. Resulting stagnant water combined with a relatively high sediment oxygen demand ( SOD) ( 1.9 mg/ m2/ day  O, measured in the forebay to MCDD1, ( Wells, personal communication, 1997) may be causing low DO readings in the sampling location on Reach 3. Additionally, there are no known sources of BOD discharge in this area. These DO concentrations may not be representative of the entire reach ( CH2MHill, Part 1, 1995). 20 Figure 7: Reach 3 summer DO The continuous monitoring equipment at Site US 8 is now placed within Fairview Lake. Currently, the closest continuous dissolved oxygen data is available from Site 158, approximately 2 miles west of the outlet of Fairview Lake. Data from summer 1996 indicates improvement in water quality, with dissolved oxygen levels above the 4.0 mg/ L instantaneous minimum. Figures 8 and 9 summarize this information.

Site 158, DO June  July 1996 0 2 4 6 8 10 12 14 16 18 6/ 9/ 96 0: 00 6/ 14/ 96 0: 00 6/ 19/ 96 0: 00 6/ 24/ 96 0: 00 6/ 29/ 96 0: 00 7/ 4/ 96 0: 00 7/ 9/ 96 0: 00 7/ 14/ 96 0: 00 7/ 19/ 96 0: 00 7/ 24/ 96 0: 00 7/ 29/ 96 0: 00 Date DO, mg/ L Figure 8: Site 158 June  July 1996 Site US 8, DO summer 92 0 1 2 3 4 5 6 7 8 9 10 7/ 23/ 92 0: 00 7/ 28/ 92 0: 00 8/ 2/ 92 0: 00 8/ 7/ 92 0: 00 8/ 12/ 92 0: 00 8/ 17/ 92 0: 00 8/ 22/ 92 0: 00 8/ 27/ 92 0: 00 9/ 1/ 92 0: 00 Date DO, mg/ L 21 Site 158, August  Sept. 96 DO 0 2 4 6 8 10 12 14 16 18 20 8/ 11/ 96 0: 00 8/ 21/ 96 0: 00 8/ 31/ 96 0: 00 9/ 10/ 96 0: 00 9/ 20/ 96 0: 00 9/ 30/ 96 0: 00 Date DO, mg/ L Figure 9: Site 158 August  September 1996 Water level management activities have led to this water quality improvement. However, as discussed previously, the chlorophyll a action level is still exceeded, throughout the year. The action level requires initiating studies to determine the cause of eutrophication. Achievement of the water quality criteria influenced by algal growth ( DO and pH) provides the TMDL requirements. The implementation section describes the water level management activities to date, as well as additional controls that will be necessary to control algal growth.

Modeling Using the CE QUAL W2 model, Wells and Berger ( 1994) demonstrated that a major cause of algal growth in the late summer ( August  September) in the Upper Slough was excessive dissolved ortho phosphate from groundwater and in Lower Slough was mainly from discharges of nutrients and algal rich water from the Upper Slough. Point source loads are minor. Most of the point source summer PO4 loads are a byproduct of the origin of the water source, because the discharges are of cooling water. Various management strategies have been simulated to evaluate their effect on water quality in the Slough. Wells ( 1995, EWR 2 95) simulated a 90% reduction in dissolved ortho phosphate in groundwater and results demonstrated that this reduction would result in the lowest chlorophyll a concentration of all the simulations. Modeling also indicated ( Wells and Berger, 1993) that reducing the water level from 8 ft to 5 ft MSL ( outflow of 70 CFS) would reduce the overall detention time from about 4 days to less than one day. Reducing the detention time decreased the time available for algal growth. The detention time determines the loading capacity of the Slough for nutrients. As a result of the modeling water level management was initiated in the Slough. Rooted aquatic vegetation is growing in the Upper Slough. A significant loss of the nutrients supplied by groundwater has been observed. The loss appears 22 associated with greater settling of solids and uptake by epiphytes associated with the macrophytes. The effect of this vegetation on Slough water quality was modeled, as was the effect of increased total phosphate loads. To account for the affect of macrophyte growth on Upper Slough water quality the base case simulations used the average 1996 data for inflow concentrations from the Upper Slough. The effect of groundwater and minor storm water inputs were simulated. Total phosphate loads were increased by increasing the ortho phosphate load. Additional simulations were conducted in which total phosphate was increased by increasing both the ortho phosphorus and algae. The algae flowing from the Upper to the Lower Slough served as a seed for algae in the Lower Slough, so this was a conservative modeling approach. The total phosphate loads and the resulting pH are graphed below ( memo from Chris Berger, Portland State University, to DEQ, draft, May 15, 1998). Simulations demonstrate that at current conditions ( the first point on each graph) the maximum pH is about 8.14. The minimum dissolved oyxgen was 7.33 mg/ L ( memo from Chris Berger, Portland State University, to DEQ, draft, May 15, 1998). The effect of summer storm water loads was also modeled and compared to the base run, which simulates existing conditions. Results indicate that the effect of summer storm water loads is minimal, with the predicted DO and pH meeting the criteria.

Algal Growth in Columbia Slough in relation to changes in PO4 load 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 15.00 20.00 25.00 30.00 35.00 40.00 Load ( kg/ d) Maximum pH Increase only Ortho Increase Ortho and Algal seed Figure 10: Total Phosphate Loads and pH Loading Capacity and Margin of Safety Defined A loading capacity is defined only for total phosphate because the Slough is so nitrogen rich that PO4 is the limiting nutrient. A review of summer 1992 data at North Portland Bridge in the Lower Slough indicated that NO3 N was present at levels 10 times greater than total phosphate levels. As seen in Figure 10, the current load of total phosphate is 23.25 kg/ day. With a total phosphate load of 27.1 kg/ day ( for simulations with both increasing ortho phosphate and algae seed) the pH will raise to 8.5. To set allocations and a margin of safety, the instream concentration which met this load was calculated by dividing the load by the estimated total flow simulated. The maximum instream concentration is 0.1549 mg/ L total phosphate ( to a pH of 8.5). To set allocations at flows of 1.98 23 m3/ sec, 2.83 m3/ sec and 5.66 m3/ sec, the instream concentrations were multiplied by flow to calculate the allowable daily load. This calculation is as follows:

1.98 m3/ sec X 0.1549 mg/ L X 1000L/ m3 X 1 kg/ 106 mg X 60 sec/ min X 60 min/ hr X 24 hr/ day = 26.5 kg/ day = loading capacity The loading capacity was then divided between groundwater, storm water, one point source discharge, the margin of safety ( MOS) and the loss due to macrophytes. The distribution between storm water and groundwater was calculated using the ratio of storm water to groundwater loads used in the modeling. The ratio is 0.27 storm water to 0.73 groundwater. The loss to macrophytes was calculated as the difference between concentrations measured upstream of MCDD1 and the concentrations at MCDD1 ( memo from Chris Berger, Portland State University, to DEQ, draft, May 15, 1998). The margin of safety is set by using the conservative modeling results in which total phosphorus is increased by increasing both ortho phosphate and algae seed concentrations. Additionally, the remaining loading capacity, after allocation to the existing loads, is set aside as the numerical margin of safety.

Allocations Allocations are set only for the spring through fall ( April October), when the Slough is water quality limited due to eutrophication. No allocations are set for the winter months. Uncontrolled sewage receives an allocation of zero. Additionally, by 2002, combined sewer overflows ( CSOs) will receive a zero allocation except for a 1 in 10 year summer event. The 1 in 10 year storm event discharge is allocated at the current CSO load. Modeling shows that new waste water point source loads during periods of algal growth would increase productivity and standards violations, so a WLA of zero for new point source loads of PO4 is established. One point source discharge may discharge phosphate and receives an allocation that results in no measurable increase above existing instream total phosphate levels. The calculation for this waste load allocation is discussed below.

Existing Point Source Discharge Oregon Fresh Farms ( OFF) operates a carrot packaging plant and discharges to the Whitaker Slough. The discharge occurs from July  December, and may extend into February. This discharge receives an allocation for total  phosphate that results in no measurable increase above current levels. Using data from BES, the median ( approximate) value for total phosphate in Whitaker Slough is 0.14 mg/ L ( 65 samples, March 1 June 30, 1995 1997). Upstream flow was calculated as the average of measured daily flow from July  February ( 161 samples. BES database). The flow from Oregon Fresh Farms was calculated as the average of the average daily flows recorded on the Discharge Monitoring Reports ( DMRs) for the facility ( DMRs dated September  November 1997.) The allocation is calculated as follows: ( Cups)( Qups) + ( Ceff)( Qeff) = ( Cmix)( Qmix) Where: Cups = upstream concentration = 0.14 mg/ L Qups = upstream flow = 27.2 CFS Ceff = effluent concentration = X Qeff = effluent flow = 1.5 CFS 24 Cmix = concentration of mixed stream = Cups + CDL = 0.16 mg/ L CDL = 0.02 mg/ L ( DEQ detection limit for total phosphate analysis) Qmix = flow of mixed stream = 28.7 CFS Solving for Ceff, yields a total phosphate concentration of 0.52 mg/ L. Using the average daily flow from the DMRs, the load allocation is:

0.52 mg/ L x 1.5 ft3/ sec x 1 m3/ 35.3 ft3 x 1 kg/ 106 mg x 60 sec/ min x 60 min/ hr x 24 hr/ day x 1000L/ m3 = 1.91 kg/ day The loading capacity is allocated as follows: LC = groundwater + storm water + OFF + MOS + Loss + CSO + untreated sewage The results are summarized in Table 5.

Table 5: Total Phosphate Loading Capacity and Allocations Allocations ( kg/ day)

Flow ( m3/ sec) Groundwater Storm water OFF Loss MOS CSO Sewage LC 1.98 20.9 7.7 1.9  5.9 1.9 0 0 26.5 2.83 29.9 11.1 1.9  8.5 3.5 0 0 37.9 5.66 59.8 22.1 1.9  16.9 8.9 0 0 75.8 Implementation Strategy Groundwater Controls Algal growth is controlled by several factors including solar radiation, stream flow and transport, nutrient cycling and nutrient loads. In the Columbia Slough the dominant factor influencing summer algal growth that can be managed and controlled is stream flow and transport, and to a lesser extent nutrient cycling and solar radiation. The previously described modeling demonstrates that the dominant source of nutrients is from groundwater. Groundwater controls have already been established for the Slough, but the effectiveness at PO4 reduction is uncertain. In 1984, a study concluded that more than 14 million gallons a day of waste from unsewered areas of Mid Multnomah County were discharged directly to the groundwater, which flowed toward the Slough ( The East County Sanitary Sewer Consortium, June 1984). Sanitary sewers will be constructed in this area and all property owners connected to it by the year 2005 ( East Multnomah County, 1995) ( Findings and Order, Environmental Quality Commission, 1/ 30/ 86). With the removal of these cesspools, a significant source of nitrate to the Slough is expected to be removed, but it will take approximately 30 years for a reduction of 40 percent of nitrogen in groundwater ( CH2MHill, Part 2, 1995). In addition, groundwater may continue to have high phosphorus concentrations ( 0.074 mg/ L PO4 P)) 4; other local 4 Average of 5 samples measured at NE112 from 7 9/ 96. NE112 is believed to be close to pure groundwater ( Wells August 1997) 25 aquifers that are unaffected by cesspools have high phosphorus content ( CH2MHill, Part 2, 1995). The influence of sewering East Multnomah County on groundwater PO4 concentration is not known.

Water level management The management strategy for eutrophication focuses on water level management in the Slough. During the summer of 1996, water level management increased the flows through the Middle Slough ( Reach 2) by decreasing water levels and increasing the groundwater inflow. The water level in the Middle Slough ( Reach 2) was dropped to 6 feet MSL, down from 8 feet. The mid dike levee was closed. Gravity flow was also used between the Middle ( Reach 2) and Lower Slough ( Reach 1) to lower the water level. There was a visible reduction of algae in many parts of the Middle Slough, but there was an increase in rooted aquatic vegetation. This increase in macrophytes is likely due to shallower depths and increased water clarity which allow sunlight to penetrate to the Slough bottom and rooted vegetation to grow. The establishment of macrophytes has resulted in reduced levels of dissolved ortho phosphate, suspended solids and turbidity. The decrease of dissolved ortho phosphate may be due to biological uptake by the macrophytes or algal epiphytes. Water level management demonstrated significant reduction of algae. The City of Portland will be required to continue instream monitoring to evaluate the effectiveness of water level management. The increased macrophyte growth results in greater flood control management problems for the Multnomah County Drainage District ( MCDD). The DEQ will work with MCDD to develop a management plan and to document the influence of the macrophyte growth on beneficial uses of the Slough.

Storm water Best Management Practices Specific responsibilities for monitoring water quality and implementing BMPs to control storm water phosphate loading will be contained in MOAs DEQ will negotiate with each DMA. Instream water quality will continue to be monitored to help assess trends in water quality and determine if BMPs are improving water quality. General requirements that will be contained within the MOAs are summarized below:

Designated management agencies 1. Identify at least 3 representative sites for the Lower ( Reach 1), Middle ( Reach 2) and Upper ( Reach 3) Slough for long term monitoring of water quality in the Slough to determine the effectiveness of the implementation strategy. 2. Identify representative site in Fairview Lake ( Reach 4) and Fairview Creek ( Reach 5) to characterize water quality in these water bodies and determine effectiveness of control strategies. Water quality parameters will include DO, pH, temperature, chlorophyll a, dissolved ortho phosphate, total phosphate and bacteria. 3. Maintain the hydrolab pH measurements as well as the grab samples of pH, dissolved ortho phosphate, chlorophyll a , DO and temperature. 4. Identify BMPs in MS4 permits which may reduce contributions of phosphate via storm water. 5. Include PO4 in assessment of BMP effectiveness by measurement of influent and effluent dissolved ortho phosphate concentrations and total phosphate concentrations. 26 6. Remove CSOs except for a 1 in 10 year summer event and one in five year winter event. 7. Implement water quality management plans as developed as part of the Lower Willamette Subbasin plan ( projected completion spring 1999).

These requirements are listed by responsible DMAs, for each reach, below:

Table 6: Nutrient Control Summary Reach Control Strategy Responsible DMA 1 1,3,4,5,6 City of Portland 1 1,3,4,5 PDX 2 1,3,4,5 City of Portland, PDX 3 1,3,4,5 City of Portland, City of Gresham 4 2,4,5 City of Fairview, Multnomah County 5 1 5 1 5 2,4,5 7 1,3,4,5 City of Fairview, City of Gresham, City of Wood Village, Multnomah County Oregon Department of Agriculture Oregon Department of Transportation BACTERIA Water Quality Criteria The purpose of the bacterial water quality standard is to protect the most sensitive designated beneficial use, which is primary water contact recreation, such as swimming. Recreational exposure to water polluted with human pathogens can cause skin and respiratory ailments, gastroenteritis, and other illnesses. Certain species of bacteria are used as indicators for the presence of other microbes because of their common fecal origin and the relative ease by which they can be counted. The State of Oregon recently adopted a new bacteria criteria which changes indicator species from fecal coliform to E. coli and contains narrative provisions that describe the requirements for a water quality plan for water quality limited waterbodies. Most of the available bacteria data for the Columbia Slough is fecal coliform, so the water quality limited designation for the Slough was determined by compliance with the historical standard. Under the historical criteria, samples may not exceed 200/ 100mL log mean based on a minimum of 5 samples in a 30 day period; no more than 10% of samples in a 30 day period may be > 400/ 100mL. Because of the difficulty in sampling frequently enough to determine compliance with the criteria, DEQ has allowed flexibility in interpretation of available data. A waterbody is considered water quality limited for bacteria, and placed on the 303( d) list, when the geometric mean of fecal coliform bacteria exceeds 200 per 100 milliliters or more than 10% of the samples and a minimum of at least two samples exceed 400 per 100 milliliters for the season of interest. ( DEQ, 1996) Under the new criteria, samples may not exceed a 30 day log mean of 126 E. coli organisms per 100 mL, based on a minimum of 5 samples. No single sample may exceed 406 E. coli organisms per 100 mL. The criteria prohibits the discharge of raw sewage into waters of the State ( OAR 340 41 445 ( 2) ( e)). The sewage must be treated in a manner approved by DEQ. Current regulations describe the implementation 27 requirements for water quality limited ( WQL) waterbodies. Bacteria management plans must be developed for waterbodies that are water quality limited for bacteria. These management plans will identify the specific technologies and BMPs to be implemented by point and nonpoint sources to limit bacterial contamination. For point sources, the bacteria management plan will be part of their NPDES permit. For nonpoint sources, the bacteria management plan will be developed by the DMAs which will identify the appropriate BMPs. Additionally, the criteria state that domestic waste collection and treatment facilities are prohibited from discharging raw sewage during November 1 through May 21 except during a storm event greater than the one in five year, 24 hour duration storm. Facilities are prohibited from discharging raw sewage during the period of May 22 through October 31, except during a storm event greater than the one in ten year, 24 hour duration storm.

Monitoring Due to the cost of collecting 5 samples in a 30 day period, insufficient fecal coliform data are available to evaluate historical compliance with the standard. Because of the scarcity of data and the change in the bacteria standard to E. coli, fecal coliform data are compared to the 303( d) listing criteria. Enterococci data are used only to provide evidence of fecal contamination. Fecal contamination appears throughout the Slough, although the magnitude of the contamination varies widely. Appendix C contains additional fecal coliform data. The highest bacteria concentrations have been found in the Lower Slough in winter months, indicative of CSO events. In Reaches 1A and 1B, winter samples often had fecal coliform levels greater than 1000/ 100 mL. In Reach 1B, about 74% of the winter samples are greater than 400/ 100 mL. For the spring, there are few fecal coliform or enterococci samples, but the available data indicate fecal contamination. In the summer, Reaches 1B and 1C had fecal coliform values greater than 1000/ 100 mL. About 31% of the summer samples in Reach 1B had fecal coliform concentrations greater than 400/ 100 mL. Enterococci concentrations for these reaches also were high (> 200/ 100 mL), indicating that the bacteria were of fecal origin. In the fall, Reaches 1B and 1C show elevated fecal coliform values (> 1000/ 100 mL). Enterococci samples confirm the evidence of fecal contamination in these reaches in the fall ( CH2MHill, Part 1, 1995). Data for the Middle Slough ( Reach 2) also indicates fecal contamination. About 14% of the winter samples for Reach 2A had values greater than 400/ 100mL. In the summer Reach 2A had fecal coliform values greater than 1000/ 100 mL. In the fall, Reaches 2A and 2C show elevated fecal coliform values(> 1000/ 100 mL). Enterococci samples confirm the evidence of fecal contamination in these reaches in the fall ( CH2MHill, Part 1, 1995). Data from 1995  1998 does not indicate a violation of the fecal coliform criteria in Reach 3. The geometric mean of the samples from east of the mid dike levee to the outlet of Fairview Lake is 73 CFU/ 100 mL. At the 90th percentile, the fecal coliform concentration is < 300 CFU/ 100 mL.

Data Analysis Part II of the Water Body Assessment ( CH2MHill, 1995) describes the modeling efforts that were undertaken in order to quantify pollutant loads to the Columbia Slough. The 28 EPA storm water model SWMM ( EPA 1992) was used to develop estimates of flows and pollutant loadings from the various land use categories and subbasins draining to the Slough. The data collected as part of the Portland storm water NPDES permit were used to calibrate flow contributions and derive land use based event mean pollutant concentrations ( EMCs) for specific pollutants. Pollutant loads were based on land use. The basin's response to storm events was calibrated by comparing monitored flow rates for numerous storm events recorded between December 1991 and December 1994. Table 7 summarizes the results by reach for fecal coliform bacteria. Model predictions using E. coli are not available, but overall trends in loads are expected to be the same.

Table 7: Estimated Percentage Breakdown of Fecal Coliform Loads Source Lower Slough Middle Slough Upper Slough summer winter summer winter summer winter storm water 1.1 1.3 4.8 21.4 90.9 90.9 CSO 67.0 84.3 NA NA NA NA unknown/ uncontrolled 9.0 8.8 94.9 76.6 0.0 0.0 upstream 1.5 2.9 0.3 2.0 9.1 9.1 Smith & Bybee Lakes 0.3 0.1 NA NA NA NA Willamette River 21.1 2.6 NA NA NA NA NA = not applicable These results indicate that Combined Sewer Overflows ( CSOs) are the dominant source of bacteria in the Lower Slough. The Upper and Middle Slough contribute only < 3% of bacteria loads to the Lower Slough. The Middle Slough is mainly affected by illicit sources such as failing septic systems and illicit connections. In the Upper Slough, the most significant source appears to be storm water. There are 13 CSO outfalls located in the Lower Slough itself, and because the Lower Slough is tidally influenced, it is additionally impacted by the presence of CSOs in the Willamette River. CE QUAL W2 modeling indicates that removal of the CSOs will bring the Lower Slough into compliance with the bacteria standard. ( Wells, EWR 2 95). Approximately 85 90% of CSOs in the Willamette will be removed when the CSO program for the Willamette River is complete. The Middle Slough does not contain any CSOs, however there are indications that illicit discharges are taking place. These indications are:   Measured instream concentrations are substantially higher than those predicted via modeling. This indicates the presence of previously unsuspected source( s) not incorporated into the model ( CH2MHill, WBA, Part II).   The staff of the Multnomah County Drainage District has observed conditions in the Middle Slough that they believe indicate houses in the area discharge directly to the Slough ( Hayford, personal communication).   A search of the City of Portland's records pertaining to the sewer system in the vicinity of the Middle Slough, indicates that there are houses for which no record of connection exists.

Table 8 compares existing instream summertime conditions to model predictions for the Middle Slough, which assumes no illicit discharges, to the fecal criteria. Comparison is of the predicted instream fecal coliform values to the two components of 29 the criteria; 200/ 100 mL as the median value for compliance and 400/ 100 mL as the instantaneous maximum.

Table 8: Comparison of Fecal Coliform Values in the Middle Slough Scenario % of values that exceed 200/ 100 mL % of values that exceed 400/ 100 mL. 1. Existing ( with illicit discharge) 30.6 15.9 2. Proposed ( with illicit discharge removed) < 1 < 1 The existing case is based on sampling results. For the proposed case, they are based on modeled results ( CH2MHill, 1995). Unknown sources appear to be the major sources of bacteria. Modeling results indicate that the elimination of storm water from Reach 2 would not have a significant effect on bacteria. In contrast, the model predicted that elimination of fecal coliform in storm water in Reach 3 ( Upper Slough) would reduce the frequency of exceedances of the fecal coliform standard from 16 percent to zero percent. Storm water was the only modeled source containing coliform in Reach 3. Because existing data on the Upper Slough is too limited to state whether or not there are problems with respect to bacteria, additional monitoring will be needed to confirm the modeling conclusions. To implement the new bacteria standard, the TMDL requires development of bacteria management plans. The management plans will include detection and removal of illicit discharges, control of bacteria from storm water and monitoring to demonstrate compliance with the criteria. The TMDL also requires the removal of sources of raw human waste.

Margin of Safety The Upper Slough is not impacted by CSOs, so the margin of safety is calculated by examination of modeling and monitoring results for the Upper Slough. Modeling of instream response to bacteria loads into the Upper Slough ( Wells, EWR 2 95) has a precision of ± 15 fecal coliforms. This measurement of precision is used to define the margin of safety. Because the model results were for fecal coliform and the criteria is now E. Coli, data from the Upper Slough ( 1995  1998) was reviewed to determine if their is a relationship between measured E. Coli data and measured fecal coliform data. The data sets are significantly related ( probability < .01) and the ratio of E. Coli/ fecal coliforms is 0.82. The ratio is multiplied by the precision to obtain the MOS: 15 fecal coliforms x ( 0.82 E. Coli/ fecal coliforms) = 12.3 E Coli.

Loading Capacity Defined The bacteria criteria contains two components; < 126 log mean based on a minimum of 5 samples in a 30 day period and no single sample > 406. To determine the loading capacity the E. coli log mean criterion is multiplied by the range of flow in the Slough.

Table 9: E. Coli Bacteria Loading Capacity 30 Flow ( m3/ s) Criteria ( MPN/ 100 mL) 5 LC ( MPN/ day) MOS ( MPN/# 100 mL) MOS ( MPN/ day) LC MOS ( MPN/ day)

Base Flow 1.98 126 2.16 x 1011 12.3 2.10 x 1010 1.95 x 1011 Storm Flow 2.83 126 3.08 x 1011 12.3 3.01 x 1010 2.77 x 1011 5.66 126 6.16 x 1011 12.3 6.02 x 1010 5.55 x 1011 8.50 126 9.25 x 1011 12.3 9.03 x 1010 8.34 x 1011 Allocations The untreated CSO discharges to Columbia Slough will be eliminated except during storms greater than or equal to a storm with a five year return frequency from November 1 through April 30 and except during storms greater than or equal to a storm with a ten year return frequency from May 1 through October 31. ( Amended Stipulation and Final Order No. WQ NWR 91 75). CSOs therefore receive a wasteload allocation of zero, except for the storms as stated in the Order. Raw sewage also receives an allocation of zero. As seen in Table 7, upstream sources contribute about 10% of the bacteria to the Slough and storm water 90%. The loading capacity ( minus the margin of safety) is allocated to these two sources proportional to their contribution. Table 10 summarizes the allocations. The allocations are annual.

Table 10: E. Coli Allocations Allocations ( MPN/ day)

Flow Source 1.98 m3/ sec 2.83 m3/ sec 5.66 m3/ sec 8.50 m3/ sec CSO 0 0 0 0 raw sewage 0 0 0 0 storm water 1.75 x1011 2.49 x 1011 5.00 x 1011 7.51 x 1011 upstream 1.95 x 1010 2.77 x 1010 5.55 x 1010 8.34 x 1010 MOS 2.10 x 1010 3.01 x 1010 6.02 x 1010 9.03 x 1010 LC 2.16 x 1011 3.08 x 1011 6.16 x 1011 9.25 x 1011 Implementation Strategy The narrative standard requires that the WLA for human sources be zero and that BMPs be implemented to the maximum extent practicable ( MEP) for urban storm water. The designated management agencies ( DMAs) will develop a bacteria management plan, as described in OAR 340 41 015, that will include:

1. CSO Program: This program will reduce the occurrence of CSO events in the Columbia Slough with a variety of projects, including roof drain disconnection, sewer and storm water separation, and construction of a consolidation conduit and wet weather treatment facility to treat storm water.

5 log mean 31 2. Sanitary surveys of septic systems, removal of direct discharges of human waste to the Slough. 3. Detect and eliminate illicit discharges to the Slough 4. Establish adequate monitoring to demonstrate compliance with E. coli criteria, including measuring E. coli concentrations and distributions. 5. Implement BMPs to control anthropogenic source of bacteria in storm water. 6. Implement water quality management plans as developed as part of the Lower Willamette Subbasin plan ( projected completion spring 1999).

Instream bacteria monitoring is intended to meet 3 goals:

1. assess long term trending 2. determine spatial distribution of bacteria 3. determine seasonal distribution of bacteria Results of the monitoring will be used to identify bacteria " hot spots" that require further investigation.

Industrial storm water permittees will be required to detect and eliminate discharges of human waste to the Slough. They will also be required to implement BMPs to the MEP to control bacteria loads from other than human sources.

The responsibilities of each DMA are summarized below, by reach:

Table 11: Bacteria Control Summary Reach Control Strategies Responsible DMA 1 1,2,3,4,5 City of Portland 1 2,3,4,5 PDX 2 2,3,4,5 City of Portland, PDX 3 2,3,4,5 City of Portland, City of Gresham 4 3,4,5 City of Fairview, Multnomah County 5 1 5 1 5 3,4,5 6 2,3,4,5 City of Fairview, City of Gresham, Multnomah County, City of Wood Village Oregon Department of Agriculture Oregon Department of Transportation Toxics Water Quality Criteria The State has water quality criteria for toxics that are intended to protect both aquatic life and human health.

OAR 340 41 445( 2)( p)( A): Toxic substances shall not be introduced above natural background levels in the waters of the state in amounts, concentrations, or combinations which may be harmful, may chemically change to harmful forms in the environment, or may accumulate in sediments or bioaccumulate in aquatic 32 life or wildlife to levels that adversely affect public health, safety, or welfare; aquatic life; wildlife; or other designated beneficial uses;

OAR 340 41 445( 2)( p)( B): Levels of toxic substances shall not exceed the criteria listed in Table 20 which were based on criteria established by EPA and published in Quality Criteria for Water ( 1986), unless otherwise noted;

OAR 340 41 445( 2)( p)( C): . . . Where no published EPA criteria exist for a toxic substance, public health advisories and other published scientific literature may be considered and used, if appropriate, to set guidance values.

The Department has developed five conditions to interpret and apply the water quality criteria and determine impact on a beneficial use:

A. Water Quality Criteria Violations occur if: 1. The freshwater chronic criteria for protection of aquatic life contained in OAR Table 20 is violated more than 10% of the time and for a minimum of two values. For hardness dependent criteria, the criteria will be calculated based on the instream hardness measured at the time of sampling. 2. The chemical is found in sediments at levels which analytical models demonstrate that water quality standards are violated. The analysis and modeling must be reviewed and approved by DEQ.

B. Measure of impairment of a Beneficial Use 1. A fish or shellfish consumption advisory or recommendation issued by the Oregon State Health Division specifically refers to this chemical. 2. The chemical has been found to cause a biological impairment via a field test of significance such as a bioassay. The field test must involve comparison to a reference condition. 3. The chemical has been detected in more than 10% of available fish tissue samples, and the population mean6 of the samples exceeds a screening value derived from Table 20. The screening value is developed as follows: Fish Tissue Screening Value ( mg/ kg) = Table 20 Criteria for Protection of Human Health( ng/ l)  BCF ( l/ kg) *( mg/ 106 ng) where BCF = Bioconcentration Factor. BCFs were obtained from the EPA Region VIII Criteria Chart ( July 1993).

The OAR Table 20 criteria are total recoverable metal criteria for the protection of freshwater aquatic life. EPA has recommended the use of the dissolved fraction of the 6 Helsel's method is used for calculating the population mean when nondetects are present. This option is available on the software uncensored v4.0 by Michael C. Newman, K. Dawn Greene, & Phillip M. Dixon from Savannah River Ecology Laboratory, Aiken, South Carolina. To simplify the initial screening for the statewide 303( d) list the condition reads "... 10% of available fish tissue samples, and the mean of the detects exceeds a screening level value from Table 20." 33 metal, as it is the most biologically available form of the metal. To calculate the dissolved Pb criterion, a two step calculation is necessary; adjust the criterion for hardness and utilize a conversion factor. The hardness correction is calculated as follows:

total lead criteria = e( 1.273[ ln( hardness)] 4.705) ( EPA 1986)

A conversion factor ( CF) for Pb is then calculated to convert the criteria to the dissolved form as follows:

CF = 1.46203  [ ln( hardness)( 0.145712)] ( EPA 1996)

If the hardness is measured with each individual sample, a conversion factor and criterion can be calculated for each sample.

Pb Monitoring Instream data BES has collected 296 dissolved Pb and hardness samples from all reaches of the Slough, throughout all seasons. Using the hardness measured with each individual sample, a conversion factor and criterion was calculated for each sample. The mean of the individual conversion factors is 0.82. From the frequency distribution of the criteria ( Figure 11), the 5th percentile criterion was calculated to be 0.0012 mg/ L Pb. The 5th percentile represents a " worst case" assumption ( EPA, 1995). As seen in Figure 12, approximately 16.7% of the dissolved Pb samples exceed this criterion 7. When the samples were compared with their respective criterion, 10.4% of the samples exceed the criterion.

Dissolved Pb criteria, frequency distribution 0 10 20 30 40 50 60 0.001 0.0012 0.0014 0.0016 0.0018 0.002 0.0022 0.0024 0.0026 0.0028 0.003 More frequency 0 10 20 30 40 50 60 70 80 90 100 Cumulative frequency Figure 11: Dissolved Pb criteria, frequency distribution 7 296 samples, non  detected values set at detection limit of 0.001 mg/ L 34 Dissolved Pb data 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0% 10% 20% 30% 40% 50% 60% 70% 80% 9 0% 10 0%

f req uenc y Pb, mg/ L Figure 12: Instream dissolved Pb data frequency distribution ( includes non detects)

The Columbia Slough is water quality limited for the metal lead ( Pb) because of criteria exceedance in the water column.

Sources Unlike the conventional pollutant analyses, detailed modeling for toxics with CEQUAL W2 has not been conducted. However, potential sources of Pb to the Slough have been analyzed. Such sources include; municipal and industrial storm water, industrial discharges, CSOs, contaminated sites, contaminated sediment, St. John's Landfill, and air emissions. The analyses to estimate the Pb loads from these sources are contained in Appendix A ( sources document). Table 12 summarizes the estimates of total lead loads to the Columbia Slough. 35 Table 12: Summary of Total Pb loads to the Columbia Slough Source Lead ( kg/ yr) Industrial Discharges 0.19 Combined Sewer Overflows 75.7 Storm water ( total) 1131 MS4 area only 9908 Industrial permitted area only 141 Groundwater Overall loading 26 NuWay Oil Site ( to Whitaker Slough) groundwater sediment partitioning soil erosion process area soil erosion  non process area 1.65 x 10 5 27.1 0.438 0.005 St. John's Landfill 1.31 Miscellaneous Sediment Partitioning 0.030 Air Deposition9 Oregon Steel wet deposition Oregon Steel dry deposition 0.014 8.99 x 10 7 Spills estimate not available Illicit Discharges estimate not available Total of Estimates: 1262 With non detected values set to the detection limit, instream Pb data appears to be close to the chronic criteria. Estimates of Pb loads to the Slough have been calculated primarily for total Pb, not dissolved. These estimates indicate that storm water from municipal and industrial property contributes most of the Pb load. However, the simple method ( EPA 1992) used to develop the storm water load estimates does not account for processes that occur during transport of storm water to the Slough, such as sedimentation and resuspension. The TMDL will focus on refining estimates of loads from various land uses, including estimates of the dissolved Pb load.

Loading Capacity and Margin of Safety Defined As stated previously, OAR Table 20 criteria are defined as total recoverable metal. In the monitoring data for the Columbia Slough, the predominant form of Pb is dissolved Pb. The loading capacity and allocations are calculated to meet the dissolved Pb criteria. To convert the allocations to total recoverable Pb, the values can be divided by the mean of the conversion factors calculated with each hardness value ( 0.82). The loading capacity of the Columbia Slough for Pb is defined as the 5th percentile aquatic life chronic criteria ( adjusted for hardness and converted to dissolved 8 The calculated total Pb load minus the load associated with industrial areas. 9 Using the 50th percentile mass load. 36 form) times the flow in the Columbia Slough. A baseflow of 1.98 m3/ sec ( groundwater flow only) and storm flows are used to calculate the loading capacity. The storm flows range from 2.83 8.50 m3/ sec, approximating the range of flows achieved by pumping at MCDD1. As described previously, the load estimates were calculated as average annual loads of total Pb. There is little data available to estimate the loads as dissolved Pb, or to model the fate and transport of Pb in storm drains and instream. In Phase I of the TMDL, the allocations are based on dissolved Pb and requirements to quantify the dissolved Pb load from the sources are outlined. Estimates of dissolved Pb loads will be refined in the next phase of the TMDL, and will allow for allocations based on these estimates.

LC ( kg/ day) = flow ( m3/ sec) x 5th percentile criterion ( mg/ L) x conversion factor Using the 5th percentile criterion means that 95% of the field samples should be < 0.0012 mg/ L. The margin of safety is set to decrease that to 0.001 mg/ L or the detection limit. This effectively means that only 5% of the samples to be measured can exceed the detection limit. The difference between the criterion of 0.0012 mg/ L and the detection limit of 0.001 mg/ L is 0.0002 mg/ L. This concentration is multiplied by the flow and subtracted from the daily loading capacity.

Table 13: Dissolved Pb Loading capacity Flow ( m3/ sec) 5th percentile criteria ( mg/ L) LC ( kg/ day) MOS ( mg/ L) MOS ( kg/ day) LC  MOS ( kg/ day) Baseflow 1.98 0.0012 0.205 0.0002 0.034 0.171 Storm flow 2.83 0.0012 0.293 0.0002 0.049 0.244 5.66 0.0012 0.587 0.0002 0.098 0.489 8.50 0.0012 0.881 0.0002 0.147 0.734 Allocations An analysis was performed to determine if there are obvious spatial trends with the Pb data. Figure 13 shows a comparison of dissolved lead levels in the different reaches of the Columbia Slough. Figure 14 shows the distribution of Pb levels in sediment in the Columbia Slough. 37 Comparison of Water Column Pb Levels 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0 2 4 6 8 10 12 14 16 18 20 River Mile Dissolved Pb ( mg/ L)

Reach 1 Reach 2 Reach 3 Buffalo Slough MCDD4 Whitaker Slough Figure 13: Instream dissolved Pb 0 50 100 150 200 250 0 2 4 6 8 10 12 14 16 18 20 River Mile Level in Sediment ( mg/ kg) Reach 1 Reach 2 Reach 3 Figure 14: Pb levels in sediment in the Columbia Slough Higher concentrations in the upper end of the Lower Slough ( Reach 1) may be due to net inflow of sediment from the Willamette ( Li, 1995). Allocations will be set for the entire Slough until spatial distribution can be better defined. 38 Allocations were calculated using flows, concentrations and estimates of annual loads as described in Appendix A. The allocations apply annually.

Industrial Point Source Discharge: The waste load for the one point source discharge is set at the current estimated load of 5 x 10 4 kg/ day.

CSOs: Because they are scheduled for removal, CSOs receive a waste load allocation of zero kg/ yr except for one in 10 year summer event and 1 in 5 year winter event.

St. John's landfill: Pb in ground water from St. John's landfill is set at the estimate of the current load of 3.6 x 10 3 kg/ day.

Ground water: Pb in ground water is set at the current estimated load of 0.07 kg/ day.

Sediment Partitioning: Sediment partitioning and diffusive flux allocation is set by multiplying the estimated water column concentration ( in Table 15 in Appendix A) by the base flow and storm flows through the Columbia Slough. As stated in Appendix A, the estimated water column Pb concentration from partitioning is 2.056 x 10 7 mg/ L. 1.98 m3/ sec x 2.056 x 10 7 mg/ L x 1000 L/ m3 x 1 kg/ 106 mg x 60 sec/ min x 60 min/ hr x 24 hr/ day = 3.52 x 10 5 kg/ day This calculation is done for each of the storm flows as well.

Air deposition: The allocation for the single air source is set at the estimate of the current load; wet and dry deposition. Total deposition = ( 0.014 kg/ yr + 8.99 x 10 7 kg/ yr) = 0.014 kg/ yr = 3.84 x 10 5 kg/ day NuWay Oil Site: The NuWay Oil Site receives an allocation for each of the contributing sources; groundwater, sediment partitioning and surface runoff. The surface runoff allocation is addressed in the storm water section. Ground water from NuWay Oil is allocated at its current load of 4.53 x 10 8 kg/ day. Sediment partitioning at the NuWay Oil Site receives an allocation with a concentration equivalent to the instream concentration contributed by the median of all the contaminated sediment in the Slough. The instream median concentration was 2.056 x 10 7 mg/ L ( see Appendix A). This concentration was multiplied by estimates of baseflow and storm flow within Whitaker Slough. These flows were 0.81 m3/ sec, 0.91 m3/ sec, 1.21 m3/ sec and 1.53 m3/ sec ( corresponding to flows of 1.98, 2.83, 5.66 and 8.5 m3/ sec in the main stem of the Columbia Slough) ( Scott Wells, personal communication)

Storm water: The allocations that are set at current loads and the margin of safety were subtracted from the loading capacity. This remaining capacity is divided between future growth and storm water runoff. Current storm water loads are given 2/ 3 of the Pb allocation and future growth receives 1/ 3 of the Pb allocation. Individual storm water sources will calculate their allocation on a unit area basis. 39 For example, the sum of the allocations for the industrial discharge, ground water, St. Johns' landfill, air deposition, sediment partitioning, and groundwater and sediment partitioning at NuWay oil and the margin of safety equals 0.108 kg/ day ( for the allocations at 1.98 m3/ sec). Subtracting this from the loading capacity of 0.205 kg/ day leaves 0.097 kg/ day to be allocated to future growth and storm water. Future growth receives 1/ 3 of this allocation or 0.031 kg/ day and storm water receives 2/ 3 or 0.065 kg/ day. Storm water allocations will be calculated on a unit area basis, for each flow. At 1.98 m3/ sec, the storm water allocation is 0.065 for the entire Slough drainage basin. The basin is about 40,000 acres or 1.62 x 108 m2 . The unit area allocation is then: 0.065 kg/ day/ 1.62 x 108 m2 = 4.01 x 10 10 kg/ day/ m2 To determine an allocation for storm water runoff from the NuWay oil site, the area of the site is multiplied by the unit area allocation. The calculation is as follows:

NuWay Oil site process and non process area = 60, 000 ft2 x 1m2/ 10.76 ft2 = 5576 m2 The allocation for surface runoff from NuWay Oil Site is: ( 5576 m2) x ( 4.01 x 10 10 kg/ day/ m2) = 2.24 x 10 6 kg/ day Table 14: Pb allocations Source Allocations ( kg/ day) 10 1.98 m3/ sec 2.83 m3/ sec 5.66 m3/ sec 8.50 m3/ sec Industrial discharge 5.4 x 10 4 5.4 x 10 4 5.4 x10 4 5.4 x 10 4 CSO 0 0 0 0 sediment partitioning 3.52 x 10 5 1.0 x 10 4 1.0 x 10 4 2.0 x 10 4 groundwater: overall St. John's landfill 0.07 3.6 x 10 3 0.07 3.6 x 10 3 0.07 3.6 x 10 3 0.07 3.6 x 10 3 air deposition 3.84 x 10 5 3.84 x 10 5 3.84 x 10 5 3.84 x 10 5 NuWay Oil Site sediment partitioning soil erosion groundwater 1.45 x 10 5 2.24 x10 6 4.53 x 10 8 1.6 x 10 5 2.24 x 10 6 4.53 x 10 8 2.17x 10 5 2.24 x 10 6 4.53 x 10 8 2.7 x 10 5 2.24 x 10 6 4.53 x 10 8 Future growth 0.031 0.055 0.1382 0.2199 storm water 0.065 0.114 0.2765 0.4397 MOS 0.0348 0.0497 0.098 0.147 LC 0.205 0.293 0.587 0.881 Implementation Strategy Pb levels in the Slough exceed the aquatic life chronic criteria, however, the instream Pb data include many values that are at the detection limit and are much lower than the practical quantification limit. As seen below, most of the samples ( 245/ 296) are lower than the criteria and the detection level.

10 Excess loading capacity was allocated to the margin of safety. 40 Table 15: Comparison of detection level and criteria exceedance detection level ( 0.001 mg/ L)

dissolved criteria less than greater than less than 245 19 greater than 1 31 Additionally, an analysis of the relative criteria exceedance on wet and dry days revealed that the wet day exceedance rate ( 10.9%) was not different than the dry day exceedance ( 10.8%). In this analysis, a wet day was defined as one in which the cumulative rainfall on that day and the three days prior exceeded 0.25 inches. Modeling of loads indicate that storm water is the largest contributor of Pb, however, the loads would be expected to result in higher instream Pb levels than what is observed. Modeling by Wells ( 1997) indicates that storm water is diluted about 2 times in the Slough. There are no synoptic data sets linking storm water loads with instream values. Examination of the Portland MS4 permit reveals that commercial, industrial and traffic corridor land uses contribute the largest loads of Pb ( unit load basis), respectively. BMPs should be developed based on land uses, but further delineation of sources based on land use must be done. Under Phase I of the Pb TMDL, DMAs will be required to develop the synoptic data sets. A lower detection limit for the analysis will also be required to gain a better understanding of when and how frequently the criteria is being violated. Phase I will also include measuring the effectiveness of controls at reducing the lead load from storm water. The requirements for all potential contributors of lead are outlined below.

Industrial permittee requirements The DEQ anticipates requiring implementation of BMPs through storm water permits. A basin specific general storm water permit will be developed by DEQ to address all 303( d) pollutants. Requirements of this permit to reduce the lead load are as follows: 1. Monitoring for total and dissolved lead 2. Implementation of BMPs to control or remove metals. 3. Monitor effectiveness of BMPs.

Environmental Cleanup Sites DEQ's Site Response section has conducted a review of the sites in the Environmental Cleanup Site Information ( ECSI) database to determine which of those merit increased attention due to the presence of 303( d) chemicals and proximity to the Slough. High priority sites have been moved to the cleanup program. DEQ water quality program will develop a monitoring protocol to be included in the statement of work for site cleanup to estimate the load of 303( d) pollutants from individual sites. The individual project managers will select BMPs for surface runoff control and metals control and require BMP implementation. 41 Designated Management Agencies 1. Conduct instream dry and storm event monitoring for total lead, dissolved lead and hardness. Conduct lead analysis using detection levels which are lower than the water quality chronic criterion. 2. Conduct monitoring at outfalls to Slough, outfalls selected based on land uses known to have high lead levels or other metals. 3. Identify and implement BMPs in the municipal NPDES permits that will be effective in controlling lead storm water inputs. 4. Monitor to determine effectiveness of BMPs to remove total and dissolved lead from storm water. 5. Estimate the load reduction of lead achieved for storm water at the end of Phase I. 6. Estimate effectiveness of BMPs to remove TSS.

The responsibilities of the DMAs, by reach, is summarized below:

Table 16: Lead Control Summary Reach Control Strategy Responsible DMA 1 1,2,3,4,5,6 City of Portland, PDX 2 1,2,3,4,5,6 City of Portland, PDX 3 1,2,3,4,5,6 City of Portland, City of Gresham 4 3,6 City of Fairview, Multnomah County 5 1 5 3,6 1,2,3,4,5,6 City of Fairview, City of Gresham, Multnomah County, City of Wood Village Oregon Department of Transportation Organics Monitoring Fish tissue sampling Fish tissue data provide the most extensive evidence of impairment of beneficial uses by toxics in the Columbia Slough. Most of the available fish tissue data were collected in the summer of 1994 as part of the sediment remediation project undertaken by BES. Different organisms can be expected to bioaccumulate chemicals differently based on age, life cycle patterns, amount of fatty tissue and feeding habits. However, since bioconcentration factors are generally available for specific chemicals rather than for specific species, results for the different species tested have been grouped together. The BCFs used to develop screening values were obtained from the EPA Region VIII Criteria Chart ( July 1993). Fish tissue screening values can be calculated directly from the OAR Table 20 criteria as follows:

Fish Tissue Screening Value ( mg/ kg) = Table 20 Criteria for protection of human health ( ng/ L)   BCF ( L/ kg) * ( mg/ 106 ng)

Screening values were exceeded for DDT, dieldrin, and PCBs. Table 17 contains a summary of the monitoring results for these chemicals. In August 1995, the Oregon Health Division issued a fish consumption advisory for PCBs and DDT/ DDE. 42 Table 17: Summary of Fish Tissue Exceedances of OAR Table 20 derived screening values Chemical Screening Value ( ug/ kg) No. of values No. of detects(% of total samples) No. of exceedances (% of total samples) 4,4' DDT 1.29 65 15 ( 23.1%) 15 ( 23.1%) aroclor 1248 ( PCB) 2.46 55 6 ( 10.9%) 6 ( 10.9%) dieldrin 3.5 61 24 ( 39.3%) 24 ( 39.3%)

Polychlorinated dibenzodioxins ( dioxins) refers to a group of highly toxic compounds that are generally found together in complex mixtures of congeners ( Parametrix, July 5, 1995). Congeners are compounds formed of the same elements that have different molecular structures. In the case of the various dioxin congeners, the chlorine substitution occurs in different locations on the base molecule. Table 20 of the water quality standards contains one criterion value for dioxin, and it is for the most toxic congener known as 2,3,7,8 TCDD. The results of fish tissue data for 2,3,7,8 TCDD are shown in Table 18.

Table 18: Summary of Dioxin Results for Fish Tissue Location Collected By Date of Collection Value ( ng/ kg) Detection Limit ( ng/ kg) Lower Slough ( above N. Slough) DEQ, National Bioaccumulation Study July 1987 2.86 not reported Lower Slough ( at SP& S bridge) DEQ, National Bioaccumulation Study July 1987 7.66 not reported Lower Slough ( river mile 0 3) Parametrix, for BES Summer, 1994 0.97 not reported Lower Slough ( river mile 6 8.6) Parametrix, for BES Summer, 1994 ND 1.0 Upper Slough ( River mile 0 3) Parametrix, for BES Summer, 1994 ND 0.8 Whitaker Slough Parametrix, for BES Summer, 1994 ND 2.1 North Slough Parametrix, for BES Summer, 1994 ND 0.9 Parametrix samples are composite samples.

The screening value for dioxin is 0.07 ng/ kg. As seen in the above table, 3 of the 7 samples collected exceed this screening value. To summarize, the Columbia Slough is considered water quality limited for PCBs, DDT/ DDE and dioxin due to elevated fish tissue levels. Fish tissue data indicates elevated levels of dieldrin, so a preventative TMDL has been calculated for dieldrin as well. An analysis of the sources of the organics is contained in Appendix A.

Loading Capacity Defined For phase I of the TMDL process the fish consumption criteria to protect human health is used. For a long term exposure, EPA recommends the use of harmonic mean flow for instream flow. Due to the lack of data to calculate harmonic mean flow, the annual average flow is used as an estimate of long term flow. According to the Waterbody 43 Assessment ( CH2MHill, 1995), the total annual inflow to the Columbia Slough, not counting tidal inflow from the Willamette, is 1.48 x 108 m3/ yr. The loading capacity is calculated as follows:

total annual inflow ( m3 / yr) x Table 20 criteria ( ng/ L) x ( 1000 L/ m3) x 1 yr/ 365 days x 1kg/ 1012 ng = loading capacity ( kg/ day)

The Table 20 criterion for DDT is used for DDT and DDE. The following table lists the OAR Table 20 criteria for the protection of human health and the corresponding LCs for the 303( d) organics.

Table 19: OAR Table 20 Criteria11 and LCs for 303( d) Organics Parameter Criteria ( ng/ l) LC ( kg/ day) DDT/ DDE 0.024 9.73 x 10 6 Dieldrin 0.071 2.88 x 10 5 Dioxin ( 2,3,7,8 TCDD) 1.3 x 10 5 5.27 x 10 9 PCBs 0.079 3.2 x 10 5 Allocations The difference between the loading capacity and the WLA for sediment partitioning and diffusive flux ( from Table 15 in Appendix A) will be split evenly into WLAs for total urban storm water and the MOS. The total urban storm water allocation is further divided to account for future growth which may expose soils containing the organics, as well as current storm water loads. The storm water allocation also includes the ECSI sites. As ECSI sites or new storm water sources are identified, they will receive an allocation based on unit area.

WLA for MOS = 1/ 2 x ( LC  WLA for sediment partitioning) WLA for total urban storm water = 1/ 2 x ( LC  WLA for sediment partitioning) Future growth WLA = 1/ 3 total urban storm water allocation Current storm water WLA = 2/ 3 total urban storm water allocation The calculations for DDE/ DDT are summarized as an example. According to Table 15, Appendix A, sediment partitioning contributes 4.87 x 10 13 mg/ L DDT to the water column. This concentration is converted to a mass load as follows:

( 4.87 x 10 13 mg/ L) x ( 1.48 x 108 m3/ yr) x ( 1000L/ m3) x ( 1 kg/ 106 mg) x ( 1 yr/ 365 days) = 1.97 x 10 10 kg/ day The same calculation for DDE yields a mass load of 2.91 x 10 10 kg/ day of DDE to the water column. The total mass load for DDT/ DDE is 4.88 x 10 10 kg/ day.

The WLA for MOS = ½ x ( 9.73 x 10 6 kg/ day   4.88 x 10 10 kg/ day) = 4.86 x 10 6 kg/ day 11 criteria for the protection of human health, water and fish ingestion 44 The WLA for total urban storm water = 4.86 x 10 6 kg/ day. The WLA for future growth = 1/ 3 x ( 4.86 x 10 6 kg/ day) = 1.62 x 10 6 kg/ day The WLA for storm water ( current) = 2/ 3 x ( 4.86 x 10 6 kg/ day) = 3.24 x 10 6 kg/ day NuWay Oil Site Storm water runoff allocation: For PCBs the storm water allocation is 5.3 x 10 6 kg/ day for the entire Slough drainage basin. The basin is about 40,000 acres or 1.62 x 108 m2 . The unit area allocation is then 5.3 x 10 6 kg/ day/ 1.62 x 108 m2 = 3.27 x 10 14 kg/ day/ m2. To determine an allocation for storm water runoff from the NuWay oil site for PCBs, the area of the site is multiplied by the unit area allocation. The calculation is as follows:

NuWay Oil site process and non process area = 60, 000 ft2 x 1m2/ 10.76 ft2 = 5576 m2 The allocation for surface runoff from NuWay Oil Site is: ( 5576 m2) x ( 3.27 x 10 14 kg/ day/ m2) = 1.82 x 10 10 kg/ day No allocations were calculated for the other organics as they have not been found at the site.

No estimates of dioxin loads from sediment partitioning are available, so the loading capacity is divided evenly between the three sources and the margin of safety. The waste load allocations are annual and summarized as follows:

Table 20: Organic Allocations ( kg/ day) 12 Parameter LC LA sediments WLA storm water WLA Future Growth MOS13 NuWay Oil DDT/ DDE 9.73 x 10 6 4.88 x 10 10 3.24 x 10 6 1.62 x 10 6 4.87 x 10 6 N/ A dieldrin 2.88 x 10 5 1.08 x 10 8 9.6 x 10 6 4.8 x 10 6 1.43 x 10 5 N/ A dioxin 5.27 x 10 9 1.31 x 10 9 1.31 x 10 9 1.31 x 10 9 1.34 x 10 9 N/ A PCBs 3.2 x 10 5 1.61 x 10 7 5.3 x 10 6 1.06 x 10 5 1.59 x 10 5 1.82 x 10 10 Implementation Strategy Monitoring as part of the Buffalo Slough sediment remediation project has indicated that the largest contributor of PCBs to the Buffalo Slough is sediment in storm water, while storm water contributes pesticides. The organics present in fish tissue in the Columbia Slough are not the result of continuing use of the chemicals, but previous use and application. The TMDL strategy focuses on implementation of BMPs to control erosion in the Slough basin and monitoring to evaluate their effectiveness. This strategy is based on limited data indicating that control of sediment input to the Columbia Slough will reduce the organic load.

12 Due to rounding, sum of WLA may not equal LC ( but does not exceed LC). For dioxin excess LC was allocated to the MOS. 13 Excess loading capacity is allocated to the MOS in the allocation table. 45 Industrial Storm water permits The DEQ anticipates requiring implementation of BMPs through storm water permits. A basin specific general storm water permit will be developed by DEQ to address all 303( d) pollutants. Requirements to reduce the organic load from industrial storm water will be as follows: 1. Monitoring for TSS. 2. Implementation of BMPs to control erosion and sedimentation. 3. Monitor effectiveness of BMPs at erosion and sedimentation control.

Environmental Cleanup Sites DEQ's Site Response section has conducted a review of the sites in the Environmental Cleanup Site Information ( ECSI) database to determine which of those merit increased attention due to the presence of 303( d) chemicals and proximity to the Slough. High priority sites have been moved to the cleanup program. DEQ water quality program will develop a monitoring protocol to be included in the statement of work for site cleanup to estimate the load of 303( d) pollutants from individual sites. The individual project managers will select BMPs for surface runoff control and require BMP implementation.

Designated Management Agencies 1. Conduct pilot monitoring projects to determine the relationship between TSS and organics in storm water. 2. Identify and implement BMPs, as listed in the municipal NPDES permits, for erosion control based on limited data suggesting storm water sediment as a current source of organics. 3. Monitor the effectiveness of BMPs at TSS removal. 4. Estimate the load reduction of TSS achieved for storm water at the end of Phase I. 5. Implement water quality management plans as developed as part of the Lower Willamette Subbasin plan.

The responsibilities of the DMAs, by reach, is summarized below:

Table 21: Organic Control Summary Reach Control Strategy Responsible DMA 1 2,3,4 City of Portland, PDX 2 ( Buffalo Slough) 1 City of Portland ( as part of sediment remediation project for Buffalo Slough) 2 2,3,4 City of Portland, PDX 3 2,3,4 City of Portland, City of Gresham 4 2 City of Fairview, Multnomah County 5 1 5 1 5 2 5 2,3,4 City of Fairview, City of Gresham, Multnomah County, City of Wood Village Oregon Department of Agriculture Oregon Department of Transportation 46 REFERENCES Berger, Chris, draft memo to DEQ, Columbia Slough eutrophication model runs, Portland State University, May 15, 1998.

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Biorn Hansen, Sonja, personal communication, May 14, 1997, DEQ, discussion of field shading estimates.

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Cole, T. and Buchak, E., CE QUAL W2 User's Manual , Corps of Engineers, Waterways Experiments Station, Vicksburg, Mississippi, 1994.

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Environmental Quality Commission, In the Matter of the Proposal to Declare a Threat to Drinking Water in a Specifically Defined area in Mid Multnomah County Pursuant to ORS 454.275 et. seq., Findings and Recommendations, 1/ 30/ 86 Environmental Protection Agency ( EPA), Quality Criteria for Water, Office of Water, Regulations and Standards, EPA 440/ 5 86 001, 1986. 47 Environmental Protection Agency ( EPA), Office of Water, Guidance Manual for the Preparation of Part 2 of the NPDES Permit Applications for Discharges from Municipal Separate Storm Sewer Systems, EPA 833 B 92 002, November 1992.

Environmental Protection Agency ( EPA) Region VIII, CWA Section 304( a) Criteria Chart, indicating published criteria and updated human health values, current as of July 1, 1993.

Environmental Protection Agency ( EPA), The Metals Translator: Guidance for Calculating A Total Recoverable Permit Limit from a Dissolved Criterion, Office of Water, EPA 823 B 96 007, June 1996.

Environmental Protection Agency ( EPA), Use of Ambient Data and Antidegradation in Calculating Wasteload Allocations, memo, Wastewater Management and Enforcement Branch, July 1995.

Gresham NPDES MS4 permit No. 101315 Annual Report, City of Gresham and copermittees August 30, 1996.

Li, Shu Guang, Columbia Slough Sediment Transport Study Results and Summary of Key Findings, Prepared for Parametrix, Inc. and the City of Portland Bureau of Environmental Services, Prepared by Portland State University, 1995.

LTI, Technical Memorandum and Excel spreadsheet, Evaluation to estimate the effect that dispersion may have on dissolved oxygen modeling conducted to develop the Columbia Slough TMDL, July 1, 1997.

Portland MS4 NPDES Municipal Storm water Permit Annual Compliance Report, submitted by City of Portland and co permittees, September 1, 1996.

Portland MS4 NPDES Municipal Storm water Permit Application, Volume II, submitted by City of Portland and co applicants, prepared by Woodward Clyde Consultants, May 17, 1993.

Tchobanoglous, George, Schroeder, Edward, D., Water Quality, 1985, Addison Wesley Publishing Company, pp. 115.

Thomann, Robert, V., Mueller, John, A., Principles of Surface Water Quality Modeling and Control, 1987, Harper and Row Publishers, pp. 306.

The East County Sanitary Sewer Consortium: Central County Service District, City of Gresham, City of Portland, City of Troutdale, Threat to Drinking Water Findings, June 1984.

U. S. Geological Survey, Water Resources Investigations Report 96 4234, Occurrence of Selected Trace Elements and Organic Compounds and Their Relation to Land Use in the Willamette River Basin, Oregon, 1992 1994, by Chauncey W. Anderson, Frank A. Rinella, and Stewart A. Rounds, 1996. 48 Water Quality Standards Review, Final Issue Paper for Temperature, DEQ, June 1995.

Wells, Scott, A. Berger, Chris, J., Hydraulic and Water Quality Modeling of the Upper and Lower Columbia Slough: Model Calibration, Verification and Management Alternatives Report, Technical Report Submitted to HDR Engineering and City of Portland, 1993.

Wells, Scott, A., Berger, Chris, J., Upper and Lower Slough Water Level Test: September 1 through October 29, 1993, Technical Report EWR 2 94, Department of Civil Engineering, Portland State University, 1994.

Wells, Scott, A., Berger, Chris, J., Hydraulic and water quality modeling of the upper and lower Columbia Slough: model calibration, verification, and management alternatives report for 1992 1995, Technical Report EWR 2 95, Portland State University, 1995.

Wells, Scott, A., Berger, Chris, J., Upper and Lower Columbia Slough Water Level Test and Winter Sampling Analysis: June 1994 through March 1995, Technical Report EWR 3 95, Portland State University, 1995.

Wells, Scott, Berger, Chris, PSU Civil Engineering Department, Memo to Mary Abrams, BES, Dawn Saunders, CH2MHill, Sonja Biorn Hansen, DEQ, Tim Hayford, MCDD1, Re: Upper Columbia Slough Shading, September 27, 1995.

Wells, Scott, A., Berger, Chris, J., Eberle, Michael, B., Modeling and Monitoring the Columbia Slough System: 1995/ 1996, Technical Report EWR 01 96, Portland State University, August 1996.

Wells, Scott, A., Berger, Chris, J., Abrams, Mary, Winter Storm Event Impacts on Dissolved Oxygen Levels in the Columbia Slough System, Proceedings Second Annual Pacific Northwest Water Issues Conference: The Flood of 1996, October 7,8, Portland, Oregon.

Wells, Scott, A., Berger, Chris, Memo to BES and DEQ, Re: results of Columbia Slough system high phosphorus load and winter tracer model simulations, April 21, 1997.

Wells, Scott, A., Annear, Robert, Memo to BES, BOD Levels in the Columbia Slough, prepared for the City of Portland, Bureau of Environmental Services, August 21, 1997. 49 Temperature Analysis Water Quality Criteria To accomplish the goals identified in OAR 340 41 120( 11), unless specifically allowed under a Department approved surface water temperature management plan as required under OAR 340 41 026( 3)( a)( D), no measurable surface water temperature increase resulting from anthropogenic activities is allowed: ( i) In a basin for which salmonid fish rearing is a designated beneficial use, and in which surface water temperatures exceed 64.0 ° F ( 17.8 ° C).

This numeric criteria is measured as the seven day moving average of the daily maximum temperatures ( OAR 341 41 006( 54)). For point sources, the surface water management plan will be part of their NPDES permit. For nonpoint sources, the surface water management plan will be developed by DMAs which will identify the appropriate BMPs or measures.

Monitoring Analysis of water quality data indicates that the 17.8

C criteria would be violated in most reaches in the Slough in the spring, summer and fall. Temperatures in Reaches 1A, 1B, 1C, 2A and 3 indicate frequent exceedances of the criteria during these seasons. The limited data for Reaches 4 and 5 also indicate frequent exceedances of the temperature criteria in the spring, summer and fall. Temperatures in the winter in the Slough are generally below the criteria. ( CH2MHill, 1995, Part 2)

Modeling Instream temperature may be influenced by loads from industrial point sources, storm water, illicit discharges, and nonpoint sources as well as the hydrology of the Slough. Loads from storm water and illicit discharges are presumed to be insignificant in comparison to the effect of solar radiation on instream temperatures. Most banks of the Slough are built up as levees and have little vegetation. Shallow water levels in the Slough exacerbate the effect of lack of shading, so solar radiation heats up the water to levels exceeding the temperature criterion. Modeling has been done to assess the impact of additional shading via tree planting on the Middle and Upper Slough ( Wells, 1995). For the Middle and Upper Slough, the average amount of shaded water surface was estimated for the month of August ( Biorn Hansen, personal communication) using field measurements in representative areas by a solar pathfinder. The pathfinder is used to measure the magnitude of the shadow cast by the treeline in a particular area. For each location where the pathfinder was used, data was also collected on stream width, bank geometry and vegetation density. Site specific shading estimates were then generated based on field measurements combined with information on azimuth, declination angle, latitude, and time of year. These estimates were then applied to the rest of the Slough. The average amount of shaded water surface was estimated to be 20%. These field estimates of shading correlated with estimates developed by Wells ( Wells, 1995, memo). 50 In the shading simulations, approximately 80% of the Upper Slough was assumed to be unshaded for existing conditions and 50% was assumed to be unshaded for future conditions. The effect of flow management alone on instream temperature was simulated; then the effect of flow management and increased shading ( to 50%) was simulated. According to the simulations, the Upper Slough would be in compliance with the temperature criteria if 50% is shaded. Shading in upstream reaches is predicted to have little effect on the temperature in the Lower Slough, because the temperature of the Lower Slough is most impacted by the incident solar radiation and relatively long residence times. Modeling indicated that additional shading in the Lower Slough, under current hydrological conditions, would have negligible effect on instream temperature. This is because of the following conditions:   Much of the Lower Slough is bordered by levees, and the Army Corps of Engineers prohibits the planting of trees on levees,   The sections of the Lower Slough that are not bordered by levees are already reasonably well vegetated, and   The Lower Slough is generally so wide ( up to 400 ft) that most of the water surface is unshaded whether or not there are trees along the banks, thus shade measurements made at various locations along the Lower Slough yielded values ranging from 0% to 5%.

Several refinements are being made to the existing model for the Columbia Slough. Some of these refinements, such as shade calculation based on vegetation height, will influence temperature simulations. The model will be used to predict the influence that management strategies will have on instream temperature. The results of these analyses will form the basis for a temperature/ solar radiation TMDL. 51 Conversion Factors To convert from: to:

kg/ day or kg/ yr lb/ day or lb/ yr divide by 0.454 1 m3 ft 3 multiply by 35.3 Equation to use flow and concentration to calculate a mass load:

( m3/ sec) x ( 1000 L/ m3) x ( mg/ L) x ( 1 kg/ 106 mg) x ( 60 sec/ min) x ( 60 min/ hr) x ( 24 hr/ day) = kg/ day