NPL U34 2 10 R9 HRS DOCUMENTATION RECORD  REVIEW COVER SHEET Name DEL AM0 Contact (415) 744 2343 Site Investigation: ' (415) 744 2399 DocumentationRecord: KateDragolovich, Ecology and Environment, Inc. ( 415) 981 2811 Pathways, Components, or Threats Not Scored:

The surface water pathway was evaluated, but not scored, because there are a limited number of targets associated with the first 7.5 iniles of the 15 mile in water segment. Runoff from the Del Am0 site enters a storm drain inlet located at the intersection of Vermont Avenue and Del Am0 Boulevard, approximately 600 feet southeast of Sources 1 and 2. The storm drain system discharges into the Torrance Lateral, which is an open channel, approximately 1,600 feet south of the storm drain inlet. The Torrance Lateral discharges into the Dominguez Channel, which is a concrete lined drainage and flood control channel, approximately 1.5 miles downstream of the storm drain system discharge point. The Dominguez Channel discharges into the Los Angeles Harbor approximately 6 miles farther downstream. The Los Angeles Harbor empties into San Pedro Bay, and San Pedro Bay opens onto the Pacific Ocean. The last portion of the 15 mile in water segment consists of an arc with a 7.5 mile radius that extends from the confluence of the Dominguez Channel and the Los Angeles Harbor into San Pedro Bay and the Pacific Ocean. Although there are fisheries and sensitive environments associated with the Los Angeles Harbor, San Pedro Bay, and the Pacific Ocean, there do not appear to be any &inking water intakes or sensitive environments associated with the first 7.5 miles of the 15 mile in water segment (i. e., the Torrance Lateral and concrete lined Dominguez Channel). In addition, there are a limited number of fish in the Dominguez Channel.

The soil exposure pathway was evaluated, but not scored, because the area of the Del Am0 site that is occupied by Sources 1 and 2 is currently vacant and covered with fill material and vegetation. In addition, Soyrces 1 and 2 are separated from Del Am0 Boulevard and a residential area to the south by a doubIe, rod'of fences. Source 3 is currently present as an area of non aqueous phase liquid (NAPL) located 60 feet below ground surface.

The air pathway was evaluated, but not scored, because no known ambient air sampling and meteorological monitoring have been conducted on or in the vicinity of the Del Am0 site. HRS DOCUMENTATION RECORD Name of Site: DEL AM0 EPA ID#: CAD02954473 1 EPA 9 I Date Prepared: August 15,2000 StreetAddress of Site: Del Am0 BoulevardandVermontAvenue, LosAngeles CountyandState: Los AngelesCounty, California TopographicMap: Torrance Latitude: 33" 50' 47.9" N. Longitude: 118" 17' 22.1" W. Reference Point: Intersection of Del Am0 Boulevard and Vermont Avenue (ref. 4)

. Scores Ground Water Pathway 94.23 Surface Water Pathway Not scored Soil Exposure Pathway Not scored Air Pathway Not scored HRS SITE SCORE 47.12 1 HAZARD RANKING SYSTEM SUMMARY SCORESHEETS SITE NAME: DelAm0 CITY/ COUNTY/ STATE: Los Angeles. Los Angeles Countv, California EPA ID #: CAD02954473 1 EVALUATOR KateDragolovich DATE: Aumst 15,2000 LATITUDE: 33" 50' 47.9" N. LONGITUDE: 118" 17'22.1" W.

sw s a 2 GROUND WATER MIGRATION PATHWAY SCORESHEET Factor Categories and Factors 1. 2.

3.

4. 5. 6.

7. 8.

9. 10. 11.

12. Likelihood of Release Observed Release Potential to Release 2a. Containment 2b. Net Precipitation 2c. Depth to Aquifer 2d. Travel Time 2e. Potential to Release [Lines 2a( 2b+ 2c+ 2d)} Likelihood of Release (Higher of lines 1 and 2e)

Waste Characteristics ToxicityMobility Hazardous Waste Quantity Waste Characteristics Targets Nearest Well Population 8a. Level I Concentrations 8b. Level 11 Concentrations 8c. Potential Contamination 8d. Population (lines 8a+ 8b+ 8c) Resources Wellhead Protection Area Targets (lines 7+ 8d+ 9+ 10)

Aquifer Score [( lines 3 x 6 x 11)/ 82,500]

Ground Water Migration Pathway Score 13. ' PathwayScore (S,), highestvaluefrom line 12 for all aquifers eva1uated) c Maximum Value 550 10 10 5 35 500 550 a a 100 50 aMaximumvalueappliestowastecharacteristicscategory. bMaximumvalue not applicable.

C Do notroundtonearestinteger. b b b b 5 20 b 100 100 Value Assigned  550  550  100 10,000  32  5  0  0 436.7 436.7  0  0 441.7 94.23 94.23 REFERENCES Reference NumberDescriptionoftheReference 1.

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U. S. Environmental Protection Agency, Superfund Chemical Data Matrix (SCDM), June 19964 pages.

Map Showing General Location of the Del Amo Site in the State of California.

U. S. Geological Survey, Torrance, Calif. Quadrangle, 7.5 Minute Series (topographic), 1964, Photo revised 198 1.

Dames & Moore, Phase I Remedial Investigation Report, Del Am0 Study Area, Los Angeles, California, for Shell Oil Company and The Dow Chemical Company, October 29, 1993,229 pages.

Map Showing Locations of Sources 1,2, and 3 at the Del Amo Site.

Dames & Moore, Feasibility Study Report, Del Amo Site, May 1991,48 pages.

Williams, T. R., Shell Oil Company, letter to Thomas E. Bailey (with attachments), California Department of Health Services, November 30, 1983,7 pages.

Page, Bruce W., Levine Fricke, Del Amo Site Report, May 21,1993,23 pages.

Rubber Producing Facilities Disposal Commission, Government owned Synthetic Rubber Facility, Plancor 929, Los Angeles, California, November 1953,7 pages.

Dames & Moore, Radian Corporation, Interim Summary of Findings, Del Am0 Site Investigation, Los Angeles, California, for Ire11 & Manella, June 1984,45 1 pages.

Dames & Moore, Draft Waste Excavation Feasibility Study Report, Del Am0 Pit Site, for Shell Oil Company and The Dow Chemical Company, November 20,1992,345 pages.

Bolton, R. L. and L. Klein, SewaEe Treatment  Basic Principals and Trends, Ann Arbor Science Publishers, Inc., Michigan, 1971, 8 pages.

Manahan, Stanley E., Environmental Chemistw, Fifth Edition, Lewis Publications, Inc., Michigan, 199 1,7 pages.

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29. State of California Department of Water Resources, Bulletin 104, Planned Utilization of the Ground Water Basins of the Coastal Plain of Los Angeles County, Appendix A Ground Water Geology, June 1961,30 pages.

Hargis + Associates, Inc., Final Draft Remedial Investigation, Montrose Site, Torrance, California, prepared for Montrose Chemical Corporation, October 29, 1992,237 pages.

Ross, J. E., California Regional Water Quality Control Board, Los Angeles Region, memorandum to Haissan Salloum, California Environmental Protection Agency, Department of Toxic Substances Control, Long Beach, supplement to General ARARs memo of October 19, 1993,3 pages.

California Regional Water Quality Control Board, Los Angeles Region, Interim Guidance for Remediation of Petroleum Impacted Site  Soil Screening Levels, November 1994,2 pages.

Hargis + Associates, Inc., Results of Aquifer Testing, Montrose Site, Torrance, California, prepared for Montrose Chemical Corporation of California, October 3 1, 1990,20 pages.

Witthoft, Terry H., Dominguez Water Corporation, letter to Kate Dragolovich (with attachments), Bechtel Environmental, Inc., November 22, 1993,5 pages.

Dames & Moore, Phase I Treatability Study Evaluation Report, Del Am0 Pit Site, LOS h g e k California, April 5, 1993,30 pages.

Dames & Moore, Quarterly Report, Groundwater Monitoring Program, First Quarterly Sampling Event, 1994, Del Amo Study Area, for Shell Oil Company and The Dow Chemical Company, July 22, 1994, 12 pages.

Johnson, Thomas M., Levine Fricke, Del Am0 Site, May 21, 1993,26 pages.

Hargis + Associates, Inc., Raw Analytical Data Submittal Part 2, Remedial Investigative Work, Phase 2B, Montrose Site, Torrance, California, April 1990 Groundwater Sampling, June 20, 1990,78 pages.

Hargis + Associates, Inc., Raw Analytical Data Submittal, Montrose Site, Torrance, California, August 1990 Quarterly Groundwater Sampling, September 18, 1990,40 pages.

Hargis + Associates, Inc., Field and Raw Analytical Data Submittal, Semiannual Groundwater Sampling, November December 1990, Montrose Site, Torrance, California, January 30, 1991, 121 pages.

Hargis + Associates, Inc., Field and Raw Analytical Data Submittal, Semiannual Groundwater Sampling, April 1991, Montrose site, Torrance, California, June 7, 1991,46 pages.

Hargis + Associates, Inc., Field and Raw Analytical Data Submittal, Semiannual Groundwater Sampling, July 1992, Montrose Site, Torrance, California, September 3, 1992,46 pages.

Hargis + Associates, Inc., Field and Raw Analytical Data Submittal, Semiannual Groundwater Sampling, January 1993, Montrose Site, Torrance, California, March 11, 1993,46 pages. . x

5 30. Hargis t Associates, Inc., Field and Raw Analytical Data Submittal, Additional Groundwater Assessment Monitor Well Installation, Groundwater and Soil Sampling, May through November 1991, Montrose Site, Torrance, California, December 19, 1991,41 pages.

3 1. Woodward Clyde Consultants, Task 2 Final Report, Additional Data Acquisition, Del Amo Hazardous Waste Site, Los Angeles, CA, prepared for the California Department of Health Services, October 2, 1987,329 pages.

32. Map Showing Locations of Drinking Water Wells Within 4 Miles of Sources 1,2, and 3 at the Del Am0 Site.

33. Goclowski; Clara Patricia, Southern California Water Company, letter to Kate Dragolovich (with attachments), Bechtel, December 3, 1993, lO pages.

34. Schaich, Chuck, City of Torrance Water Company, Telephone conversation recorded on Contact Report by Jordie Bornstein, Bechtel Environmental, Inc., March 30, 1995, 1 page.

35. Witthoft, Terry, Dominguez Water Company, Telephone conversation recorded on Contact Report by I Jordie Bornstein, Bechtel Environmental, Inc., March 30, 1995, 1 page.

36. Polarico, Anna, Southern California Water Company, Telephone conversation recorded on Contact Report by Jordie Bornstein, Bechtel Environmental, Inc., March 29, 1995, 1 page.

37. Census of Population and Housing, 1990: Summary Tape File 3 on CD ROM (machine readable data files), prepared by the Bureau of the Census, 1992. Available: http:// govinfo. library. orst. edu/ stateis. html [viewed February 29, 2000], 5 pages.

38. Witthoft, Terry, Dominguez Water Company, Telephone conversation recorded on Contact Report by Kate Dragolovich, Ecology and Environment, Inc., February 17,2000,2 pages.

39. Schaich, Chuck, City of Torrance Water Company, Telephone conversation recorded on Contact Report by Kate Dragolovicli, Ecology and Environment, Inc., February 24,2000, 1 page.

40. Hartsock, Mike, SouthernCaliforniaWaterCompany, TelephoneconversationrecordedonContact Report by Kate Dragolovich, Ecology and Environment, Inc., February 11,2000,2 pages 41. California Department of Fish and Game, Natural Diversity Data Base (NDDB) Printout (Torrance, Long Beach, and San Pedro quadrangles) and instructions for reading the NDDB Printout, Expires March 8, 1995,22 pages.

42. Smith, Tim, Los Angeles County Department of Public Works, Telephone conversation recorded on Contact Report by Jordie Bornstein, Bechtel Environmental, Inc., April 19, 1995, 1 page.

6 43.

44.

45 9 46.

47.

48.

49.

50.

51.

52.

53.

54.

55.

56.

57. Dames & Moore, Remedial Investigation Report, Del Am0 Site, April 4, 1990, 11 pages.

Map Showing Surface Water Migration Pathway, Del Am0 Site.

Hargis & Associates, Inc., Regional Hydrogeologic Assessment Report, Task 15, May 29, 1990,2 pages.

Dhont, Jeff, U. S. Environmental Protection Agency, Region 9, Memorandum to Murray Newton (OSWER R1 9ARC), Alan Youkeles, and Karen Bankert, U. S. Environmental Protection Agency, June 6, 1996,2 pp.

Dames & Moore, Groundwater Monitoring Report, Third Sampling Period 1995, Del Am0 Study Area, for Shell Oil Company and The Dow Chemical Company, February 23, 1996,590 pages.

Schaich, Chuck, City of Torrance Water Company, Telephone conversation recorded on Contact Report by Kate Dragolovich, Ecology and Environment, Inc., March 10,2000, 1 page.

Dames & Moore, Final Groundwater Remedial Investigation Report, Del Am0 Study Area, May 15, 1998,602 pages.

Dames & Moore, Focused Investigation, Nature and Extent of Non Aqueous Phase Liquid (NAPL), Monitoring Well MW 20, Del Amo Study Area, March 5, 1993, 36 pages.

U. S. Environmental Protection Agency, Record of Decision for dual Site Groundwater Operable Unit, Montrose Chemical Company and Del Am0 Superfund Sites, March 1999, 18 pp.

Figure showing Lateral Extent of Non Aqueous Phase Liquid (NAPL) and Area Used to Determine Volume for Tier A Waste Quantity Calculations.

Dames & Moore, Draft Interim Data Submittal and Proposed Laboratory Testing Program, MW 20 Pilot Program, Del Amo Study Area, September 24, 1994,22 pages.

Dames & Moore, MW 20 Pilot Program, Core Photography and Record of In Laboratory Testing and Sample Aliquot Locations, SBL0085 and SBL0086, Del Am0 Study Area, September 16, 1994,14 pages.

Dames & Moore, MW 20 Pilot Program, Core Photography and Record of In Laboratory Testing and Sample Aliquot Locations, SBL0087 and SBL0088, Del Am0 Study Area, September 16,1994,20 pages.

Dames & Moore, MW 20 Pilot Program, Core Photography and Record of In Laboratory Testing and Sample Aliquot Locations, SBL0089 and SBL0090, Del Am0 Study Area, September 16,1994,29 pages. _"

7 58. Dames & Moore, MW 20 Pilot Program, Core Photography and Record of In Laboratory Testing and Sample Aliquot Locations, SBL0091 and SBL0092, Del Am0 Study Area, September 16,1994,22 pages.

59. Dames & Moore, MW 20 Pilot Program, Core Photography and Record of In Laboratory Testing and Sample Aliquot Locations, SBL0093 and SBL0094, Del Am0 Study Area, September 16,1994,14 pages.

60. Dames & Moore, Draft Report and Work Plan, Laboratory Data and Analysis and Hydraulic ..

Extraction Work Plan, MW 20 Pilot Program, Del Am0 Study Area, September 29, 1995,41 pages.

61. ChemFinder. Com. SearchResultPage, Benzene. Available: http:// chemfinder. camsoft. com/ result. asp [viewed March 13,20001, 1 page.

62. Figure Showing Depth of Soil Contamination Beneath Source 1 in 1987 and Rising Water Table Elevations in 1987,1993,1994, and 1995.

8 SD Characterization and Containment Source 1 SOURCE DESCRIPTION 2.2 Source Characterization Source Description: Source 1  Pits 2A, 2B, 2C, 2D, 2E, and 2F Source 1 consists of six disposal pits (Pits 2A, 2B, 2C, 2D, 2E, and 2F) that are adjacent to one another and arranged in a linear east west alignment (ref. 5, Plate 3 3; ref. 6).

Aerial photographs indicate that the pits were first present sometime after 1941 and before 1947 (ref. 5, p. 3 6). They are man made excavations formed from earthen materials that were designed to hold semi '

viscous and viscous sludges (i. e. process wastes that originated from the styrene manufacturing plant that was historically on site) (ref. 5, p. 3 6; ref. 8, pp. 6 and 7; ref. 9, p. 15). Each pit has a small protrusion at its northern end (ref. 5, Plate 3 3). The function or significance of the protrusions is not known; however, it may relate to or reflect the method( s) used to excavate the pits, or to transport and discharge waste materials to the pits (ref. 7, p. 2 2). Once in the pits, the waste sludges were left open to the air, allowed to drain and dry, and then hauled away by truck (ref. 10, p. 6).

Aerial photographs indicate that, by December 1951, the pits were covered with fill material (ref. 5, p. 3 6). The source of the fill material is not known; however, it is probably natural local soil (ref. 8, p. 7). Field data and visual observations of core samples collected from the pits in 1984 indicate that the fill material covering the remaining waste ranges in thickness from approximately 1 foot overlying Pit 2A to 8 feet overlying Pit 2F (ref. 11, p. 4 30, Table 4.3 4). The fill material is covered with weeds and miscellaneous debris (e. g., old tires and broken glass) (ref. 5, p. 5 23).

The six pits are separated from Del Am0 Boulevard and a residential area to the south by a, double row of fences (ref. 5, p. 5 23).

Three wastes from the former styrene manufacturing plant (i. e., acid sludge, clay like sludge, and sulfur tar oil) are known to have been disposed of in Source 1 (ref. 9, pp. 12,13). The acid sludge resulted from the purification of crude benzene using sulfuric acid to remove the sulfur containing compounds and unsaturated components (ref. 9, pp. 3,4; ref. 10, p. 4). The clay like sludge resulted from the conversion of ethanol to ethylene using kaolin clay as a catalyst under thermal conditions (ref. 9, pp. 12, 13). The purified benzene and ethylene that were generated by these two processes were then combined to form ethylbenzene. The ethylbenzene was neutralized and purified before being fed into dehydrogenation units where it was partially converted to styrene. The crude styrene contained 35 to 40 percent styrene, ethylbenzene, and small amounts of benzene and toluene. It was fed into styrene purification units where a distillation tower was used to remove the benzene and toluene, and primary and secondary stills were used to remove the ethylbenzene. Sulfur was introduced at various steps in the purification process to inhibit thermal polymerization of the styrene. The final step in the purification process was to feed the bottoms from the ethylbenzene stills into a short packed tower where tar and sulfur were removed &d 99+ percent styrene was produced. Sulfur tar oil waste was generated during this final step (ref. 9, pp. 5 through 7; ref. 10, p. 4).

9 SD Characterization and Containment Source 1 Observations made during boring and sampling activities indicate that the waste remaining in the pits consists of black to gray black tars to day like sludges (ref. 12, p. 11). This waste contains hydrocarbons with high polynuclear aromatic and volatile aromatic content, which correlates with the chemistry of the styrene manufacturing process wastes described above. Naphthalene is the dominant polynuclear aromatic compound in the waste, while benzene and ethylbenzene are the dominant volatile aromatic compounds (ref. 5, p. 5 25; ref. 7, p. iii; ref. 9, pp. 12, 13). In addition, significant downhole emissions of hydrogen sulfide (H2S) occur in the pits (ref. 5, p. 5 24). This correlates with conditions in the pits that are conducive to the formation of H, S (e. g., the presence of sulfur in the waste and a pH in the acidic range) (ref. 5, p. 5 25; ref. 7, Table 2 9; ref. 13, pp. 11 through 18; ref. 14, pp. 156,289,290, and 508).

Source Tvpe The source type for Source 1 is "buried surface impoundment" (ref. 1, Table 2 5).

Source Location Source 1 is located in the portion of the Del Amo site that was formerly occupied by the styrene manufacturing plant. Pits 2A, 2B, 2C, 2D, 2E, and. 2F are approximately 150 feet north of De) Am0 Boulevard (ref. 5, Plate 3.3; ref. 6).

Source Containment Release to Ground Water Source 1 has no liner (ref. 5, p. 3 6). Analytical results provide evidence of vertical hazardous substance migration from the waste in Source 1 to the soil immediately beneath the pits (ref. 5, pp. 5 26, 5 29, 5 30, 5 31, Tables 5.5 3 through 5.5 16, Figures 5.5 1,5.5 10). See Section 3.1.1 (Observer Release  Direct Observation) for a more detailed discussion of the analytical results. A ground water containment factor value of 10 is assigned for "evidence of hazardous substance migration from source area" (ref. 1, Table 3 2).

10 SD  Hazardous Substances Source 1 2.4.1 Hazardous Substances Hazardous Substance Evidence ' Reference benzene waste sample nos.* 11, Table 5.2 1,

SO 14 p. B 15 S044, SO48 p. B 16 S068, SO72 p. B 17 ethylbenzene s2oo S206 s220 waste sample nos.**

SSSOOOOl thru SSSOOOO4 sssooo11, sss00012 sssooo21 wss00001 thru wssoooo3 wssooo13, wssooo14 wssooo15 WSSOOO16,

waste sample nos.*

SO14 S O U , SO48 S068, SO72 s200 S206 s220 waste sample nos.%%

SSSOOOOl thru SSSOOOO4 p. B 18 p. B 19 p. B 20 12,

pp. A3 5, A4 5 pp. A3 7, A4 19 pp. A3 3, A437 pp. A3 3, A4 37 pp. A3 6, A4 75 pp. A3 8, A4 75 pp. A3 4, A4 75 1 1, Table 5.2 1,

p. B 15 \

p. B 16 p. B 17 p. B 18 p. B 19 p. B 20 12,

pp. A3 5, A4 6 1 1 naphthalene sssooo11, sssooo12 sssooo21 wssoooo1, wssoooo2 wssooo14 wssooo15 WSSOOO16 waste sample nos.

SO14 S044, SO48 S068, SO72 s200 S206 s220 waste sample nos.%%

SSSOOOOl thru SSSOOOO4 sss00011 sssooo21 wss00001 t h wssoooo3 wssooo13, wssooo14 wssooo15 WSSOOO16 SD  Hazardous Substances Source 1 pp. A3 7, A4 20 pp. A3 3, A4 38 pp. A3 3, A4 38 pp. A3 6, A4 76 pp. A3 8, A4 76 pp. A3 4, A4 76 11, Table 5.2 1,

p. B 25 p. B 26 p. B 27 p. B 28 p. B 29 p. B 30 12,

pp. A3 5, A4 4 pp. A3 7, A4 17 pp. A3 3, A4 35 pp. A3 3, A4 35 pp. A3 6, A4 73 pp. A3 8, A4 73 pp. A3 4, A4 73 I In 1984, Dames & Moore, under contract to Ire11 & Manella, drilled eight soil borings in Source 1 (i. e., borings 2 IV, 2 IVa, and 2 IVb in Pit 2A; boring 2 111 in Pit 2B; boring 2 11 in Pit 2C; boring 2 V in Pit 2D; boring 2 1 in Pit 2E; and boring 2 W'in Pit 2F) to characterize the fill material overlying the waste, the waste, and the soil beneath the waste (ref. 11, p. 4 24, Figure 4.3 1). Five to 17 soil and/ or waste samples were collected from each boring (67 total) at 2.5 foot or 5 foot intervals from ground surface to a depth of 51.5 feet below ground surface (bgs) (ref. 11, pp. 4 26,4 27, Table 4.3 2). Of the 67 samples, the following eight samples consisting entirely of waste were selected for chemical analysis: S200 from boring 2 IV in Pit 2A, SO68 and SO72 from boring 2 III 12 SD  Hazardous Substances Source 1 in Pit 2B, SO44 and SO45 from boring 2 II in Pit 2C, S206 from boring 2 V in Pit 2D, SO14 from boring 2 1 in Pit 2E, and S220 from boring 2 VI in Pit 2F (ref. 11, Tables 4.3 2,5.2 1, Appendix A, pp. A 5 through A 10). All eight samples were analyzed for purgable aromatics using EPA Method 602 and extractable hydrocarbons using EPA Method 610. Analytical results indicated the presence of benzene, ethylbenzene, and naphthalene at concentrations up to 7,900 milligrams per kilogram (mag), 1,840 m a g , and 126 m a g , respectively, in the waste in Pit 2A; 23,000 m a g , 9,300 mgkg, and 300 m a g , respectively, in the waste in Pit 2B; 7,100 m a g , 3,800 mglkg, and 150 _.

mgkg, respectively, in the waste in Pit 2C; 6,700 m a g , 3,600 m a g , and 164 m a g , respectively, in the waste in Pit 2D; 26,700 mglkg, 13,200 mglkg, and 409 m a , respectively, in the waste in Pit 2E; and'31, OOO mgkg, 11,600 m a g , and 304 m a g , respectively, in the waste in Pit 2F (ref. 11, p. 5 6, Appendix B, pp. B 15 through B 20, B 25 through B 30).

%% In 1992, Dames & Moore, under contract to Shell Oil Company and Dow Chemical Company, drilled six soil borings in Source 1 (i. e., borings SBL0001, SBL0006, SBL0007, and SBL0008 in Pit 2C; boring SBL0002 in Pit 2D; and boring SBL0003 in Pit 2F) as part of a waste excavation feasibility study (ref. 12, p. 1, Appendix A, Figure A 1). Eight waste samples (SSS00001 through SSSOO004, and WSSOOO13 through WSS00016) collected from Pit 2C, two waste samples (SSSOOOll and SSSOOOl2) collected from Pit 2D, and four waste samples (SSSOOO21, and WSSOOOOl through WSSOOOO3) collected from Pit 2F were analyzed for volatile organic compounds using EPA Method 8240 and for polynuclear aromatic hydrocarbons using EPA Method 8270 (ref. 12, Appendix A, p. A 2, Attachment A3, pp: A3 3 through A3 8, Attachment A4, pp. A4 2 through A4 6, A4 15 through A4 20, A4 33 through A4 39, A4 71 through A4 77). Analytical results indicated the presence of benzene, ethylbenzene, and naphthalene at concentrations up to 21,000 mgkg, 8,500 mgkg, and 68 mgkg, respectively, in the waste in Pit 2C; 29,000 mgkg, 8,300 mglkg, and 120 mgkg, respectively, in the waste in Pit 2D; and 52,000 mgkg, 8,600 mgkg, and 240 mgkg, respectively, in the waste in Pit 2F (ref. 12, Appendix A, Attachment A4, pp. A4 17, A4 19, A4 20, A4 35, A4 37, A4 38, A4073, A4 75, A4 76).

The hazardous substances associated with Source 1 include:

benzene ethylbenzene * naphthalene Other hazardous substances are associated with Source 1 (e. g., toluene, styrene, and H, S) (ref. 5, pp. 5 24, 5 25). The documentation presented above is limited to benzene, ethylbenzene, and naphthalene because these three hazardous substances are the dominant constituents of the hydrocarbon waste remaining in Pits 2A through 2F (ref. 7, p. iii).

13 SD Hazardous Waste Quantity Source 1 2.4.2 Hazardous Waste Quantity *

Tier A: Hazardous Constituent Ouantitv Documentation is not sufficient to determine hazardous constituent quantity.

14 Hazardous Constituent Quantity Value: 0 SD Hazardous Waste Quantity Source 1 Tier B: Hazardous Wastestream Ouantitv Documentation is not sufficient to determine hazardous wastestream quantity.

Hazardous Wastestream Quantity Value: 0 15 SD Hazardous Waste Quantity Source 1 Tier C: Source Volume Documentation is not sufficient to determine the volumes of Pits 2A through 2F.

Volume Assigned Value: 0 J 16 SD Hazardous Waste Quantity Source 1 Tier D: Source Area A 1947 aerial photograph shows the surface areas of Pits 2A through 2F (ref. 11, Figure 1.0 1, Table 4.3 4).

Pit 2A Pit 2B Pit 2C Pit 2D Pit 2E 'Pit 2F Total Surface Area (not including protrusions) (ft2,

1,650 1,625 1,625 1,9 14 1,625 9,464 Area Value (A): 9,464 ft2 Reference: 1 1, Figure 1 .O 1, Table 4.3 4 Area Assigned Value (N13): 728 17 I SD Hazardous Waste Quantity Source 1 Source Hazardous Waste Ouantitv Based on Tier D, the hazardous waste quantity associated with this source is 728.

Source Hazardous Waste Quantity: 728 18 SD Characterization and Containment Source 2 SOURCE DESCRIPTION 2.2 Source Characterization Source Description: Source 2  Ponds 1B and 1C Source 2 consists of two rectangular evaporation ponds (Ponds 1B and 1C) that are adjacent to one another and arranged in a linear east west alignment (ref. 5, Plate 3 3; ref. 6).

Aerial photographs indicate that Ponds 1B and 1C were first present in 1946 (ref. 5, p. 3 6). They are manmade excavations formed from earthen materials that were designed to hold aqueous wastes (e. g., propane cracking oils generated by the production of ethylene from propane at the historic styrene' manufacturing plant) (ref. 8, p. 7; ref. 9, p. 15).

Aerial photographs indicate that, by 1967, both ponds had been covered with fill material (ref. 5, p. 3 6). The source of the fill material is not known; however, it is probably soil that was originally used as. diking around the perimeter of the ponds (ref. 8, p. 7). Field data and visual observations of core samples collected from the ponds in 1984 indicate that the fill material overlying the waste in Pond 1B is 3.8 feet thick. The fill material is absent from some areas in Pond lC, resulting in exposed waste at ground surface (ref. 11, p. 4 30, Table 4.3 4). The fill material is covered with weeds and miscellaneous debris (e. g., old tires and broken glass)..( ref. 5, p. 5 23).

Ponds 1B and 1C are separated from Del Am0 Boulevard and a residential area to the south by a double row of fences (ref. 5, p. 5 23).

Observations made during boring and sampling activities indicate that the waste remaining in Ponds 1B and 1C is a fairly uniform fine grained material (clays and silts) resembling a "clay like sludge" varying in color from gray to reddish black (ref. 12, p. 11). This waste contains hydrocarbons with high polynuclear aromatic and volatile aromatic content. Naphthalene is the predominant polynuclear aromatic compound, while benzene and ethylbenzene are the predominant volatile aromatic compounds (ref. 5, p. 5 25; ref. 7, p. iii).

Source Twe The source type for Source 2 is "buried surface impoundment" (ref. 1, Table 2 5).

Source Location Source 2 is located in the portion of the Del Amo site that was formerly occupied by the styrene manufacturing plant. Ponds 1B and IC are approximately 100 feet north of Del Amo Boulevard (ref. 5, Plate 3.3; ref. 6).,

19 SD Characterization and Containment Source 2 Source Containment Release to Ground Water Source 2 has no liner (ref. 5, p. 3 6). Analytical results provide evidence of vertical hazardous substance migration from the waste in Source 2 to the soil immediately beneath the ponds (ref. 5, pp. 5 26, s 29,5 30,5 31, Tables 5.5 3 through 5.5 16, Figures 5.5 1,5.5 1'0). A ground water containment factor value of 10 is assigned for "evidence of hazardous substance migration from source area" (ref. 1, Table 3 2).

20 SD Hazardous Substances Source 2 2.4.1 Hazardous Substances Hazardous Substance Evidence Reference benzene wastdsoil sample nos.% 11, Table 5.2 1,

S 148 S 172 p. B 11 p. B 12 ethylbenzene S 124 p. B 13 wastesample nos.%% 7, Table2 6 lB( 7.0)

lC( 7.0)

wastesample nos.%%% 12,

wssoooo8 pp. A3 1, A4 56 sssooo24 pp. A3 1, A4 5,6 wss00011 SSSOOO30 thru SSSOOO32 wastdsoil sample nos.%

S 148 S 172 S124 waste sample nos.%%

lB( 7.0)

lC( 7.0')

waste sample nos.%%%

wssoooo8 SSS00024andSSS00025 wss00011 SSSOOO30 thru SSSOOO32 pp. A3 2, A4 56 pp. A3 2, A4 64 11, Table 5.2 1,

p. B 11 p. B 12 p. B 13 7, Table 2 6 12,

pp. A3 1, A4 57 pp. A3 1, A4 57 pp. A3 2, A4 57 pp. A3 2, A4 65 21 naphthalene SD Hazardous Substances Source 2 waste/ soil sample nos.% 11, Table 5.2 1,

S 148 p. B 21 S 172 p. B 22 S 124 p. B 23 waste sample nos.%%% 12,

WSSOOOO8 pp. A3 1, A4 54 SSS00024 and SSSOOO25 pp. A3 1, A454 wss00011 pp. A3 2, A4 54 SSSOOO30 thru SSSOOO32 pp. A3 2, A4 62 In 1984, Dames & Moore, under contract to Ire11 & Manella, drilled four soil borings in Source 2 (i. e., borings 1 B I and 1 B I1 in Pond 1B; and borings 1 C I and 1 C I1 in Pond 1C) to characterize the fill material overlying the waste, the waste, and the soil beneath the waste (ref. 11, p. 4 24, Figure 4.3 1). Twelve to 13 soil andor waste samples were collected from each boring (49 total) at 2.5 foot or 5 fOOt intervals from ground surface to a depth of 45 feet bgs (ref. 11, pp. 4 26,4 27, Table 4.3 2). Of the 49 samples, .the following three samples consisting of a combination of waste and soil were selected for chemical analysis: S148 from boring 1 B I in Pond lB, S172 from boring 1 B I1 in Pond lB, and S124 from boring 1 C I in Pond 1C (ref. 11, Tables 4.3 2,5.2 1, Appendix A, pp. A 1 through A 4). All three samples were analyzed for purgable aromatics using EPA Method 602 and extractable hydrocarbons using EPA Method 610. Analytical results indicated the presence of benzene, ethylbenzene, and naphthalene at concentratiqns up to 140 mg/ kg, 3,500 mg/ kg, and 4,420 mg/ kg, respectively, in Pond 1B; and 160 mg/ kg, 310 mgkg, and 2,700 mgkg, respectively, in Pond 1C (ref. 11, p. 5 6, Appendix B, pp. B 11 through 'B 13, B 21 through B 23).

%% In 1990, Dames & Moore, under contract to G. P. Holdings, Inc., Dow Chemical Comp& y, and Shell Oil Company, drilled six borings in Source 2 to collect samples for treatability testing (i. e., borings 1B I, 1B 2, and 1B 3 in Pond 1B and borings 1C 1, 1C 2, and 1C 3 in Pond IC) (ref. 5, Table 5.5 1, Figure 5.5 1; Reference 7, Appendix D, pp. D 1 through D 7). Two waste samples, which were collected at a depth of 7 feet bgs, were analyzed for volatile organic compounds using EPA Method 8240. Analytical results indicated the presence of benzene and ethylbenzene at concentrations of 580 mg/ kg and 4,000 mgkg, respectively, in Pond 1B; and 140 mg/ kg and 1,700 mgkg, respectively, in Pond 1C (ref. 7, p. 2 4, Table 2 6).

%% c; k In 1992, Dames & Moore, under contract to Shell Oil Company and Dow Chemical Company, drilled two borings in Source 2 (i. e., borings SBL0004 and SBL0005 in Pond IC) as part of a waste excavation feasibility study (ref. 12, p. 1, Appendix A, Figure A 1). Three waste samples (WSSOOOOS, SSSOOOO4, and SSSOOO25) collected from boring SBL0004 and four waste samples (WSSOOOl1, SSSOOO30, SSSOOO31, and SSSOOO32) collected from boring SBL0005 were 22 . " SD Hazardous Substances Source 2 analyzed for volatile organic compounds using EPA Method 8240 and for polynuclear aromatic hydrocarbons using EPA Method 8270 (ref. 12, Appendix A, p. A 2, Attachment A3, pp. A3 1, A3 2, Attachment A4, pp. A4 54, A4 56, A4 57, A4 62, A4 64, A4 65). Analytical results indicated the presence of benzene, ethylbenzene, and naphthalene at concentrations up to 260 mglkg, 1,200 m@ g, and 9,700 mglkg, respectively, in the waste in Pond 1C (ref. 12, Appendix A, Attachment A4, pp. A4 54, A4 56, A4 57).

The hazardous substances associated with Source 2 include:

benzene ethylbenzene naphthalene Other hazardous substances are associated with Source 2 (e. g., toluene, and styrene) (ref. 5, p. 5 25). The documentation presented above is limited to benzene, ethylbenzene, and naphthalene because these three hazardous substances are the dominant constituents of the hydrocarbon waste remaining in Ponds 1B and 1C (ref. 7, p. iii).

23 SD Hazardous Waste Quantity Source 2 2.4.2 Hazardous Waste Quantity Tier A: Hazardous Constituent Ouantitv Documentation is not sufficient to determine hazardous constituent quantity.

Hazardous Constituent Quantity Value: 0 24 SD Hazardous Waste Quantity Source 2 Tier B: Hazardous Wastestream Ouantitv Documentation is not sufficient to determine hazardous wastestream quantity.

Hazardous Wastestream Quantity Value: 0 25 SD Hazardous Waste Quantity Source 2 Tier C: Volume Documentation is not sufficient to determine the volumes of Ponds 1B and 1C.

26 Volume Assigned Value: 0 Tier D: Source Area SD Hazardous Waste Quantity Source 2 A 1947 aerial photograph shows the surface areas of Ponds 1B and 1C (ref. 11, Figure 1.0 1, Table 4.3 4).

Surface Area (ft2)

Pond 1B Pond IC Total 22,040 21,600 43,640 Area Value (A): 43; 640 ft2 References: 1 1, Figure 1 .O 1, Table. 4.3 4 Area Assigned Value (N13): 3,357 27 SD Hazardous Waste Quantity Source 2 2.4.2 Source Hazardous Waste Ouantitv Based on Tier D, the hazqdous waste quantity associated with this source is 3,357.

Source Hazardous Waste Quantity: 3,357 28 SD Characterization and Containment Source 3 SOURCE DESCRIPTION 2.2 Source Characterization Source Description: Source 3  Spillage from Historic Crude Benzene Storage Tank Source 3 consists of spillage from a historic crude benzene storage tank that was located in the northwest corner of the former styrene manufacturing plant's tank farm. The tank farm, which was referred to as the 2500 area tank farm, consisted of 17 large cylindrical aboveground storage tanks and several smaller tanks (ref. 5, p. 3 5, Plate 3 1). The tanks stored crude and refined products associated with the styrene manufacturing process, including benzene, ethylbenzene, toluene, styrene, polyethylbenzene, propylbenzene, butylbenzene, and fuel oil (ref. 5, p. 3 12, Appendix A, p. A 29). The capacity of crude benzene storage tank was at least 500,000 gallons (ref. 52, p. 7 4).

Aerial photographs and site history documents indicate that spillage occurred in the 2500 area during transfer of the contents of the tanks to and from railroad cars and trucks. Aerial photographs show tonal contrasts thar may represent staining in the 2500 area (ref. 5, p. 3 12, Appendix A, pp. A 6, A 7, Plate A 1). Site history documents refer to spills which occurred during transfer operations. For example, a Request for Expenditures (dated February 7, 1968) indicates the need for lighting in the finished styrene tanks, because the tanks were typically filled during night hours and overfilling occurred (ref. 5, Appendix A, p. A 29).

Evidence of Spillage from the Historic Crude Benzen. e Storage Tank An area of non aqueous phase liquid (NAPL) accumulation is currently located proximal to the historic crude benzene storage tank. As documented below, the presence of this NAPL provides evidence of spillage from the tank, based on the location of the NAPL and its chemical composition (ref. 51, p. i, Figure ES 1).

Location of the NAPL In 1990, Hargis + Associates, under contract to the Montrose Chemical Company, constructed a monitoring well (MW 20) approximately 100 feet southeast of the historic crude benzene storage tank (ref. 51, p. 1, Figure 3; ref. 53). Upon completion, NAPL was detected floating on ground water in the well (ref. 5 1, p. 1). NAPL was not detected in monitoring well MW 1, which is located approximately 175 feet northwest of the historic location of the crude benzene storage tank; monitoring well " 27, which is located approximately 600 feet southwest of the historic location of the tank; or monitoring wells MW 21 and MW 28, which are located approximately 775 feet and 950 feet, respectively, southeast of the historic location of the tank (ref. 5 1, pp. 1, 2, 12, Figure 2).

In October 1992, Dames & Moore, under contract to the Shell Oil Company and The Dow Chemical Company, installed four additional monitoring wells (SWLOOO1 through SWL0004), 11 temporarywell points (CWLOOO1 through CWLOOl l), and four soil borings (SBL0009, SBL0010, SBLOOl 1, and SBL0017) to further delineate the NAPL (ref. 50, Appendix B, pp. B 73 through B 84, B 120 through B 123, Appendix C, Table C 1; ref. 51, pp. 3, 5,6,7, Figures 15, 16; ref. 53). Floating NAPL was observed SD Characterization and Containment Source 3 in monitoring wells MW 20 and SWLO001, and temporary well points CWLO00l through CWLOOO4, CWL0006, CWL0008, and CWL0009. In addition, a hydrophobic hydrocarbon specific dye (Sudan Red) test indicated the presence of NAPL in one of the four soil borings (SBL0017). (ref. 51, pp. 14, 15, Figures 15, 16; ref. 53).

In May, July, and August 1993, Dames & Moore drilled seven additional soil borings (SBL0049, SBL0050, SBL0068, SBL0069, SBL0070, SBL0071, and SBL0073) to further delineate the NAPL (ref. 5, p. 2 18, Figure 2.6 2; ref. 50, Appendix B, pp. B 269 through B 276, B 345 through B 358, B 361 through B 363; ref. 53). NAPL was identified in one of the seven borings (SBL0071), using the Sudan Red test (ref. 5, pp. 2 18,5 20; ref. 53). Floating NAPL was observed in monitoring well SWL0032, which was installed in December 1993 (ref. 50, p. 5 1, Appendix C, Table C 1 ; ref. 54, Figure 1).

In April and May 1994, Dames & Moore drilled 10 additional soil borings (SBLO0085 through SBL00094), as part of a hydraulic extraction pilot program (ref. 53; ref. 54, pp. 1,2, Figure 1). NAPL was detected in the saturated zone in all 10 borings, using ultraviolet light and Sudan Red tests (ref. 50, Appendix B, pp. B 429 through B 468; ref. 53; ref. 54, p. 7; ref. 55, pp. 36,40,42,72, 119, 121, 123, 127, 129, 137, 143; ref. 56, pp. 34, 38,40,42,44,56, 114, 116, 128, 130, 132, 134, 136, 138, 140, 142, 144;. ref. 57, pp. 28,34,36, 38,40,42,44,48, 50,52,54,56,68, 111, 121, 125, 127, 129, 131, 133, 135, 137, 139, 143, 145, 147; ref. 58, pp. 26,28,38,40,42,44,46,48,52, 123,125, 127, 129, 131, 133, 135, 137, 139, 141, 149, 151; ref. 59, pp. 56,58,64, 144, 146, 152, 154, 156, 158, 164, 169, 171, 173, 175). '

Based on the presence or absence of NAPL in the monitoring wells, temporary well points, and soil borings described above, the lateral extent of the NAPL has been estimated to range from 14,300 to 17,500 square feet (ref. 50, p. 5 1; ref. 51, p. 13, Figures 15, 16; ref. 54, Figure 1). The northwest edge of NAPL is located approximately 50 feet southeast of the historic crude benzene storage tank (ref. 51, p. 13, Figure 16; ref. 54, Figure 1).

Chemical Composition of the NAPL In 1992, Dames & Moore *collected NAPL samples from monitoring well MW 20 and two temporary wells points located within 50 feet of monitoring well MW 20 (CWL0006 and CWL0009). Physical and chemical testing of these samples indicated that the NAPL is composed primarily of benzene (90%) with lesser quantities of toluene, ethylbenzene, and styrene (40% total) and an unidentified C25 hydrocarbon trace) (ref. 51, pp. i, 12, Tables 7, 11, Figure 6). The low concentrations of toluene, ethylbenzene, and styrene present in the NAPL, relative to benzene, correlate with what is known about the composition of the crude benzene stock that was historically used at the styrene manufacturing plant (i. e., the stock. contained impurities) (ref. 51, p. 12).

In addition to the NAPL investigations presented above, soil sampling has been conducted in the vadose zone beneath the historic location of the crude benzene storage tank and, above the current location of the NAPL (ref. 5, pp; 2 18, Figure 5.4 3). The analytical data from these soil sampling efforts are not presented as evidence of spillage from the tank because benzene was either not detected or detected at trace concentrations in the vadose zone (ref. 5, Figure 5.4 3). The absence of significant benzene contaminated soil is inferred to be due to natural degradation processes that have occurred in an aerobic vadose zone soil environment since the benzene was released (ref. 5, p. 5 22; ref. 50, p. 1 14). Based on the time period ..  30 SD Characterization and Containment Source 3 during which the styrene manufacturing plant operated (i. e., 1942 to 1969), the release occurred between 31 and 58 years ago (ref. 5, p. 5 22).

Source Tvpe The source type for Source 3 is "other" (ref. 1 , Table 2 5).

Source Location Spillage from the historic crude benzene storage tank is currently present as an appr6ximately 14,300 to 17,500 square foot area of NAPL accumulation, 50 feet to the southeast of where the tank was located in the nofihwest portion of the former styrene manufacturing plant (ref. 6; ref. 50, Figure 5.1 1; ref. 51, p.^ 13, Figure 16; ref. 54, Figure 1).

Source Containment Release to Ground Water The presence of NAPL provides evidence of hazardous substance migration from the historic crude benzene storage tank (ref. 5 1, p. 13). A ground water containment factor value of 10 is assigned for "evidence of hazardous substance migration from source area" (ref. 1, Table 3 2).

31 SD Hazardous Substances Source 3 2.4.1 Hazardous Substances In 1992, Dames & Moore, under contract to Shell Oil Company and The Dow Chemical Company, collected NAPL samples from monitoring well MW 20 and two temporary wells located within 50 feet of monitoring well MW 20 (CWL0006 and CWL0009). Physical and chemical testing of these samples indicated that the NAPL is composed primarily of benzene (90%) with lesser quantities of ethylbenzene, toluene, and styrene (40% total) and an unidentified C25 hydrocarbon trace (ref. 51, pp. i, 12, Tables .7,

1 1, Figure 6).

The dominant hazardous substance associated with Source 3 is:

benzene 32 SD Hazardous Waste Quantity Source 3 2.4.2 Hazardous Waste Quantity Tier A: Hazardous Constituent Ouantitv C (concentration of benzene in the NAPL) = 90percent In 1992, Dames and Moore, under contract to Shell Oil Company and The Dow Chemical Company, collected NAPL samples from monitoring well MW 20 and two temporary wells located within 50 feet .of monitoring well MW 20 (CWL0006 and CWL0009). Physical and chemical testing of these samples indicated that the NAPL is composed primarily of 90 percent benzene (ref. 51, pp. i, 12, Tables 7, 11, Figure 6).

D (density of benzene) = 7.32 pounds per gallon By definition, the density of water is 1. The weight of water is 8.330 pounds per gallon. The density of benzene is 0.8786 relative to water (ref. 61). Multiplying the weight of water (8.330 pounds per gallon) x the density of benzene relative to water (0.8786) yields the density of benzene (7.32 pounds per gallon).

V (partial volume of the NAPL) = 935 gallons According to the May 15, 1998 Final Ground water Remedial Investigation (RI) Report for the Del Am0 Study Area, the NAPL in the vicinity of monitoring well MW 20 extends laterally over an area of approximately '17,500 square feet (ref. 50, p. 5 1). It is limited to the saturated zone, occurring as isolated blobs in a smear zone that extends from the water table, at approximately 60 feet bgs, to 30 feet below the water table (ref. 50, pp. 4 1, 6 20). This mode of occurrence is consistent with conditions that can be expected after a NAPL, which in this case is a NAPL that is lighter than water, has migrated through the vadose zone, intercepted the water table, and then been influenced by a rising water table. Ground water levels have been rising in the vicinity of the Del Am0 site since 1965, most likely as a result of controls that were placed on ground water pumping as part of the adjudication of the West Coast Basin in 1961 (ref. 50, p. 4 1).

The vertical and lateral components of the Tier A' volume calculations presented below are based on only that portion of the NAPL that has received detailed inspection and analysis. This portion, which is defined by eight of the 10 soil borings that Dames & Moore drilled in 1994 (SBL00086 through SBL0092 and SBL0094), represents 3.8 percent of the estimated total lateral extent of the NAPL (i. e., 657 square feet of the estimated total 17,500 square feet) (ref. 53).

Vertical Component of Tier A Volume Calculations During the 1994 NAPL investigation, Dames & Moore collected continuous core from ground surface to a depth of 90 feet bgs at each of 10 soil boring locations (SBLOOO85 through SBL00094 (ref. 53; ref. 54, pp. 1, 2, Figure 1). Ultraviolet light and Sudan Red tests were used to identify the presence of NAPL in each continuous core (ref. 54, p. 7). Dean Stark tests for effective porosity and relative pore fluid saturation (water and NAPL) were then performed on 123 plug samples (1 inch, diameter by 0.5 inch long cylinders) selected from core intervals that contained NAPL, as well as from core intervals that did not contain NAPL (ref. 60, pp. 7, 8, 13).

"

33 SD Hazardous Waste Quantity Source 3 As presented in the table below, the effective porosity and relative pore fluid saturation data from 105 of the 123 plugs (i. e., the data from all plugs from borings SBL0086 through SBL0092 and SBL0094) were used to determine the total vertical length of NAPL (0.19 feet) occupying the pore spaces in a 18.9 foot thick portion of the smear zone. The average length of the sampled intervals from the eight borings was multiplied by the average effective porosity of the 105 plugs and then multiplied by the average pore fluid saturation of the 105 plugs to obtain the total vertical length of NAPL in the pore spaces of the 105 plugs. The remaining 18 plugs were collected from borings SBL0085 and SBL0093 (ref. 60, Table 4). As ,

discussed previously in Section 2.2 (Source Characterization), NAPL was identified in these two borings using ultraviolet light and Sudan Red tests (ref. 55, pp. 36,40,42,72; ref. 59, pp. 56,58, 64, 158, 164, 169, 171, 173, 175). However, NAPL was not identified in any of the plugs that were subjected to Dean Stark tests (ref. 60, Table 4).

34 \ h m m W 2 oo 0 2 m r oo 0 0 1 rn m M 'G c 0 . m W m 0 vi 2 m m 0 s w M 'C c 0 ._ m m \4 F:

0 m W u!

N z vi W 3 2 w r

0 2 vi m m 0 2 3 0 2 2 0 W W N 0 m s % 0 c?  r

* 0 m m s VI 0 d SD Hazardous Waste Quantity Source 3 Lateral Component of Tier A Volume Calculations When a graph paper overlay with a scale of 20 squares per inch is placed over the area defined by borings SBLOO86 through SBL0092 and SBL0094 in the figure in Reference 53,657 squares fall within the boundaries. Since the scale of the figure in Reference 53 is 20 feet per inch, each square on the graph paper represents 1 square foot. Therefore, the area defined by borings SBL0086 through SBL0092 and SBL0094 is approximately 657 square feet.

Tier A Volume Calculations The average vertical feet of NAPL (0.19 feet) multiplied by the area defined by borings SBL0086 through SBL0092 and SBL0094 (657 square feet) produces 125 cubic feet. Multiplying 125 cubic feet by the standard conversion factor of 7.48 gallons per cubic foot yields a NAPL volume of 935 gallons.

HCQ (Hazardous Constituent Quantity) = C x D x V = 6,160pounds of benzene Multiplying C (0.90) by D (7.32 pounds per gallon) by V (935 gallons) yields 6,160 pounds of benzene in a portion of the NAPL.

Hazardous Constituent Quantity Value: 6,160 41 SD Hazardous Waste Quantity Source 3 Tier B: Hazardous Wastestream Quantity Documentation is not sufficient to document hazardous wastestream quantity.

Hazardous Wastestream Quantity Value: 0 42 Tier C: Volume SD Hazardous Waste Quantity Source 3 As presented in the Tier A calculations, the volume of NAF'L in the portion of the NAPL. that is defined by ~

borings SBL0086 through SBL0092 and SBL0094 is 935 gallons. There are 200 gallons in 1 cubic yard. Dividing 935 gallons by 200 gallons yields 4.68 cubic yards. Dividing 4.68 cubic yards by the Tier C divisor for the source type "other" (2.5) yields a volume assigned value of 1.87 (ref. 1, Table 2 5)..

Volume Assigned Value: 1.87 43 SD Hazardous Waste Quantity Source 3 Tier D: Source Area Tier D cannot be calculated for the source type "other," because this source type is not included in the list of source types in the Tier D sect& of HRS Table 2 5 (ref. 1, Table 2 5).

Area Assigned Value: 0 44 . SD Hazardous Waste Quantity Source 3 Source Hazardous Waste Quantity Based on Tier A, the hazardous waste quantity associated with this source is 6,160.

Source Hazardous Waste Quantity: 6,160 45 SUMMARY OF SOURCE DESCRIPTIONS Source Air Source Hazardous Waste Ground Water Surface Water GasParticulate Number Quantity Value Containment Containment Containment 1 728 . . 10 not scored not scored 2 10 not scored not 3 6,160 10 not scored Sources Not Included in Scoring In addition to the three sources that are quantified in this documentation record, the May 15; 1998 Final Ground Water RI Report identified the following 10 source areas of ground water contamination on the historic Del Am0 synthetic rubber manufacturing property (ref. 6; ref. 50, Figure 5.3 5):

1.

2. 3.

4. 5. 6. 7. 8. 9. 10. Cyclohexane tanks associated with the former copolymer plant in the northern portion of the site, Onsite "pits and trenches" in the former copolymer plant area, Volatile organic compound (VOC) tanks associated with the former styrene finishinghenzene purification unit, VOC tanks and/ or underground pipelines associated with the former styrene finishing unit, Tank f p n in the former styrene plant area, VOC storage tanks associated with the former ethylbenzene production unit #1, VOC storage tanks associated with the former ethylbenzene production unit #2, Utility @nks in the former styrene plant area, Underground benzene pipeline in the southeast portion of the site, and Laboratory underground pipelines in the former butadiene plant area in the eastern portion of the site.

These source areas were identified based on two or more of the following lines of evidence: observation of NAPL in a well or boring; water table analytical data indicating compound concentrations elevated relative to surrounding monitoring locations; historical information indicating the presence of facilities where large volumes of chemicals were stored, processed, or disposed of; and shallow soil gas data indicating elevated concentrations of VOCs (ref. 50, p. 5 20).

46 GW General 3.0 GROUND WATER MIGRATION PATHWAY 3.0.1 GeneralConsiderations The Del Amo site is located in the West Coast Basin of the coastal plain of Los Angeles County, California (ref. 15, p. 1, Plates 1 and 2). The following unsaturated soil and hydrogeologic units, in descending order, have been identified beneath the site: recent Playa deposits, Palos Verdes sand, upper Bellflower, Bellflower sand, lower Bellflower, Gage, Gage Lynwood, Lynwood, unnamed, and Silverado. A description of each of these units is presented below. Characterization of the first eight units is based on the lithologic, physical parameter, and hydraulic parameter data that were obtained during the Montrose RI field work and the Del Am0 RI field work. The Montrose site is located approximately 600 feet west of the 300 acre Del Am0 site (ref. 5, Figure 1.4 1). Between 1985 and 1991, as part of the Montrose RI, Hargis + Associates completed 121 soil borings, 17 exploratory borings, and 91 monitoring wells on and in the vicinity of the Montrose and Del Amo sites (ref. 16, pp. 4 2 and 4 12, Tables 2.1, 2.2,2.3,2.5, and 4.1, Figures 4.4 and 4.9). In 1993, as part of the Del Am0 RI, Dames & Moore completed 23 soil borings, 37 temporary well points, 26 temporary piezometers, and 19 monitoring wells on the Del Am0 Facility site (ref. 5, pp. 1 1,2 6,2 7, Table 2.9 2, Figure 2.2 1). Characterization of the lower two units (i. e., unnamed and Silverado) is based on the findings presented in the 1961 State of California Department of Water Resources report, Planned Utilization of the Ground Water Basins of the Coastal Plain of Los Angeles County (ref. 15).

Stratum 1 (shallowest)

Stratum Name: Recent Playa Deposits Description: As presented in the October 1992 Montrose RT report, recent Playa deposits comprise the shallowest geologic unit in the unsaturated zone (ref. 16, Figure 2.6). These deposits underlie suficial soils and fill material. The unit is relatively flat lying and laterally continuous. The Playa deposits consist of dark brown to light olive brown silt, clayey silt, or clay, as well as clayey sand, sandy silt, or sandy clay. The contact between Playa deposits and. the underlying Palos Verdes sand is gradational and characterized by an increase in sand content from a silt to a sand. The lower contact of the Playa deposits occurs at depths ranging from 22 feet bgs to 30 feet bgs (ref. 16, pp. 4 2,4 5, and 4 6).

Stratum 2 ,

Stratum Name: Palos Verdes Sand Description: As presented in the 1992 Montrose RI report, late Pleistocene marine deposits, which are also referred to as the Palos Verdes sand, underlie the Playa deposits in the unsaturated zone (ref. 16, Figure 2.6). The Palos Verdes sand unit is flat lying and laterally continuous. It consists of light olive brown, fine grained sand, and silty sand. The basal portion of the Palos Verdes sand is characterized by fossiliferous sand that is dense and well cemented. This fossiliferous sand marks the contact between the Palos Verdes sand and the underlying upper Bellflower unit. The lower contact of the Palos Verdes sand occurs at depths ranging from 40 feet bgs to 49 feet bgs (ref. 16, pp. 4 2 and 4 6).

"

47 GW General Stratum 3 Stratum Name: Upper Bellflower Aquifer Description: As presented in the 1992 Montrose RI report, the upper Bellflower underlies the Palos Verdes sand (ref. 16, Figure 2.6). The upper Bellflower is relatively flat lying and laterally continuous. It consists of interbedded, micaceous, olive brown sand, silty sand, silt and clay. The upper portion of this unit is unsaturated, while ground water occurs in the bottom portion (ref. 16, pp. 4 6 and 4 7). Hargis + Associates had installed 30 ground water monitoring wells in the upper Bellflower by November 1991 (ref. 16, p. 4 17, Table 4.1 1). Based on October 1991 water level measurements, ground water flow direction tends toward the southeast (ref. 16, p. 4 18, Figure 4.15). The contact between the upper Bellflower and the underlying Bellflower sand is gradational. The contact has no distinct marker beds and is generally identified by a decrease in silt interbeds with depth or by an increase in resistivity with depth. The base'of the upper Bellflower ranges in depth from approximately 47 feet bgs to 129 feet bgs (ref. 16, p. 4 15).

The upper Bellflower is considered an aquifer for HRS purposes because the State of California Regional Water Quality Control Board (RWQCB), Los Angeles Region, has determined that all ground water units in the vicinity of the Del Am0 site are to be considered potential sources of drinking. water pursuant to State Water Resources Control Board Resolution 88 63 (i. e., ground water is considered drinking water unless the total dissolved solids (TDS) > 3,000 milligrams per liter (mg/ l), deliverability e 200 gallons per day, or pre existing contamination is present that cannot reasonably be treated) (ref. 16, p. 4 24; Reference 17, p. 2). In May 1990, constant discharge tests were conducted at five monitoring wells screened in the upper Bellflower (MW 13, MW 15, MW 17, MW 25, and MW 26). Constant discharge rates ranged from 1.2 gallons per minute (1,728 gallons per day) to 12.6 gallons per minute (18,144 gallons per day) (ref. 19, pp. 4 and 5, Table 2, Figure 1). During the period from May 1985 through October 1991, inorganic water quality was assessed in 29 monitoring wells screened in the upper Bellflower (MW 01 through MW 19 and MW 21 through MW 30) during initial ground water sampling of each well, which was conducted shortly after the well was installed (ref. 15, p. 4 21, Figure 4.9, Appendix H, Table H I). The TDS concentrations ranged from 110 mg/ l to 13,740,000 mg/ l with a concentration of 3,000 mgA being exceeded in only four of the 29 wells (MW 02, MW 05, MW 06, and MW 07) (Reference 16, Appendix H, Table H I). Monitoring wells MW 02, MW 05, MW 06, and MW 07 are on the Montrose site' in or near the central process area where dichlorodiphenyltrichloroethane (DDT) was historically manufactured (ref. 16, pp. ES 1 and 4 23, Figure 4.9).

Stratum 4 Stratum Name: 'Bellflower Sand Aquifer Description: As presented in the October 1992 Montrose RI report, the Bellflower sand underlies the upper Bellflower aquifer (ref. 16, Figure 2.6). The Bellflower sand consists of fine to coarse grained sand that generally coarsens with depth. Thirty three ground water, monitoring wells had been installed in the Bellflower sand by November 1991 (ref. 16, p. 4 24, Figure 4.9). The ground water flow'direction tends toward the southeast to east southeast (ref. 16, p. 4 26, Figure 4.18). The contact between the Bellflower sand and the underlying Lower Bellflower stratum is a distinct sand or silt that ranges in depth from approximately 99 feet bgs to 146 feet bgs (ref. 16, p. 4 25). In the October 1993 Del Amo RI report, the Bellflower sand stratum is referred to as the middle Bellflower.

L 9

48 GW General According to this report, the lithologic top of the middle Bellflower occurs at an average depth of 80 feet bgs and the base. occurs at an average depth of 145 feet bgs (ref. 5, p. 4 5, Figure 4.1 3).

The Bellflower sand is considered an aquifer for HRS purposes because the RWQCB, Los Angeles Region, has determined that all ground water units in the vicinity of the Del Am0 site are to be considered potential sources of drinking water pursuant to State Water Resources Control Board Resolution 88 63 (i. e., ground water is considered drinking water unless the TDS > 3,000 mfl, deliverability c 200 gallons per day, or pre existing contamination is present that cannot reasonably be treated) (ref. 16, p. 4 30; ref. 17, p. 2; ref. 18, p. 2). In May 1990, constant discharge tests were conducted at six monitoring wells screened the Bellflower sand (BF 5, BF 7, BF 9, BF 11, BF 13, and BF 15). Constant discharge rates ranged from 19.9 gallons per minute (28,656 gallons per day) to 85.8 gallons per minute (123,552 gallons per day) (ref. 19, pp. 4 and 5, Table 2, Figure 1). During the period of January 1987 through October 1991, inorganic water quality was assessed in 33 monitoring wells screened in the Bellflower sand (BF 01 through BF 33) during initial ground water sampling of each well, which was conducted shortly after the well was installed (ref. 16, p. 4 29, Figure 4.9, Appendix H, Table H 1). The TDS concentrations in ground water samples collected from the 33 wells ranged from 346 mgA to 1,470 mg/ l, except in monitoring well BF 13, which had a concentration of 5,600 mg/ l (ref. 16, p. 4 30, Appendix H, Table H 1).

Stratum 5 Stratum Name: Lower Bellflower Aquitard Description: As presented in the October 1992 Montrose RI report, the lower Bellflower underlies the Bellflower sand (ref. 16, Figure 2.6). The lower Bellflower is heterogenous and consists of silt of varying plasticity as well as clayey sandy silt, fine grained silty sand, and sand. There are no ground water monitoring wells screened in the lower Bellflower. The contact between the lower Bellflower and the underlying Gage unit is a moderately well defied silt to fine grained sand that ranges in depth from approximately 124 feet bgs to 171 feet bgs (ref. 16, p. 4 32).

As presented in the October 1993 Del Amo RI report, the lower Bellflower has a predominance of muddy lithotypes. Its lithologic top occurs at an average depth of 140 feet bgs and the base occurs at an average depth of 170 feet bgs (ref. 5, p. 4 5, Figure 4.1 3).

Stratum 6 Stratum Name: Gage Aquifer Description: As presented in the October 1992 Montrose RI report, the Gage underlies the lower Bellflower (ref. 16, Figure 2.6). The Gage typically consists of fine grained sand with a little silt that grades to a silty sand near the base of the aquifer. Twenty one ground water monitoring wells had been installed in the Gage by November 1991. Nineteen of these wells (G 1 through G 19) are completed in the upper portion of the unit, and two (LG 1 and LG 2) are completed in the lower portion (ref: 16, p. 4 35, Figure 4.21). The contact between the Gage and the underlying Gage Lynwood stratum is gradational and is characterized by intermittent interbedding of silt and silty sand. This contact ranges in depth from approximately 180 feet bgs to 221 feet bgs (ref. 16, pp. 4 34).

49 GW General As presented in the October 1993 Del Amo RI report, the lithologic top of the Gage occurs at an average depth of 170 feet bgs and the base occurs at an average depth of 240 feet bgs (ref. 5, p. 4 5, Figure 4.1 3).

The Gage is considered an aquifer for HRS purposes because the RWQCB, Los Angeles Region, has determined that all ground water units in the vicinity of the Del Amo site are to be considered potential sources of drinking water pursuant to State Resources Control Board Resolution 88 36 (i. e., ground water is considered drinking water unless the TDS > 3,000 mg/ l, deliverability < 200 gallons per day, or pre existing contamination is present that cannot be reasonably treated) (ref. 16, p. 4 39; Reference 17, p. 2; ref. 18., p. 2). In May and June 1990, constant discharge tests were conducted at four monitoring wells screened in the Gage aquifer (G 5, G 11, G 13, and LG 2). Constant discharge rates ranged from 65.5 gallons per minute (94,320 gallons per day) to 82.6 gallons per minute (1 18,944 gallons per day) (ref. 19, pp. 4 and 6, Table 2, Figure 1). During the period from January 1987 through October 1991, inorganic water quality was assessed in 21 monitoring wells screened in the Gage (G 01 through G 19, LG 01, and LG 02) during initial ground water sampling of each well, which was conducted shortly after the well was installed (ref. 16, p. 4 38, Figure 4.9, Appendix H, Table H 1). The TDS concentrations in ground water samples collected from the 21 wells ranged from 200 mg/ l to 520 mg/ l (ref. 16, p. 4 39, Appendix H, Table H 1).

stratum 7 Stratum Name: Gage Lynwood Aquitard Description: As presented in the October 1992 Montrose RI report, the Gage Lynwood underlies the Gage (ref. 16, Figure 2.6). The Gage Lynwood consists of silt, sandy silt, and/ or clayey silt interbedded with fine grained sand. There are no ground water monitoring wells screened in this stratum. The contact between the Gage Lynwood and the underlying Lynwood is distinct because of the contrast between the silt in the Gage Lynwood and the fine to coarse grained sand in the Lynwood. This contact ranges in depth from approximately 212 feet bgs to 258 feet bgs (ref. 16, p. 4 40).

In the October 1993 Del Am0 RI report, the Gage Lynwood stratum is referred to as the El Segundo. According to this report, the lithologic top of the El Seendo occurs at an average depth of 240 feet bgs. The depth of the base of the El Segundo is not designated, since it was not reached during the Phase I RI investigations (ref. 5, p. 4 5, Figure 4.1 3).

Stratum 8 Stratum Name: Lynwood Aquifer Description: The Lynwood underlies the Gage Lynwood (ref. 16, Figure 2.6). The upper 20 feet of the Lynwood consists of fine to coarse grained sand. This sand is frequently underlain by as much as 8 feet of silt or clay of varying plasticity. Approximately 10 to 30 feet of well graded sand, gravelly sand, and sandy gravel with some silty sand interbeds underlie the top 20 to 30 feet of the Lynwood. Seven ground water monitoring wells had been installed in the Lynwood by November 1991 (ref. 16, p. 4 41 and 4 42, Figure 4.9). The ground water flow direction trends toward the southeast (Reference 16, p. 4 43, Figure 4.23). The Lynwood reaches its maximum thickness of 200 feet at a location approximately 3 miles southeast of the Del Am0 site (ref. ,15, p. 133, Plate 19B). ..

/ GW General The Lynwood is considered an aquifer for HRS purposes because the RWQCB, Los Angeles Region, has determined that all ground water units in the vicinity of the Del Am0 site are to be considered potential sources of drinking water pursuant to State Water Resources Control Boakd Resolution 88 63 (i. e., ground water is considered drinking water unless the TDS > 3,000 mgA, deliverability e 200 gallons per day, or pre existing contamination is present that carhot reasonably be treated) (ref. 16, pp. 4 46 and 4 48; ref. 17, p. 2; ref. 18, p. 2). In May 1990, a constant discharge test was conducted at one monitoring well screened in the Lynwood aquifer (LW 3). The constant discharge rate was 65.6 gallons per minute (94,464 gallons . per day) (ref. 19, pp. 4 and 6, Table 2, Figure 1). During the period from October 1989 through October 1991, inorganic water quality was assessed in seven monitoring wells screened in the Lynwood (LW 01 through LW 07) during initial ground water sampling of each well, which was conducted shortly after the wells were installed (ref. 16, p. 4 45, Figure 4.9, Appendix H, Table H 1). The TDS concentrations in ground water samples collected from the seven wells .ranged from 230 mg/ i to 296 mgA (ref. 16, p. 4 46, Appendix H, Table H 1). In addition, currently operating drinking water wells within 4 miles of Sources 1 and 2 are screened partially or wholly in the Lynwood. For example, Dominguez Water Corporation Well 75A, which is a drinking water well located 3.5 miles from the Del Am0 site, is screened at the following intervals: 210 feet to 290 feet bgs, 330 feet to 440 feet bgs, and 480 feet to 550 feet bgs (ref. 20, p. 5; ref. 32).

stratum 9 Stratum Name: Unnamed Aquitard Description: An unnamed stratum that is approximately 100 feet thick underlies the Lynwood (ref. 15, Plate 6C).

Stratum 10 (deepest)

Stratum Name: Silverado Aquifer Description: The Silverado underlies the unnamed unit. The Silverado is composed primarily of fine to coarse grained sands and gravels. These highly permeable marine deposits reach a maximum thickness of 500 feet in the West Coast Basin (ref. 15, p. 134). The Silverado is considered an aquifer for HRS purposes because the RWQCB, Los Angeles Region, has determined that all ground water units in the vicinity of the Del Am0 Facility site are to be considered potential sources of drinking water (ref. 17, p. 2). In addition, currently operating drinking water wells within 4 miles of Sources 1 and 2 are screened partially or wholly in the Silverado. For example, Dominguez Water Corporation Well 77, which is a drinking water well located 3.6 miles from the Del Am0 site, is screened at t€ ie following interval: 558 feet to 920 feet bgs (ref. 20, p. 5; ref. 32).

<IP_ADDRESS>.1 Aquifer Interconnections Ground water sampling data, discussed below, show that hazardous substances have migrated from the Upper Bellflower aquifer down to the Lynwood aquifer through the other listed aquifers. According to the HRS, these four aquifers can be combined into one aquifer for scoring purposes (ref. 1, Section <IP_ADDRESS>.1). Also documented below, the aquitard between the Lynwood and Silverado aquifers is not laterally continuous within 2 miles of the site. For this reason, the four uppermost aquifers, already combined, and "

51 GW General the Silverado can be considered one aquifer for scoring purposes (ref. 1, Section <IP_ADDRESS>.1). Ground Water Sampling Data Analytica1, data from ground water sampling events conducted for the Montrose RI and post RI monitoring programs indicate the presence of chlorobenzene and para chlorobenzene sulfonic acid (p CBSA) in monitoring wells screened solely in the upper Bellflower aquifer, monitoring wells screened solely in the Bellflower sand aquifer, monitoring wells screened solely in the Gage aquifer, and monitoring wells screened solely in the Lynwood aquifer. Along with chloral and sulfuric acid, chlorobenzene was a principal raw material in the historic production of DDT at the Montrose facility. Chlorobenzene and p CBSA were the two most widespread compounds detected in ground water during the Montrose RI (ref. 16, pp. ES 1 and ES 13). The downward migration of chlorobenzene and p CBSA may have occurred in response to the vertical downward gradients that have been reported between the upper Bellflower, Bellflower sand, Gage, and Lynwood aquifers (ref. 16, p. 6 25 and 6 33; ref. 23, pp. 2 and 3). Analytical results from selected sampling events are presented in the table below. Results indicating that the analyte was not detected above the sample quantitation limit are not included in this table. Each reported concentration is followed by the designation for the monitoring well that was sampled. All wells are within 2 miles of Sources 1 and 2 at the Del Am0 site. All wells were not sampled during each sampling event.

 Chlorobenzene concentrations in micrograms per liter @g/ l)

UpperBellflowerBellflowerSandGageAquiferLynwood Date 4/ 90 38,00O( MW01) 6( MW03) 500( MW04) 34,00O( MW05) 7,00O( MW06) lSO, OOO( MWO9) 82O( MWlO) 20,000( Mw11) 8,20O( MW 12) 2,6OO( MW 13) 400( MW 14) 22,00O( MW15) 2( MW17) 990( MW25) 6( MW26)

8/ 90 2( MW17) l( MW24) 990( MW25) 5( MW26) 480( BF01) 4,70O( BF02) 9,00O( BF03) 3 1,00O( BF04) 2,30O( BF05) 27,00O( BF06) 45,00O( BF07) 6,60O( BF08) 12,00O( BF09) 2,10O( BFll) 17800( BF14) 42,0OO( BF15) 150( BF16) 4,10O( BF17)

23,00O( BFll) 2,00O( BF14) 36,00O( BF15) 160( BF16) 4,30O( BF17) 230( GO1) 9,60O( G02) 2,20O( G03) 2,00O( G04) 14,00O( G05) 2,40O( G06) 90( G07) 120( 608) 970( G12) 1,40O( G13) 390( LG2)

99( G08) 4( G11) l, 000( G 12) 1,60O( G13) 70( LG1) 12( LWOl) 16, Fig. 2 5, Tbl~. F 1 thm F 4; 24, Tbl. D 1, APP. E 52( LW01) 16, Fig. 2 5, Tbls. F 1 thm F 4; 25, Tbl. A 1, App. B 52 GW General UpperBellflowerBellflowerSandGageAquiferLynwood Date 11/ 90 28,0OO( MW05)

12/ 90 5,80O( MW12) 5,20O( MW12) to 419 146,00O( MW05) 7,80O( MW06) 5,70O( MW12)

7/ 92 1/ 93 73,00O( MW01) 29,00O( BF04) 4,70O( BF08) 200( BF16) 3,30O( BF17) 3,60O( BF17)

23,00O( BF04) 3,40O( BF05) 3,50O( BF08) 180( BF16) 3,60O( BF17)

20,00O( BF09) 20( BF26) 18( BF26.) 370( BF3 1)

18,00O( BF09) 15( BF26) 18( BF26) 410( BF31) 310( G01) 1,30O( G04) 72( G07) SS( G08) 1,40O( G13)

170( G01) 7,00O( G02) 1,50O( G04) 63( G07) 73( G08) 1,50O( G13)

490( G03) 180( G19) 220( G19)

1,1OO( G03) 370( G19) 68( LW01) 16, Fig. 2 5, 70( LW01) Tbl~. F 1thm F 4; 26, Tbls. B 1 and B 7, App. C and APP. D 93( LW01) 16, Fig. 2 5 Tbls. F 1 thru F 4; 27, Tb: B 1, App. C 470( LW01) 16, Fig. 2 5; 520( LW01) 28, Tbls. B 1 and B 5, App. C and App. D 510( LW01) 16, Fig. 2 5; 29, Tbls. B 1 and B 5, App. C and App. D  p CBSA concentrations in ,ugA DateUpperBellflower ' BellflowerSandGageAquiferLynwoodRefs. Aquifer 11/ 9024,00O( MW05) 72,00O( BF04) 500( GOl)  16, Fig. 2 5,

12/ 90 54, OOO( MW12) 5,50O( BF16) 9,30O( G04) Tbl. B 2, to Tbl. F 6; 26,

5,5OO( MW14) l, OOO( G08) 22,00O( G13)

419 1 1,90O( MW23) 7,30O( BF05) 2,70O( G09) 270( LW01) 16, Fig. 2 5, 8,90O( BF07) 1,40O( LW02) Tbl. F 6; 27, 3,20O( BF10) Tbl. B 2, 1,10O( BF12)

53 GW General UpperBellflowerBellflowerSandGageAquiferLynwood Date 10/ 9 1 " 3,50O( BF20) 170( G15) "_ 16, Fig. 2 5, 33,00O( BF21) , 3,00O( G17) Tbl. F 6; 30, 3,40O( BF22) 210( G19) Tbl. I 1, App. 630( BF23) J 49,00O( BF24) 8,00O( BF25) 7,70O( BF26) 770( BF27) 180( BF28) 790( BF29) 7,20O( BF31) 7,10O( BF32) 1,20O( BF33)

Stratigraphic Information Stratigraphic information indicates that the unnamed aquitard between the Lynwood and Silverado aquifers is not laterally continuous within 2 miles of the Del Am0 site. The site is approximately 1 mile east of the coastal area where merging of the Lynwood and Silverado aquifers is known to occur (ref. 1, p. 51553; ref. 15, p. 75, Plates 6C and 20).

54 3.1 Likelihood of Release GW ObservedRelease I r I 3.1.1ObservedRelease Aquifer Being Evaluated: upper BellflowerLBellflower sand/ Gage/ Lynwood/ Silverado Direct Observation:

An observed release to ground water by direct observation has been established. Contaminated soil associated with Pits 2A through 2F has come to be located below the top of the upper BellflowerLBellflower sand/ Gage/ Lynwood/ Silverado aquifer, due to a rising water table (ref. 5, pp. 4 16,5 35, and 5 40). In 1987, hazardous substances were found in soil samples from borings to depths of 18 to 20 feet below mean sea level (bmsl) (depending on the boring location). Between 1987 and 1995, the water table rose from 26 to 27 feet bmsl in 1987, to 15 to 19 feet bmsl in 1995 (ref. 62).

Basis for Direct Observation: Soil sampling results indicate that, by 1987, hazardous substances present in Source 1 (e. g., benzene, ethylbenzene, and naphthalene) had migrated to a depth of at least 57 feet .bgs (boring locations B 3B 2, B 3B 3, and €3 5B 1) below the pits in, what was at that time, the unsaturated zone (Reference 31, Table 3). The depth measurement of 57 feet is reported in units of "feet bgs" because elevation data were not provided in the boring logs for the 1987 soil sampling event (ref. 3 1, Appendix A 1). At boring location B 3B 2, the depth measurement of 57 feet can be converted to units of bmsl by using elevation data from a nearby boring (SBL0002) that was drilled in 1992 as part of a waste excavation feasibility study. The reported ground surface elevation for boring SBL0002 is 37.21 feet above mean sea level (amsl) (ref. 5, Figure 5.5 1; ref. 12, Appendix A, Attachment A3, p. A3 7). Subtracting 37.21 feet amsl from 57 feet bgs yields a contaminated soil depth of 19.79 feet bmsl. At boring location B 3B 3, the depth measurement of 57 feet can be converted to units of feet bmsl by using elevation data from a nearby boring (PZL0019) that was drilled in 1993 as part of the Phase I RI for the Del Am0 site. The reported ground surface elevation for boring PZLOO19 is 38.54 feet amsi (ref. 5, Figure 5.5 1, Appendix B, p. B 7). Subtracting 38.54 feet amsl from 57 feet bgs yields a contaminated soil depth of 18.46 feet bmsl. At boring location B 5B 1, the depth measurement of 57 feet bgs can be converted to units of feet bmsl by using elevation data from an adjacent boring (VWL0006) that was drilled in 1992 to facilitate the installation of a treatability study well. The reported ground surface elevation for boriqg VWL0006 is 36.96 feet amsl (ref. 5, Figure 5.5 1; ref. 21, pp. 3 1 and 3 4, Figure 2 2, Appendix C, p. 5). Subtracting 36.96 feet amsl from 57 feet bgs yields a contaminated soil depth of 20.04 feet bmsl. 5 Water level measurements indicate that the water table in the West Coast Basin has risen at a rate of approximately 1 foot per year since the mid to late 1970s. This coincides with the timing of the adjudication of the basin, which effectively reduced ground water pumping to a prescribed annual withdrawal (ref. 5, p. 4 16). Ground water elevation data are provided on the following table to document the rising water table in the vicinity of Source 1 between 1987 and 1995.

55 :~ L". l~. uj_ ~~~~..~~.~,..~.~~,~~"~ =..,.> :~~~E Y ~~~~~~~~~~~L I . am,. ." L "." A "A t >x~*" """"

\

GW Observed Release Water Table Elevations from 1987 to 1995 in the Vicinity of Source 1 3.1 Likelihood of Release Sample 9/ 93 2/ 94 6/ 95 & 7/ 95 Location DM 1 *

DM 2"

DM 3 *

P 2"

P 3"

> PzLOO18""

PZLOO19""

PzL0020**

PZLOO22*"

PZLOO23""

PZLOO24""

PZLOO25"" 5, Fig. 4.2.1; 11, App. E; 31, Tbl. 13, Fig. 7 5 , Fig. 4.2.1; 11, App. E; 31, Tbl. 13, Fig. 7 11, App. E; 31, Tbl. 13, Fig. 7 5, Fig. 4.2.1; 22, Fig. 5; 31, Tbl. 13, Figs. 7 & 9, 46, Fig. 3 31, Tbl. 13, Figs. 7 & 10; 46, Fig. 3 5, Tbl. 2.9 2, Fig. 4.2.1, App. B; 22, Fig. 5; 46, Fig. 2 5 , Tbl. 2.9 2, Fig. 4.2.1, App. B; 22, Fig. 5; 46, Fig. 2 5, Tbl. 2.9 2, Fig. 4.2.1, App. B; 22, Fig. 5; 46, Fig. 2 5, Tbl. 2.9 2, Fig. 4.2.1, App. B; 46, Fig. 2, App. A 5, Tbl. 2.9 2, Fig. 4.2.1, App. B; 22, Fig. 5 5, Tbl. 2.9 2, Fig. 4.2.1, App. Bi 22, Fig. 5; 46, Fig. 2 5, Tbl. 2.9 2, Fig. 4.2.1, App. B; 22, Fig. 5; 46, Fig. 2 25.90 25.67 26.28 25.93 27.23 "

"e "*

e

"

"e "e 20.15 20.25 20.27 " ..

20.15 19.54 17.42 19.52 19.32 18.92 19.1 1 "e "

"e 20.19.

"e 20.08 19.32 17.70 18.88 19.71 18.68 19.37 17.96 19.29 17.31 16.88 15.16 18.83 "

16.26 16.86 56 GW Observed Release Notes: * Monitoring well completed in the water table zone ** Piezometer completed in the water table zone  Not sampled  Hazardous Substances in theRelease In 1987, Woodward Clyde, for the State of California Department of Health Services, drilled 11 soil borings in the vicinity of Source 1 (ref. 31, Figure 2). Three of the borings were within 25 feet of the pits (B 3B 2, located 15 feet north of Pit 2D; B 3B 3, located 22.5 feet north of Pit 2D; and B 5B 1, located 15 feet north of Pit 2C) (ref. 3 1, Table 3). These three borings are probably located even less than 25 feet from the pits because the protrusion at the northern end of each pit, which measures 12. to 15 feet in length, was not accounted for during the 1987 investigation (ref. 7, p. 2 2, Table 3 5; ref. 31, p. 8). An additional soil boring (B 2B 2) was drilled 50 feet south of Pit 2B and was considered to be a background location due to its distance from the pits (ref. 31, Figure 2). Soil samples were collected from the four borings at depths up to 57 feet bgs and were analyzed for polynuclear aromatics using EPA Method 8310 and volatile aromatic hydrocarbons using EPA Method 8240 (ref. 31, Table 3). Analytical results indicated the presence of benzene in a sample collected from boring B 3B 2 at a concentration of 1,300 mgkg at 57 feet bgs; in samples collected from boring B 3B 3 at concentrations of 3,000 mgkg at 17 feet bgs, 1,200 mgkg at 33 feet bgs, and 2,500 mgkg at 57 feet bgs; and in samples collected from boring B 5B 1 at concentrations of 1,500 mgkg at 17 feet bgs and 1,700 mgkg at 57 feet bgs. In the background boring (B 2B 2), benzene was detected at a concentration of 0.5 mgkg at 25 feet bgs and was not detected at 57 feet bgs. In addition, the results indicated the presence of other analytes (e. g., ethylbenzene and naphthalene) at concentrations above background levels at depths up to 57 feet bgs (ref. 31, Table 3).

A 1995 ground water monitoring report for the Del Am0 Study area shows that there is contamination under the waste pits down to ground water. Concentrations in the water table under the pits are as high as half a million ppb (ref. 47; ref. 48, pp 7, 32, 256).

An additional observed release to ground water by direct observation has been established. Spillage from a historic crude benzene storage tank has come to be located, as a NAPL, in the upper saturated zone of the upper BellflowerEiellflower sand/ Gage/ Lynwood/ Silverado aquifer, due to a rising water table (ref. 50, p. 4 1) (see Sections 2.2 and 2.4.2 for Source 3).

Chemical Analysis:

An observed release by chemical analysis can be documented using 1995 ground water sampling data that indicate that benzene concentrations have increased significantly above background levels proximal to Source 3.

Nine specific ground water monitoring events were conducted for the Del Am0 site during the period from February 1993 through February 1996. Analytical data from the third sampling period in 1995 (October through December 1995) were selected for presentation in the May 15, 1998 Del Am0 Final Ground Water FU report because "this event is relatively recent and comprehensive with respect to the number of locations and analytes for which there are data" (ref. 50, pp. 5 4,5 5). The analytical data from this event that are "

57 GW Observed Release relevant to benzene in what the 1998 Del Am0 Final Ground Water RI report refers to as the water table zone in the vicinity of Source 3 are presented in the table below. The water table zone corresponds to the Upper '

Bellflower aquifer discussed in Section 3.0.1 (Ground Water Pathway  General Considerations) (ref. 50, p. 4 2).

Water level measurements taken in October 1995 indicate that the ground water flow direction in the water table zone in the vicinity of Source 3 is to the south southwest (ref. 50, p. 4 2, Figure 4.1 3). Monitoring wells PZL0009 and EL0016 are designated as background wells in the table below because they are located hydraulically upgradient of Source 3 (i. e., approximately 900 feet northeast and 500 feet north of Source 3, respectively). Monitoring wells SWL0002, SWL0003, and SWL0004 are designated as contaminated wells because they are proximal to the NAPL area (ref. 53).

Screened Detection Monitoring Interval Sample Sampling Benzene Limit Well ID (feet bgs) ID Date . (PLg/ L) bg/ L) Reference PZLOoo9 PZLOO 16 SWLOOO2 SwL0003 SWLOOO4 Attribution 54 69 47 67 52 77 50 77 53 80 , BackgroundWells GWSO135010/ 17/ 95 940 GWSO1268lot24195Not detected Contaminated Wells GWSO131610/ 20/ 95 310,000 GWSO1317 10/ 20/ 95 330,000 GWSO1318 10/ 20/ 95 1,200,000 5 30 ..

20,000 2,000 5,000 50, Fig. 5.2 2, App.

G3, Record 93426 50, Fig. 5.2 2 App. G3, Record 86540 C, Tbl. C 2, App.

App. C, Tbl. C 2,

50, Fig. 5.2 2 App. G3, Record 91 159 50, Fig. 5.2 2 App. G3, Record 91311 50, Fig. 5.2 2 App. G3, Record 91391 App. C, Tbl. C 2,

App. C, Tbl. C 2,

App. C, Tbl. C 2,

As presented in the above table, ground water sampling results indicate that benzene meets observed release 58 GW Observed Release criteria (i. e., concentrations have increased significantly above background levels). The Source 3 NAPL, which is composed of 90 percent benzene, is located between the background monitoring wells (PZL0009 and PZL0016) and the contaminated wells (SWL0002, SWL0003, and SWL0004) that document this release (ref. 50, Figure 5.2 2; ref. 51, p. 12; ref. 53). The NAPL is located approximately 50 feet from the historic location of a 500,000 gallon tank that was used for storage of crude benzene during the years that the styrene manufacturing plant was operating (Le., 1942 to 1969) (ref. 5, p. 5 22; ref. 51, Figure 16; ref. 52, p. 7 4). Aerial photographs and site history documents indicate that spillage occurred during transfer of tank contents to and from railroad cars and trucks (ref. 5, p. 3 12, Appendix A, pp. A 6, A 7, A 29, Plate A 1). Results of a 1992 shallow soil gas sampling event indicated the presence of benzene at a concentration of 128 parts per million by volume (ppmv) at a depth of 6 feet bgs at one sampling location (SGLOOO5) iri the vadose zone beneath the historic location of the crude benzene storage tank (ref. 51, pp. 3,9, 10, Figure 8). During a subsequent soil sampling event, benzene was either not detected or detected at trace concentrations in the vadose zone (ref. 5, pp. 2 18,5 19 through 5 22, Figure 5.4 3). The absence of significant benzene contaminated soil is inferred to be due to natural degradation processes that have occurred in an aerobic vadose zone soil environment since the benzene was released (ref. 5, p. 5 22; ref. 50, p. 1 14). Based on the time period during which the styrene manufacturing plant operated (i. e., 1942 to 1969), the release occurred between 31 and 58 years ago (ref. 5, p. 5 22).

There do not appear to be any known alternate contributors. As part of the Del Am0 Ground Water RI, regional ground water contamination source areas outside of, but in the vicitiity of the historic Del Am0 synthetic rubber manufacturing plant property, were identified. Identification was based on the following publicly available information from regulatory agency files: ground water analytical data indicating elevated concentrations of one or more VOCs at water table monitoring locations relative to surrounding areas, a history of land use consistent with the reported VOC ground water contamination, and/ or data indicating elevated VOC concentrations in soil (ref. 50, p. 5 19). Water level measurements taken in October 1995 indicate that ground water flow in the water table zone (i. e., Upper Bellflower aquifer), in the vicinity of Source 3, is to the soutWsouthwest (ref. 50, p. 4 2, Figure 4.1 3). Results of the Del Am0 Ground Water RI regional ground water contamination study indicate that there are no facilities to the northeast of the historic Del Am0 plant property that were or are alternate contributors to the benzene contamination documented in Del Amo monitoring wells SWL0002, SWL0003, and SWL0004 (ref. 50, Figures 4.1 3,5.3 1). Two source areas of VOC contamination (i. e., the Amoco and Trico facilities) were identified adjacent to the western border of the historic Del Amo plant in the vicinity of these three monitoring wells; however, the VOCs associated with these facilities do not include benzene (ref. 50, Figure 5.3 l)."

Ground Water Observed Release Factor Value: 550 59 GW Waste Characteristics 3.2.1 Toxicity/ Mobility 3.2 WasteCharacteristics Hazardous Substance Source No. Toxicity Mobility Toxicity/ Mobility Reference Benzene 192, 3 100 1 100 2, p. B 2 Ethylbenzene 1,253 ' 10 0.01 0.1 2, p. B 10 '.

Naphthalene 192 100 1 100 2, p. B 14 See Section 2.4.1 (Hazardous Substances) for Sources 1,2, and 3 for evidence of the presence of benzene, ethylbenzene, and naphthalene in the sources.

The toxicity/ mobility factor value assigned for the ground water pathway is 100, based on benzene and naphthalene (ref. 1, Section <IP_ADDRESS>).

3.2.2 Hazardous Waste Quantity Source Hazardous Is source hazardous Waste Quantity constituent quantity Source Number Value (Section <IP_ADDRESS>.5) data complete? (yesino) 1 728 No 2 3,357 No 3 6,160 No Sum of Values: 10,245 The hazardous waste quantity factor value assigned for the ground water pathway is 10,000 (ref. 1, Table 2 6, Section <IP_ADDRESS>).

3.2.3 Waste Characteristics Factor Category Value Multiplying the toxicity/ mobility factor value of 100 x the hazardous waste quantity factor value of 10,000 produces 1,000,000, which yields a waste characteristics factor category value of 32 for the ground water pathway (ref. 1, Table 2 7).

Waste Characteristics Factor Category Value: 32 ..

60 GW  Targets 3.3 Targets Distance Level I Level II Potential From Contamination Contamination Contamination  Well Source Aquifer (Y/ N) (Y/ N) (Y N Reference DWC * N N Y 32,38 scwc 1.6 * N N Y 32, 40.. Dalton DWC 19A 1.8 * N N Y 32,38 DWC 79 2.6 * N N y 32,38 TWD 2.6 * N N Y 32,39 "

DWC * N N Y 32,38 scwc 3.5 * N N Y 32,40 Cerise DWC 77 3.6 * N N Y 32,38 DWC 15 3.9 * N N Y 32,38 DWC 16 3.9 * N N Y 32,38 DWC 98 3.9 * N N Y 32,38 scwc 3.9 * N N Y 32,40 Southern 3 scwc 3.9 * N N Y 32,40 Southern 4 scwc 3.9 * N N Y 32,40 Southern 5 Notes: * = interconnected upper BellflowerA3ellflower SandGageLynwoodSilverado DWC = Dominguez Water Company SCWC = Southern California Water Company TWD = City of Torrance Water Department .L  61 GW Nearest Well 3.3.1 Nearest Well Well: DWC 97 Level of Contamination (I, 11, or potential): potential If potential contamination, distance from source in miles: 1.5 miles from Source 3 (ref. 32; ref. 38, p. 2).

Nearest Well Factor Value: 5 62 GW  Potential Contamination 3.3.2Population <IP_ADDRESS> Potential Contamination Distance Category( miles) PopulationReferencesDistance WeightedPopulationValue 0 to 0.25 0 > 0: 25 to 0.5 0 > 0.5 to. 1 0 >1to2 7,682 20,32,33,35,36,37,38,40 >2to3 12,179 20, 32,34,35,38,49 >3to4 24,529 20,32,33, 35,36, 37,38,40 939 2,122 1,306 Sum ofDistance WeightedPopulationValues: 4,367 The following three water purveyors operate 14 drinking water wells within 4 miles of Sources 1, 2, and 3: Dominguez Water Company, Southern California Water Company, and the City of Torrance Water Department. The information that was used to calculate the population served by each well is presented below. ' Since the relative contributions of surface water and ground water to each system vary from year to year, this component of the calculations was based on a 10 year average (i. e., 1990 through 1999). The total population served by each system, the number of active and standby wells in each system, and individual well pumpage data were based on the most current year for which information is available (i. e., 1999).

Dominguez Water Company The Dominguez Water Company operates a blended drinking water system that serves approximately 100,000 people in the city of Carson. In 1999, there were 13 active wells, no standby wells, and one surface water intake [i. e., imported surface water purchased from the Metropolitan Water District (MWD)] contributing to the system (ref. 38, pp. 1, 2). The relative contributions of surface water and ground water for 1.990 through 1999 are as follows: ..

Contribution from IntakeContributionfromWells Calendar 1990 p. 2; 38, p. 1 1991 1992 27 20 20, p. 2; 38, p. 1 20, p. 2; 38, p. 1 1993 0 38, p. 2 1994 13 35; 38, p. 2 \

1995 64 36 38, p. 2 ."

63 GW  Potential Contamination Contribution from IntakeContributionfromWells Calendar Year (percent) (percent) Reference 1996 35 65 38, p. 2 1997 30 70 38, p. 2 1998 32 68 38, p. 2 1999 31 69 38, p. 2 Average: 61 (612 t 10) 39 (388 + 10)

Since the relative contribution of one well or intake exceeds 40 percent (i. e., 10 year average yields a 61 percent relative contribution for the surface water intake), the population served by each well was apportioned based on pumpage. As presented below, the pumpage for each well within 4 miles of Sources 1, 2, and 3 was divided by the sum of the pumpages for all 13 wells in the system (12,270 gpm). This quotient was then multiplied by the population served by ground water (0.39 X 100,000 = 39,000) (ref. 32; ref. 38, pp. 172).

Pumpage Well (am) Calculations Served (miles) DWC 97 7 10 (710 t 12,270) X 39,000 = 2,257 >1t02 DWC 19A 1,111 (1,111 t 12,270) '~ 39,000 = 3,531 >1t02 DWC 79 843 (843 + 12,270) x 39,000 = 2,679 >2t03 DWC 75A 1,160( 1,160 + 12,270) x 39,000 = 3,687 >3t04 DWC 77 703( 703 t 12,270) x 39,000 = 2,234 >3t04 DWC 15 717( 717 + 12,270) x 39,000 = 2,279 >3t04 DWC 16 442( 442 t 12,270) X 39,000 = 1,405 >3t04 DWC 98 2,609( 2,609 + 12,270) X 39,000 = 8,293 >3t04 DWC 72A 543 NIA NIA >4 DWC 23B 748 NIA NIA >4 DWC 31A 582 NIA DWC 90 861 NIA DWC 94 1,241 NIA Total Pumpage: 12,270 NIA >4 NIA >4 NIA > 4 1 64 GW  Potential Contamination Southern Cal$ ornia Water Company The Southern California Water Company's Southwest System is a blended drinking water system that had 49,344 active service connections in 1999 (ref. 40, p. 1). The average number of persons per residence for Los Angeles County is 2.91 (ref. 37, p. 4). The system, therefore, serves approximately 143,591 people (2.91 x 49,344). In 1999, there were 14 active wells, two staridby wells, and one surface water intake (i. e., imported surface water purchased from the MWD) contributing to the system (ref. 40, p. 1). The relatiye contributions of surface water and ground water for 1990 through 1999 are as follows:

ContributionfromIntakeContributionfromWells Calendar Year (percent) (percent) Reference .

1990 81 19 33, p. 1 1991 76 24 33, p. 1 1992 1993 1994 1995 1996 1997 1998 23 23 22 19 15 16 25 33, p. 1 33, p* 1 36 40, p. 1 40, p. 1 40, p. 1 40, p. 1 1999 74 26 40, p. 1 Average: 79 (788 .+ 10) 21 (212 f 10)

Since the relative contribution of one well or intake exceeds 40 percent (i. e., 10 year average yields a 79 percent relative contribution for the surface water intake), the population served by each well was apportioned based on pumpage. As presented below, the pumpage for each well within 4 miles of Sources 1, 2, and 3 was divided by the sum of the pumpages for all 16 wells in the system (9,550 gpm). This quotient was then multiplied by the population served by ground water.( 0.21 x 143,591 = 30,154) (ref. 33; p. 1, ref. 36; ref. 40, pp. 1,2).

65 GW  Potential Contamination Pumpage Well (a m ) Calculations Served (miles)

SCWCDalton 600 SCWCCerise 400 SCWCSouthern .3 300 SCWCSouthern 4 400 SCWCSouthern 5 1,000 scwc Chicago 1 scwc Compton Doty scwc Yukon 1 scwc Yukon 2 scwc Ballona 3 scwc Bellhaven 1 scwc Bellhaven 3 scwc Doty 1 scwc Doty 2 scwc Goldmedal 1 scwc 129'h Street Total Pumpage: 500 500 200 200 200 600 950 1,000 1,000 1,500 200 9,550 (600 + 9,550) X 30,154 =

(400 + 9,550) x 30,154 =

(300 + 9,550) x 30,154 =

(400 + 9,550) X 30,154 =

(1,000 + 9,550) X 30,154 =

NIA NIA NIA NIA NIA NIA NIA NIA NIA NIA NIA 1,894 1,263 947 1,263 3,158 NIA NIA NIA NIA NIA NIA NIA NIA NIA NIA NIA > 1 to2 >3t04 >3t04 >3t04 >3t04 >4 >4 >4 >4 >4 >4 >4 >4 >4 >4 >4 66 GW  Potential Contamination City of Torrance Water Department The City of Torrance Water Department operates a blended drinking water system that served approximately 95,000 people in 1999. In 1999, there was one active well and one surface water intake (i. e., imported surface water purchased from the MWD) contributing to the system (ref. 39). The relative contributions of surface water and ground water for 1990 through 1999 are as follows:

Contribution from IntakeContributionfromWells Fiscal 1989/ 1990 199011991 199111992 79 199211 92 199311994 12 21 8 2 199411995 199511,996 199611997 92 6 8 199711998 49 49 49 49 34; 49 49 49 49 199811999 86 Average: 90 (898 + 10) 14 49 10 (102 t 10)

As presented below, the population served by the one well that was active in 1999 was calculated by multiplying the 10 year average relative contribution for ground water by the total population served by the system in 1999 (0.10 x 95,000 = 9,500) (ref. 39; ref. 49).

Pumpage Well (gPm) Calculations Served (miles) TWD 6 NIA 0 9,500 >2t03 Potential Contamination Factor Value: 436.7 67 GW Resources 3.3.3 Resources There are no ground water wells located within 4 miles of the Del Am0 site that are known to be used for the following purposes: irrigation of commercial food .or forage crops, watering of commercial livestock, ingredient in commercial food preparation, supply for commercial aquaculture, or supply for a designated water recreation area.

Resources Factor Value: 0 68 GW Wellhead Protection Area 3.3.4 Wellhead Protection Area There are no designated wellhead protection areas within 4 miles of the Del Am0 site.

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Wellhead Protection Area Factor Value: 0 69 SW General Considerations 4.0 SURFACE WATER MIGRATION PATHWAY The surface water pathway was evaluated, but not scored, because there are a iimited number of targets associated with the first 7.5 miles of the 15 mile in water segment (ref. 41; ref. 42). Runoff from the Del Amo site enters a storm drain inlet located at the intersection of Vermont Avenue and Del Am0 Boulevard, approximately 600 feet southeast of Sources 1 and 2 (ref. 5, Plate 3 3; ref. 43, p. 36; ref. 44). The storm drain system discharges into the Torrance Lateral, which is an open channel, approximately 1,600 feet south of the storm drain inlet. ' The Torrance Lateral discharges into the Dominguez Channel, which is a concrete lined drainage and flood control channel, approximately 1.5 miles downstream of the storm drain system discharge point (ref. 44; ref. 45, p. 7). The Dominguez Channel discharges into the Los Angeles Harbor approximately 6 miles further downstream. The Los Angeles Harbor empties into San Pedro Bay, and San Pedro.. Bay opens onto the Pacific Ocean. The last portion of the 15 mile in water segment consists of an arc with a 7.5 mile radius that extends from the confluence of the Dominguez Channel and the Los Angeles Harbor into San Pedro Bay and the Pacific Ocean (ref. 44). Although there are fisheries and sensitive environments associated with the Los Angeles Harbor, San Pedro Bay, and the Pacific Ocean; there do not appear to be any drinking water intakes or sensitive environments associated with the first 7.5 miles of the 15 mile in water segment (i. e., the Torrance Lateral and concrete lined Dominguez Channel). In addition, there are a limited number of fish in the Dominguez Channel (ref. 41; ref. 42).

70 SE General Considerations 5.0 SOIL EXPOSURE PATHWAY The soil exposure pathway was evaluated, but not scored, because the area of the Del Amo site that is occupied by Sources 1 and 2 is currently vacant and covered with fill material and vegetation. In addition, Sources 1 and 2 are separated from De Am0 Boulevard and a residential area to the south by a double row of fences (ref. 5, p. 5 23). Source 3 is currently present as an area of non aqueous phase liquid (NAPL) located 60 feet below ground surface (ref. 50, pp. 4 1,6 20).

c 71 Air General Considerations 6.0 AIR MIGRATION PATHWAY The air pathway was evaluated, but not scored, because no known ambient air sampling and meteorological monitoring have been conducted on or in the vicinity of the Del Am0 site.

72