ARCHIVED REPORTS_WELL ABANDONMENT, SOIL AND GROUNDWATER INVESTIGATION REPORT 2009

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Monitoring Well Destruction and Soil and Groundwater Investigation Report US Can—Welty Road September 24,2009 The extent of affected groundwater has a linear pattern that encompasses the areas o affected soil described in section 5.1. Figure 3a(Area 1 and Area 2) and Figure 3b (Area 3) how contours indicating the lateral extent of affected groundwater based on SAIC's evaluation of the laboratory analytical data collected during this and previous investigations. 5.3 WATER QUALITY Grab groundwater samples were collected from SB-19, SB-25, and SB-36, and submitted for General Minerals and total dissolved solids (TDS) analyses to evaluate the suitability of the uppermost groundwater-bearing zone for drinking. TDS concentrations ranged from 779 to 1,240 milligrams per liter (mg/L) and did not exceed the Basin Plan hydrogeologic criteria for beneficial use of 3,000 mg/L (RWQCB, 2007b). However, the samples collected from SB-19 (1,240 mg/L) and SB-36 (1,110 mg/L) did exceed the drinking water Secondary Maximum Contaminant Level (MCL) of 1,000 mg/L. TDS results from all three samples also exceed all of the following current California Department of Public Health (CDPH) maximum contaminant levels (MCLs; CDPH, 2004) and RWQCB Water Quality Goals (WQG; RWQCB, 2000) for drinking water: • CDPH MCL: 500 mg/L, recommended. 0 CDPH MCL: 1,000 mg/L, upper. • CDPH MCL: 1,500 mg/L, short term. • RWQCB WQG, CDPH, and EPA drinking water standards: 500 mg/L. ' • RWQCB WQG, Agricultural Water Quality Goal: 450 mg/L. • RWQCB WQG, EPA Ambient Water Quality Criteria for Taste and Odor or Welfare: 250 mg/L. The results of the General Minerals analyses indicated boron, chloride, iron, manganese, nitrate as nitrogen, sodium, and sulfate in concentrations in excess of the respective WQOs; the ' chloride, iron, manganese, and nitrate as nitrogen concentrations also exceeded the respective MCLs. The samples exceeded the WQO levels for adverse taste and odor for boron, chloride, iron, manganese, nitrate as nitrogen, sodium, and sulfate. These waters are thus considered to contain certain taste or odor-producing substances in concentrations that cause nuisance or adversely affect beneficial uses (California Code of Regulations, Title 22). Groundwater analytical results for General Minerals are provided in Table 5. ' 6. CONCLUSIONS AND RECOMMENDATIONS SAIC evaluated the results of this investigation and concludes the following regarding the nature and extent of affected soil and groundwater at the site: 0 MW-4 and MW-5 have been properly destroyed. Well MW-3 was not destroyed due to concentrations of TPHd exceeding the WQO during the January 2008 sampling event. SAIC and the RWQCB subsequently collected split samples from well MW-3 in July 2009, and laboratory results indicated the TPHd concentrations did not exceed the WQO. t • Affected soil exceeding the TPHc ESL was encountered in SB-18, SB-20 through SB-26, SB-28, SB-29, and SB-34. Affected soil exceeding one or more PAH ESLs were 8 =�,Z �+iwa�a�® From Science to Solutions