SITE INFORMATION AND CORRESPONDENCE

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N100 1 Mr, Steven Pinkerton March 17, 2000 Page 2 Soil samples analyzed indicated that the Site contains lead as high as 184 milligrams per kilograms (mg/kg or part per million), and lead in groundwater at 75.3 micrograms per liter (ugh) (groundwater sample collected at south area of site). This lead value in groundwater exceeds Federal primary drinking water standards established as Maximum Containment Levels (MCL). However, the sample was prepared absent filtering and the lead value may be overstated and not representative of lead in groundwater. For.this reason at least, another sample is required to determine the lead levels in groundwater. F Soil samples also contained benzo(a) pyrene at 0.33 ppm. Sediment samples collected from the Stockton Channel below the pier-supported parking lot contained lead levels as high as 200 ppm, arsenic at 22.1 ppm, and benzo(a) pyrene.were detected as high as 1 .2 ppm. Samples collected from an offsite monitoring well (Well #4) indicated components associated with the underground tank release at a former ARCO gas station including MTBE at 53 ppb, benzene at 300 ppb, vinyl chloride at 61 ppb, and cis-l,2-dichloroethane at 120 ppb, which significantly exceed Federal MCL for drinking water. A human health screening evaluation was completed as part of the PEA investigation. Using the default residential land use scenario to calculate on site risk, the calculated excess risk from soil ingestion and dermal contact was 2.3 x 10' and the excess cancer risk from groundwater ingestion and showering/bathing as calculated using onsite groundwater was 1.1 x 10-5,with a total cumulative risk of 3.3 x 10-5. Based on the data presented in the PEA report, the Site poses a risk to human health and the environment as evaluated under unrestricted land use activities. Therefore DISC has determined that further action is necessary as outlined below to address investigative and remedial measure requirements associated with the hazardous substances at the Site. DTSC concurs with the recommendation in the PEA. Specifically: • Recording a deed restriction on the property to prevent future residential use and restrict use of the surface water and shallow groundwater underlying the Site. A supplemental risk assessment should be completed using future land use scenarios which show that the site does not pose a risk to future occupants and users including utility and construction workers. • Continue to evaluate data being collected from the ARCO investigation to determine the need for additional onsite remedial measures in the future to eliminate risk associated with the migration from the offsite source.