SITE INFORMATION AND CORRESPONDENCE

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• • Summary of Work Accomplished 2 8. 1993: Monitoring wells MW-1 through MW-4 were installed and sampled. Soil samples were also taken from the boreholes. USEPA's contract consultants were present to collect additional samples. Soil: The soil from MW-1 (north tank farm) had nitrate and TKN, as well as 1,2-DCP and 1,2,3-TCP. The borehole for MW-2 (north pond) had 1,2-DCP, 1,2,3-TCP, TKN, and nitrate. The soil from MW-3 (upgradient) had minimal nitrate concentrations, while the soil from MW-4 (south pond) had lindane, heptachlor, endosulfan, endrin, DDT, gamma-chlordane, TKN and nitrate. I don't know the concentrations of each pesticide, since EPA didn't list this in their report. Groundwater: The wells were sampled three times in 1993. The Sierra Pacific quarterly monitoring reports contain a cumulative results summary. However, they don't contain the EPA's results from the May 1993 sampling event. EPA analyzed the groundwater for a short list of organochlorine pesticides; none were detected. They also analyzed for 1,2-DCP and 1,2,3-TCP. The 1,2-DCP results are similar to Unocal's. However, Unocal does not routinely analyze for the volatile organic 1,2,3-TCP (an impurity found in Telone). EPA found 1,2,3- TCP at ND in the MW-3, 1 µg/l in MW-4, 63 µg/l in MW-1, and 66 µg/l in MW-1. (1,2,3- TCP is a probable human carcinogen, with a EPA Health Advisory of 5 µg/1). 9. 1994: There were four rounds of groundwater sampling. Off-site wells MW-5 and MW-6 were installed late in the year. Four soil samples were collected from the top 6' of the north and south evaporation ponds. Various chemicals and nitrogen compounds were detected. 10. 1995: Four quarters of groundwater samples were collected. Off-site wells MW-7 and MW-8 were installed, as was upgradient well MW-10. Four deeper soil borings were made in the north and south ponds. Various chemicals were detected. As part of their claim process, Western Farm Service authorized the collection of various soil samples. Three locations were sampled in front (north) of the old PureGro warehouse. Nitrate- N ranged from 3,600 to 1,100 mg/kg. Ammonia-N was found at ND to 6,500 mg/kg. TKN values ranged from 1,700 to 8,400 mg/kg. A second set of samples was collected to the west of the new tank farm. Nitrate concentrations ranged from 150 to 950 mg/kg, ammonia-N from ND to 1,200 mg/kg, and TKN from 200-5,600 mg/kg. 11. 1996: Three quarters of groundwater samples were collected. The chemical monitoring was reduced to twice-yearly. Gradient is to be determined quarterly. Off-site well MW-9 was installed downgradient of the plume. A report evaluating the remedial options for the groundwater was submitted. The north and south ponds were covered with a low permeability liner/cap. A MRP was issued, covering the cap maintenance and groundwater monitoring.