SITE INFORMATION AND CORRESPONDENCE

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Ms. Kathleen Minahan - 2 - • 31 January 2007 between 7 and 117 ug/kg. Delta-benzene hexachloride was found in the two-foot soil sample of SB-13 at concentration of 47 ug/kg. These compounds were not found at deeper intervals, were not found in groundwater, and are below the screening levels. Lead and zinc concentrations are much higher in the two-foot sample from SB-08 (550 mg/kg and 5,100 mg/kg, respectively), obtained near the railroad track to the north, than in the other soil samples. The elevated concentrations of lead and zinc were not present in the deeper soil sample, which was comparable in concentration to the other soil samples, which contained lead in concentrations from 3 to 24 mg/kg and contained zinc concentrations between 12 and 72 mg/kg. The lead and zinc concentrations found in soil are below the California Human Health Screening Levels (CHSSLs) for residential development. In groundwater, dissolved lead was not detected, and dissolved zinc ranged from 16 to 200 ug/I. These concentrations are below the screening levels and water quality objectives. Since the detections of chlorinated herbicides, organophosphate pesticides, organochlorine pesticides, lead, and zinc are either not detected, or detected below human health thresholds, or are only present in the shallow soil and do not present a threat to groundwater, Regional Water Board staff concur with the Investigation Report's conclusion that these compounds are not constituents of concern. Nickel is found in soil between 7 and 35 mg/kg, which is below the CHSSLs screening level of 16,000 mg/kg, but is found in groundwater in concentrations ranging from 18.to 180 ug/I. The water quality objective for nickel in groundwater is 12 ug/I, based on the Public Health Goal. Nitrate, ammonium, sulfate, and fuel Nitrate (as nitrogen) concentrations in soil range from 3 to 190 mg/kg, and ammonium ranges from 5 to 160 mg/kg. Since groundwater is less than 10 feet below ground surface, Regional Water Board staff assign a generic cleanup goal of 100 mg/kg for the sum of nitrate and ammonium in soil. This cleanup goal is a conservative estimate of the amount of nitrogen that could remain in soil and not migrate to groundwater. If Lesco believes that this is overly conservative, it may perform leachability tests on site soils to develop a site-specific cleanup level for nitrate and ammonium that is protective . of groundwater. To run the leachability test, at least five soil samples of varying concentrations of nitrogen should be split into two for two parallel analyses: one for total nitrate and ammonium, and one for leachable nitrate and ammonium. Leachable nitrogen is determined with the Waste Extraction Test modified using deionized water as the extractant. The extractionprocedure and the method for calculating the leachable fraction is described in the Designated Level Methodology for Waste Classification and Cleanup Level Determination (available at http://www.waterboards. ca.gov/centralvalley/available_documents/guidance/dlm.pdf). At the Lesco facility, there is not a good correlation between nitrate and ammonium concentrations in soil and those found in groundwater. The highest concentrations of nitrate and/or ammonium (above 300 mg/I as nitrogen) in groundwater occur in borings SB-11, SB-12, SB-13, and SB-15. Groundwater from these borings also contain 500-700 mg/I sulfate. Of these borings, SB-11, SB-12, and SB-13 are nearest a former unlined on-site stormwater pond (West Pond) that was