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ASSOCIATES�Tc I NC Sbetween northeast and south-southeast Figure 3 depicts groundwater elevation contours for April 20, 2004 The groundwater monitoring data are summarized in Table 1 Monitoring data ' and purge logs are provided in Attachment 1 LABORATORY ANALYSES ' The groundwater samples collected on April 20, 2004 were submitted to Excelchem Environmental Labs (FLAP #2119) in Roseville, California for analyses of hexavalent ' chromium using EPA Method 7199, total chromium, potassium, sodium, and calcium using EPA Method 6010B, chloride and sulfate by EPA Method 300 0, phosphorus by EPA Method 365 3, and total hardness as CaCO3 by method SM2340C Additionally, ATC's turbidity meter was malfunctioning so the samples were for turbidity by Excelchem using EPA Method 180 1 Hexavalent chromium was not present above laboratory detection limits in the sample collected from the facility well Hexavalent chromium was detected in the groundwater samples collected from monitoring wells MW-3 and MW-6 at concentrations above the California Primary Maximum Contaminant Level (MCL) for total chromium in drinking water of 0 05 milligrams per liter (mg/1) The reported hexavalent chromium concentration in the groundwater sample collected from MW-3 was 3 1 mg/l The reported hexavalent chromium concentration in the groundwater sample collected from MW-6 was 0 057 mg/l Hexavalent chromium was also detected in water samples collected from wells MW-1, MW-2, MW-4, MW-5, MW-7, MW-8, and MW-9, but at concentrations below the MCL for total chromium The distribution of hexavalent chromium in groundwater is shown on Figure 4 ' Total chromium was detected in the groundwater samples collected from MW-3 and MW-6 above the California Primary MCL for total chromium in drinking water of 0 05 mg/l The reported total chromium concentration in the groundwater sample collected from MW-3 was 3 2 mg/1 The reported total chromium concentration nn the groundwater sample collected from MW-6 was 0 064 mg/l Total chromium was also detected in water samples from wells MW-2, MW-4, MW-5, MW-7, and MW-9 but at concentrations below the respective MCL for total chromium Total chromium was not present above laboratory detection limits in the water samples collected from MW-1, MW-8, or the facility well Potassium in the groundwater samples collected from MW1 through MW9 and FW ranged from 2 7 to 5 5 mg/l Sodium in the groundwater samples collected from MW1 through MW9 and FW ranged from 38 to 63 mg/1 Calcium in the groundwater samples collected from MW1 through MW9 and FW ranged from 94 to 320 mg/l Chloride in the groundwater samples collected from MW1 through MW9 and FW ranged from 28 to 430 mg/l Sulfate in the groundwater samples ' collected from MW1 through MW9 and FW ranged from 13 to 110 mg/l Hardness as a measure of calcium carbonate in the groundwater samples collected from MWI through MW9 and FW ranged from 330 to 740 mg/l with the highest concentration detected in the groundwater sample collected from MW-2 Dissolved oxygen concentrations ranged from 1 06 mg/l to 9 17 mg/l with the highest concentration measured in MW-6 sIenviromnental1625831quarterlyl2gr-2004 doc 2