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tes F (YVATC STC venue Su Inc I l I— Lone Falm avenue quite d ' Modesto California 45351 zo4_574_'�^I a s s n d a r e s i N c Fax _'09-57q-_'-Z.~5 historical parameters which have indicated the predominant groundwater gradient direction is to the east with variation between northeast and south-southeast Figure 3 depicts groundwater elevation contours for �kpnl 19 3005 The groundwater monitoring data are summarized in Table I Monitoring data and purge logs are provided in -attachment I LABORATORY ANALYSES The groundwater samples collected on apnl 19, 2005 were submitted to Excelchem Environmental Labs, Environmental Laboratory Accreditation Program (ELAP) 42119 in Roseville California for analyses of hexavalent chromium (Cr +6) using EPA Method 7199, total chromium by EPA Method 200 8, aluminum and calcium by EPA ylethod 200 7 chloride by EP 4 Method 300 0, VOCs by EPA Method 8260B, and total hardness as CaCO3 by EPA Method 2340C Cr +6 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/I) The reported Cr +6 concentration in the groundwater sample collected from MW-3 was 2 2 mg/1 The reported Cr +6 concentration in the groundwater sample collected from MW-6 was 0 071 mg/l Cr +6 was also detected in water samples collected from wells MW-1 MW-3, MW-4, MW-5, MW-7 1VIW-8, and MW-9, • but at concentrations below the IVICL for total chromium The distribution of Cr r6 in groundwater is shown on Figure 4 Total chromium was detected in the groundwater samples collected from wells 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 samples collected from MW-3 and MW-6 were 2 0 mg/1 and 0 088 mg/l, respectively Total chromium was detected in water samples from wells MW-1, MW-2, MW-4 MW-5, MW-7, MW-8, MW-9 at or above laboratory detection limits, but below the California Primary MCL Tetrachloroethene also known as perchloroethene (PCE) was not present above laboratory detection limits in the groundwater samples collected from wells MW-2, MW-4, MW-5, or MW- 6 PCE was detected in the groundwater samples collected from monitoring wells MW-7 and MW-9 at concentrations above the MCL for PCE in drinking water of 0 005 milligrams per liter (mg/L) The reported PCE concentrations in the groundwater samples collected from MW-7 and MW-9 were 0 0070 and 0 046 mg/L. respectively PCE was also detected m water samples from wells MW-1, MW-3, and MW-8, but at concentrations below the respective MCL The distribution of PCE in groundwater is shown on Figure 5 TCE was not present at or above laboratory detection limits in the groundwater samples collected from MW-1 through MW-9 Chloride in the groundwater samples collected from wells MW-I through BMW-9 ranged from 23 mg/L (MW-4) to 470 mg/L (MW-3) Hardness as a measure of calcium carbonate in the groundwater samples collected from wells MW-1 through MW-9 ranged from 300 mg/L (MW- s lenveronmenta1162583tiquarterlyllgr-2005 doc 2