ARCHIVED REPORTS XR0003293 - Laserfiche WebLink

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• Field work consisted of measuring depth to water, purging the wells and collecting samples from each of the three monitoring wells Groundwater levels in the monitoring wells ranged from 60 19 to 64 41 feet below grade, an average increase in water level of 2 17 feet since water depth was last measured in January 1996 Groundwater measurements indicate flow direction on April 8, 1996 was easterly with an average gradient of approximately 0 002 ft/ft This is a slight departure from tustoncal groundwater flow which has been predominantly to the north and northeast Figure 2 depicts groundwater elevation contours for April 8, 1996 The groundwater monitoring data are summarized in Table 1 Monitoring data and purge logs are provided in Attachment 1 LABORATORY ANALYSIS Groundwater samples were collected after purging the monitoring wells and verifying the stabilization of pH, electrical conductivity, and temperature Samples were submitted to Sequoia Analytical Laboratories (FLAP #1210) in Redwood City, California for analysis of hexavalent chromium (EPA method 7196) Hexavalent chromium was detected in the samples collected from MW-1, MW-2 and MW-3 The hexavalent chromium levels present in wells MW-1 and MW-2 were below the California Primary Maximum Contaminant Level (MCL) for drinking water of 0 05 mg/l Hexavalent chromium levels in well MW-3 exceeded the MCL Analytical results are summarized in Table 2 Laboratory data sheets and chain-of-custody documentation are provided in Attachment 2 ADDITIONAL SITE ACTIVITIES On May 17, 1996, eleven drums of soil cuttings generated during the installation of on-site monitoring wells were transported off-site and disposed of at the Forward Landfill in Stockton, California A letter from Forward confirming the disposal of the soil drums is contained in Attachment 3 On May 31, 1996, approximately 865 gallons of purge water generated during cumulative groundwater sampling events was disposed of at the Enviropur West facility in Patterson, Califon ua A copy of the manifest is contained in Attachment 4 CONCLUSIONS/RECOMMENDATIONS Based on a review of previous work performed at this site and the data presented in this report, it can be concluded that groundwater flow direction varied slightly from historical data This may be due to the fact that the groundwater elevation is at its highest since monitoring began in 1991 The groundwater samples collected from wells MW-1 and MW-2 continue to contain concentrations of hexavalent chromium at levels below the California Primary MCL, however, the sample collected from MW-3 contained hexavalent chromium in excess of the California Primary MCL • W 194319kN ��'aril 96 doc 2 • 3R*H