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OVERHEAD/LODI DOOR COMP• -3- • 19 November 1990 <br /> The week prior to this inspection, roughly 1000 cubic yard of excavated soil from the <br /> surface impoundment was sent to Forward Landfill . Bay Area Tank and Marine <br /> Environmental Technologies was contracted to backfill the impoundment excavation and <br /> were on site. The backfill material was installed in lifts and compacted. I only <br /> observed the initial stages. Mr. Pletcher tested the density of the compacted material <br /> with a nuclear density probe. I spoke to Mr. Pletcher on 6 November 1990. He stated <br /> that the backfilling of the impoundment is complete, except for the asphalt. <br /> INSPECTION SUMMARY <br /> Speciation of chromium was included in the analyses for this round of ground water <br /> sampling at the facility. The sample results show that a high percentage (up to 100 <br /> percent) of the chromium in the ground water samples collected is hexavalent chromium. <br /> Hexavalent chromium is more mobile and toxic than trivalent chromium. Therefore, it <br /> is of greater concern. Additional monitoring for hexavalent chromium is required. <br /> Ground water monitoring should continue in accordance with monitoring Order No. 90-903. <br /> Analysis for hexavalent chromium should continue in all wells, except MW-4 and MW-6. <br /> Total chromium has not been detected in samples collected from MW-4 and MW-6 above <br /> detection limits, which ranged from 0.05 to 0.005 mg/l . <br /> Once sufficient information is compiled, we can determine if the existing monitoring <br /> system is adequate or if installation of additional downgradient monitoring wells is <br /> necessary. <br /> AN McCUE <br /> ater Resource Control Engineer <br /> JEM:jm <br /> Attachments <br />