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Results Report for Subsurface Investigation and <br /> Second Quarter 1999 Groundwater Monitoring Report <br /> Moore Petroleum,5491 F Street,Santa,California <br /> Page 5 <br /> shown a slight increase in MW-1 since the last sampling event, and as a result, quarterly <br /> groundwater monitoring should continue for MW-1 and MW-3 to verify this result. <br /> Laboratory results for groundwater from the eight borings show that concentrations of TPHg <br /> exceed the Taste and Odor Threshold of 5 ug/L for GP-1, GP-3, GP-7, and GP-8. In addition <br /> groundwater collected from GP-7 contains levels of benzene, toluene, ethylbenzene, and total <br /> xylenes above their respective Maximum Contaminant Levels (MCLS). MTBE was detected in' <br /> GP-1 and GP-5 through GP-8. However, the primary drinking water standard is exceeded in GP- <br /> 5, GP-6, and GP-7, only. <br /> Based on soil and groundwater samples, contamination is present primarily in groundwater and <br /> not in the vadose zone. The soil sample collected from GP-1 at the 15-foot interval was <br /> collected below the encountered groundwater level and is not indicative of vadose zone soil <br /> conditions. This also occurred in GP-3 and GP-7. <br /> RECOMMEDATIONS <br /> Apex recommends abandoning monitoring wells MW-2, MW-5, and MW-6 and replacing these <br /> wells with monitoring wells MW-2A, MW-4A, MW-5A, and MW-6A shown on Figure 5. <br /> The purpose of the proposed monitoring well MW-2A is to define the western portion of <br /> petroleum impacted groundwater associated with the former Ioading rack. The purpose of <br /> proposed monitoring well MW-5A is to monitor the petroleum impacted groundwater associated <br /> with the seven former underground storage tanks (USTs). The purpose of proposed monitoring <br /> wells MW-4A and MW-6A is to define the extents of contamination in the eastern and northern <br /> portions of the property as a result of two former UST's and the dispenser island. <br /> REPORT DISTRIBUTION <br /> A copy of this report was forwarded to: <br /> Ms. E. Thayer <br /> Central Valley Regional Water Quality Control Board <br /> 3443 Routier Road, Suite A <br /> Sacramento, California 95827=3098 <br /> Ms. M. Lagorio <br /> San Joaquin County Environmental Health Division <br /> P. O. Box 2009 <br /> Stockton, California 95201 <br /> SB:C:1Project PileAN[oore Petroleum%gp_rr.doc <br />