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i Quarterly Groundwater Monitoring Report, June - August, 1992 October 15, 1992 Manna Pro, 4004 South EI Dorado, Stockton, CA 3 TPH-as-diesel fuel using modified EPA Methods 3510/8015, v Total dissolved lead using EPA Method 7421 The results of laboratory analyses are Included in Table 2, Historical Groundwater Quality Data The laboratory analytical reports are also included as an attachment to this letter As shown in Table 2, pH ranged from 6 9 to 7 4 Specific conductance ranged from 1,000 to 2,200 micro-mhos per centimeter (umho/cm) at 25 degrees celsius Because the results of pH and specific conductance In the samples collected were generally similar, this suggests that the water is from the same hydrologic zone Aromatic volatile organics analyzed for and detected included benzene, toluene, ethyibenzene, and xylenes (BTEX) Total BTEX ranged from 1 microgram per liter (ag/L), or parts per billion (ppb) in the sample from well MW-4 to 76,000µg/I in the sample from well MW-1 Concentrations of TPH-as- gasolEne similarly ranged from 51 jag/I in well MW-4 to 160,000 fag/i in well MWA In general, the analytical data for TPH-as-gasoline and total BTEX have fluctuated between quarterly sampling events Measured fluctuations in TPH-as-gasoline and BTEX concentrations may be attributable to the effects of seasonal water level changes on data and not caused by the lateral migration of these SllbStanCBS Concentrations of TPH-as-diesel fuel were not observed above the detection limit of 10 fag/I in samples collected on July 31, 1992 Because TPH-as-diesel fuel has not been detected for four consecutive quarters of groundwater monitoring and sampling, the frequency of TPH-as-diesel fuel analyses will be reduced to once a year as permitted in the September 4, 1992, PHS letter to Manna Pro Corporation The next TPH-as-diesel analysis will be performed on samples collected in July 1993 Figure 2 Illustrates the TPH-as-gasoline plume constructed from July 31, 1992, analytical results The results are generally similar to previous interpretations regarding the extent of petroleum hydrocarbon impact to groundwater Previous data are presented in Soil and Groundwater Investigation at Manna Pro. Inc Facility, dated December 1990, prepared by ERM-West, Inc Total dissolved lead was not detected in the samples collected this quarter Previous analytical results (October 1991 and January 1992) reported total lead concentrations in groundwater samples from selected wells ranging from 11 to 33 p g/I However, those samples were unfiltered and the reported concentrations included lead adsorbed to sediment In the samples Groundwater Technology recommends that analyses for lead be discontinued, because dissolved lead has never been detected in groundwater samples from thls site GROUNDWATER EE9TECHNOLOGY, INC