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r <br /> MM= MAAWWAWOOW <br /> Working To Restore Nature <br /> January 11, 1993 <br />► ARCO Service Station No 2130, Stockton, California <br /> MW-4 and MW-5 were submitted to Sequoia Analytical for TPHg and BTEX using EPA <br /> Methods 8015/602 The results of analyses are summarized in Table 2 Copies of the <br /> laboratory analysis reports are attached and in the Appendix <br /> 1 <br /> The results of analyses indicated that TPHg was detected in samples from the five wells at <br /> concentrations ranging from 55 to 6,500 parts per billion (ppb), concentrations of benzene <br /> ranged from 1.5 to 1,900 ppb Fecal coliform bacteria was detected in sample collected <br /> from the well MW-1 but was not detected in the other wells The concentrations of TPHg <br /> 1 and benzene in ground water are shown on Plate 4 <br /> WORK IN PROGRESS ofre Or! bid <br /> In August 1992, RESNAerved the drilling of twelve soil borings and the construction <br /> of two ground-water mons oring wells (MW-4 and MW-5), six vapor-extraction wells, one <br /> 1 air sparge well point, and three sparge monitoring wells in the borings. Plate 2 shows the <br /> new well locations The groundwater data from the two new wells are presented in this <br /> report The drilling and installation data from this work will be presented in a separate <br /> report The sparging pilot test was performed in October 1992 to evaluate ground-water <br /> remediation. The results of this test are currently being evaluated and will also be discussed <br /> lie in a separate report <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> The ground-water flow direction has consistently been to the southeast since January 1992 <br /> 1 The depth to ground-water dropped approximately 12 feet since the previous quarter <br /> TPHg was detected in water from the five w sat concentrations ranging from 55 to 6,500 <br /> pp , and benzene was detected at concentrations above MCL's In our opinion, continued <br /> quarterly monitoring is warranted. We understand that Emcon will conduct the next <br /> quarterly monitoring event in October 1992 We recommend that copies of this report be <br /> forwarded to Mr Michael Infurna of the an Joaquin Public Health Services, P O Box 2009, <br /> Stockton, California 95201 and Mr James Mangham of the Central Valley Regional Water <br /> Quality Control Board, 3443 Routier Road, Sacramento, California 95827-3098 <br /> . <br /> 1031kchr <br /> 30003-63-6 <br /> 3 <br />