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5400-5606 Pacific Avenue -2 - 4 October 2004
<br /> Stockton, San Joaquin County
<br /> contaminant distribution in deeper aquifer zones Also,there appears to be some recent plume movement •
<br /> in shallow groundwater to the north and east of 5606 Pacific Avenue
<br /> • By 15 November 2004, submit a geochenucal evaluation (GE)report signed by a geochemist,which
<br /> compares the results of the soil and groundwater analyses, and thoroughly discusses the expected worst- '
<br /> case scenario reactions, i e , 100% conversion of constituents of concern into contaminants,reporting the
<br /> chemical reactions in molar concentrations
<br /> 1 If metals of concern(Cr6+,etc) are not detected,or general minerals (SO4, etc) are not present at
<br /> levels favorable for adverse reactions in saturated soil,then submit a Pilot Study Workplan with the
<br /> GE Report Note that all Pilot Study analytical detection limits must be sufficiently low to test the
<br /> theories proposed in the GE Report and provide comparisons to Water Quality Objectives You will
<br /> continue to monitor groundwater during the Pilot Study for the know petroleum hydrocarbon
<br /> i contaminants and general parameters(dissolved oxygen,pH, specific conductance,temperature)
<br /> 2 If metals of concern(Cr6+,etc) are detected,or numerals of concem(SO4,e£c)are detected at '
<br /> potentially harmful levels,then include a Workplan for a Bench Scale Test(BST)with the GE report
<br /> j The BST should show which contaminant(s)are produced and whether the produced contaminant(s)
<br /> i` will persist after termination of oxygen injection, using the graphed slope of the declining
<br /> contaminants)concentrations versus time to calculate a decay rate(time to revert to non-detect) If a
<br /> contaminant(s)is produced and persistent,provide that information in the BST report for my '
<br /> evaluation If contammant(s)produced are not persistent,provide Workplan for the Pilot Study with
<br /> the BST Report containing modifications to the Pilot Study monitoring program, specifically,the
<br /> frequency of analyses needed to confirm contaminant decay rates as calculated from BST analytical
<br /> evidence • '
<br /> + By 15 December 2004,begin the Pilot Study During the Pilot Studyphase, groundwater sampling and
<br /> analyses will be conducted, at a minimum,immediately before startup of the ozone injection system, and
<br /> at intervals of one and 2 hours afterwards, in order to validate all contarninant(s) analyses and proposed
<br /> decay rates, if applicable If a BST is not required prior to the Pilot Study,then, at a minimum, analyze
<br /> at least once before and i hour after startup of ozone injection
<br /> • Install automated data loggers in selected monitoring well(s) to record changes in dissolved oxygen, pH,
<br /> specific conductance, and temperature during the Pilot Study The test data will be helpful to determine
<br /> the effectiveness of ozone injection ,
<br /> You may c all me at(916)464-4615 for questions or additional information
<br /> II
<br /> AMES L BARTON,R G ,
<br /> ` Engineering Geologist
<br /> cc Mr Mark Owens,UST Cleanup Fund, SWRCB, Sacramento
<br /> M- Mike Infurna, San Joaquin County Environmental Health Division, Stockton
<br /> Ms Jill Tracy, Esq ,UNOCAL,Brea
<br /> Mr Ben Hennmgburg,ENSR International, Sacramento
<br /> Mr Gary Hall GHH Environmental, Auburn
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