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5) Completion of the conceptual site model(CSM) with plume map and description of plume disposition and <br /> behavior. The groundwater plume on the attached is estimated and is presented to illustrate the rationale for the <br /> CPT borings.WESTON can complete the C M with the information obtained from the proposed CPT groundwater <br /> samples and the fate and transport modeling. ykj Go(lac I,<r] t vv f <br /> 6) if site qualifies for Low Threat Closure Policy criteria, demonstrate how each of the criteria is met. WESTON can <br /> address each of the Low Threat Closure Policy criteria in a report.The state's Low Threat Closure Policy criteria are as <br /> follows: <br /> a.The unauthorized release is located within the service area of a public water system; <br /> b.The unauthorized release consists only of petroleum; <br /> c.The unauthorized ("primary") release from the UST system has been stopped; <br /> d. Free product has been removed to the maximum extent practicable; <br /> e.A conceptual site model that assesses the nature,extent,and mobility of the release has been developed; <br /> f.Secondary source has been removed to the extent practicable; <br /> g.Soil or groundwater has been tested for methyl tert-butyl ether(MTBE) and results reported in accordance with <br /> Health and Safety Code section 25296.15; and _ q /S 1 0. 5`aOwe ev,-k7r'a1 <br /> h. Nuisance as defined by Water Code section 13050 does not exist at the site. h„f-pf,.r,.f }Fcd 192r�<< s)Ouf . <br /> Cis*hq <br /> v WESTON can prepare a work plan for the investigation for submittal to the EHD for their approval. Encroachment <br /> permits and Access Agreements will be obtained from the City of Stockton(City)and boring permits from the EHD will <br /> be obtained prior to field work.The drilling will be conducted in two days by a C-57 licensed water well driller using a <br /> CPT drill rig to collect up to eight groundwater samples from six boring locations. Groundwater samples would be <br /> collected from six shallow borings(between 40 to 50 feet)to assess the extent of the contaminant plume in the upper <br /> aquifer at the depths of the majority of the monitoring wells at the site.Two of the six borings(CPT-2 and CPT-5)will be <br /> advance to 105 feet to collect groundwater samples from the deeper aquifer at the depth of monitoring well MW-10.—n�dfjaJ <br /> The two deeper borings locations will also be electronically logged by the CPT to provide lithologic information to K, ID <br /> identify aquifers and clay/silt aquitard layers.Groundwater samples will be analyzed by a California certified laboratory oK <br /> for TPH-d analysis by EPA Method 8015 and TPH-g/BTEX analyses by EPA Method 8015M/8260.After the field is <br /> completed and analytical results have been received. <br /> -'-WESTON will utilize a fate and transport model based on USEPA's screening tool BIOSCREEN-AT.The model will predict <br /> how far will the dissolved benzene plume will extend if no engineered controls or further source zone reduction <br /> measures are implemented and how long will the plume persist under groundwater flow conditions. <br /> A report will be prepared and submitted to the EHD.The report will include a summary of field activities and analytical <br /> results, CPT logs, data interpretations to address the EHD concerns,and a request for site closure dependent on the <br /> investigation findings.The report will present a revised CSM using data from the CPT investigation,fate and transport <br /> modeling of the benzene plume,and the preparation of a geological cross-section across the axis of the plume. <br /> Please let me know if you have any questions. <br /> Thanks, <br /> Tom <br /> Tom Fortner <br /> Senior Project Scientist <br /> Weston Solutions, Inc. <br /> 1340 Treat Blvd., Suite 210 <br /> Walnut Creek, CA 94597 <br /> (925) 948-2655 <br /> 2 <br />