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ATC Associates Inc. <br /> amOVV <br /> 1117'*one Palm Avenue, Suite 201 <br /> Modesto, California 95351 <br /> 209-579-2221 <br /> �.r ASSOCIATES I N C . fax: 209-579-2225 <br /> Soil sampling at five-foot intervals will be conducted from approximately 30 to 55 feet bgs in the <br /> off-site Zone C monitoring well borehole. Soil sampling and lithological data associated with the <br /> r„ proposed off-site Zone A and Zone B wells will be assumed to be applicable to the off-site Zone <br /> C well, as these three wells are proposed to be installed adjacent to each other. Selected soil <br /> samples will be submitted for laboratory analyses. One of the samples submitted for laboratory <br /> .. analyses will be from approximately 55 feet bgs within the silty clay unit that lies directly above <br /> the Zone C water unit. The silty clay unit may serve as an aquitard between the Zone B and Zone <br /> C groundwater units. The soil sample(s) collected for laboratory analyses from this silty clay unit <br /> .r will aid in determining if this unit is water bearing or dry and attempt to define the vertical extent <br /> of adsorbed phase hydrocarbon contamination above the Zone C water unit. <br /> "' Soil sampling at five-foot intervals will be conducted to approximately 55 feet bgs in the on-site <br /> Zone C monitoring well boreholes. Selected soil samples will be submitted for laboratory <br /> analyses from each of the two on-site Zone C wells. A soil sample collected from the vadose60 Q � <br /> zone will be submitted from each borehole along with selected samples collected at depth. A 6 <br /> sample collected from approximately 55 feet bgs from each borehole will also be submitted. AP" <br /> aw Drilling will be conducted by a State-licensed (C57) drilling company. A field geologist will be <br /> ot <br /> present to log drill cuttings. Descriptions of soil types encountered will be recorded on well logs. <br /> OEM Sample Analyses / <br /> Soil samples collected during installation of the monitoring wells, and groundwater samples <br /> r, collected from the monitoring wells will be submitted under chain-of-custody procedures to a <br /> State-certified laboratory. The groundwater samples will be analyzed for TPHg or gasoline range <br /> organics utilizing EPA Method 801513; and BTEX, MTBE, ethyl tertiary butyl ether (ETBE) di- <br /> Im ether (DIPE), tertiary amyl ether (TAME), tertiary butyl ether (TBA), 1,2- <br /> dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB) utilizing EPA Method 8260B. <br /> aw Well Survey and Groundwater Monitoring <br /> Once the proposed monitoring wells are installed, the top of each well casing will be surveyed to <br /> sub-meter accuracy relative to a known benchmark. At least 48 hours after installation, the new <br /> wells will be developed using surging and bailing techniques until the purged groundwater is <br /> relatively sediment free. The wells will be sampled at least 48 hours after they are developed. <br /> Prior to the collection of groundwater samples, the depth to groundwater will be measured in <br /> each well to evaluate the direction and magnitude of the groundwater gradient beneath the site <br /> and a minimum of three well volumes (casing and sand pack) of groundwater will be purged <br /> `r from each well. Temperature, pH, dissolved oxygen (DO), oxidation-reduction potential (ORP) <br /> and electric conductivity (eH) will be measured and allowed to stabilize. Water samples will be <br /> r <br /> collected using disposable bailers, one dedicated to each well. <br /> 9 ATC Associates Inc. <br /> S:\Environmental\25847.0037\Work Plan additional vert-hor delineationTH2.doc <br /> r <br />