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` S ECOR - w 7-Eleven Store 432262 �i Work Plan for Additional Site Assessment and Interim Remediation March 19, 2004 Page 8 Pressure transducers will be placed into wells EX-1, MW-5, and S-1 prior to conducting the test to establish baseline groundwater levels. The step-drawdown test will be conducted by incrementally increasing (steps) the pumping rate at selected time intervals (usually 60 to 90 minutes per step) and monitoring groundwater levels in the pumping well. Hydraulic responses during the test will be monitored using a pressure transducer. Extracted groundwater will be discharged to the 6,900 gallon holding tank and flow rates will be monitored using a flowmeter. The step-drawdown test will be conducted to estimate: 1) the optimum discharge rate for the long-term (e.g. 48 hour) constant-discharge pumping test; 2) well losses; 3) well efficiency; and 4) a preliminary assessment of aquifer characteristics. After conducting the step-drawdown test, the pump will be shut down and recovery water levels will be monitored until over 95% of the total drawdown has recovered. The recovery water levels can be analyzed with the weighted average of the discharge rate to estimate the hydraulic properties (transmissivity and hydraulic conductivity) of the tested interval. A constant-discharge pumping test will be performed for 24 to 48 hours or until the cone of depression reaches near steady-state conditions. Because the pumping test is being conducted in an unconfined aquifer, a delayed yield response in the drawdown curve may be observed. If that is the case, a longer pumping test may be required to obtain sufficient data for analysis by delayed yield methods. Groundwater levels in the extraction well EX-1, S-1, and MW-5 will be monitored using the pressure transducers. After terminating the pumping test, groundwater levels will be monitored in the extraction well EX-1, S-1, and MW-5 until the levels have reached over 95% of pre- pumping levels. The resulting drawdown and recovery data will be analyzed to estimate the aquifer parameters of transmissivity, hydraulic conductivity, and storativity. The resulting hydraulic parameters can then be used as part of the parameters input for the groundwater flow and transport modeling. The data from the step-drawdown and constant-discharge pumping tests will be analyzed by methods described by Cooper and Jacob (1946), Theis (1935), and Moench (1997) that are Jf contained in the computer program AQTESOLV. Groundwater samples will be collected from EX-1 before the step-draw down test and after completion of the test. The water samples will be submitted to a California-certified laboratory for the analysis of TPHg, BTEX, and fuel oxygenates by EPA Method 8260B. Interim,Remediation Using Groundwater Extraction The pump test results will be used to determine if periodic or continuous extraction of groundwater will be an effective interim remedial approach. The groundwater extraction rate and groundwater concentrations observed during the test can be used to determine if groundwater treatment or offsite water disposal is a more cost effective. REPORTING SECOR will prepare an assessment report summarizing the fieldwork completed and data collected including: • Details of field procedures and operations • Boring logs • Tabulated results of the soil and groundwater sample analyses • Survey data for the new wells 32262 Offsite well install and interim remediation workplan.doc SECOR Intemational Incorporated