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Ms.Margaret Lagorio, SJCEHD October 21,2003 Joe's Truck Plaza Project No. 2033-15600-01 Work Plan for Additional Site Assessment Page 14 Dual Phase Extraction(DPE) Test DPE involves concurrent extraction of groundwater and soil vapors from a common extraction well under vacuum conditions. The objective of this test is to measure soil vapor and groundwater flow rates per unit vacuum applied at the wellhead. Additionally, the corresponding groundwater drawdown in the aquifer and the ROI will be measured. Stratus proposes to conduct the DPE test, for a minimum of 48 hours, using well EX-1. The wellhead for well EX-1 will be temporarily modified to conduct DPE. Stratus proposes to use a trailer-mounted DPE system, which incorporates a liquid ring extraction pump capable of up to 28 inches of mercury vacuum and 500 cubic feet per minute (cfin) flow. The trailer-mounted unit also incorporates a thermal oxidizer, which will be used to abate the extracted soil vapors. The extracted groundwater will be stored on-site in a 21,000-gallon storage tank pending analysis and disposal. Stratus proposes to use the drop-tube entrainment method of DPE. The drop-tube system is constructed by inserting a suction tube (pipe) into a sealed wellhead of the extraction well. Soil vapor and groundwater are transported through the drop-tube to an air-water separator (knock out tank), from which the vapors are routed to the thermal oxidizer, and groundwater to a storage tank. If site conditions and equipment performance warrant, adjustments in the field will be made to conduct DPE. DPE Test Procedure The DPE test will be initiated by setting the drop tube approximately 1-foot below groundwater and then slowly lowered to approximately 5-feet below static groundwater elevation, based on soil vapor and groundwater flow rates. Applied vacuum in well EX-1 will be controlled to achieve approximately 1 gallon per minute (gpm) of groundwater extraction. Applied vacuum to the drop tube will be increased gradually to identify an optimum vacuum for groundwater drawdown and soil vapor extraction (applied vacuum not to exceed 18 inches of Hg at the wellhead). Given the extraction dynamics, maintaining a constant vacuum or extraction rate may be difficult. Additional time might be required if equipment or wellhead reconfiguration is required. Once an optimum vacuum has been identified, this vacuum will be held constant to conduct a long-term test. The optimum vacuum should be the most energy- efficient vacuum, beyond which excess vacuum would result in a diminishing rate of return (groundwater extraction and airflow rate). Monitoring wells MW-1, MW-2, MW-7, MW-8, MW-18, and DW-2 will be used as observation wells. The following parameters will be monitored during the test and recorded on field data sheets. P:\Joe's Truck Plaza\Work Plans\Joes workplan 102103.doc