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+r Work Plan for Refined Plume Definition and Management of Floating Product-7500 W 11th St., Tracy, C1 Page 67 <br /> 9.4.3 Technology C: Skimming of LNAPL from Extraction Wells <br /> This proposed floating product remediation method is based on use of skimmer pumps <br /> ._ installed in borings to extract floating product from the surface of the groundwater. A set of <br /> three 6-in. diameter, 20-ft. deep extraction wells, similar to that described in Section 9.4.2 for <br /> Technology B would be installed to the east and west of Monitoring Well MW-7. As for that <br /> remediation technology, the proposed extraction well locations are shown on Figure 13. <br /> Note: <br /> The extraction well locations and spacing shown on Figure 13 have been <br /> preliminarily selected to spread over the complete estimated lateral extent of the <br /> }. plume of floating product in the area beneath the northern shoulder of West <br /> Eleventh Street. Final well locations will be selected following installation of the <br /> floating-product monitoring wells that are described in Section 8.0. However, <br /> due to the limitations of skimmer systems in extraction wells, including the very <br /> limited zones of influence that they generate(see Section 9.3)and the consequent <br /> tendency for a small quantity of floating product to be rapidly removed from and <br /> not reappear in a well except after an extremely long delay, it is not possible to <br /> assure that floating product migrating down-gradient will not by-pass the wells. <br /> Such local removal of floating product from a well might lead to the false <br /> conclusion that all floating product has been removed from the subsurface of the <br /> whole of the area where it is present on the plume of contaminated groundwater. <br /> When the extraction wells have been installed and have been permitted to come to <br /> �-� equilibrium for at least one week, the thickness of floating product on the groundwater in the <br /> wells will be measured, using the procedure described in Section 8.8, before the skimmer <br /> pumps are installed. <br /> When the skimmer pumps are commissioned, they will discharge floating product together <br /> with a minimum of groundwater into a holding tank, which will be located in the parking lot <br /> on the frontage of 7501 West Eleventh Street. Periodically, the contents of the holding tank <br /> will be discharged into a vacuum truck and shipped to a permitted facility where the fuel <br /> hydrocarbons will be separated and recycled in beneficial use and the remaining <br /> contaminated groundwater will be treated prior to discharge. <br /> Note: <br /> All installations described below will be performed by a qualified contractor <br /> holding a General Engineering Class A contractor's license with hazardous waste <br /> `— endorsement issued by the California State Contractors Licensing Board, <br /> 9.4.3.1 Pneumatic Skimmer Pump and Holding Tank System <br /> Figure 16 is a Process and Instrumentation Diagram (PID) for the skimmer pump and <br /> holding tank system for removal of floating product from the surface of the groundwater. <br /> r. <br /> SJC <br />