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Corrective Action Plan Page 14 Groundwater Recovery Wells Well aA To recover contaminated groundwater, a linear array of three 5 in diameter, recovery wells will be located along the East 11th Street frontage of the site as shown on Figure 6 This arrangement of wells is designed to 1 ) recover contaminated groundwater from the central area of the subsurface zone where the highest concentrations of components of hydrocarbon fuels have been found, 2 ) draw contaminated groundwater to the recovery wells from the periphery of the affected zone, including from up-gradient locations beneath the site and from down gradient and co-gradient locations under East 11th Street and "F" Street, 3 ) to cut off the slow down gradient migration of contaminants and 4 ) to provide complete hydraulic containment of the subsurface zone affected by gasoline released from the underground tanks formerly located on the 152, East 11th Street property (Note Installation of the recovery wells will require removal of the existing canopy structure located close to the East 11th Street frontage of the site ) Well Construction Each groundwater recovery well will be installed in a 26 ft deep, 12 in diameter boring drilled using hollow-stem augers To control the loose, flowing sands present in the subsurface and maintain the stability of the boring so that the well casings can be installed, disposable, stainless steel, cutting plugs will be used to close the bottom of the augers while the borings are being advanced The well borings will be drilled and the wells installed by a contractor holding the requisite C-57 license issued by the California Contractors State License Board The borings will be logged by a qualified geotechnician working under the direction of a California-licensed geotechnical engineer The 25 ft long, 5 in diameter well casings will be constructed from stainless steel and will g have 0 02 in, aperture, continuously wound, wire screens There will be a 3 ft length of blank casing at the bottom of the wells to serve as a sand trap Monterey No 8/20 will be used to form the filter pack in the annual space between the screens and the walls of the borings Each well will be sealed with a minimum 2 ft thickness of bentonite beneath Portland cement grout that will fill the annual space between the boring walls and the well casings from the top of the bentonite seal to close to the ground surface The well heads will be enclosed in 2 ft by 2 ft cast-iron box equipped with a bolted, water-tight cover These and other details of the well construction are shown of Figure 9 Following construction, the wells will be fully developed by swabbing and bailing until the casings are free of sand, silt and other particulate matter and a sustained flow of clear `' water can be produced