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6.. 2.2.1 Monitoring Well Construction, Development and Elevation Survev The wells will be installed in 8-inch diameter soil borings drilled by a truck-mounted drill rig, equipped with hollow stem augers. The wells will consist of approximately 15 feet of two-inch diameter, Schedule 40, flush-threaded and machine-slotted (0.020-inch) PVC well screen. Since groundwater was previously encountered at approximately 15 feet below the parking area y subgrade, the two wells installed in the parking area will be drilled to a total depth of approximately 25 feet, and constructed with a screen interval of approximately 10 to 25 feet below the subgrade. Since the surface street grade is approximately 12 feet above the parking area subgrade, the well proposed to the northeast of the former UST will be drilled to a total depth of approximately 35 feet, and constructed with a screen interval of approximately 20 to 35 feet below street grade. Blank PVC casings will thread into the tops of the well screens and extend to the surface. Filter packs of Monterey#3 graded and washed sand will be placed through the hollow stem augers as they are slowly retrieved, and until the sand reaches approximately two feet above the tops of the screened intervals. The wells will be surged and purged by the driller, following the placement of the sand pack and prior to the installation of the well seals. Periodic surging and purging will continue until the amount of suspended sediment in the groundwater decreases and '-' stabilizes and/or until at least five well volumes have been removed. �. Overlying the sand packs, two feet of hydrated bentonite chips will be placed within the annular spaces between the boreholes and the well casings. Over the hydrated bentonite, surface seals of 20:1 cement:bentonite grout mixture will be installed. The tops of the wells will be secured with water-tight locking caps and traffic-rated, flush-mount street boxes. A licensed land surveyor will survey each of the newly-installed wellheads. The surveyor will measure the elevation of the tops of well casings to the nearest 0.01 foot, referenced to a benchmark. The locations of the wells and other site features will also be surveyed. 2.2.2 Soil Sampling and Analysis During the drilling, undisturbed soil samples will be collected at 5-foot intervals using a modified California split-spoon sampler lined with two-inch diameter by six-inch long brass or stainless steel sample sleeves. A geologist will log the core and each of the undisturbed soil samples for hydrogeologic and lithologic characteristics according to the Unified Soil Classification System and screen each sample for organic vapors using a photoionization detector(PID). 7