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documentation, and placed into a chilled cooler for transport to the analytical laboratory. Soil in the remaining tubes will be retained for lithologic description and organic vapor analysis. Headspace organic vapor analysis will be accomplished by placing a hand sample of soil into a sealable plastic bag and allowing the sample to rise to ambient temperature. The probe of the PID will used to penetrate the bag to sample the headspace. The peak organic vapor reading is recorded on the well log. Classify soil types and log observations using the Unified Soil Classification System (ASTM Visual Manual Procedure D 2488-84) and Munsell Soil Color Charts. Include observations on lithology, moisture, density, plasticity, and sample depths on the boring logs as appropriate. An aquitard or aquiclude (clayey layer), three feet in thickness or greater, encountered beneath a saturated permeable layer, should be considered to be a possible confining layer to deeper aquifers. In order to prevent possible cross-contamination of a deeper aquifer, drilling will be stopped and the project manager or geologist consulted to determine how to proceed. Soil drill cuttings are stockpiled on plastic and covered with additional plastic to control runoff or stored in 55-gallon DOT approved drums and left on site. Waste soil is sampled and analyzed to prepare a profile necessary for disposal and hauled by a licensed transporter to an appropriate licensed facility. All waste stored on site is labeled at the time of production. 6. WELL DESIGN AND CONSTRUCTION All well construction is performed in accordance with Department of Water Resources"California Well Standards"and all requirements of local oversight agencies. Borings for two inch monitoring wells will be a minimum of 8 inches in diameter and a minimum of 10 inches in diameter for four-inch wells. Monitoring wells are constructed of schedule 40 PVC casing unless site geochemistry or contaminant types dictate use of another material. The wells are constructed with factory-cut slots and threaded coupling between casing sections and caps. The screened portion of the well is positioned so that it extends approximately ten feet into the water- bearing zone and approximately five feet above the maximum expected water elevation. The screened interval may extend less than five feet above the maximum water level to prevent intersection of well screen with the confining layer at the top of a confined aquifer, or where the water table is too shallow to allow for adequate construction of the well seal. Careful consideration should be given to the specific gravity of the contaminants of concern and screening the upper or lower portion of the aquifer. A graded sand filter pack is placed in the annular space across the screened interval and extended at least one foot above the screen. This additional sand helps to prevent bentonite from entering the well screen if compaction of the filter pack occurs. The well screen slot size should be capable of retaining 90% of the filter pack material. Typically, 0.010-inch slots are used where the aquifer material is predominantly clay and/or silt or poorly graded fine sand. A slot size of 0.020 inch is used when the water bearing formation is well-graded medium to coarse sand and/or gravel. The silica sand filter pack grain size is selected according to aquifer material type as follows: • For poorly graded fine sand or silt and clay—four times the 70% retained grain size of the formation; • For medium to coarse sand, gravels or well-graded sediments—six times the 70% retained grain size. GHD SOP MW Install$Dev 3 of 6 Rev 2/14