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BALE' CHANG ASSOCIATES or impervious layer is encountered in the saturated zone, and if.it-is greater than 5 feet in thickness, drilling would stop and the boring would be backfilled with grout to the top of the clay or impervious layer. The monitoring well is then constructed above the backfilled layer. Our monitoring wells are constructed with 2-inch I.D. schedule 40 PVC pipes having 0.02-inch slot-perforated sections. The well screen is placed such that the screeNlength will accommodate seasonal groundwater fluctuations and extended at least 5 feet above the saturated zone. The annular space between the pipe and the wall of the boring is backfilled witlt..#3 clean Monterey sand to about two feet above the top of the perforated section. A two to three feet of bentonite plug is then placed over the sand pack to provide a seal against surface water infiltration. The remaining space is then backfilled with concrete. Screw-on or friction cap is used to seal the bottom of the well casing. All well casing heads are secured with water-tight locking caps and protected by either concrete Christy box or metal vault. All wells are recorded with the Department of Water Resources by means of "Water Well Drillers Report". The report states the name of current owner, location of well including a well location sketch, well construction, well tests, and subsurface soil descriptions. A copy of the report is filed in our office and field files, and with the drilling company. Groundwater Sampling Technique All monitoring wells are thoroughly developed to stabilize the sand pack surrounding the screen section of the well and to provide optimum yield. Each monitoring well is also purged to stabilize the temperature, electro-conductivity,and pH of the water in the well prior to sampling. The purging of the wells are accomplished by using a teflon hand pump or a disposable bailer. A minimum of approximately four well-volume of water is removed and/or the turbidity has subsided prior to sampling. A TSP solution is used to wash the hand pump and later rinsed with water prior to purging each monitoring well to eliminate the possibility of cross contamination. After purging, groundwater samples are taken after the water level recovers to a minimum of 80 percent of its initial level. Water samples are collected by using an individually packed disposable bailer, which is properly disposed of after each sampling. The groundwater sample collected by the bailer is transferred into either 1-liter amber glass bottles for Total Petroleum Hydrocarbon analysis (modified EPA 8015) or 40-milliliter VOA vials for Volatile Organics analysis (EPA 602) after the bailer is recovered from the monitoring well. Each'of the groundwater sample bottles is sealed with a teflon-lined cap with no head space presents n the sample container and labeled. The water samples are then placed in a refrigerated ice-chest for transportation and storage. 2of3