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May 23, 1988 <br /> Page 4 <br /> report with attachments of the analytical laboratory analysis. <br /> Laboratory testing programs are also coordinated with Mr. Chris <br /> Winsor of ARCO Petroleum Products Company. <br /> Groundwater Monitoring Well Installation <br /> All groundwater monitoring wells are installed according the <br /> CRWQCB. As stated earlier, our office has simplified these <br /> guidelines into a flow chart for installing monitoring wells. <br /> The "Monitoring Well Flow Chart" is attached to this letter. <br /> This flow chart was designed to be used by personnel of this <br /> office only and should not be recommended for others to use. <br /> All well locations are located within 10 feet or as directed by <br /> Mr. Winsor of underground storage tanks and/or pip:.ng. Also, <br /> these wells are located down gradient of the area, and if <br /> feasible, in the backfill of suspected area. Samples are taken <br /> at 5 foot intervals and explored to a depth of at least 30 feet <br /> . below the lowest point of the underground storage tank or to a <br /> maximum depth of 45 feet below existing grade. Should <br /> groundwater be encountered in the course of exploration, then the <br /> well is drilled to at least 15 feet into the saturated layer or <br /> below the elevation of encountered groundwater. If a clay or <br /> impervious layer is encountered in the saturated zone and if it <br /> is greater than 5 feet in thickness, drilling would stop and <br /> backfilled with concrete to the top of the clay or impervious <br /> layer. The monitoring well is then constructed above the <br /> backfilled layer. <br /> Our monitoring wells are constructed with 2 inch I.D. PVC pipes <br /> with 0. 02 inch slot perforated sections. The well screen is <br /> placed such that the screen length will accommodate seasonal <br /> groundwater fluctuations and extended at least 5 feet above the <br /> saturated zone. The annular space between the pipe and the wall <br /> of the boring is backfilled with #3 clean Monterey sand to about <br /> one foot above the top of the perforated section. A two foot <br /> bentonite plug is then placed over the sand pack to provide a <br /> seal against surface water infiltration. The remaining space is <br /> then backfilled with concrete. Screw--on or friction caps are <br /> used to seal the bottom of wells. Currently, all Well heads are <br />