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Mr. Harlin Knoll �Iw San Joaquin County Environmental Health Division ORION 1 May 2001 Page 4 L Well Installation Following permitting with the SJCEHD, Orion installed a direct push pre-packed groundwater monitoring well on 20 April 2001 (designated as MW-4 on Figure 2), to delineate the hydrocarbon plume. Orion marked the well location on the site and gained permission from the current landowner before initiating drilling activities. The L well permit is included as Attachment 4. The monitoring well was installed by Vironex, Inc., of San Leandro, California, using a Geoprobe' 5400 Direct Push Rig. The Geoprobe® advanced a 2.0-inch-diameter rod casing while simultaneously coring the hole. As the rod was being pushed hydraulically, a dual-walled sampling system was advanced collecting a continuous core within an acetate liner. Once the desired depth of 25 feet below grade was attained, a new 3/4-inch-diameter flush-threaded Schedule 40 polyvinyl chloride (PVC) well casing was installed down the center of the rods and locked into an expendable anchor. The boring log and well completion diagram are included in Attachment 5. Immediately after the sampler was retrieved from the Geoprobe®, the acetate liner was cut at the desired sample depth. The ends of the acetate liner were covered with Teflon sheeting, capped with PVC end caps, and the sample placed in a sealable plastic bag. The sealed tubes were placed in a portable ice chest and cooled with ice until delivery to a State-certified laboratory. �- The boring was drilled to a depth of approximately 25 feet below grade. Water was encountered at approximately 18 feet below grade. New 3/4-inch-diameter pre-packed L well casing was installed to a depth of 25 feet below grade, with 10 feet of screen from 15 to 25 feet below grade. L The pre-packed well consisted of new flush-threaded Schedule 40 polyvinyl chloride (PVC) casings with 0.010-inch slotted screen. The annular space around the well screen was filled with a filter pack of RMC 2/12 Lonestar filter sand to about 3 feet above the L top of the screen. • An approximately 3-foot-thick layer of bentonite was placed above the filter pack to L provide an annular seal. After placement, the seal was hydrated with potable water. The remainder of the well annulus was filled with bentonite grout to approximately 1 foot below grade. A new 7-inch well box was installed and cemented flush to grade. L The well was developed with a peristaltic pump prior to placement of the well grout to (1) remove fines from the filter pack and well screen and (2) reduce sediment in the water. New polyvinyl tubing was used and the pump was allowed to run for L L5:16111sTOCKTON11TRATR008.DOC 111/01