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Martin Thorpe ��/�/�/�■ weissnssocu7Fs 16 October 1987 g i L 1 SUBSURFACE CONDITIONS Soils beneath the site consist predominantly of silts and sands of moderate to high estimated permeability, with occasional interbeds of clays and silts of low estimated permeability. Although minor variations in soil composition and unit thickness are seen between borings, there is generally good stratigraphic correlation across the site. Ground water was encountered during drilling at approximately 50 ft below ground surface. Boring logs are included as Attachment C. MONITORING WELL INSTALLATION Monitoring wells were installed on 23 July 1987 by EGS and Spectrum - Exploration of Stockton, California under the supervision of WA geologist Joseph Theisen. MW-1 was drilled to a total depth of 71.5 ft and was completed to a depth of. 65 ft. This well monitors ground water adjacent to and beneath the tank excavation. MW-2 was drilled to a total depth of 65.5' ft, was completed to 60 ft and monitors ground water southwest of the tank excavation. MW-3 was drilled to a total depth of 65.5 ft and was . completed. to a depth of 59 ft. This well monitors ground water between the tank excavation and the City of Lodi municipal well. Monitoring wells were constructed of 4-in. ID factory-threaded Schedule 40 PVC casing and screen and were screened from 10 to 13 ft above the static water level to allow for seasonal ground water fluctuations. To prevent surface infiltration into the wells, a 1-1/2 ft bentonite seal was placed in the annulus above the sand pack and the remaining annulus was then filled with neat cement grout to the ground surface. Placement of the grout was witnessed by Dan Guerra of the SJLHD. WELL DEVELOPMENT AND WATER SAMPLING Monitoring wells were developed on 11 August 1987 by airlift evacuation. A total of 240 gallons were withdrawn from the three wells. Approximately 110