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07 May 1998 AGE-NC Project No. 95-0167 Page 2 of 5 2.4, GROUND WATER DEPTH AND FLOW DIRECTION The estimated depth to ground water at the properties is approximately 20 feet below surface grade (bsg), based on the map titled Lines of Equal Depth to Groundwater Spring 1993 published by the San Joaquin County Flood Control District and Water Conservation District (FCD&WCD). The map titled Lines of Equal Elevation of Groundwater Spring 1996, also published by the FCD&WCD, shows the properties to be in an area where ground water flows toward the northeast, but this may be modified by changing recharge and discharge patterns. Ground water was observed at 8 to 10 feet bsg in soil borings established on the site in 1997. The historical depth to ground water at the properties based on the San Joaquin County FCD&WCD map titled Lines of Equal Depth to Groundwater 1978 was reported to be approximately 40 feet bsg. 3.0. SCOPE OF WORK 3 . 1 , DRILLING AND SAMPLING The analytical results from the installation of soil boring grab-water samples indicated that ground water at the site is impacted by petroleum hydrocarbons. Therefore, the PHS-EHD has request the lateral and vertical definition of both the hydrocarbon-impacted soil and ground water. The proposed scope of work presented in this addendum includes the installation of four soil borings, the completion of the borings as two-inch ground water monitoring wells and the collection of ground water samples. The proposed soil boring locations are illustrated in Figure 3 . The typical well design specifications are illustrated in Figure 4 - Monitoring Well Design. Each boring will be advanced utilizing a truck mounted, hollow stem drill rig and 8 .25-inch hollow- - stem augers. Soil samples will be collected at five-foot intervals beginning at 5 feet bsg in each boring. Samples will be collected using a California split-spoon sampler and brass sleeves. Samples will be driven by dropping a 140-pound weight from a height of 30 inches. The number of blows required to drive each &inch length of the sampler (blow counts) will be recorded on boring logs by an AGE staff geologist. Upon sample retrieval, the middle brass sleeve will be removed from the sampler. The ends of the sleeve will be immediately covered with Teflon tape or aluminum sheets, sealed with plastic end caps, secured with tape and immediately placed under ice in a chilled container for transportation to a State-certified laboratory. Each soil sample sleeve will be labeled with the following: boring location, vertical depth, time, date and sampler's initials.