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MAR-17-1999 13:54 HLTON GEOSCIENCE 925 606 9260 P.03i10 Subsurface Investigation Workplan CHP Facility, 3330 North Ad Art Road, Stockton February 19 1999 constitute the major aquifer of the Central Valley and yield large quantities of water to wells. Lithologically, these deposits are heterogeneous mixtures of poorly sorted clay, silt, sand, and gravel, and in places some beds of claystone, siltstone, sandstone, and conglomerate. The maximum thickness reported for these formations is 3,000 feet(USGS 1986). Continental deposits of Quaternary age out crop primarily along the major rivers and streams of the valley, as well as along other low-lying areas; the deposits include river and flood-basin deposits, and sand dunes. River deposits, including channel and flood-plain deposits, are considered to be the most permeable deposits in the valley, however, they are generally not tapped by wells. Flood- basin deposits consist largely of fine-grained beds that restrict the vertical movement of water (USGS 1986). 3.0 PLANNED SITE ASSESSMENT ACTTVITIFS 3.1 PRE-FIELD WORK AC71VPI'1FS Boring permits, and property access will be acquired prior to drilling. Underground Service Alert (USA) will be notified approximately 3 days prior to field activities. 3.2 DRILLING AND SOIL SAMPLING Four borings will be advanced near the four sides of the existing UST, to a depth of approximately 24 fbg (per conversation with Steve Sasson on December 1, 98). See Figure 2 for the approximate boring locations. Boxings have been located in the most feasible positions to detect impacted soil, if any. Soil. samples will be collected at 5-foot intervals, changes in lithology and were hydrocarbon affected soil is encountered in the borings, if any. Samples will be collected for soil description, and field hydrocarbon vapor screening. Samples collected near the base of the UST will be submitted to a state-certified laboratory for analysis. Upon completion of sampling activities each boring will be filled with neat cement from the total depth to surface. Refer to Appendix A for general field procedures. Select soil samples will be analyzed for the following: • total petroleum hydrocarbons modified for gasoline (TPH-G) using EPA Method 8015 modified;