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SITE INVESTIGATION WORKPLAN u approximately 13 feet below ground surface. Depth to regional groundwater is approximately 25 feet below ground surface (Margaret Lagoria, SJCEHD). TOPOGRAPHY AND SURFACE FEATURES, I.E. WATERCOURSES, LAKES, AND GROUNDWATER RECHARGE FACILITIES The USGS Stockton West, California 7.5 minute quadrangle, edition of 1968, indicates the site is relatively level with an elevation of approximately 8 to 9 feet above mean sea level (amsl). The surface gradient as shown on the topographic map appears to be in a northeasterly direction. No watercourses or lakes are depicted on or adjacent to the site. The Calaveras River is located -r approximately 1,800 feet north of the site. The condition of the site with respect to aquitards, aquicludes, and perched water zones has not yet been determined. SAMPLING.AND ANALYSIS PLAN The objective of the investigation proposed under this workplan is intended to determine the vertical and lateral extent of MTBE in the soil and groundwater and whether it will be necessary to conduct further investigation or remediation. SOIL AND GROUNDWATER SAMPLING NUMBER AND LOCATION OF SOIL BORINGS Approximately five (5) soil borings will be advanced to the soil-groundwater interface. Exact locations and total number of borings will be dependent on observed field conditions. At this ` time,ESA proposes that one soil boring will be advanced in the center of the former tank pit with four additional borings advanced at locations approximately 15 feet from the tank pit corners. The locations of the proposed soil borings are provided in Figure 4 attached to this document. r Prior to commencement of field activities, the area will be cleared for utilities through the Underground Service Alert(USA) system, as required by law. SOIL SAMPLING METHOD, DEPTH AND NUMBER OF SAMPLES Direct-push soil sampling technology will advance the soil borings to desired depths. This drilling method will provide a full-length soil core extending from the surface to the groundwater interface. Once the soil core is extracted, the field geologist will describe and record the soil types and characteristics such as odor, staining, or signs of fill material. Select sections of the recovered soil core will be removed from the continuous core sections, sealed with Teflon and end caps and placed in cooled storage prior to transportation to a state-certified analytical laboratory. Two soil samples per soil boring will be submitted for chemical analysis of MTBE. The soil samples will be representative of the general lithology and soil conditions. At this time, it is expected that soil samples intended for laboratory analysis, will be obtained from depths of 8 �. and 15 feet (expected groundwater interface) below the ground surface. These depths may vary due to soil conditions and sample recovery. However, ESA will endeavor to collect soil samples Environmental Science Associates 4 University of the Pacific Site htvesrigarion Work Plan June 2000 200252