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.+ 'move WORKPLAN FOR ADDITIONAL G16UNDWATER ASSESSMENT TASK I Under Task I,ESA will review available SJCEHD files of current groundwater monitoring sites located near the UOP campus. Through this review,ESA will attempt to determine a local and regional flow direction for the water table and establish estimates of the groundwater gradient. The Calaveras River located 1,800 feet north may influence the flow direction of the shallow aquifer. If a shallow groundwater MTBE plume is identified during Task II, it is expected that water table flow data will help determine the eventual migration path of the plume. TASK II - GROUNDWATER SAMPLING NUMBER AND LOCATION OF SOIL BORINGS As shown on Figure 3, ESA proposes to advance 13 additional borings in the vicinity of the former UST excavation. These borings will be spaced on a grid pattern with 15 to 20- foot centers and will extend approximately 40 feet from the former UST excavation. Exact locations and total number of borings may vary and will depend on observed field conditions, utility locations, and surface obstructions. Prior to field activities, as required by law, Underground Service Alert(USA) will be notified for utility clearance. GROUNDWATER SAMPLING Groundwater samples will be collected using a direct-push Hydro-Punch groundwater-sampling device advanced by a Geo-Probe system. At most locations, these borings will be advanced to the first saturated zone, approximately 25 feet below ground surface (bgs). In select borings, the Hydro-Punch will be advanced beyond 25 feet (to approximately 40 foot depth, if feasible) to evaluate the vertical extent of MTBE impacted groundwater. Deeper groundwater samples may be collected from borings located closest to areas of previously detected MTBE concentrations such as TP-10, TP-14, TP-15, and TP-16. The locations of deeper groundwater samples will depend on the groundwater flow direction established from Task I. It should be noted that this workplan does not include soil sampling and analysis because previous soil sampling results did not identify significant concentrations of TPH-g,BTEX, or MTBE. When the desired sampling depth is reached, groundwater will be allowed to enter the borehole through a screened, temporary Hydro-Punch sampling point placed by the down-hole direct-push equipment. Groundwater will be extracted using a bottom-fill bailer or a peristaltic pump, depending on conditions. Approximately four well-point volumes of water will be purged prior ,.., to collecting the groundwater sample. After purging, groundwater will be transferred into appropriate laboratory-cleaned and preserved glassware, labeled and placed in cool storage prior to transportation to a state-certified analytical laboratory for chemical analysis. v Water samples from borings TP-10, TP-12, TP-13, TP-14, TP-15, TP-16, TP-17, and TP-18 will be analyzed for volatile organic compounds, including MTBE using US EPA Method 8260. The `— deeper groundwater samples discussed above will be analyzed for MTBE and the fuel oxygenates di-isopropyl ether (DIPE) ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME), Environmental Science Associates 3 University of the Pacific November 2000 Workplan For Additional Site Assessment 200252 r..r