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Geomatrix Mr. Dean Hubbard California Regional Water Quality Control Board - Central Valley Region January 30, 2007 Page 3 Groundwater Investi ag tion During the last investigation(August 2005), groundwater was encountered at approximately 35 to 45 feet bgs. We anticipate advancing a cone petrometer test(CPT) to a depth of 70 feet bgs at nine locations to determine lithology. Upon identifying the depth to first water, a Hydropunch-type sampling tool will be advanced adjacent to the CPT borings at the nine locations to obtain grab groundwater samples (Figure 4). Each groundwater sample will be collected using a disposable bailer and will be decanted into the appropriate containers provided by the laboratory. Six grab groundwater samples will be collected at downgradient off-site locations and three will be collected at on-site locations. An encroachment permit will be obtained to advance the downgradient borings in the City of Tracy right-of-way. The six grab groundwater samples collected downgradient of the site will be analyzed for TPH quantified as gasoline (TPHg), TPHd, benzene, toluene, ethlybenzene, and xylene (BTEX), PAHs, total dissolved solids (TDS), general minerals, electrical conductivity, ammonia as nitrogen, nitrate as nitrogen, and total nitrogen. Groundwater samples from the on site borings will only be analyzed for TDS, general minerals, electrical conductivity, ammonia as nitrogen, nitrate as nitrogen, and total nitrogen. If separate phase hydrocarbons are observed (including a sheen), a grab groundwater sample will not be collected. All borings will be grouted to ground surface using a tremie pipe upon completion. A storm water retention basin associated with the housing development to the north lies between the site and several of the planned downgradient borings (Figure 4). Geomatrix proposes to implement the groundwater sampling several months after the end of the rainy season to allow groundwater mounding that can occur from the storm water retention basin to dissipate. Industrial Well Sampling The Water Board requested that groundwater from the industrial well located at the property immediately west of the site be sampled and analyzed. Based on the results of the well survey summarized in Geomatrix's October 6, 2007 Investigation Report, the industrial well is 8 inches in diameter and 75 feet deep. Upon approval of this work plan, Geomatrix will contact the adjacent property owner to obtain access. Prior to sampling the well, Geomatrix will attempt to measure the water level in the well using an electrical sounder. Geomatrix will purge a minimum of three casing volumes of water from the well prior to sampling. Water quality parameters (pH, specific conductance, and temperature) will be monitored during purging. Purging will continue until water quality parameters stabilize to within 10 percent. If the well does not have a pump, Geomatrix will