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ti Chevron Products Company 5 Former Chevron station #9-5775 301 West Kettleman Lane Lodi California October 9 2000 Based on the assessment activities performed to date and as summarized in the recently submitted Problem Assessment Report, dated July 24, 2000, two water -bearing zones have been identified beneath the site. A shallow water -bearing zone was reported within an approximate 5 -foot layer of primarily coarser -grained soils (silts and sands) at depths of approximately 55 to 65 feet bgs. A deeper water -bearing zone of unknown thickness was reported within primarily fine-grained soils at depths of approximately 60 to 70 feet bgs and was encountered to the bottom of some of the borings at approximately 90 feet bgs. A coarser -grained unit was encountered directly below the finer -grained unit in boring MW -12B. This coarser -grained unit was also saturated and was encountered to the bottom of the boring at a depth of 90 feet bgs. Monitoring data from July 2000 indicates depth to water in shallow zone wells ranging from 55 to 57, and from 56 to 59 feet bgs in deeper zone wells. Groundwater flow direction is currently to the west in the shallow zone wells at an approximate gradient of 0.005, and is currently to the southwest in deeper zone wells at an approximate gradient of 0.003. PROPOSED SCOPE OF WORK The scope of work proposed for this assessment includes the drilling, soil sampling, and installation of twenty-three (23) remedial wells (oxygen diffusion or iso -gen), one (1) groundwater extraction well, and eleven (11) groundwater monitoring wells (Figure 3). Based on recent data, groundwater is anticipated to be encountered at approximately 55 feet below ground surface (bgs). An overview of oxygen diffusion treatment is presented as Attachment B. Details of the oxygen diffuser are described in the attached patent (Attachment C). An overview of iso -gen treatment is presented as Attachment D. Due to the time constraints, both technologies (oxygen diffusion and iso -gen) are proposed for approval at this time, though, depending upon many factors, likely only one of the two technologies will be implemented. If the technology initially selected for installation proves to either be prohibitively difficult logistically or to be relatively ineffective given site conditions, the other technology may replace it. The specific scope of work is discussed below: • Soil Borings. Thirty-five soil borings (OD -1 through OD -23, EX -3, MW -7B, MW -8C, MW -9B, MW -10C, and MW -15 through MW -19C, MW -20A and MW -20B) will be drilled at the general locations shown on Figure 3. Borings OD -1 through OD -23 will be converted into remedial wells appropriate for the use of either oxygen diffusion or iso- -gen technologies. -Boring EX=3 will be converted into a groundwater = ° extraction well. Borings MW -15 and MW -20A will be converted into A -zone groundwater monitoring wells. Borings MW -7B, MW -9B, MW -16B, MW -17B, MW -18B, and MW -20B will be converted into B- �l zone monitoring wells. Monitoring wells MW -16B and MW -17B 077.41991.043/9-5775 WP 100900.doc