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o(ogicafTechnics 2nc. L../ Page 6 C&B Equipment Additional Site Characterization WP Addendum. Project No. 336.2 i April 7, 1997 46- Based on field screening observations we recommend that at least three soil samples including one from the capillary fringe be submitted for analyses. If necessary additional soil samples collected from beneath the water table may be submitted for analyses. These L samples may be useful in determining the sorbed portion of the groundwater plume. Soil samples submitted to the laboratory will be analyzed for benzene, toluene, ethylbenzene and xylene (BTEX by EPA method 8020), and gasoline range petroleum hydrocarbons analyses (TPH-Gasoline by EPA method 5030/8015m). Groundwater samples including the domestic well will be tested for BTEX by EPA method �. 602, TPH-Gasoline using EPA method 5030/8015(m), and MTBE by EPA method 602 with positive detection confirmed by mass spectroscopy EPA 8260. The detection limits for these compounds are listed below. DetectionLimits: B I EX ITPH-Uasoline water µ . .. or µ g . 4.3 Groundwater Monitoring �- The new wells will be added to the existing quarterly groundwater monitoring schedule. The first monitoring event will be performed shortly after these new wells are installed. The local regulatory agency will be notified 48 hours prior to the sampling event. .. We recommend that the depth to groundwater be measured and gradient and flow direction be calculated on a monthly basis for a period of one year to evaluate the effects seasonal changes (i.e. precipitation and irrigation). After a annual cycle is on record, quarterly measurements may be appropriate thereafter. .. 5.0 GEOTECHNICAL & GEOCHEMICAL TESTING Responding to the SJCPHSEHD's request for a better understanding of the site with respect ` to health risk and contaminant fate and transport we propose the following scope of work which is intended to provide critical site specific information for risk assessment modeling. 5.1 Lithologic Unit Testing Schedule v Based on geologic information gathered during the earlier investigation we have summarized the geology of the site in the upper 20 feet below ground surface in a sketch cross section. �. For planning purposes we have identified simply two distinct typeS of lithologic units present; sand with varying amounts of matrix and a silty clay. For this purpose we will assume that a good portion of the subsurface geology of the site will be represented by this testing. V We propose to collect a sample representative of each of these units and test each for geotechnical parameters and chemical concentration. V V v