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04/03/2000 16:39 209-579-227` MODESTO ATC PAGE 05 <br /> Working To Restore Nature <br /> Groundwater parameters of electrical conductivity (EC), pH, and temperature were allowed to <br /> stabilize prior to sample collection to ensure that representative samples of formation water were <br /> collected. Purged 'water was contained in DOT approved drums and stored on-site. <br /> Groundwater samples Were transported to Sequoia Analytical and analyzed for 13TFX and TPHd <br /> by appropriate EPA methodologies. <br /> 4.4 Hydropunch Sampling <br /> Discrete groundwater samples were collected from the four soil borings (SB-3, SB-7, SB 8 and <br /> SB-9) nearest MW-4. After each boring was drilled to within one foot of the zone of saturation <br /> (to approximately 16 feet below grade), a Hydropunch groundwater sampler was driven ahead <br /> of the lead auger. As groundwater flowed into the exposed screen under natural hydrostatic <br /> pressure, an undisturbed groundwater sample was collected by lowering a one-inch outside <br /> diameter bailer into the screened interval. The collected sample was transferred into the <br /> appropriate sample container while taking care to avoid agitation. The presence of fine-grained <br /> rlow yield soil (lean clay, elastic silt) in borings SB-8 and SB-9 hindered sample collection by <br /> Hydropunch in the borings. Groundwater samples in borings SB-8 and SB-9 were collected by <br /> drilling approximately five feet below the water table and collecting a sample through the augers <br /> using a disposable bailer. Samples were submitted to Sequoia Analytical for analysis of TPHd <br /> and BTEX. <br /> 5.0 SUBSURFACE CONDITIONS <br /> Soil encountered beneath the project site consist predominately of clays and silts to an <br /> approximate depth of 8 feet in the eastern portion of the site and 24 feet in the western portion <br /> of the site. Silts and sands exist below the clay to a depth of at least 36 feet, the maximum <br /> depth explored. Much of the site has been overlain with imported gravel to a depth of two to <br /> four feet. The gravel fill extends to a depth of approximately 16 feet in the vicinity of the <br /> former tank locations. The orientation of cross sections A-A' and B-B' are shown on Figure 4. <br /> Cross sections of subsurface stratigraphy are shown on Figures 5 and 6. <br /> RHP0RT5/PAA1097.FNL 6 <br />