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Artesian Environmental Consultants =� Page 2 1992 sampling event Based on the low gradient and wide fluctuations in flow direction, it appears that tidal influences may exist in this area A three dimensional groundwater elevation projection by computer (Figure 5) shows geneially a southeastern groundwater flow A contour map of the TPH-g concentration (lower Figure 4), shows free product near MW -2 to MW -1 and decreasing concentrations toward the other wells A three dimensional TPH-g concentiation projection shows a view from the southwest CROSS SECTIONS Three cross sections (A -A', B -B', and C -C') were prepared by Aitesian (Figure 7) The depth to the first encounteied water is shown on the cross sections, since these depths may indicate the true depth of the top of the permeable units within the water bearing zone Cross section A -A' (Figure 8), shows the main aquifer sand between MW -b, MW -3 and MW -4 The main aquifer consists of poorly graded sands (SP) Note that free product was not interpreted to exist at the location of the cross section Cross section B -B' (Figure S) shows the main aquifer sand between MW -2 and MW - 1 Free product is shown on the figure Ci ass section C -C' (Figure 10) shows all six monitor wells on the figuie The main aquifer is shown to have the thickest ' section of sand in MW -1 and MW -2 Based on the present data, free product appears to be located near MW -1 and MW -2 in a continuous zone RECOMMENDATIONS Artesian recommends that additional soil bonngs and wells be drilled to define the zero contarnination line in the soil and groundwater and to address the August 19, 1992 Public Health Services letter by Ms Laurie A Cotulla to Mr Dante Nomellini The details on the numbers of borings and wells will be submitted in the workplan, which will be forthcoming An aquifer pump test and recovery test is recommended to define aquifer chaiac.tenstics Artesian proposes to use MW -1 as the pump -down well and use the other wells for observation purposes The two aquifer tests will provide information on ttme-drawdown and distance -drawdown, so that parameters such as aquifer storativity, transmissivrty, and radius of influence can be calculated From these aquifer test data, the feasibility of a pump and treat system c,an be evaluated r 3175 Kerner Boulevard Suite E • San Rafael CA 94901 - (415) 257- 4801 - FAX (415) 257- 4805