ARCHIVED REPORTS_XR0003669 (2) - Laserfiche WebLink

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i 2 . 0 GROUNDWATER FLOW DIRECTION AND GRADIENT On August 12, 1999, ASE associate geologist Ian Reed measured the depth to water in each site groundwater monitoring well using an electric water Ilevel sounder The surface of the groundwater was also checked for the presence of free-floating hydrocarbons or sheen Monitoring well MW-5 contained 0 40-feet of free-floating product The free-floating hydrocarbons appeared yellow and is believed to be gasoline A thick hydrocarbon sheen was present on the groundwater surface in monitoring I well MW-6 No free-floating hydrocarbons or sheen were observed in any other site monitoring well Groundwater elevation data is presented as I Table One F Due to the presence of free-floating hydrocarbons in monitoring wells MW-5 and MW-6, ASE began measuring the thickness of the free-floating Ihydrocarbons in these wells every two weeks and then removing any accumulated product in these wells with a bailer Following August 12, 1999, all subsequent free-floating hydrocarbon measurements were completed with an oil/water interface probe Groundwater elevation (potentiometric surface) contours are plotted on Figures 2, 3 and 4 On August 12, 1999, groundwater in the shallow zone (less than 19-feet bgs) appeared to flow to the north and northeast beneath the site at a gradient of approximately 0 002-feet/foot, which is not consistent with the flow direction to the northwest last quarter Potentiometric surface contours for the deeper zones (55 to 70-feet bgs and below 100-feet bgs) could not be plotted because three non-linear points for each zone are required for contouring However, since the potentiometric surface in monitoring well MW-7 is higher than the potentiometric surface in monitoring well MW-9 (both wells screened between 55 and 70-feet bgs) and since the potentiometric surface in monitoring well MW-8 is higher than the potentiometric surface in monitoring well MW-10 (both wells screened below 100-feet bgs), it appears that groundwater in these deeper zones may have a flow component to the south, probably being influenced by pumping from the on-site drinking water well In addition, there was a hydraulic head decrease with depth between monitoring wells MW-6, MW-7 and MW-8, all installed adjacent to each other and screened at different depths, suggesting downward groundwater flow This decreasing hydraulic head with depth relationship is also present in monitoring wells MW-9 and MW-10 installed adjacent to each other and screened at different depths Once again, this suggests that there is a downward component to groundwater flow probably related to pumping Frank's One Stop Quarterly Report - August 1998 Sampling -2-