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4.3 GROUNDWATER ELEVATIONS AND CONTOURS Prior to purging and sampling, each well was sounded for water depth using a weighted electronic sounder, and the static water level was recorded on a Well Data Sheet (Appendix Q. The groundwater elevations were calculated for each well by subtracting the depth-to-water measurement from the top-of-casing reference elevation. The current and historical groundwater elevation data for the French Camp Landfill is summarized in Table 5. The groundwater elevation data obtained during the monitoring period were used to generate the groundwater elevation contour maps shown on Figures 1 A and 1 B, which indicates that groundwater generally flows to the southeast with an average hydraulic gradient of 0.001 ft/ft. To calculate the approximate linear groundwater flow velocity for the site, conservative assumptions were used, including a hydraulic conductivity of 0.014 cm/sec, and an estimated effective porosity of 35 percent(CH2M Hill, 2000). An estimated range in groundwater flow velocity was calculated using Darcy's Law: Ki cm 0.001 sec— ft V = — = [(0.014 —)* 1* 2835 �z- 0.113 ftlday ne sec 0.35 cm – day where: V=Groundwater flow velocity. K=Hydraulic conductivity of the water-bearing unit(0.014 cm/sec). i=Hydraulic gradient: i;z�0.001 for the site during the monitoring period. ne=Effective porosity(ne=035);an estimated value. The groundwater flow rate is calculated to be 0.113 feet/day (41 feet/year). 4.4 DETECTION MONITORING PROGRAM Field and laboratory results from the current monitoring period for DMP monitoring wells (MW-6A, MW-7A, MW-8A, MW-9A, MW-9B, and MW-10A) are summarized in Table 2. During the monitoring period, chloroform and trichlorofluoromethane (TCFM) were measured above the PQL in the samples collected from wells MW-6A and MW-9A, respectively. Confirmation sampling was not performed since chloroform and TCFM have already been confirmed in these wells. However, given the distance well MW-6A is from the landfill (approximately 0.25 miles), it is not believed that the chloroform concentrations recently measured in well MW-6A are the result of a release from the landfill,particularly since chloroform has almost never been detected in groundwater monitoring wells at the landfill. The TCFM concentration measured in well MW-9A is well below risk-based concentrations and a statistically significant decreasing trend was calculated for the TCFM concentrations measured in well MW-9A. CA2012-0027FCISA12.dce 3 Geo-Logic Associates