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4.3 GROUNDWATER ELEVATIONS AND CONTOURS Prior to purging and sampling, each well was sounded for water depth using weighted p g a g electronic sounder, and the static water level was recorded on a Well Data Sheet (Appendix C). The groundwater elevations were calculated for each well by subtracting the depth-to-water measurement from the top-of-casing reference elevation. The current groundwater elevation data for the French Camp Landfill are summarized in Table 5. The groundwater elevation data obtained duringthis quarterly rly momtortng period were used to generate the groundwater elevation contour map shown on Figure 1, which indicates that groundwater flows to the south with an average hydraulic gradient of approximately 0.002 ft/ft. To calculate the approximate linear groundwater flow velocity for the site, conservative assumptions were used, including a hydraulic conductivity of 300 gallons per day per square foot(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 em 0.002 sec– ft V = — = [(0.014 —)* ]*2835 0.227 ft /day 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;:�5 0.002 for the site during the current(fourth quarter 2007) monitoring period. ne=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 0.227 feet/day(83 feet/year). 4.4 DETECTION MONITORING PROGRAM Fourth quarter 2007 field and laboratory results for DMP monitoring wells (MW-6A, MW-7A, MW-8A, MW-9A, MW-913, and MW-lOA) are summarized in Table 2 and time-series plots are presented in Appendix D. As shown in the time-series plots, the general chemistry and metals constituents are generally consistent with historical concentrations. Organic results indicate that a trace concentration of 1,2-dichloroethane (1,2-DCA) was measured in the sample collected from well MW-913 and a trace concentration of trichlorofluoromethane(TCFM) was measured in the sample collected from well MW-9A. Concentration Limits For DMP monitoring wells at the French Camp Landfill, concentration limits (CLs) are used for the water quality protection standards (WQPS). The CLs shown in Table 2 were calculated by Herst& Associates using Sanitas®, a state-approved statistical software program, using historical data from background wells MW-6A and MW-7A, and are D:\2003_021\FC_4Q07.doc 3 Geologic Associates