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2-1. Historically, groundwater generally flows to the north and northeast towards the 0 Austin Unit, at an average hydraulic gradient of approximately 0.001 ft/ft. However, based on lower levels associated with observed pumping from adjacent agricultural wells, groundwater during the third quarter 2007 monitoring period appears to flow in a radial pattern from the center of the Forward Unit at a gradient ranging from 0.003 to 0.005 ft/ft. To calculate the approximate linear groundwater flow velocity for the site, conservative assumptions were used,including a hydraulic conductivity of 875 gallons per day per square foot(0.04 cm/sec) and an estimated effective porosity of 35 percent(CH2M Hill 2000). An estimated groundwater flow velocity was calculated using Darcy's Law: Ki cm 0.005 sec–ft V = —_ [(0.04 —)* ]*2835 1.62 ft l day ne sec 0.35 cm –day where: V=Groundwater flow velocity. K=Hydraulic conductivity of the water-bearing unit(0.04 cm/sec). i=Hydraulic gradient:i�0.005 for the site during the third quarter 2007. n,=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 1.62 feet/day(591 feet/year). 2.1.4 Detection Monitoring Program Field and laboratory results for the groundwater monitoring wells for the third quarter 2007 are summarized in Table 2-2 and Appendix D presents time-series charts of select parameters. As shown on Table 2-2, estimated trace VOC constituent concentrations (between the method detection limit [MDL] and the practical quantitation limit [PQL]) of 1,1-dichloroethane(1,1-DCA), cis-1,2-dichloroethene(cis-1,2-DCE), dichlorodifluoromethane(DCDFM), tetrachloroethene(PCE), trichloroethene(TCE), and trichlorofluoromethane(TCFM) were measured in the sample collected from well MW- 10; 1,1-DCA and TCE were measured in the sample collected from well MW-14A; ethylbenzene(a suspected field contaminant)was measured in the sample collected from well MW-17; and PCE was measured in the samples collected from wells MW-16 and MW-21. In addition,PCE was detected above the PQL in the sample collected from well MW-14; and toluene and xylenes(both suspected field contaminants)were detected above the PQL in the sample collected from well MW-17. On behalf of Forward Inc., GLA prepared a letter report dated February 14, 2001 (RWQCB Case No. 2209), to assess the source and potential impacts of low-level VOCs in groundwater adjacent to the Forward Landfill. The letter report concluded that the sporadic detection of low-level VOCs in groundwater(and lysimeter samples) at the Forward Unit are most likely due to landfill gas from unlined unit WMU-B. Forward has continued to minimize gas related impacts to groundwater by minimizing interim fill areas that promote ponding of water. Furthermore, in accordance with CCR Title 27, DA200700437orwardAusNn sum07.doc _ — 5 Geologic Associates