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well by subtracting the depth-to-water measurement from the top-of-casing reference elevation. The current groundwater elevation data for the Forward Unit is summarized in Table 2-3. The groundwater elevation data obtained during the fourth quarter 2011 monitoring period were used to generate the groundwater elevation contour map shown on Figure 2-1, which indicates that groundwater generally flows to the northeast towards the Austin Unit, at an average hydraulic gradient of approximately 0.003 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 0.003 sec- ft V [(0.04 —)* —]* 2835 — � 0.972 ft/day ne sec 0.35 em - day where: V=Groundwater flow velocity. K=Hydraulic conductivity of the water-bearing unit(0.04 cm/sec). i=Hydraulic gradient: i�0.003 for the site during the fourth quarter 2011. n,=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 0.972 feet/day(355 feet/year). 2.1.4 Detection Monitoring Program Field and laboratory results for the Forward Unit groundwater monitoring wells for the fourth quarter 2011 monitoring period are summarized in Table 2-2 and time-series plots are presented in Appendix D. As shown in Table 2-2, diisopropyl ether(DIPE) was measured above the practical quantitation limit(PQL) in the sample collected from well MW-2A. In addition, the following VOCs were measured at estimated trace concentrations (between the method detection limit [MDL] and the PQL) during the fourth quarter 2011 monitoring period, DIPE in the sample collected from well MW-2A; acetone and dichlorodifluoromethane (DCDFM) in the sample collected from well MW-10; and 1,1-dichloroethane (1,1-DCA), cis-1,2-dichloroethene (cis-1,2-DCE), DCDFM,tetrachloroethene (PCE), trichloroethene (TCE), and trichlorofluoromethane (TCFM) in the samples collected from well MW-14. 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. The particular VOCs detected in samples during the current monitoring period appear to support this conclusion. Forward has continued to minimize gas related impacts to groundwater by limiting interim fill areas that promote ponding of water. Furthermore, c:\mu-ooso\FA_4QILdoc Jr Geo-Logic Associates