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samples collected from the Forward Unit appear to be representative of water quality at the site. Groundwater Elevations and Contours Prior to purging and sampling, each well was sounded for water depth using a weighted electronic sounder to an accuracy of 0.01 foot, 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 groundwater elevation data for the Forward Unit is summarized in Table 2-3. The groundwater elevation data obtained during the fourth quarter 2012 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, although a localized southwest gradient of 0.010 to 0.013 was noted along the northeast perimeter of the Forward Unit. 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 cm – 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 third quarter 2012. n,=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 0.972 feet/day (355 feet/year). Detection Monitoring Program Field and laboratory results for the Forward Unit groundwater monitoring wells for the fourth quarter 2012 monitoring period are summarized in Table 2-2. Volatile Organic Compounds As shown in Table 2-2, quantifiable concentrations of acetone and diisopropyl ether (DIPE) were measured in samples collected from wells MW-10 and MW-2A (respectively) at quantifiable concentrations during the fourth quarter 2012 monitoring period. Of note, acetone is a common laboratory contaminant and the detection of this constituent in well MW-10 is a suspected laboratory contaminant. C:\2012-0025TA4Ql2.doc 5 Geo-Logic Associates