ARCHIVED REPORTS_2007_18 - Laserfiche WebLink

Home Browse Search

Review of second quarter 2007 sampling dates and laboratory analytical certificates indicates that the laboratory analyses were completed within required holding times. Based on the results of the laboratory blank and duplicate analyses,it is concluded that the laboratory data generated for the second quarter 2007 monitoring period are generally acceptable. 2.1.3 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 second quarter 2007 monitoring period were used to generate the groundwater elevation contour map shown on Figure 2-1,which indicates that groundwater generally flows to the north and northeast towards the Austin Unit, at an average hydraulic gradient of approximately 0.001 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 0.001 sec– ft V = —_ [(0.04 —)* 1*2835 ;z� 0.324 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:zz�0.001 for the site during the second quarter 2007. n,=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 0.324 feet/day(118 feet/year). 2.1.4 Detection Monitoring Program Field and laboratory results for the groundwater monitoring wells for the second 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),trichloroethene(TCE), and trichlorofluoromethane (TCFM)was measured in the sample collected from well MW-10;toluene(a suspected field contaminant)was measured the sample collected from well MW-IA; and tetrachloroethene(PCE)was measured in the sample collected from well MW-14A. In D:\2007_0043\ForwardAustin_sp07.doc 5 GeoLogic Associates