ARCHIVED REPORTS_2010_13 - Laserfiche WebLink

Home Browse Search

3.1.3 Groundwater Elevations and Contours Prior to purging and sampling, each well was sounded for water depth using a weighted electronic sounder, 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 Austin Unit are summarized in Table 3-4. The groundwater elevation data obtained during this quarterly monitoring period were used to generate the groundwater elevation contour map shown on Figure 3-1, which indicates that groundwater beneath the Austin Unit generally flows to the north and northeast at 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 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 0.002 sec– ft V R0.04 —)*—1*2835 ;:e 0.65 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�0.002 for the site during the current the first quarter 2010. n,=Effective porosity(n,=0.35); an estimated value. The groundwater flow rate is calculated to be 0.65 feet/day(237 feet/year). 3.1.4 Detection Monitoring Program Field and laboratory results for the DMP wells for the first quarter 2010 are summarized in Table 3-1 and time-series plots are presented in Appendix D. As shown in Table 3-1, trace concentrations of PCE were measured in the samples collected from wells AMW-6 and AMW-12; PCE and TCE were measured above the PQL, and 1,1-DCA, DCDFM, and TCFM were measured at trace concentrations in the sample collected from well AMW-13; and PCE was measured above the PQL, and 1,2-dichloropropane (1,2-DCP), DCDFM, and TCE were measured at trace concentrations in the sample collected from well AMW-14. For the DMP wells at the Austin Unit, CLs are calculated for the water quality protection standards(WQPS). The CLs shown in Table 3-1 were calculated by Herst& Associates using Sanitass, a state-approved statistical software program. Based on a comparison of the data obtained during the first quarter 2010 monitoring period, the following analytes were found to exceed a CL. The results of the statistical analyses performed by Herst & Associates are presented in Appendix D. D:\2010_0013TA_1QI0.doc 10 Geologic Associates