ARCHIVED REPORTS_2007_5 - Laserfiche WebLink

Home Browse Search

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 = — _ [(0.04 —)* 1*2835 Pt; 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 fourth quarter 2007. ne=Effective porosity(ne=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 fourth quarter 2007 are summarized in Table 3-1 and time-series plots are presented in Appendix D. As shown in Table 3-1, estimated trace VOC constituent concentrations measured included, 1,1- DCA in the sample collected from wells AMW-13 and AMW-14; and PCE in samples collected from wells AMW-6 and AMW-12. In addition, cis-l,2-dichloroethene(cis-1,2- DCE)was measured above the PQL in the sample collected from well AMW-13; PCE was measured above the PQL in samples collected from well AMW-13 and AMW-14; and TCE was measured above the PQL in the samples collected from wells AMW-13 and 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 Sanitase, a state-approved statistical software program. Based on a comparison of the data obtained during the fourth quarter 2007 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. CONSTITUENT Concentration DMP MONITORING WELL Limit AMW-2" AMW-6 AMW-7 I AMW-12 I AMW-13 AMw-14 MONITORING PARAMETERS(m 1) Barium245 0. 4 E=f�09 liromium,Hexavalent 0.005 0.0056 VOLATILE ORGANIC COMPOUNDS( /1) is-1,2-Dichloroethene 1 0.5 0 2 Vtrachloroethene 0.5 12 16 e iichloroethene 0.5 3.8 1.4 NOTES: (B)-Background Well. DMP- Trend Analyses In order to evaluate changes in water quality in DMP wells at the Austin Unit,historical trends in groundwater were evaluated beginning in 1994 when the groundwater treatment D A2007_0043%Forw a rd A ust in_4Q07.d oc 10 Geologic Associates