ARCHIVED REPORTS XR0004082 - Laserfiche WebLink

Home Browse Search

,CvvATC A S S O C I A T E S I N C T r The Theis type-curve solution for a confined aquifer was used to estimate aquifer parameters. The 1 results are presented in Table 3. The calculated storage coefficient indicates the aquifer exists in a confined condition. The storage coefficients for unconfined aquifers are typically between 0.01 and 0.3, while those for confined aquifers are typically between 0.00005 and 0.005 (Driscoll page 210, ' 1986). The average storage coefficient calculated using the Theis solution was 2.4E-3. The average hydraulic conductivity value(0.00012 meters per second [m/s]) calculated and presented in Table 3, fall within the average range for fine to coarse sand (1 to 10.5 m/s) (Driscoll page 74, 1986). A distance versus drawdown plot is shown on Figure 4. 3.4 Groundwater Sampling and Analysis 1 Grab groundwater samples were collected from well EW-1 prior to beginning the pump test and at the completion of the pump test after the groundwater elevation had been allowed to recharge. Groundwater samples were transferred to appropriate sample containers, using clean, disposable bailers with bottom emptying devices to reduce volatilization. Sample containers were then ' Iabeled with sample identification, placed on ice, and shipped under chain-of-custody to State- certified Argon Laboratories for chemical analysis. Samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) by EPA method 8015; benzene, toluene, ethyl benzene, and xylenes (BTEX) by EPA method 8020; and methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), di-isopropyl ether (DIPE), tertiary butyl alcohol (TBA), tertiary amyl ether (TAME), 1,2-dichloroethane (1,2-DCA), and ethyl dibromide (EDB) by EPA method 8260. 1 Groundwater analytical results are summarized in Table 2, and laboratory data sheets are presented in Appendix C. ' 33.5 Results of Groundwater Pumping Test The observed maximum drawdown in each of the observation wells was plotted against the ' distance of each well from well EW-1. Based on ATC's experience at groundwater remediation sites, the radius of influence is typically the point where the drawdown in the observation well is at t least 0.10 feet. The maximum drawdown in well MW-4 was 0.15 feet which yields a radius of influence (ROI) for groundwater extraction at the site of approximately 90 feet (Figure 3). Laboratory results of the groundwater samples indicated that TPHg and BTEX were detected in the samples collected from well EW-1 before and after the pump test. Assuming 5,280 gallons of groundwater was extracted from well EW-1, as stated in Section 3.2, and averaging ' concentrations of TPHg and BTEX from the beginning and ending pump test samples, approximately 0.135 pounds of TPHg and 0.04 pounds of BTEX were removed during the groundwater extraction pilot test as shown below: w:12595Treportslpumptest.doc 4