ARCHIVED REPORTS_2006_1 - Laserfiche WebLink

Home Browse Search

The results of the QA/QC program indicate that five VOCs (benzene, ethylbenzene, ® toluene,total xylenes, and MEK)were detected in the field and equipment blanks, and three VOCs(acetone,methylene chloride, and MTBE)were detected in method blanks during the second quarter 2006 monitoring event. Review of the analytical data results indicates that similar concentrations of benzene and MTBE were detected in three of the primary samples collected from the Austin Unit. These suspected field or laboratory contaminants were flagged in the summary tables. A duplicate groundwater sample was collected from well AMW-3 and was labeled AMW-DUP. Duplicate groundwater test results are presented along with the primary data in Table 3-2. As shown in Table 3-2, comparison of the primary sample results with the duplicate indicates good agreement(within 10%). Of note, concentrations less than the practical quantitation limit(PQL)were not included in the duplicate comparison since these are estimated values. Review of laboratory analysis dates with required holding times indicates that all samples were submitted and analyzed within the required holding times during the second quarter 2006. It is concluded that the laboratory data generated for the second quarter 2006 monitoring period are generally acceptable. However,the field sampling crew was notified of the BTEX constituents in the field and equipment blanks. 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 3-5. 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 central and western areas of the Austin Unit flows west to southwest at an average hydraulic gradient of approximately 0.002 ft/ft,while groundwater to the northeast of the site,in the vicinity of the EMP wells, generally flows to the east and southeast. 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). The maximum groundwater flow velocity was calculated using Darcy's Law: D:\2003-021\ForwardAustin_spo6.doe 10 Geologic Associates