ARCHIVED REPORTS_XR0012641 - Laserfiche WebLink

Home Browse Search

Hill GROUNDWATER REMEDIATION Groundwater remediation for the Sebastiani Vineyards/Woodbridge Cellars facility has been developed to reduce VOC concentrations detected in groundwater samples taken from monitor wells at the site to below State Department of Health Services Drinking Water Standards. The estimated lateral extent of groundwater contamination identified in the Site Assessment Report is shown on Figure 3. A groundwater remediation system consisting of extraction, treatment by air stripping, and infiltration of treated groundwater has been designed based on information generated by the site assessment investigation and subsequent aquifer characteristic testing, as described below. Aquifer Characteristic Testing Aquifer testing was conducted at the Sebastiani Vineyards/Woodbridge Cellars site to estimate aquifer characteristics, specifically hydraulic conductivity, which affect the movement of groundwater beneath the site and to evaluate groundwater extraction and treatment options. The aquifer testing consisted of slug tests performed at Wells MW-i, MW-3, and MW-6 on June 19 and 20, 1989. Each slug test was performed by causing an instantaneous change in the water level in a well through both a sudden introduction and then withdrawal of a known volume of water, Prior to the slug tests, the wells were sounded with an electronic interface probe to determine the static water level in the well. A pressure transducer was then submerged to about 7 feet below the water surface. The pressure transducer, which is connected to an automatic data logger, measures the weight of the coltLnn - of water above it (i.e. , the head). Subsequent to the installation of the pressure transducer, a solid cylinder S feet long by 1.65 inches in diameter was completely submerged below the water surface in the well, while maintaining a position above the pressure transducer. The increase in the static water surface (and head) induced by the submergence of the solid cylinder was recorded by the pressure transducer and the data logger. The change in water level in the wells was monitored by the pressure transducer and data logger until it had recorded to within 0.1 feet of original equilibrium water level. The slug was then rapidly removed from the well, and well recovery was monitored until static water level returned to within 0.1 feet of the original equilibrium level. Data plots for the slug tests are included in Appendix II. The Bouwer and Rice method (1976) was used to analyze the slug test data. This method of analysis is appropriate for fully or partially penetrating wells in a water table aquifer, which site specific lithologic and water level data indicate characterize the wells tested at the Sebastiani - Vineyards/Woodbridge Cellars site. However, in a recent article (Bouwer, 1989) , it is indicated that use of the Bouwer and Rice analysis method for the slug injection portion of a test is valid only if the ----- -- equilibrium-water--level--is--above-the-screened-section-of- thee-well-.-- -That------------.._... . was not the case for the wells test-,d at the Sebastiani Vineyards/Woodbridge Cellars site, and hydraulic conductivity was ' 17