SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

the well was allowed to recover to at least approximately 80% of the pre-purge level and a groundwater sample was collected from the monitoring well using the new disposable bailer. Groundwater samples were transferred from the bailers into laboratory-supplied containers, labeled for identification, and stored on ice in an insulated chest pending delivery to the laboratory for analysis. Samples were collected, retained, and transported using chain-of-custody procedures to Kiff Analytical, LLC, of Davis, California, a State-certified analytical laboratory. Kiff analyzed the groundwater samples for the following analytes in accordance with the U.S. Environmental Protection Agency(USEPA)Method listed below. The chain-of-custody form and laboratory report are presented in Appendix C. Analysis USEPA Method Nitrate as NO3(nitrate) 300.0 Total Petroleum Hydrocarbons as Diesel(TPH-d) 8015M DHS Total Petroleum Hydrocarbons as Gasoline(TPH-g) 8260B Benzene,Toluene,Ethylbenzene,and Xylenes(BTEX)and MtBE' 8260B beta-Benzene Hexachloride([b-BHC] an Organochlorine Pesticide [OCP]) 8081A •MtBE=Methyl tett Butyl Ether,a fuel oxygenate compound 4.0 SUMMARY OF GROUNDWATER MONITORING DATA The October 2011 monitoring results are discussed below followed by a discussion oftrends observed in water levels and concentration data since monitoring began at the site. 4.1 GROUNDWATER MONITORING, OCTOBER 2011 Groundwater monitoring well construction details, and current and historic water level data are presented on Table 1. The most recent groundwater elevation data were used to develop the interpretive groundwater surface contour map presented as Figure 3. Because MW-7 is screened in a deeper water bearing zone, data obtained from this well was not used in evaluating the shallow water table. Current and historic groundwater analytical data are summarized in Table 2. JDS collected water levels on 13 October 2011. The overall groundwater surface, occurring between 4.9 and 5.6 feet below mean sea level, was approximately 1.6 feet higher than observed during the same time period in 2005 (JDS, 2005). The shallow groundwater was interpreted to flow east- southeast at an approximate gradient of 0.003 foot/foot(Figure 3),which was consistent with the last interpreted flow direction of 2005 (JDS, 2005). Nitrate was detected in five of the six monitoring wells sampled (water table wells MW-1 through MW-5). Deeper well MW-7 lacked detectable nitrate. To facilitate comparison with historic data (Table 2), concentrations of nitrate(Appendix C)were converted from milligrams per liter(mg/1)to micrograms per liter(ug/1). cru ayo-u 4 m saw,co Wan,wWrzou