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02 May 2013 <br /> AGE-NC Project No. 04-1168 <br /> Page 4 of 10 <br /> 2.4.2. Groundwater Flow Direction and Gradient <br /> Based on quarterly data collected from 2005 to 2012,the groundwater flow direction at the <br /> site can be characterized as flowing predominantly towards the southwest,with variations <br /> from southeast and northwest. Groundwater at the site has generally been calculated at <br /> flat gradients. Groundwater elevation data is summarized in Table 2. Groundwater <br /> elevation maps depicting groundwaterflow directions and gradients from 2005 to 2012 are <br /> included in Appendix D.The most current groundwater elevation and gradient map(August <br /> 2011), which includes a historical rose diagram is included as Figure 7. <br /> 2.4.3. Dissolved Petroleum Hydrocarbon Concentrations <br /> Based on historical groundwater monitoring results,TPH-g, BTEX and methyl tertiary butyl <br /> ether(MTBE) compounds have been established as the main contaminants of concern at <br /> the site and to a lesser extent tertiary amyl methyl ether (TAME) and 1,2-dichloroethane <br /> (1,2-DCA). Laboratory analysis of groundwater samples historically detected TPH-g, BTEX <br /> and MTBE in all three installed wells at the site. TAME has been on detected during one <br /> sampling event in well MW-1 and 1,2-DCA has been detected on once in wells MW-1 and <br /> MW-3.Maximum TPH-g, MTBE, BTEX concentrations were at concentrations of 2,600 pg/I <br /> (TPH-g; MW-1),4 pg/I (benzene; MW-3), 8.9 pg/I(toluene; MW-1),4.1 pg/1 (ethylbenzene; <br /> MW-1), 31.5 pg/I (total xylenes; MW-1), 26 pg/I (TAME; MW-1) and 5.9 pg/I (1,2-DCA; <br /> MW-3). Groundwater analytical data is summarized in Table 3. <br /> 2.5. STRATIGRAPHY <br /> The site stratigraphy is composed of alternating layers of silt and clay with some minor <br /> lenses of sand to a maximum investigated depth of 70 feet bsg. Soil boring and well <br /> completion logs are presented in Appendix C. Cross section A-A'depicts the generalized <br /> stratigraphy beneath the site (Figures 3). <br /> 3.0. SENSITIVE RECEPTOR SURVEY <br /> A sensitive receptor survey is required as part of site characterization requirements under <br /> the California Code of Regulations - Title 23, Division 3, Chapter 16, Section 2654. The <br /> scope of work is to identify use and location of wells potentially affected by the UST <br /> release including municipal, domestic, irrigation or groundwater monitoring wells within a <br /> 2,000 foot radius of the site. <br /> Advanced GeoEnvironmental,Inc. <br /> v <br />