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N{ { <br /> Mr Sasson then directed Upgradient to drill the third boring somewhere between monitoring <br /> well GT-I and the domestic well that is used by the tenants of 3851 Newton Road The domestic well <br /> is Iocated on the front portion of that property, near Newton Road Therefore, GT-6 was located <br /> approximately 50 feet to the northeast of GT-1, near the fence separating the front and rear portions of <br /> the Gilkes property(Figure 2) <br /> Boring GT-6 was drilled to the same depths and specifications as GT-5, except that no water <br /> sample was analyzed because the mobile laboratory had reached the end of its 10-hour day No <br /> hydrocarbon odors were evident in any of the soil samples, so only sample GT-6-50' was analyzed No <br /> contaminants were detected, and the boring was completed as a groundwater monitoring well, as <br /> shown in Appendix B <br /> Mr Sasson requested Upgradient to collect a water sample from the Gillies domestic well (G I <br /> in Figure 2) and have it analyzed for TPH-diesel This was an extra sample that was not included in the <br /> original cost estimate or work plan for the investigation Diesel was not detected <br /> No groundwater samples have been collected from either of the new wells However, in order <br /> to determine the optimum locations for the bonngs and wells that remam to be drilled in this phase of <br /> investigation, Upgradient returned to the site on August 28 to gather data regarding the direction of <br /> groundwater flow The elevations of the new wells were surveyed and the water depth in all five of the <br /> monitoring wells was measured A description of these procedures will be included in the final third- <br /> quarter report Here, only the data are shown(Table 3 and Appendix Q <br /> The depth data were used to map the piezometric surface and determine the groundwater flow <br /> direction with greater accuracy than was previously possible (Figure 3) Groundwater flows to the <br /> south at a gradient of 0 011 ft/ft This gradient is more than twice as steep as previously calculated <br /> when only three wells were available for measurement, and implies that groundwater flow is more <br /> rapid than was assumed At the present time, groundwater contamination extends downgradhent <br /> beyond the existing well grid <br /> The boring logs from this and previous phases of investigation were used to construct two new <br /> cross sections across the site (Figures 4 and 5) The new borings help to clarify the subsurface <br /> stratigraphy, witch will be discussed in detail in the final report They also provide useful data on the <br /> extent of soil contamination to the north and northeast of the former UST cavity Figures 6 and 7 show <br /> the soil analytical results and diesel isochon lines for the same cross sections It appears that <br /> contamination extends to the east and north approximately 50 feet from the former center of the <br /> excavation However, there is a data gap to the north of GT4, and the extent of contamination in that <br /> direction is uncertain(Figure 8) <br /> The extent of contamination is also uncertain between GT-2 and GT-5 (Figure 8) The results <br /> obtained from GT-4 indicated that contamination is surprisingly extensive to the north of the UST <br /> cavity, if the situation is similar to the southwest of the cavity, the volume of contaminated soil in that <br /> area could also be greater than anticipated Therefore, based on the information obtained to date, we <br /> recommend drilling two additional borings on the Gilkes property and an additional well on the <br />