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S .A' <br /> which is just above the current groundwater level indicates <br /> degradation of the groundwater has probablysuch, a occurred. <br /> As <br /> the extgn �,{ mil ine <br /> tion. To <br /> provide for <br /> preliminary definition of groundwater flow and <br /> quality conditions a minimum of three groundwater monitoring <br /> wells will be required. These wells should be placed in a <br /> triangular pattern around the former tank pit with two wells <br /> in the down groundwater gradient direction (westerly) as <br /> shown on Figure 3. To provide for immediate source control <br /> the contaminated soils to a depth of 32 feet could <br /> b <br /> excavated and treated on site. Due to the proximity of a <br /> building, the lateral extent and vertical depth of soil <br /> removal may be restricted. <br /> 3 The presence of gasoline hydrocarbons in the 15 foot sample <br /> from the north side of Tank B indicates leakage and/or <br /> Spillage of product has occurred. The non-detectable BTEX <br /> and TPH-G concentrations in the 15 foot sample collected on <br /> the south side of the tankit suggest ggest the lateral extent of <br /> spreading is limited to a radius of approximately 15 feet. <br /> ?: The non-detectable levels of gasoline hydrocarbons in three <br /> t ' samples collected between a depth of 20.5 to 30.5 feet <br /> indicate the contamination_ is limited to the upper 15 feet <br /> of soil. Although field inspection noted slight paint <br /> thinner odors below 15 feet the absence of TPH-PT in the <br /> 30.5 foot sample indicates levels, it present, are below <br /> method detection limits of the analysis. <br /> Based on this data, a volume of approximately 450 cubic <br /> yards of soil have been impacted by varying concen=trations <br /> of gasoline hydrocarbons. The limited extent of soil . <br /> contamination around Tank B indicates no immediate threat to <br /> groundwater resources exists. The 32 foot depth to water <br /> provides a small buffer17 feet uncontaminated soil) which <br /> reduces the potential for the shallow soil contamination <br /> from adversely affecting groundwater quality. The more. <br /> permeable sandy soil types occurring below a depth of 21 <br /> feet reduce the effectiveness of this soil interval from <br /> attenuating vertical migration of contaminants. <br /> 6.0 RECOMMENDATIONS <br /> - -- Based on the data collected to date from Tank B there does - - <br /> not appear to have been significant leakage of waste oil <br /> product from this tank. As such we recommend no further `7 <br /> assessment for the tank B area. <br /> 417, <br /> To .prevent the limited area of <br /> gasoline <br /> contamination associated with the north endof Tankrgcafrom <br /> adversely affecting groundwater quality,we recommend that <br /> . v the soils to a depth of approximately 15 feet. be excavated. <br /> Excavation of the shallow soil contamination and. treatment <br /> on-site (aeration) or disposal at u certified waste <br /> 5 <br /> Y <br />