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3 � <br /> r <br /> d Y <br /> f <br /> e � <br /> detect3:,le concentrations of dissolved gasoline hydrocarbons <br /> in MW-4. The saraaples from wells MW3, MW5 and MW6 recorded <br /> non-•detectable levels of hydrocarbons. The laboratory <br /> ^M results are summarized in Table 1. The water sample from <br /> the irrigation well on the adjacent property also recorded <br /> non-detectable levels of hydrocarbons. The laboratory <br /> r reports and chain-of-custody are presentel in Appendix IV. <br /> 4.0 CONCLUSIONS AND RECOMMENDATIONS <br /> The investigation conducted to date has shown the presence <br /> of groundwater contamination by gasoline hydrocarbons <br /> -. beneath the site. Groundwater contamination appears to be <br /> confined to a small area around MW-4. The extent of the <br /> dissolved contaminant plume is defined to the south, east <br /> and north by the• non-detectable hydrocarbon levels in wells <br /> MW3, MW5 and MW6. The edge of the plume as well as the <br /> presence of possible contaminate sources to the northwest <br /> ^ could not be determined. Al, <br /> y•, The benzene concentration reported in MW-4 is above State <br /> action levels for drinking water. The other gasoline <br /> constituents detected in this well are below action levels. <br /> The groundwater contamination has not impacted the <br /> irrigation well on the adjacent property. Well construction <br /> details are not available for this well from the property <br /> w_ owner or the Department of Water Resources. Under current <br /> conditions, groundwater flow is away from this well. <br /> However previous work by Exceltech Inc. and WaterWork has <br /> shown the . shallow gradient to vary from westerly to <br /> northeasterly. <br /> The presence of the underground storage tank on the adjacent <br /> property in such close proximity to MW4 suggests the <br /> documented groundwater contamination may not be related to <br /> the contamination on the Tri Valley Growers property. We <br /> recommend that contact be established with the property <br /> owner and the San Joaquin Local Health District to determine <br /> when the tank is to be removed. The status of this tank <br /> with respect to hydrocarbon leakage must be determined in <br /> order to, 1), define both the source(s) of the groundwater <br /> contamination and its extent, and, 2), prevent a recovery <br /> system at Tri/Valley Growers from potentially drawing <br /> contaminated water from an off-site source onto the <br /> _.. property. <br /> Since it appears that the soil contamination at Tri/Valley <br /> did not extend to the confined/semi-confined water table at <br /> - 16 feet and there is an- old tank immediately adjacent to the - - -only contaminated well we recommend maintaining a quarterly <br /> groundwater monitoring program until the other tank has been <br /> fully investigated. This program should include gradient <br /> determination and BTEX sampling from the wells 3, 4, 5 and <br /> 6. An important part of this program will be to document <br /> t <br /> F:� <br />