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mow . x <br />'r <br /> Although the MW4 sample recorded 32000 ppb TPH-D, the non- <br /> detectable level of benzene and concentration of TEX below <br /> state drinking water standards indicates the impact on water <br /> 'y quality from the volatile hydrocarbon fraction is not <br /> significant. It is our opinion that the documented soil <br /> s contamination and groundwater contamination by diesel <br /> j ; hydrocarbons does not adversely affect the beneficial use of <br /> surface water or groundwater resources u _ <br /> tia ons. a coliform in the shallow <br /> groundwater indicates beneficial uses are already <br /> restricted. <br /> Fy <br /> ; s 6.0 Recommendations <br /> ►s Because there is no conclusive evidence that groundwater <br /> �., contamination by diesel hydrocarbons is present above <br /> drinking water standards and no significant impact upon <br /> beneficial uses of surface or groundwater resources has <br /> occurred we would propose no active groundwater remediation <br /> t'S of diesel contamination be conducted at this site. Natural <br /> degradation of the residual hydrocarbon contamination <br /> �-" recorded in both the soil and w es. , should occur <br /> t r <br /> over time. <br /> .To remove a."potents send x=Contaminant' <br /> migration,7 the. on site irrigation we_11 should, be d, <br /> s4= "abandoned as soon :as :possible If nea5ssa'y..:to;provide':fo <br /> a perimeter , of non-detectable TPH concentrations"mrin \ <br /> groundwater samples, .monitori.ng wells would..b8 required. to: !l <br /> the. northeast of:�MW3 `and east;southeast..'of SH2.- ` Due ;to a <br /> r steep slope from the adjacent Interstate 5 freeway drilling <br /> is ;these: directions .would be ,difficult if not `impossible. We.. <br /> recommend3 quarterly monitoring/samp3 zig","of the':existing-' <br /> monitoring wells wl thru MW4 "and' any`additional wells to <br /> ;. p�tovide 'assurance `:that,: 1}; gxcundwater:s flow; is...;away: .from <br /> the :,nearby. Smiths ;Canal and, 2 the :dracumento�d .diesel,j <br /> � z hydrocarbon concentrations in groundwater do. not increase <br /> above drinking standr,--d a. <br /> The presence of fecal coliform concentrations exceeding <br /> state standards warrants further investigation. As a first <br /> step the four wells should be resampled to confirm the <br /> levels of fecal coliform. If confirmed, the source and <br /> ' extent of the fecal coliform contamination should be <br /> investigated. <br /> 7.0 REFERENCES <br /> Tri Regional Guidelines, Revised May 18, 1989, Regional <br /> Water Quality Control Boards <br /> Semi-Annual Groundwater Report, Spring 1989, San Joaquin <br /> Flood Control and Conservation District <br /> 7 <br />