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1 <br /> �\V7_ A S S O C I A T E S I N C <br /> 6.0 EVALUATION OF LOW RISK CRITERIA <br /> 6.1 Low Risk Groundwater Case Evaluation <br /> Using the criteria listed in CRWQCB's No Further Action (NFA) requirements, as outlined by <br /> CRWQCB (Appendix B of the Tri-Regional Recommendations), conditions at the subject site <br /> were evaluated to determine if NFA as a "low risk, groundwater case site" is appropriate for this <br /> site. <br /> Criterion 1: Contaminants remaining in the vados zone must not reverse or threaten to <br /> reverse the mass reduction rate of groundwater pollutants discussed in <br /> V <br /> Criterion #4 below. <br /> As previously noted, laboratory analytical data indicate the majority of petroleum <br /> hydrocarbon-affected soils are present at depths from approximately 6 to 12 feet <br /> bgs. Because of this, one might expect maximum groundwater degradation to <br /> occur when water rises to 6 feet and desorbs hydrocarbons from the soil matrix. <br /> Between July 1995 and June 1999, a total of 16 quarterly groundwater monitoring <br /> ��. events have been performed at the site. Groundwater level measurements indicate <br /> that during this period, the water table was highest in July 1995 and lowest in <br /> October 1995 with an average fluctuation of approximately 1.18 feet between <br /> these two monitoring events. A review of the site's groundwater measurements <br /> suggest that water table reaches it's seasonal height during the summer months <br /> where it was measured within 0.20 feet of the historic 1995 measurement in June <br /> 1997 and June 1998. A comparison of analytical data corresponding to these dates <br /> does not show an overall increase of hydrocarbon concentrations at the site. <br /> In addition, the site is capped by concrete and asphalt with an engineered storm <br /> drain system to channel surface water away from the area of hydrocarbon-affected. <br /> This will further impede the vertical migration of surface water through the upper <br /> clay strata and thus prevent surface infiltration from leaching contaminants to <br /> groundwater. <br /> Y�r <br /> Criterion 2: Separate phase product has been removed to the extent practical. <br /> Free-product was initially observed on-site during the collection of a groundwater <br /> grab sample from soil boring SB2 in September 1996. However, subsequent soil <br /> borings advanced near SB2, including FPB-1, FPB-2, and MW-4, not reveal the <br /> presence of free-product. The nonexistence of free product at the site is especially <br /> evident from the analysis of water samples collected from MW-4 in June 1999. <br /> wA95122Veports\RequeA for NFA doc 15 <br /> r.r <br />