FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

No Further Action Required Request Report US Can—Welty Road September 24,2013 3.1 NO FURTHER ACTION REQUEST FOR CASES EXCEEDING WATER QUALITY OBJECTIVES A narrative response follows to address each numbered item in section 6.5 of the Tri-Regional Recommendations. 1. Demonstrate that the plume is stable with either an overall annual decrease in size or an annual decrease in contaminant concentration trend The Site consists of three areas of affected soil encompassed within a larger area of affected groundwater. The residual weathered crude-oil hydrocarbons in the subsurface are not very mobile. Crude oil is composed of long hydrocarbon chain lengths,and is therefore slow to degrade. The former OVP and TAOC systems were decommissioned at least 40 years ago. Therefore,the residual hydrocarbons at the Site have been present at least 40 years, and the extent of hydrocarbons in the subsurface is certainly decreasing. Groundwater monitoring was conducted at the Site between 1996 and 2009. Monitoring wells MW-1 and MW-2, located within the Area 2 and Area 3 hydrocarbon-affected soil plumes, respectively,were rarely sampled due to the presence of separate phase oil (SPO). MW-3, located between affected soil plume Areas 1 and 2, had detections of TPH as diesel (TPHd), ranging from<50 micrograms per liter(gg/L) to 6,700 µg/L; fluctuations in TPHd concentrations appear to be inversely proportional to changes in groundwater elevation. MW-4 and MW-5, located up gradient(southwest) and down gradient(northeast), respectively, of hydrocarbon-affected media did not have any detections of TPHd or PAHs above environmental screening levels. Significant changes in groundwater plume size or COPC concentrations would not be expected on a quarterly, semi-annual, or even an annual basis. Plume size and current COPC concentrations at the Site are believed to be less than levels recorded during the SAIC investigations due to natural attenuation of the residual hydrocarbons. Affected groundwater is anticipated to remain localized as it slowly and naturally attenuates to TPH concentrations less than applicable WQOs. 2. Calculations or modeling results, including monitoring verification of'modcl conclusions, which show when WQOs are predicted to be achieved. SAIC did not perform calculations or modeling to predict when WQOs would be achieved. Meaningful modeling that predicts when the WQOs would be obtained cannot be performed because initial concentrations are unknown. Residual weathered crude oil at the Site is relatively immobile. Natural attenuation will continue to remove hydrocarbons from the subsurface; however,natural attenuation will occur at a relatively slow rate. As a result, concentrations of the COPCs in groundwater are expected to be stable or declining. Current or future uses of the affected groundwater are not anticipated, as described in the response to Item 3. 3. Verification that there are no current or anticipated uses of the impaired water within the timeframe projected to meet WQOs. Institutional controls may be needed to prevent such use if this period is not sufficiently short. SAIC performed a California Department of Water Resources (DWR)well search in 2010 and a supplemental well search in 2012. Eight water-supply wells were identified within or proximal to a 2,000-foot radius of the Site(Figure 1 and Table 2). Based on review of the DWR Water 4 SAIE