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•IJ <br /> include nitrates,_ ferric iron and sulfates. <br /> The following electron acceptor data was analyzed at the site (see <br /> attached Laboratory Analysis Data Table) : <br /> (a) Dissolved Sulfate - concentrations are uniformly elevated <br /> at all sampled wells (see attached Site Map/Dissolved Sulfate <br /> Concentrations) . The presence of relatively abundant dissolved <br /> sulfate indicates sufficient concentrations of the anaerobic <br /> electron acceptor to facilitate the biodegradation of dissolved <br /> hydrocarbons both on-site and off-site. <br /> The presence of elevated values of dissolved sulfate in wells MW-9 <br /> and MW-2R (35 and 38 mVL, respectively) , suggests that the <br /> formerly impacted portion of the site is presently characterized by <br /> relatively low concentrations of dissolved hydrocarbons. As noted <br /> in Observation No. 3 , recent groundwater samples from MW-9 are <br /> collected from a submerged screen, representing aquifer conditions <br /> wholly below the water table. <br /> (b) Dissolved Ferrous Iron - the uniformly low concentrations <br /> of ferrous iron in all sampled wells implies the relative abundance <br /> of the anaerobic electron acceptor ferric iron (see attached Site <br /> Map/Dissolved Ferrous Iron) . The implied presence of ferric iron <br /> suggests that the dissolved hydrocarbon presence is minimal in the <br /> vicinity of all sampled wells, and sufficient electron acceptor is <br /> available to inhibit the migration of dissolved hydrocarbons. <br /> (c) Dissolved Nitrate - the nondetect to minimal <br /> concentrations of dissolved nitrate, in upgradient, downgradient <br /> and on-site wells, indicates that the electron acceptor is locally <br /> depleted in the subsurface (see attached Site Map/Dissolved <br /> Nitrate) . The absence of dissolved nitrate is apparently a <br /> characteristic of the vicinity of the site. <br /> (d) Dissolved Oxygen - the concentrations of dissolved oxygen <br /> in all site wells indicate a sufficient presence to facilitate the <br /> aerobic degradation of available dissolved hydrocarbons in the <br /> saturated zone (see attached Site Map/Dissolved Oxygen) . The areal <br /> distribution and concentrations of the DO further suggests that the <br /> dissolved hydrocarbons values at the site are minimal. <br /> In summary, the biologic data indicates that sufficient <br /> concentrations of electron acceptor compounds are present at the <br /> site to inhibit the off-site migration of dissolved phase <br /> hydrocarbons. <br /> 5) I recommend that future strategy at the site consist of periodic <br /> groundwater monitoring of selected wells, with a natural <br /> attenuation approach toward the remaining hydrocarbon <br /> concentrations in the dissolved phase plume. The recommended <br /> activity is based on the following factors: <br /> 4 <br />