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' 35 V <br /> sampled in NP-1 represents the influence of the intruding salt water front <br /> documented in the 1997 San Joaquin County Flood Control&Water Conservation <br /> Report <br /> • The Site release has resulted in a dissolved petroleum hydrocarbon groundwater <br /> plume of limited extent Free-phase petroleum hydrocarbons and MTBE have not <br /> ' been detected at the Site <br /> • The lateral extent of soil impacts has been identified Hydrocarbon impacts in the <br /> ' soil appear to be limited to the area around the former product islands <br /> • The lateral extent of groundwater impacts has been identified and is constrained by <br /> ' data from the monitonng well array The downgradient extent of impacts to <br /> groundwater by TPHg is less than 100 ft The downgrachent extent of Site benzene <br /> ' impacts to groundwater at concentrations greater than 1 ug(L are less than 100 ft <br /> • Based on data from NP-1, the vertical extent of soli impacts at the Site have been <br /> ' identified and do not extend below 70 ft bgs <br /> • While the vertical extent of groundwater impacts have not been precisely <br /> Mdelineated, concentrations of TPHg and benzene are significantly attenuated below <br /> 50 to 60 ft bgs Field sampling evidence indicates that the impacted water at <br /> ' depths below 60 ft is moving in horizontal"stringers" of somewhat permeable soil <br /> matenal mterlayered with lower permeability soils <br /> • Based on the presence of significant thicknesses of low permeability zones as <br /> ' evidenced by the NP-1 boring log, the significant attenuation of concentrations <br /> with depth, and the pattern of electron acceptor data consistent with natural <br /> ' biodegradation, it can be reasonably concluded that the vertical migration is also <br /> being stabilized and remediated by natural bioremedial processes <br /> ' • Concentrations of petroleum hydrocarbons in groundwater have declined <br /> significantly over the 11-year penod of the monitoring record <br /> ' . An examination of the longest record of continuous monitoring data available at <br /> the site (9 years) shows that the groundwater plume front is stable and has not <br /> ' substantially moved <br /> I <br />