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WZ1 INC <br /> plume has been stable over time and does not extend outside the well network, 2) the <br /> estimated areal extent of the hydrocarbon-contaminated groundwater plume is <br /> approximately 18,000 feet, 3) the areal extent of the hydrocarbon plume has been reduced <br /> with time, 4) the concentrations of petroleum hydrocarbon constituents, such as total <br /> petroleum hydrocarbons as gasoline, benzene, toluene, ethylbenzene and xylene have <br /> diminished with time, 5) maximum concentrations of benzene within monitoring well MW-1 <br /> have been reduced from 520 to 4 3µgll from May 1991 to August 1997, and represent the <br /> only hydrocarbon constituent that is above analytical detection limits within all of the <br /> monitoring wells <br /> Groundwater surface elevations have risen over the past five years Groundwater gradient <br /> has been predominantly to the southeast or in a non-preferential flow path or mound <br /> immediately below the site A requirement to test wa Methyl Tertiary Butyl <br /> Ether (MTBE) by using a modified U S Envlro ental Test Method 8020 was Included in <br /> the final groundwater monitoring round of th site No MTBE concentrations the t were <br /> above analytical detection limits were found to resent in the groundwater amples <br /> collected <br /> WZI reviewed the Tri-Regional Board Recommendations Checklist of Required Data for <br /> Closure of Underground Tank Sites and recommends that the site be given closure status <br /> as the site does not pose a substantial threat to the health and safety of the community and <br /> does not impact the beneficial use of groundwater WZI also recommends that all <br /> monitoring wells be abandoned in accordance with all provisions established by County <br /> Public Health and that monitoring of the main water supply well should continue on an <br /> annual basis <br /> 19950011 005 3 <br />