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U U I <br /> Messrs Trommer and Larson April 29 2009 <br /> March 2010 Draft Five-Year Review Recommendation Page 3 of 3 <br /> Various Sites ' <br /> (TPHg) and benzene, toluene, ethylbenzene and total xylenes (BTEX) in MW16-90, thell <br /> EHD directed preparation of a feasibility study to remediate the intensely impacted; <br /> groundwater. The RP's consultant proposed conducting a cone penetrometer testing <br /> (CPT) investigation first to better characterize the hydrogeological setting and <br /> contaminant distribution before preparing a remedial corrective action plan, which the <br /> EHD has approved. As free product has been encountered .in the recent past, <br /> groundwater is intensely impacted locally, and the plume has migrated onto adjacent <br /> site(s), the EHD believes that the people of California, and the adjacent property <br /> owners, will benefit from remediation of the core of this plume to accelerate its return to <br /> background conditions or water quality objectives. <br /> 1717 W. Charter Way, Stockton, CA, Claim Number 4423- In 2008, you concurred <br /> with additional site investigation and in 2009 you recommended reinitiation of the site <br /> remediation system and consideration of a more aggressive remedial technology; this <br /> year you recommend site closure consideration, although the responsible party has not " <br /> undertaken any remedial activity since cessation of the SVE operation. The recent CPT <br /> investigation developed data that in the opinion of the EHD connects the site source <br /> area to impacted groundwater near the north margin of the site, which would greatly <br /> increase the modeled area of the plume of impacted groundwater At this time, the EHD <br /> is not certain that monitoring well MW-4 is a reliable down-gradient monitoring point, j <br /> which would mean the plume extent in the down-gradient direction may not be <br /> accurately known. G <br /> While contaminant concentrations in the core area wells have declined since monitoring ` <br /> began in 1999, they have varied in a fairly steady range for the last five years that does <br /> not show an obvious decline on the tables. With a mass that has not been estimated, an <br /> uncertain lateral extent and,a degradation rate that has also not been estimated, the <br /> EHD cannot be reasonably sure when site conditions will return to background <br /> conditions or achieve water quality objectives, or certify that it will do so in a reasonable <br /> time frame. The EHD will give the responsible party an opportunity to address these <br /> concerns. <br /> Questions or comments should be directed to Nuel Henderson at (209) 468-3436 or to <br /> the appropriate case worker as indicated on GeoTracker I <br /> ` I <br /> Sincerely, <br /> Nuel Henderson, PG <br /> Engineering Geologist <br /> i <br /> i E <br /> i <br /> 5-Year Reviews for March 2010 Comment Letter 0410.doe <br />