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ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY - <br /> Unit Supervisors <br /> Donna K.Heran,R.E.H.S. Carl Borgman,R.E.H.S. <br /> Director 304 East Weber Avenue, Third Floor Mike Huggins,R.E.H.S.,R.D.I. <br /> Al Olsen,R.E.H.S. Stockton, California 95202 Douglas W.Wilson,R.E.H.S. <br /> • 0_7_ - P Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> +joR`' Laurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 <br /> g g Mark Barcellos,R.E.H.S. <br /> MANUEL & MARY SANCHEZ FEB 2 0 200z <br /> 1633 W WALNUT STREET <br /> STOCKTON CA 95203 <br /> Former Underground Storage Tanks SITE CODE: 1844 <br /> 1876 Country Club Blvd ROM 0000474 <br /> Stockton, CA. 95203 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed the"Revision to <br /> November 27, 2000 Work Plan for Limited Over-excavation" dated January 10, 2002 as <br /> submitted by Western Geo-Engineers (WEGE)on February 4, 2002 and has the following. <br /> comments. <br /> This revision included the recommendation that three (3)existing monitoring wells onsite be <br /> destroyed prior to conducting the aquifer pump test. Support for this recommendation was <br /> based on hypothetical situations and included a calculation with Hazen-Williams formula for <br /> "anticipated flow thru a pipe". WEGE concluded that two water bearing zones exist below <br /> this site and MW-1, MW-2, and MW-3 are constructed through these two "aquifers" and any <br /> dewatering attempts for over-excavation would not be successful. WEGE goes on to <br /> conclude that any groundwater pumping from the shallow aquifer would be impracticable <br /> since the monitoring well construction would provide constant recharge from the lower <br /> aquifer. <br /> EHD recently evaluated similar remedial alternatives with another UST site at 2103 Country <br /> Club. The consultant for this site calculated that aquifer pumping at this site would provide a <br /> cone of depression in the immediate area of the extraction well and increase the area of <br /> vadose petroleum impacted soil so that soil vapor extraction would be viable. A pump test <br /> was conducted at the site from wells screened from 10 feet below ground surface (' bgs)to <br /> 20' bgs. Conclusions from this pump test revealed that high pumping rates were needed to <br /> significantly dewater the groundwater and surrounding recharge from the `discontinuous' <br /> lithology at this site made dewatering an expensive and non-cost effective alternative. <br /> EHD has discussed this WEGE submittal with a representative from the Central Valley <br /> Regional Water Quality Control Board and has concluded that since a pump test was <br /> performed recently very close to this site and from approximately the same depths, an <br /> additional pump test and destruction of the three monitoring wells is not warranted. <br /> Initially EHD was concerned with WEGEs proposal to over-excavate the petroleum impacted <br /> soil because the groundwater infiltration was not discussed.. EHD required WEGE to <br /> evaluate whether the shallow groundwater at this site would be a significant problem (and <br /> cost)in effectively utilizing over-excavation as the final remedial alternative. <br /> Other UST sites that have over-excavation utilized as the most cost-effective remedial <br /> alternative at shallow groundwater sites have only planned to containerize the very wet <br /> excavated soils and did not attempt to dewater the entire zone impacted by the digging_ <br /> Quick digging through the saturated zone proved to be the best method to successfully <br /> remove the petroleum impacted soil. <br />