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RPBrown and Caldwell <br /> M Consultants <br /> 723 S Street <br /> Sacramento <br /> California 95814-7092 <br /> (916)444-0123 <br /> FAX(916)444-8437 ��"' <br /> 4L <br /> AUG 1 6 1991 <br /> ENVIRONMENTAL HEALTH <br /> August 13, 1991 PERM i'f/SERViCES <br /> Ms. Laurie A. Cotulla, Program Manager <br /> Environmental Health Division <br /> Public Health Services <br /> San Joaquin County <br /> Post Office Box 2009 <br /> Stockton, California 95201 017-3258-03/3 <br /> Subject: Groundwater Elevations and Flow Directions, ARCO Station 6080, <br /> Lathrop, California <br /> Dear Ms. Cotulla: <br /> As a supplement to my letter of July 26, 1991, enclosed are Figures 1 through 4 that show water- <br /> level elevations and flow directions for ARCO Station 6080 located.at 85 East Louise Avenue <br /> in Lathrop, California. As indicated,on the figures and'summarized below, the groundwater flow <br /> direction has varied significantly, under a low hydraulic gradient. <br /> Date Flow direction Hydraulic gradient Figure <br /> 4/28/87 -SE. 0.001 1 <br /> 12/21/87 W-1-SW 0.0005 2 <br /> 8/26/88 NW` 0.003 3 <br /> 5/23/91 SE 0.002 4 <br /> These data indicate there is no single up- or downgradient well; each well is sometimes <br /> upgradient and sometimes downgradient. <br /> As discussed previously, three rounds of groundwater;monitoring have indicated that .there are <br /> no detectable petroleum hydrocarbons in.the groundwater.. Furthermore, with the exception of <br /> very low levels of hydrocarbons detected in two.soil samples (attributed to.minor surface spills <br /> or cross contamination), there is no'known source of contamination at the site. Therefore, further <br /> work is not warranted at this site and.it is requested that this site be "closed_" and removed from <br /> San Joaquin County's list of environmental-impacted sites. <br />