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Beacon Station No 3641 May 1, 2001 <br /> Stockton. California Quarterly GroundwaWE Monitoring Report <br /> custody documentation, to Kiff Analytical (Kiff), a California-certified analytical laboratory <br />• (ELAP No 2236) located in Davis, California The groundwater samples were analyzed for <br /> total petroleum hydrocarbons as gasoline (TPHg), the volatile aromatic compounds benzene, <br /> toluene, ethylbenzene and total xylenes (BTEX), and the fuel oxygenate methyl tert-butyl <br /> ether (MTBE) by Environmental Protection Agency (EPA) Method 8260B The laboratory <br /> data sheets and the chain-of-custody document are included as Attachment C <br /> Results <br /> Groundwater level data, summarized in Table 1, were used to construct a groundwater <br /> contour map (Figure 2) Depth-to-groundwater measurements were subtracted from the <br /> surveyed TOC elevations to calculate static groundwater elevations Calculated <br /> groundwater elevations for monitoring wells MW-6, MW-7 and MW-8 were used to <br /> construct groundwater elevation contours because the water table intersected the screened <br /> intervals in only those wells <br /> Analytical data are summarized in Table 2 Benzene concentration data were used to <br /> construct a benzene isoconcentration map (Figure 3) Benzene concentration data from <br /> wells screened below the water table were not used to construct the benzene <br /> isoconcentration contours <br /> Recommendations <br /> Horizon recommends continued quarterly monitoring and evaluation of groundwater quality <br />.� trends in accordance with the Assessment Report and Corrective Action Plan as <br /> recommended in the Horizon document Results of Additional .Subsurface Inyestigation <br /> dated June 15, 2000 <br /> Distribution <br /> A copy of this report should be forwarded to <br /> i <br /> Mr Michael Inf ima Jr , R E H S <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 East Weber Avenue, Third Floor <br /> P O Box 388 <br /> Stockton, California 95201-0388 <br /> Mr Gordon Boggs <br /> Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443 Routier Road, Suite A <br /> Sacramento, California 95827-3098 <br /> 641gmrOIQI doc <br /> 164143 2 HORIZON ENVIRONMENTAL INC. <br />