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TreaIo <br /> A LANEAN COMPANY <br /> Request for Low-Threat Case Closure 6 June 2013 <br /> RWQCB case#391149 and#391162 Page 12 <br /> 420 and 423 N Madison Street <br /> Stockton,California <br /> Project:731589001 <br /> LTCP Guideline Justification for Site Closure(Carando <br /> criteria for class number two are satisfied as <br /> follows: <br /> a) The contaminant plume that exceeds The length of the benzene plume is estimated to be <br /> WQOs is less than 250 feet in length. approximately 140 feet in length. <br /> b) There is no free product. Free product has not been observed at this Site <br /> during soil or groundwater sampling, UST removal, <br /> or remedial excavation. <br /> c) The nearest existing water supply well or The nearest surface water body, McCleod Lake, is <br /> surface water body is greater than 1,000 located approximately 350 feet to the southeast <br /> feet from the from the defined plume from the site and shallow groundwater at the <br /> boundary. adjacent Site has consistently flowed away from <br /> the lake to the north-northeast away from McCleod <br /> Lake. The nearest existing water supply well is <br /> greater than 1,000 feet from the site. <br /> d) The dissolved concentration of benzene is The maximum detected benzene concentration was <br /> less than 3,000 pg/L and dissolved 46 lag/L collected from groundwater within the <br /> concentration of MTBE is less than 1,000 excavation source area in April 2004. MTBE has <br /> lag/L. not been detected in groundwater at the site. <br /> 423 N Madison Street LTCP Justification <br /> UST B-6 was removed in 2004 and the surrounding soil was over-excavated. Samples collected down- <br /> gradient from the former UST B-6 indicate groundwater impacts to the shallow zone have been minimal <br /> with low TPHd and TPHmo concentrations at 15B-8-GW and no BTEX or MTBE. Natural attenuation <br /> parameters and microbiological testing results for 423 N Madison indicate degradation likely occurs in the <br /> A and B groundwater zones, limiting the lateral and vertical extent of TPH. The Site meets LTCP criteria <br /> as outlined below: <br /> Guideline Justification for Site Closure(423 N Madison) <br /> The unauthorized release is within the service area The unauthorized release is within the City of <br /> of a public water system. Stockton, which is served by California Water <br /> Service Company. California Water Service <br /> Company operates municipal supply wells in the <br /> City of Stockton but there are no supplywells <br />