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C7eologual Tecknccs tnc Page 4 <br /> In Situ Recnediation <br /> Pilot Test Work Plan <br /> Project No 507 2 <br /> June 10,2003 <br /> Vertical gradients were calculated for the MW-9/MW-109 pair for nine events in the <br /> ' investigation The vertical gradients were negative (a downward direction) for all nine of <br /> the events <br /> ' 2.3 Contaminant Distribution <br /> ' Figures 6 and 7 illustrate the cross section profiles with soil sample contaminant <br /> concentrations superimposed on the profile The diagrams also include the groundwater <br /> TPH-G data from the March 18, 2003 monitoring event placed adjacent to the wells' <br /> ' screened intervals Tables 3 and 4 contain the historical groundwater and soil contaminant <br /> concentrations, respectively The Wm J Hunter & Associates analytical data is included in <br /> Appendix B <br /> ' The soil contaminant plume is limited in lateral extent and appears to be localized as a <br /> "core" in the vicinity of MW-9/MW-109 It is defined laterally (clockwise- from north) by <br /> ' soil borings MW-6, MW-2, MW-8, MW-1, MW-7, SB-6 and MW-10 The highest levels of <br /> soil contamination are present in soil boring MW-9 that is located dust east of the former <br /> UST excavation The vertical distribution of the contamination is concentrated in the <br /> silt/clay units at 10 — 30 feet bgs The TPH-G concentrations detected in soil attenuate <br /> vertically and laterally with distance from the core location <br /> ' The groundwater plume is also localized in the core area described above Figure 8 <br /> illustrates the groundwater TPH-G concentrations for the March 2003 event The lateral <br /> ' extent of the contamination plume is defined to the east, northeast and southeast by wells <br /> MW-3, MW-2 and MW-1 respectively The plume is defined to the northwest and <br /> southwest by wells MW-10 and MW-7 respectively In-situ chemical oxidation is proposed <br /> to address the core area <br />' 3.0 INSITU CHEMICAL OXIDATION <br /> The purpose of this pilot test is to evaluate the effectiveness of the in situ oxidation for <br /> destruction of the petroleum hydrocarbons and to determine the optimum remedial design <br /> for the corrective action plan We have selected in situ chemical oxidation approach <br /> because site conditions limit effectiveness of other methods such as excavation, pump and <br />' treat, or vapor extraction <br /> The process of in situ chemical oxidation has been used successfully in many applications <br />' Advanced Oxidation Processes (AOPs) are processes that create and use a highly reactive <br /> radical that effectively oxidize organic compounds by chemical reaction The most <br /> prominently used radical is the hydroxyl radical, designated as OH The OH ion will <br /> capture a hydrogen atom from a molecule of contaminant, which then causes the <br /> contaminant molecule to become unstable and breakdown further <br />