Laserfiche WebLink
1 v <br /> A s s o c i a r e s i N c <br /> �J <br /> ' REMEDIAL ALTERNATIVES - <br /> SOIL <br /> ATC evaluated three remedial alternatives to further reduce petroleum hydrocarbons in soil The alternatives <br /> include natural attenuation,vapor extraction and removal <br /> ' Natural Attenuation <br /> The former USTs were removed from the site and replaced by three 12,000-gallon gasoline USTs and one <br /> ' 550-gallon waste oil UST in 1988 Degradation of the gasoline is expected to continue over time without <br /> artificially modifying the subsurface conditions Natural attenuation is advantageous because of its low cost <br /> and because potential exposure of contaminated soil or soil vapors is very low It is considered a good <br />' method of remediation if the contaminant plume is stable in the vadose zone ` <br /> Vapor Extraction <br /> Vapor extraction at the site could be useful to reduce the highest concentrations of TPH and benzene The <br /> effectiveness of vapor extraction is directly related to the permeability of the contaminated soil The <br /> subsurface conditions at the site generally consist of variable layers of silty and sandy clay, silty sand, clay, <br />' and silt from the surface to approximately 26 5 feet bgs A soil vapor extraction pilot test would need to he <br /> conducted to evaluate the potential effectiveness of vapor extraction at the site <br /> Excavation <br /> g Excavation in general is considered a good method of quickly removing impacted soil from a site <br /> Excavation is generally not cost effective in removing soils deeper than approximately 20 feet because of the <br /> depth restrictions of most excavating techniques and due to the cost of disposal or ex-situ remediation and <br /> replacement material Approximately 450 to 500 cubic yards of soil was excavated in 1988 Laboratory <br /> analytical data collected since 1988 indicate petroleum impacted soil is present along the western property <br /> boundary and southeast of the fuel dispenser island The location of the existing USTs overlaps a large <br /> portion of the location of the former USTs <br />' REMEDIAL ALTERNATIVES — GROUNDWATER <br />' ATC evaluated four remedial alternatives to further reduce petroleum hydrocarbons in the groundwater <br /> beneath the subject property The alternatives mclude pump and treat, air sparging, natural attenuation and <br /> enhanced natural attenuation <br /> Pump and Treat <br /> This remedial approach involves pumping of ground water to the surface for treatment It would require the <br />' installation of additional four-inch diameter extraction wells Prior to installation of the extraction wells, <br /> aquifer testing using existing monitoring wells would be conducted to determine aquifer characteristics The <br /> results would be used to determine the most effective pumping rate, capture zone, draw down, and design of <br /> the extraction wells <br /> A variables speed electrical um would be laced in each extraction well Groundwater would be laced in a <br /> P pump P P <br /> surface holding tank prior to treatment The groundwater would then be pumped through dual 1,000-pound <br /> Former Cheaper#37 January 29 2004 <br />' ATC Project Number 5425847 0037 Page 7 <br />