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� r <br /> Environmental Assessment Report g <br /> . San Joaquin Catholic Cemetery,Cemetery lane and Harding Way,Stockton CA June 29 1995 <br /> hydrocarbon-impacted material in the shallow zone (Figure 6) In addition,it appears that extraction <br /> from wells screened discretely in the shallow zone create measurable vacuum in separate wells <br /> screened discretely in the deep zone <br /> 50 CONCLUSIONS AND RECOMMENDATIONS <br /> 51 Conclusions <br /> Since environmental investigation was initiated, approximately 31 soil samples have been collected <br /> from two tank pits,four sod bonngs, five groundwater monitoring wells and four vapor extraction wells <br /> Data from these samples indicate that hydrocarbon-impacted soil encompasses an area of <br /> approximately 2,055 square feet and is concentrated between 10 and 70 feet BGS Groundwater has <br /> been impacted in monitoring wells MWA,2 and 3 and flows to the north at a low (<0 01) hydraulic <br /> gradient The total mass of hydrocarbons in the subsurface is estimated to be between 6,000 and <br /> 7,000 pounds It is estimated that less than one percent of all hydrocarbons existing in the subsurface <br /> are dissolved in groundwater Vapor extraction testing conducted on the newly installed vapor <br /> extraction wells indicates an achievable radius of influence between 59 and 75 feet Modeling indicates <br /> an effective radius of influence of between 5 and 18 feet depending on the desired cleanup time Using <br /> an estimate of 15 feet radius of influence,the current array of vapor extraction wells will provide <br /> approximately 80 percent plume coverage in the shallow zone Considering the response of the deep <br /> . zone to shallow zone extraction it is likely that similar plume coverage will exist for both the deep and <br /> shallow zones with the current extraction well network Air sparging into MWA in conjunction with <br /> vapor extraction from vapor extraction wells should enhance remediation of hydrocarbon-impacted <br /> water and accelerate cleanup of the impacted sod in the saturated and vadose zones <br /> 52 Recommendations <br /> Based on the results of this investigation, Groundwater Technology recommends the following <br /> ► Continuation of quarterly groundwater monitoring and sampling <br /> ► Negobabon of cleanup goals for soil and groundwater with Regional Water Quality Control <br /> Board and San Joaquin County Environmental Health <br /> ► Installation and operation of a soil vapor extraction and treatment system for treatment of <br /> hydrocarbon-impacted soil <br /> ► Air sparging using selected, existing groundwater monitonng wells to enhance cleanup of <br /> hydrocarbon-impacted groundwater, as well as soil <br /> Land-farming of soil cuttings cin site, charactenzafion and on-site spreading with County <br /> approval <br /> Drill and sample confirmation bonngs upon termination of system operation <br /> SJCCEAR rptlM4c 17) <br /> ❑l:] GROUNDWATER <br /> ❑C�❑ TECHNa WY <br />