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Environmental Assessment Report 5 San Joaquin Catholic Cemetery,Cemetery Lane and Harding Way,Stockton CA June 28 1995 Table 4 is a summarizes the results of the soil vapor extraction test Graph 4 shows the relationship between flow rate and radius of influence and applied vacuum 43 Vadose Zone Modeling Pilot test data were used as input for VENT-ROI, a design tool which provides a rough estimate of the effective cleanup radius for soil vapor extraction (SVE) systems The effective radius is defined as "the maximum distance from a vapor extraction point through which sufficient air is drawn to remove the required fraction of contamination in the desired time" The model was developed by Groundwater Technology in 1992 (Bass, 1993) Critical assumptions made by the model are summarized below ► subsurface is laterally uniform and anisotropic ► air infiltration through the ground surface is proportional to the subsurface vacuum,which is approximated as dissipating exponentially with distance from the vapor extraction well ► contaminants equilibrate between the soil and the gas flowing through the subsurface with the equilibrium soil gas concentration proportional to the soil concentration ► biodegradation is assumed to follow Michaelis-Menten kinetics The effective radius, calculated using the above assumptions,is the distance from the vapor extraction well at which subsurface air flow is just sufficient to achieve the remediation goals It Is specific to the desired remediation time, required extent of remediation, and site contaminant For modeling purposes the following were assumed for the site ► required extent of remediation = 99 percent ► site contaminant= fresh gasoline The model was run on data collected from VW-3 and VW-2D due to the extended time-penod and multi-flow data Simulations were run for time periods corresponding to one,two and three years for each well As calculated by the model, effective radii range from 5-7 feet for one year and 16-18 feet for cleanup times of three years Model output is included in Appendix D 44 Summary of Test Results The results of vapor extraction testing are summarized in Table 4 The radius of influence in the subsurface material ranges from 32 to 75 feet based on conventional calculation methods (linear regression) Using the vadose zone modeling tool VENT-ROI effective radii of influence ranged from 5- 7 feet for one-year cleanup times up to 16-18 feet for 3-year cleanup times From the extraction test data it is estimated that hydrocarbons could be extracted at a rate of approximately 70 pounds per day from the shallow zone and 30 pounds per day from the deep zone Based on an radius of influence estimate of 15 feet,the current vapor extraction system will provide 80 percent coverage of SJCCEAR rptlMnc 171 1-1–J9 GROUNDWATER ❑O❑ TECHNUMY