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A P. <br />' APPENDIX A <br /> i <br /> RESULTS OF BIOSCREEN MODELING <br />' INTRODUCTION <br /> BIOSCREEN (1996) was used to predicate the benzene concentrations within the area 400 feet <br />' downgradient of the source area BIOSCREEN is a screening model which simulates intnnsic <br /> remediation through natural attenuation of dissolved hydrocarbons at petroleum release sites, <br /> The software is based on the Domenico (1987) analytical solute transport model and has the <br />' ability to simulate advection, dispersion, adsorption and aerobic decay as well as anaerobic <br /> reactions that have been shown to be the dominant biodegradation processes at many petroleum <br /> release site BIOSCREEN was developed for the Aar Force and the U S. EPA. BIOSCREEN <br />' version 1.4 was used for this project <br /> BIOSCREEN has been adapted to provide three different model types representing 1) transport <br /> with no decay, 2) transport with first order decay and 3) transport with instantaneous <br /> biodegradation reactions <br /> ISolute transport with no decay is used for predicting the movement of conservative (non- <br /> degrading) chemicals The only attenuation mechanisms are dispersion and adsorption of <br /> • contaminants to the soil matrix. <br /> Solute transport with first-order decay is the conventional method for simulating biodegradation <br /> radation <br /> in dissolved hydrocarbon plumes The first order decay is generally based on literature values <br /> for half-life of a chemical <br /> Solute transport with "instantaneous" biodegradation reaction describes natural attenuation <br />' processes as the instantaneous reaction assumption. <br /> IDATA ASSUMPTIONS <br /> Hydraulic Conductivity (K) <br /> Average hydraulic conductivity from slug tests = 8.6 x 10-4 cm/sec <br /> Hydraulic gradient (i) <br /> From site specific data = 0 003 <br /> IEffective Porosity (n) <br /> IFrom literature values = 0 4 <br /> I <br /> LTR0JECrWANJ0QWA%ACr"PA A-1 <br />