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APPENDIX B <br /> MODEL OUTPUT CONVERSION TO ppb CONCENTRATION <br /> VLEACH output data is generated as annual contaminant mass loading to the groundwater <br /> The Federal EPA Health Advisories and CAL EPA MCLS for drinking water are provided in <br /> ppb concentrations In order to compare the modeling output to regulatory standards, a unit <br />' conversion must be done The procedure for accomplishing this is described below <br /> In general, to predict the potential contaminant concentration (c) in the groundwater, one can <br /> simply apply <br />' (1) c = mjm, <br /> where mc is the annual contaminant mass loading and in is the groundwater mass passing <br /> directly beneath the soil column in a year <br /> Given a soil column with a cross sectional area of a feet by a feet, an aquifer thickness of b <br /> feet, macro-velocity of groundwater flow at v feet per year (Figure A-1, Appendix A), and <br /> aquifer material with an effective porosity of n, the annual volume (vol) of groundwater <br /> passing beneath the soil column is <br /> (2) vol = (abv) x n <br /> The mass of water, m, in the volume vol is <br /> (3) m = vol x (density of water) <br /> The macro-velocity v is given by <br />' (4) v — qln <br />' where q is the Darcy velocity, which is based on calculations using Darcy's law and k is the <br /> hydraulic conductivity <br /> MZ/04-06-95/UST/95-0089 APP 1 <br />