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i may be an over-estimate due to the fact that monitor well MW--5 is <br /> not directly downgradient of MW-4 . <br /> K = Degradation Decay Rate = 2 . 303/t log(a/a--x) <br /> where: a = initial concentration = 10, 000 ppb - MW-4 , <br /> April 13 , 1989 <br /> a-x = reduced concentration = 2300 ppb - MW-5 , <br /> July 12 , 1989 <br /> t = d/v = 30 ft/0 . 02 ft/day = 1500 days <br /> 2 . 303 = constant of the equation <br /> K = 0. 001 days-' <br /> K = 0. 693/tin <br /> tI�2 M 6 9 3 days <br /> The degradation/attenuation decay rate is likely the product of a <br /> variety of processes, including biodegradation, dilution, <br /> adsorption, volatilization and abiotic chemical reactions such as <br /> hydrolysis. <br /> 3) Calibration of the model <br /> Calculated maximum dissolved benzene concentrations expected in <br /> monitor well MW--3 ; assuming that MW-3 is directly downgradient of <br /> theresumed source MW-4. <br /> p , <br /> K = 2 .303/t log(a/a--x) <br /> where: a = 101000-ppb - MW--4 , April 13 , 1989 <br /> a-x = calculated reducedwcdncentration, MW-3 <br /> t = d/v = 28 ft/0. 02 ft/day ~1400 days <br /> K = 0. 001 days-' <br /> a-x = calculated maximum benzene concentration = 2580 ppb <br /> The maximum observed dissolved benzene concentration in MW-3 is <br /> 2700 ppb, measured on November 15, 1988. The similarity of the <br /> calculated benzene concentration with that observed in the well <br /> suggests that the derived degradation/attenuation rate is adequate <br /> for further calculations at the site. <br /> 4 <br />