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U <br /> 4 ' <br /> RISKPRO'S SESOIL for Windows User's Guide <br /> The SESOIL hydrolysis' algorithm allows the simulation of neutral, acid- or base-catalyzed <br /> reactions and assumes that both dissolved-and adsorbed pollutant are susceptible to hydrolysis ' <br /> (Lyman et al., 1982). Since hydrolysis is,the reaction of the pollutant with water, this reaction <br /> may occur at any"depth as the pollutant moves through the soil coldmn. The-hydrolysis I <br /> subroutine requires user-supplied rate constants for the neutral, acid and base hydrolysis <br /> reactions of the pollutant, and the pH for each soil layer. ,The model does not correct for the <br /> temperature of the modeled soil ' <br /> As for the biodegradation process, the-algonthm,for hydrolysis uses Eq. (15), except that the <br /> rates ku and k,, are both replaced by the rate constant Ich, defined as (from' Bonazountas and f <br /> Wagner, 1984): <br /> kh= ko+kH[H+]+kOH[OH-] (16) <br /> where- <br /> kh = the hydrolysis rate constant (day-) <br /> ko = rate constant for neutral hydrolysis (day'') ' <br /> kH = rate constant for acid-catalyzed hydrolysis (days-'moPQ <br /> (H+J = 10 pH, the hydrogen ion`concehtration,(mol/L) " <br /> kOH = rate constant for base-catalyzed hydrolysis (days'mol`L) <br /> [OH-] = IOP"", the hydroxyl ion concentration (mol/L) <br /> If cation exchange is considered, the following formula is used <br /> - _ - - W -P =-MCEC 4 k p A d :a t - - (17) I <br /> d h b s <br /> where the parameters are as defined for Eqs (9), (14), (15), and (16) ' <br /> Extrapolating hydrolysis rates measured in a laboratory to the environment increases the ' <br /> uncertainty of model results if the hydrolysis rate is not corrected for the influences of <br /> temperature, adsorption, the soil ionic strength, and the possible-catalytic effect of dissolved <br /> material or solid surfaces Since there are usually laze uncertainties in hydrolysis rates the <br /> � g <br /> SESOIL model results for hydrolysis should be considered only as approximations. The rate of <br /> hydrolysis for'vanous organic chemicals may vary over more than 14 orders of magnitude. In ' <br /> addition, the hydrolysis routine does not consider the influence of ionic strength or the presence <br /> of other dissolved organics on the hydrolysis rate of the pollutant. <br /> I <br /> Page 28 <br /> I <br />