Analytical models of steady-state plumes undergoing sequential first-order degradation

An exact, closed-form analytical solution is derived for one-dimensional (1D), coupled, steady-state advection-dispersion equations with sequential first-order degradation of three dissolved species in groundwater. Dimensionless and mathematical analyses are used to examine the sensitivity of longitudinal dispersivity in the parent and daughter analytical solutions. The results indicate that the relative error decreases to less than 15% for the 1D advection-dominated and advection-dispersion analytical solutions of the parent and daughter when the Damköhler number of the parent decreases to less than 1 (slow degradation rate) and the Peclet number increases to greater than 6 (advection-dominated). To estimate first-order daughter product rate constants in advection-dominated zones, 1D, two-dimensional (2D), and three-dimensional (3D) steady-state analytical solutions with zero longitudinal dispersivity are also derived for three first-order sequentially degrading compounds. The closed form of these exact analytical solutions has the advantage of having (1) no numerical integration or evaluation of complex-valued error function arguments, (2) computational efficiency compared to problems with long times to reach steady state, and (3) minimal effort for incorporation into spreadsheets. These multispecies analytical solutions indicate that BIOCHLOR produces accurate results for 1D steady-state, applications with longitudinal dispersion. Although BIOCHLOR is inaccurate in multidimensional applications with longitudinal dispersion, these multidimensional multispecies analytical solutions indicate that BIOCHLOR produces accurate steady-state results when the longitudinal dispersion is zero. As an application, the 1D advection-dominated analytical solution is applied to estimate field-scale rate constants of 0.81, 0.74, and 0.69/year for trichloroethene, cis-1,2-dichloroethene, and vinyl chloride, respectively, at the Harris Palm Bay, FL, CERCLA site.