Modeling Water Table Mounding to Design Cluster and High-Density Wastewater Soil Absorption Systems

Abstract

Water table mounding warrants consideration in the design of cluster and high-density wastewater soil absorption systems (WSAS). Use of iterative analytical solutions with the design approach presented here provides a useful initial assessment of the potential for mounding beneath a WSAS, but cannot account for anisotropy, heterogeneity, regional flow, and local hydraulic boundaries. The relative influence of these factors may not be intuitive, but can be evaluated with site-specific numerical models in cases where the failure of these systems may have severe consequences. There is a greater difference of calculated mound height for isotropic analytical solutions and anisotropic numerical solutions in low hydraulic conductivity materials and thicker aquifers. In all cases, increased vertical anisotropy increases mounding, but not nearly as much as would be calculated by using the vertical hydraulic conductivity value for hydraulic conductivity in the analytical solution. Increased gradient has less influence on mound height in thicker aquifers.