Underground Aggregate Stormwater Infiltration Bed Case Study

Stormwater infiltration systems, such as permeable pavement systems, are strategies for runoff reduction and flood mitigation, especially within urban environments, but there are still unknowns as to their efficacy in regions with low infiltration rates in the subgrade soils. This research developed a model for the infiltration of underground stormwater infiltration beds based on a percolation constant (kp) and used the model on field data from two sites with soils that have low saturated hydraulic conductivity, one in Pullman, Washington, and one in Beaumont, Texas. The model was converted into a linear function and the data in Pullman fit this well. At the Beaumont site, the linear behavior diverged when the water in the infiltration bed was level with ponded water on the surrounding grounds, implying groundwater head impacts. In Beaumont, the infiltration rates had decreased after one year of measurement prompting interest in further long-term studies. The relationship between measured percolation rates (kp) versus saturated hydraulic conductivity (KH) was explored at these two sites and from the literature on other urban underground infiltration systems such as onsite wastewater treatment systems (OWS). These systems may function in urban areas where the soil has low saturated hydraulic conductivity, but the systems may be affected by partially saturated conditions in the surrounding area, and the percolation constant is typically much higher than the saturated hydraulic conductivity.