THE POTENTIAL FOR PERMEABLE PAVEMENT TO MITIGATE STORMWATER RUNOFF AT SMITH COLLEGE, NORTHAMPTON, MA

Higher precipitation associated with climate change together with expanding impervious surfaces associated with urban and suburban development is increasing stormwater runoff and reducing groundwater recharge. This coupled with an aging stormwater infrastructure is driving municipalities like the City of Northampton to introduce annual fees for property owners that are charged on the basis of the percentage of their land covered by impervious surface. Permeable pavement offers a potential solution to this problem

Permeable pavement systems have two principle components, a permeable surface material either asphalt or concrete based, overlying a porous base material that serves as a storage reservoir for infiltrated water. The most effective systems allow stored water in the porous reservoir to infiltrate into the surficial geologic units upon which the systems are built.

Understanding the surficial geology of an area is essential for determining where permeable pavement can be successfully deployed. The Smith College Campus is located within the area of Glacial Lake Hitchcock that occupied the Connecticut River Valley at the close of the last glaciation. The entire Smith campus lies at elevations lower than the stable surface elevation of the lake (75m) so it might be expected that impermeable varved clays would dominate. But a 57m surface on the upper part of the campus represents a delta built into a late stage, lower level of the lake. Topset and foreset sands beneath this surface produce high infiltration rates within the subsoil. A lower surface, at 52m, was subsequently cut by the Mill River after the lake drained, and this erosion removed the delta sands exposing the underlying varved clays, making subsoils here relatively impermeable.

A permeable pavement experiment is currently being conducted on a small (12 vehicle) Smith College parking lot. Instrumentation at the site will monitor water levels in the underlying porous reservoir and runoff from the parking lot surface. Lysimeters will collect samples of infiltrated water that will be used to evaluate the ability of the system to attenuate chemical contaminants.