Infiltration Rate Response to Accumulation of Fines in a Stormwater Bioinfiltration Basin.

Engineered best management practices (BMPs), such as rain gardens and bioinfiltration basins, are designed to infiltrate stormwater runoff and reduce pollutant transport to surface waters. These BMPs are thought to have a limited effective lifespan based on the composition of sediments in runoff water. Settling of fine sediments may clog soil pore spaces, reducing the infiltration capacity of the soil, and reducing the potential benefits of this BMP. A study was conducted on a Villanova campus parking lot bioinfiltration basin to determine the impact accumulation of fine sediments over time has on infiltration capacity and BMP function. Excavated soil from the site, characterized as a silty loam, was mixed at a 1:1 ratio with coarse sand to produce a silty sand soil. The soil textural profile was characterized prior to BMP installation, after five years, and after seven years of receiving stormwater runoff. Infiltration data was collected both by the single ring infiltrometer method two times during the study, as well as throughout the study using an ultrasonic pressure transducer.  Accumulation of surface soil organic carbon and total nitrogen content were also measured. Heterogeneous accumulation of fines within the basin over the study period were observed, which were related to single ring infiltrometer tests.  Implications for BMP effectiveness will be discussed.