Infiltration Trench

Executive Summary

Construction of the infiltration trench began in the spring of 2004. The SCM was retrofitted into a small area between an academic building and a parking garage. Previously the area had a steep eroding slope and was considered unsightly by the University. The original stormwater system of the parking garage directed runoff through piped gutters and concrete channels directly into the road where it entered inlets and was piped to a local stream. There were three main components included in the design for the Infiltration Trench:

  • To collect and infiltrate runoff from the upper deck of the adjacent bi-level parking garage.
  • To provide sufficient research and demonstration opportunities for students to study the BMP’s hydrologic and water quality performance.
  • To improve the common area’s aesthetic appeal and function for the University.

Before the Infiltration Trench was built, a retaining wall was erected to stop the erosion of the adjacent slope. The SCM’s construction entailed the excavation of the trench, lining the trench with a geotextile, filling the trench with stones to provide temporary storage, and finally the laying of EP Henry Eco-Pavers to create a pervious patio area for student and staff of the University.

A network of PVC pipes collect runoff from approximately half of the parking garage (~1/2acre). The flow is routed into a monitoring bench where debris and sediment are removed. The flow is also measured and water samples can be taken inside the bench. The flow then enters a perforated distribution pipe where it is released into the stone bed. The stone bed provides temporary storage as the water slowly soaks into the surrounding soil. At the top of the storage bed there is an overflow pipe that allows flows in excess of the capacity of the trench to flow into an existing stormwater inlet. During extremely intense periods of rainfall the porous paver patio acts as a secondary overflow and the water flows over a grass strip and into the same stormwater inlet. One topic that has been investigated through the research at the Infiltration Trench is what the longevity of the system is. In order to maintain the infiltration capacity of the soil it is necessary to remove as much sediment and debris as possible. The inflow at the Infiltration Trench carries some small debris and sediment. Inside the pretreatment / monitoring bench, a system of flow baffles and screens help remove the trash and sediment that would otherwise find its way into the stone bed.

The monitoring and research conducted at the Infiltration Trench focuses on both water quantity and water quality. The site has been instrumented to record rainfall, inflow, temperature, and depth within the stone storage bed. These parameters have are being used to document how effective the SCM is at reducing the volume of runoff from the parking garage. Groundwater samplers (lysimeters) were installed at two and four feet beneath the bottom of the trench.  These water samples along with samples taken from the inflow and from within the storage bed make it possible to study the water quality benefits provided by the site.  Research at the infiltration trench has focused on the performance over time in an urban setting.  As of 2014, past data from the infiltration trench is being used to compare the performance of the infiltration trench at the treatment train.

Figure 1: The Infiltration Trench Site Prior to Construction
Figure 1: The Infiltration Trench Site Prior to Construction
Figure 2: The Completed Infiltration Site
Figure 2: The Completed Infiltration Site