Location: The bio-infiltration area is located in a grassy traffic island in the parking lot of Villanova's West Campus. The West Campus parking lot serves a dormitory complex and a recreation area. The traffic island was retrofitted into the shape of a shallow bowl, allowing the inflow of water to accumulate within.

The drainage area is approximately 1.21 acres , with 52 percent impervious cover.

Figure 1: Drainage area site plan

Figure 2: As built contour drawing

Drawn by William Heasom, PE

Bio-infiltration: Bio-infiltration is accomplished by using a combination of porous soils and vegetation. The area consists of a 4-foot layer of sand mixed with the existing soil located at the traffic island. The species of vegetation planted at the site can survive in both dry and wet conditions over long periods of time. The area also has a grass buffer zone extending from the curb to the sand.

Figure 3: Essential features of a bio-infiltration basin

Table 1:  Vegetation grown within the traffic island

Design Calculations: The total volume of the excavation, as well as the volume of the sand/soil fill are calculated in the table below. Using a range of porosities, the volume of void spaces in the fill was calculated.

Table 2: Volumes and porosity

Inflow: Inflow was controlled by making two cuts in the curbs as shown in Figure 1 and 2. Placement of these cuts was determined by observing the flow of runoff on the parking lot. The inlet for the storm sewer on the north end of the pond was filled with gravel and then sealed with asphalt. A second curb cut was made where the now-filled inlet is located. The curb cuts were connected to the pond via channels lined with rip-rap. A 12" corrugated black PVC pipe was installed in the south inlet. It diverts flow in the storm sewer into the bio-infiltration pond. A diversion weir was placed in the inlet. The elevation of the weir determines the maximum water surface elevation in the pond. When this elevation is reached all additional incoming flows will bypass the pond and continue downstream to an existing detention basin.

Figure 4: Profile of Bio=Infiltration Basin

Weir Construction: To better monitor the amount of runoff captured, a V-notch weir was inside the south inlet. The weir was machined from an 18-inch square aluminum plate. The top width of the weir is 9 inches and the maximum head on the weir is 9 inches. The weir design was based on ASTM standards.