Assessing the continuing performance of the trench infiltration rates is one of the major areas of research focus currently underway at Villanova University. Since the conception of the Villanova University Infiltration Trench, the performance of the trench has seen a significant reduction in infiltration rates. The investigation into this reduction in infiltration rates is a very complex issue. Causes may include seasonal effects, clogging due to sediment, or the system moving toward an equilibrium state. When investigating this reduction in infiltration rates, one very important design aspect to consider is the overall "under sizing" of the design of this site. The ratio of the drainage surface area to the trench surface area is nearly 160:1, which is a considerably large ratio thus possibly making our trench an "accelerated" research test site. It is important to note that, despite seeing decreasing infiltration rates, it is functioning, and does empty.

A simple look at the monthly plots of the depth of water within the trench since 2004 shows the decline in the infiltration rates. In the below plots, the red line represents the depth of water within the trench and the blue lines represent the rainfall. (Click on the links to see an enlarged plot of the monthly data.) Note that the trench is 6 feet deep and there is an overflow pipe at 5.2 feet.
 

As depicted in the above plots, the infiltration rates (especially at lower levels within the trench) have decreased since the trench was put into operation in July 2004. The time it takes for water to drop from the 3-0 foot range has increased. The decrease in infiltration rates for the bottom 3-0 feet, but the relatively constant infiltration rates in the upper 6-3 feet suggests that the bottom of the trench has become impaired by pollutant loading, however the water is still successfully seeping out the side walls without the detriment of "clogging" pollutants. This may be a normal process in infiltration trench life spans and needs to be investigated further. Pollutant loading (especially regarding total suspended and dissolved solids) within the trench has become a major area of research focus at Villanova University for investigating the performance of infiltration trenches.

Another interesting phenomena observed since the conception of the Villanova Infiltration is the varying of the infiltration rates with respect to temperature/season. The below plot shows the average infiltration rates from 1.5 to 0.3 feet within the trench from May 2005 to April 2006. From the plot it can be seen that the infiltration rates are typically the highest in the late summer/early fall seasons, and the lowest infiltration rates are typically observed in the spring.

Figure 1. Seasonality of Single Event Infiltration Rates from the 1.5 to 0.3 Feet Depth