Treatment Train

Executive Summary

Construction of the treatment train began in the fall of 2011. The location of the treatment train is on the eastern side of the Saint Augustine Center (SAC) parking garage. This area was chosen as the site for the treatment train to allow stormwater runoff to be routed from the parking garage to the treatment train. The treatment train includes a vegetated swale, two rain gardens in series, and an infiltration trench (IT). The main goals of the construction and research of the treatment train were:

  • To collect and infiltrate runoff from the upper deck of the adjacent bi-level parking garage
  • To examine water quantity and quality effects of stormwater control measures (SCMs) in series
  • To determine if applying SCMs in series decreases maintenance needs and increases system longevity
  • To improve the common area’s aesthetic appeal and function for the University

A network of PVC pipes collect runoff from approximately one quarter of the SAC parking garage (10,000 ft2). The flow is routed into a concrete weir box where debris and sediment can settle out prior to entering the treatment train.  A series of baffles plates and a v-notch weir steady the flow of runoff entering the system to allow for accurate flow measurements.  Rrunoff then enters the vegetated swale, followed by two rain gardens in series and an IT. There are pervious pavers on top of the infiltration trench to allow overflow to flow out of the top of the trench and into an adjacent storm sewer. Six monitoring locations and five 90 degree v-notch weirs throughout the treatment train provide flow measurements and sampling points throughout the system.

Aerial of the treatment train
Figure 1. Aerial of the treatment train (Adapted from Google Earth) Green, yellow, and red arrows signify the swale, rain gardens, and infiltration trench, respectively. White arrows indicate monitoring and sampling points.

The monitoring and research conducted at the treatment train currently focuses on water quantity. The site has been instrumented to record rainfall, flow rates through the system, temperature, and depth within the IT. These parameters are being used to determine how effectively the treatment train is reducing stormwater runoff volume and peak flows from the parking garage runoff. Additionally, infiltration and recession rates in the IT at the treatment train are monitored to determine the effect of using multiple SCMs for pretreatment has on system longevity and maintenance. Future research will focus on water quality and the performance of each SCM at the treatment train.

The treatment train site prior to construction
Figure 2. The treatment train site prior to construction
Figure 3: The completed treatment train site
Figure 3: The completed treatment train site

Budget and Funding

Funding for this project came from the Pennsylvania Department of Environmental Protection 319, Non-Point Source Pollution Program. A table outlining the total construction costs is provided below. Construction of the treatment train began in the fall of 2011. Villanova University contributed substantial matching funds to the project.

Funding

The pervious pavers for the Infiltration Trench were donated by Xeripave. The construction costs do not include research and monitoring equipment costs. Thanks to the Villanova Facilities Management office for their help in the construction process.

Design Components

The treatment train is located to the east of the SAC bi-level parking garage.  The drainage area is approximately 10,000 ft2 and 100% impervious.  The treatment train was designed to capture and control a 1 inch storm over the entire contributing drainage area.  Each component of the system was designed to capture approximately one third of the total design volume.  Table 1 summarizes the capture volume for each SCM in the treatment train.

Table 1: SCM design summary and capture volumes
Table 1: SCM design summary and capture volumes

The weir box is the first piece of the treatment train as it serves as the collection point for stormwater from the contributing drainage area.  A network of PVC pipes route runoff from the parking garage to the weir box.  A series of two baffle plates are designed to steady the flow of runoff coming into the weir box to allow more accurate readings from instrumentation.  At the most downstream end of the weir box is the first of five 90 degree v-notch weirs.  The flow of runoff going through the system can be calculated using water depth readings from a level sensor and the v-notch weirs.

Figure 1: Weir box
Figure 1: Weir box

The vegetated swale is the first SCM in the series at the treatment train.  The swale begins at the weir box and is approximately 120 feet long.  Engineering media was used for the swale construction and is composed of 85% sand, 10% fines, and 5% organics.  The same engineered media was used for the rain gardens in the treatment train as well.  There is a 90 degree weir plate halfway through the swale and at the downstream end along with instrumentation to provide flow rates as water passes through the system.  The bottom width of the swale is approximately one foot and side slopes are at a 2:1 ratio.  Soil capacity in the swale is considered minimal and is a source of additional capture potential.  

Figure 2: Vegetated Swale
Figure 2: Vegetated Swale

Following the vegetated swale are two rain gardens in series.  Elliptical in shape, the rain gardens longer lengths run in the direction of flow.  The rain gardens have a bottom width of three feet and a bottom length of six feet.  The engineered media fill depth is approximately 18 inches with an additional 18 inches of ponding depth.  Side slopes are approximately 2:1.  Each rain garden is designed to capture 0.2 inches of rain.  Rain garden capture design volume is based  only on storage above the soil surface.  There are weir plates at the end of each rain garden, which are intended for flow measurements as well as water quality grab sample points.  

Figure 3: Rain garden sketch
Figure 3: Rain garden sketch

The infiltration trench serves as the final SCM in the treatment train.  Formed from crates known as R-Tanks by the manufacturer ACF Environmental, the infiltration trench covers an area of approximately 6.56 feet by 9.38 feet and is just over 4.2 feet deep.  The R-Tanks, have 95 percent porosity and are designed to store the final 0.3 inches of a 1 inch storm.  The design of the infiltration trench intentionally does not include an under drain or an overflow system.  The trench is designed with 30 Xeripave pervious pavers with a flow rate over 1 gallon per second per square foot at the surface to serve as the overflow.  When the infiltration trench is filled, water flows through the pavers and over the downstream curb to the storm sewer system.   

Figure 4: R-Tank
Figure 4: R-Tank
Figure 5: infiltration trench with Xeripave pavers
Figure 5: Infiltration trench with Xeripave pavers

Instrumentation for water quality and quantity monitoring of the site was incorporated into the design from the onset of the project.  Rainfall is measure with a tipping bucket rain gage located on the roof of the parking garage. Flow through the system is measured with pressure transducers and other instrumentation, and aluminum 90 degree v-notch weirs located throughout the system. The weirs were purchased from Rickly Hydrological CO. and were designed to USGS standards. The pressure transducers used at the treatment train also provide temperature readings. Inflow to the infiltration trench from the second rain garden is conveyed via a 12 inch diameter plastic pipe.  

Construction

The construction of the treatment train included excavation of the vegetated swale, rain gardens and the infiltration trench. An erosion control mat was used to stabilize the vegetated swale and keep topsoil and media in place. The planting plan for the vegetated swale and rain gardens consisted of approximately 1,000 plants selected by the Villanova University campus horticulturalist.  Layers of stone and geotextile matting were added to the infiltration trench. The most downstream rain garden in the system and the infiltration trench were connected via a 12 inch plastic pipe. 

Figure 1: Site conditions before construction.
Figure 1: Site conditions before construction.
Figure 2: Excavation of swale and rain gardens.
Figure 2: Excavation of swale and rain gardens.
Figure 3: The Infiltration Trench was outlined and excavated with a backhoe.
Figure 3: The Infiltration Trench was outlined and excavated with a backhoe.
Figure 4:Once the IT excavation was completed, the trench was lined with geotextile and stone before R-Tanks were inserted.
Figure 4:Once the IT excavation was completed, the trench was lined with geotextile and stone before R-Tanks were inserted.
Figure 5: Installation of pipe going into IT.
Figure 5: Installation of pipe going into IT.
Figure 6: Placements of v-notch weirs for system monitoring.
Figure 6: Placements of v-notch weirs for system monitoring.
Figure 7: Placement of erosion control matting and planting.
Figure 7: Placement of erosion control matting and planting.
Figure 8: Completed treatment train.
Figure 8: Completed treatment train.

Storm Events

One of the research goals for the treatment train was to determine how a system of SCMs in series performed at reducing the quantity of runoff from an impervious area.  Furthermore, performance of the infiltration trench at the treatment train will be monitored over time and compared to the infiltration trench on Villanova’s campus that was constructed in 2004.  The volume and infiltration rates in the infiltration trench at the treatment train are monitored using a pressure transducer to determine the height of the water in the trench at a given time.  The following examples illustrate monitoring of the treatment train infiltration trench during storm events.

Figure 1: Superstorm Sandy IT depth and rainfall data.  There was approximately 4.3 inches of rain over 67 hours at the treatment train.
Figure 1: Superstorm Sandy IT depth and rainfall data. There was approximately 4.3 inches of rain over 67 hours at the treatment train.
Figure 2: Picture of the most downstream rain garden on October 30, 2012 during Superstorm Sandy.
Figure 2: Picture of the most downstream rain garden on October 30, 2012 during Superstorm Sandy.
Figure 3:  IT depth and rainfall data for the March 12, 2013 storm.  There was approximately 1.2 inches of rain over 12 hours.
Figure 3: IT depth and rainfall data for the March 12, 2013 storm. There was approximately 1.2 inches of rain over 12 hours.
Figure 4: The downstream portion of the vegetated swale and the two rain gardens during the March 12, 2013 rain event.
Figure 4: The downstream portion of the vegetated swale and the two rain gardens during the March 12, 2013 rain event.

Performance

Assessing the performance of the treatment train has focused on several factors.  The total system performance has been monitored for large storm events to determine the runoff volume capture of the entire system compared its design.   The treatment train seems to perform better than expected during large storms events.  For example, there was approximately 4.3 inches of rain during Superstorm Sandy.  Although the treatment train was designed to capture 1 inch of rain, the total system captured approximately 98 percent of the volume of runoff from the drainage area during Superstorm Sandy.  Capture performance during rain events seems to be linked to rainfall intensity, temperature, and antecedent soil moisture.

Figure 1: Total system performance based on system capture volume over total runoff.  Expected system capture is shown as a basis for comparison.
Figure 1: Total system performance based on system capture volume over total runoff. Expected system capture is shown as a basis for comparison.

Additionally, performance of the treatment train is monitored through determining infiltration and recession rates at the IT.  Pretreatment from the vegetated swale and two rain gardens allows sediment and pollutants to be removed from runoff prior to entering the IT.  The goal is to increase the longevity and reduce maintenance at the IT by removing sediment, debris, and pollutants that could potentially decrease system performance.  Infiltration rates over time will be compared with data from the IT constructed at Villanova in 2004.  Current research has shown that infiltration rates are dependent on seasonal temperatures.  Figure 2 illustrates the seasonal effect on the infiltration rates.  As temperatures increase, infiltration rates generally increase as does variability.  However, there is a decrease in infiltration rates and variability during colder temperatures.

Figure 2: Infiltration rates and temperature in the IT.
Figure 2: Infiltration rates and temperature in the IT.

Infiltration rates and total system performance during storm events will continue to be monitored during research.  Further research will include quantitative and qualitative analysis of each specific SCM performance in the treatment train.

Frequently Asked Questions

Q: What is the BMP's drainage area?

A: The contributing area is approximately 10,000 ft2. The area consists of a Villanova University parking deck and is 100% impervious.

Q: What watershed is the site located in?

A: The Infiltration Trench is located in the headwaters of the Mill Creek watershed which drains into the Schuylkill River. Both of which are part of the Delaware River watershed.

Q: What kind of maintenance is required?

A: Sediment and small debris periodically (monthly basis) need to be removed from the weir box.  Plants are trimmed in the vegetated swale and the rain gardens during the early spring before the growing season begins.  Additionally, instrumentation should be calibrated several times a year.

Q: How is the inflow monitored for the BMP?

A: The inflow is monitored using a Gem’s XT-1000 float level sensor and a V-notch weir. The weir equation can be applied to the XT-1000 readings to calculate the flow.

Q: What water quality parameters have been monitored at this BMP?

A: pH, Conductivity, Copper, Total Nitrogen, Total Phosphorus, Chloride, Total Suspended Solids, and Total Dissolved Solids.

Q: What depth of rainfall was this BMP designed for?

A: The treatment train was designed for a 1 inch rainfall event.  Each SCM within the treatment train was designed to capture approximately one third of the total volume from a 1 inch rainfall event.   

Q: What happens to this BMP when the rain event exceeds design limits?

A:  The treatment train has performed better than anticipated by often capturing storms greater than 1 inch.  However, overflow can occur during large storms or very intense rainfalls.  The IT at the treatment train is designed so water can flow through the top, over an adjacent curb, and into the storm sewer system.  Runoff that overflows the systems drains through the storm sewer system to a constructed wetland downstream.  

Q: What size rain events typically create overflow from the BMP?

A:   There is not one specific size rain event that creates overflow at the treatment train.  Overflow can occur during storms larger than 1 inch, during high intensity rainfall events, during colder winter months, or when multiple rain events occur within a short amount of time. 

Q: What factors have shown to have the greatest effect on the performance of this BMP?

A: Similarly to the IT constructed in 2004, research at the treatment train has shown that system performance responds to temperature, antecedent dry time since the last rain event, rain event duration, and total precipitation. 

Q: How were the plants used at the treatment train selected?

A: Plants were selected for the treatment train by the Villanova campus horticulturalist and are intended to provide stabilization of the soil.  The plants were chosen based on the soil type and the wet-dry conditions at the site.