The Robinson’s Branch is a tributary of the Rahway River located in Union and Middlesex Counties. Its watershed is approximately 22 square miles and over 80% of the land use is urban.Rutgers Cooperative Extension Water Resources Program (RCE WRP) completed a Regional Stormwater Management Plan for the Robinson’s Branch Watershed. In 2010, a 319 (h) nonpoint source pollution reduction grant was awarded to Rutgers Cooperative Extension (RCE) of Union County and the WRP in cooperation with the Township of Clark to implement a portion of the plan. One of the goals of the project is to disconnect impervious surfaces and treat stormwater runoff from the 1.25” rainfall event. An additional goal is to use the implementation projects to demonstrate how stormwater can be managed using green infrastructure techniques in heavily urbanized communities of New Jersey.
Green Infrastructure Implementation
Green infrastructure is an approach to managing stormwater by infiltrating it in the ground where it is generated using vegetation or porous surfaces, or by capturing it for later reuse. There are many benefits to green infrastructure including reducing stormwater volume, decreasing impervious cover, and reducing nonpoint source pollution. In addition, green infrastructure can help save money by reducing energy costs, maintenance, and reducing potable water demand.
Working closely with Clark Township, project partners identified two municipal properties to disconnect within the watershed using green infrastructure practices; the public works building and the town hall parking lot. Both of these properties, in addition to Arthur L. Johnson High School, are located next to each other on the banks of the Clark Reservoir, part of the Robinson’s Branch stream.
The first project focused on the new town hall parking lot. The township’s engineering department (Grotto Engineering Associates, LLC), worked with RCE WRP to design and install 650 ft2 of permeable asphalt in the lot. The project was installed in the spring of 2012 by a subcontractor. In order to reduce costs, conventional asphalt was used in the driving lane, and a 4” layer of permeable asphalt was used in the parking spaces and gutter. Sub-base materials consisted of a 6” choker coarse layer to help remove sediment, and a 20” reservoir coarse layer to provide storage. The reservoir layer was designed to be deeper than normal because of the underlying clay soils, which are slow to drain. Additionally, a perforated, 4” underdrain pipe was installed in the reservoir to carry excess drainage to the storm drain inlet.
In a 1.25” rainfall event, approximately 10,000 gallons of water will be captured for potential infiltration via the 1,233 ft2 parking lot. This project demonstrates how green infrastructure practices can be utilized to reduce stormwater runoff in communities with poorly drained soils.
Figure 2. Image shows porous aspahlt in parking lanes and conventional asphalt in the driving lane.
The second project focused on the public works building and installing a 5000 gallon cistern to store water for washing public vehicles. In addition, the students at Arthur L. Johnson High School in Clark were in need of a more environmentally friendly method for holding their car wash fundraiser events. The high school students and local youth groups frequently use the high school parking lot to hold car wash fundraiser events. Based on personal communications with the township and youth groups, over 100 cars are washed at each of these events discharging polluted car wash runoff directly into the storm drain. Car wash runoff has been shown to be a source of petroleum hydrocarbon waste, heavy metals, phosphorus, nitrogen, ammonia, total suspended solids (TSS), and surfactants from car wash soap. In an effort to reduce polluted runoff, conserve water, and facilitate more environmentally friendly car wash events, this “green” car wash was designed and installed in the fall of 2011 and spring of 2012. The car wash consists of:
• A 5000 gallon cistern that harvests stormwater runoff from the roof of the 4,900 ft2 public works building. With the help of a booster pump, harvested stormwater is used to wash cars and public works vehicles;
• A concrete vehicle wash pad where cars and public works vehicles are washed and a swale that discharges dirty car wash runoff to a rain garden;
• A 360 ft2 rain garden located next door in the high school parking lot. Car wash pollutants that would have otherwise discharged directly to the stream are now removed by the rain garden. Due to the slow draining, clay soils, the rain garden was installed with a 4” perforated underdrain that flows to a storm drain overflow and connects to a french drain in the adjacent soccer field.