Final Report: Moving Towards a Sustainable Campus: Design of a Green Roof Monitoring ExperimentEPA Grant Number: SU832507
Title: Moving Towards a Sustainable Campus: Design of a Green Roof Monitoring Experiment
Investigators: Reese, Margaret , Brynildsen, Vickie , Dodds, Krystian , Malcolm, Elizabeth , Ozmon, Ivy , Redding, Tara , Rowe, Michelle , Schaus, Maynard H.
Institution: Virginia Wesleyan College
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: September 15, 2005 through April 30, 2006
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2005) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Built Environment , Pollution Prevention/Sustainable Development , P3 Awards , Sustainability
Virginia Wesleyan College is currently in the design phase for construction of a new green science building. The science and mathematics faculty have identified the new building as an opportunity for our students to learn about sustainable design and to contribute to the building plans. The building will also be a pedagogical tool when completed, with interactive displays on green design and ongoing measurement and monitoring of the building’s environmental impact. As a first step towards this goal we initiated a green roof monitoring experiment to inform the designs of green roofs for campus buildings.
The wide-ranging benefits of green roofs to people and the planet include reduced stormwater runoff, reduced heat-island effects, reduced atmospheric carbon dioxide, and improved energy conservation. Of these benefits, the most apparent has been stormwater reduction, which can minimize risks from flooding, and in areas with combined sewer overflows, prevent water pollution. As such vegetated roofs are increasingly used as a best management practice (BMP) in stormwater management. Despite these P3 benefits, little research had been done on runoff quality. Previously it has been assumed that reduced runoff volume would cause reduced runoff of total pollutants.
The goals of Phase I were 1) to assess the benefits of installing green roofs on our campus buildings, 2) to optimize the design of green roofs in our region, and 3) to recommend a roof design to the college for implementation on older buildings scheduled for roof replacement and for the new science building.
We conducted a preliminary study using fifteen 2.5 x 4 ft test roof plots to compare green roof configurations and measure the impact of green roofs on water quality. Five treatments were chosen for the test roofs, with three replicates of each: green roof, green roof with a waterretention layer, green roof with a drainage layer, green roof with both water-retention and drainage layers, and conventional gravel-covered built-up roof (BUR).
We found that all green roof treatments significantly reduced stormwater runoff as compared to the conventional roof treatment in every analyzed rain event (p<0.0001). The volume of runoff was not significantly different among the four green roof treatments.
In one of the first studies on green roof runoff quality, we found that green roofs may actually increase nutrients in runoff depending on implementation and fertilizer application to the roof. We were surprised to find high concentrations of total nitrogen in every green treatment (1.8-29 mg/L). Conversely, concentrations in precipitation and the gravel roof runoff were always below the detection limit (0.5 mg/L). It is likely that fertilizer had been added to the commercially purchased pre-vegetated pods to establish the plants. The concentrations measured in the green treatments decreased over time from a mean of 19 mg/L in November to a mean of 4.5 mg/L in January indicating that the fertilizer levels were decreasing. This indicates that green roofs as constructed in our study are a source of nitrogen to a watershed. Similar results were seen for total phosphorus with higher concentrations from the green roofs than from the rain or gravel roof suggesting that fertilized green roofs are a source of phosphorus.
The concentration of mercury in the runoff from the green roof plots was, as hypothesized, significantly higher than the concentration in the runoff from the control. The green treatments did not significantly differ from each other. Preliminary findings however suggest that the reduction in volume of runoff from a green roof compensates for the higher concentration; that is, the total load of mercury seems not to be increased by the green roof treatment as compared to a standard gravel roof. Furthermore, the total nanograms (ng) of mercury estimated to have been deposited to the roof by rain was less than that of the runoff for both rain events sampled. Many questions remain about what will happen to the retained mercury. Will it re-vaporize, adsorb to the plants, or wash out in the next storm?
Integration of P3 Concepts as an Educational Tool
The test roof plots have high-visibility on campus, located between the library and student center in the heart of the campus. Students, faculty, staff, and visitors witnessed the progress of the project as team members built the plots and collected samples. This display built excitement for student research and P3 concepts in the campus community. The biggest challenge to the success of our project is also one of its biggest accomplishments: involving a large number of students. More than 35 students and faculty from three departments were directly involved in this project, which was integrated into several courses. Our project has been hugely successful in bringing the message of sustainability to our campus.
Our most intriguing finding from Phase I of this project was that although a typical green roof has many P3 benefits, it can negatively impact local and regional surface water quality. This is particularly important for locations in sensitive watersheds such as the Chesapeake Bay. We have determined in Phase I that the special enhancements for retention and drainage offer no significant benefit to runoff volume over the green treatment without these layers. Preliminary data also suggests that with simple modifications green roofs can have minimal impacts on mercury runoff. We plan to continue our study through summer 2006 to confirm these findings and investigate whether runoff quality changes during the growing season.