State Water Resources Research Institute Program


Project ID: 2011OK213B
Title: Investigation of the Viability of Rainfall Harvesting for Long-term Urban Irrigation: Bioaccumulating Organic Compounds and the First Flush in Rooftop Runoff
Project Type: Research
Start Date: 3/01/2011
End Date: 2/29/2012
Congressional District: 3
Focus Categories: Water Use, Non Point Pollution, Conservation
Keywords: Rainfall Harvesting, PAHs, flame retardants, first flush
Principal Investigators: Vogel, Jason (Oklahoma State University); Belden, Jason B; Brown, Glenn
Federal Funds: $ 25,000
Non-Federal Matching Funds: $ 51,082
Abstract: Rainwater harvesting (RWH) is a low impact development (LID) stormwater best management practice (BMP) that involves the capture, diversion and storage of rainwater for later non-potable and sometimes potable use while also helping reduce stormwater runoff volume. The proposed research will focus on RWH collection from rooftop catchment areas in central Oklahoma. The majority of a rooftop's dust and debris is washed away during the initial periods of a rainfall event, a phenomenon known as the "first flush". The removal of the first flush in RWH can dramatically increase the collected water's quality. Research has shown varied conclusions in how much runoff should be diverted in the first flush in order to have satisfactory water quality in the RWH system. In order to best utilize harvested rainfall, the first flush from different roof types must be quantified and this information incorporated into the design of an improved first-flush diverter.

Rooftop stormwater runoff has also been shown to be a major source and pathway of contaminants such as heavy metals and bacteria into surface waters. Polycyclic aromatic hydrocarbons (PAHs), contaminants of emerging concern known to cause carcinogenic and mutagenic effects in humans and biota, have been found in stormwater runoff due to atmospheric deposition on rooftops, especially in urban areas. Polybrominated diphenyl ethers (PBDEs), which are used as flame retardants, are also being found in water, surface sediments, and marine biota. PBDEs are of concern as research has shown that they bioaccumulate and have potential endocrine disrupting properties. If these compounds occur in harvested rainfall, even in low concentrations, they may build up over time in lawns and other areas that are irrigated over the long-term by harvested rainfall.

This research will develop and evaluate strategies for implementing the recommendation from the Marginal Quality Workgroup report for determining the potential for use and storage of stormwater runoff for non-potable demands. This research will be used to partially support the Master's work of National Science Foundation Fellow Jessica Lay in the Biosystems and Agricultural Engineering department as Oklahoma State University, and will also provide a 4-month half-time assistantship for a zoology master's student. The objective of this research will be to investigate two questions that remain regarding the implementation of rainwater harvesting as a solution for decreasing demand on water systems from water used for urban irrigation. This objective will be investigated by testing two hypotheses: (1) a more site specific, first flush can be quantified based on the roofing material, roof orientation, and geographical location by continuous monitoring and analysis of contaminants found in the rooftop runoff throughout a storm event, and (2) PAHs and flame retardants have the potential for long-term accumulation in soils from harvested rainfall used as urban irrigation. These hypotheses will be investigated by a combination of continuous and discrete monitoring of harvested rainfall from three buildings in central Oklahoma; discrete monitoring of harvested rainfall from 18 smaller structures to be constructed near Stillwater, Oklahoma; a survey of accumulation in soils below downspouts from 30 buildings (representing 3 roof types) in central Oklahoma; a column test to simulate long-term bioaccumulation of PAHs and PBDEs in soils; and, a leaching test on the parent roofing material to determine leaching potential.

Progress/Completion Report, 2011, PDF

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