Stormwater Consortium

Bill Hunt, NC State

With urbanization the need for stormwater control measures (SCMs) to meet federal and state stormwater regulations grows. Maintenance is necessary and typically required by state and local regulations to ensure SCMs remain functional and continue to mitigate the impacts of urbanization. In addition to functional drivers, SCMs are also maintained for aesthetic appeal. Previous research has quantified maintenance costs for SCMs in North Carolina but (1) this study is dated, (2) there remains a lack of data regarding costs for routine, preventative/proactive, and restorative maintenance, and (3) the relationship of curbside appeal (aesthetic need) and maintenance frequency (i.e., how does the location of a SCM affect its aesthetics and the level of maintenance performed) has not been evaluated. North Carolina State University Biological & Agricultural Engineering (NCSU BAE) is seeking to partner with the Urban Stormwater Consortium (USC) of the Water Resources Research Institute of the University of North Carolina (WRRI) to answer these questions. Updated information will provide municipal guidance for budgeting and maintenance optimization (i.e., cost effectiveness of preventative versus restorative maintenance SCM maintenance), which will allow entities responsible for SCM maintenance to better allocate their resources (human and financial capital). Additionally, the researchers anticipate these findings will improve SCM implementation with respect to available resources. These results will be disseminated through a final report to WRRI, a peer-reviewed journal publication, state and national conferences, and the NCSU Stormwater BMP Inspection & Certification Workshop series.

Charles Stillwell and Bill Hunt, NC State

Urbanization has resulted in many alterations to the natural hydrologic cycle. Land development converts vegetated areas to impervious surfaces, reducing evapotranspiration and infiltration. Consequently, urban areas have a higher proportion of surface runoff1. As a result, flood frequency is increased2 while streamflow regimes exhibit high peak flow rates and low baseflow3. Higher surface runoff volumes and velocities result in streambed erosion4. Additionally, urban streams have higher levels of pollution5. All the aforementioned problems contribute to an ecologically unstable environment for streams located in urbanized areas6. Low impact development (LID) is a technique aimed to protect streams. The goal of LID is to develop land in a way that minimizes changes to the natural hydrologic cycle by promoting new opportunities for infiltration and evapotranspiration7. The goal of this project is to compare various design scenarios for a newly developed site, in terms of stormwater treatment effectiveness, water quality improvement, and mitigation of impervious surfaces on stream health. This study is an extension of an existing monitoring study at the site, and hydrologic modeling will be used to expand upon the findings to investigate long-term (e.g. 30-year) hydrologic performance. A cost/benefit analysis will also be conducted for each of the different design scenarios.

Bryan Maxwell and Francois Birgand, NC State

Increasing urbanization and agricultural impacts have rallied efforts for mitigating our impact on water quality. North Carolina has passed a wide range of measures to regulate discharges, point and non-point, to surface waters including SWCMs and TMDLs. Improvements in water quality have been observed, however continued growth will put increasing strains on the state’s waters and current treatment infrastructure. Additionally, changing atmospheric composition and mutable precipitation patterns will require existing practices to perform as good or better to maintain water quality. Many current practices implemented around the state are yesterday’s solutions to today’s conditions when we need to be refining solutions to handle tomorrow’s crises. Floating treatment wetlands (FTW) are an emerging practice in water quality improvement. Free-floating vegetation is suspended in the water column using a soilless support matrix. Theoretical benefits of this method are numerous. Plant roots in the water column rather than the soil increase access to nutrients and facilitate plant uptake. Hanging root mats provide high surface area for biofilms for microbial water treatment. Studies have shown reductions in phosphorus and nitrogen (Van de Moortel et al., 2010; Winston et al., 2013; Nahlik and Mitsch, 2006); both contaminants are of concern for the Tar-Pamlico and Neuse River Basins and both known to cause spikes in toxin-producing algal blooms found in stormwater ponds (Lewitus et al., 2008). Tanner and Headley (2011) showed significant reduction in metals with Cu, Zn, and fine solids. Winston et al. (2013) saw high removal of suspended solids which decreases turbidity and sediment-bound pollutants such as phosphorus, metals, and pathogens.  The project itself will be broken up into three separate goals:

• Goal #1 : Evaluating performance and understanding processes of FTW systems using new technologies developed by the author’s lab group to determine usefulness as a water quality tool.
• Goal #2 : Perform a comprehensive literature review on all research on FTW with the objective of developing performance estimates for given pollutants. This extensive review will be shared with regional and state stakeholders to inform future WQ policy decisions.
• Goal #3 : Dissemination of results of this study, project research and literature review, to local and state agencies to increase awareness and understanding of these systems as a potential water quality tool.

Michael Paul, Tetra Tech

A review of statewide biological assessment data was conducted to identify biologically attaining sites in urban areas and to support further investigation into variation of bioclassification scores in urban areas throughout the state. Data were requested from NC Department of the Environment and Natural Resources (NCDENR), the Urban Water Consortium Stormwater Group (UWC-SWG) member jurisdictions, and several additional local governments. Data requirements included use of statecertified labs and collection using NCDENR’s standard qualitative (Full Scale) method. Upon review of several urban land use/ land cover thresholds, urban watersheds were defined as having greater than 10% imperviousness based on the 2006 National Land Cover Dataset (NLCD). Watersheds were delineated for each sample location, and sample locations with urban watersheds (>10% imperviousness) were identified. Maps of sample locations with good-fair or better bioclassifications verified that bioclassification scores are generally higher in western NC and in rural areas. Within urban watersheds, 50 sites had bioclassification scores of good-fair or better at least once during their sampling period, and these 50 sites represent less than 5 percent of the sites with at least one good-fair or better bioclassification statewide (urban and non-urban watersheds). Similarly, 68 sample bioclassification scores were good-fair or better in urban watersheds, which represents less than 3 percent of the 2672 samples with these scores statewide. Also within the urban watersheds, 10 locations declined below a good-fair bioclassification between their highest rating and their most recent sample, and none improved. For samples taken 2006 to present in urban watersheds, 12 sites were rated good-fair at least once, and none were rated good or excellent. Potential methods are discussed for a Phase 2 study to identify features of watersheds in urban areas supporting good-fair or better bioclassification scores to improve understanding of why some urban watersheds support higher biological quality than others. In addition, proposed policy options for using Phase 2 information to more wisely manage aquatic life use in urban watersheds is discussed.

Bill Hunt, NC State

Gross and coarse solids in stormwater runoff are an un- or under-quantified source of nutrients to receiving waters. Capturing these solids at urban drain inlets and then removing them via vacuum truck represents an opportunity for communities needing to remove nutrients (& and other pollutants) to do so without dedicating any land or constructing a larger stormwater device. North Carolina State University is seeking to partner with four UNC-WRRI urban stormwater consortium member municipalities (exact communities chosen later) to determine the mass, volume, and composition of stormwater-borne gross solids (trash/litter, organic debris, and sediment) entering drain inlets. Data to be collected from gross solids collection and analysis include mass, volume, bulk density, total nitrogen (mg/kg), total phosphorus (mg/kg), total carbon, and composition (i.e. percent urban litter, organic debris, and coarse sediment).The scope of work involves selecting four drain inlets per community, with up to four land types represented in each city, for a total of 16 drain inlet monitoring points. Drain inlets will have a 5-mm metal or fabric mesh installed near the outflow pipe of the catch basin in order to capture gross solids. Sampling of the gross solids trapped by the monitoring nets will be performed at three distinct depths to represent differential temporal settling patterns. The goals of the study are to: (1) Quantify the mass and volume of gross solids potentially reaching water bodies from 4 different land uses, (2) Determine the amount of nutrients captured by these devices, and (3) Devise general maintenance recommendations for potential treatments in each land use tested.These data will result in scholarly article publication in a peer-reviewed journal, a report to WRRI on each municipality’s respective catch basins, and a summary of the results for consideration by state water quality regulation entities (namely, NCDENR). Ultimately, the baseline study proposed will inform municipalities whether pollutant loadings associated with gross solids for a given land use type do or do not exceed receiving body water quality limits. Additionally, by observing solids build-up, a window into the needed maintenance activities for catch basins will be explored. Pollutant data may enable communities to account for nutrient and sediment loads prevented from reaching receiving waters as a part of a larger watershed management program. Recommendations to optimize maintenance of city drain inlets will be addressed, as this is a large cost to municipalities.