Enhancing Construction Stormwater Management Nationwide: A Focus on Design Innovations and Training Programs

Abstract

A study of enhancing construction stormwater management was conducted through the completion of two distinct projects. One project focused on improving technology transfer methods through providing stormwater education and outreach to underserved communities, specifically counties within the Black Belt region of Alabama. The service area encompassed 47 individual U.S. Census Bureau tracts within 17 counties of Alabama. This area has experienced a population migration out of the area due to a lack of opportunities. In fact, populations in the service area are less than 2,500 and have median household incomes well below 80% of the State Non-metropolitan Median Household Income. In addition to socioeconomic disadvantages within the service area, there are also environmental concerns. Alabama is highly vulnerable to erosion and is at high risk for construction stormwater pollution due to the heavy rainfall and erosive soils. The Black Belt region of Alabama had highly fertile soil that led to cotton production, and due to the heavy production of cotton, the topsoil is now depleted which compounds flooding and pooling effects. This project seeks to fill the gap between researchers and practitioners through developing training specific to on-site needs which have been assessed through a state-of-the-practice survey as well as interviews with various county engineers. Common challenges faced by stormwater professionals in the area have been determined which has allowed for the creation of targeted outreach materials. Overall, this study found that communication with stakeholders is essential for successful transfer. In addition, rural communities have distinct needs that differ from urban communities due their socioeconomic status. Thus, working directly with such communities and involving them in the decision-making process is necessary to provide long-term benefits. Ultimately, working with the service area community members and targeting specific needs are essential for successful technology transfer implementation. The second project focused on developing recommendations for future volumetric sizing guidance of the live storage component of sediment basins on construction sites. To do so, a study of the long-term performance of four proposed sizing guidance methods for sediment basins compared to two standard designs was conducted using the USEPA SWMM for 150 distinct locations. Such proposed sizing methods include applying a sizing factor of 1,800 ft3 per acre (125 m3 per ha) of disturbed land and calculating the volume of runoff generated using the local 85th, 90th, and 95th percentile precipitation events. The two standard design sediment basins include calculating the runoff generated from the local 2-yr, 24-h storm event and applying the sizing factor of 3,600 ft3 per acre (250 m3 per ha) of disturbed land. The results of the analysis of the original six basins were used to determine the optimal size of a sediment basin for each study location. This optimal design considered the relationship between basin storage volume and runoff capture rate and utilized a method to determine the point at which larger basins result in diminishing returns. Stormwater runoff from construction sites is a leading cause of environmental degradation, yet sizing guidance for sediment basins lacks scientific justification and relies on industry rules-of-thumb. This study aims to provide scientific justification for sediment basin sizing regulations by investigating the mean percent of live storage volume utilized and the mean percent of overflow through the auxiliary spillway for each proposed sizing method compared to the standard methods. Sediment basins were designed and sized in Excel for 150 locations across the United States, each with varying annual precipitation amounts. At each location, sediment basins were designed for each of the 4 proposed sizing methods, the 2 standard methods, and each of the tested optimal designs. The geometry data, along with several other parameters, were input into SWMM to run long-term simulations using the local historical precipitation and air temperature data. This project seeks to provide a further understanding of the long-term performance of sediment basins and hopes to both provide future sizing guidance as well as be used as a basis for future testing and analysis of the long-term performance of sediment basins to ensure that a sufficient amount of live storage volume is utilized while ensuring that overflow from the basin is not detrimental to water quality and downstream communities. Analysis showed that each proposed sediment basin design utilized a statistically higher mean percentage of live storage volume when compared to each standard sediment basin design across the entire simulation period. This means that the standard basin designs may be oversized. In addition, the study found that 120 of the 150 optimal design basins had a VSF of less than 3,600 ft3 per acre (250 m3 per ha), the current USEPA standard. Thus, further testing and analysis may supplement the research conducted in this study to ensure that a sufficient amount of live storage volume is utilized and that overflow from the basin is not detrimental to water quality and downstream communities.