Hydrology and Biochemistry of Storm Water Management II Posters
Presiding: D M Roseen, Center for Stormwater Technology Evaluation and Verification, University of New Hampshire; D J Sansalone, Lousiana State University
H21D-01 0830h
A Comparative Study of Mass Removal Loads for a Range of Stormwater Treatment Strategies
When evaluating performance efficiencies for stormwater BMPs, there are significant challenges with regards to normalizing the variations in design, and hydraulic and hydrological conditions. There can be significant variations that must be considered such as rainfall intensity and duration, influent quality, watershed characteristics, loading functions, antecedent dry period, and maintenance. This study assessed mass removal loads for different stormwater management measures, all located in the same facility. The research facility is unique because it enables monitoring of 12 different treatment devices in parallel. For this purpose, a 9-acre commuter parking lot at the University of New Hampshire was chosen to provide runoff. There are three classes of devices examined at the site, conventional structural Best Management Practices (BMP), Low Impact Development (LID) designs, and manufactured devices. These include a subsurface gravel wetland, a detention pond, a sand filter, a bioretention system, a vegetated swale, and 7 different manufactured devices. Flow was evenly distributed and piped to each stormwater treatment. An on-site rain gauge provided rainfall data and samples of stormwater influent and effluent (for each stormwater treatment) were collected during monitoring rainfall events between August (2004) and April (2005). Temperature, dissolved oxygen and conductivity were measured continuously. Runoff constituents such as TSS, TP, TN, Cu, metals, nutrients and bacteria were measured in temporal water samples for each monitoring rainfall event. Results are presented as both concentration and Event Mean Concentrations (EMCs) to evaluate mass load removal. The watershed rainfall-runoff pattern was investigated as well as a statistical analysis to determine whether or not the differences between inflow and effluent water quality parameters were statistically significant. Earlier results have shown significant differences in the effluent water quality including temperature, dissolved oxygen and conductivity for the types of stormwater management measures evaluated here. This research is on-going and further results will be presented.
http://www.unh.edu/erg/cstev
H21D-02 0830h
Finding Order in Stormwater Chaos
A true understanding of baseline stormwater quality is important when defining the scope of a stormwater quality problem and the application of a solution. This is critical when determining regional stormwater quality goals and when assessing the efficacy of stormwater treatment processes relative to these goals. To better understand baseline stormwater quality in the Pacific Northwest for the purpose of designing stormwater treatment processes, raw stormwater quality data from a comprehensive, yearlong study of 5 parking lots and roadways in the Pacific Northwest was thoroughly analyzed for relationships and patterns. Over 60 individual storm events were sampled in an identical fashion using automated, composite methods under a monitoring plan approved by the local regulatory agency (Washington State Department of Ecology). Event mean concentration values were assessed for 15 different physical and chemical water quality parameters. The concentration data was then analyzed using statistical methods to elucidate relationships between water quality parameters and chemical, seasonal, and storm event variables. Several statistically significant relationships were found that both support and challenge common hypotheses regarding stormwater quality dynamics. For example, the observation that parameter concentration decreases with increasing storm depth is contradictory to the theory that larger storms are more important than smaller storms with respect to water quality. This theory is reflected in the specification of a minimum event depth by many stormwater monitoring protocols for the purpose of defining an event of concern. From a toxicity standpoint, the observation contradicts this theory by suggesting that larger storms are less harmful to aquatic ecosystems--and thus less important--due to a dilution effect. Also observed is a significant (P<0.001), predictable relationship between suspended solids and total Zn concentrations. This supports the hypothesis that the removal of suspended solids will result in the removal of metals, an observation this is supported both by logic and the research of others. However, the observation of a predictable relationship of substantial strength is curious and potentially valuable for modeling purposes. Ultimately, this information will: 1) help to accurately define the baseline stormwater quality of the Pacific Northwest; 2) improve the design and implementation of stormwater treatment processes in the region; and 3) advance the fundamental understanding of stormwater.
H21D-03 0830h
Impacts of Stormwater Management Measures on E. coli and Enterococci Populations in Stormwater Effluent
In our efforts to improve the quality of runoff entering our streams and waterways, stormwater management measures (or BMPs) are being implemented at a rapid pace. Usually designed to treat one or more specific types of contamination or loading, these measures may have unintended consequences that are not well understood. One issue that has not been fully explored is the potential effect these systems have on microbial contamination of the treated runoff. This study evaluates 11 types of treatment systems and their impact on E. coli and Enterococci contamination. Recent research has demonstrated that near-shore sediment may act as a continuous source of bacterial loading in the overlying waters, rather than bacterial loading being solely a temporal, storm-driven phenomenon. Similarly, stormwater management measures that utilize a soil media for filtration or incorporate a sediment sump may also provide conditions conducive to the incubation of fecal coliforms that can then be released into the environment during runoff events. Following with EPA regulatory guidelines for receiving waters, E. coli and Enterococci are used as surrogates for the presence of other potential disease-causing pathogens typically associated with mammalian and avian enteric bacteria. The stormwater management measures being investigated include: subsurface infiltration, surface sand filter, standard detention pond, bioretention area, hydrodynamic separation, subsurface gravel wetland, street sweeping, and vegetated swale. An adjacent porous parking area and a standard asphalt lot that drains to a tree filter are similarly monitored. Influent is supplied by runoff generated by a 9-acre commuter parking lot at the University of New Hampshire in Durham, NH. This influent is distributed equally to the different treatment devices that operate in parallel. Water quality parameters (DO, pH, specific conductivity, temperature) and flow are continuously monitored upstream from the distribution chamber (influent) and downstream from each device (effluent). Automated samplers are used to collect samples during storm events and grab samples are taken between storm events to evaluate the effect of each device or BMP on bacterial populations. Initial data indicate that influent concentrations of fecal coliforms for this parking area often exceed EPA limits for Class A waterbodies. Several of the treatment units appear to substantially reduce (>90% reduction) bacterial loading, while others appear to increase loading during some storm events (>500% increase). This study is on-going and additional sample events from the Spring of 2005 will also be presented.
http://www.unh.edu/erg/cstev
H21D-04 0830h
Modeling the Influence of Stormwater from Riparian Development on Small, Groundwater-Dominated Lakes
Accelerated phosphorus movement from terrestrial to aquatic ecosystems has been linked to deleterious increases in the biological productivity of many lakes. As lakeshores become more intensively developed, there is increasing concern over how this development alters the transfer of phosphorus. Small, groundwater dominated lakes may be particularly vulnerable to this transfer because of their relatively large shoreline/volume ratio, but they are often considered resilient to trophic status change when they have long hydraulic residence times and substantial calcium carbonate precipitation. A multi-disciplinary effort was made to understand the possible impacts of stormwater runoff from riparian development on twenty-two small lakes where water inflow is dominated by direct groundwater seepage. An in-lake phosphorus response model that accounts for phosphorus association and burial with precipitating calcium carbonate was developed and calibrated using the lake set. Nutrient and hydrologic budgets for the study lakes were developed using current and historical land use, historical water quality, recent monitoring, groundwater flow modeling and physical measurements. The calibrated in-lake response model was coupled with a stormwater runoff simulation model using both average annual and extreme precipitation distributions, and a variety of development approaches to estimate phosphorus loads for different development scenarios. The results were used in a sensitivity analysis to identify and communicate the considerations that should accompany efforts to increase development on small, groundwater-dominated lakes.
H21D-05 0830h
Assessment of porous asphalt pavement performance: hydraulics and water quality
The objective of this study is to focus on the water quality treatment and hydraulic performance of a porous asphalt pavement parking lot in Durham, New Hampshire. The site was constructed in October 2004 to assess the suitability of porous asphalt pavement for stormwater management in cold climates. The facility consists of a 4-inch asphalt open-graded friction course layer overlying a high porosity sand and gravel base. This base serves as a storage reservoir in-between storms that can slowly infiltrate groundwater. Details on the design, construction, and cost of the facility will be presented. The porous asphalt pavements is qualitatively monitored for signs of distress, especially those due to cold climate stresses like plowing, sanding, salting, and freeze-thaw cycles. Life cycle predictions are discussed. Surface infiltration rates are measured with a constant head device built specifically to test high infiltration capacity pavements. The test measures infiltration rates in a single 4-inch diameter column temporarily sealed to the pavement at its base. A surface inundation test, as described by Bean, is also conducted as a basis for comparison of results (Bean, 2004). These tests assess infiltration rates soon after installation, throughout the winter, during snowmelt, after a winter of salting, sanding, and plowing, and after vacuuming in the spring. Frost penetration into the subsurface reservoir is monitored with a frost gauge. Hydrologic effects of the system are evaluated. Water levels are monitored in the facility and in surrounding wells with continuously logging pressure transducers. The 6-inch underdrain pipe that conveys excess water in the subsurface reservoir to a riprap pad is also continuously monitored for flow. Since porous asphalt pavement systems infiltrate surface water into the subsurface, it is important to assess whether water quality treatment performance in the subsurface reservoir is adequate. The assumed influent water quality is derived from that which is entering the stormwater treatment system in the adjacent parking lot. Since the facility is new, parking has been less intensive here, and influent concentrations will be adjusted down accordingly. Several wells have been installed in and around the facility. Screened intervals are at two levels; in the reservoir and beneath the facility. One well in the facility is continually monitored for basic water quality parameters (temperature, specific conductivity, pH, dissolved oxygen) and level, and is also sampled with an automated refrigerated sampler. Grab samples are collected from the other wells as a basis for comparison. Water samples are collected during several storm events and during interstorm periods to assess water quality treatment performance. The samples are analyzed for nutrients, metals, petroleum hydrocarbons, and pathogens. The potential for leaching of pollutants from the asphalt binder will also be assessed during these storm events. Water quality treatment performance is compared to those of several other studies. Updates on spring 2005 data are also included in the presentation.
http://www.unh.edu/erg/cstev/
H21D-06 0830h
The geomorphic context of flood hazards in Haiti
Devastating floods struck Fonds Verrettes, Mapou, and Gonaives, Haiti in 2004, killing thousands and calling attention to the threat of catastrophic flooding in that country. That threat provides a focus for expanding collaborations in field and service learning in Haiti. Past field and service-learning collaboration with Universite Notre Dame d'Haiti (UNDH) resulted in an invitation to evaluate the flooding potential of Haiti's largest city - Port-au-Prince. High population densities, land cover change, the geomorphic setting of Port-au-Prince, combine to make that city particularly vulnerable to catastrophic flooding. Climate change and associated sea level rise are also a concern. Port-au-Prince lies at the foot of steeply sloping mountain areas of the Massif de La Selle. Much of the urban area is built on alluvial fans, coastal plains, and recent deltaic deposits. While data are rare to nonexistent, deforestation in the mountain areas upstream from the city and extensive urbanization, especially in the last few decades, is virtually certain to have increased storm runoff volumes and reduced lag times. Different flood hazards can be identified in four geomorphic zones: 1) valleys in steeply sloping areas, where channel erosion and associated slope failures threaten streamside communities; 2) alluvial fans, where rapid aggradation, mudflow deposition and channel avulsion contribute to channel instability; 3) coastal plains, where gentle slopes impede drainage of flood water; and 4) deltaic areas formed and settled in the last few decades subject to storm surge and possibly subsidence in addition to runoff-derived flooding. These zones can serve as a framework for flood hazard identification and management. With the cooperation of the Haitian government and non-profit organizations, students and faculty from Miami University and UNDH will combine talents to measure the flood potential of a single, critical watershed in Port-au-Prince and establish a community-based monitoring system.