Hydrology and Biochemistry of Storm Water Management I
Presiding: D M Roseen, Center for Stormwater Technology Evaluation and Verification, University of New Hampshire; D J Sansalone, Lousiana State University
H14A-01 15:30h
The Fate of De-icing Salts in Stormwater Management Systems
The traditional paradigm behind the design of stormwater management systems is to minimize the water quantity and water quality impacts resulting from land modification. The intent is to yield post-development hydrology similar to pre-development hydrology. The water quality aspect has been primarily focused on sediment removal, however, rarely are stormwater management systems designed for removal of de-icing salt. Chloride toxicity effects upon aquatic organisms resulting from snowmelt runoff are pronounced, routine, and problematic in northern climates. The capacity of current management strategies to treat chloride is in question. This paper explores the fate of de-icing salt through 13 different stormwater management systems. The systems include swales, retention pond, infiltration systems, bioretention systems, wetlands, manufactured devices, and porous asphalt. All systems exist at a field site and are delivered the same runoff (quantity and quality). The devices were designed and installed in accordance with existing drainage manual recommendations. None were designed for salt removal. As expected, devices with minimal water storage do not remove salt. Devices that do have significant amounts of storage do not remove salt, however the effluent concentrations are not as high as the influent concentrations: the peak influent salt concentration is attenuated similar to how the peak inflow discharge is attenuated by storage routing. The porous asphalt has displayed some remarkable characteristics. This surface has remained permeable throughout the winter, even though in addition to the de-icing chemicals, sand is applied. It appears that very little de-icing salt is needed on the surface, which has enormous economic and environmental implications.
H14A-02 15:45h
The Potential Impact of Coupled Physical and Chemical Processes on the Retention Efficiency of Ponds
Ponds can attenuate the concentration of nutrients, metals and other pollutants in storm water through particle settling and biological uptake. However, the percent removal of a particular constituent varies widely over multiple ponds and storm events. In some cases ponds can export more of a constituent than they import (negative retention). The factors that effect the retention efficiency of ponds are not well documented. The retention efficiency may be affected by the coupled physical and biogeochemical dynamics in ponds between storm events. During quiescent periods, ponds may undergo a diel thermal stratification/destratification cycle. The night time destratification is not always complete and residual density gradients can remain. The magnitude and persistence of the stratification is strongly affected by the geometry of the pond, the diffuse attenuation coefficients for shortwave radiation and the dominant primary producer type (phytoplankton or macrophytes). High spatial and temporal resolution measurements in two shallow, eutrophic ponds in Storrs, Connecticut demonstrate that chemical stratification is closely linked to the diel thermal stratification cycle and the dominant primary producer type. A 3-dimensional hydrodynamic model and a 1-dimensional biogeochemical model are used to evaluate the impacts of mixing frequency and the coupled physical and biogeochemical processes on internal nutrient and iron loading in shallow aquatic systems.
H14A-03 16:00h
The Hydrology and Chemistry of Bioretention During Storm Events
Bioretention is a key technology in the Low Impact Development (LID) approach to stormwater management. The LID principal is to capture and treat stormwater runoff as close to its source as possible and to restore watershed functions at the most localized level. Small bioretention units dispersed throughout an LID site are defined as infiltration/filtration systems composed of plants, engineered soils, mulch and (typically) an under drain system with contributing drainage areas of less than five acres. The goal is to avert the general degradation of physical characteristics, and periodic flushes of increased pollutant concentrations, by steering clear of a single collection point for stormwater runoff from larger expanses of developed land. Additionally, large sacrifices of land, difficult and costly maintenance issues, as well as the introduction of safety hazards and the general decline in overall aesthetics are avoided. Existing performance data on bioretention from simulated storm events in the field and laboratory models support the use of bioretention for peak flow and volume attenuation, as well as a suite of pollutant removals, including total suspended solids, lead, copper, zinc, phosphorus and nitrogen. The University of Maryland, in cooperation with the Prince George's County Government, has constructed a research and education bioretention site on the UMD campus. Automated sampling devices at the site have collected inflow and outflow hydrographs as well as water quality samples over the course of several storm events over eighteen months. Clear evidence of peak flow reduction and timing delays has evolved. Pollutant removals rates are consistent with simulation and laboratory experiments.
http://www.ence.umd.edu/~apdavis/Rain%20Gardens.htm
H14A-04 16:15h
Sources and Patterns of Pollutant Washoff in Urban Storm Water
Urban storm water typically conveys a broad spectrum of pollutants that may pose ecologic and human health concerns to downstream receiving waters. Traditional storm water monitoring programs have focused on evaluation of peak flows and mean concentrations, often derived from composite samples, for a limited set of constituents. As the regulatory and management focus on storm water increases, there is an increasing need to understand the sources and temporal patterns of washoff and loading for a broad suite of pollutants. This study investigated washoff of bacteria, metals, nutrients, and organic pollutants from 24 homogenous land use sites and 10 in-river (mass emission) sites in the greater Los Angeles area. Multiple discrete samples were collected over the duration of each storm in order to generate time vs. concentration (i.e. pollutograph) curves. In addition, storms with differing rainfall intensities and antecedent dry periods were sampled to better understand seasonal patterns in washoff. Results show that pollutant runoff generally exhibits intra and inter storm variability. A "seasonal flush" was observed for some pollutants, generally related to the amount of accumulated annual rainfall. For example, PAH mass loading during early season storms was 4-7 times higher than during comparably sized late season storms. For most constituents, concentrations peaked prior to peak flows. Peak PAH concentrations in the Los Angeles River averaged 3,000 ng/L and the peak occurred approximately 5 hours prior to the peak flow. The ability to attribute pollutants to specific land use types varied by constituent. For some constituents, such as zinc and lead, concentrations varied by land-use type: Washoff form industrial land uses had mean zinc concentrations between 2.5 and 5 times higher than other developed land uses. For others, such as PAHs concentrations were similar between land uses, suggesting a consistent regional source. The increased understanding of spatial and temporal patterns of storm water runoff may aid in the development of more refined dynamic models, improved monitoring, and may be used to guide development of management practices.
H14A-05 16:30h
Fecal-borne bacteria in stormwater and treatment systems in coastal New Hampshire
Bacterial contamination is the most common use limitation in New Hampshire's coastal waters. Past studies have shown consistently elevated levels of fecal-borne bacteria in surface waters occur during and following runoff events. Follow-up investigations have shown many stormwater conduits in urban areas that discharge directly into tidal rivers to contain high levels of bacteria, even during dry weather conditions. One of the results of these conditions is the need to close shellfishing waters throughout coastal New Hampshire, especially in Hampton Harbor, following rainfall events. Several recent studies have involved investigation of stormwater treatment system impacts on bacterial pollutants. Influent and effluent water samples from parking lot and storm drain treatment systems, runoff from urban streets, effluent from urban storm drains and receiving water samples were collected during different stages of stormwater runoff and analyzed for fecal coliforms, Escherichia coli and enterococci. E. coli isolates from one storm drain system were also ribotyped to identify source species. The stormwater treatment systems showed different capabilities for removing bacteria. Most were inconsistent at removing bacteria while others showed evidence of possible re-growth of bacteria between storms, especially during warmer weather. Re-growth or illicit connections appear to impact effluent bacterial levels in many urban storm drains. The source species identified for E. coli isolates in one storm drain changed between different stages of a storm event, reflecting runoff dynamics and human behavior patterns. Further work is focused on identifying the most significant sources of bacterial contaminants in receiving waters to help focus ongoing pollution abatement measures.
H14A-06 16:45h
Constitutive Properties of Cementitious Porous Pavement as a Passive Filtration Unit Operation for Rainfall-Runoff Quantity and Quality Control in the Built Environment
There is no abstract associated with this presentation.