Marie L. O'Shea

CONSTRUCTED WETLANDS FOR STORMWATER MANAGEMENT

Wetland systems have long been used for treating municipal and industrial wastewater, and are often more cost-effective than advanced wastewater-treatment systems. The available literature on the performance of wastewater-wetland systems is fairly extensive; however, information on the use of natural or constructed wetlands for controlling stormwater pollution, a newer application, is relatively scarce. In addition, the data available on wastewater wetlands may not apply directly to stormwater wetlands because of the unique characteristics of stormwater runoff, including: highly variable flow rates that are usually intermittent and seasonal; two-tothree order of magnitude between-storm differences in the chemical and suspended solids composition of stormwater runoff; and, site-specific nutrient ratios and concentrations. Consequently, in stormwater wetland systems, plant species’ performance and removal efficiency is often tied to the biotas ability to tolerate these extremely variable conditions. Additional factors which effect pollutant removals include: the comparative contributions of settling, sorption, plant uptake under various hydrologic (e.g., detention time) conditions, and a pollutant’s partitioning between the substratum, water column, and plant tissue. To address these unknowns and design concerns, a bench-scale vegetative-treatment-cell study is being conducted for the purpose of examining nutrient and metal dynamics and removal efficiencies of three individual plant species under various stormwater pollutant loadings and detention times. The plant species being evaluated are: cattails ( Typha latifolia), reeds (Phragmites sp.), and bulrushes (Scirpus sp.). For each of these species, two detention times (7 day and 14 day) and two pollutant loading levels (e.g., COD and SS >100 mg/l and <75 mg/l, respectively) are being investigated to determine wetland-process dynamics; relative removal efficiencies of stormwater-associated pollutants (e.g., total phosphorus and copper) as a function of detention time, water depths, and pollutant loadings, and expected solids removal and effluentparticle-size distributions.

An evaluation of bacterial standards and disinfection practices used for the assessment and treatment of stormwater.

Publisher Summary This chapter presents an evaluation study of bacterial standards and disinfection practices used for the assessment and treatment of stormwater. The Environment Protection Agencys (EPAs) current emphasis on water-use attainability and risk assessment warrants the reevaluation of existing disinfection requirements and bacteriological criteria. Water quality and disinfection criteria based on human disease contraction potentials of pathogenic microorganisms are needed for stormwater as well as combination with stormwater (CSO). The results of some epidemiological studies strongly suggest that total coliform (TC) or fecal coliform (FC) indicators cannot be used to assess accurately the pathogenicity of recreational waters receiving stormwater from uncontaminated separate storm sewers or surface water runoff. Carefully planned strategy should be adopted for storm sewers containing evidence of human-fecal contamination to indicate the presence of illicit or inappropriate cross-connections. In stormwater outfalls where cross-connections are too numerous or too costly to be corrected, it is advisable to deal with the separate storm sewer system as a combined sewer system.

The Role of Stormwater BMPs in Mitigating the Effects of Nutrient Overenrichment in the Urban Watershed

Nutrient overenrichment from agricultural and urban nonpoint and diffuse sources, including urban stormwater, is a leading cause of impairment to our nations rivers, lakes, and coastal waters. For receiving waters that do not meet existing water quality standards, the United States Environmental Protection Agencys (US EPA) Total Maximum Daily Load (TMDL) program tasks authorities with developing and implementing management plans for the control of point and nonpoint pollutant loads in excess of those allocated. To control pollutants from diffuse sources such as urban stormwater runoff, management efforts will rely heavily on the use of Best Management Practices (BMPs). The implementation of BMPs for the control of stormwater-associated pollutants is already an important component of the US EPAs recently promulgated Phase II stormwater regulations, coastal and surface source water protection programs, and state and local watershed protection plans. Load allocations mandated by the TMDL program may result in additional treatment requirements, e.g., numeric effluent limits for specific pollutants exceeding current ambient standards or future nutrient criteria now under development. The TMDL effort, the Phase II stormwater regulations, and the eventual adoption of more protective nutrient criteria and eutrophication-associated endpoints, together serve to increase the importance of obtaining consistent, seasonal, and species-specific BMP removal data and predictive capabilities to ensure that controls implemented to reduce nutrients have the desired effects of reducing eutrophication in impaired receiving waters.

Stormwater Treatment: Ponds vs. Constructed Wetlands

Extant data were used to assess the relative effectiveness of ponds vs. wetland-type BMPs. Compared to wet ponds, wetlands tended toward higher constituent concentrations in effluent, were inefficient at nitrogen removal, and appeared to preferentially retain phosphorus. These differences were hypothetically evaluated in terms of emergent macrophyte growth dynamics.

Effect of Phosphorus Concentration on the Growth of Cattail Callus Cells

Abstract This investigation examined the growth of Typha latifolia (cattail) callus cells grown in five (0, 11, 22, 33, 44 mg L−1) different phosphorus concentrations. The cells were grown for two successive subcultures on semi‐solid media, and subsequently in suspension culture with the same phosphorus levels. On semi‐solid media, the fresh weight of the cells varied by a maximum of 36% through both subcultures. The 33 mg L−1 phosphorus supplied in the original Gamborgs B5 media promoted the greatest fresh weight of the cells in suspension culture over all other concentrations tested. When grown in suspension culture with 0 and 11 mg L−1 phosphorus, the cells showed a 42 and 29% reduction in fresh weight, respectively. Incubating the cells with 22 and 44 mg L−1 phosphorus caused a 20 and 13% reduction in fresh weight, respectively. In addition, this study compared the phosphorus concentration of callus cells against literature‐reported values of whole cattail plants incubated at similar phosphorus concentrations. Data from this study demonstrate that when the cattail callus cells and whole plants are exposed to similar phosphorus concentrations, the phosphorus concentration in the plant leaves is within the confidence interval ( p ≤ 0.05) of the phosphorus concentration in the cattail callus cells. This suggests that cattail callus cells can be used to predict the concentration of phosphorus in cattail leaves when they are supplied with similar phosphorus levels. If this relationship between callus cells and whole plants is found to be applicable to other marsh plant species, stormwater wetland managers can use callus cells as a rapid method to screen plants for their capacity to absorb phosphorus before the plant is established in a wetland. This can increase the effectiveness of the wetland to absorb unwanted pollutants from the stormwater entering the site.

EPA's Watershed Management and Stormwater Modeling Research Program

Watershed management presumes that community groups can best solve many water quality and ecosystem problems at the watershed level rather than at the individual site, receiving waterbody, or discharger level. After assessing and ranking watershed problems, and setting environmental goals, watershed management options can be analyzed. This analysis typically considers system constraints, cost-effectiveness, the probability of meeting the watershed goal, the time required to achieve the goal, and the likelihood of a sustained change. Watershed management research at ORD’s National Risk Management Research Laboratory’s (NRMRL) address the following question: what effective watershed management strategies are available and how do communities select the most appropriate subset from these to match specific watershed needs? Watershed managers rely on various tools to enumerate, evaluate, and select management options. An important tool available to evaluate the array of available management alternatives available is a decision support system, i.e., a collection of approaches enabling water resource planners to select consistent, appropriate interventions with reasonable a priori estimates of their effectiveness. NRMRL watershed management research is creating a set of holistic, adaptive tools that enable local communities to select cost-effective approaches to protect or restore the water resources within their watershed. NRMRL’s research concentrates on identifying, collating, and developing techniques with associated data on cost, efficiency, execution, performance, and longevity emphasizing approaches likely to be within the pooled resources of watershed managers coupling flexibility with incremental quality improvements that allow adaptive management. Mathematical models that simulate facets of the watershed are among the most powerful tools employed in the watershed management decision-making process. Consequently, a significant part of NRMRL’s watershed research emphasizes modeling and assessment tools to promote the planning better control strategies, understanding the limitations and uncertainties of individual and connected models, and interaction among models.