Targeting treatment technologies to address specific stormwater pollutants and numeric discharge limits.

Stormwater filter media (SFMs) play a vital role in decreasing flooding and preventing urban contaminants from polluting surface and ground waters. The infiltration rate of a SFM is a governing factor in the hydrological and environmental performance of the stormwater management systems. This paper describes the effect of a common deicing salt (sodium chloride) in reducing the infiltration capacity of two types of SFMs, which were prepared using a clayey silty sand, one with compost and another without compost. This paper also describes the effect of sodium chloride application in the release of zinc, calcium, nitrogen, magnesium, phosphorous, potassium, and sulfur from the SFM, and whether their release was accelerated or reduced from the SFM with compost. Laboratory constant-head infiltration tests were conducted using sodium chloride (as the deicing salt) at concentrations of 150 and 1,200  mg/L. After conducting the tests for comparable cumulative pore volumes of infiltration, soil only SFM ex...

Effects of Deicing Salts on the Clogging of Stormwater Filter Media and on the Media Chemistry

To address water quality concerns and numeric effluent limits, the designers of bioinfiltration/bioretention systems will need to integrate water and soil chemistry into the selection of filtration media mixtures. For the dissolved metals, designers will need to consider the ratio of valence states of the metals as they consider the proportion of ion exchange resins versus organic-based media in the final media mixture. As the correlations between pollutant capacity and soil/media chemistry showed, metals' capacity is directly related to organic matter content and the effective cation exchange capacity of the soil. Available stormwater treatment organic media provides a wide range of treatment sites, but possibly smaller numbers of each site type, compared to ion exchange resins such as zeolites. An activated organic media, such as granular activated carbon (GAC), will have an increased number of surface active sites potentially available for treatment, but this media may not sustain plant growth and may not be desired as a component of bioretention media. Other trade-offs also have to be considered in a complete analysis of a potential media component, such as the trade-off between organic content for plant growth versus nutrient leaching. Finally, there is a lower limit to treatment, after which no further pollutant removal occurs, especially given the contact time requirements based on draindown times required for many bioretention devices. Slightly improved removals for many metals may be achieved with much longer contact times, but the substantial increase in surface area devoted to bioinfiltration may not be cost-effective (given the draindown time requirements). This paper uses dissolved copper as an example of how to use both soil and water chemistry to design an optimal bioretention media from a subset of potential mixture components.

Filtered Metals Control in Stormwater Using Engineered Media

In 2005, Wetland Studies and Solutions, Inc. (WSSI) installed an extensive Low Impact Development (LID) stormwater management system on their new office site in Gainesville, Virginia. The 4-acre site is serviced by a network of LID components: permeable pavements (two proprietary and one gravel type), bioretention cell / rain garden, green roof, vegetated swale, rainwater harvesting and drip irrigation, and slow-release underground detention. The site consists of heavy clay soils, and the LID components are mostly integrated by a series of underdrain pipes. A comprehensive monitoring system has been designed and installed to measure hydrologic performance throughout the LID, underdrained network. The monitoring system measures flows into and out of each LID component independently while concurrently monitoring rainfall events. A sensitivity analysis and laboratory calibration has been performed on the flow measurement system. Field data has been evaluated to determine the hydrologic performance of the LID features. Finally, hydrologic models amenable to compact, underdrained LID sites have been reviewed and recommended for future modeling and design.

/pdf/hydrologic-monitoring-of-an-integrated-low-impact-sxyoyaqqyb.pdf

Hydrologic monitoring of an integrated low impact development (LID) underdrained stormwater management system

Groundwater Contamination Potential from Infiltration of Urban Stormwater Runoff

Sustainable Stormwater Management: Infiltration vs. Surface Treatment Strategies

It has been well-documented that, in stormwater runoff, many of the problem pollutants are associated with the particulate fraction. Past characterization of urban runoff and source contributions has shown the following: (a) soil disturbance increased the TSS and turbidity in the runoff; and (b) correlations were observed between TSS and particulate runoff concentrations of chromium, copper, and zinc, indicating that solids removal may reduce total metals concentrations. The first concern when investigating innovative treatment methods is determining the needed level of stormwater control. Specific treatment goals usually specify about 80% reductions in suspended solids concentrations. In most stormwater, this would require the removal of most, if not all, particulates greater than about 10 μm in diameter, which is about 1% of the 1-mm size that must be removed to prevent sewerage deposition problems. The ability of inclined cells (inclined plates/tube settlers) to provide excellent treatment of stormwater for a variety of pollutants was demonstrated by Pitt et al. (1999) in the report on the multi-chambered treatment train (MCTT) at the University of Alabama at Birmingham. This project is adding to that body of knowledge by investigating the potential of inclined plate settlers to treat stormwater runoff both in the field (at the City of Harrisburg Public Works Yard) and through a full-scale “laboratory” demonstration. Inclined plate settlers can be designed in one of two ways – through the use of Stokes’ Law and through the use of the Hjulstrom diagram, which accounts for scour and re-suspension. The test device in this research was sized using the Hjulstrom diagram. The results showed that the Hjulstrom diagram may be a very effective tool to predict the performance of inclined plate sedimentation devices based on the particle size for which 100% control is desired. Once the runoff’s particle size distribution is known, estimating the average percent removal for the system would be trivial, and could be done using Stokes’ Law. A sieve analysis of the influent and effluent, using a 250-μm sieve, demonstrated that the inclined plates were capable of removing particles in >250-μm size range, even when these particles were a substantial part of the mass load to the system. An analysis of the TSS and SSC

Inclined plate settlers to treat stormwater solids

Increasing impervious surfaces in the urban landscape has created a need for stormwater management practices that control both volume and peak flow rate. Infiltration systems are preferred because they address both issues. However, the potential for groundwater contamination is a concern when siting an infiltration practice. In addition, soil is not homogeneous and its variety of layers provides a heterogeneous environment for pollutant removal. This study, started in November 2007 and to be completed by October 2008, is using undisturbed natural soil columns of a Wharton silt loam and Leetonia loamy sand to treat stormwater runoff from roofing, parking lots and sidewalk. This research is a temporal study of runoff treatment and soil accumulation as a function of soil horizon and resultant soil chemistry. Early water results show leaching of total nitrogen and removal of total phosphorus by all soil horizons of both soil types. Potassium and sulfate removal has been seen in the AB/A1A2 and OAB/OA1A2 soil horizon columns of both soils but may only be temporary. The lower horizons and the entire profile are able to retain the leaching potassium and sulfate from the organic horizon. All soil horizons of both soil types have lowered the pH of influent stormwater and increased conductivity, turbidity, color, and hardness.

Pollutant Transport within the Vadose Zone of Natural Soils: With Focus on the Interactions of Individual Soil Horizons

Pollutant Transport within the Vadose Zone: Interactions of Soil Horizon Chemistry on Water Quality

Stormwater managers use infiltration to promote groundwater recharge in urban areas and to reduce the volume and flow rate of stormwater runoff created by post development conditions. However, the potential for groundwater contamination exists. Studies have shown that some areas are more prone to groundwater contamination than others. As a result, methods for easily predicting contamination potential beneath infiltration devices are being developed. One such method involves the use of computer programs, such as SESOIL — a one-dimensional vadose zone model. SESOIL was selected because of the multitude of processes available in the program for predicting pollutant removal. SESOIL was first evaluated using a full factorial design, considering six potential factors that were thought to influence the predictions (rainfall, concentration, vadose zone thickness, intrinsic permeability, soil pH, and soil organic matter). The results showed that, at the concentrations typical of urban stormwater runoff, only rainfall, concentration and intrinsic permeability were important. Difficulties of application were encountered due to a lack of available input values and data sets. Therefore, laboratory research on partitioning factors between the water and the soil were undertaken. The results showed that the partitioning coefficients calculated from the removal of pollutants from a multicomponent mix at typical stormwater concentrations were similar to the low range found in the literature. However, the literature did not have values for sparingly-sorbable compounds such as the nutrients. This research is using a vadose zone model, such as SESOIL which incorporates these numerous chemical reactions in the calculations, as a design tool for infiltration devices with both engineered and natural soils. This research will support the development of guidance for protecting groundwater from unintentional contamination by stormwater runoff passing through an infiltration structure.

J. Bradley Mikula

Papers

Sustainable Stormwater Management: Infiltration vs. Surface Treatment Strategies

Inclined plate settlers to treat stormwater solids

Pollutant Transport within the Vadose Zone of Natural Soils: With Focus on the Interactions of Individual Soil Horizons

Pollutant Transport within the Vadose Zone: Interactions of Soil Horizon Chemistry on Water Quality

Evaluation and Verification of a Vadose Zone Model Applied to Stormwater Infiltration