Shirley E. Clark

Groundwater contamination potential from stormwater infiltration practices

Abstract The potential effects of stormwater on groundwater quality was estimated based on the likely presence of problem constituents in the stormwater, their mobility through soils, the type of treatment received before infiltration, and the infiltration method used. The constituents of most concern include chloride, certain pesticides (lindane and chlordane), organic toxicants (1,3-dichlorobenzene, pyrene and fluoranthene), pathogens, and some heavy metals (nickel and zinc). Reported instances of groundwater contamination associated with stormwater was rare in residential areas where infiltration occurred through surface soils (except for chloride), but was more common (especially for toxicants) in commercial and industrial areas where subsurface infiltration was used.

The Role of Traditional and Novel Toxicity Test Methods in Assessing Stormwater and Sediment Contamination

Traditional effluent and ambient water column toxicity tests have been used widely for evaluating the contamination of stormwaters and sediments. These assays consist of a routine bioassay exposure design of 1 to 9 days using freshwater and marine/estuarine species known to be sensitive to a wide range of toxicants. While effluent toxicity may be indicative of sediment or stormwater toxicity in the receiving system, the exposure is different, and therefore toxicity cannot be readily predicted. Traditional, standardized, whole effluent toxicity (WET) test methods have been used effectively and also misused in evaluations of whole sediments, pore (interstitial) water, elutriates (extracts), and stormwaters. Results show these methods to be very sensitive to sediment and stormwater toxicity. These traditional toxicity tests are predictive of instream sediment or stormwater effects where significant contamination exists or where exposure concentrations are similar. Modifications of these standardized test methods to include sediments or pore waters have been shown to be as sensitive as short-term, whole sediment toxicity tests using benthic species. However, the added complexity of sediments and stormwaters (e.g., partitioning, high Kow compound bioavailability, suspended solids, sporadic exposures, multiple exposure pathways) dictates that traditional toxicity test applications be integrated into a more comprehensive assessment of ecologically significant stressors. The limitations of the WET testing approach and optimized sample collection and exposure alternatives are frequently ignored when implemented. Exposure to sporadic pulses of contaminants (such as in stormwaters) often produce greater toxicity than exposure to constant concentrations. Lethality from short-term pulse exposures may not occur for weeks after the high flow event due to uptake dynamics. Pore water and elutriate exposures remove sediment ingestion routes of exposure and alter natural sorption/desorption dynamics. Traditional toxicity tests may not produce reliable conclusions when used to detect the adverse effects of: fluctuating stressor exposures, nutrients, suspended solids, temperature, UV light, flow, mutagenicity, carcinogenicity, teratogenicity, endocrine disruption, or other important subcellular responses. This reality and the fact that ecologically significant levels of high Kow compounds may not produce short-term responses in exposures dictates that additional and novel assessment tools be utilized in order to protect aquatic ecosystems. This inablilty to predict effects is largely a result of the complex biological response patterns that result from various combinations of stressor magnitudes, duration, and frequency between exposures and also the interactions of stressor mixtures, such as syngergistic effects of certain pesticides, metals, and temperature. In watersheds receiving multiple sources of stressors, accurate assessments should define spatial-temporal profiles of exposure and effects using a range of laboratory (such as WET tests) and novel in situ toxicity and bioaccumulation assays, with simultaneous characterizations of physicochemical conditions and indigenous communities.

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

Stormwater treatment is entering a new phase with stormwater management systems being required to meet specific numeric objectives, as opposed to the historic approach of meeting guidance-document-provided percent removal rates. Meeting numeric discharge requirements will require designers to better understand and apply the physical, chemical, and biological processes underpinning these treatment technologies. This critical review paper focuses on the potential unit treatment operations available for stormwater treatment and outlines how to identify the most applicable treatment options based on the needed pollutant removal goals.

Urban wet-weather flows.

This literature review summarizes significant technical literature published in 2009 regarding the field of urban wet-weather flows. The review addresses characterization, pollution sources, monitoring and sampling, surface and groundwater impacts, decision support systems, regulatory policies, and control and treatment technologies.

Compacted Urban Soils Effects on Infiltration and Bioretention Stormwater Control Designs

The effects of urbanization on soil structure can be extensive. Infiltration of rain water through soils can be greatly reduced, plus the benefits of infiltration and bioretention devices can be jeopardized. Basic infiltration measurements in disturbed urban soils were conducted during an EPA-sponsored project, along with examining hydraulic and water quality benefits of amending these soils with organic composts. Prior EPA-funded research examined the potential of groundwater contamination by infiltrating stormwater. In addition to the information obtained during these research projects, numerous student projects have also been conduced to examine other aspects of urban soils, especially more detailed tests examining soil density and infiltration during lab-scale tests, and methods and techniques to recover infiltration capacity of urban soils. This paper is a summary of this recently collected information and it is hoped that it will prove useful to both stormwater practice designers and to modelers.

Review of Historical Street Dust and Dirt Accumulation and Washoff Data

Many complex models that utilize continuous simulation (SWMM, HSPF, SLAMM, SIMPTM, etc.) require information pertaining to the accumulation rate of pollutants …

Storm-Water Filter Media Pollutant Retention under Aerobic versus Anaerobic Conditions

Storm-water runoff entering filters is usually aerobic and therefore the removal processes in the filter normally occur under oxidizing and aerobic conditions. However, storm-water filters differ from water and wastewater treatment filters because there are quiescent times when no influent enters the filter and the pore water stagnates. During this stagnation period, anaerobic conditions on a macro- or microscale could develop. This note presents the results of experiments conducted to determine if four potential filter media (sand, activated carbon, peat moss, and compost) could retain previously trapped pollutants when anaerobic conditions develop during interevent periods. The results indicated that permanent retention of heavy metals may occur even in an anaerobic environment (for the media and metals investigated). However, retention of some nutrients may not occur under these conditions, particularly for the organic media. This is an area of concern when the design of filters and bioretention devices includes an internal water storage zone where, between events, anaerobic conditions for nitrate removal are encouraged.

Pollutant Associations with Particulates in Stormwater

Many studies have identified metals in urban runoff as a major contributor to the degradation of urban streams and rivers. Metals of most concern are copper, cadmium, chromium, lead, mercury, and zinc. Metals in urban runoff can occur as dissolved, colloidal and particulate-bound species. Therefore, it is important to measure all forms of heavy metals, especially the particulate and filterable fractions, when determining their fate and effects. The objectives of these tests were to determine the associations of heavy metals (along with some major constituents and nutrients) with different-sized particulates using cascade sieves and filters. Sequential extraction experiments were also conducted to examine the treatability and other characteristics of the filterable (<0.45 µm) portion of the heavy metals using Chelex-100 resin, UV-light exposure, and Anodic Stripping Voltammetry (ASV). Preliminary results show that total phosphorus and chemical oxygen demand are associated with the particulates and in general decrease with a decrease in particle size. Obviously, concentrations should all decrease with filtration. However, there were periodic jumps in concentrations for some conditions, reflecting variability in the analytical method and the sample handling. Results using ASV show the metals of concern (Zn, Cd, Pb and Cu) all present in the dissolved (<0.45µm) fraction of the stormwater samples with Zn normally present in the highest concentration. Exposure of the samples to UV light increases the concentration of most of the metals, indicating a dissociation of metals from organic complexes or colloids. Sampling and analyses is continuing through April 2005. Sample fractions will be analyzed for Zn, Cd, Pb and Cu using ICP-MS, and the sequential extraction procedures and toxicity tests will be completed.

Sources of Pollutants in Urban Areas (Part 1) - Older Monitoring Projects

Information concerning source area runoff characteristics during wet weather events can be very important when developing stormwater management plans that inco…

Peristaltic pump autosamplers for solids measurement in stormwater runoff.

Regulatory agencies approve automatic samplers containing peristaltic pumps as a sample collection method for stormwater characterization and for treatment-device evaluation. Autosampler performance, as discussed in the limited available literature, can vary across the entire particle size range typically found in stormwater from different source areas and outfalls-reasonably consistent performance for particle sizes < 250 microm, but much less consistency for particles > 250 microm. Therefore, a series of experiments was undertaken to quantify the upper range of consistent particle capture that may occur with sampling stormwater suspended sediment and particulate-bound pollutants. These experiments, based on triplicate sampling at each experimental condition, found that peristaltic pump autosamplers commonly used in stormwater monitoring could not repeatedly and effectively capture particles > 250 microm from a simulated stormwater whose particles have a specific gravity of 2.65. It was expected that the effective size for autosamplers would be correspondingly larger for particles having smaller specific gravities. The height of the sampler had no influence on particle recovery up to a height of 2.5 m, with slightly decreasing recoveries of large particles occurring at greater heights, as a result of reduced sampler intake velocity. Therefore, to characterize the solids across the entire size range and specific gravities that may occur in stormwater runoff, autosamplers should be deployed in conjunction with bedload and floatables sampling.