Michael Borst

Particle-associated microorganisms in stormwater runoff

This research investigated the effects of blending and chemical addition before analysis of the concentration of microorganisms in stormwater runoff from a single summer storm to determine whether clumped or particle-associated organisms play a significant role. The standard membrane filtration method was used to enumerate the microorganisms. All organisms, except for Escherichia coli, showed an increase in the measured concentration after blending samples at 22,000 rpm with or without the chemical mixture. Other than fecal streptococci, the organism concentrations decreased with the addition of the Campers solution in both blended and unblended samples before analyses. There was a statistically significant interaction between the effects of Campers solution and the effects of blending for all the organisms tested, except for total coliform. Blending did not alter the mean particle size significantly. The results show no correlation between increased total coliform, fecal coliform, and fecal streptococcus concentrations and the mean particle size.

Nutrient infiltrate concentrations from three permeable pavement types

While permeable pavement is increasingly being used to control stormwater runoff, field-based, side-by-side investigations on the effects different pavement types have on nutrient concentrations present in stormwater runoff are limited. In 2009, the U.S. EPA constructed a 0.4-ha parking lot in Edison, New Jersey, that incorporated permeable interlocking concrete pavement (PICP), pervious concrete (PC), and porous asphalt (PA). Each permeable pavement type has four, 54.9-m(2), lined sections that direct all infiltrate into 5.7-m(3) tanks enabling complete volume collection and sampling. This paper highlights the results from a 12-month period when samples were collected from 13 rainfall/runoff events and analyzed for nitrogen species, orthophosphate, and organic carbon. Differences in infiltrate concentrations among the three permeable pavement types were assessed and compared with concentrations in rainwater samples and impervious asphalt runoff samples, which were collected as controls. Contrary to expectations based on the literature, the PA infiltrate had significantly larger total nitrogen (TN) concentrations than runoff and infiltrate from the other two permeable pavement types, indicating that nitrogen leached from materials in the PA strata. There was no significant difference in TN concentration between runoff and infiltrate from either PICP or PC, but TN in runoff was significantly larger than in the rainwater, suggesting meaningful inter-event dry deposition. Similar to other permeable pavement studies, nitrate was the dominant nitrogen species in the infiltrate. The PA infiltrate had significantly larger nitrite and ammonia concentrations than PICP and PC, and this was presumably linked to unexpectedly high pH in the PA infiltrate that greatly exceeded the optimal pH range for nitrifying bacteria. Contrary to the nitrogen results, the PA infiltrate had significantly smaller orthophosphate concentrations than in rainwater, runoff, and infiltrate from PICP and PC, and this was attributed to the high pH in PA infiltrate possibly causing rapid precipitation of orthophosphate with metal cations. Orthophosphate was exported from the PICP and PC, as evidenced by the significantly larger infiltrate concentrations compared with influent sources of rainwater and runoff.

Evaluation of Surface Infiltration Testing Procedures in Permeable Pavement Systems

AbstractThe ASTM method for measuring the infiltration rate of in-place pervious concrete provides limited guidance on how to select test locations and how results should be interpreted to assess surface condition and maintenance needs. The ASTM method is written specifically for pervious concrete, so additional research is needed to determine the applicability of this method to other permeable pavement types. In 2009, the U.S. Environmental Protection Agency constructed a 0.4-ha parking lot surfaced with permeable interlocking concrete pavers (PICP), pervious concrete (PC), and porous asphalt (PA). Surface infiltration testing was conducted for almost three years, and two methods were used to select test locations: monthly testing at randomly selected locations and quarterly testing at fixed locations. Infiltration rates were significantly different for each pavement type. With almost three years of use, maintenance has yet to be required, although infiltration has decreased in areas immediately downgrad...

Novel Use of Time Domain Reflectometry in Infiltration-Based Low Impact Development Practices

AbstractLow impact development (LID) practices intercept storm-water runoff and infiltrate it through a range of media types and underlying soils. Hydrologic performance is typically evaluated by comparing inlet and underdrain outlet flows, but there is no standard practice for defining and measuring performance in LID structures designed without underdrains that infiltrate into the ground. Water content reflectometer (WCR) sensors were installed in the aggregate storage layer under permeable pavement and rain garden media to test their ability to measure the size and timing of the wetting front in infiltrating LID practices. WCR data were also used to monitor infiltration rates in the underlying soil beneath both practices. Bench-scale testing was performed to quantify the response of WCRs to saturated and unsaturated conditions and calibrate sensors to a range of water content values. Bench-scale testing revealed that WCRs installed in the aggregate were calibrated to volumetric water content (VWC) as t...

Hydraulic Test of a Bioretention Media Carbon Amendment

Rain gardens effectively remove some stressors from storm water, but in most cases they show much smaller removal rates of nitrate, likely due to the high sand and low organic matter content of rain garden media inhibiting denitrification. A bench-scale experiment was conducted to test the drainage capability of media containing shredded newspaper layers as a carbon amendment. Storm water was introduced at low and high rates to bins containing zero, one, and two layers of newspaper at varying depths. While there were differences in effluent volumes and flow rates between control and newspaper treatments, surface ponding occurred in all three treatments, suggesting that some other factor besides the newspaper had an effect on drainage properties. Grain size and clay mineralogy analyses indicated the migration of finer particles into the deeper soils, which could have inhibited drainage.

Pervious Pavement System Evaluation

The use of a pervious pavement can be effective as a low impact development stormwater control. The Urban Watershed Management Branch is evaluating interlocking concrete paver systems as a type of porous pavement. Although the pavers are impermeable, the spaces between the pavers are backfilled with washed, graded stone that acts as structural support for the pavers and also allows water to infiltrate. After passing the paving stones, the stormwater moves through several bedding layers where pollutants are removed. Recent literature shows that the concentration of total suspended solids in the exfiltrate is substantially less than in the infiltrate. Other pollutant constituents are subject to removal by microbial communities that develop with time. Concrete paver systems were chosen for this investigation for several reasons. Layers of the system can be removed, examined, and replaced, facilitating long-term system monitoring and maintenance. The overall objective of this ongoing project is to assess the pollutant removal efficiency of a pervious pavement system from parking lot runoff. One bench-scale study (hydraulic study) determined the flow rates and materials necessary for the full-scale experiment. Another bench-scale study (microbial study) will examine the role of microbial colonies in pollutant removal performance of this porous pavement micro-environment. Results from the two bench-scale experiments will be used to refine the full-scale investigation. This paper focuses on the hydraulic bench-scale study.

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.

Factorial Study of Rain Garden Design for Nitrogen Removal

AbstractNitrate (NO3−-N) removal studies in rain gardens show great variability in removal rates, and in some cases NO3−-N was exported. A three-way factorial design (2×2×4) was devised for eight outdoor unvegetated rain gardens to evaluate the effects of hydraulic loading (two sizes and two flow rates), the presence/absence of a buried wood chip layer (2), and the presence/absence of a subsurface saturated zone (SZ) (2) on nitrate-nitrite (NO3−-NO2−) removal. Captured stormwater runoff was used in this study. Results showed that the presence of a SZ reduced the NO3−-NO2− mass by 75% compared to a 7% reduction without this zone. The presence of a SZ significantly decreased ammonia-N (NH3-N) mass reduction (p<0.00001). The difference in total nitrogen (TN) mass reduction with the introduced SZ was not significant, largely due to NO3−-NO2− mass reduction that was offset by NH3-N mass increases in rain gardens with the SZ. The buried wood chip layer showed no significant effect on N removal. No significant i...

Modeling the Hydrologic Processes of a Permeable Pavement System

AbstractA permeable pavement system can capture stormwater to reduce runoff volume and flow rate, improve onsite groundwater recharge, and enhance pollutant controls within the site. A new unit process model for evaluating the hydrologic processes of a permeable pavement system has been developed in this study. The developed model can continuously simulate infiltration through the permeable pavement surface, exfiltration from the storage to the surrounding in situ soils, and clogging impacts on infiltration/exfiltration capacity at the pavement surface and the bottom of the subsurface storage unit. The exfiltration modeling component simulates vertical and horizontal exfiltration independently based on Darcy’s formula with elaborating Green-Ampt approximation. The developed model can be arranged with physically-based modeling parameters, such as hydraulic conductivity, Manning’s friction flow parameters, saturated and field capacity volumetric water contents, porosity, and density. The developed model was...

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.