The potential to manage releases of Bacillus anthracis using bioretention and a high flow media filter: Results of simulated runoff testing with tracer spores Bacillus globigii.

The threat of bioterrorism has spurred research on the decontamination and containment of different agents. Anthrax [causative agent Bacillus anthracis (Ba)] is a disease that can lead to severe infections within human and animals, particularly when inhaled. This research investigated the use of spore-contaminated simulated runoff events into stormwater control measures (SCMs), which are designed to retain and improve the quality of runoff and may have the potential to filter and contain the spores. In this study, the effectiveness of a bioretention cell (BRC) and high flow media filter (HFMF) in Huron, Ohio, were evaluated for removal of Bacillus globigii (Bg) spores (a harmless cognate of Ba). Three 4-8 mm simulated runoff events were created for each SCM using a fire hydrant and Bg spores were injected into the runoff upstream of the SCM inlets. The BRC significantly (p < 0.001) outperformed the HFMF in reducing Bg concentrations and loads, with an average load reduction of 1.9 log (∼99% reduction) compared to 0.4 (∼60% reduction), respectively. A probable critical design factor leading to these differences was the infiltration rate of the media and subsequent retention time within the filters, which was supported by similar disparities in suspended solids reductions. Differences in spore removal may also have been due to particle size distribution of the HFMF, which was more gravelly than the bioretention cell. At 3 and 6 months after the-simulated runoff tests, soil samples taken from both SCMs, yielding detectable Bg spores within the top 15 cm of media, with increased spore concentrations where ponding occurred for longer durations during the tests. This suggests that forebays and areas near inlets may be hotspots for spore cleanup in a real-world bioterrorism incident.

Survey of the operational status of twenty-six urban stormwater biofilter facilities in Sweden.

This study evaluates the operational status of twenty-six biofilter facilities across nine cities in Sweden, with respect to their functional design criteria, engineered design features (filter media composition, hydraulic conductivity, and drawdown time), and includes a visual inspection of the biofilter components (pre-treatment, in/outlet structures, filter media, and vegetation). These indicators were used to examine the performance level of each biofilter in achieving their design objectives set by the operators. Furthermore, it was investigated whether the biofilter facilities had been properly maintained to meet the objectives. Results indicate that the soil media used was consistent with respect to percentage sand, fines, and organic matter and comparable to design recommendations used by municipalities in other countries. The field-tested hydraulic conductivity for the biofilters ranged from 30 to 962 mm/h. This range of values, along with noticeable sediment accumulation within the biofilter indicate that not all the sites were operating optimally. Pre-treatment stages in poor condition with high volumes of sediment and litter accumulation were the primary causes for, and indicators of, low hydraulic conductivity rates. The ponding volume calculations revealed that at least 40 % of facilities did not have enough capacity to retain every-day and/or design rainfall due to design and/or construction flaws. These analyses raise concerns that, for a considerable number of the biofilters surveyed, water retention and flood protection identified by operators as prioritised objectives are not being met. This raises significant concerns about the functionality of biofilter in practice. Finally, some suggestions are given for tackling the design and maintenance problems discovered.

Next generation swale design for stormwater runoff treatment: A comprehensive approach.

Swales are the oldest and most common stormwater control measure for conveying and treating roadway runoff worldwide. Swales are also gaining popularity as part of stormwater treatment trains and as crucial elements in green infrastructure to build more resilient cities. To achieve higher pollutant reductions, swale alternatives with engineered media (bioswales) and wetland conditions (wet swales) are being tested. However, the available swale design guidance is primarily focused on hydraulic conveyance, overlooking their function as an important water quality treatment tool. The objective of this article is to provide science-based swale design guidance for treating targeted pollutants in stormwater runoff. This guidance is underpinned by a literature review. The results of this review suggest that well-maintained grass swales with check dams or infiltration swales are the best options for runoff volume reduction and removal of sediment and heavy metals. For nitrogen removal, wet swales are the most effective swale alternative. Bioswales are best for phosphorus and bacteria removal; both wet swales and bioswales can also treat heavy metals. Selection of a swale type depends on the site constraints, local climate, and available funding for design, construction, and operation. Appropriate siting, pre-design site investigations, and consideration of future maintenance during design are critical to successful long-term swale performance. Swale design recommendations based on a synthesis of the available research are provided, but actual design standards should be developed using local empirical data. Future research is necessary to identify optimal design parameters for all swale types, especially for wet swales.

Hydrologic and water quality performance of two aging and unmaintained dry detention basins receiving highway stormwater runoff.

Dry detention basins (DDBs) are a type of stormwater control measure (SCM) designed to provide flood storage, peak discharge reduction, and some water quality improvement through sedimentation. DDBs are ubiquitous in the urban environment, but are expensive to maintain. In this study, two overgrown DDBs near Raleigh, NC, receiving highway runoff were monitored for up to one year to quantify their water quality and hydrologic performance. Both basins, B1 and B2, have not received vegetation maintenance since construction in 2007. Flow-weighted composite samples were collected during storm events and analyzed for nutrients (Total Phosphorus (TP), Ortho-phosphorus (OP), Ammonia-N (NH3), NO2-3-N (NOX), and Total Kjeldahl Nitrogen (TKN)), total suspended solids (TSS), and total Cd, Cu, Pb, and Zn. An annual water balance was also conducted to quantify runoff volume reduction. Despite low influent concentrations from the highway, significant removal efficiencies were found for all constituents except NH3 in B1. TP, OP, NOX, TSS, and Zn were reduced in B2. Both basins achieved greater than 41% volume reduction through soil infiltration and evapotranspiration, resulting in significant pollutant load reductions for all detected constituents, between 59% and 79% in B1 and 35% and 81% in B2. This study provides evidence that overgrown and unmaintained DDBs can reduce pollutant concentrations comparable to those reported for maintained DDBs, while reducing more volume than standard DDBs. Moreover, carbon sequestration likely increases while maintenance costs decrease.

Insights from using in-situ ultraviolet-visible spectroscopy to assess nitrogen treatment and subsurface dynamics in a regenerative stormwater conveyance (RSC) system.

Regenerative stormwater conveyance (RSC) is a recently developed stormwater control measure that marries the concepts of bioretention and stream restoration. RSC mitigates stormwater runoff by converting surface flow to subsurface seepage using a series of pools and riffles built over a sand media bed. Subsurface seepage flows through media and exits the RSC beneath the outlet weir. Previous studies on RSC pollutant mitigation have focused on surface flow discharges from the RSC. To date, no known research has been conducted on the potential pollutant contributions of RSC seepage, despite the fact that this water also enters receiving waters. This research used Multi-Point Sampling coupled with in-situ ultraviolet-visual spectroscopy to measure nitrogen in seepage during simulated storm events (n = 9) at a field-scale RSC in Raleigh, North Carolina. Calibrations between light absorbance and concentrations were acceptable (Nash-Sutcliffe coefficient > 0.65) for nitrate and total ammoniacal nitrogen (TAN) and very good (Nash-Sutcliffe coefficient > 0.90) for total Kjehdahl nitrogen (TKN). Early storm simulations revealed some initial nutrient flushing from the substrate, which subsided by the third simulation. Overall, subsurface seepage nitrate, TAN, and TKN concentrations were lower by 29%, 57%, and 4% relative to storm inflow concentrations, respectively. Computed subsurface nitrogen concentrations demonstrated temporal variability, highlighting dynamic transport and biogeochemical transformations in saturated and unsaturated conditions. Nitrogen concentrations were lower in seepage than in surface flow; however, due to the high volume of runoff converted to seepage, nitrogen loads discharged in seepage can be larger than those of surface flow. Further research is needed to examine subsurface pollutant reductions under varying hydrologic and seasonal conditions.

Stormwater management in nutrient-sensitive watersheds: a case study investigating impervious cover limits and pollutant-load regulations.

The objective of this research project was to compare two stormwater management strategies within a nutrient-sensitive watershed: impervious cover limits versus pollutant-load regulations. A case study was conducted in the nutrient-sensitive Falls Lake watershed in North Carolina, USA, where a commercial fitness complex was constructed in a zone previously restricted to low-density housing. The Falls Lake watershed has a stormwater regulation that limits total nitrogen and total phosphorus export loads to 2.47 kg/ha/yr and 0.37 kg/ha/yr, respectively. Hydrology and water quality were monitored pre- and post-development to quantify changes to stormwater volumes, pollutant concentrations, and annual export loading rates. On-site stormwater control measures (SCMs) reduced nutrient export loading rates below the regulatory standard. However, increased stormwater volumes and nutrient export loading rates were observed from pervious surfaces that were disturbed during construction (total nitrogen increased from 2.06 to 4.24 kg/ha/yr, total phosphorus increased from 0.41 to 0.73 kg/ha/yr). Results from this case study suggest that (1) impervious cover limits do not adequately account for a parcel's nutrient export loads and (2) SCMs that reduce volume and treat pollutants can reduce nutrient export loads below regulatory levels in the Falls Lake watershed.

Hydrologic and water quality performance of permeable pavement with internal water storage over a clay soil in Durham, North Carolina.

Permeable pavement is an effective tool for improving stormwater hydrology and water quality when sited over soils with high infiltration rates, but its efficacy over less permeable soils is uncertain. This study examined permeable pavement performance when built over a low-conductivity, clay soil. Four parking stalls (50 m2 total area) were retrofitted with permeable interlocking concrete pavement (PICP) to treat 15.2 m2 of contributing impervious area (0.3:1 run-on ratio). Using an elevated underdrain, the site incorporated a 150-mm internal water storage (IWS) zone to increase exfiltration and promote anaerobic conditions for denitrification. From March 2014-April 2015, 22% of influent runoff volume was reduced via exfiltration and evaporation. Inter-event drawdown of the IWS zone created storage to capture and exfiltrate more than 70% of the runoff volume from precipitation events less than 8 mm, and peak flows were significantly reduced (median 84%). Relative to stormwater runoff from a nearby impermeable asphalt reference watershed, the permeable pavement produced significantly lower event mean concentrations (EMCs) of all pollutants except nitrate, which was significantly higher. Permeable pavement effluent and reference watershed runoff were 99%, 68%, and 96% different for total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP), respectively. Significantly lower permeable pavement effluent EMCs for copper (Cu, 79%), lead (Pb, 92%) and zinc (Zn, 88%) were also observed. The median effluent concentrations of TN (0.52 mg/L), TP (0.02 mg/L), and TSS (7 mg/L) were all very low relative to the literature. Sampling of nitrogen species in the IWS zone 12, 36, 60, and 84 h post-rainfall was done to better understand mechanisms of nitrogen removal in permeable pavement; results indicated denitrification may be occurring in the IWS zone. Effluent pollutant load from the permeable pavement was at minimum 85% less than from nearby untreated asphalt runoff for TP, TSS, Cu, Pb, and Zn, and was 73% less for TN. Permeable pavements built over low-permeability soils with internal water storage can considerably improve long-term hydrology and water quality.

Air quality considerations for stormwater green street design.

Green streets are increasingly being used as a stormwater management strategy to mitigate stormwater runoff at its source while providing other environmental and societal benefits, including connecting pedestrians to the street. Simultaneously, human exposure to particulate matter from urban transportation is of major concern worldwide due to the proximity of pedestrians, drivers, and cyclists to the emission sources. Vegetation used for stormwater treatment can help designers limit the exposure of people to air pollutants. This goal can be achieved through the deliberate placement of green streets, along with strategic planting schemes that maximize pollutant dispersion. This communication presents general design considerations for green streets that combine stormwater management and air quality goals. There is currently limited guidance on designing green streets for air quality considerations; this is the first communication to offer suggestions and advice for the design of green stormwater streets in regards to their effects on air quality. Street characteristics including (1) the width to height ratio of the street to the buildings, (2) the type of trees and their location, and (3) any prevailing winds can have an impact on pollutant concentrations within the street and along sidewalks. Vegetation within stormwater control measures has the ability to reduce particulate matter concentrations; however, it must be carefully selected and placed within the green street to promote the dispersion of air flow.

Evaluating the spatial distribution of pollutants and associated maintenance requirements in an 11 year-old bioretention cell in urban Charlotte, NC.

Bioretention cells (BRCs) are an increasingly popular Stormwater Control Measure used to mitigate the hydrologic and water quality impacts of urbanization. Previous BRC research has demonstrated a strong capacity for pollutant removal; however, long-term sequestration of pollutants within soil media can elevate concentrations to levels fostering environmental and human health risks. Soil media samples were collected from an 11 year-old BRC in Charlotte, NC, and analyzed for the accumulation and spatial distribution of zinc, copper, and phosphorus. Pollutant distribution varied significantly with respect to depth and ordinate distance from the BRC inlet. Zinc concentrations (0.9-228.6 mg kg-1 soil) exceeded environmental thresholds and phosphorus concentrations (5.1-173.3 mg kg-1 soil) increased from initial levels by a factor of seven; however, notable accumulation was restricted to the BRC forebay. Maximum zinc and copper concentrations in soil media did not exceed 1% of mandatory cleanup levels and with regular maintenance of the forebay, the effective life of BRC media should exceed the life of the developments they treat.

Quantifying volume reduction and peak flow mitigation for three bioretention cells in clay soils in northeast Ohio.

Green infrastructure aims to restore watershed hydrologic function by more closely mimicking pre-development groundwater recharge and evapotranspiration (ET). Bioretention has become a popular stormwater control due to its ability to reduce runoff volume through these pathways. Three bioretention cells constructed in low permeability soils in northeast Ohio were monitored for non-winter quantification of inflow, drainage, ET, and exfiltration. The inclusion of an internal water storage (IWS) zone allowed the three cells to reduce runoff by 59%, 42%, and 36% over the monitoring period, in spite of the tight underlying soils. The exfiltration rate and the IWS zone thickness were the primary determinants of volume reduction performance. Post-construction measured drawdown rates were higher than pre-construction soil vertical hydraulic conductivity tests in all cases, due to lateral exfiltration from the IWS zones and ET, which are not typically accounted for in pre-construction soil testing. The minimum rainfall depths required to produce outflow for the three cells were 5.5, 7.4, and 13.8mm. During events with 1-year design rainfall intensities, peak flow reduction varied from 24 to 96%, with the best mitigation during events where peak rainfall rate occurred before the centroid of the rainfall volume, when adequate bowl storage was available to limit overflow.

Maintenance measures for preservation and recovery of permeable pavement surface infiltration rate--The effects of street sweeping, vacuum cleaning, high pressure washing, and milling.

The surface infiltration rates (SIR) of permeable pavements decline with time as sediment and debris clog pore spaces. Effective maintenance techniques are needed to ensure the hydraulic functionality and water quality benefits of this stormwater control. Eight different small-scale and full-scale maintenance techniques aimed at recovering pavement permeability were evaluated at ten different permeable pavement sites in the USA and Sweden. Maintenance techniques included manual removal of the upper 2 cm of fill material, mechanical street sweeping, regenerative-air street sweeping, vacuum street sweeping, hand-held vacuuming, high pressure washing, and milling of porous asphalt. The removal of the upper 2 cm of clogging material did not significantly improve the SIR of concrete grid paves (CGP) and permeable interlocking concrete pavers (PICP) due to the inclusion of fines in the joint and bedding stone during construction, suggesting routine maintenance cannot overcome improper construction. For porous asphalt maintenance, industrial hand-held vacuum cleaning, pressure washing, and milling were increasingly successful at recovering the SIR. Milling to a depth of 2.5 cm nearly restored the SIR for a 21-year old porous asphalt pavement to like-new conditions. For PICP, street sweepers employing suction were shown to be preferable to mechanical sweepers; additionally, maintenance efforts may become more intensive over time to maintain a threshold SIR, as maintenance was not 100% effective at removing clogging material.

Improving bioretention/biofiltration performance with restorative maintenance.

One of the most popular Stormwater Control Measures is bioretention, or biofiltration. Anecdotal evidence suggests that well-designed bioretention cells are often not adequately installed and that maintenance is lacking, leading to less-than-adequate water storage volume and/or surface infiltration rates post-construction. In March 2009, two sets of bioretention cells were repaired by excavating the top 75 mm of fill media, increasing the bioretention surface storage volume by nearly 90% and the infiltration rate by up to a factor of 10. Overflow volume decreased from 35 and 37% in the pre-repair state for two different sets of cells, respectively, to 11 and 12%. Nearly all effluent pollutant loads exiting the post-repair cells were lower than their pre-repair conditions. The bioretention systems employed two different media depths (0.6 and 0.9 m). The deeper media cells discharged less outflow volume than the shallower cells, with 10-11% more runoff volume leaving as exfiltration from the 0.9-m than from the 0.6-m media depth cells. This study showed that maintenance is both critical and beneficial to restore otherwise poorly performing bioretention. Moreover, while deeper media cells did outperform the shallower systems, the improvement in this case was somewhat modest vis-à-vis additional construction costs.

Ecosystem service provision by stormwater wetlands and ponds - a means for evaluation?

Stormwater control measures (SCMs) such as constructed stormwater ponds and constructed stormwater wetlands (CSWs) are designed to regulate runoff hydrology and quality. However, these created ecosystems also provide a range of other benefits, or ecosystem services, which are often acknowledged but rarely quantified. In this study, additional ecosystem services, including carbon sequestration, biodiversity, and cultural services, were assessed and compared between 20 ponds and 20 CSWs in North Carolina, USA. Carbon sequestration was estimated through the carbon content of pond and wetland sediments across a gradient of system age. Biodiversity was quantified in terms of the richness and Shannon diversity index of vegetative and aquatic macroinvertebrate communities. Cultural services were qualitatively assessed based on the potential for recreational and educational opportunities at each site. Ponds and wetlands were found to support similar levels of macroinvertebrate diversity, though differences community composition arose between the two habitat types. CSWs demonstrated greater potential to provide carbon sequestration, vegetative diversity, and cultural ecosystem services. This assessment provides an initial framework upon which future assessments of ecosystem service provision by SCMs can build.

Overview of regulatory/policy/economic issues related to carbon dioxide.

This is an overview of Session 2c dealing with the regulatory, policy and economic issues related to carbon dioxide and its impact on global climate change. The information is taken from the two papers presented in this session (the U.S. Perspective by Dennis Leaf and the European Perspective by Hans J.H. Verolme) and from the panel discussion that took place at the end of the session. The overview focuses primarily on the policy responses of both the United States (US) and the United Kingdom (UK) to changes in global atmospheric pollution. To a lesser extent, the progress of policy responses to these changes is discussed. The United Nations Framework Convention on Climate Change (UNFCCC) has been signed and ratified by over 180 countries. The UNFCCC contained no binding targets or timetables for emissions reductions. The Kyoto Protocol [United Nations. Kyoto Protocol to the United Nations Framework Convention on Climate Change. UNEP.IUC/99/10. Chatlelaine, Switzerland: United Nations Environment Programme's Information Unit for Conventions, for the Climate Change Secretariat, 1997] to the UNFCCC did contain targets and timetables for reductions of greenhouse gases on the part of developed countries. The US has signed but not ratified the Kyoto Protocol. The US has experienced some movement to reduce greenhouse gas emissions on the part of various levels of government, as well as the private sector. The UK's commitment to reducing green house gases is laid down in the UK Climate Change Programme 2000. The UK is a member of the European Union (EU). In this context, an example of EU-wide progress, the voluntary agreement with car manufacturers to reduce CO(2) emissions in new vehicles, will be discussed. In addition, there will be some discussion on the UK CO(2) trading scheme that created the first market in the world in April 2001. Overall, the policy process is constantly informed by scientific research. In the case of climate change, much of this work is carried out under the auspices of international scientific panels.