Combined Sewer Overflow Abatement Research Articles

Assessing the system performance of an evolving and integrated urban drainage system to control combined sewer overflows using a multiple-layer based coupled modeling approach

Many earlier developed and densely populated metropolises served by combined sewer systems have been implementing additional stormwater control measures to reduce the impacts of combined sewer overflows (CSO) driven by severe rainstorms. These mitigation measures call for robust modeling strategies to assess the overall performance before development and to predict vulnerabilities, and examine the underlying mechanisms causing them during or after development in a systematic manner. This paper first introduces a hydrologic and hydraulic coupled modeling program-MetroFlow that interacts and integrates multiple models built via diverse methods and tools. A typical integrated urban drainage system (IUDS) in the greater land area of Chicago in the US was investigated as a testbed. In addition, a large-scale Tunnel and Reservoir Plan in construction was evaluated as a mitigation measure to alleviate CSO risks. In this effort, three models were coupled into MetroFlow to account for the best available data of the multiple structural layers involved in this evolving system. Hydrological responses were analyzed under existing and projected system conveyance and storage capacities considering the full spectrum of rainfall conditions employing synthetic storms and real-time simulations of four historical extreme events to account for the anomalies exemplified by individual natural events. The overall effectiveness and resilience of the system were further assessed by the evaluation of normalized performance indicators (PIs) quantifying the reduction of total volume, duration and spread of CSOs. The cluster of simulation results collectively suggests that: (a) the proposed structural layer-based modeling approach is applicable in reproducing distributed rainstorm-driven CSOs for an evolving IUDS based on emerging digital-physical data; (b) CSO characteristics are rather multivariate functions of the rainfall tempo-spatial characteristics as well as the hydraulic performance of the collection system and (c) consistent improvement of CSO abatement was predicted with increasing conveyance and storage provided by the deep tunnel system. The projected system is predicted to capture 24-h storms of return period up to 10 years. MetroFlow’s framework may also promote collaborative modeling, in which community-scale models can be utilized and merged to support extended-scale water and wastewater infrastructure planning, design and management.

The Impacts of Climate Change and Porous Pavements on Combined Sewer Overflows: A Case Study of the City of Buffalo, New York, USA

Combined sewer overflows (CSOs) release pollutants collected in urban runoff into local waterways, impacting both aquatic life and human health. The impact of climate change on precipitation may result in an increase in the frequency and magnitude of heavy precipitation events, with a corresponding increase in CSO discharges. The installation of Green Infrastructure (GI) such as Porous Pavements (PP) is a resilient approach to mitigate CSO events. However, an understanding of the impact of climate change on CSO events and the effectiveness of GI practices is crucial for designing sustainable urban stormwater management systems. Using the Storm Water Management Model (SWMM), the performance of PP as a CSO abatement strategy was studied for the city of Buffalo, New York, USA. This paper used the Intensity-Duration-Frequency (IDF) curves for current (1970–1999) and future (2070–2099) design rainfall scenarios, with four rainfall durations (1, 6, 12, and 24 hours) and four return periods (2, 10, 50, and 100 years). The simulation results show that (1) current 100-year events generate CSO volumes similar to predicted 50-year events; (2) CSO volumes could increase by 11–73% in 2070–2099 compared to 1970–1999 when no GI intervention is performed; and (3) the installation of PP can reduce 2–31% of future CSO volume. This case study demonstrates the regional CSO challenges posed by climate change and supports the use of GI as a mitigation strategy.

How Surface Water Management Can Benefit Fish Conservation in Urban Streams

Abstract We analyzed 33 y of fish community data collected from a low-order, urban stream in central Illinois, USA, to determine the effects of municipal wastewater management projects and urbanization on fish communities. From 1985 to 2017, species richness, number of pollution-intolerant species, and alternative index of biotic integrity significantly increased at sites across this system. Species diversity likewise increased, but was mostly significant only at sites downstream of the effluent outflow. Ceasing the chlorination of wastewater in 1990 resulted in significant increases in fish community metrics both upstream and downstream of effluent outflow, although effects varied from site to site. Completing a combined sewer overflow abatement project in 2008 resulted in some significant increases in species richness, diversity, and number of pollution-intolerant species at sites downstream of effluent outflow. From 2001 to 2016, the change in the number of pollution-intolerant species correlated inversely with the increased percentage of impervious cover in the study system. There was no significant correlation of other metrics with the change in percent impervious surfaces. These results suggest that urbanization at upstream sites limited to some extent the benefits of water management interventions that improved fish community metrics at downstream sites.

Water quantity and quality response of a green roof to storm events: Experimental and monitoring observations

Syracuse, New York is working under a court-ordered agreement to limit combined sewer overflows (CSO) to local surface waters. Green infrastructure technologies, including green roofs, are being implemented as part of a CSO abatement strategy and to develop co-benefits of diminished stormwater runoff, including decreased loading of contaminants to the wastewater system and surface waters. The objective of this study was to examine the quantity and quality of discharge associated with precipitation events over an annual cycle from a green roof in Syracuse, NY and to compare measurements from this monitoring program with results from a roof irrigation experiment. Wet deposition, roof drainage, and water quality were measured for 87 storm events during an approximately 12 month period over 2011–2012. Water and nutrient (total phosphorus, total nitrogen, and dissolved organic carbon) mass balances were conducted on an event basis to evaluate retention annually and during the growing and non-growing seasons. These results are compared with a hydrological manipulation experiment, which comprised of artificially watering of the roof. Loadings of nutrients were calculated for experimental and actual storms using the concentration of nutrients and the flow data of water discharging the roof. The green roof was effective in retaining precipitation quantity from storm events (mean percent retention 96.8%, SD = 2.7%, n = 87), although the relative fraction of water retained decreased with increases in the size of the event. There was no difference in water retention of the green roof for the growing and non-growing seasons. Drainage waters exhibited high concentration of nutrients during the warm temperature growing season, particularly total nitrogen and dissolved organic carbon. Overall, nutrient losses were low because of the strong retention of water. However, there was marked variation in the retention of nutrients by season due to variations in concentrations in roof runoff.

Interceptor Maintenance Cleaning Plan: Evaluating Sewer Cleaning Needs May Yield Combined Sewer Overflow Abatement The Metropolitan District – Hartford, Connecticut

Interceptor Maintenance Cleaning Plan: Evaluating Sewer Cleaning Needs May Yield Combined Sewer Overflow Abatement The Metropolitan District – Hartford, Connecticut

Rapid assessment of the cost-effectiveness of low impact development for CSO control

This paper presents a simple model for assessing the cost-effectiveness of investments in low impact development (LID) for reducing combined sewer overflows (CSOs) in urban watersheds. LID systems, including green roofs, porous pavement, and stormwater treatment wetlands, are site-specific controls for stormwater runoff. If applied throughout a watershed, LID systems like these can reduce the amount of runoff entering the sewer system and reduce CSOs. To be conservative, we focus solely on the function of LID systems as stormwater management techniques, neglecting the other environmental benefits commonly associated with these technologies. A model is presented that can be used to simulate the cost-effectiveness of reducing CSOs through incremental installation of LID technologies across urban watersheds, when they are introduced alone, or in combination with conventional CSO abatement technologies. The potential reduction in CSOs resulting from various levels of LID adoption is simulated using a modified Rational Method. A life-cycle cost analysis is used to compare LID with other alternatives. Given that LID implementation on private property leads to reduced CSOs, a cost sharing scheme is presented that divides the total LID cost into a private cost fraction (born by the property owner) and a public cost fraction (provided by a public agency). The implications of such a policy are discussed with reference to a CSO-shed that drains to the Gowanus Canal (Brooklyn, NY). The results indicate that individual LID systems have differing levels of cost-effectiveness in terms of CSO reduction, but that under a variety of performance and cost scenarios a public subsidy to encourage LID installation represents a cost-effective alternative for public agencies to consider in their efforts to reduce CSOs. Future areas of research in this field are outlined.

Continuous Monitoring of Conventional Parameters to Assess Receiving Water Quality in Support of Combined Sewer Overflow Abatement Plans

As part of its long-term control plan for combined sewer overflow (CSO) abatement, the city of Buffalo, New York, maintained a network of Hydrolab Datasondes (Hydrolab-Hach Company, Loveland, Colorado) to assess receiving water-quality effects by continuously logging dissolved oxygen, pH, temperature, conductivity, and turbidity. Although the effect of individual CSOs could be visualized, turbidity levels entering the Buffalo River from the upper watershed often were greater than from CSO discharges. Turbidity data showed that the Buffalo River was a net-sediment sink. Low dissolved oxygen levels were observed in the summer during dry weather, baseflow, and watershed-wide storms and CSO events. Some CSOs did not produce dissolved oxygen sags in the receiving waters, but others did. This information, together with the sampling done for organic and inorganic contaminants, can aid the decisionmaking process when prioritizing outfalls for abatement work and provides a baseline against which receiving water-quality improvements can be measured.

Sampling and Modeling Approaches to Assess Water Quality Impacts of Combined Sewer Overflows—The Importance of a Watershed Perspective

As part of the planning effort for combined sewer overflow (CSO) abatement, a combination of sampling and mathematical modeling was used to characterize both CSO and receiving water quality in the city of Buffalo, NY. Samples collected during storm events showed that while CSOs within the city boundary are a source of fecal coliform to the Buffalo River, higher concentrations enter the river from the upper watershed, upstream of the city. Loading estimates of Pb, Zn, Cu, and Hg were made for design storms and on an annual basis using a combined model and sampling approach. While the metals loads were quantifiable from the CSOs, the loads associated with the upper watershed discharge were greater, for example, by a factor of 3 to 18 times for the design storms. Continuous, automated sampling of conventional parameters at 15 minute time steps indicated that the river experienced non-compliant periods for dissolved oxygen. In some cases, low dissolved oxygen levels may be associated with CSO inputs, but the hydraulics of the river system also had an important negative impact on dissolved oxygen. In developing CSO abatement options for the Buffalo River, it is essential to recognize that there are other significant contaminant sources in the upper watershed that will continue to negatively impact water quality.

Planning and Design of Combined Sewer Overflow Treatment

Abstract A newly produced (2004) Combined Sewer Overflow (CSO) Treatment Technologies Manual provides an overview of practices in, and guidance for, planning, design and implementation of CSO treatment. Towards this end, the manual first addresses CSO abatement program planning in order to provide an overall framework within which the application and design of CSO treatment facilities may be considered. Following the establishment of a planning framework, guidance is provided for CSO treatment facility preliminary design, which encompasses such steps as the development of CSO control and treatment objectives, assessment of design flows, development of a treatment process train, site-specific considerations, and costs and operating and maintenance (O&M) factors. Finally, preliminary design considerations are developed in more detail for CSO retention treatment basins (RTBs), which are commonly applied to control and treat CSOs in the Great Lakes municipalities. Well-designed RTBs can meet the Ontario requirements for CSO pollution abatement and thereby contribute to the remedial action in the Great Lakes Areas of Concern.

URBAN WET-WEATHER FLOWS: SOURCES OF FECAL CONTAMINATION IMPACTING ON RECREATIONAL WATERS AND THREATENING DRINKING-WATER SOURCES

Discharges of urban stormwater and combined sewer overflows (CSOs) contribute to fecal contamination of urban waters and need to be considered in planning the protection of recreational waters and sources of drinking water. Stormwater characterization indicates that Escherichia coli counts in stormwater typically range from 103 to 104 units per 100 ml. Higher counts (105 units/100 ml) suggest the presence of cross-connections with sanitary sewers, and such connections should be identified and corrected. Fecal contamination of stormwater may be attenuated prior to discharge into surface waters by stormwater management measures, which typically remove suspended solids and attached bacteria. Exceptionally, stormwater discharges in the vicinity of swimming beaches are disinfected. The levels of indicator bacteria in CSOs can be as high as 106 E. coli per 100 ml. Consequently, the abatement of fecal contamination of CSOs is now considered in the design of CSO control and treatment, as for example stipulated in the Ontario Procedure F-5-5. CSO abatement options comprise combin ations of storage and treatment, in which the CSO treatment generally includes disinfection by ultraviolet (UV) irradiation. Finally, indicator bacteria data from Sarnia (Ontario) were used to demonstrate some fecal contamination impacts of wet-weather flows. In wet weather, the microbiological quality of riverine water worsened as a result of CSO and stormwater discharges, and the recreational water guidelines for indicator organisms were exceeded most of the time. Local improvements in water quality were feasible by source controls and diversion of polluted water.

COMBINED SEWER OVERFLOW ABATEMENT PROJECT ENHANCES WATERFRONT PARK AND REDEVELOPMENT PROJECT, AND HIGHWAY IMPROVEMENT PLAN IN THE BRONX

COMBINED SEWER OVERFLOW ABATEMENT PROJECT ENHANCES WATERFRONT PARK AND REDEVELOPMENT PROJECT, AND HIGHWAY IMPROVEMENT PLAN IN THE BRONXThis paper focuses on a description of a highway improvement project that in the course of its development incorporated input from several New York State and New York City agencies to produce a multifaceted project including highway improvements, development of waterfront parks, and water quality improvements resulting from CSO abatement. The practicality of the project centers upon a swapping of...Author(s)Les KlomanRalph DinkleRobert CurtiKevin LloydSourceProceedings of the Water Environment FederationSubjectSession 31 - Surface Water Quality and Ecology Symposium I: Wet Weather CSO IssuesDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2000ISSN1938-6478SICI1938-6478(20000101)2000:11L.62;1-DOI10.2175/193864700784544415Volume / Issue2000 / 11Content sourceWEFTECFirst / last page(s)62 - 79Copyright2000Word count105

Combined Sewer Overflow Abatement: The East River Project

The methodology used by New York City to abate pollution from Combined Sewer Overflows in the receiving harbor waters is presented in a case study for the East River facility planning. The approach integrates water quality studies, facility planning, environmental assessment and public participation. The project suggests construction of three underground storage tanks. Results from the recent water quality survey are summarized and discussed.

Water‐quality modeling of combined sewer overflow effects on Newtown Creek

The upstream branches of Newtown Creek, which receive major combined sewer overflow (CSO) discharges, exhibit stratification of salinity, anoxic conditions below the pycnocline, and emission of hydrogen sulfide (H2S) odors throughout the summer. As high sediment oxygen demand (SOD) levels were coincident with these upstream branches, the modeling approach focused on the mechanisms of solids settling, organic carbon flux, and sediment diagenesis for CSO as well as other sources of solids. Extensive field measurements of the CSOs and the water and sediments within Newtown Creek and the adjoining East River were performed to evaluate model parameters and calibrate/verify the models. Continuous simulations of a 4‐mon summer period for existing (baseline) conditions and CSO abatement alternatives projected the water‐quality improvements that could be expected in the Creek. Because of the extremely low dissolved oxygen (DO) in Newtown Creek, the response to CSO abatement is inhibited, as the model's reaction kinetics would indicate; however, measures that would relieve these conditions and increase DO would also enhance the change in DO achievable through CSO abatement.

DESIGN OF STORMWATER INFILTRATION FOR REDUCTION OF COMBINED SEWER OVERFLOW (CSO)

Stormwater infiltration is a significant tool for combined sewer overflow abatement because it involves a decrease in the impervious area connected to the sewer system. When allowing the infiltration structures to overflow into the existing sewer it is shown that for a required reduction in CSO-volume there exists an unambiguous relation between the infiltration structure volume and the size of impervious area connected to infiltration. Further, the presence of an optimal solution minimizing the total trench volume is pointed out. For a Danish sewer system with a travel time of 30 min and an interceptor capacity of 0.2 μm/s the optimal solution for reducing the CSO-volumes by 40 percent involves connecting 65 percent of the impervious area to infiltration trenches with a total storage volume of 3.6 mm. This corresponds to designing the trenches according to an exceedence return period of 0.04 yrs compared to the commonly applied design return periods of 2 to 10 yrs.

The Role of Computer Modeling in Combined Sewer Overflow Abatement Planning

Increased concern regarding water quality impacts from combined sewer overflows (CSOs) in the U.S. and elsewhere has emphasized the role of computermodeling in analyzing CSO impacts and in planning abatement measures. These measures often involve the construction of very large and costly facilities, and computer simulation during plan development is essential to cost-effective facility sizing. An effective approach to CSO system modeling focuses on detailed hydraulic simulation of the interceptor sewers in conjunction with continuous simulation of the combined sewer system to characterize CSOs and explore storage-treatment tradeoffs in planning abatement facilities. Recent advances in microcomputer hardware and software have made possible a number of new techniques which facilitate the use of computer models in CSO abatement planning.

Model for Selection of Stormwater Control Alternatives

Abstract In urban centres, the degree of pollution from combined sewer overflows and stormwater runoff is becoming ever more noticeable and critical. Among the many stormwater management alternatives for combined sewer overflow abatement, remote monitoring/real-time control is emerging as a cost-effective method in large urban centres. Its advantage is that it does not require additional facilities, but uses the existing system more effectively. A general computer model is needed in the planning stage, which can estimate the overall performance of real-time control and other stormwater management alternatives, without employing expensive, single-event models like WREM. The well-established and most widely used initial planning model STORM is unable to provide an overall system description. Therefore, a new programme, named RAFFI, was devised which can be combined with STORM. The RAFFI is a simple model which provides hourly information on flows and pollutants (BOD and SS) diverted into receiving waters from various overflow points and treatment and by-pass operations at the plant. The model can simulate the overall behaviour of existing and proposed systems in multi-basin urban areas for single storms, or for many storms over a long period, such as one year. In-system storage can be simulated by assuming that the interceptor acts as a common reservoir which can store flows from all watersheds, while each trunk can store flows only from the watershed that it serves. Dynamic regulators can be simulated according to a built-in control strategy, which changes the flow capacity of diversion pipes and outfalls, based on plant, trunk and interceptor flow and storage values at each hour. Capacities for primary, secondary or by-pass operations at the plant can be varied during storms. Treatment of overflows at each outfall can also be simulated. The model is equally applicable to separate storm sewer systems. The objective was not to produce yet another new model, but to integrate programme RAFFI with STORM, in order to increase its capabilities in the initial planning stage. By using STORM-RAFFI, a decision-maker can estimate the overall performance of an existing system during wet