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Technologies to keep an eye on the weather and the infrastructure The United States’ aging underground infrastructure, increasing development, federal mandates, and the relative unpredictable temperament of nature mean stormwater program managers are eyeing the best technologies on the market to help plan programs and model storm systems in order to correctly size stormwater infrastructure, such as pipes, drainage systems, and retention/detention ponds. Working Across Jurisdictions “Many of our ongoing projects involve developing plans to address current capacity issues and capacity required to support future growth and development,” says Cantrell. “At present, many of our clients are in the process of addressing required reductions of combined and sanitary sewer system overflows as required by the EPA. “Many options exist to address these problems, including combined sewer separation, storage, high-rate treatment, and reduction of inflow and infiltration,” he adds. “Key to this is utilizing a sufficiently detailed model that can support the development of accurate cost-benefit comparisons between levels of control and resulting improvements in water quality.” Over the past 10 years, there have been significant advancements in both monitoring and modeling technologies, Cantrell points out. “For example, we regularly use Doppler-based radar rainfall data to supplement ground-based rain gauges,” he says. “This gives us a much better understanding of the true spatial distribution of storms we monitor to calibrate our models. “In terms of models, vast improvements have been made, which now allow us to model these complex systems very closely to how they operate in reality,” he says. “This includes advanced real-time control systems, which can be used to modify how a collection system operates dynamically to achieve optimal performance.” Cantrell has been involved with many stormwater programs, ranging from small areas (less than 1,000 acres) to very large areas (countywide). Currently, Metcalf & Eddy is working on two systems that involve multiple cities and counties. Annual rainfall totals for the two areas range from 40 to 50 inches. One project in which the firm was involved was for the City of Dayton, OH, and the Montgomery County Integrated Wastewater Model and Master Plan. The two utilities joined forces to create a joint wastewater master plan for their connected wastewater collection systems, which serve a population of 159,000 in Dayton per the 2005 US Census and 844,000 residents in the greater Dayton metropolitan area. “The county’s sewers flow into the city sewers at several locations,” says Cantrell. “Our project has involved the development of an integrated GIS [geographical information system] and model to represent both sewer systems in a holistic manner—essentially ignoring political jurisdiction boundaries. “Using the model—which is in the final stages of calibration—we will develop short- and long-term solutions to address ongoing problems and capacity needs for future development. The model is one of the largest in Ohio, with more than 12,000 manholes and pipes.” The Metcalf & Eddy team is utilizing advanced radar rainfall data to enhance the calibration accuracy. The model represents all complex details of the collection system and accurately predicts what is going on during dry- and wet-weather conditions, notes Cantrell. Metcalf & Eddy is also assisting with the Sanitation District No. 1 (SD1) of Northern Kentucky Infrastructure Plan. SD1 currently provides wastewater collection and treatment services for 90,000 customer accounts. “Recently, SD1 entered into a federal consent decree with the US Environmental Protection Agency to address overflows within its combined and separate sewer systems,” Cantrell explains. He says SD1 has taken a unique approach to develop plans focusing on watershed issues to ensure a high cost benefit for any capital investments made, a plan endorsed by the EPA as a model for other utilities to follow. “SD1 has previously developed models of its collection systems and key receiving waters and is currently in the process of updating and refining these models,” says Cantrell. “Once this effort is completed, the agency will develop integrated watershed plans to address pollution from both point and nonpoint sources.” New CSO Policy Sacramento is generally flat with elevations ranging from 10 feet in the southwest corner of the city and between 20 and 30 feet going north and east from the southwest low-lying area. The city receives about 18 inches of rainfall annually and is located at the confluence of the Sacramento River and the American River. Years ago, the downtown area frequently flooded, and in the late 1800s, a significant portion of the downtown ground and floor elevations was raised 12 feet. Later, a system of levees was constructed to prevent severe flooding from seasonal high flows in the Sacramento and American rivers.
Due to the levee system, the CSS pipelines—which used to discharge directly into the Sacramento River—now terminate at two major pumping facilities known as Sump 1/1a and Sump 2, constructed in 1908 and 1914, respectively. Today, Sacramento operates the CSS under a National Pollutant Discharge Elimination System (NPDES) permit for controlling combined system overflows (CSOs) to the river and the surcharging of combined sewer outflows to streets, says Bruce Barboza, a senior engineer for the City of Sacramento. The LTCP consists of increasing the pumping and treatment capacities of the existing system, constructing large relief sewer pipelines that serve as in-line pipe storage of excess combined sewer, and constructing several local and regional underground storage facilities designed to fill before outflows reach the street, says Barboza. Initially, all combined wastewater is sent to two sump pumps. In the first-stage operation, dry-weather flows and runoff from small storm events are sent to the Sacramento Regional Wastewater Treatment Plant (SRWTP). Flows that exceed 60 million gallons per day start up the second-stage operation. In those operations, the flows are routed to Pioneer Reservoir for storage (23 million gallons) and to the Combined Wastewater Treatment Plant (CWTP) for primary treatment of flows up to 130 million gallons per day to be discharged to the Sacramento River. When this treatment plant is at capacity, Stage 3 operations are started. In those operations, the city operates Pioneer Reservoir as a primary treatment plant for discharging up to 250 million gallons per day of treated flows to the Sacramento River. When these capacities are exceeded and the capacities of the upstream pipeline system and storage facilities are surpassed, untreated combined sewage is released to the river. In April 1994, the USEPA issued its Combined Sewer Overflow Policy for controlling discharges to the nation’s waters from combined sewer systems. One of the cornerstones of the CSO policy is the requirement for nine minimum controls (NMCs), which apply to every CSS nationwide, Barboza points out. The NMCs are defined as the minimum technology-based actions or measures designed to reduce CSOs and their effects on receiving water quality without extensive engineering studies or major construction. This policy stipulates that at least 85% of the average annual CSS storm flow be captured and receive primary treatment with disinfection prior to discharge. The results of a five-year monitoring effort and study (Effluent and Receiving Water Quality and Toxicity Summary Report for 1991–1995) found Sacramento was in compliance with this policy during the study period and treated approximately 92% of the total CSS storm flow volume prior to discharge, says Barboza. This monitoring effort was completed prior to implementation of the improvements detailed in the 1995 CSS Improvement and Rehabilitation Plan, which significantly reduced the occurrence of CSOs. The 1995 LTCP was based on modeling evaluations conducted with the city’s Combined System SWMM Model, which is a modified version of the EPA’s Storm Water Management Model, says Barboza. The city has added other modeling features for measuring combined sewer outflow volumes to the street and re-entrance of the outflows, among others, he says. The goal of Sacramento’s efforts is to ensure that new development within the CSS addresses its downstream impacts either by paying a mitigation fee or by directly providing mitigation, says Barboza. “Additionally, we are studying areas of the CSS on its perimeter that can be removed from the system by diverting the sewage into regional sewer interceptors,” he says. “For major development projects—as well as general infill development identified in the General Plan—we develop regional projects using the CSS SWMM Model that mitigate the impacts and also provide continuous reduction in overall flooding.” Many of the 1995 LTCP improvements have been completed, and others are in design or under review as part of an ongoing process to improve the CSS system and update the LTCP. “The overall goal is to mitigate the occurrence of combined sewer outflows to the street for storm events at or below the 10-year, six-hour storm [about 1.65 inches in six hours],” says Barboza. “The combined system area is experiencing a lot of new growth, which will increase the combined sewer outflows to the street if not controlled and planned for. “The future combined area sewer flows from the city’s 20-year projected growth and land-use development plan have been superimposed into the SWMM model. We are in the process of looking at future combined system mitigation improvement projects that will now include these added future sewer flows from growth projections.” In carrying out its mission, Sacramento is implementing several types of technologies:
Modeling Improvements Among the many goals of the municipalities’ stormwater programs is the expansion of the storm drain system as the city grows, the separation of a combined sewer system, and mitigation of flooding problems, among others. Vasarhelyi’s firm deals with all such goals. “When you do master plans in the municipal context, the primary purpose is essentially to evaluate the system for four months and then develop a capital improvement program so they can decide which elements of the stormwater management system need to be updated and when,” he says. “From then, the software is used for supporting more detailed designs.” Vasarhelyi remembers the days when he used slide rules for mapping. “When engineers use the non-modeling techniques, they essentially need to make an evaluation based on a much more limited set of data,” he says. “Modeling programs ensure you can create a digital model of a physical system in the ground and expose it to a number of different potential conditions, which you can phase. “You can evaluate it, and your recommendations are really much better founded than any other ways or approaches. With automation, you can define and develop an ultimate system.” Maurico Herrera, a water resources engineer with CH2M Hill, says the models have evolved more into a user-friendly format than in the past. “Originally, they were DOS-based programs, and now they are Windows-based,” he says. “They have a better range with GIS and are more efficient because we can compile lots of data, put it in the model, and analyze different scenarios a lot quicker now than when this program started.” The ability to illustrate numbers with aerial photographs is another plus, Vasarhelyi says. “There is a picture behind the numbers, so the engineer has a much better connection to the actual physical system that’s on the ground,” he says. “That is a revolutionary change compared to modeling techniques that use DOS techniques. You just had numbers and tried to visualize the numbers. Now you can actually work with real pictures of the land.” Other modalities are used for long-term forecasting for water supplies and considering the potential impact of climate change on water availability in the long run. Modeling also is used to project the impact of mining impacts on streams and how major highway projects will impact the drainage and irrigation patterns of the land. The two key technologies used by CH2M Hill include GIS for data management and analysis and hydrologic, hydraulic, and water-quality modeling for system evaluations, planning, and design. The GIS systems used by CH2M Hill include ArcView GIS and analytical tools and 3D-Analyst and Spatial Analyst. Of the hydrologic, hydraulic, and water-quality modeling tools, CH2M Hill uses EPA SWMM5, xpswmm, PCSWMM (for which Herrera is an instructor), DHI Mouse, UBC Watershed Model, HEC-RAS, and HEC-GeoRAS, among others. At HDR Engineering Inc., an architectural, engineering, and consulting firm based in Omaha, NE, Suresh Hettiarachchi, an engineer with the company, says his firm uses SWMM, HMS, and HEC-RAS in assisting municipalities in dealing with stormwater programs. As such, the firm assists municipalities in meeting certain goals, such as expanding the storm drain system as the city grows, separating a combined sewer system and mitigating flood programs, and examining water-quality issues as they relate to the quantity of runoff. “We are using GIS a lot more,” says Hettiarachchi. “Integration with GIS is making things easier. We relate to the ‘real world’ well with it and can easily manage data.” Carol Brzozowski is a journalist in Coral Springs, FL. SW November/December 2007 |
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