Shape Up Your Compliance

Hydraulic modeling software can assist you in meeting the requirements set out in stormwater and wastewater regulations

• By Seth Johnson, John R. Haestad
• Apr 01, 2004

With the promulgation of new laws and regulations pertaining to water quality, extensive stormwater and sanitary sewer management plans are no longer a luxury for rapidly growing and affluent communities. Neglecting corrective action to bring systems into compliance can have far-reaching consequences, including polluted drinking water sources, heavy state and federal fines and jail time. In this regard, cities and municipalities are being mandated to assume roles as water resources managers and enforcers of water quality protection.

Many of the regulations stipulated by the Clean Water Act (CWA) allow the U.S. Environmental Protection Agency (EPA) to transfer permitting and regulatory authority to the states. Two such policies are the National Pollutant Discharge Elimination System (NPDES) Phase II programs for reducing pollutants in urban stormwater and the imminent Capacity, Management, Operations and Maintenance (CMOM) program for reducing sanitary sewer overflows (SSOs) at municipal sanitary sewer collection systems. Compliance with these regulation policies involves comprehensive assessments of physical, biological, ecological and socioeconomic impacts to the systems. When dealing with complex stormwater and sewer systems, the calculations involved in the analysis and design can be daunting and time-consuming.

Such assessments require the type of innovative data processing techniques and assessment methodology that only a computer simulation model can provide. Computer simulation models afford engineering professionals the technical tools for synthesizing, visualizing and analyzing data to assess a number of variables on their systems. Not only can a model of a system be used to achieve regulatory compliance, it can also produce the most-efficient and cost-effective solutions that save cities and municipalities valuable amounts of time and money.

For example, the primary elements of the NPDES Phase II programs require municipalities to select and implement a series of Best Management Practices (BMPs) and measurable goals that comprehensively address specific stormwater problems in their respective areas. Hydraulic models can be used to address three of the six elements, which pertain to the technical control measures including (1) detecting and eliminating illicit discharge and combined sanitary sewer overflows (CSOs); (2) controlling construction site stormwater runoff; and (3) addressing discharges of post-construction stormwater runoff from new development and redevelopment areas.

Making Use of Hydraulic Models
As such, many municipalities are already using hydraulic models to meet BMPs for designing facilities and for simulating the operation of short- and long-control structures. For example, the following table (Table 1) highlights a few of the BMPs analyzed by municipalities to meet NPDES Phase II regulatory requirements using Haestad Methods' software.

Modeling can also be an extremely useful tool for complying with CMOM regulations. A key component of the CMOM regulations, known as the System Evaluation and Capacity Assurance Plan, requires communities to collect and manage information about their sanitary sewer collection systems. Municipalities with combined systems are restricted from having more than four overflow events or combined sewer overflows (CSOs) per year and are also required to capture or eliminate at least 85 percent of sewage overflow.

With a model simulation of a sanitary sewer system, engineers can determine the capacity of those components to predict the locations of potential sanitary sewer overflows, establish plans to correct hydraulic deficiencies, identify the sources contributing to overflows and determine the impact of adding new flows. With sophisticated modeling features such as extended-period simulations (EPS), users can create a continuous time-based model that realistically simulates sewage pumping operation and assists utilities in determining how much overflow will occur and where it will happen. Modeling capabilities such as these give engineers the tools they need to quickly gain comprehensive insight into how sanitary sewer systems operate and enable them to take proactive measures toward implementing a sound CMOM program.

Getting the Right Computer Model for the Job
However, it should be noted that not all engineering computer models are created equal. One recently released commercial model, for example, doesn't account for backwater effects through the sewer system. This means that if a pipe is under capacity, engineers won't see its effects upstream. As a direct result, engineers can overlook problem areas and may be misled into making decisions that won't prevent overflows. With an industry-leading computer model, hydraulic deficiencies in a system can be clearly identified.

Haestad Methods is a recognized industry leader in the development and support of computer models that are both easy to use and driven by the most up-to-date numerical methods. To this end, Haestad has been able to bridge the gap between the needs of engineers and managers and the advances developed by top-notch researchers at universities and the government. This means that when civil and environmental engineering professionals are faced with a problem such as "determining the frequency of sewer overflows" or "sizing a detention pond to maintain runoff at predevelopment levels," they don't need to reinvent the wheel to perform these calculations. Software that allows for easy data entry and editing and the creation of report quality graphics and tables can be an invaluable resource in the development of management plans.

Get the Training and Resources You Need
However, there is a caveat: powerful software in the hands of an uneducated user can be dangerous. To guard against the misuse of computer modeling products, professionals are encouraged to enroll in accredited training programs. There are also many textbooks on the market on stormwater conveyance modeling and design and wastewater collection systems.

In short, computer models provide critical tools to help establish efficient and economical stormwater management and wastewater collection programs that meet regulatory standards and include short- and long-term contingency plans to avoid potential problems for whatever the future may bring.

References
Web Sites and Other Resource Centers:

• EPA Phase II Home Page -- www.epa.gov/npdes/stormwater
• National Menu of Best Management Practices for NPDES Storm Water Phase II -- www.epa.gov/npdes/menuofbmps/menu.htm
• National Stormwater Best Management Practices Database -- www.bmpdatabase.org
• CMOM.net -- www.cmom.net
• American Water Resources Association -- www.awwa.org
• Water Environment Federation -- www.wef.org
• Haestad Methods -- www.haestad.com

Publications

• Stormwater Conveyance Modeling and Design, Haestad Press, 2003
• Storm Water Phase II Final Rule Fact Sheet Series, EPA 833-F-00-002, January 2000
• Storm Water Phase II Compliance Assistance Guide, EPA 833-R-00-002, June 2000
• Report to Congress on the Phase I Storm Water Regulations, EPA 833-00-01
• Report to Congress on the Phase II Storm Water Regulations, EPA 833-R-99-001

This article originally appeared in the 04/01/2004 issue of Environmental Protection.