Pipe Networks Demanding More Attention, Resources
During the past 30 years, managers of water and wastewater utilities have faced a variety of challenges in managing their treatment plants.
By Jeroen Olthof and Dave Keil
During the past 30 years, managers of water and wastewater utilities have faced a variety of challenges in managing their treatment plants. Regulatory changes in the Safe Drinking Water Act and the Clean Water Act, population growth, and changes in treatment technology have driven utilities to expand and improve their treatment facilities. In the future, these pressures can be expected to continue.
Condition assessment and maintenance management can extend the useful life of storage tanks, pumping stations, and other infrastructure.
Now, a new set of pressures is presenting itself. The pipe networks of water and wastewater utilities have historically received less attention than the treatment plants. Systems have been expanded to serve new growth areas, but few utilities have been able to implement a comprehensive asset management program for their pipe networks. Potential results include water main breaks, poor water quality in water distribution networks, and sewer overflows. The economic, environmental, and public health costs of these failures can be considerable.
To avoid these types of failures, utility managers can expect to devote more resources to their pipe networks. The drivers for increased attention on pipe networks include continued population growth, regulatory requirements, and aging infrastructure.
The U.S. population is not growing as quickly as it has in the past, but many utilities continue to see consistent growth. Much of the growth consists of expanded suburban development that requires new pipelines to distribute water and collect wastewater. New storage tanks, booster pump stations, sewage lift stations and other facilities also may be required. Often the expectation is that these new facilities will be financed through impact fees or some other mechanism to allow growth to pay for growth. However, the maintenance of these new facilities places an added workload on utilities that are already being pressed to do more with less. The geographic expansion of service areas also leads to longer residence times in distribution networks and longer travel times in collection networks, both of which can lead to water quality or corrosion issues.
Growth patterns in other parts of the country are better described as urban redevelopment and infill. This type of development presents its own set of challenges. For water distribution systems, denser development means higher water demands, which can sometimes be offset by less lawn irrigation.
If an area is redeveloped with multifamily housing or commercial development, the required fire flows and peak demands may be considerably higher than for which the pipe network was originally designed. In addition, internal corrosion and tuberculation in aging pipes could greatly reduce the available pipe capacity concurrently with an increase in water demand from re-development. Given these trends, some utilities are investigating the impacts if fire flow is removed from their mission, weighing customers' expected higher insurance premiums against increased usage costs for expensive rehabilitation and replacement programs in aging systems.
For wastewater collection systems, infill development leads to higher sanitary flows that can potentially overwhelm gravity pipes and pump stations. In these urban areas, construction to add new hydraulic capacity is typically very expensive and time-consuming.
New development, in addition to creating the need for water/wastewater infrastructure that must be maintained, affects the performance of existing water and wastewater systems.
Another effect of expanding development is that the community places an increased value on remaining undeveloped land. Often the remaining undevelopable, open space is along streams or in canyon or ravine areas that provide the preferred route for gravity sewer pipelines. Planners of new sewer lines may be forced to construct pump stations and force mains to avoid routing new gravity pipelines through environmentally sensitive areas. Utilities with existing sewers in undeveloped ravines can expect increased scrutiny of maintenance and spill prevention practices on these pipelines, as regulatory agencies and environmental groups focus attention on remaining open space.
Distribution and collection systems are facing higher levels of scrutiny from regulatory agencies. For water distribution systems, one of the focus points is disinfection by-products. Upcoming EPA regulations will require increased monitoring throughout the distribution system for these potentially dangerous by-products of disinfection. The water quality in pipes and tanks must be monitored, and tank inlet and outlet modifications, flushing programs, and other corrective actions may be required. Computer hydraulic models of distribution systems can be used to simulate water quality in the distribution systems and pinpoint potential areas of concern while reducing the extent of required monitoring.
For wastewater collection systems, the focus of attention has been the proposed Capacity, Management, Operation and Maintenance (CMOM) regulations. Although these regulations may not be finalized for some time, elements of the regulations are already being adopted by some state regulatory agencies. In California, some Regional Water Quality Control Boards are asking collection system operators to prepare Sanitary Sewer Management Plans that have many of the same elements as CMOM. These elements may include a program for assessing hydraulic capacity, a program for cleaning and maintenance of the collection system, and a condition assessment program to evaluate system assets and prepare for their replacement.
Many utility managers in smaller communities have also been responsible for managing the area's storm water system. Storm water infrastructure has historically been orphaned to other established revenue-generating utilities, such as wastewater and water systems. However, the Storm Water NPDES Phase 2 regulations have prompted the formation of self-sufficient storm water utilities in smaller communities with dedicated revenue streams. The focus and intent of the Storm Water NPDES Phase 2 regulations are to improve water quality in receiving waters in urban watersheds. To this end, many of its elements are similar to the CMOM regulations for wastewater, e.g., improved and established maintenance and management programs.
Many large U.S. cities installed their first water and sewer pipes in the 19th century. The country's impressive growth during the 20th century led to an exponential increase in the size of distribution and collection systems. As we move into the 21st century, many of these assets will need increased maintenance, rehabilitation or replacement.
As an example, the Seattle Public Utilities (SPU) water system contains over 1,600 miles of distribution mains. Approximately 40 percent of these mains are unlined cast iron mains installed prior to 1940. Due to substantial internal corrosion and tuberculation, these unlined mains have significantly reduced flow capacity and are a primary cause of low pressure and impaired fire flow in the SPU distribution system. The overall extent of these problems is too large to quantify based on operational history and field records alone, and blanket replacement or rehabilitation of unlined mains would not be an economical solution for the SPU system.
In 1999, SPU initiated a comprehensive study of hydraulic capacity in the SPU water distribution system. In the analysis, hydraulic models of individual pressure zones were generated from the city of Seattle GIS database and were calibrated based on extensive hydrant flow tests, pipe roughness (Hazen-Williams C-factor) tests, and operation records for an extended 24-hour period. System improvements to satisfy planning-level pressure and fire flow were identified and planning-level cost estimates for the improvements were developed.
In addition to evaluating hydraulic capacity, proactive utilities are embarking on condition assessment programs to evaluate their pipes, pump stations and storage tanks. The findings of these programs are being used to prepare capital improvement plans to ensure the continued reliability of water and sewer networks. In some cases, comprehensive maintenance programs are able to extend the useful life of some assets.
These replacement or rehabilitation projects are occurring in already-developed areas that present numerous potential conflicts with other utilities, transportation improvements, and local residents and businesses. The execution of $10 million in distribution system or collection system improvements will require considerably more community involvement, environmental permitting, program coordination and other "soft costs" than the execution of $10 million in improvements on a treatment plant site.
Managers of water and wastewater utilities can expect to continue to face challenges in keeping their treatment facilities up to date. However, they can expect to spend an increasing portion of their resources on their pipe networks. At a time when maintenance budgets are stretched, new development will continue to place new demands on distribution and collection systems. Federal and state regulatory agencies are increasing their focus on water quality in water distribution systems and the management of wastewater collection systems to prevent sewer overflows. As these pipes, tanks, and pump stations continue to get older, managers face expensive rehabilitation and replacement projects, or the potential for expensive system failures. A comprehensive asset management program can allow utilities to meet these challenges in a fiscally responsible manner.
About the Authors:
Jeroen Olthof is a project manager in HDR's San Diego office and works with clients on planning and management of water/wastewater infrastructure. He can be reached at 858-712-8312 or firstname.lastname@example.org. David Keil is a project manager in HDR's Bellevue, WA, office focusing on analysis and design of distributed assets such as water distribution and storage systems. He can be reached at 425-450-6200 or email@example.com.