Decentralized strategies for sustainable water

October 2012 » Features » PROGRESSIVE ENGINEERING
A life cycle management approach to infrastructure assets optimizes capital for communities.
Tom Birkeland
Jackson Meadow is a cluster development that preserves open space and integrates water and wastewater infrastructure into the environment. A constructed wetland treats and recycles a total of 11,000 gallons per day of domestic sewage. The development utilizes gravity sewer for collection and a series of septic tanks for primary treatment.

The advent of decentralized water and wastewater technologies during the last 15 years has provided many significant opportunities for engineers, planners, and communities to create a sustainable water infrastructure for both new and existing development. Adopting a decentralized approach to water supply and wastewater treatment has many benefits. It effectively enables communities to meet their environmental requirements, reduce the impact of developments on groundwater, conserve natural open spaces, and recycle treated wastewater for beneficial purposes such as irrigation. While there are many different types of technologies available for implementing decentralized strategies, any operations program should consider adopting a life cycle approach to management as part of a long-term solution for creating a sustainable water infrastructure.

Decentralized infrastructure
The traditional centralized approach to water supply and wastewater treatment involves extracting water for use, sending it to a central system for treatment, and then discharging the treated water into a river where it is carried downstream. The centralized approach is a necessary part of supporting large populations, but it can create unintended consequences. For example, effluent discharged to rivers adds additional pollutants to already impaired waters with no water being returned to underground aquifers. With a centralized approach, each additional home connection to the sewer line exhausts more of our water resources.

Planning for ongoing sampling and testing of effluent must be considered as part of a long-term management strategy.

A newer strategy is to apply a decentralized approach to wastewater treatment, making it possible to provide a sustainable water use model for future development. Through this strategy, new clusters of homes extract groundwater locally, consume it, treat the wastewater onsite, and return it close to its point of origin. This recharges the aquifer and prevents water from being pulled out of the ground and sent down a river. Decentralized systems provide a paradigm shift when thinking about wastewater. In a centralized system, wastewater effluent is considered a waste product and is commonly sent downstream. Decentralized systems, however, consider all water as a resource and keep it local, safely treated, cleaned, and recharging the aquifers through the soil.

Onsite wastewater treatment can also enable water reuse options such as irrigation and aid in creating sustainable systems and new wastewater treatment technology, thus leading to better development practices. Whereas traditional onsite wastewater systems – including single septic tanks – often require extensive land for soil to treat wastewater, new wastewater technology is less land intensive and provides better long-term treatment, especially for nitrogen.

One problem with decentralized technology is that it can be complex to operate, manage, and maintain. The scale of many systems, the regulatory requirements put on them, and the need to manage decentralized water and wastewater infrastructure assets for the long term can present many social, economic, and environmental challenges for owners of decentralized systems. Because many systems are privately owned, the assessment, repair, and replacement of assets that make up water and wastewater infrastructure are ongoing expenses that must be paid for over the lifetime of the system. Understanding the life cycle approach to managing this infrastructure can help owners of decentralized systems move toward a more sustainable management approach.

Benefits of a life cycle management strategy
Implementing life cycle management strategies to manage decentralized water infrastructure can help increase treatment and energy efficiency. They can also contribute to greater financial health and security for communities and end users. A life cycle approach to managing water and wastewater infrastructure enables communities to efficiently allocate their assets and to maximize the value of capital as they plan for future operations and maintenance expenditures. Adopting this model can lead communities to make sound planning decisions for setting rate structures that reflect current and future usage and help to meet the changing regulatory requirements. It can also allow communities to effectively plan for the large capital expenditures needed to keep their infrastructure operating efficiently for the long term.

The goal of life cycle management is to deliver the desired level of service for end users while at the same time maintaining the infrastructure assets at the lowest life cycle cost. By establishing the appropriate cost and timing for repairing or replacing an asset, life cycle management provides a workable framework for understanding and achieving sustainable infrastructure. Managing infrastructure capital assets and minimizing the total cost of owning and operating them, while also delivering the desired service levels to end users, creates a long-term sustainable future.

Treatment components must be maintained and periodically upgraded to provide ongoing service.

A life cycle management program incorporates detailed asset inventories, operation and maintenance tasks, and the long-range financial planning necessary to build out to system capacity. By creating a management platform that measures and documents infrastructure conditions and is proactive in keeping infrastructure working well regardless of the age of components or the availability of additional funds, this approach ensures the long-term health of the system. Maintaining accurate data is critical to success. This includes asset attributes (e.g., age, condition, and criticality), life cycle costing, proactive operations and maintenance, and capital replacement plans based on cost-benefit analyses of individual components.

While the benefits of life cycle management range across many aspects of managing water and wastewater infrastructure, outcomes that can be realized include the following:

  • prolonging asset life and facilitating in the repair and replacement decisions through efficient and focused operations and maintenance;
  • meeting user service demands with a focus on sustainability;
  • setting rates based on sound operational and financial planning;
  • budgeting focused on activities critical to sustained performance;
  • meeting regulatory requirements;
  • improving responses to emergencies;
  • enhancing treatment performance while diminishing electrical usage; and
  • reducing overall costs for both operations and capital expenditures.

Core questions
Life cycle management is centered on a framework of five core questions, which provide the foundation for all planning and future decisions:

  1. What is the current state of the infrastructure and associated assets?
  2. What is the required level of service and performance required by the end users and stakeholders?
  3. Which assets are critical to sustained performance and how long will they last?
  4. What are the minimum life cycle costs of individual assets?
  5. What is the best long-term funding strategy to replace assets and pay for ongoing operational costs?

Answering these key questions and using them to create a life cycle management program can begin to address the growing trend for communities to be required to do more with less. A large part of life cycle management is ensuring that the delivery of core services in water and wastewater infrastructure is provided in an efficient, sustainable, and cost-effective manner. It ensures that end users and stakeholders are getting the level of service required, at the lowest sustainable life cycle cost.

Life cycle management in action
Jackson Meadow is a 60-home community designed as a village, located in the historic settlement of Marine on St. Croix in Washington County, Minn. The homes are clustered on 40 acres, which allows conservation of 300 acres of land that is dedicated as permanent open space. The greatest development challenge was to provide onsite wastewater treatment to a small lot cluster development in an unsewered community, without the environmental issues created by standard septic systems.

A decentralized approach to water supply and wastewater treatment has many benefits, including the ability to recycle treated wastewater for beneficial purposes such as irrigation.

To accomplish this, Jackson Meadow installed two constructed wetlands to treat and recycle a total of 11,000 gallons per day (gpd) of domestic sewage. The development utilizes gravity sewer for collection and a series of septic tanks for primary treatment. A time-actuated lift station periodically doses effluent from the septic tanks into one of two 11,000-square-foot wetland treatment cells. Wastewater effluent is then passed into the soil for additional polishing, prior to reaching the surficial groundwater.

Although this is a fairly simple system from a technology perspective, having a sound financial model in place from the very beginning has enabled the community to create a reserve fund capable of addressing both the expected capital replacement costs of key assets such as lift station pumps and septic tank pumping, as well as unexpected expenses such as gopher damage, prairie fires, sewer blockages, and changing environmental regulations. The management model developed for Jackson Meadow suggests that a life cycle approach to managing water and wastewater infrastructure offers hope for communities as they seek to get the most out of their treatment system for the long term.

Conclusion
Adjusting the way we think about managing water and wastewater infrastructure assets to provide a cost-effective, sustainable service delivery model enables communities to optimize capital resources. This in turn provides them with the ability to conserve operational costs and invest in critical operations and maintenance programs including the planned upgrades necessary for long-term program success. Implementing life cycle management strategies allows communities to embark on an infrastructure management program that accesses current assets and plans for the future based on a triple bottom line approach – financial, social, and environmental effects. Using this approach in evaluating any infrastructure investment, communities can derive significant benefits and protect the environment for the future.


Adjusting the way we think about managing water and wastewater infrastructure assets to provide a cost-effective, sustainable service delivery model enables communities to optimize capital resources.


Tom Birkeland, senior project manager, Natural Systems Utilities, MN (formerly EcoCheck), is a licensed water and wastewater operator whose projects have received more than 15 wastewater operation awards for excellence from the Minnesota Pollution Control Agency. Prior to EcoCheck, Birkeland worked with North American Wetland Engineering (NAWE). He can be contacted at tbirkeland@ecocheck.com.

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