Small Communities

Watershed Management and Decentralized Wastewater Treatment

Barry Tonning

In their book The Starfish and the Spider: The Unstoppable Power of Leaderless Organizations, authors Ori Brafman and Rod Beckstrom discuss how fragile and inefficient centralized organizations can be, and how decentralized organizations — which might appear to be somewhat disorganized at times — often prove to be efficient, adaptive, and durable. The examples provided in the book support this thesis. The Spaniard Hernando Cortez was able to defeat the Aztecs in Mexico by tricking and killing the central chief, Montezuma, but could not suppress the loosely confederated and highly independent bands of Apaches in the American Southwest. Al Qaeda is likewise decentralized and still very much in operation around the world, despite our best efforts. The brain itself operates as a network of nodes that interact to produce, store, and retrieve memories and use them to decide future actions. User-driven, decentralized networks — such as Napster, Craigslist, and the blogosphere — are on the rise worldwide.

The book’s title refers to the different anatomies of the starfish and the spider. The spider’s is centralized: Cut off its head, and it dies. The starfish, however, will grow a new arm if one is cut off. Moreover, the severed arm can grow an entirely new body, as every major organ is replicated across each arm.

This discussion mirrors a wide-ranging, fulsome, and sometimes rambunctious dialogue among wastewater professionals. Until recently, wastewater treatment usually meant “big pipe” centralized facilities in high-density areas or low-tech individual “septic” systems in rural areas. Between those two extremes were the package plants, many of which discharged to surface waters without strict National Pollutant Discharge Elimination System permit oversight and the operation and maintenance attention required.

But now, there are many choices. Decentralized wastewater treatment technologies include an array of both collection systems and treatment–dispersal facility options that provide a high level of performance when properly designed, operated, and maintained. A range of pretreatment options exist, allowing a tailored approach that balances treatment levels with the sensitivity of the receiving environment. Soil-discharging cluster systems distributed across the landscape offer several benefits. The most obvious groundwater protection benefit is the capacity of dispersed facilities to treat and release high-quality effluent to the soil, where it can be purified further as it recharges upper and lower groundwater tables. Shallow aquifers in urbanized areas have been compromised by the proliferation of impervious land cover — which lowers infiltration, recharge, and stream baseflows — and sewer collection lines that drain streams or contaminate them because of infiltration and inflow or sewer line leaks.

Surface water quality also can be improved through decentralized soil-dispersal facilities. Plants that discharge directly to surface waters have little room for error: Upsets, equipment failure, or unexpected inflows quickly can result in bypasses or poor-quality effluent discharges despite the best efforts to manage the situation. When dispersed soil-based systems fail, the problems are usually smaller, more manageable, and less likely to contaminate surface waters. In addition, the growing pressure to reduce nutrient discharges to threatened and impaired waterbodies has spiked interest in systems that process phosphorus and nitrogen loads away from surface waters, where they can be treated through common chemical, physical, and biological processes.

Decentralized wastewater treatment also has the potential to serve as a cornerstone for planning and zoning policies designed to protect surface waters, groundwater, and other natural resources, such as forest or meadow lands. But this potential is being ignored, misused, or poorly applied in some areas where planning and zoning practices depended on wastewater service limitations to control growth. For example, in many cases, planning and zoning approaches allow development to occur only in areas that are currently served — or will be served in the future — by centralized sewer collection lines. Planners in effect have managed and directed growth by controlling sewer pipe construction, since areas without sewer service usually are served by individual septic systems that require the right mix of soils, slopes, water tables, and rock — conditions found in only about one-third of the United States.

Decentralized treatment technologies, however, can produce a cleaner effluent that can be infiltrated on sites with higher water tables, greater varieties of vegetated cover — even forest — and steeper slopes. These advantages have allowed builders to serve new development on land formerly acknowledged to be off limits.

Fortunately, planners are beginning to recognize that two key aspects of decentralized wastewater treatment can provide a basis for an approach to smart, low-impact growth that can target and preserve landscape features near and dear to almost everyone. Under this approach, certain areas are targeted for protection, such as streams and drainage system features, along with their vegetated buffers; forest patches and areas of mature trees; and farmland, wetlands, meadows, and critical habitat. Structures are clustered in moderate-to-high-density small-footprint nodes among these protected areas, which should be preserved permanently through conservation easements or transfer of ownership to park districts or nonprofit land trusts. Some of the protected areas can serve as water recharge and recycling infiltration sites for clustered treatment and stormwater systems, providing a strong rationale for permanent protection and preservation.

The resulting landscape accommodates development efficiently, protects desired features effectively, and provides necessary infrastructure for new homes and businesses cost-effectively. When coupled with the key principles of stormwater management — minimization of impervious surfaces and maximization of precipitation infiltration, both of which are relatively easy to incorporate on such a landscape — you end up with a powerful strategy for watershed protection.

Of course, decentralized facilities are not a panacea for all problems in all places. Large centralized treatment plants have played a major role in cleaning up the nation’s waters during the past 30 years, and they will continue to provide a valuable service in densely developed areas. However, distributed or decentralized systems offer a field-tested, viable, and cost-effective approach for addressing capacity, effluent quality, and water resource protection issues in rural, urban, and suburban areas. They should be considered an important tool in the wastewater and watershed management toolbox.

Barry Tonning is an associate director in the Fairfax, Va., office of Tetra Tech (Pasadena, Calif.).

©2007 Water Environment Federation. All rights reserved.