The entire wastewater treatment industry has evolved dramatically during the last 15 to 20 years. The need for new approaches because of the cost of available land, the high cost of sewering, reduced funding, a crumbling infrastructure, and increasing environmental concerns has catalyzed the acceptance of decentralized wastewater treatment strategies and applications as a viable solution to compare with centralized options. Scientists, engineers, regulators, and product manufacturers continue to develop new ways of thinking about how decentralized wastewater treatment is accomplished and managed and advanced products that offer cost and environmental advantages.
It has taken decades for the decentralized wastewater treatment model to fight and claw its way up from the perception as an “ugly stepchild” to a scientifically based and cost-effective wastewater treatment solution. What is offered today is an effective alternative for communities, engineers, and developers who need a wastewater treatment solution.
Additionally, more restrictive codes with the goal of protecting vulnerable environments are causing municipalities to push engineers and developers to present wastewater treatment solutions that can perform long term and contribute to sustainable development. Health codes that regulate onsite wastewater system design and installation are increasingly stringent with the growing awareness of nutrient damage to the environment from nitrogen and phosphorus and with the goal of aquifer protection. The value of preserving water resources is recognized worldwide as one of the greatest challenges of our time.
The good news is that the new codes are resulting in an expanded number of choices for communities needing to upgrade onsite septic systems or expand existing centralized treatment facilities. Product designers and manufacturers have risen to the challenge to provide a host of advanced wastewater treatment and disposal products and system design options.
Focus on vulnerable sites and watersheds
Developing viable economic and environmental solutions for wastewater treatment in environmentally vulnerable areas has been a strong focus during the last 10 years. Replacing or rehabilitating outdated onsite systems such as cesspools and eliminating surface discharge and nitrogen pollution have been leading initiatives to develop new ways of treating wastewater at individual sites as well as community and municipal systems. Finding less capital extensive solutions that can extend the life and expand the capacity of existing centralized systems is also a high priority in many communities open to smart sustainable development but that have aging or undersized wastewater treatment plants. Complicating the challenge is the shortage and cost of easy-to-build sites.
One example of forward thinking in action is Suffolk County, N.Y., which introduced the “Reclaim Our Water” initiative. Nitrogen from residential septic systems has been identified as a significant factor in the degradation of Long Island estuaries. Sewering most of the county was investigated and determined to be financially unfeasible. Therefore, the Suffolk County Health Department has been proactive instituting a septic demonstration program that will implement advanced treatment technologies and shallow dispersal drainfields to reduce nitrogen. In addition, the county sanitary code has been upgraded to allow for these changes. The demonstration program results in a public-private partnership where manufacturers donate systems as part of the program.
As is the case with Suffolk County and other states and provinces, regulators have embraced new products and engineered wastewater treatment solutions by adjusting codes to reflect the increased performance of new products, including the higher throughput rates of aggregate-free products such as plastic leaching chambers and engineered geosynthetic aggregate. The scientific research findings and third-party performance testing data available is helping regulators to be proactive to the benefit of the communities they serve, which benefit from the inclusion of advanced treatment systems in their wastewater arsenal.
Options for engineers and developers
If developers and builders had to rely solely on centralized sewering to dispose of wastewater from their projects, development in many areas would be unfeasible. Potential constraints can include a lack of capacity to accommodate additional flows, the high unit cost of sewering, or a lack of funding to expand the centralized wastewater treatment plant. This continues to elevate a decentralized wastewater treatment solution as the friend of smart, responsible growth. In more and more cases, the size and construction of the decentralized wastewater treatment system influences the way land can be used and developed.
In many communities where centralized wastewater treatment facilities are overburdened and the addition of new sewer lines is prohibited, or where individual septic systems are frowned upon, local health departments and planning agencies are recommending cluster systems to developers. Recognizing the need to advocate advanced wastewater treatment systems of a scale that will support positive development, they also recognize and often require these systems to be managed professionally. Professional management provides more control on the quality of the waste treatment process. If competent management is available, some utilities are even favoring this approach as the most cost-effective, long-term solution.
The availability of advanced technologies in onsite wastewater systems has allowed engineers and system designers working for developers and builders increased land use flexibility. Onsite wastewater system engineers embracing these new options are finding the space-saving and flexible technologies can be adapted easily to site conditions, installed at a reduced size, and even contoured to match the available landscape.
A new generation of onsite wastewater treatment products that enhance design options and system performance, ease installation, and reduce management dilemmas are the key to responsible and sustainable growth and environmental protection. Two examples are chambers and tanks.
It is estimated that one in every three onsite wastewater treatment systems constructed in the United States today is a plastic leaching chamber system. What engineers and system designers have found is that in addition to using chambers in septic system leaching trenches and beds, chambers are highly adaptable and effective for specialized system designs and treatment needs. Chambers are now commonly used in sand filters, mound systems, evapotranspiration beds, community (cluster) systems, constructed wetlands, large-scale wastewater treatment plants, with pretreatment devices, and even on toxic waste remediation sites. New chamber designs offer even more flexibility in system design and installation, including contouring and shallow installations. Recognizing the advantages of chambers, regulators have adjusted their perspectives on leach field sizing and now base it on the level of treatment provided.
Engineers designing large community or commercial wastewater treatment systems now prefer specifying chambers due to their large storage capacity and improved infiltration capacity. They also have more confidence in an engineered product rather than relying on unknown stone quality. Commercial facilities can be subject to large peak flows that the chamber can readily retain. Engineers often use a combination of technologically advanced filters, pumps, tank configurations, and chambers to provide a higher level of treatment. However, like sewers, these systems need a Responsible Management Entity (RME) to operate and maintain the system.
In the case of community wastewater treatment facilities that are close to or over capacity, adding an exfiltration bed utilizing chambers can extend the life and community investment in the wastewater treatment plant and have the added benefit of reducing phosphorus and eliminating outfall discharges to bodies of water.
The Town of Foxboro, Mass., advised the private developers constructing Gillette stadium that they could not furnish enough water or treat the wastewater from the planned 68,000-seat project, making reuse of reclaimed water the only viable answer. The design was to capture 1.2 million gallons per day of effluent from the stadium, treat it to a high degree, and store it for reuse when necessary. Wastewater is reused for toilet flushing, irrigation, cooling water, and flushing of streets and sidewalks. Excess water is discharged below the surface of the parking lot via a 2.4-acre groundwater chamber recharge field utilizing Infiltrator plastic leaching chambers, which allow recharge of the local aquifer.
The need for compact systems for small lots and for systems in environmentally sensitive areas is serving as a catalyst for tank innovation, including increased safeguards to ensure water tightness. On difficult sites, the ability to install a tank in a shallow, low-profile configuration to leverage the available space while avoiding rock or problematic soil conditions is another need pushing designers to innovate.
Additional advances in manufacturing process related to plastic tanks have resulted in increased strength and durability compared with previous tanks. The manufacturing process allows inclusion of corrugations and ribbing and interior structural bulkheads to increase tank strength. Recent, significant breakthroughs in injection molding have allowed larger tanks (1,500 gallons) to be manufactured and offer many benefits. The tank has a consistent wall thickness and the process allows for a much higher-strength plastic material, yielding a high-strength yet low-weight tank. Tanks are conveniently manufactured in “halves,” allowing them to nest for increased shipping density.
In Surgoinsville, Tenn., a $4.5 million project serves 247 residences, two schools, and nine businesses. Installed on lots with existing homes, outbuildings, driveways, and landscaping, the project was designed with the additional capacity to serve approximately 700 properties. The low-pressure sewer system delivers wastewater to the city of Church Hill’s wastewater plant. The system is comprised of approximately nine miles of low-pressure sanitary sewer collection lines, two pump stations, and individual STEP services at more than 200 residences that include Infiltrator IM-Tanks. Difficult Appalachian sites with steep slopes and limited backyard access to existing homes made tank installation challenging and the ease of handling the plastic tanks provided the ideal solution. As well, the tanks were delivered nested to the installer’s onsite staging yard and staff assembled the tanks as needed to complete the project. This saved time and space prior to installation.
As the need increases to develop areas away from sewers or to add to existing overburdened infrastructure, so has progress in development and acceptance of advanced onsite systems and the science behind them. Most states and local health departments have created or revised regulations that accommodate advanced onsite systems. The introduction of chamber technology more than 30 years ago was a revolutionary step in the increased effectiveness and acceptance of standard and advanced onsite systems, but it was just the beginning. In the future, we will surely see many new system designs and advanced treatment options developed in response to changing environmental and economic needs.
Dennis F. Hallahan, P.E., technical director, Infiltrator Water Technologies (www.infiltratorwater.com), is responsible for technology transfer between Infiltrator and the regulatory and design communities and consults on product research and testing for universities and private consultants. He has more than 25 years of experience with onsite wastewater treatment system design and construction. He may be contacted at firstname.lastname@example.org.