Environmental Science & Engineering - www.esemag.com - September 2005
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The evolution of diverse chamber system applications

By Dennis F. Hallahan P.E.

Chambers are used on remediation sites. Here a large wetland cell utilizing chambers will help to clean up a toxic waste site.
The use of chambers has expanded to include sand filters. The chambers allow a better effluent dispersal and gas exchange.
Chamber systems have long been used in arid regions of the US and Canada in evapotranspiration beds. This chamber ET is serving a state park.
After an extensive value engineering review the Port Burwell Wastewater Treatment Plant installed an "onsite outfall" with substantial cost savings.
On-site wastewater treatment systems serve over 25 percent of homes in the United States and Canada. Over the past 30 years, chambers have evolved dramatically in design and are now commonly used for onsite treatment in basic and advanced applications.

The first chambers to be used commercially were constructed of concrete and installed in New England in the early 1970s. These initial concrete “gallery” chamber systems or “ameration chambers” (USEPA, 1980) were more efficient than previous traditional stone and pipe systems. They were, however, heavy and unwieldy to transport, and labor intensive to install. It became clear that an alternative material was needed to manufacture chambers that would not sacrifice strength, durability, and treatment performance.

The rapid advancement of plastics technology made plastic the next logical step in the evolution in chamber design. Several years of research and design culminated with the introduction of plastic chambers to the marketplace by Infiltrator Systems Inc. in 1987. Today, plastic chambers are manufactured by four different companies and have become widely accepted by installers, designers, and regulators.

In Ontario, Infiltrator plastic chambers are included in over 15 percent of all septic systems. In some areas, that number is as high as 74 percent. In Manitoba, where Infiltrator chambers are the only chambers approved for use in the province, it is estimated that 46 percent of all septic systems installed utilize these chambers. In the United States, it is estimated that one in every four wastewater treatment systems constructed today is a chamber system.

While the principles of treatment remain the same, plastic chambers offer tremendous benefits over their concrete predecessors and even greater benefits when compared to the older methods of installations that involved stone and pipe trenches.

Initially, chambers were used for the leachfield component of the onsite wastewater treatment system. As the needs evolved, designers and installers began to specify the technology for a number of differing applications. What they found is that the chamber is highly adaptable and effective for specialized system designs and treatment needs.

In addition to the traditional use in septic system leaching trenches and beds, chambers have been used in sand filters, mound systems, evapotranspiration beds, community systems, constructed wetlands, wastewater treatment plants, with pretreatment devices, and even on toxic waste remediation sites.

In most chamber applications, no stone or geotextile is required. This eliminates concern over stone quality and fines content and the need for heavy trucks used to transport stone. Installations are faster and save on heavy equipment operation costs. Chamber installations also reduce site disturbance and minimize compaction of the soils, a definite plus for system longevity.

Chambers are currently manufactured using technologically advanced moulds that cost in the millions of dollars. These produce precisely engineered products with uniform dimensions. Typically, they are very complex with tight tolerances that allow for interlocking joints and open louvered sidewalls that prevent soil from entering the system. Chambers can be moulded in various sizes ranging from six to 30-inch heights and to a width over 50 inches.

Advanced chamber system designs and applications
Commercial facilities can be subject to large peak flows that the chamber can readily retain. These decentralized cluster septic systems serve multiple residential dwellings or commercial establishments. They use technologically advanced filters, pumps, tank configurations, and drainage chambers to provide a higher level of treatment. Decentralized cluster systems treat wastewater and return it to the ground very near to where the wastewater was generated as opposed to transporting it long distances to a centralized sewer facility. The driving force behind this trend is the high cost of sewers and lack of quality land available, forcing builders to consider developing sites that would have previously been deemed unusable due to location or geology.

Sand filters
Some sand filters today are designed utilizing the benefits of chamber technology. Chambers provide increased distribution coverage, allowing the effluent to be applied over the entire surface area of the bottom of the chamber. A sand filter is a type of packed bed filter that has been used for over a century. Newer packed bed technologies consist of peat, textile, or foam media and are generally very reliable, providing good treatment.

Evapotranspiration systems
Another common application for chambers is their use in evapotranspiration (ET) systems. In the arid regions of the United States and Canada, systems have been specifically designed for evapotransipiration. With these systems, people thought that the solid arch at the top of the chamber would inhibit evapotranspiration. However, upon investigation of the physics of water and air movement through soil, it can be understood that evapotranspiration occurs with chambers for the same reasons it occurs in stone trenches.

Once ponding occurs in the trench the effluent will flow laterally out the trench sidewall, allowing capillary action of the soil to take place. From capillary action, water is pulled upward in the soil matrix. The water then changes to vapour form (gas phase), which allows it to move vertically through the soil pores to the atmosphere.

Wetland treatment systems
Natural wetlands have been used as convenient wastewater discharge sites for as long as sewage has been collected. By the early 1970s, research into the treatment capabilities of natural wetlands led to the development of engineered, or “constructed” wetlands that replicated the cleansing capabilities of these natural marsh systems. Wetland treatment systems are typically used to polish treated wastewater, and are often designed as multi-function treatment and wildlife habitat systems.

These systems may be large commercial or community systems, or small wetland treatment cells serving an individual home. One of the most common types is the subsurface flow (SSF) constructed wetland. Effluent is treated through shallow subsurface channels in which emergent plants are established. The treatment cells produce a high quality treated effluent that is required to be disposed to the subsurface. Chambers have frequently been specified for the wetland cell and the subsurface disposal applications due to cost savings and chamber reliability as compared to older traditional construction options. In areas with sensitive soils, the ease and speed of installation and minimal construction traffic (less time to be exposed to rainstorms and construction machinery) can protect the structure of the soil and its infiltration capacity.

Wastewater treatment facilities
A great example of the use of chambers in extending the life of wastewater treatment facilities is in Bayham, Ontario, at the Port Burwell Sewage Treatment Plant. Here the outfall discharges to a creek in close proximity to Lake Erie. Expansion of the plant required a major upgrade to the outfall extending out a distance into the lake. The creek could not assimilate the increase in minimum contaminants and, therefore, an outfall to the lake was proposed.

After an extensive investigation of options, an onsite solution was recommended to convert the outfall to an exfiltration bed utilizing chambers. The chamber system saved considerable cost and also provided additional pollutant removal. The benefit of installing an exfiltration bed at the treatment plant is the reduction in phosphorous. Additional phosphorous will be removed by the natural ability of the soil to absorb the nutrient, thereby removing the impact to the sensitive lake environment.

Biofilters
Chambers are also now being specified in biofilters, beds of organic media that are used to scrub objectionable odours from the air. Odorous air vented from compost facilities, rendering operations, and pumping stations can be passed through a biofilter, removing ammonia and reducing sulphur compounds such as mercaptans, amines, and VOCs. These odours are biodegraded to odorless substances in the biofilter. Water flowing through the biofilter will leach these non-toxic chemicals from the media, lengthening the life of the media. According to Lew Naylor, Ph D., of Black and Veatch, chambers used in biofilters can improve air distribution through the media, provide more efficient drainage, increase media life, ease of construction of the biofilter, and simplify media replacement.

Remediation site clean-up
Environmental clean-up sites have many treatment schemes, one of which is known as “pump and treat”. In this scenario, contaminated groundwater is pumped to the surface, treated, and then discharged subsurface to recharge groundwater levels and maintain flow patterns. The size of the recharge bed is determined by the infiltration rate of the soil and the quantity of flow.

Previous methods of recharging ground water included stone beds. However, the fines associated with stone can have a significant adverse effect on the infiltration rate, thereby increasing the size of the recharge bed. Engineers have determined that if chambers are installed as the recharge solution the concerns regarding the adverse affect of fines can be minimized.

In the future we will surely see many new system designs and advanced treatment options developed in response to changing environmental and economical needs. As designers and engineers are challenged to create innovative solutions to the world’s wastewater problems, chambers could be in the forefront of those solutions.

Dennis F. Hallahan P.E., is Technical Director,
Infiltrator Systems Inc.
Contact: www.infiltratorsystems.com

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