Feb 06, 2017

Recharging Sustainability

Decentralized wastewater treatment system contributes to green goals

In many regions across the U.S. and Canada, water tables are lowering, causing wells to run dry and saltwater to intrude inland, and leaving an increasing number of people without a reliable water source. As populations continue to grow and shift, it is imperative for all aspects of the water cycle to be optimized for sustainability.

Artificial aquifer recharge (AAR) is a growing method of water table stabilization and water supply in the U.S. Conventional methods of AAR include open-air recharge basins and injection wells that replace water into the aquifer. However, when adequately designed and installed, decentralized wastewater systems have the capacity to discharge large quantities of wastewater into the underlying soils, making them one of the most passive, sustainable forms of AAR. Decentralized systems provide both wastewater treatment and groundwater recharge in one step.

An increasing number of municipalities across the U.S. are turning to decentralized wastewater treatment for groundwater recharge as a barrier to prevent saltwater intrusion. The U.S. Environmental Protection Agency (EPA) defines aquifer recharge as, “the enhancement of natural groundwater supplies using man-made conveyances such as infiltration basins or injection wells.” As currently defined by EPA, aquifer recharge systems typically are used in areas with limited groundwater or surface water availability.

Dealing With Drought

In California, drought remains a major challenge and no area of the state has been completely spared, according to the U.S. Drought Monitor. In addition, excessive groundwater pumping for irrigation and a growing population have stressed water supplies. California regulators took a step toward allowing direct potable reuse, releasing a study about the feasibility of using this treatment practice in the state. “The State Water Board recommends that short-term research be conducted to identify suitable treatment options for final treatment processes that can provide some attenuation with respect to potential chemical peaks (in particular, for chemicals that have the potential to persist through advanced water treatment), which may be best conducted by the water and wastewater industry as an engineering application,” the report said.

This is where soil-based decentralized systems can provide extra public health protection. Contaminants of emerging concern, including pharmaceuticals and personal care products are a major concern they can help address.

Blue Oak Ranch Reserve

Blue Oak Ranch Reserve is a member of the world’s largest network of university owned and operated biological field stations and ecological reserves. It supports the University of California’s commitment to excellence in teaching, research and public service. The 3,280-sq-acre property on Mount Hamilton near San Jose, Calif., was donated to the university in 2007, becoming part of a system of 39 reserves throughout the state that comprise the UC Natural Reserve System.

A renovation of the Blue Oak Ranch Reserve facilities proposed by the University of California, Berkeley, included new construction of facilities and housing to accommodate up to 50 people. It was a significant increase to the existing facility, so a suitable wastewater system was required to serve the facilities and protect the surrounding environment. A key consideration in system selection was aquifer recharge.

The new buildings consisted of two faculty residences, four year-round cabins, eight seasonal cabins and a large building to house the utility infrastructure. Also in the plan was a large off-the-grid solar array, battery backup power, generators, solar hot water heaters, water storage and fire sprinkler pumps. A renovated barn with a research lab, accessible bathrooms and showers, a large community kitchen and a presentation space would complete the renovation.

Andrew Brownstone of Biosphere Consulting was tasked with the onsite wastewater system design. Brownstone calculated the design flow from all of the facilities at a total peak usage of 3,280 gal per day. Due to the layout of the proposed expansion and the topography of the site, he determined it was best to disperse the wastewater in two separate leachfields.

The first leachfield serves the faculty residences and student cabins utilizing a combination of gravity flow and pressurized (pump up) trenches. The second leachfield is a conventional gravity flow system that serves the barn. The two systems have septic tanks as primary treatment, and then soil provides final treatment and polishing of the effluent prior to its return to the local aquifer. The site is served by an onsite well.

Biosphere Consulting designed the wastewater recharge system with Infiltrator chambers, which are manufactured with recycled materials. This specification allowed a shallow system installation, which provides better treatment than systems installed deep. Chambers were installed in trenches with equal distribution with minimal invasiveness and site disruption. The specification of recycled products for the wastewater system resulted in a reduced carbon footprint compared to labor-intensive, mined aggregate. This is an additional benefit to the research station and its philosophy of sustainability. The decentralized wastewater treatment system design also met the goal of completing the water cycle and replenishing the local aquifer.

With funding from the California Wildlife Conservation Board, the new facilities were completed in 2016. In addition to the decentralized wastewater treatment system, the facilities are nearly energy self-sufficient with an off-the-grid solar photovoltaic power system, solar hot water heaters, wood stoves and well water. Roads also were improved as part of the restoration project to provide year-round access to users for their field courses, research projects and public outreach activities.

The project exemplifies full-spectrum thinking to achieve water conservation, wastewater treatment and energy sustainability goals. 

About the author

Dennis F. Hallahan, P.E., is technical director for Infiltrator Water Technologies. Hallahan can be reached at [email protected].

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