Wastewater system rehab

Rufus, Ore., wastewater system upgrade
Civil engineer
AndersonPerry and Associates, Inc., La Grande, Ore.
Product application
Subsurface drip-line irrigation handles treated wastewater safely and allows economic land development.

Challenging site prompts use of new beneficial wastewater reuse technology.

On Nov. 29, 2001, as Rufus, Ore., Mayor Clifford Jett sorted through his daily mail he found a letter from the Oregon Department of Environmental Quality (DEQ). The mayor and other city staffers had been assessing the city’s compliance with public health and environmental requirements with the DEQ and the Oregon Department of Human Services Drinking Water Program (DWP) to determine how to avoid a potential crisis. But Jett did not need to read more than the letter’s first few sentences to confirm that the DEQ had issued a Mutual Agreement and Order (MAO) to address past and future violations of the city’s permit to operate its 27-year-old wastewater treatment system.

The DEQ suspected that the system’s sewage disposal trenches and treatment lagoons were contaminating area groundwater and water wells with elevated levels of nitrogen, which can cause methemoglobinemia, or "blue baby" syndrome. The agency wanted primarily to address remediation of the suspected contamination sources: periodic leakage of wastewater from the city’s facultative wastewater treatment lagoons, and the practice of disposing of treated wastewater by using on-site seepage trenches, which causes problems when large amounts of discharged water flood the trenches and saturate the surrounding soil.

Concerned by the potential impact on public health, the city, the DEQ, and the DWP joined forces through the Environmental Partnerships for Oregon Communities program to develop a plan for removing the potential source of contamination by upgrading the city’s wastewater treatment system. The health of the 270 residents of this small community located in the eastern Columbia River Gorge at the John Day River Dam depended on the partnership’s response.

The Rufus City Council then asked its city engineers, contracted from La Grande-based AndersonPerry and Associates, Inc. (AP), to join the partnership and offer technical assistance. System improvements not only needed to address contamination concerns, but also had to correct equipment deficiencies and operating problems, provide the treatment capacity to accommodate growth, and improve system reliability, controls, and monitoring capabilities.

Aerial photo shows the land use constraints addressed by use of a drip irrigation system for reusing treated wastewater.

Planning efforts were guided by the city’s two highest priorities: addressing the suspected nitrate contamination in an environmentally friendly manner, and accommodating future commercial and industrial growth. After evaluating alternatives, the city and the DEQ agreed that constructing a 7-acre, center-pivot irrigation system to reuse treated wastewater would best meet the city’s needs and priorities. But when another variable entered the planning equation, the conventional irrigation option became less attractive.

In development of the Wastewater System Facilities Plan for the new system, the city council approved the premise that a piece of city property planned for use as an industrial park could instead function as the site for reuse of treated wastewater. However, the council approved that premise before an opportunity emerged to expand an existing recreational vehicle park and develop the property for industrial and business use. Located on Interstate 84, halfway between Portland and Pendleton near the John Day River Dam, Rufus is an ideal location for businesses catering to interstate highway travelers, and officials could not let the chance for current and future economic growth bypass their city.

The planned 7-acre conventional irrigation reuse system would require a 3-acre buffer zone to protect against exposure to the treated wastewater through overspray and aerosol drift. The buffer would encroach upon a portion of the industrial park development that connects the area to the city’s transportation system.

Another alternative considered in the plan—beneficial reuse of treated wastewater using wetlands complexes—was rejected because it required an 11-acre property. So, how could the city deal with its wastewater effluent in an environmentally responsible manner and in a way that optimized the limited amount of land available for reuse?

Subsurface solution
Troy Baker, AP’s project manager, recalled a technology he had learned about at a conference several years earlier. Geoflow’s Wasteflow subsurface drip line irrigation system technology directly disperses treated wastewater underground at agronomic rates, where it is absorbed into the biologically active soil layer, rather than spraying the wastewater over crops. The Wasteflow drip line technology circumvents the main problem with previous underground irrigation systems—root growth into the emitters, the perforations in the drip line that disperse effluent on a time-activated dose cycle. Each Geoflow emitter features Rootguard, containing a non-toxic active ingredient (Treflan) that directs root growth away from the emitters and prevents roots from entering into the flexible, half-inch polyethylene tubing.

New wastewater lagoons and drip line irrigation area (to the right of the lagoons) address water quality problems and allow use of adjacent land for industrial development.

Baker was intrigued by the possibilities presented by a technology that could facilitate wastewater reuse through irrigation without contaminating surface and groundwater (as seepage trenches do), or necessitating a large amount of property for both the reuse site and buffer zone (as a conventional irrigation dispersal system does). But there were several challenges to implementing this approach.

The first challenge in designing and implementing an underground method of wastewater reuse irrigation was the novelty of the approach. The DEQ had not previously considered how drip irrigation could be used on such a large scale for beneficial wastewater reuse, and the agency did not know how to permit the proposed system. To address the agency’s concerns, AP prepared a Reclaimed Water Use Plan to prove the city’s case to use treated wastewater in a drip line irrigation system. The firm studied the feasibility of the proposed approach in terms of characterization of the site’s soil and the city’s wastewater, compatibility of the city’s land use goals, and water balances to show that the reused water would not adversely affect ground and surface water.

With the detailed Reclaimed Water Use Plan and projections developed by AP, Baker convinced the DEQ that the rate of wastewater discharge was low enough, based on agronomic usage calculations, to be permitted as an effluent reuse system under the DEQ’s standard permit for treatment system operation (the Water Pollution Control Facilities Permit). What was originally a new breakthrough in wastewater reclamation technology—which no one in the state had ever implemented on such a large scale—became an established and state-regulated form of reuse.

Rehab results
The six-year process of rehabilitating the city’s wastewater treatment system involved AP’s performance of planning, funding acquisition, surveying, design, permitting, and construction administration services on behalf of the city. Overall improvements included the following:

  • new packaged influent flowmetering manhole;
  • new influent lift station;
  • lagoon system improvements consisting of sludge removal, new geosynthetic liners, and dike raising to increase storage capacity;
  • new drip irrigation dosing pump station;
  • new effluent filtration building and filtration system;
  • new 5.4-acre drip irrigation system; and
  • new controls, electrical, instrumentation, and standby power generator set.

The drip irrigation system functions much like a residential yard irrigation system, although with approximately 165,000 feet (31 miles) of drip line and several thousand feet of supply and flush mains, it is far larger than the average lawn sprinkler system. Based on water quality and other testing completed to date, the city’s new system is in full compliance with the DEQ’s regulations, and the city, with the assistance of AP engineers, has just completed improvements to prepare the industrial park site for development. This initial preparatory project involved completing bedrock and grading work, excavation, and pavement, and permitting the road approach leading to the future industrial park.

In addition to meeting the MAO and regulatory requirements, this project provided a wide array of benefits to the city’s public health and economy. With the underground drip line irrigation system, human and animal contact with effluent is minimized even more than with conventional irrigation and wetland disposal systems, and the invisibility of the subsurface irrigation equipment protects against vandalism and mechanical damage. Plus, the uniform rate of irrigation and depth of percolation increases the plant material’s consumption of nitrates, which addresses the source of the original water quality problems, and eliminates aerosols and the need for gas chlorination, creating a safer working environment for the plant operator.

In terms of economic development and efficiency, the subsurface irrigation approach allowed the city not only to maintain its industrial development area and its capacity for growth, but also to use the irrigated water for landscaping in the industrial park development. The reuse site will not pose any liability or public health concerns for the city’s future developments on the adjacent property, and the new system has the capacity to handle the city’s growth plans for the next 20 years.

Additionally, the subsurface irrigation conserves water typically lost to evaporation and waters the area continuously, promoting healthy growth of the crops and landscape plantings. AP’s project solution resolved the city’s problem of how to serve as a responsible steward of the community’s health and economic development with an innovative new application of beneficial wastewater reuse technology.

Margaret McGladrey is the marketing coordinator for Anderson·Perry and Associates, Inc., an engineering, surveying, and natural resources firm based in La Grande, Ore., with a second office in Walla Walla, Wash. She can be contacted at mmcgladrey@andersonperry.com.

Posted in Uncategorized | January 29th, 2014 by

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