City of Tillamook

Tillamook's Waste Treatment System

Like many Oregon cities, the City of Tillamook has an aging sanitary sewer system and wastewater treatment plant.

In recent years, this aging system has made it difficult for the City to meet tougher state and federal regulations for the treated wastes that are pumped into the Trask River.

Because of this, in 2001 the Oregon Department of Environmental Quality (DEQ) ordered the City to undertake a major expansion and upgrade of its sanitary sewer and wastewater treatment facilities.

This order was not optional. The DEQ stated that, if treatment plant capacity and performance are not improved, the City of Tillamook could face heavy fines and be forbidden to do any future residential development.

So in 2002, the City began planning for the project. It hired Portland consultants Kennedy/Jenks to do the work.

They began by assessing the situation. They found that nearly every component of Tillamook’s existing wastewater system had problems – from collection lines that occasionally backed up during heavy rains, to the treatment plant, which was costing the city a small fortune to maintain. The lifespan for working parts of a plant is usually 20 to 25 years and the concrete and pipes are usually expected to last 50 years. The city’s system is older than that.

Tillamook’s plant was constructed in 1948. It underwent a major upgrade in 1958 with new influent pumps, primary clarifier modifications, a trickling filter and a new primary digester. That digester is still in service today, but is at the end of its functional life.

In 1969, disinfecting equipment was added to the trickling filter and the rotating biological contactors (RBC’s) were installed. These are huge, rotating discs that oxygenate the sewage and enhance the growth of biological agents that break it down. The normal lifespan of an RBC is 15 to 20 years.

In 1998, the city installed a new head works and a primary clarifier at a cost of about $1.4 million. However, the aging facilities in the rest of the plant prompted DEQ to put Tillamook under a corrective action plan.

In April of 2003, a Technical Advisory Committee comprised of city engineers held a series of meetings to discuss alternatives. In August of 2003, a Public Advisory Committee composed of more than a dozen local citizens who volunteered to help, began meeting with the TAC and the consultants, studying the facilities and evaluating options. The two committees selected their preferred plan in November of 2003. They came up with a plan that would have re-used the clarifier and added other components to dramatically improve the plant’s performance. It relied on existing “anaerobic” technologies.

However, DEQ ultimately ruled that the City must implement a different technology – “aerobic” digestion. This method requires injecting oxygen into the process, relies on a different type of microbe and a different type of plant. These newer aerobic technologies produce a much cleaner effluent.

In the end, a combination solution was adopted. The City will continue to make use of its 1998 primary clarifier by converting it into a “pre-treatment” tank before dumping the effluent into the new system to finish it off. The result will be a hybrid process that employs anaerobic microbes and settling at the front end, and aerobic microbes at the finish. This system also will help handle the high flows that Tillamook gets in the rainy season and it will dramatically reduce the size of the footprint required for the new system.

To accommodate structures for the new process, in 2006 the City was able to purchase a tract of land on 3rd Street at the Trask River bridge, adjacent to the existing treatment plant. Construction of the new facilities began there in 2007.

The cost of constructing the treatment plant improvements is expected to total $10 million. Overall costs of the entire project, including acquisition of the additional land, improvements to transmission lines, Evergreen Drive sewer improvements, 12th Street pump station improvements, engineering and construction management, are expected to reach about $14 million. The City received two grants to assist with these expenses, but the bulk of the cost must be borne by the City.

The only way to pay for this is through increased sewer rates. Rates were raised to $44 per month, and additional increases will be necessary in the coming years. These increased rates allow the City to repay the loans.