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City starts work on tweaking sewer system in Hayhurst, Hillsdale

The Portland Bureau of Environmental Services is planning pilot projects to reduce the risk of sewage overflows — and, hopefully, avoid having to build a separate stormwater system — in Southwest Portland.

Sometimes, pipes that carry sewage can also fill with rain and groundwater during wet weather, causing sewers to back up through manholes or household drains and thereby threatening human and environmental health.

According to a July 2013 newsletter distributed by BES, compared to the rest of the city, Southwest Portland is particularly susceptible to this inflow of stormwater runoff and infiltration of groundwater (I & I) “due to its unique geology, geography and the lack of storm sewers.”

“The area does not have storm sewers, and its topography makes it difficult for property owners to manage stormwater on their property,” BES Public Information Officer Linc Mann said. “The area’s clay soils don’t drain or absorb water well; hills and steep slopes increase the likelihood of stormwater runoff from properties affecting downhill neighbors.”

He added: “If we were working in Southeast Portland where it’s relatively flat and the soils drain well then we could alleviate this problem by disconnecting downspouts and letting the water filtrate into a yard or a garden area. In Southwest Portland, because of the hills, that’s difficult to do because you can’t really disconnect downspouts safely and not affect your neighbor’s property.”

Through these pilot projects, BES is offering to repair or replace eligible privately owned lateral pipes that connect properties to the public sewer at no cost to the property owners. Property owners who agree to participate give the city a 10-year easement over the lateral pipe, meaning that BES may monitor the pipe and step onto their property to fix it.

“Comparing our information with that of cities that have already initiated I & I programs — and specifically with King County, Washington’s program — indicated to us that rehabilitating the sewer pipes, including the private laterals, should be the most cost-effective way to reduce I & I,” said Wrandoll Brenes, project engineer. “We have designated our early projects as pilot projects because we will do post-construction monitoring of our sewer system to evaluate the effectiveness of this method in our region and determine if we need to modify this approach.”

Work started this spring on a pilot project in Upper Hillsdale, to be followed by two more projects — one in Middle Hillsdale and one in the area around Southwest Pendleton Street and 45th Avenue in Hayhurst.

The Hillsdale projects in essence chose themselves.

According to Brenes, a city manhole near Southwest Dewitt Street and 25th Avenue overflowed several times in winter 2011, causing sewage to spill out onto a street and violating the BES permit with the Oregon Department of Environmental Quality.

“As a result, the city entered into a mutual agreement and order with DEQ that committed the city to stopping … these sanitary sewer overflows (SSOs) … in this basin,” he said. “The solution to stopping SSOs is to increase capacity in the sewer system by either increasing pipe sizes or by reducing the flow in the pipes. Our evaluation of the alternatives concluded that the most cost-effective solution is to remove the I & I flow from the system. The upper Burlingame sewer basin, where the Upper and Middle Hillsdale projects are located, is upstream of the Southwest Dewitt manhole.”

Mann noted that if BES fails to meet a schedule, set out in the agreement with the DEQ for the bureau to investigate the I & I problems in the Burlingame Basin, it would be required to pay a penalty of $1,600 for each day of violation.

The Hayhurst project, meanwhile, will be a second attempt at solving an existing problem.

“We chose the area around Southwest Pendleton and 45th because we have already repaired the sewer mainlines and public laterals in this neighborhood, and post-construction monitoring shows that the reduction in I & I … was not enough,” Brenes said. “We are therefore following up in this project area with repair of the private laterals. We will again conduct post-construction sewer flow monitoring to determine if we met our goal of 60 percent reduction of I & I flow.”

These projects have been a long time in coming.

“Since the area was annexed into the city of Portland many years ago, the city has been looking at the best ways to manage stormwater,” said the July 2013 newsletter, and Brenes said that city annexation maps show that the Upper and Middle Hillsdale areas and Southwest Pendleton Street and 45th Avenue were annexed around 1890 and 1940, respectively.

According to the agreement between the DEQ and BES, Mann said, the city must “develop and evaluate alternatives for addressing the problem, implement early action (pilot) projects to remove stormwater from the sanitary system and design a basinwide solution by December 2016.”

If the pilot projects don’t work, Mann said, the city might be forced to build a separate stormwater system in Southwest.

“A separate stormwater system would mean major sewer construction in Southwest Portland neighborhoods for many years. The work would include improving roadside ditches, constructing swales and ponds and installing separate pipes to carry stormwater runoff,” he said. “It would be an additional expense for Portland ratepayers, and the construction would be disruptive to Southwest Portland neighborhoods.”

If these projects are successful, however, the benefits could be manifold.

“Reducing inflow and infiltration will improve sanitary sewer service, protect public health and the environment by reducing sewer backups and overflows, will reduce sewage treatment costs for sewer ratepayers and will avoid the costs of constructing a costly separate storm system,” Mann said.