Cities make headway in addressing inflow/infiltration
The approaches to stopping inflow and infiltration (I/I) of clear water into sanitary sewers are as varied as the communities that are tackling the problem. But the efforts are adding up.
By the end of 2008, nine of the 47 communities identified by the Metropolitan Council as adding excessive I/I to the regional wastewater collection system three years ago will have completed their reduction programs. All the remaining communities have committed to doing the level of work needed in 2009 to achieve the Council’s reduction goals, according to Kyle Colvin, manager of the Council’s I/I program.
When excess clear water makes its way into the sanitary sewer system during a large storm event through cracks in pipes or through illegally connected sump pumps, foundation drains and roof leaders, the consequences can be dire. See larger graphic. (Graphic courtesy City of Golden Valley.)
“For the third consecutive year, we will defer the surcharge to the communities that have demonstrated their commitment to solve the problem,” Colvin said.
Primary sources of I/I include roof drains, rain leaders, foundation drains and sump pump systems illegally connected to the sanitary sewer system; and cracks or holes in sewer pipes. Excess clear water robs the regional wastewater collection and treatment system of capacity needed for future growth, and accelerates the need for expensive infrastructure improvements. It also can cause sewer backups, resulting in threats to human health and the environment.
Golden Valley: A multi-pronged approach
Even before the Metropolitan Council adopted its surcharge program in 2006, Golden Valley had initiated a free voluntary sump pump inspection program. Inspectors found that about 11% of sump pumps were noncompliant, which meant that these pumps were only a minor contributor to the community’s I/I problem, explained Jeanine Clancy, Golden Valley’s Public Works Director.
“We knew that one of the problems had to be in the sanitary sewer service connections,” Clancy said. For the purposes of study, the city was divided into “sub-sewer” districts. By looking at rain gauges and sewer flow data in each area, the City was able to determine where the excess water was most likely coming from.
The City is tackling the problem on both the public and private side. It asked the Metropolitan Council to take a look at its facilities in the City and fix any problems with those. The City’s 113 miles of sanitary sewer pipe are regularly inspected and cleaned, and city sewer mains are repaired or replaced during street construction projects.
Properties in the City’s annual pavement management projects can get a free inspection before street construction begins. And in early 2007, the City adopted an ordinance that requires property owners to have their private sanitary sewer lateral inspected before advertising their house for sale or transferring title to property.
An inspector talks with a Golden Valley resident before bringing into the home equipment that will televise the condition of the home's private sanitary sewer pipe. (Photo courtesy City of Golden Valley.)
Clancy said that the City, on behalf of residents, has taken advantage of the Metropolitan Council’s I/I grant program. The program provides funds to help residents disconnect sump pumps and foundation drains, and in 2008 was expanded to help residents repair cracked service lines. “The revision of the grant program was a key indication that the Council is being responsive to community needs,” she said.
Addressing I/I thoroughly is a “long, drawn-out process,” Clancy said. But Golden Valley is committed to it, she said, adding that “it’s the right thing to do.”
Eden Prairie: Inspecting every property in the city
Eden Prairie is somewhat unique because of its relative lack of major city trunk sewers, said Gene Dietz, Public Works Director for the City. As Eden Prairie developed, the City built interceptors which it later sold to the Southwest Sanitary Sewer District, one of the precursors to Metropolitan Council Environmental Services (MCES). As a result, “our lateral system is connected to the MCES interceptors in more than 100 places, requiring a significant flow monitoring program to quantify I/I,” Dietz said.
For the past two years, the City and its consultant, SEH, Inc., has been studying flow data in the sewer system. Below-average rainfalls hindered efforts to collect meaningful data, Dietz said, but enough information was obtained for the City to proceed with development of an ordinance. The ordinance, which had its second reading in early December, puts in place a comprehensive private-property inspection program starting in 2009.
A camera is lowered into the house lateral sewer pipe via a flexible hose to examine the condition of the pipe. (Photo courtesy City of Golden Valley.).
On a pilot basis, approximately 10% of the City’s customers will receive a notice that they must have their sump pumps, foundation drains or other illegal connections to the sanitary sewer system disconnected and that they have 30 days to schedule a free city inspection. The inspection will include televising private service lines that connect homes and businesses to the street lateral pipe to check for damage and leaks, Dietz said.
Depending on the results of this pilot program – along with completion of a smoke testing program and public system inspections – final strategies will be adopted and the balance of the private and public system will be subjected to a rigorous I/I reduction program, Dietz said.
Hopkins: Replacing sewers as streets are reconstructed
“We don’t have a huge problem [with I/I] here,” said John Bradford, Hopkins City Engineer. By tracking flows at seven lift stations, the City was able to pinpoint central Hopkins as the source of most of the I/I. In 2009, the sanitary sewers in an entire neighborhood in central Hopkins will be replaced. “We think we’ll get a pretty significant reduction in this area,” he said.
Bradford said that the City is televising about one-third of its sewer lines each year, to “get a much better handle on the condition of the pipes.” Pipes are lined or replaced concurrent with street construction. The City is also replacing all its vented manhole covers.
Efforts are adding up
The interior of a sewer pipe is captured on camera during a residential inspection. (Photo courtesy City of Golden Valley.)
All told, communities will spend an estimated $12 million in 2009 to reduce I/I – about the same as 2008 and a little less than the $14 million spent in the first year of the program. The Council estimates that if the problem were not solved at the local level, the cost to add interceptor and treatment capacity to handle the excess flow from I/I would top $900 million.
Any communities that have not eliminated their excessive I/I by 2012 could face an annual demand charge on their wastewater bills to cover the extra cost of treating the clear water.
“Communities have recognized that this is a regional issue and are taking the steps needed to address it,” said Bill Moore, general manager of Metropolitan Council Environmental Services. “We really appreciate their continued efforts.”