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I & I drives need for wastewater expansion
The City of Pipestone has been repairing and replacing faulty underground plumbing for the past decade, trying to stanch the flow of excess water getting into the wastewater treatment system through inflow and infiltration, or I & I.
The city has invested approximately $7.5 million since 2000 in projects which replaced infrastructure, according to the “Sanitary Sewer Inflow and Infiltration Evaluation 2009,” recently completed in February 2010. Using the 2000 Census, that means approximately $1,750 per resident worth of improvements over nine years, according to the report.
“They’re still bad pipes out there, but they’re taking a good whack at it every year,” said Lance Weatherly of Banner Associates. “But it costs money ultimately for taxpayers and that can be an issue for smaller communities.”
According to the facility plan for the wastewater treatment facility expansion, I & I is analyzed on a per inch-diameter mile basis. The average between 1995 and 2000 was 972 gpd (gallons per day) per inch-diameter mile; for the period between 2000 and 2008, the average I & I was 856 gpd per inch-diameter mile, with further reductions recorded for 2009.
However, I & I should not exceed 200 gpd per inch-diameter mile, according to the facility plan. For Minnesota, the requirement is even more stringent: 100 gpd per inch diameter mile.
“Although these guidelines are for new collection systems, it is clear that the city of Pipestone has a severe problem with infiltration and inflow throughout the system,” according to the facility plan.
“The average day flow is coming down, however the ponds need to be designed for a peak flow,” Weatherly said. “That’s why there’s still an expansion required (by the MPCA).”
What’s that mean?
Pipestone’s Wastewater Treatment Facility experiences hydraulic overloading during significant precipitation/snowmelt contributed by inflow and infiltration, or I & I.
Inflow = water entering the wastewater collection system from surface sources after rainfall or snowmelt through manhole lids, cross-connections between sanitary and storm sewers, roof drains and service cleanouts.
Infiltration = water entering the system from the ground through leaks in defective pipes, sewer line joint connections, defective manholes and sump pumps connected to the sanitary sewer.
What you can do: City residents are required to turn their sump pumps outside by April 1. “If they can get them out sooner, that would be great,” said Joel Adelman, Pipestone water/wastewater supervisor.
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