The amount of water that was “unaccounted for” after leaving the Grand Marais water plant in 2010 was 34½ percent, Water/ Wastewater Superintendent Tom Nelson told the Public Utilities Commission (PUC) on February 16.
That might sound like a lot, but it’s much lower than the 65% it used to be. Letting the clean water filter back into Lake Superior is less costly than trying to track the leaks down, Nelson said.
Lake Superior water is cheaper to treat than the water a lot of municipalities have to work with. It has fewer organics than a lot of places, and the city doesn’t have to treat for taste like some places do, Nelson said.
A new requirement that the city test for mercury in its sewer water will cost the city about $1,000 more each year in lab fees. Superintendent Nelson was paying attention to the cost, however, and switched labs in order to reduce a bill that would have been one-third higher otherwise. The city’s total annual cost for lab analysis will be about $5,000 a year.
Sewer report
The city’s sewer system is doing well and has the capacity for growth, Nelson reported at the PUC meeting on March 2. He thinks the system, built in 1988, will be good for at least another decade. Such a system is likely to last 30 or 40 years, he said.
City Administrator Mike Roth noted, “The operating cost for the plant is staffing it and running the machinery in it.”
Nelson had statistics on the amount of flow going into and out of the system over the past few years. What goes into the system is affected by the amount of precipitation. Grand Marais’ flow is sometimes low enough to allow it to sit in the plant for a few days, which is an unusual asset for a municipality, Nelson said. The longer it sits there, the fewer chemicals are needed because bacteria have more opportunity to do their job.
During the three years from 2008 through 2010, the nutrient load coming into the system averaged 334,272 pounds a year. The amount leaving the system and going into Lake Superior averaged 6,486 pounds, which is only 9.26 percent of the 70,035 pounds per year that would have been allowed by law.
Biosolids are taken out during the treatment process and hauled to a facility in Duluth. Over the last three years, that amount has averaged 611,000 gallons, or 118,184 pounds.
Generally, three things (called “effluent nutrient loading”) go into the lake, Nelson said: biological organisms measured in terms of their “biochemical oxygen demand,” total suspended solids (such as sand particles), and phosphorus. Especially noteworthy is the reduction in effluent nutrient loading over the past three years, from 9,344 pounds in 2008 to 4,827 pounds in 2010.
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