Mound Wastewater Spill

October 8, 2021

Seton Lake north bay recovers from wastewater spill

Elevated bacteria levels from a wastewater spill into a bay at the north end of Seton Lake on Sept. 19 have decreased and now are well within the acceptable levels for public contact with the water.

Metropolitan Council Environmental Services (MCES) collected and analyzed water samples from up to eight locations in the lake on 10 days of water sampling from Sept. 20 to Oct. 7. Six of the locations registered acceptable bacteria levels before the end of September. Two sampling locations nearest to where wastewater spilled into the lake through a storm sewer continued to show elevated bacteria levels through Oct. 4. (These sites are labeled “Outfall” and “Shore 2” on the map below in the previous spill update.) On Oct. 7, these sites had bacteria levels below the state water quality standard of 126 bacteria counts per 100 milliliters.

Based on water quality monitoring, including dissolved oxygen and nutrients, MCES does not anticipate any long-term effects to the water from the wastewater spill. Now that bacteria levels are consistently below the state water quality standard, signs posted the day of the spill to alert people to avoid contact with the water are being removed.

E. coli bacteria counts at Seton Lake monitoring sites.

Map of the Seton Channel showing the monitoring locations.

September 24, 2021

Update on wastewater spill in City of Mound

Spill volume: Metropolitan Council Environmental Services (MCES) estimated the volume of the Sept. 19 wastewater spill at 62,000 gallons. This is based on measuring wastewater flow at a meter in the sewer downstream of the spill, comparing it with previous flow data collected during normal conditions, and factoring in that 26,000 gallons of wastewater were trucked past the sewer break and discharged into another sewer for approximately two hours so that the pipe could be isolated and repaired.
How much is 62,000 gallons? It would fill a pool that is 5 feet deep, 55 feet long, and 30 feet wide.
Clean-up efforts: MCES is making progress this week with clean up from the wastewater spill. We are taking the following measures to recover as much wastewater and its residue as possible for proper disposal and to prevent further spread of the spilled wastewater:

  • Part of the spill went into a small pond just north of Shoreline Drive and Norwood Lane. On Sept. 23, an MCES contractor suctioned 2,300 gallons of contaminated water out of the pond and two nearby storm sewer catch basins. This water was then discharged into an MCES regional sanitary sewer and will go to the Blue Lake Wastewater Treatment Plant in Shakopee.
  • Excavated soil from the sewer pipe repair area was soaked with wastewater. The contaminated soil is being stored at MCES’s maintenance facility in Mound, where it is covered with plastic and surrounded by bio-logs to contain it in the event of rain. Early the week of Sept. 27, the contractor will haul the soil to MCES’s Metropolitan Wastewater Treatment Plant in Saint Paul for disposal.
  • MCES also will clean out the local storm sewer that carried the spilled wastewater from Shoreline Drive and into the north side of Seton Lake.
In addition, MCES will restore the areas of Shoreline Drive, curb, and sidewalk that were affected by repairing the sewer pipe. We will attempt to schedule this work within the next 1-2 weeks.
Seton Lake water quality monitoring: MCES has collected water samples from Seton Lake this week to monitor the impact of the wastewater spill on the lake and track the extent of the spill to inform the public of exposure risks. The map below shows the location of the sewer pipe break and spill (denoted with a star) and the water sampling locations. The graph below shows the bacteria levels at these sites over three days of monitoring Sept. 20-22. Here are our findings:
  • As we expected, there were high bacterial levels consistent with a wastewater spill on Sept. 20 (the day after the spill) localized near the “outfall,” which is where the storm sewer carried the wastewater spill into the lake.
  • Results from the second day of monitoring (Sept. 21) show the mixing of the wastewater with the water in the north end of the lake and at the Seton Channel – this was due in part to large amounts of storm water entering the lake during the heavy rain on Sept. 20.
  • Our monitoring on Sept. 22 showed a sharp decrease in bacteria levels from the previous two days. Two of the north shore monitoring locations had bacteria levels drop to within the state water quality standard. The Park Island and Wychwood areas appear unaffected by the wastewater spill.

We expect the bacteria in the water will adequately decompose in the water and we do not anticipate any long-term effects from the wastewater spill. We will continue water quality monitoring and posting of warning signs where appropriate until bacteria levels return to within levels where the water is considered suitable for public contact (the state water quality standard of less than 126 bacteria counts per 100 milliliters).

E. coli bacteria counts at Seton Lake. Levels at all 7 locations were lower on September 22 than they were on September 21.

September 20, 2021

MCES responds to wastewater spill into Seton Lake in the City of Mound

Metropolitan Council Environmental Services (MCES), operator of the regional wastewater collection and treatment system, responded early afternoon Sunday, Sept. 19, to a break in its regional sanitary sewer pipe at the intersection of Shoreline Drive and Norwood Lane in the City of Mound. The pipe break spilled an undetermined amount of wastewater onto the local streets and into a stormwater pipe that discharges into the north side of Seton Lake between the homes at 4937 and 4925 Bartlett Blvd. Some of the wastewater also spilled into a low area to the north of Shoreline Drive.

Crews from MCES and its emergency contractors stopped the wastewater spill at approximately 6 p.m. Sunday. They blocked the wastewater flow at a nearby City of Spring Park pumping station, pumped it into tank trucks, and transported and discharged the wastewater back into the regional sanitary sewer near the City of Mound fire station on Wilshire Blvd., downstream of the spill location.

MCES’s emergency contractor excavated about 10 feet deep in the south side of Shoreline Drive to locate the pipe break and repair it. They also repaired a City of Mound local sanitary sewer pipe that appears to have been damaged from the break in the regional sanitary sewer pipe. The wastewater facilities were back in full operation by approximately 8:30 p.m. Sunday.

Signs warning the public “Do Not Enter Water/Contains Raw Sewage/No Fishing/No Swimming” have been set up at about a dozen private docks at homes on Bartlett Blvd. on the north shore of Seton Lake, as well as at Carlson Park.

MCES crews are scheduled to begin water quality testing the morning of Monday, Sept. 20, along the north shore of Seton Lake to determine the area impacted by the spill.


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