Metropolitan Council Environmental Services (MCES), operator of the metro-area
wastewater collection and treatment system, is continuing its response to a wastewater spill caused by a hole in one of its regional force main sanitary sewers that occurred on Thursday, June 20, in the City of Chanhassen.
Spill impact area:
MCES water quality monitoring results verified that the spill mainly affected a stormwater streambed, stormwater holding pond and the north end of a 200-yard-long channel extending north out of the north end of Lake Minnewashta (see map below). Very high bacteria levels consistent with a wastewater spill were found in these areas, which we posted for the public to avoid. Bacteria levels in the pond and north end of the channel reduced significantly from water samples collected June 21 to samples collected June 24, but remained above the state water quality standard. ES staff are exploring options to address very high bacteria levels still present in the stream bed.
Water quality monitoring at three sites along the north end of the lake showed normal levels at the south end of the channel and west of the channel, and bacteria levels above the state water quality standard east of the channel. As a precaution, this area also is posted to avoid (i.e. no swimming and no fishing). Typically, wastewater will adequately decompose in the water, and MCES does not anticipate any long-term effects from the wastewater spill.
Water samples at the regional park beach and boat launch on the east side of the lake and the city beach and a lake outlet on the west side of the lake (0.75 mile to 1.5 miles from the spill) showed very low bacteria levels, confirming these areas were not affected by the spill.
Precautionary warning signs posted June 21 are being removed from those sites.
Leak stopped:
The wastewater spill was reported to MCES at about 8:00 p.m. June 20, but appears to have begun earlier in the day. Upon learning of the spill, MCES staff diverted wastewater flow to an alternate regional sewer about 10 minutes later, thus stopping the spill. The spill occurred along the south side of Highway 7 near Arbor Lane and near the north end of Lake Minnewashta. Wastewater flowed along a bike path then through a local storm sewer and stormwater stream into a stormwater holding pond and a channel north of the lake, located between Dartmouth Drive and Washta Bay Court. MCES estimates the spill volume at 500,000 gallons, which is about three-fourths of an Olympic-sized pool.
Pipe repaired:
MCES’s emergency contractor finished repairing the pipe late Friday night (June 21), backfilled the excavation and re-opened all lanes on Highway 7. The contractor will return to finish restoring the site and bike trail. Workers found a tennis ball-size hole in the force main (pressurized pipe), which otherwise was in good condition. A rock in shifting soils may have worn away the pipe wall over many years, finally opening a hole.
Water quality monitoring:
MCES will continue water quality monitoring (approximately every other day) until bacteria levels return to within levels considered suitable for public contact with the water. MCES staff are collecting the third round of water samples today (June 26).
For more information, please contact Tim O’Donnell, Senior Information Coordinator at MCES, at tim.odonnell@metc.state.mn.us or 651-602-1269.
