Obsolete Septic Systems Spoil St. Croix Streams

Help is available for homeowners to prevent bacteria from contaminating their water.




3 minute read

Angie Hong is an educator for East Metro Water.

Kelle's Creek, looking upstream from St. Croix Trail
Kelle’s Creek, looking upstream from St. Croix Trail (Washington Conservation District photo)

On the south end of Afton, just before the road heads out of town, a small stream flows down from the wooded bluffs to meet the St. Croix River below. A little less than three miles long, Kelle’s Creek is groundwater fed and surrounded by mostly undeveloped land. The stream is home to an unusually large number of macroinvertebrate species (insects and other water critters), which is an indication of very good water quality and a healthy, intact biological web. A few years ago, however, the Valley Branch Watershed District and Washington Conservation District discovered a problem in this otherwise healthy stream — E. coli.

E. coli is a type of bacteria that can sometimes make people sick and is an indicator organism for other harmful pathogens as well. E. coli in our waterways can come from dog and goose poop, manure or even human wastewater.

Across Minnesota, 533 streams and river reaches have unsafe levels of E. coli or fecal coliform (another variant). Along with Kelle’s Creek, eight other creeks in Washington County have E. coli impairments: Brown’s Creek (from Lansing Avenue to Manning Avenue in Grant); Trout Brook (which flows through Afton State Park); Perro Creek (Bayport); Gilbertson Creek (near the Log Cabin landing in Scandia); Swedish Flag (Copas); and three unnamed streams (one running from Boutwell Road to the diversion structure in Stillwater, one flowing into Big Carnelian Lake in May Township, and one connecting Bone Lake in Scandia to Birch Lake in Chisago County).

Down in Afton, the Valley Branch Watershed District has spent the past year conducting additional research to determine where the E. coli is coming from in Kelle’s Creek. In addition to testing water at the existing monitoring station in town near St. Croix Trail, they’ve also collected samples further upstream and at the headwaters of the stream where it begins to flow from groundwater springs. The results show that E. coli levels are high even at the headwaters and even during low-flow conditions, which are both indications that the bacteria are coming from groundwater, not surface runoff. As a result, the district has concluded that outdated and failing septic systems in the area are most likely to blame for the E. coli contamination in Kelle’s Creek.

Septic systems, officially known as subsurface sewage treatment systems (SSTS), use biological, physical and chemical processes to treat and clean household wastewater. A typical SSTS consists of a septic tank followed by a soil-based treatment system such as a mound, trench or at-grade drainfield. If designed and installed properly, septic systems are very effective.

In many places, however, extra precautions are needed to make sure they work right. For example, if there is a high water table, the soil-based treatment component of the system won’t work, and pathogens can move quickly through the soil without being adsorbed or filtered, thus polluting the shallow ground water which can, in turn, infiltrate into deeper aquifers as well.

Karst topography creates another challenge for SSTS. In southern Washington County there are many places where there is less than 50 feet of sediment over limestone bedrock. Over time, rainwater has cracked the limestone, creating passageways for pollutants on the land’s surface to travel down into both shallow and deep aquifers. Two unfortunate examples of this process in action include bacteria from outdated septic systems working their way into Kelle’s Creek, as well as nitrates from fertilizers contaminating many private wells in Cottage Grove and Denmark Township.

The city of Afton has a large improvement project underway to upgrade roads, flood protection and septic systems in town. As part of the project, the city plans to build a shared sanitary sewer system to replace individual systems within the downtown village. Most of the 160 septic systems in the Kelle’s Creek watershed are outside of the downtown area, however, so this project alone won’t solve the problem. Testing has not yet identified the sources of E. coli in other streams in the county, but it is possible that septic systems may be to blame for contamination in some of those streams as well.

This year, Washington County introduced a new program to help homeowners throughout the county replace failing and noncompliant septic systems. Low interest loans are available for anyone, and there are grants for low income households as well. To qualify for this assistance, septic systems must be deemed noncompliant by the county or a private inspector. Learn more about these programs at co.washington.mn.us or 651-430-6655.

Contact Angie Hong at 651-330-8220 ext.35 or angie.hong@mnwcd.org.


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Obsolete Septic Systems Spoil St. Croix Streams