Mendota Heights Pond Study Gives Passing Marks, Despite the Algae

For residents of Mendota Heights, the water quality of the 90+ ponds in town affects the sites and smells of daily living.

Copperfield Drive resident Audrene Lojovich called the algae blooms on Copperfield Pond “the creeping crud.”

In response to complaints like Lojovich’s, the a handful of ponds last summer to find out what’s going on below the surface.

A study of three ponds—Copperfield, Burrows and Park Place—was ultimately conducted by Bonestroo/Stantec.

What the report found is not what homeowners were expecting to hear.

A Passing Grade

All three ponds are performing within acceptable performance standards, meaning they provide storm water storage in heavy rain and they have the capacity to absorb excess nutrients and sediment from runoff before it progresses into bigger bodies of water like the Mississippi River.

Those are standard guidelines that would be used by the Minnesota Pollution Control Agency as well, said consultant Phillip Elkin in a presentation to the Mendota Heights City Council Nov. 16.

Copperfield was deemed in the best condition, while Park Place was deemed the worst, mainly due to a large sediment accumulation in Park Place Pond leftover from construction 20 years ago.

Residents might define “performance” a bit differently.

Algae and Plant Growth in Copperfield

“When we built here, in the summertime, there was never any junk or algae growing on the lake until the typical dog days of August,” said Lajovich, who was one of the first residents in Copperfield. “Now it starts already within weeks of the ice going out and it warming up. It’s green now from May until late October. … It doesn’t go away any more.”

But algae growth is a sign that the pond is doing its job and storing nutrients like fertilizer and animal waste rather than passing it downstream, said Elkin. The algae feed on those nutrients. In addition, the algae on Copperfield are not thick enough to block light, so aquatic plants can easily grow in the otherwise-clear water.

The ponds need to remove 50 percent of phosphorus and most sediment to meet performance standards, which Copperfield does, according to the findings.

Shallow, Unshaded

Burrows Pond was reported to have a small silt delta by one of the pond’s inlets, which affects capacity, but also met those standards.  

“Because it’s so shallow, because there’s a lack of shade, algae has a tendency to grow excessively in that area,” said Elkin, who showed a picture of the pond covered in green.

Park Place Pond just missed the mark for phosphorus removal at 45 percent, but is still considered within acceptable guidelines by the report. It was described as a “borderline candidate” for an excavation and restoration process.

Paul Plunkett has lived on Park Place Pond for approximately 20 years. “What I’ve noticed over the last 20 years is the size of the pond has shrunk tremendously,” said Plunkett. “The depth of the pond is nowhere near where it used to be. It needs to be dredged. In terms of quality, this summer was awful. At times I thought it was the Red Sea there was such a scum on it. It was red. It was disgusting.”

Too Expensive to Clean?

However, the report estimated the cost of dredging Park Place Pond to be $37,000. Compared to the pond’s relatively small 17-acre watershed, that may not provide “the most bang for your buck,” as Elkin put it.

Elkin wagered that the small watershed could be contributing to the algae. “Because it is a small watershed you don’t have the regeneration of water. Water sits in the pond for a long period of time. Plus there’s a lot of nutrients in the pond to feed on.”

The estimate to dredge and restore all three ponds was $57,306.

The report instead offered some pond best management practices for homeowners, including keeping grass clippings and fertlizer out of ponds. (Follow the link for the full list.)

The council didn't take any action in response to the report, but continued development of a program for pond quality is likely to be on the city’s agenda for 2012 goals.