More salt, sand than expected in Mirror Lake
LAKE PLACID – The AuSable River Association was surprised to find high concentrations of road salt and suspended solids such as sand in unexpected locations along the southeast shore of Mirror Lake, which Mayor Craig Randall has described as the “crown jewel” of this village.
Brendan Wiltse, the association’s science and stewardship director, presented the winter 2016 stormwater sampling report to the Lake Placid village board Monday and the North Elba Town Council last week. With help from the Paul Smith’s College Adirondack Watershed Institute, 21 stormwater discharge points and the lake’s inlet and outlet were tested on Feb. 25 and March 9. The testing found higher concentrations of salt than anticipated in the stormwater drains on the southeast portion of the lake. More than a dozen of the locations tested were along the southeast shore.
“The highest reading we had for chloride was 955 milligrams per liter, and you compare that to what’s flowing out of the inlet, which is closer to 1 milligram per liter. So there is a lot more salt coming out of the storm drains than there is naturally,” Wiltse said Monday.
The southeast lake location was a surprise since, “Our initial thought was that the ones along Main Street would have higher concentrations,” he said.
Wiltse said the high chloride concentration is attributed mainly to road salt. The suspended solids include such things as silt and sand.
Mirror Lake has one of the highest chloride concentrations for a lake tested in the Adirondack Park, consistently in the 95th to 97th percentile, he added.
Adirondack Park-wide, he said, lakes without development growth around their shores find less than 1 milligram per liter of chloride concentration. He said the average in the park is 24, and Mirror Lake is around 40, with some of bottom water samples as high as 70.
“That’s because when it runs off, it’s basically salt water; it’s heavier than the fresh water and goes right to the bottom of the lake,” Wiltse said. “So that’s one thing we are keeping our eye on: how that is remixing with the rest of the lake, and is that impacting how the lake turns over every spring and every fall?”
When the village board approved borrowing up to $10.5 million for Main Street sewer, stormwater and water projects in March, it also agreed to design a Main Street Green Innovation Grant Project, which includes plans to divert the stormwater lines that currently dump into Mirror Lake. The approved resolution requires regulatory agency approval and permits from the state Department of Environmental Conservation, Department of Transportation, Department of Heath and Office of Parks, Recreation and Historic Preservation.
“We do think that when you combine all of those together, that there is a good bit of flow coming out of those 14 (stormwater drains) along that (southeast) side,” Wiltse said. Diverting that from the lake is “going to be huge for seeing the chloride concentration starting to go down rather than up.”
Wiltse also expressed interest in testing a new de-icer the village plans to use next winter, Cargill’s ClearLane. It’s a sodium chloride-based de-icer claimed to be anti-corrosive and better for the environment than traditional road salt. In March, village Department of Public Works Superintendent Brad Hathaway said the state uses ClearLane, mostly around lakes and streams in a number of towns, including the Lake George area. Hathaway plans to make ClearLane 25 percent of the village’s salt purchase for next year. The de-icer the village tested out this past winter, Street Treat, did not work as well as expected, and the village will not use it in the future.
As for suspended solids, the Feb. 25 testing showed the Main Street side of the lake, where hydro-dynamic separating units are in place, had milligram-per-liter numbers not nearly as high as the southeast shore. But the March 9 readings told a different story, as total suspended solid numbers spiked up.
“Because we had so many melt events throughout the winter, we don’t know what the cause of that was,” Wiltse said.
Randall asked for a reference for an ideal total suspended solid number, and Wiltse pointed to the natural inlet at the northeast corner of the lake, which reported a reading of 0 to 50 milligrams per liter on March 9, compared to some readings of more than 1,200 milligrams per liter toward the north part of Main Street and on the south shore.
Mirror Lake Watershed Association President Bill Billerman, in attendance at the meeting, asked Randall about the scheduled cleanings of the vortex units. Randall said they are cleaned periodically.
Wiltse also reported higher-than-expected phosphorous numbers for the lake, but said the phosphorous is currently bound to the lake’s sand and sediment, which helps prevent algae blooms.
“If you look on the second day (of testing), (there were) 6,200 micrograms per liter (of phosphorous), and the ambient concentration of Mirror Lake is 4 – so over 1,000 times higher,” Wiltse said. “We think this might be coming from the sand that’s put down.
“Sand has a lot of bound inorganic phosphorous with it, so getting that diverted away is going to be good,” he added. “And because it’s bound so tightly to the sand and we are not seeing algae blooms in Mirror Lake, we think a lot of that is staying bound to the sand.”
Wiltse said the association is compiling all data on Mirror Lake dating back to the 1970s, to combine with the past two years of “intense” monitoring. For the first time this summer, the bottom portions of the lake will be tested, and in the future, the association would like to measure discharge of stormwater locations as well as concentration.