Alum levels drop, exceed expectations
ST. MARYS — A multi-million dollar alum treatment on a portion of Grand Lake St. Marys in June reduced phosphorus levels by more than 50 percent in a development officials say exceeded their expectations.
Directors of the Ohio departments of Natural Resources, Agriculture and the EPA released a report Wednesday afternoon detailing the effectiveness of the alum treatment on 4,000 acres of Grand Lake St. Marys. The report, compiled by Dr. Harry Gibbons of Tetra Tech, noted the treatment successfully reduced levels of phosphorus in the test region as well as the lake as a whole.
“This was a high priority of the administration when we came in in January,” Ohio EPA Director Scott Nally said during a teleconference with regional media. “We’re very pleased to report, based on Tetra Tech’s analysis that the treatment that we did this past summer was very successful.”
The target goal, once the treatment was scaled down to the middle 4,000 acres of the lake, was to get a reduction of 50 percent. Nally noted the treatment reached a reduction of 56 percent — which he termed “exciting.”
Nally also noted state officials coupled the alum treatment with a handful of other projects to reduce the amount of phosphorus in the lake. Rough fish removal and dredging helped remove a large amount of phosphorus on the lake.
“This was just one leg of multiple legs that we were trying to do to reduce the toxic algae bloom issue there,” Nally said. “One thing DNR assisted with was dredging and rough fish removal and we were able to remove over 210,000 cubic yards of sediment out of the lake and also 13 tons of rough fish, which is roughly 43 percent phosphorus by weight. Each of those contributed to the highly successful season that we had at the lake and the proof in the pudding is that the lake stayed open all season.”
Nally said he plans to talk state officials to determine if another alum treatment will be applied next year to Grand Lake St. Marys. The state secured $5 million for the project, but ended up using approximately $3.5 because officials scaled back the project. The remaining balance could be applied toward a future application, Nally noted.
“We are trying to work on what the game plan would be and what it would look like,” Nally said. “As we go through the report and visit with Tetra Tech and formulate what would be a good response going into early spring, which more than likely we would be doing an alum treatment, but we are (having that) discussion right now.”
Nally said a decision to treat the lake is expected to be made in the next 30 to 45 days.
“We are going to take advantage of the time we have this fall and this winter to properly plan this out so it’s not a fire drill post-January,” Nally said. “There were several other items that were tee’d up as possible solutions. In fact there were over 50 of them.”
The timing of a future alum project is expected to be revamped. Nally said dosing the lake in early spring probably could yield more beneficial results.
“One thing that was evident was the timing issue,” Nally said. “We know that in the future, if we are going to go down the alum route again, we know to get out earlier and not later because of the temperature swings in the lake when you get out there later. We need to be out there March/April versus June/July.”
Alum is not the lone treatment to help heal Grand Lake St. Marys, ODNR Interim Director Scott Zody noted. In order to keep the lake progressing, he stressed the important of a multi-faceted approach that includes best management practices for farmers in the watershed.
“We know that alum treatments are not the long-term solution here,” Zody said. “The alum here is to try and get the lake knocked back down to the point to where it can start healing itself. Now we turn to getting some of the good farming and land management practice in the watershed implemented.”
Zody said approximately 68 percent of the crop land in the watershed is under a comprehensive nutrient management plan.
In his report, Gibbons noted the test area experienced a 56 percent reduction in phosphorus while the whole lake experienced a reduction of 20 to 30 percent. Gibbons wrote the lakewide reduction may be linked to the alum treatment.
“This decrease occurred despite continued internal and external P (phosphorus) loading throughout the untreated portions of the lake that added P to the water column, along with the expanding cyanobacteria bloom,” Gibbons wrote. “The cyanobacteria bloom may have been actually higher if the alum treatment had not limited P availability to some degree. This is consistent with expectations for a partial alum treatment to provide a short-term decrease in P concentration.”