A pilot project in which alum was spread on the water to see how effective it would be to reduce harmful cyanobacteria in Grand Lake St. Marys has failed, a report released by the state Thursday said.
Tetra Tech, the private company that performed the demonstration project, used alum in September to treat the lake in two channels and at a marina. The treatment indicated less-than-desired improvements in two of the areas and no improvement in the third. The company recommended that another demonstration project be undertaken in the spring.
“Initially, the treatments clarified the water column within an hour or so, which was expected,” Tetra Tech’s report said. “However, the improvement did not persist.” It added: “While alum was significantly effective in two of the three coves, the degree of effectiveness was poorer than expected.”
Tetra Tech said it be- lieves the demonstration failed to more strongly lower phosphorous concentrations in the lake because of the high amounts of blue green algae present there at the time. Spring would be a better time because of lower cyanobacteria levels, it added.
It is estimated that treating the entire lake could cost up to $10 million, and that is a short- or medium-term solution. While alum treatment has been used on more than 150 lakes worldwide, it’s never been attempted on a scale that would be required at Grand Lake. The cyanobacteria outbreak that killed fish and caused intense odors shut down tourism at the lake this summer, crushing a hospitality and recreation industry worth up to $200 million annually.
State experts have said that fixing the lake could take up to 20 years and require that manure from farm runoff that makes it to the lake via tributaries be drastically reduced and eventually shut off. The manure fuels cyanobacteria growth.
The Ohio Environmental Protection Agency, which sponsored the study, declined comment Thursday, saying officials there as well with the Ohio Department of Natural Resources will meet with Tetra Tech on Monday to get a better understanding of the project’s results.
Other efforts, including tough new rules for farmers that became effective Dec. 23 and artificial test wetlands that could absorb nutrient runoff where tributaries enter the lake, are under way. In January, the Ohio Soil and Water Conservation Commission will consider designating Grand Lake as a distressed watershed, which permits heavier regulation.