We are required by our State permit to analyze water samples from the lake periodically after the herbicide treatment to determine the concentration of triclopyr present. The removal of various restrictions on lake use depend on the concentration declining below certain levels.
The first samples were taken on Saturday, June 2nd, approximately 48 hours after the treatment. They were collected from four locations around the lake where the herbicide was applied, and one downstream, as directed by the State. Samples were obtained using a Van Doren collector, a device that allows collection from a specified depth in the water column. We took samples from four feet from the bottom, or less in shallow locations.
The samples were refrigerated until Monday morning, when they were dispatched via FedEx overnight in their own little cooler to the SePro lab in North Carolina. This is the company that manufactures the Renovate OTF formulation of triclopyr that we used. They have a GCMS which can measure the concentration of triclopyr down to less than 1 part per billion.
A few days later the results came back. The herbicide was applied at 2.0 parts per million (ppm), which is 2000 parts per billion (ppb). The concentrations measured two days later in the areas treated ranged from 36 ppb to 370 ppb.
|5||1 mile downstream||32.8|
This tenfold difference between the lowest and highest concentrations measured is unexplained, but repeats our experience three years ago LINK.
The restriction on use of the lake for swimming, fishing, and boating was lifted on Sunday, June 2nd. The restriction on using the water from the lake for drinking or food preparation will be lifted once the herbicide concentration is less than 75 ppb. Based on our earlier experience we are hopeful that this will occur two weeks or so after the treatment. Therefore we plan to test again the week of June 17th.