May 25, 2012
GOOD NEWS: We received our NPDES permit from DEQ for the application of Diquat dibromide to our weeds. If all goes as planned we should have a reasonably weed free lake for the summer.
There are certain conditions for the use of this herbicide. Diquat is a contact herbicide with a very short half life of about 6 hours. The contacted plants show results in a week or so. As they die the bacteria etc. that break them down will require oxygen from the water, so by EPA label requirements we can only treat 50% of the lake at a time, requiring two treatments. The first will be to treat the edges of the lake (shallow); however, we must stay 6 feet from the shoreline. This will insure safety for fish and wildlife. The lake will be lowered by 18 inches to half pool and then refilled during the treatment which will contain all of the herbicide until it is fully degraded and none of it is discharged downstream. Refilling with take 7 – 14 days. Water quality testing will occur throughout the treatment period and with test results below our design limits we will lower the lake a second time and repeat the treatment process in the center of the lake (deep). Once the lake refills it will remain at full pool for the remainder of the summer. Boating will be restricted only on the two treatment days along with cautions for swimming, drinking, and keeping pets away from the water.
THE TIME LINE: First, the weeds need to grow to about 12 inches in height in the shallow areas. The lake will be lowered 18 inches at this time which will take several days. We are estimating that this will begin about June 11, but will depend on the growth of the plants. You will be notified as we begin to lower the lake. Boats tied to fixed docks need extra slack in their mooring lines to accommodate for the lowering of the lake. Second, we need a calm day with a weather forecast for a week of little rain (< 1 inch total) at which time we will make the treatment. This step may take a while as it is weather dependent. The lake will begin filling (7 – 14 days). Third, as the lake discharges we will be taking water quality tests to make sure the diquat has been eliminated and oxygen levels are above lower limits. Test results may take a few days to obtain. If all goes well, we will lower the lake a second time and repeat the treatment process for the center of the lake. We will do our best to have the lake up for the 4th of July, but we must treat the plants in the center of the lake as soon as we can. If the lake is lower on the 4th we believe there will still be enough water for most boats to participate in the annual parade. Once we make the second treatment, the lake will begin filling again and take 7 – 14 days. This will complete our treatment process.
We have spent many hours and days developing and refining this plan, working with DEQ, Gresham, Fairview, Portland, MCDD, Mr. Chereghino, and the Columbia Slough Watershed Council (CSWC). Everyone helped with positive and valuable input in this process and we’re amazed and grateful that we can implement this plan this year. That being said, those of you that live on the lake, please, please do not try to implement a weed eradication plan of your own. We will be taking water quality measurements throughout this process and if we can’t meet our water quality standards we will have to abandon the treatment process. We don’t want that to happen. We have every reason to believe that we will be successful in reducing the number of plants for boating and swimming while maintaining more diversity for fish and wildlife and reducing negative effects to downstream from the previous huge plant population.
Thank you to all that have helped in this process,
Jim Graybill, Mike Johnson, Doug Dorling (NW Aquatic EcoSystems)
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