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Sacheen Lake, a 320-acre lake located in Pend Oreille County in Northeastern Washington, supports a variety of beneficial uses including fishing, wildlife observation, swimming, water skiing, and boating. The lake is heavily used by lakeshore residents and is regarded as an amenity by the local community. A lake restoration project performed between 1990 and 1998 appears to have controlled the growth of algae and temporarily controlled a serious infestation of Eurasian watermilfoil (Myriophyllum spicatum). In recent years the continued growth of milfoil has presented a considerable challenge to the lake residents who have been funding ongoing management efforts. These efforts have included spot treating with granular 2,4-D and using diver hand removal techniques.
Sacheen Lake was treated with 2,4-D (AquaKleen) on
September 5, 2002. The herbicide was applied by a licensed applicator using a granular blower at a rate of 100
pounds per acre. A total of 31.5 acres were treated
at scattered locations around the littoral zone of the lake. Surface water samples
were collected from inside and outside of three treated areas by Sacheen
Lake residents that had been trained in sample collection by an
environmental consultant. Samples were also taken at 24 hours and three days
after treatment from a fourth untreated site located
about 800 feet from a treatment area. All samples were analyzed for
2,4-D by an Ecology- accredited laboratory
using method number 8151A. (see the map below for the sampling
locations)
Sacheen Lake was visually surveyed on October 7th and 8th, 2002 and the treatment efficacy was rated at about 85 percent for milfoil control. Secchi disk readings were 3.9 m and 4.5 m (average of two mid-lake sites).
All 2,4-D samples were below the EPA drinking water standard of 70 ppb by one day after treatment.
Treatment Site: Northeast end of Lake (approximately 2.3 acres treated)
| Time | Inside Treatment Area | 200 Feet Outside Treatment Area |
| 1 Day after Treatment | 9.2 ppb | 12.8 ppb |
| 3 Days after Treatment | 27.9 ppb | 22.2 ppb |
Treatment Site: North side of the lake (approximately 3.7 acres treated)
| Time | Inside Treatment Area | 200 Feet Outside Treatment Area |
| 1 Day after Treatment | 24.6 ppb | 7.0 ppb |
| 3 Days after Treatment | 28.3 ppb | No sample reported |
Treatment Site: West end of the lake (approximately 3 acres treated)
| Time | Inside Treatment Area | 200 Feet Outside Treatment Area |
| 1 Day after Treatment | 9.2 ppb | 66.8 ppb |
| 3 Days after Treatment | 36.9 ppb | No sample reported |
Treatment Site: South side of the lake (Granite Shores Area - This area was not treated)
| Time | 800 feet Outside Treatment Area | |
| 1 Day after Treatment | 7.3 ppb | |
| 3 Days after Treatment | 16.2 ppb |
Click here to see the NPDES monitoring form for Sacheen Lake (Word Document)
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.html.
