2002 Sacheen Lake Monitoring Data

Description of Site

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.

Treatment

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)

Efficacy

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).

Summary of 2,4-D (AquaKleenâ„¢) Residues from Sacheen Lake

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)