2004 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. In 2004, the lake group switched from the granular formulation of 2,4-D to the liquid formulation.

Treatment

Sacheen Lake was treated with 2,4-D (DMA*4IVM™) on July 22, 2004. The herbicide was applied by subsurface injection at an application rate of 2.5 gallons per acre foot. A total of 40.5 acres were treated which included the entire littoral zone of the lake except for the southeastern corner of the lake south of the Moon Creek inlet.

Sacheen Lake: Samples were collected from inside and outside (see map below) two treated areas by Sacheen Lake residents who had been trained in sample collection by an environmental consultant. The samples were taken using a Kemmerer sampler at a depth of 2 meters at 24 and 72 hours after treatment. Additional samples were taken ten days after treatment at sites 2 and 4.

All 2,4-D samples were stored on ice until delivery the next day to the laboratory. All samples were analyzed by an Ecology- accredited laboratory using method number 8151A.

Efficacy

Sacheen Lake was visually surveyed by boat-towed SCUBA divers on September 17, 2004. Most areas showed complete removal of the milfoil plants with only an occasional plant remaining in a few areas. The treatment efficacy was rated very good with about 95 percent of the milfoil removed. No adverse impacts such as algae blooms or fish kills were observed. Secchi disk readings were 4.5 m on 7/18/04, 4.3 m on 8/28/04, and 3.7 m on 9/26/04 (average of two mid-lake sites each).

Summary of 2,4-D (DMA*4IVM™) Residues from Sacheen Lake

Treatment Sites 2 and 3: West end of the lake

Time After Treatment Inside Treatment Area Outside Treatment Area
1 Day 488 ppb 186 ppb
3 Days 346 ppb 218 ppb
10 Days 133 ppb Not Sampled

 Treatment Sites 4 and 5: Northeast end of the lake

Time After Treatment Inside Treatment Area Outside Treatment Area
1 Day 141 ppb 183 ppb
3 Days 133 ppb 130 ppb
10 Days 77.5 ppb  

See the NPDES monitoring form for Sacheen Lake (Word Document)