Steel Lake 2,4-D Monitoring - 2002

Description of Site

Steel Lake is a 46-acre urban lake located within the city limits of Federal Way (near Seattle) in King County. It is a shallow lake (mean depth of 13 feet) with a watershed area of 243 acres which are primarily developed as residential and commercial property. The lake has a fully developed shoreline with the majority comprising single-family homes with lakefront access. Eurasian watermilfoil (Myriophyllum spicatum) was successfully removed from Steel Lake after a 1994 Sonar® treatment. The lake remained free of milfoil through 1997 when a change in city personnel and a lack of interest by lake residents resulted in lake surveys being stopped. Milfoil was detected in 2001 by King County staff.

Treatment

Areas of Steel Lake were treated with 2,4-D (AquaKleen) using a granular blower at a rate of 100 pounds per ace on August 26, 2002 (see map below). About 4.5 acres total were treated in the lake. Samples were taken by city of Federal Way staff at approximately 24 hours and 4 days after treatment both inside and outside of the largest treatment area. Sample 1 was taken 24 hours after treatment from the middle of Steel Lake and north of the treatment area. It was comprised of a composite of four subsamples from the surface and approximate depths of 2, 4, and 8 feet (13.1 ppb). Sample 2 was taken 24 hours after treatment inside the treated area (about 1-1.5 acres at that treated site) and was a composite of two subsamples from the surface and approximate depth of 2 feet (16.6 ppb). Sample 3 was taken approximately four days after treatment and was taken at the same site and the same way as sample 1 (23.8 ppb). Sample 4 was taken approximately four days after treatment and was taken at the same site and same way as sample 2 (33.1 ppb). These samples were analyzed by an Ecology- accredited laboratory using method number 8151 GC/MS modified. All samples were below the EPA drinking water standard by one day after treatment.


 

Efficacy

Steel Lake was visually surveyed following treatment and staff reported excellent treatment results. In 2003, the amount of milfoil remaining was so limited that the City did not need to treat with herbicides.

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

Time after Treatment Inside Treatment Area Outside Treatment Area
1 Day 16.6 ppb 13.1 ppb
4 Days 33.1 ppb 23.1 ppb

Click here to see the sampling forms (word document)