2004 Newman Lake Monitoring  - Fall Treatment

Description of the Site

Newman Lake is a 1,200-acre lake located approximately 20 miles northeast of the city of Spokane. Eurasian watermilfoil (Myriophyllum spicatum) was discovered in Newman Lake in 2002. Small areas of the lake were treated with 2,4-D in the summer and fall 2003 and summer and fall 2004 (see also the results from those treatments).

Treatment

Newman Lake was treated with 2,4-D (AquaKleen) on September 21, 2004. The herbicide was applied using a granular blower at a rate of 100 pounds per acre by a licensed applicator. Surface water samples were collected from inside and outside of the largest contiguous area of 2,4-D application within the lake (4.8-acres) by Spokane County staff. Samples were taken inside the treatment area and 500 meters east northeast of the treatment area at three days and ten days after treatment. A pre-treatment sample was also taken in the treatment area. These samples were analyzed by an Ecology- accredited laboratory using method number 8151A. The areas treated in the fall of 2004 were not the same areas that were treated in the summer of 2004.

Efficacy

The areas treated in September were visually surveyed on October 8, 2004. The smaller milfoil plants appeared dead while the larger plants were still at least partially green. The treatment efficacy will be evaluated in 2005.The Secchi disk reading was 2.0 meters.

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

2,4-D residues were below the EPA drinking water standard of 70 ppb at both sampling times inside and outside of the treatment area.  

Time Inside the Treatment Site off Cherokee Resort Dock 500 Meters Outside the Treatment Site
Pre-treatment Sample bottle damaged & sample not analyzed No sample taken
3 days after treatment 51.7 ppb Non Detect
10 days after treatment 25.7 ppb 4.1 ppb