2004 Newman Lake Monitoring  - Summer 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 2003 (see also the 2003 sampling results) and 2004 (both summer and fall treatments). The lack of water clarity in Newman Lake may hinder effective diver hand pulling efforts and increase the reliance on aquatic herbicides to control this infestation of milfoil.

Treatment

Newman Lake was treated with 2,4-D (AquaKleen) on July 6, 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 (5-acres) by Spokane County staff. Samples were taken inside the treatment area and 200 meters south 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.

Efficacy

Newman Lake was visually surveyed on August 18, 2004 and the treatment efficacy was rated at 95 percent for milfoil control. Only two small brown milfoil plants were observed, although they appeared to be regrowing. The Secchi disk reading was 1.5 meters. Although a fall treatment of 2,4-D was needed in other areas of Newman Lake, this treated area remained free of milfoil though the fall.

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

2,4-D residues were well 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 200 Meters Outside the Treatment Site
Pre-treatment No Detection No sample taken
3 days after treatment 11.0 ppb 6.4 ppb
10 days after treatment 10.2 ppb 3.4 ppb