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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. A September 2002 boat survey showed that Eurasian watermilfoil was contained in an area at the south end of the lake near the lake outlet. The goal of this project was to take immediate action to remove the existing milfoil in Newman Lake using 2,4-D, followed by diver hand pulling and other appropriate control techniques. Although great efforts have been taken to improve the water quality in Newman Lake, the lake is on the 303(d) impaired waterbody list. This lack of water clarity may hinder effective diver hand pulling efforts and increase the reliance on aquatic herbicides to control this infestation of milfoil.
Newman Lake was treated with 2,4-D (AquaKleen) on July 28, 2003. 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 (13.5 acres) by Spokane County staff. Although the treatment area was adjacent to the outlet, the outlet was closed during the treatment. One sample was taken inside the treatment area before treatment and 2,4-D was not detectable. At approximately 24 hours after the treatment, one sample was taken in the approximate middle of the treatment area (34.1ppb) and one sample was taken about 100 feet outside of the treatment area (19.9 ppb). Samples were also collected approximately three days after treatment. The sample taken from the middle of the treatment area was 111 ppb and the sample taken 100 feet outside of the treatment area was 29.7 ppb. These samples were analyzed by an Ecology- accredited laboratory using method number 8151A. A sample analyzed by the Cerexagri laboratory two days after treatment and taken in the same location inside the treatment area as the one and three day samples had a concentration of 110 ppb.
In addition surface samples were taken inside a secondary treatment location of about 0.5 acre and were analyzed by the Cerexagri Laboratory using an ELIZA test. This laboratory is not yet accredited by Ecology. The concentration at 24 hours after treatment was 40 ppb and the concentration at two days after treatment was 21 ppb. The EPA drinking water standard for 2,4-D is 70 ppb. Two samples were above this concentration within the treatment area two and three days after treatment.
Newman Lake was visually surveyed on August 6, 2003 and the treatment efficacy was rated at 95 to 100 percent for milfoil control. Some burn back and wilting of the water lilies Nuphar polysepala and Nymphaea odorata was observed in the treatment areas, but the plants did not seem to be killed.
Large Treatment Area (13.5 acres treated)
|Time||Inside the Treatment Site||100 Feet Outside the Treatment Site|
|Pre-treatment||No Detection||No sample taken|
|1 day after treatment||34.1 ppb||19.9 ppb|
|2 days after treatment||110 ppb *||No sample taken|
|3 days after treatment||111 ppb||29.7 ppb|
Small Treatment Area (.5 acre)
|Time||Inside the Treatment Site|
|1 day after treatment||49 ppb *|
|2 days after treatment||21 ppb *|
*Analyzed by Cerexagri using an ELIZA method.
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