Water Quality Improvement Project
Excessive nutrient discharges into lakes encourage the rapid growth of aquatic plants and algae. Phosphorus and nitrogen are two nutrients commonly found in lakes. Excessive algae growth reduces water clarity. This lessens the amount of sunlight for other plants and aquatic life, killing them or limiting their growth. When algae die, they sink to the bottom of the lake and begin to decompose. Oxygen demand in the bottom sediments increases, as bacteria feed on this decomposing algae. This results in reduced dissolved oxygen (DO) levels in the lake, severely impacting coldwater aquatic habitat, and can, depending on the dominant algae present, pose a human health risk.
In 1968 the Liberty Lake Property Owner's Association requested water quality analyses. Results from early monitoring showed high nutrient levels, high chlorophyll a, and poor clarity. In 1973, the Liberty Lake Sewer District formed. The District identified two actions needed for lake improvement: sewering the lake drainage basin, and lake restoration work. Sewering of the drainage basin began and a lake monitoring/restoration plan was developed. Monitoring begun in the late 1970s.
In 1976, a sewer facilities plan was prepared and a sewer bond issue passed. In 1979, the wastewater collection system was completed and the lake restoration plan published. The restoration plan included dredging nutrient-rich sediments from the lake; application of alum; improving existing stormwater diversion structures; and the preparation of a storm water management plan.
Data from 1978-79 showed the marsh was the highest source of total phosphorus (TP). Diversion of flood flows around the marsh at south end of lake had the greatest effect on reducing TP loads to the lake, reducing them by 47 kilograms/yr (or from 7 percent to 1 percent of total TP budget by 1987). The restoration plan was implemented in 1981 and the lake monitored through 1983. A post-restoration analysis showed that nutrient loads in 1984 and 1985 were well below the TMDL goal.
Although Liberty Lake was not on Washington's 303(d) list of impaired waters, Ecology submitted a total maximum daily load (TMDL) for total phosphorus to EPA for approval as a federal Clean Lakes project. EPA approved the submittal in March 1993.
In 2008, Ecology evaluated the lake's water quality based on available data. Though inconclusive, the data suggested that the lake met water quality standards for phosphorus at that time.
Liberty Lake Total Phosphorus Total Maximum Daily Load (Ecology publication)
Liberty Lake Dataset Evaluation (Ecology Technical Memo)
Reducing Phosphorus Pollution to Improve Water Quality (Ecology website)
Liberty Lake: Finding Pollution Problems to Solve (Ecology water
Spokane River and Lake Spokane Dissolved Oxygen Total Maximum Daily Load:
Water Quality Improvement Report (Ecology publication)
WRIA 57: Middle Spokane Watershed Information (Water website)
# of TMDLs: 1
Approved by EPA
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