Newman Lake Flood Control Zone District
Oxygen Generator Update - Fall 2015
The Newman Lake Aerator system was installed in 1992 to raise the dissolved oxygen levels of the hypolimnion (lower cold layer of the lake) during the summer when the lake stratifies. When the lake begins to warm in the spring, the lighter warmer water stays on top and the heavier colder water stays on the bottom. The warmer layer on top stays oxygenated from the surface air movement. The lower layer does not mix with the surface, and therefore during the summer the lower layer does not receive any added oxygen. By injecting oxygen into the hypolimnion, the Aerator not only improves the habitat for fish and other aquatic species, it also helps cap the nutrient rich sediments to keep them from recycling phosphorus back into the water column.
The Aerator system includes two 50-HP air compressors and associated oxygen generation equipment located in the Compressor Building on Sutton Bay Rd. A two-inch oxygen line runs from the Compressor Building down the hill along a ten-foot wide easement to the Lake, and then approximately 1,200 feet along the lake bottom to the aerator itself. In the lake, a 60 HP pump circulates 9,450 g.p.m. of lake water down through a large nine-foot diameter cone and out through a 24-inch diameter, 120 foot long distribution manifold. The oxygen is injected at the top of the cone and is dissolved into the water as it slows and expands into the bottom of the cone. After leaving the cone, the oxygenated water is ejected through 2 ½ inch diameter holes every 2 feet along the north face of the distribution pipe. The natural circulation of the lake then carries the oxygenated water throughout the Lake.
To maintain the highest levels of dissolved oxygen possible throughout the summer, the aerator system should be operated at maximum capacity (both compressors and oxygen generators) beginning as soon as the lake begins to stratify in the spring.
This spring the oxygen purity being generated by the oxygen generator (AirSep) units was tested and found that one unit was found to be significantly below the designed oxygen purity. In order to continue the success that we have had improving the water quality of Newman Lake, both generators need to continue running at maximum capacity. The deficient unit will need to be replaced, as repairs are not an economic option due to the age of the unit and lack of available parts.
It is estimated the costs to purchase a new AirSep unit, receiver tank, and re-pipe the system in the compressor building will cost approximately $69,000. This amount is not in reserves, so the budget proposes a 10% assessment increase for replacement of equipment, and maintaining the current operations in the District.
A postcard notice has been sent to all assessment paying property owners with the dates and times of the 2016 NLFCZD Budget Hearing and Board of Equalization Hearing. A copy of that notice can be found here: 2016 Notice of Assessment Increase Postcard