One of the main causes of the persistent water pollution in southern Cayuga Lake is wastewater discharged by two local treatment plants: the Ithaca Area Wastewater Treatment Plant and the Cayuga Heights Treatment Plant.
As wastewater pours from thousands of individual household, industrial and commercial sources in the sewered portions of Tompkins County, it drains into a collection system that lies buried beneath the streets. Ultimately this wastewater flows into the two local treatment plants that employ physical and biological methods to remove pollutants from wastewater and render it less harmful. These treatment processes fall into four major categories:
Plant History: Constructed in 1987 based on a 1981 design. No major plant revisions since. Possible plant upgrade pending multi-million dollar areawide wastewater treatment grant, including improved tertiary removal of phosphorus. The treatment capacity of the plant also would be expanded.
Treatment Process:Secondary treatment: screening, grit removal, aeration, sedimentation; chlorination; sludge processing: gravity thickening, anaerobic digestion; phosphorus removal with chemical precipitation.
Plant Capacity: 10 Million Gallons Per Day (MGD). Current average dry flow of 6.5 MGD
Service Area Population: approximately 50,000 people served (34% Town of Ithaca, 2% Dryden, 64% City of Ithaca.
Plant History: Constructed in 1960's. Plant revised in 1970's. Possible plant upgrade pending multi-million dollar areawide wastewater treatment grant, including improved removal of phosphorus.
Treatment Process: Secondary treatment: aerated grit chamber, by-pass bar screening, primary settling tanks, trickling filtration, intermediate settling, flocculation, final settling, chlorination; primary and secondary sludge processing: gravity thickening, anaerobic digestion, off-site disposal by land filling; phosphorus removal with chemical precipitation.
Plant Capacity: 2.0 Million Gallons Per Day (MDG). Current average dry flow of 1.5 MGD, Current average wet flow of 2.0 MGD;
Service Area Population: Entire village of Cayuga Heights; small portion of Town of Lansing that is sewered; very small portion of Northeast area of the Town of Ithaca; very small portion of Dryden.
The biological treatment technologies employed by both local treatment facilities have several limitations. First, the treated effluent discharge contains phosphorus that can promote the growth of algae and aquatic weeds in Cayuga Lake. Second, the treated effluent contains biodegradable wastes that consume additional dissolved oxygen in Cayuga Lake.
Finally, a wide variety of toxic pollutants can be present in sanitary wastewater, including heavy metals and synthetic pollutants. Since these contaminants are neither broken down nor rendered harmless by biological treatment, they also can be released into Cayuga Lake.
Biological treatment is designed to utilize the same breakdown mechanisms employed by nature to degrade nutrients. Toxic chemicals that persist in nature, such as heavy metals, can survive sewage treatment systems. The United States Environmental Protection Agency has estimated that between 20% and 70% of the heavy metals that enter municipal sewage plants pass through into receiving waters.23
For a more complete set of arguments and data, please see the printed version of the Guide.
CLDF 1998