OCWA performs routine observation and monitoring of Otisco Lake with regard to algae as it relates to the drinking water supply. This monitoring consists of two forms of observation. The first is visual identification of algae in the water. At a minimum of once a week during the summer months, OCWA travels the length of the lake by boat and retrieves water samples at varying depths from several locations. These samples are then analyzed under a microscope in our lab at the Otisco Lake Water Treatment Plant. If algae are present, it is identified by species and its apparent quantity is recorded. This information allows OCWA to track the relative progression of algae throughout the lake and determine if it is approaching the intakes to the treatment plant, at the bottom of the lake.
The second observation is a water quality analysis on the water entering the treatment plant and the treated water leaving the plant. Blue-green algae can release a chemical called Microcystin which is a cyanotoxin. OCWA utilizes a testing kit manufactured by Abraxis to measure low levels of Microcystin. The test method utilized can measure levels between 0 and 5 parts per billion (ppb) of Microcystin.
(Otisco Lake April 2017)
Should Microcystin be identified in the water entering the treatment plant, OCWA has two barriers of treatment that have the ability to remove these compounds. The primary treatment is our filters. We have a total of six granular media filters. Each filter is comprised a several feet of granular activated carbon (GAC) over a fine sand layer. The GAC can absorb low levels of the cyanotoxins and help prevent them from entering the treated water. The second treatment option is powder activated carbon. This is essentially a very fine activated carbon powder than can be added to the water at the treatment plant itself. The high level of absorption capacity combined with very high specific surface area allows this to more readily absorb contaminants in the raw water. This material is then filtered out by the treatment process. This combination, along with the other treatment chemicals (i.e. coagulant), provides a robust treatment process. It is worth noting that to-date, OCWA has not had to utilize the powder activated carbon because we have not detected Microcystin in the water.