Herrera just finished the monitoring of a second alum treatment of Black Lake in Thurston County. A total of 324,382 gallons of aluminum sulfate and 117,191 gallons of sodium aluminate buffer were applied over 17 days to provide long-term control of toxic algae blooms. Our team provided quality control for the Black Lake Special District by monitoring the application and lake water quality that went far beyond permit requirements, and documented the improved water quality and protected fishery.
Herrera prepared the algae management plan and monitored the first alum treatment in 2016 in response to toxic algae blooms that exceeded state recreation guidelines in 5 of 6 previous years and resulted in lake closures. The first treatment applied only 18 percent of the alum applied this year and eliminated toxic blooms for 5 years through 2020, but it did not increase water clarity. The second treatment was designed to increase water clarity and is expected to prevent toxic blooms for at least another 5 years.