LESJWA says alum application is successful

The following information was provided by Mark Norton, water resources and planning manager for the Santa Ana Watershed Project Authority (SAWPA), on behalf of the San Jacinto Lake Elsinore Watershed Authority (LESJWA).

It is report from Risk Sciences on the justification for extending and expanding the pilot Alum Application Program in Canyon Lake.

In September of 2013, stakeholders in the San Jacinto River watershed initiated a pilot program to apply aluminum sulfate (“alum”) in Canyon Lake. The purpose of this program was to evaluate the efficacy of using alum to reduce phosphorus concentrations in the lake and thereby prevent the growth of excess algae in the lake.

The pilot program was scheduled to apply approximately 840 tons of alum to the lake in five separate events spread over 25 months. The final alum application for the pilot program occurred in September of 2015.

Throughout the pilot project, routine water quality monitoring was performed to assess the effectiveness of the program. Each ton of phosphorus is expected to neutralize at least nine pounds of phosphorus. Therefore, the pilot alum application program sequestered more than 7,600 pounds of phosphorus.

Preliminary water quality monitoring data confirms that average phosphorus concentrations have declined significantly. By mid-2015, the Main Lake was already meeting the TMDL target for total phosphorus five years ahead of the regulatory deadline. And, the East Bay was almost there as well.

Compared to the two years prior to initiation of the pilot alum project, average Chlorophyll-a concentrations have fallen 27 percent in the Main Lake and 37 percent in the East Bay. As a result, water clarity is improving dramatically throughout Canyon Lake.

Results from the pre- and post-project water quality monitoring program show that regular alum applications are significantly reducing average phosphorus and Chlorophyll-a concentrations in the lake while dramatically improving water clarity.

Dr. Michael Anderson of UC Riverside estimates that, to date, the pilot program has sequestered approximately 30 percent of the bioavailable phosphorus in Canyon Lake. Empirical evidence from the pilot project is sufficient to demonstrate that the program should be extended to allow, but not require, additional alum applications for the next 10 years.

In addition, the program should be expanded to allow alum applications in the area where the San Jacinto River broadens and begins forming Canyon Lake. Recent satellite monitoring data shows this is the only area of Canyon Lake with elevated Chlorophyll-a concentrations and would likely benefit from alum applications similar to those that have been performed throughout the rest of the lake.