Lakewood says alum treatment has prevented toxic cyanobacteria; residents press concerns about lake ecology

City staff and contractor Tetra Tech presented an update March 17 on treatments at Wauchaup Lake, saying the alum applications reduced phosphorus and have so far prevented toxic cyanobacterial blooms, while residents and some council members pressed the city to study whether the treatments altered habitat and water chemistry.

City Engineer Jeff Westenott summarized the lake’s history and the 2020–2023 alum applications. “The treatment was successful. It did meet the goal, which is to prevent toxic algal blooms,” Westenott told council. He said the 2020 program included two higher-dose treatments and a reduced dose in 2023; total contractor costs cited in the presentation were about $128,000 for the 2023 work and $297,000 for the 2020 treatments.

Shannon Bridal, senior limnologist for Tetra Tech, told council the monitoring required by the Department of Ecology showed phosphorus and chlorophyll reductions and that the city had not received health advisories since the work. “I am not aware of any scientific evidence of impacts of alum on waterfowl,” Bridal said when asked about wildlife effects. She and Westenott said the sediments at Wauchaup contain historically large phosphorus stores, the lake is shallow and groundwater-affected, and managers can re-treat periodically if needed.

Several public commenters urged additional study or remediation. Christina Manetti of the Gary Oak Coalition Lakewood said private sampling and reporting in the Suburban Times paint a different picture: “The city of Lakewood has at great cost to taxpayers, essentially killed Wauchaup, while killing the toxic algae,” she said, adding concerns about a green, sterile color and high alkalinity measurements reported by a local observer. Derek Faust, who said he has water-quality expertise, told council the lake no longer supports waterfowl to the degree it did before treatment and offered to help with future monitoring and recovery planning.

Westenott and Bridal responded to specific claims: they said alum binds phosphorus in the water column and sediment, that sediment chemistry and the lake’s very shallow depth make restoration more complex, and that reported pH differences can reflect differing measurement methods (city/consultant use calibrated multiparameter sondes; volunteer monitors use colorimetric test kits). Bridal also noted that documented adverse fish kills in other projects typically follow improper application that causes acute pH drops; she said Tetra Tech used buffered applications to avoid that risk.

Council members asked about options beyond repeated alum treatments, including dredging, shoreline restoration, floating wetlands, planting rooted aquatic vegetation and dilution. Westenott said dredging was studied and estimated at $8–35 million in 2018 dollars and carries complex disposal and contamination questions; he said dredging would be expensive and disruptive. Bridal noted some jurisdictions now use smaller maintenance alum doses annually or every few years and that other in-lake products exist but alum is a well-studied, commonly used option.

The city said a summary report of the monitoring and the Ecology-required data will be posted on the city website. Council discussion indicated a desire to revisit and possibly broaden council goals for the lake — to retain the ban on toxic algal blooms but also consider habitat and recreational values before deciding on future maintenance or restoration approaches.