Consultants tell Ocean Shores high phosphorus likely causes black 'slime'; pilot test of aluminum coagulant planned

Consultants from SCJ Alliance and Univar Solutions told Ocean Shores residents at a public meeting that unusually high phosphorus levels in groundwater are the most likely cause of recurring black “slime” in household water and shower fixtures, and recommended a pilot-scale test of an aluminum-based coagulant (UC1902) to reduce orthophosphate before distribution.

The finding matters because the black deposits have appeared across multiple homes and fixtures and have prompted repeated resident complaints; the city is pursuing a near-term pilot and a longer-term option to secure county water service to replace the local groundwater source.

Scott Rivas, consultant with SCJ Alliance, reviewed the city’s water system and recent laboratory results. He said the system is served by multiple shallow wells (about 50–75 feet deep), a multistep treatment plant last updated in 2012, and a roughly 3,000,000-gallon storage tank that feeds the distribution system. Rivas said treated iron and manganese generally tested below regulatory thresholds but that “Phosphorus, as you can imagine from what I've been saying, that's what really stands out.”

Casey Chartier of Univar Solutions described bench (jar) testing and early coagulant trials. He said the city’s raw water contained about 23 milligrams per liter of orthophosphate, “which is really above what is normally seen in water systems.” Chartier said the city’s current…