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 coagulant (certified for use up to ~24 mg/L) did not reduce orthophosphate in jar tests, while Univar’s UC1902 (an aluminum‑based coagulant; NSF/ANSI 60‑certified at higher concentrations) substantially lowered orthophosphate and cleared particulates. In the tests Chartier presented, doses in the 115–250 mg/L range produced large improvements; at about 205 mg/L the orthophosphate concentration dropped to roughly 0.3 mg/L.

City and consultant briefing: the consultants and city staff described next steps and constraints. The city intends to run a pilot plant that uses the same filter media and processes as the full plant but operates at a small scale; none of the pilot water will enter the public distribution system, the consultants said. The pilot’s purpose is to determine the optimal UC1902 dosing, test finished‑water pH effects (the chemical can lower pH), and confirm there are no unintended chemistry or corrosion issues. Rivas said the plant’s finished‑water pH is currently about 8.2 and that the Department of Health will require a pilot plan and a pilot report before any changes go into the distribution system.

Timing: consultants and staff said they are preparing a pilot study plan for Department of Health review. They estimated the city could be ready to initiate pilot work in roughly 30 days to prepare equipment and paperwork and that the Department of Health review could take about two to three weeks, with some back‑and‑forth expected. Until the pilot and DOH approval are complete, no chemical changes will be introduced to the distribution system.

Health and risk: consultants said the black slime itself appears to be a biomass with heavy iron‑oxide particles and plant/fungal organisms observed in sampled deposits but that they did not see test results that “jumped out” as an immediate public‑health alarm. Rivas repeated that, based on review of the documents provided, “I didn't see anything in reviewing that the documents that jumped out at me is alarming on that at all.” The city reported one finished‑tap lead result below detection at 0.001 (units not detected above that limit) but noted individual home plumbing materials vary and can affect lead or copper levels.

Public questions and alternatives: residents asked about whether flushing mains, pipe materials, in‑home filtration, silver‑ion sterilization and other approaches had been considered. Chartier said the usual drinking‑water approaches for phosphorus removal are coagulant addition or major biological upgrades (the latter being far more costly and more common in wastewater treatment). He said silver ions are not typical for this issue and could raise regulatory concerns. Rivas and Chartier said increased flushing had not consistently reduced slime for all homes; one resident reported temporary improvement after a hydrant flush, but consultants said their data do not show flushing as a reliable fix citywide.

Longer term: the mayoral representative reported the city has signed a document of interest with the county to pursue a county water supply from the Hogan’s Corner system; county engineers say they have capacity to serve Ocean Shores and the connection would require a larger transmission pipe. City staff described that as a long‑range plan to reduce reliance on the local shallow aquifer and its variable chemistry.

Resident observations: commenters described cyclic appearances of slime in fixtures, black deposits in refrigerator filters and shower heads, and personal reactions. One resident said of visible deposits, “It's gross. I mean, it's like sickening.” Several residents said they sometimes drink tap water and others reported no health effects but expressed concern about aesthetics and frequency.

What’s next: staff and consultants will finalize a pilot plan and submit it to the Department of Health for approval, run the pilot (with waste handling so no pilot water enters the distribution system), and report results to the city and Department of Health before any full‑scale change. The city also said it will update a published flushing schedule to increase cul‑de‑sac flushing frequency while longer‑term options are developed.

The presentation ended with an invitation to upcoming public meetings and reminders staff will post progress updates online.