7.2 Corrosion Control, Lead and Copper, and Fluoridation
Key Takeaways
A negative Langelier Saturation Index means water tends to dissolve calcium carbonate and is corrosive; a positive LSI means it tends to deposit scale.
Corrosion control treatment adjusts pH and alkalinity (caustic soda, soda ash, lime, CO2) or adds orthophosphate to form a protective scale on lead and copper.
The lead action level is 0.015 mg/L at the 90th percentile of tap samples, and copper is 1.3 mg/L; the Lead and Copper Rule Improvements lower the lead action level to 0.010 mg/L starting November 1, 2027.
The U.S. Public Health Service recommends 0.7 mg/L fluoride; the fluoride MCL is 4.0 mg/L, and Oregon systems must report on-site fluoride results above 4.0 mg/L within 48 hours.
Fluoride feed must be interlocked with plant flow and sized to prevent overfeed; a sodium fluoride saturator delivers about 18,000 mg/L fluoride ion.
Why Oregon Water Is Corrosive
Snowmelt- and rain-fed rivers draining Oregon's volcanic ranges often have alkalinity under 20 mg/L as CaCO3, pH near neutral and very low hardness. Water like that has little buffering capacity. Pipes, service lines and household plumbing slowly dissolve, releasing iron (red water), copper (blue-green stains) and, where present, lead. Corrosion also wastes chlorine and roughens pipes.
Corrosion Basics
- Electrochemical cells: corrosion needs an anode (where metal dissolves), a cathode, an electrolyte (the water) and a connection. Joining dissimilar metals, such as copper and galvanized steel, creates a galvanic cell that speeds attack on the less noble metal.
- Factors that increase corrosivity: low pH, low alkalinity and dissolved inorganic carbon, high dissolved oxygen, high chloride and sulfate relative to alkalinity, warm temperature, high velocity and stray electrical currents.
- Indices: the Langelier Saturation Index (LSI) compares actual pH with the pH at which calcium carbonate is saturated (LSI = pH − pHs).
| LSI | Tendency |
|---|---|
| Negative | Undersaturated; dissolves CaCO3 and is corrosive |
| About zero | Balanced |
| Positive | Supersaturated; tends to deposit scale |
The Ryznar index and the marble test are related tools. Because corrosivity indices only describe calcium carbonate behavior, lead and copper control is verified by tap sampling and water quality parameters.
Corrosion Control Treatment
| Approach | Chemicals | How it works | Watch for |
|---|---|---|---|
| pH and alkalinity adjustment | Caustic soda, soda ash, lime, sodium bicarbonate, CO2 | Raises pH and buffering so metals dissolve less and pH stays stable in distribution | Stable pH at the far ends of the system; calcium carbonate deposits if overdone |
| Orthophosphate inhibitor | Phosphoric acid, zinc orthophosphate, blended phosphates | Forms a protective lead or copper phosphate scale; commonly 1-3 mg/L as PO4 | Steady residual system-wide; added phosphorus load at the wastewater plant |
| Silicates | Sodium silicate | Raises pH and forms a thin film | Less common |
Optimal corrosion control treatment (OCCT) is set with OHA after studies. Operators then hold the approved water quality parameters, such as entry-point pH, alkalinity and orthophosphate residual, within their ranges. Sudden changes in treatment (a new source, a switch to chloramines, or a new coagulant) can destabilize old pipe scales. OHA reviews these changes before they are made.
Lead and Copper Rule Requirements
| Item | Requirement |
|---|---|
| Lead action level (AL) | 0.015 mg/L (15 µg/L) at the 90th percentile of first-draw tap samples, through October 31, 2027 |
| Copper AL | 1.3 mg/L at the 90th percentile |
| Sample sites | Tiered; highest-risk homes with lead service lines or lead solder first |
| Exceeding the AL | Not an MCL violation. It triggers corrosion control steps, water quality parameter monitoring, public education, source monitoring and lead service line work. A lead AL exceedance requires Tier 1 public notice within 24 hours under the 2021 revisions. |
| Service line inventory | Initial inventory of every service line's material was due October 16, 2024, with customer notification |
| Lead and Copper Rule Improvements (LCRI) | Compliance date November 1, 2027. Lead AL drops to 0.010 mg/L, sampling protocols change, and lead and galvanized-requiring-replacement service lines must generally be replaced by December 31, 2037. |
Oregon systems follow these federal requirements through OHA and OAR 333-061-0034 and -0036. Check OHA for adoption details and deadlines specific to your system.
Fluoridation
Fluoridation is a local decision in Oregon. There is no statewide mandate, and Portland, for example, does not fluoridate. Where systems do add fluoride:
- Target: the U.S. Public Health Service recommends 0.7 mg/L.
- Limits: MCL 4.0 mg/L (skeletal fluorosis); secondary MCL 2.0 mg/L (dental fluorosis).
- Oregon reporting: on-site analyses are reported to OHA within 10 days after the end of the month, but results showing fluoride above 4.0 mg/L must be reported within 48 hours (OAR 333-061-0040).
| Chemical | Form | Available fluoride |
|---|---|---|
| Fluorosilicic (hydrofluosilicic) acid, H2SiF6 | Liquid, about 23-25% | about 0.79 of the acid weight is fluoride (about 19% of the solution) |
| Sodium fluorosilicate, Na2SiF6 | Powder | about 61% |
| Sodium fluoride, NaF | Powder or crystals, often in a saturator | about 45%; a saturated solution holds about 18,000 mg/L fluoride ion |
Safety and overfeed prevention: interlock the feed pump with plant flow so it cannot run when the plant stops, use a small day tank, and size the pump close to the needed rate. Acid fumes are corrosive, and powders need dust control and respirators. Verify the dose with daily analyses (SPADNS colorimetric or ion-selective electrode) and compare them with chemical used.
Worked saturator example
A 1.0 MGD well needs to rise from 0.1 to 0.7 mg/L fluoride using a sodium fluoride saturator.
- Fluoride needed = 1.0 MGD × 0.6 mg/L × 8.34 = 5.0 lb/day
- Saturator strength = 18,000 mg/L × 8.34 ÷ 1,000,000 = 0.150 lb fluoride per gallon
- Feed rate = 5.0 ÷ 0.150 = about 33 gallons per day of saturated solution
A finished water has a calculated Langelier Saturation Index of −1.8. What does this indicate?
The water is balanced and needs no stability treatment
The water exceeds the copper action level of 1.3 mg/L
The water will deposit a heavy calcium carbonate scale
The water is undersaturated with CaCO3 and tends to corrode
Beginning November 1, 2027, what lead action level applies under the federal Lead and Copper Rule Improvements?
1.3 mg/L at the 90th percentile
0.015 mg/L at the 90th percentile
0.010 mg/L at the 90th percentile
0.005 mg/L as a running annual average
An Oregon operator's daily on-site fluoride test shows 4.4 mg/L. When must this result be reported to OHA?
With the monthly report, within 10 days after the end of the month
Only in the annual consumer confidence report
Within 48 hours
No report is needed if the next test is lower
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