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Certification of Copper Tubing for Conditional Use

Certification of Copper Tubing for Conditional Use

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Certification of Copper Tubing for Conditional Use

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  1. Certification of Copper Tubing for Conditional Use Michael R. Schock Treatment Technology Evaluation Branch National Risk Management Research Laboratory ORD, USEPA Cincinnati, OH

  2. Background • Copper has health-based MCLG = 1.3 mg/L • Cu levels > 1.3 mg/L found in many • Homes in public water systems • Residences with wells • Buildings (schools, day care, office, dormatory) • Non-community water systems • Remodels/renovations • Not technically, environmentally or economically feasible for individuals, buildings, schools, small systems, to treat the DW

  3. Early LCR When Many Sites < 10 y Marshall, WQTC, 1994

  4. Ground Waters Problematic Marshall, WQTC, 1994

  5. Significant Small % above MCLG Bear in mind that the youngest range of age of copper tubing sampled would be 2-11 years (1983-1989) Courtesy USEPA Region 5

  6. Specific Issue When manufacturers elect to use the pH 6.5 test water, NSF 61 requires that they mark any product literature or use instructions which mention the standard with the following text per section 4.5.3.2. “Copper [tube, pipe, or fitting] (Alloy [alloy designation]) has been evaluated by [Testing Organization] to NSF/ANSI 61 for use in drinking water supplies of pH 6.5 and above. Drinking water supplies that are less than pH 6.5 may require corrosion control to limit leaching of copper into the drinking water.”

  7. Immediate Problems • Many people are exposed to Cu > MCLG • New Cu installation not homogeneously distributed geographically across water systems • Warning/literature rarely seen or made known to purchasers and users • Cu leaching is often high in water pH > 6.5 • Standard 61 does not protect consumers from exposure to Cu above MCLG • Single water testing/certification paradigm doesn’t work for metallic plumbing materials like Cu tubing

  8. Why Treatment for Cu is Difficult • Installing treatment involves • Physical cost of design and installation • Monitoring requirements from state • Licensing requirements for operators • Long-term analytical, sampling, reporting costs • Long-term chemical and O&M costs • Safety training and chemical handling requirements • Procurement/contracting overhead

  9. Why Treatment for Cu is Difficult • Alkalinity/bicarbonate removal is hard and not small-system friendly • Anion exchange (not very selective) • Lime softening • RO + post-treatment or blending • High doses of orthophosphate (too little perpetuates problem) • Chemical cost • Side-reactions with hardness reduces effectiveness

  10. What do we know that might improve the standard? Copper corrosion in Drinking water

  11. Major Factors in Copper Release • Oxidizing conditions that favor Cu+2 • Disinfection/oxidation • Natural DO • pH • Bicarbonate/Carbonate ion concentration • Phosphate concentration • Concentration • Type • Varied effects • Plumbing age (impact related to chemistry above) • Other chemical factors (NOM, chloride, sulfate, etc. of minor consequence

  12. ORP-pH Effects in High DIC Water Water Oxidized PO2 = 1 atm Water Reduced PN2 = 1 atm

  13. Effect of Oxidant Level on Cu Solubility 100x INCREASE in Cu solubility for Cu(II) vs Cu(I) at pH 7

  14. Copper Solubility & pH AdjustmentNew Plumbing • If pH > 7.5, no problems if DIC < 35 • If DIC < 5, no problems if pH > 7 • If DIC > 40, scaling probably prevents sufficient pH adjustment to solve problems

  15. Why Carbonate/Bicarbonate Matter

  16. Example Aging in High Alkalinity GW“Overnight Standing” samples, not LCR monitoring Theory…. and “real world” practice! pH = 7.5 Alk= 250 (DIC = 65)

  17. Orthophosphate Inhibits Aging at High DIC Cu(OH)2 Fresh Scale No real benefit at high pH Cu3(PO4)32 H2O • Aging Process is Impeded: • Slows oxidation • Prevents or drastically slows reaction with CO32- or HCO3- • Immediate benefit • Does not continue on to stable malachite deposit

  18. Conclusions and recommendations

  19. Basic Recommendations • Requiring a use limitation better defining those conditions where copper pipe will be unlikely to ever cause copper release in excess of the MCLG • For manufacturer using this use limitation, not test the copper pipe for copper release, rather restrict the NSF 61 extraction test to be screening for other items such as residual drawing lubricants and general introduction of contaminants during manufacture. • Form a Task Group • Evaluate literature and gather data on developing use limitation water chemistry criteria • Investigate how Cu tubing standards in other countries incorporate water chemistry to see if those concepts can add insight • Propose language for change in NSF 61

  20. Other Useful Possible Tasks • Investigate developing a collaboration with drinking water plumbing standards and code organizations to address the problem • Investigate the applicability of a similar approach for other metallic pipe/tube materials

  21. Questions?