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Certification of Copper Tubing for Conditional Use

Michael R. SchockTreatment Technology Evaluation Branch

National Risk Management Research LaboratoryORD, USEPA

Cincinnati, OH

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

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Early LCR When Many Sites < 10 y

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Marshall, WQTC, 1994

Ground Waters Problematic

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Marshall, WQTC, 1994

Significant Small % above MCLG

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Bear in mind that the youngest range of age of copper tubing sampled would be 2-11 years (1983-1989)

Courtesy USEPA Region 5

Specific Issue

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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.”

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

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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

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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

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COPPER CORROSION IN DRINKING WATER

What do we know that might improve the standard?

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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

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ORP-pH Effects in High DIC WaterCu species = 1.3 mg /L; DIC = 96 mg C/L

I=0; 25øC

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

pH

E

(vol

ts v

s S

HE

)

CO

2- 3

HC

O3-

HC

O3-

H C

O * 3

2

H

C u(s )

Cu 2+

C u O (s )2

Cu(OH) 3-

CuC

O 3o C u(O H ) (s )2

Water Reduced PN2 = 1 atm

Water Oxidized PO2 = 1 atm

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Effect of Oxidant Level on Cu Solubility

pH6 7 8 9 10

mg

Cu/

L

0.001

0.01

0.1

1

10Copper (II) Solids

CuOH(s)

Cu2O(s)

96 mg C/L 11 mg C/L

4.8 mg C/L

100x INCREASE inCu solubility for Cu(II) vs Cu(I) at pH 7

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

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mg C/ L DIC0 10 20 30 40 50 60 70

mg

Cu/L

0.01.02.03.04.05.06.07.08.09.0

10.0

ACTION LEVEL

pH = 7.0

pH = 8.0

pH = 9.0

pH = 10.0

pH = 6.5

pH = 7.5

pH = 8.5

pH = 9.5

Why Carbonate/Bicarbonate Matter

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Example Aging in High Alkalinity GW“Overnight Standing” samples, not LCR monitoring

pH6 7 8 9 10

mg

Cu/L

0.001

0.010

0.100

1.000

10.000

Cu(OH)2

Cu2(OH)2CO3

CuO (varying solubilities)

Age, years (based on date installed)

Cop

per,

mg/

L

-0.2

0.4

1.0

1.6

2.2

2.8

3.4

0 10 20 30 40 50 60 70

Theory…. and “real world” practice!

pH = 7.5 Alk= 250 (DIC = 65)

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pH6.0 7.0 8.0

mg C

u/L

0.01

0.1

1

10

100

22 3

Orthophosphate Inhibits Aging at High DIC

Cu(OH)2 Fresh Scale

Aging Process is Impeded:Slows oxidationPrevents or drastically slows reaction with CO3

2- or HCO3-

Immediate benefitDoes not continue on to stable

malachite deposit

Cu3(PO4)32 H2O

No real benefit at high pH

CONCLUSIONS AND RECOMMENDATIONS

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Basic Recommendations1. Requiring a use limitation better defining those conditions

where copper pipe will be unlikely to ever cause copper release in excess of the MCLG

2. 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.

3. Form a Task Group1. Evaluate literature and gather data on developing use limitation

water chemistry criteria2. Investigate how Cu tubing standards in other countries

incorporate water chemistry to see if those concepts can add insight

3. Propose language for change in NSF 6119

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

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Questions?