Dr. Ted StetsU.S. Geological Survey

Side Effects of Elevated Chloride in Drinking Water Distribution Systems

10:00 AM CDT

SIDE EFFECTS OF ELEVATED CHLORIDE IN DRINKING WATER DISTRIBUTION

SYSTEMS

Ted Stets

US Geological Survey

Mounds View, MN

SALT CONCENTRATIONS ARE INCREASING IN URBAN AREAS

SODIUM

(mg/l)

CHLORIDE

(mg/l)

Stets et al. 2020

CHLORIDE AND WATER QUALITY

• Aquatic life criteria

• Corrosion

▪ Expensive.

▪ Linked to metal contamination of drinking water.

▪ Primary concern in Lead and Copper Rule.

CORROSION IN WATER DISTRIBUTION SYSTEMS

• Lead contamination is a corrosion problem.

• Lead (Pb) contamination of drinking water typically

originates with –

• Pb pipes

• Pb solder

• Pb-bearing fixtures.

• Drinking water facilities are required to control

corrosion under Lead and Copper Rule

CORROSION AND LEAD CONTAMINATION

CORROSION AND LEAD CONTAMINATION

• Lead pipes are being phased out.

• This process is slow, expensive, and complicated in

some places.

• Expensive – Pittsburgh example.

• Complicated – Lead service line ownership.

• Lead solder is also being phased out.

• Less attention paid to lead-bearing fixtures.

More than 200 facilities in

New York and New Jersey

LEAD CONTAMINATION OF DRINKING WATER IS STILL WITH US

• Oxygen concentration

• Alkalinity (buffering capacity)

• pH (acid / base)

• Hardness (Ca2+ and Mg2+)

• Temperature

• Ions (chloride and sulfate)

• Disinfectants (chlorine)

• Abrupt changes in water quality

WHAT FACTORS CONTROL CORROSIVITY IN DRINKING

WATER?

INDICES OF POTENTIAL CORROSIVITY

Chloride-sulfate mass ratio

CSMR = (Cl-) / (SO42-)

*parameters expressed in mg/L

Larson ratio

[(Cl-) + (SO42-)]

(Alkalinity)

*parameters expressed in equivalents per liter

INDICES OF POTENTIAL CORROSIVITY

Chloride-sulfate mass ratio

(CSMR)

• Linked to lead and copper

corrosion.

Larson ratio

• Related to iron and steel

corrosion.

INDICES OF POTENTIAL CORROSIVITY

Chloride-sulfate mass ratio

• Linked to lead and copper

corrosion.

Larson ratio

• Related to iron and steel

corrosion.

Chloride-sulfate mass ratio

n = 74 Chloride-sulfate mass ratio

Change in ratio 1992-2012

Land use categorized using 2011 National Land Cover Dataset

Increasing, high likelihood

Decreasing, medium likelihood

Trend about as likely as not

Decreasing, high likelihood

Increasing, medium likelihood

Stets et al. 2017

More

corr

osi

ve w

ater

CHLORIDE-SULFATE MASS RATIO TRENDS 1992-2012

CHLORIDE-SULFATE MASS RATIO IS RELATED TO

URBANIZATION

More

corr

osi

ve w

ater

CS

MR

0

2

4

6

8

Status Assessment (2010-2015)

Undev. Agric. Mixed Urban

Chloride-sulfate mass ratio

n = 248

Stets et al. 2017

Corrosion can be difficult to control

Increased potential to cause corrosion

Seasonal patterns and ranges in potential corrosivity

differ among sites

Connecticut River at Thompsonville

Northeastern US

Chloride-sulfate

mass ratio

Platte River at Louisville, NE

Interior West Region

Provisional

data – subject

to revision

Chloride-sulfate

mass ratio

LINKING LEAD ACTION LEVEL EXCEEDENCES TO SURFACE

WATER QUALITY

▪ Action level exceedance – violation of the

Lead and Copper Rule by a drinking water

facility.

▪ Occurs when the 90th percentile of tap

water samples have lead concentrations > 15

ppb.

▪ Reported to EPA and documented in the

Safe Drinking Water Information System.

LINKING LEAD ACTION LEVEL EXCEEDANCES TO SURFACE WATER

QUALITY

• Identified all surface drinking water intakes upstream of trend locations.

• Counted the number of action level exceedances at those facilities.

• Related action level exceedances to surface water quality.

WQ Sampling

location

Drinking water

intake

P < 0.05

Number of

lead action

level

exceedances

(per 10

intakes)

LINKING LEAD ACTION LEVEL EXCEEDANCES TO SURFACE WATER

QUALITY

More corrosive water

Large increases in chloride

and chloride-sulfate mass

ratio, particularly in urban

areas.

Seasonal and long-term

patterns in the potential

corrosivity of surface waters.

Statistical relationship

between potential corrosivity

in surface water and

probability of lead

exceedance in tap water.

ADDITIONAL RESOURCES

Publications

Stets, E.G., C.J. Lee, D.A. Lytle and M.R. Schock. 2017. Increasing chloride in rivers of the conterminous U.S. and linkages to

potential corrosivity and lead action level exceedances in drinking water. Science of The Total Environment.

doi:http://dx.doi.org/10.1016/j.scitotenv.2017.07.119.

Stets, E. G., L. A. Sprague, G. P. Oelsner, H. M. Johnson, J. C. Murphy, K. Ryberg, A. V. Vecchia, R. E. Zuellig, J. A. Falcone, and M. L.

Riskin (2020), Landscape Drivers of Dynamic Change in Water Quality of U.S. Rivers, Environmental Science & Technology, 54(7),

4336-4343, doi:10.1021/acs.est.9b05344.

Methodology and datasets

Oelsner, G.P., L.A. Sprague, J.C. Murphy, R.E. Zuellig, H.M. Johnson, K.R. Ryberg, et al. 2017. Water-quality trends in the nation’s

rivers and streams, 1972–2012—Data preparation, statistical methods, and trend results. Scientific Investigations Report. Reston,

VA. p. 158.

Online resources

Trends mapper: https://nawqatrends.wim.usgs.gov/swtrends/