Chloride increases in surface

waters and the relationship to

potential corrosivity

National Water Quality Program

National Water Quality Assessment (NAWQA)

Surface Water Trends Team

1

Edward G. Stets, November 19, 2018

Salinity,

total dissolved solids, and

specific conductance.

Total dissolved solids (Salinity) – the mass of all solutes dissolved in a volume of water (typically as ppm or mg/l).

Specific conductance- the capacity of water to conduct an electrical current. It is directly related to total dissolved solids.

(expressed as µS cm-1)

2

(mg /

l)

(µS cm-1)

Delaware River at Trenton, NJ

Any ion can contribute to TDS or SpCond

• A change in the concentration of any ion can cause a change in TDS or SpCond.

• Sometimes TDS or SpCond are important, sometimes specific ions or ratios of ions are of interest.

• Salt control in arid areas has been a concern for decades.

• Increasing use of road salt in snow-dominated areas is an emerging concern.

3

Increasing salinity or

chloride found in recent

regional and national

studies

• Sonzongni et al. 1983

• Kaushal 2005

• Corsi 2010

• Stets 2017

• Dugan 2017

• Kaushal 2018

• Stets, in prep.

4

Increasing chloride concentration in rivers of the northeastern U.S.

Kaushal et al. 2005

Chloride increases were related to urbanization, especially in snow-dominated areas.

Corsi et al. 2010

Chloride trends 1992-2012

Chloride concentrationn = 141

Increasing – high likelihood

Increasing – medium likelihood

Trend about as likely as not

Decreasing – high likelihood

Decreasing – medium likelihood

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Chloride trends 1992-2012

Chloride concentrationn = 141

Increasing, high likelihood

Decreasing, medium likelihood

Trend about as likely as not

Decreasing, high likelihood

Increasing, medium likelihood

Increasing – high likelihood

Increasing – medium likelihood

Trend about as likely as not

Decreasing – high likelihood

Decreasing – medium likelihood

6

Chloride trends 1992-2012

Chloride concentrationn = 141

ChlorideChange in concentration 1992-2012 (mg/L)

Land use categorized using 2011 National Land Cover Dataset

Increasing trend

Decreasing trend

Increasing, high likelih0od

Decreasing, medium likelihood

Trend about as likely as not

Decreasing, high likelihood

Increasing, medium likelihood

7

Chloride trends 1992-2012

Chloride concentrationn = 141

ChlorideChange in concentration 1992-2012 (mg/L)

Land use categorized using 2011 National Land Cover Dataset

Increasing trend

Decreasing trend

Increasing, high likelih0od

Decreasing, medium likelihood

Trend about as likely as not

Decreasing, high likelihood

Increasing, medium likelihood

8

Sources of chloride to urban areas

ChlorideChange in concentration 1992-2012 (mg/L)

Land use categorized using 2011 National Land Cover Dataset

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Chloride and water

quality

• Aquatic life criteria

• Corrosion

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• Expensive.

• Linked to metal contamination of drinking water.

• Primary concern in Lead and Copper Rule.

Corrosion in water

distribution

systems

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What steps are taken to

control corrosion?

• Carbonation / decarbonation (controls pH and alkalinity)

• Lime / soda additions (can promote scale formation)

• Addition of corrosion inhibitors• Silicate• Orthophosphate• Zinc orthophosphate

12

Lead contamination of

drinking water in the news More than 200 facilities in

New York and New Jersey

Denver, CO

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USGS research on the potential

corrosivity of source waters

• USGS NAWQA study on groundwater corrosivity.

• Trends, seasonality, and geographic distribution of potential corrosivity of surface waters

https://www.usgs.gov/news/new-study-shows-high-potential-groundwater-be-corrosive-half-us-states

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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

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Indices of potential

corrosivity

Chloride-sulfate mass ratio• Linked to lead and copper

corrosion.

Larson ratio• Related to iron and steel

corrosion.

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Indices of potential

corrosivity

Chloride-sulfate mass ratio• Linked to lead and copper

corrosion.

Larson ratio• Related to iron and steel

corrosion.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Chloride-sulfate mass ratio

Larson ratio

Promotes corrosion

Corrosion can be hard to control

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• Changes in major ions can indicate a change in the potential corrosivity of surface water.

• A trend analysis is used to look for changes in water quality over a specific period of time.

• A status assessment gives information about central tendencies and spatial patterns.

Trends in chloride,

sulfate, and

alkalinity

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Chloride-sulfate mass ratio trends 1992-2012

Chloride-sulfate mass ration = 74 Chloride-sulfate mass ratio

Change in ratio 1992-2012

Land use categorized using 2011 National Land Cover Dataset

Increasing, high likelih0od

Decreasing, medium likelihood

Trend about as likely as not

Decreasing, high likelihood

Increasing, medium likelihood

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CS

MR

0

2

4

6

8

Status Assessment (2010-2015)

Undev. Agric. Mixed Urban

Chloride-sulfate mass ration = 248

Corrosion can be difficult to control

Increased potential to cause corrosion

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Seasonal patterns and ranges in potential corrosivity differ among sites

Connecticut River at ThompsonvilleNortheastern US

Chloride-sulfate mass ratio

Platte River at Louisville, NEInterior West Region

Provisional data –

subject to revision

Chloride-sulfate mass ratio

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• 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

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• 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.

Linking lead action level exceedances to surface water quality

WQ Sampling location

Drinking water intake

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Linking lead action level exceedances to surface water quality

P < 0.05

Number of lead action level exceedances (per 10 intakes)

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Pro

bab

ilit

y o

f P

bexceed

an

ce

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.

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Pro

ba

bil

ity o

f P

be

xc

ee

da

nc

e

Ch

lori

de

-su

lfate

ma

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• Monitoring of critical elements, for example chloride and sulfate concentrations, will be needed to optimize corrosion control.

• Trends suggest potential corrosivity is likely to become worse in certain areas.

• Effects of increased corrosion control.

• Increased orthophosphate inputs to wastewater treatment facilities?

• Increased zinc loading?

Implications

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On-line interactive trend mapper

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

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https://nawqatrends.wim.usgs.gov/decadal/

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Additional resources –Edward (Ted) Stets (estets@usgs.gov)

National Trend Results – all constituents –

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

Groundwater corrosivity report –

https://www.usgs.gov/news/new-study-shows-high-potential-groundwater-be-corrosive-half-us-states

Surface water corrosivity report –

http://www.sciencedirect.com/science/article/pii/S0048969717318223

Trend analysis – data preparation, statistical methods, and trend results –

https://pubs.er.usgs.gov/publication/sir20175006

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