Chloride increases in surface. waters and the relationship to potential corrosivity

Transcription

1 Chloride increases in surface 1 waters and the relationship to potential corrosivity Edward G. Stets, November 19, 2018 National Water Quality Program National Water Quality Assessment (NAWQA) Surface Water Trends Team

2 (mg / l) 2 Salinity, total dissolved solids, and specific conductance. Delaware River at Trenton, NJ 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 ) (µs cm -1 )

3 3 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.

4 4 Increasing salinity or chloride found in recent regional and national studies Sonzongni et al Kaushal 2005 Corsi 2010 Stets 2017 Dugan 2017 Kaushal 2018 Stets, in prep. Increasing chloride concentration in rivers of the northeastern U.S. Kaushal et al Chloride increases were related to urbanization, especially in snow-dominated areas. Corsi et al. 2010

5 5 Chloride trends Chloride concentration n = 141 Increasing high likelihood Increasing medium likelihood Trend about as likely as not Decreasing medium likelihood Decreasing high likelihood

6 6 Chloride trends Chloride concentration n = 141 Decreasing, high likelihood Decreasing, medium likelihood Trend about as likely as not Increasing, medium likelihood Increasing, high likelihood Increasing high likelihood Increasing medium likelihood Trend about as likely as not Decreasing medium likelihood Decreasing high likelihood

7 7 Chloride trends Chloride concentration n = 141 Chloride Change in concentration (mg/l) Increasing trend Decreasing, high likelihood Decreasing, medium likelihood Trend about as likely as not Increasing, medium likelihood Increasing, high likelih0od Decreasing trend Land use categorized using 2011 National Land Cover Dataset

8 8 Chloride trends Chloride concentration n = 141 Chloride Change in concentration (mg/l) Increasing trend Decreasing, high likelihood Decreasing, medium likelihood Trend about as likely as not Increasing, medium likelihood Increasing, high likelih0od Decreasing trend Land use categorized using 2011 National Land Cover Dataset

9 9 Sources of chloride to urban areas Chloride Change in concentration (mg/l) Land use categorized using 2011 National Land Cover Dataset

10 10 Chloride and water quality Aquatic life criteria Corrosion

11 11 Corrosion in water distribution systems Expensive. Linked to metal contamination of drinking water. Primary concern in Lead and Copper Rule.

12 12 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

13 13 Lead contamination of drinking water in the news More than 200 facilities in New York and New Jersey Denver, CO

14 14 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

15 15 Indices of potential corrosivity Chloride-sulfate mass ratio CSMR = [Cl - ] / [SO 4 2- ] *parameters expressed in mg/l. Larson ratio [Cl - ] + [SO 4 2- ] (Alkalinity) * Parameters expressed in equivalents per liter

16 16 Indices of potential corrosivity Chloride-sulfate mass ratio Linked to lead and copper corrosion. Larson ratio Related to iron and steel corrosion.

17 Chloride-sulfate mass ratio Corrosion can be hard to control Promotes corrosion Larson ratio Indices of potential corrosivity Chloride-sulfate mass ratio Linked to lead and copper corrosion. Larson ratio Related to iron and steel corrosion.

18 18 Trends in chloride, sulfate, and alkalinity 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.

19 19 Chloride-sulfate mass ratio trends Chloride-sulfate mass ratio n = 74 Chloride-sulfate mass ratio Change in ratio Decreasing, high likelihood Decreasing, medium likelihood Trend about as likely as not Increasing, medium likelihood Increasing, high likelih0od Land use categorized using 2011 National Land Cover Dataset

20 Status Assessment ( ) 20 8 Chloride-sulfate mass ratio n = CSMR 4 Corrosion can be difficult to control 2 Increased potential to cause corrosion 0 Undev. Agric. Mixed Urban

21 21 Seasonal patterns and ranges in potential corrosivity differ among sites Connecticut River at Thompsonville Northeastern US Platte River at Louisville, NE Interior West Region Chloride-sulfate mass ratio Chloride-sulfate mass ratio Provisional data subject to revision

22 22 Linking lead action level exceedances to surface water quality Action level exceedance violation of the Lead and Copper Rule by a drinking water facility. Occurs when the 90 th percentile of tap water samples have lead concentrations > 15 ppb. Reported to EPA and documented in the Safe Drinking Water Information System.

23 23 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. Drinking water intake WQ Sampling location Related action level exceedances to surface water quality.

24 Probability of Pb exceedance 24 Linking lead action level exceedances to surface water quality Number of lead action level exceedances (per 10 intakes) P < 0.05

25 Chloride-sulfate mass ratio Probability of Pb exceedance 25 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.

26 26 Implications 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?

27 On-line interactive trend mapper 27

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29 29 Additional resources Edward (Ted) Stets National Trend Results all constituents Groundwater corrosivity report Surface water corrosivity report Trend analysis data preparation, statistical methods, and trend results

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