1. Association of State Drinking-Water Administrators,
Understanding Chemical and Microbial Contaminants in Drinking Water: Raw, Treated, and Tap Water Groundwater Sources – Bruce Lindsey Water Quality from Source Through Treatment - Ed Furlong, Susan Glassmeyer, and John Sullivan Water Quality from Distribution to the Consumer - Paul Bradley
Association of State Drinking-Water Administrators,
September 5th, 2018

2. Groundwater sources: Untreated Water From Principal Aquifers
Bruce Lindsey, USGS

3. Objective:
What is the quality of groundwater used as a source of public supply in the United States?

4. We can answer that question
Spatially weighted sampling of principal aquifers
Identify contaminants of concern
Are contaminants widespread or regional?

5. National Assessment: 18 Principal Aquifers
85 percent of public supply use (by pumping volume)
1,300 public-supply wells sampled
Maupin, M.A., and Barber, N.L., 2005, Estimated Withdrawals
from Principal Aquifers in the United States, 2000, US Geological Survey Circular 1279

6. Aquifer Assessment:
Each aquifer evaluated individually by spatially weighted sampling
Assess proportion of the aquifer with high concentrations
Given a grid of 60 cells, a contaminant is unlikely to be missed if it is present in more than 4 % of the aquifer.
Belitz, K., B. Jurgens, M. K. Landon, M. S. Fram, and T. Johnson (2010), Estimation of aquifer scale proportion using
equal area grids: Assessment of regional scale groundwater quality, Water Resour. Res., 46, W11550,
doi: /2010WR

7. GROUNDWATER: A THREE DIMENSIONAL RESOURCE
Monitoring wells
20 to 50 feet deep
Solid Casing
Domestic wells
100 to 200 feet deep
Screened or
Open interval
Production wells
150 to 750 feet deep
Irrigation wells
Public supply wells

8. Summary of Principal Aquifer Survey Results
Compare Concentrations to Water-Quality Benchmarks*
*USEPA MCLs, SMCLs, Health Advisories, USGS HBSLs
HIGH (concentration > benchmark)
MODERATE (concentration % benchmark for inorganic compounds or % of benchmark for organic compounds)
LOW (concentration <50% benchmark for inorganic compounds or <10% of benchmark for organic compounds) 8

9. INORGANICS
All 18 principal aquifers,
assessed by aquifer area
34 trace elements and major and minor ions, of which 19 have human-health benchmarks
8 radioactive constituents, of which 4 have benchmarks
5 nutrients, of which 2 have benchmarks
HIGH
MODERATE
LOW
Percentages are area weighted
Data are provisional and subject to revision

10. ORGANICS 90 VOCs, of which 38 have human-health benchmarks
227 pesticide compounds (pesticides and their breakdown products), of which 119 have benchmarks
For organics, low concentrations are less than 10% of the benchmark
HIGH
MODERATE
LOW
Percentages are area weighted
Data are provisional and subject to revision

11. Summary of Constituents Exceeding Benchmarks in all 18 Aquifers
Exceedance Frequency
Number of aquifers with exceedances 
Radium Radium 228 5% 8
Arsenic
12 
Gross-alpha radioactivity, 72 hour count 4% 12
Manganese
Strontium 3% 9
Radon-222 2% 5
Fluoride 1% 6
Gross-beta radioactivity, 72 hour count
Percentages are area weighted
Data are provisional and subject to revision

12. Summary of Constituents Exceeding Benchmarks in all 18 Aquifers
Exceedance Frequency
Number of aquifers with exceedances 
Uranium
0.9% 3
Nitrate plus nitrite, as nitrogen
0.5% 5
Molybdenum
0.2% 2
Lead
Thallium
Beryllium
0.1% 1
Percentages are area weighted
Data are provisional and subject to revision

13. HIGH MODERATE LOW Radium Radium (Combined 226+228)
WELL LOCATION
AND CONCENTRATION
HIGH
HIGH
MODERATE
MODERATE
LOW
LOW
Percentages are area weighted
Data are provisional and subject to revision

14. HIGH MODERATE LOW Arsenic Arsenic Percentages are area weighted
WELL LOCATION
AND CONCENTRATION
HIGH
HIGH
MODERATE
MODERATE
LOW
LOW
Percentages are area weighted
Data are provisional and subject to revision

15. HIGH MODERATE LOW GROSS ALPHA ACTIVITY Gross Alpha Activity
WELL LOCATION
AND CONCENTRATION
HIGH
HIGH
MODERATE
MODERATE
LOW
LOW
Percentages are area weighted
Data are provisional and subject to revision

16. HIGH MODERATE LOW Manganese Manganese Percentages are area weighted
WELL LOCATION
AND CONCENTRATION
HIGH
HIGH
MODERATE
MODERATE
LOW
LOW
Percentages are area weighted
Data are provisional and subject to revision

17. HIGH MODERATE LOW Radon Radon Percentages are area weighted
WELL LOCATION
AND CONCENTRATION
HIGH
HIGH
MODERATE
MODERATE
LOW
LOW
Percentages are area weighted
Data are provisional and subject to revision

18. HIGH MODERATE LOW Nitrate Nitrate Percentages are area weighted
WELL LOCATION
AND CONCENTRATION
HIGH
HIGH
MODERATE
MODERATE
LOW
LOW
Percentages are area weighted
Data are provisional and subject to revision

19. HIGH MODERATE LOW AT LEAST ONE CONTAMINANT OF CONCERN
Percentages are area weighted
Data are provisional and subject to revision

20. Detection Frequency
Provisional data subject to revision

21. Unique aspects of NAWQA sampling
Groundwater age
Extrapolating to aquifer scale
Emerging contaminants
Full radionuclide suite, Pb 210 and Po 210
Unregulated Contaminant Monitoring Rule (UCMR) contaminants:
Perfluorinated compounds and cyanotoxins
Pharmaceuticals and hormones
Pesticide breakdown products

22. Percentages are area weighted
Data are provisional and subject to revision

23. Rosecrans, Nolan, and Gronberg, 2017, Prediction and visualization of redox conditions in the groundwater of Central Valley, California, Journal of Hydrology, 23

24. Conclusion: blindsey@usgs.gov
What is the quality of groundwater used as a source of public supply in the United States?
Concentrations were less than human-health-benchmarks in 84 percent of the groundwater from public supply wells.
Radionuclides and trace elements are the contaminants that most frequently exceeded human-health benchmarks.