Characterization of the Quality of Source and Finished Water of Community Water Systems (CWSs)

1. Characterization of the Quality of Source and Finished Water of Community Water Systems (CWSs) Greg Delzer May 10, 2006 San Jose, California U.S. Department of Interior U.S. Geological Survey

2. Focus of Today’s Talk • Source Water-Quality Assessments (SWQAs) • Compound selection process • Occurrence, comparison to human-health benchmarks, and comparison of source and finished water

3. Source Water-Quality Assessments

4. Why SWQAs? • Increase the number of large public supply wells monitored • Increase sampling at/near CWS intakes • Need to relate ambient NAWQA findings to source water used by CWSs • Include compounds not previously monitored by NAWQA (or CWSs)

5. SWQA Design • Ground Water • 30 Studies • 15 CWS wells per study • Sampled once • Surface Water • 30 Studies • 1 intake per study • Sampled monthly plus 5 other times

6. SWQA Design (cont.) Sampling • Phase 1 • 1st year • Source water • 260 Compounds • Phase 2 • 2nd year • Frequently occurring compounds • Source and finished water

7. SWQAs About 1/2 Complete Surface Water - 9 completed; 4 in progress - Reports begin in 2007 Ground Water - 12 completed; 3 in progress - Reports began in 2006

8. Compound Selection (1) Human-Health Effects (2) Occur in public water systems (3) Not monitored by CWSs Focus on Compounds With Known/Potential:

9. Compound Selection Process MCLs Lifetime HA Cancer Group HBSL CCL UCMR Children’s List USGS Analytical Methodology Exist? Yes Typically monitored by CWSs? No • 260 SWQA Compounds • - Primarily organic compounds • - Unregulated (221) • - Some regulated (39)

10. Occurrence and Comparisons

11. More Compounds Occur More Frequently in Surface Water than Ground Water Ground Water Surface Water 125 Detected 143 Detected 15 most frequently occurring 15 most frequently occurring (8 – 37%) (41 – 69%) - Herbicides and degradates - Personal care/domestic use compounds - Solvents - Disinfection by-products

12. Most CWS Wells Did Not Have Concentrations Greater than Benchmarks 2% Wells with concentrations > benchmarks 60% Wells without detections > 0.1 parts per billion Wells with concentrations < benchmarks 26% 12% Wells with detections but no benchmarks

13. Most CWS Intake Samples Did Not Have Concentrations Greater than Benchmarks 2% 29% Samples without detections > 0.1 parts per billion Samples with concentrations > benchmarks 13% Samples with detections but no benchmarks 56% Samples with concentrations < benchmarks

14. Half of Finished-Water Samples Had Concentrations Similar to CWS Wells Concentrations within 75-100% of source water 51% 5% 424 detectable concentrations in source water 37% Concentrations between 0-25% of source water 12% Concentrations between 25-75% of source water

15. Most Finished-Water Samples Had Concentrations Similar to CWS Intakes Concentrations within 75-100% of source water 42% 1,643 detectable concentrations in source water 37% Concentrations between 0-25% of source water 20% Concentrations between 25-75% of source water

16. Conclusions • More compounds detected more frequently in SW than GW • Concentrations typically below human-health benchmarks • Half of concentrations in wells detected in finished water at similar concentrations • Most concentrations at intakes detected in finished water at similar concentrations

17. Additional Information NAWQA: Email:nawqa_whq@usgs.gov World Wide Web: http://water.usgs.gov/nawqa SWQA: Email: gcdelzer@usgs.gov Phone: (605) 394-3230