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

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

Source Water-Quality Assessments

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

SWQA Design Ground Water 30 Studies30 Studies 15 CWS wells per study15 CWS wells per study Sampled onceSampled once Surface Water 30 Studies30 Studies 1 intake per study1 intake per study Sampled monthly plus 5 other timesSampled monthly plus 5 other times

SWQA Design (cont.) Sampling Phase 1 1st year1st year Source waterSource water 260 Compounds260 Compounds Phase 2 2nd year2nd year Frequently occurring compoundsFrequently occurring compounds Source and finished waterSource and finished water

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

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

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

Occurrence and Comparisons SampleType Number of Samples Surface Water Ground Water Source Water Source and Finished Water 9086

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

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

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

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

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

Conclusions More compounds detected more frequently in SW than GWMore compounds detected more frequently in SW than GW Concentrations typically below human-health benchmarksConcentrations typically below human-health benchmarks Half of concentrations in wells detected in finished water at similar concentrationsHalf of concentrations in wells detected in finished water at similar concentrations Most concentrations at intakes detected in finished water at similar concentrationsMost concentrations at intakes detected in finished water at similar concentrations

Additional Information NAWQA: World Wide Web: SWQA: Phone: (605)