Table 2:
75th and 95th percentiles of metal concentrations in CWSs nationwide and stratified by subgroup (n=37 915, 2006–11)
| Arsenic | Barium | Chromium | Selenium | Uranium (2000–11) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| n | 75th, 95th percentiles, μg/L | n | 75th, 95th percentiles, μg/L | n | 75th, 95th percentiles, μg/L | n | 75 th, 95th percentiles, μg/L | n | 75th, 95th percentiles, μg/L | |
| All CWSs | 36 798 | 1·66, 7·40 | 34 371 | 79, 253 | 34 347 | 0·62, 5·30 | 34 365 | <0·60, 3·81 | 14 503 | 3·1, 18·5 |
| Source water type | ||||||||||
| Groundwater* | 33 155 | 1·86, 7·77 | 30 863 | 87, 265 | 30 838 | 0·70, 5·59 | 30 858 | <0·60, 4·10 | 12 996 | 3·4, 19·5 |
| Surface water | 3643 | 0·63, 2·39 | 3508 | 40, 107 | 3509 | 0·27, 2·36 | 3507 | <0·60, 2·10 | 1507 | 1·5, 7·1 |
| p value | NA | <0·0001 | NA | <0·0001 | NA | <0·0001 | NA | 0·43 | NA | <0·0001 |
| Size of population served† | ||||||||||
| ≤500 | 21 269 | 1·90, 8·08 | 19 458 | 76, 255 | 19 442 | 0·53, 5·56 | 19 454 | <0·60, 3·89 | 8565 | 3·5, 20·7 |
| 501–3300 | 8839 | 1·58, 6·94 | 8372 | 94, 275 | 8370 | 0·76, 5·43 | 8375 | <0·60, 4·38 | 3136 | 2·9, 17·9 |
| 3301–10 000 | 3428 | 1·43, 5·94 | 3323 | 83, 240 | 3318 | 0·62, 4·53 | 3318 | 0·68, 3·56 | 1293 | 2·3, 14·7 |
| 10 001–100 000 | 2877 | 1·16, 4·96 | 2836 | 58, 186 | 2835 | 0·71, 4·35 | 2836 | 0·75, 3·01 | 1259 | 2·9, 11·2 |
| >100 000 | 385 | 1·10, 4·19 | 382 | 44, 120 | 382 | 0·84, 3·28 | 382 | 0·81, 2·73 | 250 | 3·4, 11·0 |
| p value | NA | 0·0020 | NA | <0·0001 | NA | <0·0001 | NA | <0·0001 | NA | <0·0001 |
| Region‡ | ||||||||||
| Alaska and Hawaii | 486 | 1·17, 9·53 | 429 | 37, 141 | 429 | 1·10, 3·63 | 428 | <0·60, 1·56 | 346 | 0·7, 1·6 |
| Central Midwest | 2655 | 2·64, 7·23 | 2609 | 149, 304 | 2609 | 3·10, 8·69 | 2609 | 2·71, 12·50 | 797 | 11·4, 32·2 |
| Eastern Midwest | 6085 | 2·15, 7·49 | 5714 | 111, 309 | 5712 | <0·08, 5·88 | 5712 | 1·01, 3·54 | 1395 | 1·0, 3·7 |
| Mid-Atlantic | 4902 | 0·35, 3·32 | 3809 | 97, 338 | 3798 | <0·08, 2·78 | 3805 | <0·60, 1·16 | 2367 | 2·2, 9·9 |
| New England | 1728 | 2·10, 6·95 | 1702 | 20, 75 | 1702 | 1·02, 3·54 | 1700 | <0·60, 2·52 | 736 | 4·0, 25·1 |
| Pacific Northwest | 4456 | 2·50, 8·50 | 3840 | 27, 150 | 3839 | <0·08, 1·90 | 3842 | <0·60, 1·01 | 1668 | 2·7, 16·0 |
| Southeast | 7866 | 0·35, 2·00 | 7765 | 21, 130 | 7764 | <0·08, 2·54 | 7763 | <0·60, 1·46 | 3980 | 2·1, 7·8 |
| Southwest | 8617 | 3·20, 10·73 | 8503 | 115, 270 | 8494 | 1·49, 7·68 | 8506 | 1·03, 6·50 | 3214 | 9·6, 28·3 |
| p value | NA | <0·0001 | NA | <0·0001 | NA | <0·0001 | NA | <0·0001 | NA | <0·0001 |
| Sociodemographic county cluster§ | ||||||||||
| Semi-Urban, High SES | 14 604 | 1·41, 6·30 | 13 330 | 75, 250 | 13 313 | 0·28, 4·64 | 13 323 | <0·60, 3·08 | 6062 | 2·3, 15·8 |
| Semi-Urban, Middle-to-Low SES | 1409 | 0·35, 1·58 | 1405 | 16, 107 | 1404 | <0·08, 1·30 | 1403 | <0·60, 0·71 | 862 | 1·0, 2·8 |
| Semi-Urban, Hispanic | 4635 | 3·60, 11·71 | 4555 | 110, 279 | 4558 | 1·49, 8·00 | 4557 | 1·27, 8·49 | 2045 | 10·9, 31·7 |
| Mostly Rural, Middle SES | 9100 | 0·86, 6·00 | 8434 | 64, 240 | 8429 | 0·53, 4·10 | 8433 | <0·60, 2·59 | 2803 | 2·0, 9·5 |
| Rural, Middle-to-Low SES | 533 | 0·73, 4·50 | 526 | 62, 198 | 523 | 0·59, 5·00 | 526 | <0·60, 4·29 | 194 | 2·0, 14·7 |
| Young, Urban, Middle-to-High SES | 1038 | 2·67, 9·35 | 1006 | 110, 227 | 1010 | 0·65, 6·97 | 1009 | <0·60, 3·79 | 538 | 6·3, 17·7 |
| Rural, American Indian | 486 | 3·17, 10·17 | 444 | 90, 252 | 444 | 0·98, 5·35 | 448 | 0·74, 4·85 | 382 | 2·7, 10·3 |
| Rural, High SES | 5188 | 2·55, 8·08 | 4853 | 100, 266 | 4851 | 1·38, 6·35 | 4851 | 0·82, 7·21 | 1716 | 3·7, 22·2 |
| p value | NA | <0·0001 | NA | <0·0001 | NA | <0·0001 | NA | <0·0001 | NA | <0·0001 |
| Correctional facility CWSs¶ | 203 | 2·48, 9·22 | 192 | 56, 227 | 191 | 1·33, 7·04 | 192 | 0·62, 3·12 | 74 | 3·2, 12·4 |
| p value | NA | 0·13 | NA | 0·35 | NA | 0·042 | NA | 0·28 | NA | 0·64 |
All concentration estimates (excluding uranium) are based on EPA SYR3 records and cover 2006–11; uranium concentration estimates are based on EPA SYR2 and SYR3 records and cover 2000–11. p values are from non-parametric Kruskal-Wallis tests (comparing the distribution of concentrations across subgroup categories). CWS=community water system. NA=not available. SES=socioeconomic status. EPA=Environmental Protection Agency. SYR=Six-Year Review.
CWSs served by groundwater include those served by surface water under the influence of groundwater and groundwater under the influence of surface water.
Standard US EPA categories; population served is the adjusted total population served (as defined by EPA), which accounts for systems that sell or purchase water and avoids overcounting.
States included in geological regions are: Alaska and Hawaii (AK, HI), Central Midwest (ND, SD, NE, KS, MO), Eastern Midwest (WI, IL, IN, MI, OH, MN, IA), Mid-Atlantic (PA, MD, DC, DE, NY, NJ, CT, RI), New England (MA, VT, NH, ME), Pacific Northwest (WA, OR, MT, WY, and ID), Southeast (OK, AR, LA, MS, AL, FL, GA, TN, KY, SC, NC, VA, WV), and Southwest (CA, NV, UT, CO, AZ, NM, TX).
143 CWSs served more than one county; of these, approximately half served counties categorised to different sociodemographic county-clusters (eg, the CWS NY7003493 serves New York, NY [Young, Urban, Middle-to-High SES] and Bronx, NY [Semi-Urban, Hispanic]); sociodemographic clusters were classified on the basis of Wallace et al;23 the CWSs are represented for each county that they serve in the sociodemographic county-cluster analyses (n=36 674 CWSs analysed in sociodemographic county-cluster analyses).
CWSs exclusively serving correctional facilities were identified via a keyword search of CWS names for “prison”, “correction”, “corr”, “juvenile”, “detention”, “jail”, “penitentiary”, “women”, “TDCJ” (Texas Department of Criminal Justice), “ADOC” (Arizona Department of Corrections), “ADC” (Arkansas Department of Correction), and “sheriff”. Values lower than the EPA maximum limit of detection for each metal are displayed as < the value of the detection limit in μg/L.