Chlorate
Town of Hempstead Water Department
Chlorate forms in drinking water as a byproduct of disinfection. Chlorate impairs thyroid function, making chlorate exposure most harmful during pregnancy and childhood. Read More.
In 2002, California scientists proposed an advisory value, called an action level, for chlorate at 200 parts per billion. Between 2013 and 2015, the EPA collected data through the Unregulated Contaminant Monitoring Rule program and found that over 15 percent of water tests from 38 percent of utilities had chlorate levels above a health-protective concentration, which federal scientists defined as 210 parts per billion, nearly equivalent to the California advisory value.
Samples
Samples exceeding legal limit (MCL)
Samples exceeding
health guidelines
Testing results - average by year
| Year | Average result | Samples taken | Detections | Range of results |
|---|---|---|---|---|
| 2014 | 82.3 ppb | 35 | 35 | 23.0 ppb - 200.0 ppb |
| 2015 | N/A | 0 | 0 | N/A |
| 2016 | N/A | 0 | 0 | N/A |
| 2017 | N/A | 0 | 0 | N/A |
| 2018 | N/A | 0 | 0 | N/A |
| 2019 | N/A | 0 | 0 | N/A |
ppb = parts per billion
State and national drinking water standards and health guidelines
EWG Health Guideline 210 ppb
The EWG Health Guideline of 210 ppb for chlorate was defined by the Environmental Protection Agency as a benchmark for testing under the Unregulated Contaminant Monitoring Rule program. This health guideline protects against hormone disruption.
ppb = parts per billion
All test results
| Date | Lab ID | Result |
|---|---|---|
| 2014-06-09 | 08956 062014 | 23.0 ppb |
| 2014-06-09 | 08474 062014 | 55.0 ppb |
| 2014-06-09 | 04756 062014 | 75.0 ppb |
| 2014-06-10 | 07957 062014 | 120.0 ppb |
| 2014-06-10 | 09846 062014 | 36.0 ppb |
| 2014-06-10 | 03456 062014 | 51.0 ppb |
| 2014-06-11 | 12560 062014 | 73.0 ppb |
| 2014-06-11 | 09521 062014 | 28.0 ppb |
| 2014-06-11 | 05302 062014 | 82.0 ppb |
| 2014-06-12 | 99001 MAX1 06201 | 100.0 ppb |
| 2014-06-12 | 99001 MAX3 06201 | 84.0 ppb |
| 2014-06-12 | 99001 MAX2 06201 | 81.0 ppb |
| 2014-06-12 | 08321 062014 | 28.0 ppb |
| 2014-06-12 | 05322 062014 | 100.0 ppb |
| 2014-06-12 | 07797 062014 | 140.0 ppb |
| 2014-06-18 | 08279 062014 | 89.0 ppb |
| 2014-06-30 | 05304 062014 | 94.0 ppb |
| 2014-06-30 | 05318 062014 | 82.0 ppb |
| 2014-12-08 | 08956 122014 | 34.0 ppb |
| 2014-12-08 | 04756 122014 | 66.0 ppb |
| 2014-12-08 | 05302 122014 | 61.0 ppb |
| 2014-12-09 | 99001 122014 | 40.0 ppb |
| 2014-12-09 | 05318 122014 | 58.0 ppb |
| 2014-12-09 | 07797 122014 | 200.0 ppb |
| 2014-12-09 | 05322 122014 | 150.0 ppb |
| 2014-12-10 | 08279 122014 | 100.0 ppb |
| 2014-12-10 | 08474 122014 | 200.0 ppb |
| 2014-12-10 | 05304 122014 | 98.0 ppb |
| 2014-12-10 | 03456 122014 | 100.0 ppb |
| 2014-12-11 | 99001 122014 290 | 81.0 ppb |
| 2014-12-11 | 99001 122014 290 | 87.0 ppb |
| 2014-12-11 | 12560 122014 | 69.0 ppb |
| 2014-12-11 | 09521 122014 | 42.0 ppb |
| 2014-12-22 | 09846 122014 | 110.0 ppb |
| 2014-12-22 | 08321 122014 | 45.0 ppb |