Chloroform
Bear Mountain Water Supply
Chloroform, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Chloroform and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Read More.
In addition to tap water disinfection, chloroform pollution in the environment also comes from industrial discharges from pulp and paper mills, and from urban wastewater effluent. Human studies show that chloroform damages the kidneys, liver and central nervous system. In animals, chloroform causes infertility, birth defects and cancer.
Samples
Samples exceeding legal limit (MCL)
Samples exceeding
health guidelines
Testing results - average by year
| Year | Average result | Samples taken | Detections | Range of results |
|---|---|---|---|---|
| 2018 | 42.8 ppb | 4 | 4 | 31.0 ppb - 53.0 ppb |
| 2019 | 33.6 ppb | 5 | 5 | 12.0 ppb - 55.0 ppb |
| 2020 | 27.7 ppb | 4 | 4 | 0.800 ppb - 54.0 ppb |
| 2021 | 46.2 ppb | 4 | 4 | 35.2 ppb - 57.0 ppb |
| 2022 | 60.6 ppb | 2 | 2 | 55.1 ppb - 66.0 ppb |
| 2023 | 49.2 ppb | 5 | 5 | 26.9 ppb - 58.0 ppb |
ppb = parts per billion
State, National, and Health Guidelines for Drinking Water
EWG Health Guideline: 0.4 ppb
The EWG Health Guideline of 0.4 ppb for chloroform was based on the California Office of Environmental Health Hazard Assessment's public health goal, the level of a drinking water contaminant that does not pose a significant health risk. This health guideline protects against cancer and harm to fetal growth and development.
ppb = parts per billion
All test results
| Date | Lab ID | Result |
|---|---|---|
| 2018-02-05 | TTHMS 02061811:3 | 42.0 ppb |
| 2018-05-07 | DBP 05071819-1 | 31.0 ppb |
| 2018-07-25 | TTHM 07251829-1 | 45.0 ppb |
| 2018-11-13 | TTHM 11151803:1 | 53.0 ppb |
| 2019-02-05 | TTHMS 02061903A:1 | 12.0 ppb |
| 2019-02-05 | TTHM 02061903A:1 | 12.0 ppb |
| 2019-05-08 | TTHMS 05081905 | 35.0 ppb |
| 2019-08-07 | TTHM 08141907 | 54.0 ppb |
| 2019-11-04 | TTHMS QB192747 | 55.0 ppb |
| 2020-02-05 | DBP 02062004:1 | 16.0 ppb |
| 2020-05-13 | DBP9 05132006:1 | 40.0 ppb |
| 2020-08-13 | TTHM 08132013 | 54.0 ppb |
| 2020-11-04 | DBP 11042008-1 | 0.800 ppb |
| 2021-02-16 | TTHM 11042008:1 | 35.2 ppb |
| 2021-05-05 | DBP 05052105:1 | 48.6 ppb |
| 2021-08-04 | TTHMS 08042105C | 57.0 ppb |
| 2021-11-17 | TTHMS 11172114-1 | 44.0 ppb |
| 2022-05-25 | TTHMS 05262203 | 66.0 ppb |
| 2022-10-25 | TTHMS 10262215B:4 | 55.1 ppb |
| 2023-01-27 | TTHMS 01272306-10 | 26.9 ppb |
| 2023-06-15 | TTHM 06152304:1 | 55.1 ppb |
| 2023-10-02 | TTHM 10042313B:1 | 58.0 ppb |
| 2023-10-13 | TTHMS 12132334:1 | 53.0 ppb |
| 2023-12-13 | TTHM 12132334-1 | 53.0 ppb |