Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

Bear Mountain Water Supply

Trihalomethanes are cancer-causing contaminants that form during water treatment with chlorine and other disinfectants. The total trihalomethanes group includes four chemicals: chloroform, bromodichloromethane, dibromochloromethane and bromoform. Read More.

Studies conducted in the U.S. and Europe have found that drinking tap water that carries disinfection byproducts increases the risk of developing bladder cancer. In animal studies, all trihalomethanes cause liver, kidney and intestinal tumors. Some human epidemiological studies also reported an association between disinfection byproducts and an increased risk of problems during pregnancy, including spontaneous miscarriage, cardiovascular defects, neural tube defects and low birth weight.

The health guideline of 0.15 parts per billion, or ppb, for the group of four trihalomethanes, or THM4/TTHM, was defined in a peer-reviewed scientific study by EWG and represents a one-in-one-million lifetime cancer risk level.

Click here to read more about disinfection byproducts.

 

24

Samples

0

Samples exceeding legal limit (MCL)

24

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201848.5 ppb4435.0 ppb - 56.0 ppb
201940.4 ppb5515.0 ppb - 67.0 ppb
202048.6 ppb4420.4 ppb - 67.0 ppb
202154.7 ppb4441.8 ppb - 69.0 ppb
202269.4 ppb2264.7 ppb - 74.0 ppb
202355.7 ppb5529.0 ppb - 66.0 ppb

ppb = parts per billion

State, National, and Health Guidelines for Drinking Water

EWG Health Guideline: 0.15 ppb

The health guideline of 0.15 parts per billion, or ppb, for the group of four trihalomethanes, or THM4/TTHM, was defined in a peer-reviewed scientific study by EWG and represents a one-in-one-million lifetime cancer risk level.

EPA Maximum Contaminant
Level (MCL): 80 ppb

The legal limit for the group of four trihalomethanes, established in 1998, was based on the need for residual disinfectant levels in water served to customers and the cost of treatment. This limit does not fully protect against the risk of cancer due to exposure to trihalomethanes.

ppb = parts per billion

All test results

Date Lab ID Result
2018-02-05TTHMS 02061811:349.0 ppb
2018-05-07DBP 05071819-135.0 ppb
2018-07-25TTHM 07251829-156.0 ppb
2018-11-13TTHM 11151803:154.0 ppb
2019-02-05TTHMS 02061903A:115.0 ppb
2019-02-05TTHM 02061903A:115.0 ppb
2019-05-08TTHMS 0508190541.0 ppb
2019-08-07TTHM 0814190767.0 ppb
2019-11-04TTHMS QB19274764.0 ppb
2020-02-05DBP 02062004:120.4 ppb
2020-05-13DBP9 05132006:140.0 ppb
2020-08-13TTHM 0813201367.0 ppb
2020-11-04DBP 11042008-167.0 ppb
2021-02-16TTHM 11042008:141.8 ppb
2021-05-05DBP 05052105:154.9 ppb
2021-08-04TTHMS 08042105C69.0 ppb
2021-11-17TTHMS 11172114-153.0 ppb
2022-05-25TTHMS 0526220374.0 ppb
2022-10-25TTHMS 10262215B:464.7 ppb
2023-01-27TTHMS 01272306-1029.0 ppb
2023-06-15TTHM 06152304:163.7 ppb
2023-10-02TTHM 10042313B:166.0 ppb
2023-10-13TTHMS 12132334:160.0 ppb
2023-12-13TTHM 12132334-160.0 ppb