Total trihalomethanes (TTHMs)
CTWC - Shoreline Region-Guilford System
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.
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 | 24.0 ppb | 21 | 18 | ND - 62.9 ppb |
| 2019 | 24.3 ppb | 16 | 16 | 9.10 ppb - 35.5 ppb |
| 2020 | 29.3 ppb | 16 | 16 | 12.0 ppb - 43.8 ppb |
| 2021 | 36.8 ppb | 16 | 16 | 14.5 ppb - 82.8 ppb |
| 2022 | 28.8 ppb | 16 | 16 | 15.4 ppb - 43.3 ppb |
| 2023 | 37.8 ppb | 16 | 16 | 13.3 ppb - 67.2 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 |
|---|---|---|
| 2018-03-15 | CA03073TTHM | 21.3 ppb |
| 2018-03-15 | CA03074TTHM | 15.9 ppb |
| 2018-03-15 | CA03075TTHM | 23.6 ppb |
| 2018-03-15 | CA03076TTHM | 24.7 ppb |
| 2018-06-26 | CA80045TTHM | 44.6 ppb |
| 2018-06-26 | CA80046TTHM | 40.5 ppb |
| 2018-06-26 | CA80047TTHM | 33.7 ppb |
| 2018-06-26 | CA80048TTHM | 27.5 ppb |
| 2018-09-12 | DBP 200505042 | 36.7 ppb |
| 2018-09-12 | DBP 200505043 | 62.9 ppb |
| 2018-09-12 | DBP 200505044 | 54.5 ppb |
| 2018-09-12 | DBP 200505047 | 62.2 ppb |
| 2018-09-13 | VOC1 200505275 | ND |
| 2018-09-13 | VOC1 200505276 | ND |
| 2018-09-13 | VOC1 200505266 | ND |
| 2018-09-19 | VOC1 200506116 | 3.90 ppb |
| 2018-09-20 | VOC1 200506324 | 0.600 ppb |
| 2018-12-17 | DBP 200516235 | 11.8 ppb |
| 2018-12-17 | DBP 200516237 | 8.90 ppb |
| 2018-12-17 | DBP 200516238 | 14.8 ppb |
| 2018-12-17 | DBP 200516239 | 16.9 ppb |
| 2019-03-11 | DBP 200524150 | 9.10 ppb |
| 2019-03-11 | DBP 200524151 | 12.9 ppb |
| 2019-03-11 | DBP 200524152 | 17.2 ppb |
| 2019-03-11 | DBP 200524154 | 18.2 ppb |
| 2019-06-14 | DBP 200536672 | 17.9 ppb |
| 2019-06-14 | DBP 200536674 | 23.4 ppb |
| 2019-06-14 | DBP 200536680 | 27.7 ppb |
| 2019-06-14 | DBP 200536682 | 27.4 ppb |
| 2019-09-17 | DBP 200549478 | 28.6 ppb |
| 2019-09-17 | DBP 200549479 | 32.7 ppb |
| 2019-09-17 | DBP 200549480 | 34.8 ppb |
| 2019-09-17 | DBP 200549481 | 35.5 ppb |
| 2019-12-10 | DBP 200559642 | 16.1 ppb |
| 2019-12-10 | DBP 200559643 | 24.6 ppb |
| 2019-12-10 | DBP 200559644 | 29.1 ppb |
| 2019-12-10 | DBP 200559645 | 33.5 ppb |
| 2020-03-03 | DBP 200567998 | 16.5 ppb |
| 2020-03-05 | DBP 200568574 | 12.0 ppb |
| 2020-03-05 | DBP 200568575 | 20.3 ppb |
| 2020-03-05 | DBP 200568576 | 20.9 ppb |
| 2020-06-16 | DBP 200579543 | 28.8 ppb |
| 2020-06-16 | DBP 200579545 | 38.0 ppb |
| 2020-06-16 | DBP 200579546 | 43.8 ppb |
| 2020-06-16 | DBP 200579547 | 39.0 ppb |
| 2020-09-17 | DBP 200591051 | 21.6 ppb |
| 2020-09-17 | DBP 200591052 | 32.6 ppb |
| 2020-09-17 | DBP 200591053 | 39.5 ppb |
| 2020-09-17 | DBP 200591054 | 42.5 ppb |
| 2020-12-22 | DBP 200602030 | 18.3 ppb |
| 2020-12-22 | DBP 200602031 | 33.9 ppb |
| 2020-12-22 | DBP 200602032 | 30.9 ppb |
| 2020-12-22 | DBP 200602033 | 29.6 ppb |
| 2021-03-15 | DBP 200609842 | 15.6 ppb |
| 2021-03-15 | DBP 200609843 | 20.7 ppb |
| 2021-03-15 | DBP 200609844 | 23.1 ppb |
| 2021-03-15 | DBP 200609845 | 23.9 ppb |
| 2021-06-02 | DBP 200619263 | 30.1 ppb |
| 2021-06-02 | DBP 200619264 | 38.7 ppb |
| 2021-06-02 | DBP 200619265 | 41.2 ppb |
| 2021-06-02 | DBP 200619266 | 43.1 ppb |
| 2021-09-14 | 300059734 300059739 | 53.0 ppb |
| 2021-09-14 | 300059735 300059741 | 52.7 ppb |
| 2021-09-14 | 300059736 300059743 | 77.9 ppb |
| 2021-09-14 | 300059737 300059745 | 82.8 ppb |
| 2021-12-09 | D300117672 300117677 | 14.5 ppb |
| 2021-12-09 | D300117673 300117679 | 19.6 ppb |
| 2021-12-09 | D300117674 300117681 | 27.0 ppb |
| 2021-12-09 | D300117675 300117683 | 25.6 ppb |
| 2022-03-09 | CK83519 | 15.4 ppb |
| 2022-03-09 | CK83520 | 17.2 ppb |
| 2022-03-09 | CK83521 | 20.0 ppb |
| 2022-03-25 | CK95230 | 21.9 ppb |
| 2022-06-16 | CL58844 | 21.3 ppb |
| 2022-06-16 | CL58845 | 37.3 ppb |
| 2022-06-16 | CL58846 | 30.3 ppb |
| 2022-06-16 | CL58847 | 39.8 ppb |
| 2022-09-13 | CM30714 | 17.3 ppb |
| 2022-09-13 | CM30695 | 39.2 ppb |
| 2022-09-13 | CM30696 | 27.4 ppb |
| 2022-09-13 | CM30697 | 40.1 ppb |
| 2022-12-01 | CM97587 | 24.5 ppb |
| 2022-12-01 | CM97588 | 43.3 ppb |
| 2022-12-01 | CM97589 | 30.1 ppb |
| 2022-12-01 | CM97590 | 35.4 ppb |
| 2023-03-22 | CN66487 | 13.3 ppb |
| 2023-03-22 | CN66488 | 23.4 ppb |
| 2023-03-22 | CN66489 | 16.9 ppb |
| 2023-03-22 | CN66490 | 22.1 ppb |
| 2023-06-15 | CO31996 | 22.8 ppb |
| 2023-06-15 | CO31997 | 38.9 ppb |
| 2023-06-15 | CO31998 | 33.2 ppb |
| 2023-06-15 | CO31999 | 35.0 ppb |
| 2023-09-05 | CO90683 | 51.4 ppb |
| 2023-09-05 | CO90684 | 61.1 ppb |
| 2023-09-05 | CO90685 | 52.7 ppb |
| 2023-09-05 | CO90686 | 67.2 ppb |
| 2023-12-07 | CP65078 | 27.0 ppb |
| 2023-12-07 | CP65079 | 58.1 ppb |
| 2023-12-07 | CP65080 | 35.7 ppb |
| 2023-12-07 | CP65081 | 45.7 ppb |