EWG's Tap Water Database — 2021 UPDATE


Heptachlor epoxide

Rolling Acres S/d

Heptachlor epoxide is a breakdown product of heptachlor, a highly toxic and carcinogenic pesticide banned in the U.S. since the 1980s.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
20140.0482 ppb110.0482 ppb
20150.0427 ppb330.0350 ppb - 0.0490 ppb
20160.0435 ppb440.0330 ppb - 0.0490 ppb
20170.0343 ppb440.0290 ppb - 0.0440 ppb
20180.0403 ppb440.0240 ppb - 0.0530 ppb
20190.0370 ppb440.0270 ppb - 0.0530 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 0.006 ppb

The EWG Health Guideline of 0.006 ppb for heptachlor epoxide was defined by the California Office of Environmental Health Hazard Assessment as a public health goal, the level of a drinking water contaminant that does not pose a significant health risk. This health guideline protects against cancer.

EPA Maximum Contaminant
Level (MCL) 0.2 ppb

The legal limit for heptachlor epoxide, established in 1991, was based on analytical detection limits at the time that the standard was set. This limit may not fully protect against the risk of cancer.

ppb = parts per billion

All test results

Date Lab ID Result
2014-05-07C403248-010.0482 ppb
2015-04-210.0350 ppb
2015-07-210.0490 ppb
2015-10-200.0440 ppb
2016-01-13C516091-010.0460 ppb
2016-05-04CZ03384-010.0460 ppb
2016-07-27CZ08458-010.0330 ppb
2016-10-20CZ13860-010.0490 ppb
2017-01-25CZ18925-010.0440 ppb
2017-04-12CA03062-010.0320 ppb
2017-07-20CA07810-010.0320 ppb
2017-11-16CA13313-010.0290 ppb
2018-01-25CA18436-01 0.0390 ppb
2018-04-03CB03485-01 0.0240 ppb
2018-07-31CB08232-01 0.0450 ppb
2018-10-04CB14410-01 0.0530 ppb
2019-01-14CB18911-01 0.0530 ppb
2019-04-16CC04293-01 0.0400 ppb
2019-07-23CC10674-01 0.0280 ppb
2019-10-29CC15925-01 0.0270 ppb