EWG's Tap Water Database — 2019 UPDATE


Heptachlor epoxide

Dalewood-monteray Water System

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
20120.0661 ppb220.0532 ppb - 0.0789 ppb
20130.0769 ppb110.0769 ppb
20140.0547 ppb110.0547 ppb
20150.0305 ppb21ND - 0.0610 ppb
20160.0810 ppb110.0810 ppb
20170.0310 ppb21ND - 0.0620 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
2012-02-13C115241-010.0789 ppb
2012-09-03C207493-010.0532 ppb
2013-07-08C306707-010.0769 ppb
2014-07-28C406520-010.0547 ppb
2015-08-120.0610 ppb
2016-07-28CZ08134-010.0810 ppb
2017-07-27CA07958-010.0620 ppb