EWG's Tap Water Database — 2019 UPDATE


Heptachlor epoxide

Ashebrook Park

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
20120.150 ppb440.138 ppb - 0.172 ppb
20130.140 ppb330.0939 ppb - 0.200 ppb
20140.133 ppb880.118 ppb - 0.162 ppb
20150.108 ppb440.0940 ppb - 0.130 ppb
20160.110 ppb440.0940 ppb - 0.130 ppb
20170.0320 ppb21ND - 0.0640 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
2012-05-29C202008-010.138 ppb
2012-05-29C202008-020.140 ppb
2012-09-03C207476-010.149 ppb
2012-11-07C210067-010.172 ppb
2013-02-04C213930-020.200 ppb
2013-02-04C213930-010.126 ppb
2013-05-20C302376-010.0939 ppb
2014-01-14C400144-010.144 ppb
2014-01-22C316522-010.118 ppb
2014-04-08C402857-020.162 ppb
2014-04-08C402857-010.132 ppb
2014-07-23C406507-010.138 ppb
2014-07-24C406507-020.118 ppb
2014-10-16C411356-020.123 ppb
2014-10-16C411356-010.130 ppb
2015-01-210.0940 ppb
2015-01-220.0970 ppb
2015-07-210.130 ppb
2015-10-140.110 ppb
2016-01-19C516505-010.0960 ppb
2016-01-25CZ01132-010.0940 ppb
2016-04-19CZ02766-010.119 ppb
2016-10-10CZ12924-010.130 ppb
2017-04-11CA02612-010.0640 ppb