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Water: Chemical Contaminant Rules

Basic Information on the Chemical Contaminant Rules

EPA established Maximum Contaminant Levels (MCLs), Maximum Contaminant Level Goals (MCLGs), monitoring requirements and best available technologies for removal for 65 chemical contaminants over a five year period as EPA gathered and analyzed occurrence and health effects data. This series of rules are known as the Chemical Phase Rules and they define regulations for three contaminant groups:

  • Inorganic Chemicals (IOCs),
  • Synthetic Organic Chemicals (SOCs), and
  • Volatile Organic Chemicals (VOCs).

The Chemical Phase rules provide public health protection through the reduction of chronic risks from:

  • cancer;
  • organ damage; and
  • circulatory,
  • nervous, and
  • reproductive system disorders.

They also help to reduce the occurrence of Methemoglobinemia or "blue baby syndrome" from ingestion of elevated levels of nitrate or nitrite. All public water systems must monitor for Nitrate and Nitrite. Community water systems and Non-transient non-community water systems must also monitor for IOCs, SOCs, and VOCs.

Regulated Chemical Contaminants

For more information on each of these contaminants, click on the links in the table below.

Phased Rules VOC SOC IOC
Phase I, July 7, 1987
(52 FR 25690)
Effective: 1989

Read this Federal Register Notice

benzene
carbon tetrachloride
p-dichlorobenzene
trichloroethylene
vinyl chloride
1,1,1-trichloroethane
1,1-dichloroethylene
1,2-dichloroethane


Phase II, January 19911
(56 FR 3526)
Effective: 1992
Read this Federal Register Notice
cis-1,2-dichloroethylene
ethylbenzene
monochlorobenzene (chlorobenzene)
o-dichlorobenzene
styrene
tetrachloroethylene
toluene
trans-1,2-dichloroethylene
xylenes
1,2-dichloropropane
alachlor
atrazine
carbofuran
chlordane
EDB (ethylene dibromide)
DBCP (1,2-dibromo-3-chloropropane)
heptachlor
heptachlor epoxide
lindane
methoxychlor
toxaphene
PCBs
2,4-D
2,4,5-TP
asbestos
cadmium
chromium
fluoride
mercury
nitrate
nitrite
selenium
Phase IIB, July 1991
(56 FR 30266)
Effective: 1993
Read this Federal Register Notice

pentachlorophenol barium
Phase V, July 1992
(57 FR 31776)
Effective: 1994
Read this Federal Register Notice
dichloromethane
1,1,2-trichloroethane
1,2,4-trichlorobenzene
benzo(a)pyrene
dalapon
di(ethylhexyl)-adipate
di(ethylhexyl)-phthalate
dinoseb
diquat
endothall
endrin
glyphosate
hexachlorobenzene
hexachlorocyclo-pentadiene
oxymal
picloram
simazine
2,3,7,8-TCDD (dioxin)
antimony
beryllium
cyanide
nickel (remanded 1995)
thallium

1Aldicarb, aldicarb sulfone, and aldicarb sulfoxide are considered regulated chemicals although their MCLs are stayed. Therefore PWS are not required to meet an MCL.

For each contaminant, EPA set a health goal, or Maximum Contaminant Level Goal (MCLG). This is the level at which a person could drink two liters of water containing the contaminant every day for 70 years without suffering any ill effects. This goal is not a legal limit with which water systems must comply; it is based solely on human health. For known cancer-causing agents (carcinogens), EPA set the health goal at zero, under the assumption that any exposure to the chemical could present a cancer risk.

The rules also set a legal limit, or Maximum Contaminant Level (MCL), for each contaminant. EPA sets legal limits as close to the health goal as possible, keeping in mind the technical and financial barriers that exist. Except for contaminants regulated as carcinogens, most legal limits and health goals are the same. Even when they are less strict than the health goals, the legal limits provide substantial public health protection.

Federal Register Notices for the Chemical Phase Rules

You will need the free Adobe Reader to view some of the files on this page. See EPA's PDF page to learn more. If you need help accessing these PDF documents below, please contact EPA's Safe Drinking Water Hotline at 1-800-426-4791.


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The Standardized Monitoring Framework

The Standardized Monitoring Framework (SMF), promulgated in the Phase II rule on January 30, 1991 and revised under Phases IIB and V, includes contaminants regulated under Phases I, II, IIB, V, the revised Arsenic Rule, and the Radionuclides Rule. Monitoring under the SMF began in 1993. The goal of the Standardized Monitoring Framework is to standardize, simplify, and consolidate drinking water monitoring requirements across contaminant groups. In order to do this, EPA has established nine-year compliance cycles. Each nine-year compliance cycle is divided into 3 three-year compliance periods, which may be further subdivided into annual and quarterly periods. Compliance periods run on a calendar year basis, from January 1 through December 31. Compliance cycle 1 began January 1, 1993 and ended December 31, 2001; the second compliance cycle began January 1, 2002 and ends December 31, 2010; the third compliance cycle begins January 1, 2011 and ends December 31, 2019. Monitoring schedules and sample requirements are standardized for each compliance cycle for each contaminant group.

Standardized Monitoring Framework – Compliance Cycles and Period
2nd Compliance Cycle 3rd Compliance Cycle
1st Period 2nd Period 3rd Period 1st Period 2nd Period 3rd Period
2002 2005 2008 2011 2014 2017
2003 2006 2009 2012 2015 2018
2004 2007 2010 2013 2016 2019

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Monitoring Waivers

The SMF allows States to grant waivers to water systems to reduce the sampling frequencies to once every 3, 6 or 9 years for inorganic compounds, synthetic organic compounds, and volatile organic compound. Waivers of sampling requirements are granted for specified contaminants based on both a vulnerability assessment and the analytical results of previous sampling. The vulnerability assessment may be based on a determination that either the contaminant has not been used in the area or that the system is not susceptible to contamination.

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