Hexachlorocyclopentadiene in drinking water
1,236 active public water systems in 38 states had a Hexachlorocyclopentadiene violation in the past three years, and 65 have one that is still unresolved.
You are on Tapcensus, an independent guide to the EPA compliance records of every public water system in the United States. This page explains Hexachlorocyclopentadiene and lists the water systems whose records include a related violation. It does not show measured levels.
Is Hexachlorocyclopentadiene in the records for your water system?
Enter a ZIP code, town, or street address to see the water systems that serve your area, their status, and which rules and contaminants appear in their violations.
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What it is and where it comes from
Hexachlorocyclopentadiene (HCCP) is a chlorinated cyclic compound used as a chemical intermediate in the manufacture of pesticides, flame retardants, and resins. It is not used directly as a pesticide. It enters drinking water through discharge from chemical manufacturing facilities. It is reactive and degrades relatively quickly in the environment.
Health effects
Chronic exposure to hexachlorocyclopentadiene is associated with kidney and stomach damage in animal studies. EPA has not classified it as a human carcinogen based on available data. Short-term high-level exposure may cause irritation of mucous membranes. Long-term exposure above the MCL is the primary concern for public water system violations.
The standard and what a violation means
EPA limit: 0.05 mg/L (50 ppb).
Water systems with a Hexachlorocyclopentadiene violation, by state
Active public water systems that reported at least one related violation to EPA in the past three years. Each state links to the list of its affected systems.
| State | Systems with violations, 3 yr | Share of active systems | Unresolved |
|---|---|---|---|
| Pennsylvania | 201 | 3% | 9 |
| New York | 120 | 1% | 1 |
| Texas | 115 | 2% | 0 |
| Oklahoma | 96 | 7% | 0 |
| Oregon | 72 | 3% | 3 |
| Illinois | 62 | 1% | 12 |
| Washington | 44 | 1% | 8 |
| Colorado | 39 | 2% | 5 |
| Montana | 37 | 2% | 1 |
| Idaho | 36 | 2% | 3 |
| West Virginia | 32 | 4% | 4 |
| Connecticut | 31 | 1% | 1 |
| Utah | 29 | 3% | 1 |
| Michigan | 28 | 0% | 1 |
| California | 27 | 0% | 1 |
| Indiana | 27 | 1% | 2 |
| Alaska | 25 | 2% | 0 |
| Alabama | 25 | 4% | 0 |
| Wyoming | 24 | 3% | 1 |
| Vermont | 22 | 2% | 3 |
| Wisconsin | 18 | 0% | 0 |
| Missouri | 16 | 1% | 1 |
| North Carolina | 16 | 0% | 1 |
| Nevada | 16 | 3% | 0 |
| Arizona | 15 | 1% | 1 |
| Massachusetts | 12 | 1% | 1 |
| Maine | 11 | 1% | 0 |
| Rhode Island | 9 | 2% | 0 |
| Minnesota | 8 | 0% | 2 |
| New Jersey | 7 | 0% | 2 |
| Maryland | 3 | 0% | 1 |
| South Dakota | 3 | 0% | 0 |
| Virginia | 3 | 0% | 0 |
| North Dakota | 2 | 1% | 0 |
| New Mexico | 2 | 0% | 0 |
| Kentucky | 1 | 0% | 0 |
| Nebraska | 1 | 0% | 0 |
| New Hampshire | 1 | 0% | 0 |
Largest water systems with a Hexachlorocyclopentadiene violation
The ten biggest systems, by people served, whose records include a related violation in the past three years.
| System | Serves | Status | Rules violated, 3 yr | Unresolved |
|---|---|---|---|---|
|
Denver Water Board Denver County |
1,287,000 | 3 | 0 | |
|
Pittsburgh Water & Sewer Auth Allegheny County |
520,000 | 3 | 0 | |
|
Gilbert, Town of Gilbert · Maricopa County |
247,600 | 9 | 1 | |
|
Corona, City of Corona · Riverside County |
169,380 | 6 | 0 | |
|
City of Sunnyvale Sunnyvale · Santa Clara County |
157,566 | 5 | 0 | |
|
Naperville Naperville · DuPage County |
156,406 | 1 | 0 | |
|
Epcor Agua Fria Surprise · Maricopa County |
128,040 | 5 | 0 | |
|
Pasco Water Department Franklin County |
115,102 | 2 | 0 | |
|
Inima USA / Aquaria LLC Dighton · Bristol County |
105,643 | 1 | 0 | |
|
Lehi City Utah County |
93,446 | 2 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Hexachlorocyclopentadiene, including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Hexachlorocyclopentadiene alone. Counts cover active systems in all 50 states and the District of Columbia.
Source: the U.S. EPA's Enforcement and Compliance History Online system (ECHO), which publishes the federal Safe Drinking Water Information System. EPA's terms and values are shown as published. The records are from EPA's data refresh of Oct 7, 2026; EPA refreshes this data quarterly, and states report to EPA with a lag of three to six months, so the newest violations may not appear yet.