Benton County, Washington: drinking water report. Benton County in south-central Washington has about 204,000 residents in the Tri-Cities area (Kennewick
Benton County in south-central Washington has about 204,000 residents in the Tri-Cities area (Kennewick and Richland). The Columbia River provides the primary water source. The Hanford Site – the DOE's most contaminated nuclear weapons production complex – occupies 586 square miles in the northern part of the county, making water quality inseparable from the nation's nuclear legacy.
Hanford produced plutonium for the U.S. nuclear arsenal from 1943 to 1987, generating 56 million gallons of radioactive and chemical waste stored in underground tanks. According to DOE's 2024 Hanford environmental report, groundwater contamination beneath the site covers over 80 square miles and includes tritium, iodine-129, strontium-90, chromium, carbon tetrachloride, and nitrate. Some plumes are migrating toward the Columbia River.
The Columbia River at the Tri-Cities intake is upstream of the most concentrated contamination discharge points, and monitoring by the Washington Department of Health shows river water meets all drinking water standards. However, tritium from Hanford operations has been detected in the river at levels above background but below the MCL of 20,000 pCi/L.
Benton County's Columbia River supply is treated and monitored extensively, with radiation monitoring that few other communities require. The Hanford cleanup is the largest environmental remediation project in the world and will continue for decades.
Check your water for current data, including radiological monitoring that is unique to this area. For comprehensive household protection, reverse osmosis removes both chemical and radiological contaminants. Our water filter guide covers systems rated for the full contaminant spectrum. Get your detailed report for historical data, and visit our Washington page for statewide context.
Drinking water is one exposure route. These federal datasets also cover Benton County, WA.
The EPA places Benton County, WA in Zone 2 - a moderate-risk category, with a predicted average indoor radon level between 2 and 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
47% of homes in Benton County, WA were built before 1980, and 11% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Benton County, WA averages 10 µg/m³, above the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
29 public water systems serving Benton County, WA have EPA lead testing on record. The reported lead sample skews toward systems that already flagged a problem, so its exceedance rate is not directly comparable with other areas. 7 water systems serving Benton County, WA carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Nitrate | 5 |
| Arsenic | 1 |
| Total Trihalomethanes (TTHM) | 1 |
| Haloacetic Acids (HAA5) | 1 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.