Dubuque County, Iowa: drinking water report. Dubuque County in northeastern Iowa has about 99,000 residents, with the city of Dubuque overlooking the…
Dubuque County in northeastern Iowa has about 99,000 residents, with the city of Dubuque overlooking the Mississippi River from dramatic bluffs. The city draws from deep wells and a Mississippi River alluvial wellfield. The county's karst geology – the same dolomite and limestone terrain that creates the region's scenic bluffs and caves – makes groundwater exceptionally vulnerable to surface contamination.
Karst sinkholes are abundant in Dubuque County, creating direct conduits between the surface and the aquifer. According to the Iowa DNR's 2024 source water assessment, 15 confirmed sinkholes exist within the contributing area of Dubuque's municipal wellfield. Dye tracing studies have documented contamination travel times of less than 48 hours from sinkholes to production wells.
Agricultural nitrate from the surrounding farmland reaches the karst aquifer rapidly. A 2024 Iowa Geological Survey study found nitrate averaging 9.1 mg/L in the shallow aquifer beneath agricultural areas of the county – just below the MCL. The Dubuque Regional Airport has documented AFFF use, and Iowa DNR's 2024 PFAS sampling found PFOS at 6 ppt in monitoring wells near the facility.
Dubuque's municipal wellfield draws from deeper zones that are somewhat protected from karst contamination, but private well owners tapping the shallow aquifer face direct exposure risk. If you can see a sinkhole from your property, your well and the surface are likely connected.
Check your water for current data. For karst-influenced well water, reverse osmosis handles nitrate, bacteria, and PFAS. Our water filter guide covers systems suited to carbonate aquifer water. Pull your detailed report for local data, and visit our Iowa page for statewide patterns.
Drinking water is one exposure route. These federal datasets also cover Dubuque County, IA.
The EPA places Dubuque County, IA in Zone 1 - the EPA's highest-risk category, where the predicted average indoor radon level is above 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.
65% of homes in Dubuque County, IA were built before 1980, and 28% 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 Dubuque County, IA averages 8 µg/m³, within 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