State Well Water Guide
Illinois Private Well Water Guide
About 20% of Illinoisans rely on private wells, concentrated in rural agricultural counties downstate and suburban fringe communities outside Chicago's water service area. Illinois's groundwater reflects its heavy agricultural use: nitrate contamination from corn and soybean production is the most pervasive statewide concern. Naturally occurring radium in some deep sandstone aquifers, arsenic from glacial deposits in specific areas, and PFAS from industrial and military sites are additional concerns. IDPH regulates well construction; the Private Sewage Disposal Code governs septic proximity.
Testing Guidance
IDPH recommends annual testing for coliform bacteria and nitrates for all private wells. Central and southern Illinois agricultural area well owners should prioritize nitrate testing. Deep sandstone aquifer users in northeast Illinois should test for radium and barium. Wells near the Waukegan/Lake County industrial corridor or Chanute Air Force Base should be tested for PFAS and VOCs.
What to Test For in Illinois
Total coliform bacteria and E. coli — annual minimum
Nitrates — statewide agricultural areas; highest priority in corn belt counties
Radium-226 and -228 — deep sandstone aquifer users in northeastern Illinois (Cambrian-Ordovician aquifer)
Barium — deep sandstone aquifer wells; naturally elevated
Arsenic — some shallow glacial drift wells in northern Illinois
PFAS — near Chanute AFB (Rantoul), Scott AFB, and industrial sites in the I-55 and I-80 corridors
Volatile organic compounds — near industrial sites in the Chicago metropolitan fringe
Iron and manganese — shallow glacial aquifer wells throughout the state
Common Contamination Risks in Illinois
Nitrate contamination from corn and soybean agriculture — Illinois's intensive row crop agriculture creates the most widespread groundwater contamination in the state; many shallow wells in agricultural areas exceed the 10 mg/L nitrate MCL
Radium in deep sandstone aquifers — the Cambrian-Ordovician sandstone aquifer used by many northeast Illinois communities has elevated naturally occurring radium
Iron and manganese from glacial sediments — common throughout the glaciated portions of the state
PFAS from military and industrial sites — Chanute AFB and Scott AFB are identified PFAS sources
Bacterial contamination from agricultural runoff and failing septic systems — particularly during spring planting season
Contaminant Guides Relevant to IL Wells
PFAS
Synthetic Chemicals
EPA limit: 4 ppt
Lead
Heavy Metals
EPA limit: 15 ppb (action level)
Nitrates
Agricultural Chemicals
EPA limit: 10 mg/L
DBPs
Disinfection Byproducts
EPA limit: 80 µg/L (TTHMs) / 60 µg/L (HAA5)
Arsenic
Heavy Metals
EPA limit: 10 ppb
Hard Water
Minerals
EPA limit: No federal limit
Chlorine
Disinfection Chemicals
EPA limit: 4 mg/L (MRDL)
Microplastics
Emerging Contaminants
EPA limit: No federal limit
Bacteria
Microbial Contamination
EPA limit: Zero E. coli / < 1 coliform per 100 mL
Fluoride
Minerals
EPA limit: 4 mg/L (MCL) / 2 mg/L (Secondary MCL)
Chromium-6
Heavy Metals
EPA limit: 100 ppb (total chromium)
Copper
Heavy Metals
EPA limit: 1.3 mg/L (action level)
Radon
Radioactive Contaminants
EPA limit: No finalized MCL
Iron & Manganese
Minerals
EPA limit: 0.3 mg/L iron / 0.05 mg/L manganese (aesthetic SMCLs)
Atrazine
Agricultural Chemicals
EPA limit: 3 ppb (0.003 mg/L)
Uranium
Radioactive Contaminants
EPA limit: 30 µg/L (30 ppb)
Perchlorate
Industrial Chemicals
EPA limit: 0.056 mg/L (56 ppb)
VOCs
Industrial Chemicals
EPA limit: Varies by compound: benzene 5 ppb; TCE 5 ppb; PCE 5 ppb; vinyl chloride 2 ppb
Radium
Radioactive Contaminants
EPA limit: 5 pCi/L (combined Ra-226 + Ra-228)
Crypto & Giardia
Microbial Contamination
EPA limit: Zero (treatment technique standard)
Hydrogen Sulfide
Naturally Occurring Compounds
EPA limit: No MCL; Secondary MCL (aesthetic) of 0.05 mg/L
Selenium
Minerals
EPA limit: 50 ppb (0.05 mg/L)
Cadmium
Heavy Metals
EPA limit: 5 ppb (0.005 mg/L)
Mercury
Heavy Metals
EPA limit: 2 ppb (0.002 mg/L)
Barium
Heavy Metals
EPA limit: 2 mg/L
Find a Certified Lab in Illinois
Use the Illinois state-certified laboratory program to find accredited labs for private well testing. Always verify current certification before submitting samples.
IL Certified Lab Directory ↗Illinois Well Water FAQs
Related Pages
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
Quick Reference
State program
IL Certified Labs ↗EPA guidance
EPA Private Wells Program ↗State lab directory
IL Certified Labs ↗Minimum Annual Tests
Plus state-specific contaminants listed above
Other State Guides