Well Water in Penobscot County, Maine

Penobscot County · Population ~153,000 (county) · Aquifer: Bedrock / Penobscot River Valley Sand & Gravel

Penobscot County, centered on the Bangor metro area, is Maine's third most populous county. While Bangor proper has a public water system, many surrounding communities — Hermon, Hampden, Orono, Old Town, Brewer suburbs, and rural towns — rely entirely on private wells. The county has documented arsenic and manganese issues in bedrock wells and emerging PFAS concerns near Bangor International Airport.

Arsenic and Manganese

Penobscot County wells drilled into bedrock commonly show elevated arsenic and manganese. The geology here is a mix of metamorphic and igneous formations that can release both contaminants into groundwater.

Manganese is a particular concern in this area. While it causes obvious aesthetic issues (black staining on fixtures and laundry), recent research has linked chronic manganese exposure to neurological effects in children, including reduced IQ and attention problems. Maine has set a health-based guideline of 100 µg/L for manganese, well below the EPA's secondary standard of 300 µg/L.

Arsenic, as always, is invisible. Test through the free Maine CDC program.

PFAS Near the Airport

Bangor International Airport, a former Strategic Air Command base, used AFFF (aqueous film-forming foam) for firefighting training for decades. AFFF contains PFAS, and the foam was used extensively in training exercises.

PFAS contamination has been detected in groundwater near the airport. If you have a private well within a few miles of Bangor International, PFAS testing is strongly recommended.

The Maine DEP is investigating PFAS contamination from military and airport sources statewide. Contact them for information about testing near your location.

Sand and Gravel vs. Bedrock Wells

Penobscot County has two distinct aquifer types, and your water quality depends significantly on which one your well taps:

Sand and gravel aquifers (Penobscot River valley) — generally lower arsenic but more vulnerable to surface contamination (bacteria, nitrate, road salt)
Bedrock aquifers (upland areas) — higher risk of arsenic, uranium, radon, and manganese from natural geological sources

Know what type of well you have. Your well driller's report (filed with the Maine Geological Survey) will tell you.

Testing Recommendations

Test for arsenic (free), manganese, bacteria, nitrate, and pH at minimum. Add PFAS if near Bangor International Airport or known sludge sites. Add radon if your home also has elevated indoor air radon (common in this area).

See our testing guide for details.

Every well is different. Two wells on the same street can produce completely different water. The data on this page reflects documented conditions in the Penobscot County area, but the only way to know what's in your water is to test it.

Sources

Maine Geological Survey — Arsenic Prevalence Data
Maine CDC — Manganese in Drinking Water
Maine DEP — PFAS Investigation at Bangor International Airport
USGS — Groundwater Quality in the Penobscot River Basin