Well Water in Cumberland County, Maine

Cumberland County · Population ~300,000 (county); well-dependent areas vary · Aquifer: Bedrock / Surficial Sand & Gravel

Cumberland County is Maine's most populous county, anchored by Portland. But outside the city's public water system, tens of thousands of homes in Windham, Gorham, Scarborough, Gray, New Gloucester, and other towns rely entirely on private wells drilled into Maine's fractured bedrock. The county sits squarely in the arsenic belt that runs through southern and central Maine.

Arsenic in Bedrock Wells

Cumberland County's bedrock geology — primarily granitic and metamorphic formations — is a known source of naturally occurring arsenic. The Maine Geological Survey has documented elevated arsenic across much of the county, particularly in wells drilled into bedrock rather than surficial sand and gravel deposits.

Unlike surface contamination, bedrock arsenic cannot be avoided by drilling deeper. In fact, deeper wells in granitic formations often have higher arsenic concentrations because the water has had more contact time with arsenic-bearing minerals.

See our arsenic guide for health effects, testing, and treatment details.

PFAS Concerns

Cumberland County has been affected by Maine's statewide PFAS crisis. The legacy of spreading treated sewage sludge ("biosolids") on agricultural land has contaminated groundwater in multiple locations. PFAS contamination has been detected in wells near former sludge-application sites.

Even in areas without direct sludge history, PFAS can be present from other sources: firefighting foam (AFFF) used at airports and fire training facilities, industrial discharges, and septic systems receiving PFAS-containing household products.

See our PFAS guide for the full Maine story and testing options.

Radon in Well Water

Maine's granitic bedrock produces some of the highest radon levels in the country — both in indoor air and in well water. When well water contains dissolved radon, it's released into your home's air every time you run the tap, shower, or do laundry.

The EPA has proposed (but never finalized) a maximum contaminant level of 300 pCi/L for radon in water, with an alternative level of 4,000 pCi/L for states with indoor air programs. Many Maine wells exceed both thresholds.

See our radon guide for more details.

Testing Recommendations

Every private well in Cumberland County should be tested for arsenic at least once — and retested every 3-5 years, as concentrations can change over time. The Maine CDC offers free arsenic testing for private well owners.

Given the county's mix of contaminant risks, a comprehensive panel should include arsenic, PFAS (if near known sludge sites or other sources), radon, uranium, manganese, bacteria, nitrate, pH, and hardness.

See our testing guide for labs, costs, and free testing programs.

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 Cumberland County area, but the only way to know what's in your water is to test it.

Sources

  • Maine Geological Survey — Arsenic in Maine Groundwater
  • Maine CDC — Private Well Water Testing Program
  • Maine DEP — PFAS Investigation and Remediation
  • USGS — Radon in Ground Water of the United States