Well Water in Weld County Rural, Colorado

Weld County · Population ~330,000 (county); rural areas vary · Aquifer: South Platte Alluvium / Various

Hardness: Moderate to Hard

Nitrate Contamination

Nitrate is one of the most common groundwater contaminants in Colorado, and Weld County's intensive agriculture makes it ground zero. Sources include:

• Fertilizer application — excess nitrogen leaches through soil to groundwater
• Concentrated animal feeding operations (CAFOs) — there are approximately 400 CAFOs in Colorado, most on the eastern plains. Large quantities of animal manure can contaminate groundwater if not properly managed
• Septic systems — in rural areas without sewer connections

The EPA maximum contaminant level for nitrate is 10 mg/L. Groundwater monitoring in Weld County has found wells exceeding this limit. Nitrates are especially dangerous for infants (blue baby syndrome) and pregnant women. They cannot be removed by boiling — boiling actually concentrates them.

Oil and Gas: Methane in Water Wells

Weld County has over 35,600 oil and gas wells drilled since 1998, and 74% of pending new well permits in Colorado are in Weld County. This density of drilling creates groundwater risks.

A study of the Greater Wattenberg Area — the densely drilled field underlying much of Weld County — found that 26.5% of oil and gas wells show evidence of leaks (gas, oil, or water buildup in outer pipes). Chemical analysis showed most leaks come from failures of well pipes or cement, not natural gas migration.

In a baseline study, dissolved methane was detected in all nine water wells sampled. Six of the nine exceeded the Colorado Oil & Gas Conservation Commission's threshold of 2 mg/L. While isotopic analysis suggested biogenic (natural) origin for most, the research by CU Boulder investigators found that compromised oil and gas wells pose real risks to groundwater.

When methane enters a water well, it can create explosion risks in enclosed spaces and indicates potential pathways for other contaminants.

Agricultural Chemical Contamination

Beyond nitrates, agricultural operations can introduce pesticides and other chemicals into groundwater. Colorado's Agricultural Chemicals and Groundwater Protection Program — a collaboration between the Department of Agriculture, CSU Extension, and the Water Quality Control Division — monitors groundwater in agricultural basins.

Agriculture accounts for 86% of Colorado's groundwater withdrawals. In areas where intensive farming occurs above shallow alluvial aquifers, the potential for contamination is significant. Monitoring has prioritized sampling in basins where agriculture predominates and rural homes use groundwater — a description that fits much of rural Weld County.

Testing Priorities for Rural Weld County

If you're on a private well in rural Weld County, your testing priorities should include:

• Nitrates — test annually, given the agricultural and CAFO activity
• Bacteria — test annually; shallow wells are vulnerable
• Methane — if you're within a mile of oil and gas operations (dissolved gas analysis)
• Selenium — found in some Weld County groundwater
• Basic mineral panel — hardness, iron, manganese, TDS, pH

The Weld County Department of Public Health and Environment operates a water testing laboratory in Greeley serving northern Colorado. See our testing guide for details and costs.