Weld County · South Platte Alluvium / Various

Well Water in Weld County Rural, Colorado

Weld County produces more oil and gas than any other county in Colorado and is one of the most intensive agricultural regions in the state. Rural residents on private wells face a unique combination of contamination risks: nitrates from fertilizer and animal waste, methane from both natural and oil/gas sources, and the general vulnerability of shallow alluvial aquifers to surface contamination.

Hardness: Moderate to Hard

220 fttypical depth drilled (middle half 60–440 ft)

100 fttypical depth to water when drilled

11 gal/mintypical pump-test yield

11,584household wells on the state's records here

Typical (median) depth of household wells completed in each period, drawn to scale; the dashed outline reaches the depth that the deeper quarter of wells go past. Blue is where water stood when the wells were finished, where enough records give it. The rock pattern is a sketch of this area's ground, not a log of any one well.

What tested wells showed

Uranium limit 30 µg/L6% of 66 tests over the limit

Arsenic limit 10 µg/L2% of 156 tests over the limit

Nitrate limit 10 mg/L16% of 1,741 tests over the limit

Bacteria limit any coliform7% of 30 tests over the limit

Weld County, CDPHE private-well lab results 2011–2020. People usually test because they have a reason to, so these rates describe tested wells, not every well. Bacteria counts any coliform detected.

What to test for and where →

635 permits here are for wells that replaced an earlier well. Wells get replaced when they fail, run dry or are re-drilled deeper, among other reasons.

Every well on record around Weld County Rural

Depth drilledunder 100 ft100–200200–400400–700700 ft +

A random sample of up to 2,500 household wells from the state's permit records, placed by their recorded location and coloured by how deep each was drilled. Locations on permits are often approximate, sometimes only to a section, quarter-section or 40-acre parcel, so a dot marks an area, not a house.

How deep wells have been drilled, decade by decade

Each line hangs from the ground to the median depth of household wells completed that decade; the shaded band is the middle half. Wells drilled later are not the same wells, so a deeper decade can mean falling water, new homes on higher or drier ground, or deeper aquifers being permitted. It is a record of what was drilled, not a single cause.

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.

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

Sources

USGS — Greater Wattenberg Area Baseline Study (2007)
CU Boulder Environmental Engineering — Compromised Oil and Gas Wells and Groundwater Risk in Weld County (2023)
Colorado Department of Agriculture — Agricultural Chemicals and Groundwater Protection Program
FracTracker Alliance — Groundwater Risks in Colorado
Weld County Department of Public Health and Environment — Laboratory Services