Drilled vs. Dug Wells: How Well Type Affects Pump Selection

Well construction method is one of the primary determinants of pump selection in private groundwater systems. Drilled wells and dug wells differ in depth, casing diameter, aquifer access, and contamination exposure — each difference carrying direct consequences for pump type, motor sizing, and installation configuration. Understanding the structural distinctions between these well categories is foundational to any service, replacement, or inspection decision in the residential and agricultural pump sector.

Definition and Scope

Dug wells are large-diameter excavations — typically 3 to 10 feet in diameter — constructed by hand or with mechanical equipment to a depth generally not exceeding 30 feet. They draw from shallow, unconfined aquifers and are lined with stone, brick, concrete tile, or precast concrete rings. Because they terminate in permeable soil above the first confining layer, they are classified by the U.S. Environmental Protection Agency (EPA) as high-risk groundwater sources for surface contamination.

Drilled wells are constructed using rotary, cable tool, or air rotary drilling equipment to depths ranging from 50 feet to over 1,000 feet. Casing diameter for drilled wells typically runs 4 to 8 inches for residential applications, with 6-inch casing being the most common residential standard across state codes. Drilled wells penetrate confining layers to access confined or deep unconfined aquifers, providing substantially greater protection from surface-originated contamination.

The National Ground Water Association (NGWA) maintains technical reference publications covering both well types, and the EPA's Drinking Water from Household Wells guidance document outlines the contamination risk differential between shallow and deep wells. State well codes — administered through agencies such as the California State Water Resources Control Board or the Texas Commission on Environmental Quality — establish minimum construction standards, casing requirements, and setback distances for each well type.

How It Works

The pump selection process flows directly from the well's physical configuration, static water level, and yield capacity.

Dug well pump mechanics:
Dug wells require pumps that can operate at shallow lift depths, typically 25 feet or less of total dynamic head from the pump intake to the pressure system. A standard suction-lift centrifugal pump or jet pump in its shallow-well configuration handles this range. Shallow-well jet pumps operate by creating a vacuum that draws water upward; because atmospheric pressure limits suction lift to approximately 25 feet, these pumps must be installed at or near surface level. Piston hand pumps and pitcher pumps are also historically associated with dug wells, though these are no longer common in active residential service.

Drilled well pump mechanics:
Drilled wells — particularly those deeper than 25 feet to static water level — require either a deep-well jet pump (which uses a two-pipe ejector assembly lowered into the casing) or, more commonly in modern construction, a submersible pump installed below the water line. Submersible pumps are sealed motor-and-pump units suspended on a drop pipe inside the casing. For a 4-inch casing, 3-inch or 4-inch submersible pumps are standard; 6-inch casings accept 4-inch or 5-inch submersibles. Submersibles operate at pump efficiencies ranging from 55% to over 80% depending on design, and are the dominant technology for drilled wells deeper than 50 feet (NGWA Groundwater Foundation reference standards).

The wellpump-listings section of this resource catalogs service providers by well type and pump configuration for regional matching.

Common Scenarios

1. Shallow dug well, residential, water table at 15 feet: A single-pipe shallow-well jet pump rated at 1/2 to 3/4 horsepower serves typical household flow demand (4–8 gallons per minute). Pressure tank sizing follows from the pump's service flow rate.

2. Drilled well, 200-foot depth, 6-inch casing: A 4-inch submersible pump rated at 1 to 1.5 horsepower with a drop pipe to within 10–20 feet of the static water level is the standard configuration. Wire sizing must comply with NFPA 70 (National Electrical Code), Article 430 governing motor circuits.

3. Drilled well, 400+ feet, agricultural irrigation demand: High-yield submersible turbine pumps (10 gallons per minute or more) require 1.5–3 horsepower motors or greater, with pump selection matched to the well's specific capacity test results.

4. Dug well being converted to drilled-well service: When a property replaces a dug well with a drilled well, the pump type changes entirely. A shallow-well jet pump cannot serve the new well; a submersible or deep-well jet pump must be installed, and the pressure system must be resized. The how-to-use-this-wellpump-resource page outlines how to navigate professional categories for these transitions.

5. Older dug well with contamination risk: EPA guidance flags dug wells as particularly vulnerable to coliform bacteria, nitrates, and agricultural runoff. Remediation may include grouting, proper sealing, or well abandonment per state code requirements.

Decision Boundaries

The principal decision boundaries separating appropriate pump configurations by well type are:

• Depth to static water level below 25 feet: Eliminates single-pipe shallow-well jet pumps; requires deep-well jet or submersible technology.
• Casing inside diameter below 4 inches: Eliminates standard residential submersibles; limits options to slim-line 3-inch submersibles or jet pump configurations.
• Yield below 1 gallon per minute: Indicates the need for a storage tank and booster pump system rather than a direct-to-pressure-tank configuration, regardless of well type.
• Well depth exceeding 400 feet: Requires motor sizing and wire gauge calculations that fall outside standard residential pump specifications; submersible turbine pump engineering applies.

Permitting requirements vary by state. Drilled wells in most jurisdictions require a licensed well driller and a construction permit issued by the state environmental or health agency; pump replacements may require separate inspection sign-off. Dug well modifications are also subject to state well codes in jurisdictions including Minnesota (Minnesota Department of Health Well Code, Minnesota Statutes § 103I) and Wisconsin (Wisconsin Administrative Code NR 812).

Safety classification under NGWA standards separates grouted drilled wells (lower contamination risk) from ungrouted or improperly cased wells (higher risk). The EPA's Source Water Protection program identifies unprotected dug wells as a primary nonpoint-source contamination vector. The wellpump-directory-purpose-and-scope page describes how licensed professional categories are organized within this reference framework.

References

• U.S. Environmental Protection Agency — Private Wells
• U.S. Environmental Protection Agency — Drinking Water from Household Wells
• National Ground Water Association (NGWA)
• NFPA 70 — National Electrical Code, Article 430
• Minnesota Department of Health — Well Code, Minnesota Statutes § 103I
• Wisconsin Administrative Code NR 812 — Well Construction and Pump Installation
• California State Water Resources Control Board — Well Standards
• Texas Commission on Environmental Quality — Water Well Drillers