Photograph of a drilled well casingWell Caps, Covers & Vents
Requirements for caps, covers & vents on wells

  • WELL CAPS & COVERS - CONTENTS: water wells require a water-tight cap or cover to prevent contamination from surface runoff or flood waters. But some well caps also require an air vent. This article explains the requirements for well caps & covers & well cap or cover venting.
  • POST a QUESTION or READ FAQs about steel casing drilled water wells at residential properties
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Well Cover & Cap Requirements & Well Cap Venting:

Water wells require a water-tight cap or cover to prevent contamination from surface runoff or flood waters. But some well caps also require an air vent. This article explains the requirements for well caps & covers & well cap or cover venting for drilled wells, well casings, dug wells & well pits.

This article series describes the properties & construction of drilled wells that use a steel well casing, modern drinking water wells. We discuss well problem diagnosis, testing, & repair procedures - advice about what to do when things go wrong with the well such as loss of water pressure, not enough water volume, contaminated wells, wells that have smelly water, wells that just run out of water or have a low recovery rate. We describe the parts of a water well and its piping and controls including the pitless adapter.

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Well Caps, Covers, & Vents

Photograph of a drilled well casingHere we describe requirements & recommendations for a sanitary, sealed cap or cover on drilled wells, bored wells, and cover requirements for dug wells and well pits.

The page top photo is of a modern well casing, in good condition, extended properly above ground. The small-diameter pipe parallel to the six-inch steel well casing is an electrical conduit - so we know that for this particular water supply system a submersible water pump is used and it is installed in the well itself.

The photo shown here is of an older drilled-well casing which has been placed with its casing cap at ground level - increasing the risk of well contamination from surface runoff. We also see that this well cap is not vented.

We cannot see from just the photo how successfully this well casing cover has been sealed against water entry from surface runoff.

[Click to enlarge any image]

Well casing covers on older drilled or bored wells that used a steel casing are often buried several feet below ground. Those well casing caps must also be tightly sealed against water entry from surface runoff or groundwater.

Where the pump is offset from the well or where a submersible pump is used, the opening between the well casing and any pipes or cables which enter the well shall be closed by a watertight seal or "well cap". - California DWR Chapter 10, 2016 cited below

In our sketch below we show the typical construction of a drilled water well in cross section.

A typical drilled well steel casing diameter is 6" (4" in some areas), that the well depth can be considerable (from 50 ft. to 900 ft. or more). Typically the steel well casing extends down into the bedrock or to a depth at which it can be sealed against un-wanted surface water entry.

Pitless adapter sketch (C) InspectApedia

We discuss the construction of drilled wells at DRILLED WELLS, STEEL CASINGS.

 The water pipe leaving this well to carry water to the building will be buried below ground, and in freezing climates, below the frost line. A special fitting, the "pitless adapter" is used to seal the passage cut into the round well casing. Details are at PITLESS ADAPTER

Question: What is the function of a well vent?

Well casing cap and vent on a drilled well with steel casing, Two Harbors MN (C) Daniel Friedman2016/06/10 Julian said:

What is the function of a well vent?

This question was posted originally at WATER ODORS, CAUSE CURE


Good question Julian; Here are some reasons that many drilled wells with a sealed casing top or sealed cover require a vent:

  1. Well cap/casing vent prevents casing vacuum: On some water wells the presence of a water tight (and thus air tight ) well casing cap can mean that when the pump is running and drawing down the static head in the well it can create a vacuum that could impede pump operation; The vent lets equalizing air into the casing.
  2. Well cap/casing vent allows air to vent out: The well casing top vent also allows air to exit the well as the water column rises in the well, perhaps assisting in well recovery in some well installations.
  3. Well cap/casing vent allows gases to vent out: A well vent also allows the venting out of any gases that might accumulate in the well bore above the static head; that can be a concern for wells whose water supply includes absorbed methane or other gases.

Below: a closer look at the older compression-style well casing cap removed from the well shown above. This cap achieved a water tight seal to the interior of the well casing when the cap bolts were tightened to in turn squeeze and expand the thick rubber gasket. A small diameter hole in the well casing cap (yellow arrow) connected to an air vent elbow on the top of the casing cover (visible in the photo above).

Well cap using an expanding rubber seal or bushing (C) Daniel Friedman

Below: new well cap sealed to the well casing; note that the well driller determined that this well no longer needed an air vent, probably because in the well a snifter valve (SNIFTER & DRAIN BACK VALVES) was eliminated as part of installation of a new internal-bladder type pressure tank (WATER TANK BLADDERS & CAPTIVE AIR) in the building served by this well in Two Harbors MN, USA.

New well cap without vent, sealed on the well casing (C) Daniel Friedman

Requirements & Standards for Well Casing Cap Vents

Here's an excerpt from the California DWR well standard

Air Vents. In community water supply wells to minimize the possibility of contamination caused by the creation of a partial vacuum during pumping, a casing vent shall be installed (Figure 7). In addition, to release air trapped in the pump column when the pump is not running, air release vents shall be installed (Figure 7).

Air vents are also recommended for other types of wells except those having jet pump installations requiring positive pressure (which cannot have a vent). - California DWR Chapter 10, 2016 cited below, [Emphasis by underscoring added by editor -]

Here is another excerpt from California's Chapter 10 on well construction codes:

Openings. Openings into the top of the well which are designed to provide access to the well, i.e., for measuring, chlorinating, adding gravel, etc., shall be protected against entrance of surface waters or foreign matter by installation of watertight caps or plugs. Access openings designed to permit the entrance or egress of air or gas (air or casing vents) shall terminate above the ground and above known flood levels and shall be protected against the entrance of foreign material by installation of down-turned and screened "U" bends (see Figures 6 and 7). All other openings (holes, crevices, cracks, etc.) shall be sealed. - op. cit.

You'll see that the vent must be properly constructed so as to prevent entry of surface runoff, flood waters or other contaminants into the well bore.

Safety Requirements for Well Caps & Covers

Abandoned hand dug well in Guanajuato (C) Daniel FriedmanWe have explained above that the top of a water well needs to be sealed against surface runoff or flood waters as those waters are not sanitary and would contaminate the well water. Well construction also requires that all below-ground well openings such at a pitless adapter must also be sealed against the entry of outside water.

But well caps and covers must also be secured to prevent other safety hazards such as the following:


Continue reading at WELL CONSTRUCTION & MAINTENANCE - home or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see PITLESS ADAPTERS - Definition & use of a pitless adapter at water wells


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