Spring is getting near and the snow we’ve received this winter will soon begin to melt, if it hasn’t already in your part of the state. Now would be a great time to give some thought to your storage tank air vents, evaluate whether they are properly protected to prevent contaminants from entering the tank and, if not, make a plan to fix them. In addition to being a risk to public health, improperly protected air vents also put your water system at risk of being cited for a significant deficiency during a sanitary survey or perhaps even a Tier 2 violation for permitting a known sanitary defect.
What factors should suppliers consider when evaluating their storage tank air vents?
Air vents allow the pressure inside a storage tank to equalize as the water level inside it fluctuates. Tanks without air vents or with vents that become blocked can buckle from the differential pressure.
Keep in mind that the air vent opening needs to be located up above the top of the ground surface or roof of the tank to prevent contaminants such as dirt or bird feces from being drawn into the tank. Case in point, the specs in the photo below are bird feces around the air vent on the roof of a tank.
Additionally, the average snow accumulation for the area should be considered and the air vent should be designed to prevent an accumulation of snow (or ice) from blocking the opening(s).
One particular issue that is frequently discovered during sanitary surveys are air vents that are not fully covered to protect from rainwater or that do not open downward. This could allow contaminants that have collected on the screen to be washed off of the screen and carried into the interior of the storage tank by rainwater. Several more examples of improperly protected air vents are discussed below.
Example 1: The photos below (and the one above) show air vents that are not fully covered to properly protect the air vent from the entrance of contamination from rainwater and blowing debris. “Mushroom” type air vents that are not fully covered to protect from rainwater must be corrected by being modified so that the screened area is fully covered.
Example 3: The photos below show storage tank air vents that are not downturned. Air vents that open sideways are not permitted and must be corrected by being modified to open downward.
- Air Vent issues to check for and correct if found (the following conditions are not allowed):
- Storage tanks with no air vent
- Storage tanks with the overflow pipe also used as the air vent
- Storage tanks with open construction between the sidewall and the roof
- Air vents that are not screened or that have damaged or blocked screens
- Air vents that are made of corrodible materials that can rust
- Air vents with screen openings that exceed 0.07 inches (typically 12 or 16 mesh screen is needed for the openings to be smaller than 0.07 inches)
- Air vents that do not open downward or are not fully covered to protect from rainwater (see examples 1-3 above)
- Air vents with openings that are less than 24-inches above the top of the ground surface or roof
- Air vents that are susceptible to vandalism
- Air vents that are not accessible for replacement
(Deviations from the requirements above may be allowed in certain cases, such as for storage tanks that are stored in clean climate controlled rooms and have a total volume of less than 11,000 gallons or other situations.)
If suppliers identify a sanitary defect, it must be documented upon discovery. Also, a corrective action schedule in accordance with the Storage Tank Plan must be developed to fix it as soon as possible. Take photographs before and after making repairs. By doing so, suppliers can avoid a violation for not correctly implementing the storage tank rule.
Sanitary defects that are discovered during sanitary surveys may be cited as significant deficiencies or possibly even as a Tier 2 (treatment technique) violation of the storage tank rule for permitting a known sanitary defect. The risk of violations is especially true for defects that should be ‘obvious’ to anyone performing a periodic tank inspection.
Additionally, if suppliers do not follow the corrective action schedule that they developed, they will also be in violation of the storage tank rule. Avoid violations of the storage tank rule by proactively identifying sanitary defects and then documenting that the supplier is following a corrective action schedule to fix them.
Conclusion: Unprotected or improperly designed air vents can provide a pathway for contamination to enter the water stored in the tank and can be a source of contamination. Properly protected storage tank air vents are a critical part of the multiple barrier approach to providing safe drinking water and are a safe and effective way of protecting our communities and promoting a culture of health.
Does your storage tank have an improperly protected air vent? If so, identify and document problems with air vents and develop a corrective action schedule with appropriate timelines to correct the sanitary defect(s) that were identified and include it as part of the supplier’s storage tank inspection plan. Otherwise, don’t be surprised if improperly designed air vents are cited as significant deficiencies and/or violations of the storage tank rule during sanitary surveys.
Please reach out to the field services section at cdphe_wqcd_fss_questions@state.co.us with any related questions.
Guidance & Resources:
Monique Morey, PE, field services section
