Gas Station Borehole Drilling Safety: Why Critical Zones Matter
- Grant Piraine
- Sep 2
- 4 min read
Updated: Sep 8
Gas stations are some of the most complex and hazardous properties when it comes to excavating or drilling boreholes. Over the years, my teams and I have performed locates for hundreds of fuel sites, often as part of portfolio acquisitions or redevelopment projects performing environmental due diligence. If there is one thing I have learned, it is that gas station borehole drilling safety requires a completely different approach. You cannot treat gas station digging or drilling like any other site.
These properties are packed with critical infrastructure including underground storage tanks (USTs), fuel piping, vent lines, electrical conduits, communication cables, and propane systems. Many of these lines are bundled together in trenches, often undocumented, and some are non-conductive such as fiberglass or plastic. This means they cannot be detected with standard electromagnetic locating tools, and ground penetrating radar is not a method I would rely on in this environment. I have witnessed firsthand the risk of relying on ground penetrating radar data at gas stations and you do not want to be on the receiving end of a damage. The last one I investigated cost three quarters of a million dollars in damages.
This reminds me of a client back in 2006. They wanted a borehole close to a mom and pop gas station fuel UST that did not have a concrete apron. I warned them that ground penetrating radar may or may not see the tank, and in this case, I could not see it because the tank was fiberglass. I moved their borehole well away from the tank and after I left, they moved it back. They hit the fiberglass tank with a Geoprobe drill. Later they tried to come back at my company, but I had taken photos of the borehole I agreed was far enough from the UST, and it was clearly documented in my locate report. That claim cost them about four hundred thousand dollars. They had to remove the tank and replace it with a new one. And that cost was without a fuel release.
What Makes Gas Stations Different
Bundled trenches: fuel, electrical, and communication lines often share the same corridor.
Non-conductive piping: fiberglass and plastic cannot be traced with conventional EM equipment.
Pea gravel backfill: if you encounter pea gravel while digging or drilling, stop immediately. It signals fragile infrastructure below, where compaction equipment could crush tanks or piping.
Critical zones everywhere: tanks, pump islands, canopy areas, and everything in between.
The Danger of “Rolling the Dice”
I’ve seen boreholes drilled in the middle of asphalt cuts, directly between tanks and pump islands, without vacuum excavating the location. That’s rolling the dice in the worst possible way. These are no-drill zones unless you’ve daylighted and confirmed no utility lines intersect the borehole. The consequences of being wrong aren’t minor, we’re talking about potential fuel releases, fire, or explosion.
What POST Told Us
In 2012, the Petroleum Oriented Safety Training (POST) program published a guideline on gas station Critical Zones. Their conclusions are still relevant today:
General Critical Zone: The entire work area of a gas station should be treated as a critical zone. This includes the space between underground tanks, the canopy, and the pump islands where multiple utilities are concentrated.
Tank Critical Zone: If you do not know the length of the tank, you must assume the worst case. I have never seen drawings provided for a tank at a gas station. The critical zone around each manhole is 57 feet or 17 meters. This means you should never drill off the end of a UST unless you have vacuum excavated to at least 8 feet.
Canopy Critical Zone: Risks increase depending on whether the piping is rigid or flexible.
Surface Zone: Everything between the tanks, the canopy, and the dispensers is high risk.
Within 10 feet of any buried utility line: POST recommends no borehole should be drilled until the utility line is vacuum excavated.
Miscellaneous rules: Obtain tank length measurements if available, locate observation wells, and always account for minimum safe distances.
POST’s takeaway was simple. Soft digging with vacuum excavation is highly recommended across gas station sites before any intrusive work begins.
Note: Our company uses a tolerance distance of 2 meters or 6 feet to account for uncertainty when utility records are not provided. POST’s 10-foot rule is more conservative, but it shows how seriously the petroleum industry treats the risks around their buried utility infrastructure. We also have many clients that have an internal policy of a 10-foot tolerance distance.
Mitigation Strategies That Work
Many petroleum companies now have strict corporate policies in place, requiring vacuum excavation of every borehole to a set depth, sometimes 4 feet, sometimes 8 or even 10 feet, depending on the critical zone. I recommend the same approach on all gas station projects.
If soils data is required at that exact location, you can still do it safely:
Vacuum excavate a chevron trench around the borehole location to a safe depth.
Confirm no utility lines intersect the borehole path.
Backfill the trench with a non-shrink material.
Drill your borehole inside the chevron.
This method allows engineering consultants to collect samples without putting buried fuel systems at risk.
Why This Matters to Contractors and Petroleum Companies
Contractors and consultants: reduce liability and protect your crews.
Petroleum companies: protect your assets, enforce your safety policies, and reduce environmental exposure.
Shared benefit: Both groups gain from a specialized private locate and a clear Critical Zone management plan before any borehole is drilled.
High cost of mistakes: A fuel release into the subsurface at a gas station can lead to millions of dollars in soil and groundwater remediation along with tank removal and replacement costs.
Looking Ahead: Beyond Gas Stations
Gas stations aren’t the only properties with underground fuel systems. Many businesses such as trucking companies, shipping depots, bus garages, and manufacturing plants, have their own fueling tanks buried on site.
Stay tuned for more posts about USTs — because whether it’s a gas station or a private yard, the risks are real, and the lessons can save your project.
