Hydrovac Potholing: A Complete Guide
8-step process guide with equipment, safety, and cost information.
Potholing is the process of creating a small test hole to expose and verify the exact location of underground utilities. Also known as "daylighting," potholing is the most common application of hydrovac excavation and is considered the gold standard for utility verification before construction or excavation projects begin.
The process uses pressurized water to break up soil while a powerful vacuum simultaneously removes the loosened material into a debris tank. This non-destructive method allows workers to visually confirm the horizontal position, depth, size, material, and condition of buried utilities without risking damage from mechanical equipment.
Potholing is typically required by engineering specifications to achieve Quality Level A utility data under ASCE 38 standards. This is the highest level of subsurface utility information and requires physical exposure of the utility. Most state DOTs, municipalities, and private developers now require potholing as part of their pre-construction utility investigation programs.
Step-by-Step Process
Utility Locate Request
Contact 811 at least 2-3 business days before digging. Wait for utility owners to mark approximate locations of their buried facilities with paint and flags using APWA color codes.
Site Assessment
Evaluate site conditions including soil type, surface material (asphalt, concrete, grass), access for hydrovac truck positioning, water source availability, and traffic control requirements.
Equipment Setup
Position the hydrovac truck with boom access to the pothole location. Connect water supply if needed. Select appropriate nozzle type based on soil conditions and proximity to known utilities.
Surface Breaking
If the surface is asphalt or concrete, use a saw cut, core drill, or jackhammer to create an opening. The hydrovac water jet alone cannot efficiently cut through hard surfaces.
Hydrovac Excavation
Direct the pressurized water jet into the opening to loosen soil while the vacuum hose removes the slurry. Work gradually downward, adjusting water pressure based on soil conditions and proximity to utilities.
Utility Exposure
Once the utility is exposed, carefully clean around it to reveal the top and at least one side. Note the utility type, material, size, depth, and condition.
Documentation
Record utility information including GPS coordinates, depth below grade, horizontal offset from reference points, pipe material and diameter, and utility owner. Photograph the exposed utility.
Backfill and Restoration
Backfill the pothole with approved material (flowable fill, compacted sand, or native soil depending on specifications). Restore the surface to match existing conditions.
Equipment Recommendations
- Standard hydrovac truck with 8-12 cubic yard debris tank
- Fan-tip nozzle for general soil conditions
- Straight jet nozzle for hard or compacted soils
- Boom with minimum 8-foot reach for roadway potholing
- Surface cutting equipment (concrete saw or core drill)
- Measuring tape, depth rod, and GPS unit for documentation
Safety Considerations
- ⚠Always call 811 before digging — it is the law in every state
- ⚠Reduce water pressure when approaching expected utility depth
- ⚠Never direct the water jet at an exposed utility
- ⚠Maintain safe distances from traffic when working in roadways
- ⚠Watch for unmarked or abandoned utilities not shown on locate marks
- ⚠Use appropriate PPE including steel-toed boots, hard hat, safety glasses, and high-visibility vest
- ⚠Follow OSHA excavation standards for holes deeper than 5 feet
Cost Factors
- ●Mobilization fee ($250-$500 per trip for urban areas)
- ●Hourly rate ($175-$350/hour depending on market and truck size)
- ●Number of potholes per mobilization (more holes = lower per-hole cost)
- ●Depth of utilities (deeper = more time per hole)
- ●Soil conditions (clay and rocky soil take longer)
- ●Surface restoration requirements (asphalt/concrete repair adds cost)
- ●Travel distance to site from contractor base
- ●Traffic control requirements for roadway work
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