Every GC in California knows to call 811 before digging. What most don't fully appreciate is what that call actually protects them from — and, more importantly, what it doesn't. DigAlert covers public utilities: gas mains, water mains, sewer laterals from the property line to the street, telecommunications lines running under public rights-of-way. That's it. Everything on the private side of the property line, and everything embedded in concrete, is your responsibility to locate before you break ground or start cutting.
This is where most utility strikes happen. Not on the public side, where 811 does its job. On the private side — post-meter gas lines, private irrigation, electrical from a transformer to a building, communication lines between buildings on the same parcel, and every conduit and post-tension cable inside a concrete slab. According to Common Ground Alliance's DIRT Report, private-side facilities account for roughly 40-50% of all reported utility damage events annually — and those are just the ones that get reported.
Here's what every GC, superintendent, and estimator should understand about private utility locating and where liability sits when things go wrong.
The Three Layers of Utility Locating
Layer 1: Public Utility Locating (DigAlert / USA / 811)
Free, mandatory, and legally required in California under Government Code §4216. Call 811 at least two working days before excavation. The service dispatches representatives from each public utility owner (SoCalGas, Southern California Edison, water district, telecommunications carriers) to mark their own facilities in the public right-of-way and up to the property line or the meter, depending on ownership.
What DigAlert does not cover: anything downstream of the meter, private irrigation, private security or fire alarm lines, private telephone or data lines, private septic, private storm drainage, private stormwater retention, private site lighting, private-property gas lines, private electrical runs between buildings, and everything embedded in concrete.
Layer 2: Private Utility Locating (surface-level, radio-frequency methods)
For everything DigAlert doesn't cover on the surface (soil, landscaping, dirt), a private utility locator uses electromagnetic locating equipment (radio-frequency tools that induce a signal on metallic pipes and cables) and sometimes traceable rodding for non-metallic pipes. This finds most private utility runs in soil down to about 8-10 feet.
What surface locating does not cover: anything embedded in concrete, pipes with no metallic component that can't be rodded (some older PVC waste lines, buried plastic irrigation), and dielectric fiber-optic runs. And it doesn't identify voids, rebar, post-tension cables, or anything you actually need to know about before cutting concrete.
Layer 3: Concrete Scanning (GPR)
For anything embedded in a concrete slab, wall, or column, you need ground-penetrating radar. This locates rebar, conduit (metallic and non-metallic), post-tension cables, voids, delamination, and moisture. This is a separate service from surface utility locating and requires different equipment and different operator training.
The layered rule: 811 covers public soil. Private locators cover private soil. GPR covers concrete. If your job involves both trenching and coring, you likely need all three services — DigAlert, a private locator, and a GPR scanner. Skipping any layer creates an unmitigated risk.
Where the Liability Actually Sits
In California, the legal framework distributes liability based on who had the responsibility to locate and mark before excavation. If you (the GC) called 811 and a public utility either failed to mark or mismarked their line, they carry most of the liability. If a public utility marked correctly and your crew still hit the line, you carry the liability.
On the private side, the property owner carries some of the liability for maintaining accurate as-builts of their private facilities, but the burden is heavily on the excavator or coring contractor to verify before breaking ground. Courts have consistently held that "the owner didn't have good drawings" is not a defense — the GC and their subcontractors are expected to independently locate private facilities using appropriate technology (private locating, GPR) before excavation or coring.
The practical translation: if your coring subcontractor hits a live 480V conduit inside a slab because nobody scanned it first, that lands on the GC and the coring sub, not the property owner. Insurance carriers know this and will typically deny claims from GCs who can't document that appropriate locating and scanning were performed before the work.
When to Book Each Service
Book 811/DigAlert whenever you:
- Excavate for a foundation, footing, utility trench, or landscape feature in soil
- Set fence posts or landscape lighting
- Do any grading that changes existing site elevations by more than a few inches
Book a private utility locator whenever you:
- Excavate on the private (post-meter) side of the property
- Work at a site with private irrigation, security, fire, or communication runs
- Add a new foundation or utility connection to an existing building
- Work on any commercial or industrial property with multiple buildings on the same parcel
Book GPR concrete scanning whenever you:
- Core or cut any concrete slab, wall, or column, especially anywhere near known post-tension work
- Saw-cut a slab for a new plumbing, electrical, or drain line
- Demo a portion of a slab where reinforcement details are uncertain
- Anchor new equipment into structural concrete with expansion or epoxy anchors deeper than 2 inches
- Investigate suspected voids or delaminations in a slab
Working on a post-tension slab specifically? Read How to Scan a Post-Tension Slab Before Coring for the full field procedure.
How to Vet a Private Locator or GPR Contractor
Not all locating contractors are created equal. Here's what to ask:
- Certifications and licensing. In California, a General Engineering Contractor (Class A) or specialty concrete contractor (C-8) license is expected. Ask for the CSLB license number. Verify at cslb.ca.gov.
- Insurance. Minimum $1M general liability, and preferably $2M for public works. Ask for a current COI.
- Equipment. For GPR, they should be running current-generation dual-frequency units (typically 1.5 GHz + 2.6 GHz for concrete). Old single-frequency units miss PT signatures.
- Operator training. Ask what specific training the field techs have. Look for RadioDetection, GSSI, or Sensors & Software certified operator training. In some markets, NULCA (National Utility Locating Contractors Association) certifications are also relevant.
- Documentation practice. Ask if they produce written scan reports and photograph markings before work begins. If they don't document, you have no paper trail if a line gets hit later.
- Response time. For active job sites, same-day or next-day response matters. Weekly-scheduled vendors don't fit a fast-moving construction schedule.
What Good Documentation Looks Like
After every scanning or locating job, you should receive:
- A written report identifying the scan area, date, technician name, equipment used, and findings
- Photographs of the marked concrete or ground surface
- Depth measurements for each critical identified embedment or utility
- Explicit callouts of any locations where coring or excavation is not recommended, with reasons
- A hand-off note to the crew performing the follow-on work
This documentation is the record that protects the GC if something goes wrong later. Insurance carriers will ask for it. Attorneys will ask for it. Structural engineers will ask for it. If your locator doesn't provide it, insist — or find a locator who does.
Common GC Mistakes We See in the Field
Mistake 1: Using DigAlert markings for private-side excavation
DigAlert marks stop at the meter or property line. If your excavation continues past that point, those markings are meaningless for the private-side utilities beyond them. You need a private locator for anything past the meter.
Mistake 2: Assuming as-builts are accurate
As-built drawings represent what the original installer said was installed. Between then and now, tenants add lines, remodel change conditions, and old lines get abandoned or forgotten. Never core based on drawings alone.
Mistake 3: Scanning only some of the core locations
Scanning 3 of 10 core points and extrapolating to the rest is the fastest way to hit a line. Every core location gets scanned. No exceptions.
Mistake 4: Not budgeting for locating and scanning in the estimate
Locating and scanning together typically add 1-3% to a coring subcontract on a commercial job. Estimators who leave this out either don't get the work or make it up by cutting corners later. Include it up front and price the job honestly.
Mistake 5: Treating "the scanning company said we're good" as bulletproof
The scanning report is evidence you did due diligence, not an insurance policy. If the scanner missed something (rare with a competent contractor, but possible), the responsibility still runs through your subcontractor chain. Vet your scanning contractor the same way you'd vet a critical structural or MEP sub.
The California Legal Backdrop
California's excavation safety law (Gov Code §4216) requires excavators to notify DigAlert at least two working days before starting work in soil and to use "commercially available" locating methods for private-side utilities. Courts have interpreted "commercially available" to include private electromagnetic locating and, for concrete, GPR scanning. Failure to use these methods when they're readily available creates statutory liability, not just negligence liability.
The California Public Utilities Commission publishes annual reports on excavation damage under the state's damage prevention program. GCs and subcontractors named in reported damage events face administrative penalties and, in serious cases, prosecution referrals. Insurance rates for construction firms with damage history rise steeply.
The Bottom Line for GCs
Utility locating isn't just an 811 call. It's a layered process — public utilities via DigAlert, private utilities via a certified locator, and embedded concrete via GPR scanning. Each layer covers a different set of risks, and skipping any layer creates unmitigated exposure that carriers will price accordingly (or deny claims against).
Build these three services into your standard job templates, budget them into every estimate that involves excavation or concrete cutting, vet your locating contractors the same way you vet your structural subs, and require documentation on every job. It's cheap insurance against the events that end contractor careers.
Earthworks Engineering provides GPR scanning across the greater Inland Empire and Los Angeles / Orange County market. Explore our GPR services or the city-specific pages for Rancho Cucamonga, Riverside, San Bernardino, and Ontario.