Testing, Detection and Survey Instruments

Reviewed October 2026 · 31 terms

The instruments used to find buried utilities, check air and soil, survey a site and monitor vibration on demolition and site work in California, explained in plain words.

Prices for this work: excavation and grading · demolition · tank and hazardous materials · concrete cutting and coring · testing · all 2026 prices

Related services: Site verification and utility coordination · Concrete removal

Underground and utility detection

Active vs. passive locating
Active locating puts a signal on a line with the locator’s transmitter, by direct connection, a clamp or induction, and then traces it. Passive locating sweeps for signals already on lines, such as current in live power cables. Good locators use both, because a passive sweep alone misses dead or isolated lines.
Electromagnetic (EM) pipe and cable locator
The main tool utility locators use: a transmitter that puts a signal on a metal pipe or cable and a handheld receiver that follows it and estimates depth. It can’t find plastic or concrete pipe unless the line has a tracer wire or a sonde is pushed through it.
Scanning a site with a magnetometer, a buried-metal detector or GPR to find abandoned underground tanks, piping and buried debris before demolition, grading or a property sale. It is common at old gas stations, auto shops, dry cleaners and older homes that once burned heating oil.
GPR concrete scanner
A small, high-frequency GPR unit rolled across a slab or wall to map rebar, post-tension cables and conduit before saw cutting or coring. It reads only the first foot or so of concrete, and it is the tool used for the concrete scanning step on most commercial jobs. Concrete removal service
GPR utility cart
A push-cart GPR unit with a lower-frequency antenna that looks several feet into the soil for pipes, conduits, tanks and buried foundations. Sandy soil reads well; wet clay and caliche read poorly.
Ground-penetrating radar (GPR)
A scanner that sends radio pulses into the ground or into concrete and records the echoes that bounce back from buried objects such as pipes, rebar, tanks and voids. Unlike a metal locator, it can find plastic and concrete pipe. Its reach drops sharply in wet clay, which is common in Southern California, so results depend on the soil. Site verification and utility coordination
Hydro-excavation (vacuum excavation)
Digging with pressurized water or air while a vacuum truck pulls the loosened soil into its tank. It is the usual way to pothole and to dig safely next to marked lines, because it exposes a pipe without striking it.
Private utility locating
Locating lines on private property that DigAlert members don’t mark, such as parking lot lighting, irrigation, private sewer laterals, fire lines and lines between buildings. A private locator uses EM and GPR equipment and marks in the same colors utilities use. Utility locating coordination
Sonde
A small battery-powered transmitter pushed through a sewer, storm drain or empty conduit on a rod or snake, so a locator can trace a nonmetallic line from the surface and find its depth, route or a break.
Subsurface utility engineering (SUE)
An engineering service that maps underground utilities and states how reliable each line’s location is, using the ASCE 38 quality levels. Level D comes from records only, C adds visible features such as valves and manholes, B adds locating with EM and GPR equipment, and A means the line was exposed by potholing and surveyed. Public works plans often note which level was used. Site verification and utility coordination

Gas, vapor and air monitoring

Air sampling pump and cassette
A small battery pump that draws air through a filter cassette at a set flow rate for a set time. The filter goes to a lab for fiber counts (PCM) or fiber identification (TEM) on asbestos jobs, or for metals on lead jobs. A pump worn by a worker gives a personal sample; one on a stand gives an area or clearance sample.
Bump test and calibration
A bump test exposes a gas meter to a known gas to prove its sensors and alarms respond, usually before each day’s use. Calibration adjusts the readings against certified gas on the manufacturer’s schedule. Both are logged, because readings from an unchecked meter may not be accepted by an inspector or air district.
Flame ionization detector (FID)
An organic vapor meter that burns a tiny hydrogen flame to measure hydrocarbons, including methane, which a PID misses. It is used where methane may be present, such as near landfills, oil fields and Los Angeles methane zones.
Four-gas meter
A portable monitor, clipped to a worker or lowered into a space, that reads oxygen, combustible gas (as a percent of the lower explosive limit), carbon monoxide and hydrogen sulfide, with alarms. It is used for confined space entry, tank work, vaults and deep trenches. Cal/OSHA’s confined space permit form calls for oxygen above 19.5 percent and combustible gas below 10 percent of the lower flammable limit before entry.
Methane zone (Los Angeles)
Areas the City of Los Angeles has mapped as a Methane Zone or Methane Buffer Zone, where gas from oil fields and natural deposits can collect in the soil. New buildings there need methane site testing by a qualified tester and, depending on the results, a gas mitigation system under the city’s methane code.
Photoionization detector (PID)
A handheld organic vapor meter that uses an ultraviolet lamp to read gasoline, solvents and other volatile organic vapors in parts per million. It is widely used for SCAQMD Rule 1166 soil screening on tank and piping removals. It does not read methane. Soil contamination and tank removal service

Survey, layout and field testing

Drone survey (photogrammetry and LiDAR)
Mapping a site from a drone with overlapping photos (photogrammetry) or a LiDAR sensor to produce aerial maps, surface models and stockpile volumes. Commercial drone pilots need an FAA Part 107 certificate, and many cities and parks add their own rules.
GNSS / RTK rover
A GPS-style survey receiver on a pole that uses a base station or correction network to place points to within about an inch. It is used to stake grades, check pad elevations and measure earthwork quantities.
LiDAR (laser scanning)
A scanner that measures millions of points with laser pulses to build a 3D model of a building or site. It is used for existing-conditions surveys before demolition or renovation, as-built records and volume measurements.
Machine control (GPS grading)
GPS or laser sensors on a dozer, grader or excavator that compare the blade or bucket position with a 3D design model, so the operator can cut and fill to grade with fewer survey stakes.
Nuclear density gauge
The standard field tool for compaction tests. A small sealed radioactive source measures soil density and moisture, which are compared with the lab maximum to report relative compaction. In California the gauge is used under a radioactive materials license from the Department of Public Health, and Caltrans testing follows California Test 231.
Point cloud
The set of 3D points a laser scanner or drone produces. It can be viewed and measured on a computer and is used to draw existing-conditions plans and check quantities.
Robotic total station
A survey instrument that measures angles and distances to a prism and is aimed by remote control, so one person can lay out or check points. It works where GPS signals are blocked, such as next to tall buildings, and is used to read monitoring points during excavation.
Rotating laser level
A tripod-mounted laser that sweeps a level beam across a site. A receiver on a grade rod shows how far above or below grade the ground is. It is common on building pads, footings and flatwork.
Stockpile volume survey
Measuring the volume of a pile of soil, base rock or crushed concrete by drone, laser scanner or GPS rover, to bill import or export by the yard or to track material kept on site.

Vibration, noise and movement monitoring

Crack gauge (crack monitor)
A small two-piece plastic gauge fixed across an existing crack, with a grid that shows whether the crack widens or shifts during nearby work.
Peak particle velocity (PPV)
How fast the ground moves during vibration, measured in inches per second. Caltrans vibration guidance, which many California projects use, sets damage thresholds for occasional (transient) vibration from 0.12 in/sec for extremely fragile historic buildings to 2.0 in/sec for modern industrial and commercial buildings. Limits for continuous vibration are lower, from 0.08 to 0.5 in/sec.
Preconstruction condition survey
Photos, video and notes of neighboring buildings, walls and pavement taken before demolition or excavation starts, so any later damage claim can be compared with the condition before work began.
Seismograph (vibration monitor)
A monitor placed on the ground or on a structure next to the work that records vibration from demolition, hoe ramming, compaction or pile driving. Readings are in peak particle velocity (PPV) and are compared with the limits in the project specifications or vibration study.
Settlement and shoring monitoring points
Survey targets set on shoring, neighboring buildings and streets and read on a schedule by a surveyor during deep excavation, to catch movement early. The soils engineer sets how much movement is allowed and what happens if it’s exceeded.
Sound level meter
A meter that reads noise in A-weighted decibels (dBA). It is used to show compliance with city noise ordinances and project noise limits, which usually also set the hours work is allowed.

Finding what’s underground and checking the air

Who’s involved

Engineers, environmental consultants, utility locators, surveyors, inspectors and contractors who rely on field measurements, and the owners who receive their reports.

What the work involves

These terms cover the tools used to find what’s underground, check air and soil for vapors, gas and dust, survey and lay out a site, and watch for vibration and movement near the work.

Why it matters

Instrument readings decide whether digging can start, whether a trench or tank is safe to enter, whether soil is contaminated, and whether neighboring buildings are protected. Knowing what each tool can and can’t detect helps you ask for the right service and read the results.

Where it applies in Southern California

California rules call for these readings at set points: utility marks before digging under the 811 law, gas testing before confined space entry under Cal/OSHA, vapor readings on excavated soil under SCAQMD Rule 1166, dust monitoring under Rule 1466, and compaction tests under city and Caltrans specifications.

How SoCal Removal fits in

SoCal Removal does not perform utility locating, land surveying or laboratory testing in-house. It arranges qualified locators, surveyors and consultants, uses their results to plan the work, and keeps the records in the project file. See site verification and utilities.

See all 2026 pricesCall (949) 446-0000

SoCal Removal is the business name of Abajian Enterprise, a California corporation. CSLB #980451 (A, B, C-21). Certifications: HAZ, ASB (ASB for bidding only). Verify the license · Insurance and project bonding