Know your ground before you build on it.
California Soil Testing Inc. specializes in residential projects: homes, ADUs, additions, decks, and pools. We deliver the PE-stamped soil reports and field testing that get your project through plan check, backed by our own in-house laboratory and a 3-week turnaround guarantee.
From the first boring to final inspection
Residential work is our specialty. Whether you're adding an ADU, rebuilding a deck, putting in a pool, or building a custom home on a hillside, we provide the data your engineer and building department require.
Soil Reports & Geotechnical Studies
PE-stamped geotechnical investigation reports required for residential building permits, including foundation recommendations, bearing capacity, and seismic design parameters.
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Compaction Testing
Field density testing and earthwork observation to verify your fill, subgrade, and trench backfill meet the compaction specs on your grading plan.
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Liquefaction Studies
Site-specific evaluations of earthquake-induced ground deformation, required for projects within state-designated seismic hazard zones.
Learn more →A straightforward process, start to finish
Same-day quote
Send us your address and project description. You'll have a fixed-price proposal within 24 hours, usually the same day.
Site investigation
We drill borings or excavate test pits, log the soil profile, and collect samples for laboratory analysis.
In-house testing
Samples are tested in our own laboratory per ASTM and AASHTO standards, with no third-party delays.
PE-stamped report
You receive a signed, stamped geotechnical report ready for submittal, within our 3-week turnaround guarantee.
A family-run firm with an engineer's discipline
We keep our lab in-house, our pricing low, and our phones answered. When you call, you talk to the people doing the work, not a call center.
In-house laboratory
Project-specific testing in full compliance with AASHTO and ASTM standards, under our own roof. Faster results, tighter quality control.
Speed & pricing
Low prices, same-day quotes and proposals, and a 3-week report turnaround guarantee that keeps your permit timeline on track.
Responsive support
Immediate telephone consultation and a friendly, family-oriented approach. Your questions get answered by an engineer, not a voicemail.
Serving the Bay Area and Surrounding Regions
Ready to break ground?
Get a fixed-price quote and a professional geotechnical scope for your project within 24 hours.
Geotechnical services for every stage of your project
We focus on residential projects: new homes, ADUs, additions, decks, pools, and septic systems, with select commercial work as well. All photos below were taken on our own job sites across Northern California.
Soil Reports & Geotechnical Studies
The foundation of every safe home project, from ADUs and additions to new custom houses. Our reports are signed and stamped by a licensed Professional Engineer and accepted by building departments across Northern California.
- Subsurface exploration: borings and test pits with full soil logging
- Foundation type and bearing-capacity recommendations
- Seismic design parameters per the California Building Code
- Expansive-soil evaluation and slab/foundation mitigation measures
- Grading, drainage, and retaining-wall design criteria
Liquefaction Studies
When loose, water-saturated soils are shaken by an earthquake, they can temporarily behave like a liquid, and structures above them can settle or tilt. Homes inside state-designated Seismic Hazard Zones require a site-specific evaluation before permits are issued.
- Site-specific liquefaction-potential analysis
- Estimated seismic settlement and lateral-spreading evaluation
- Mitigation recommendations for foundations and ground improvement
- Reports formatted for city and county plan-check requirements
Compaction Testing
Fill that isn't properly compacted settles, taking foundations, slabs, and driveways with it. We verify in the field that your earthwork meets the specifications on your grading plan.
- Field density testing of engineered fill, subgrade, and trench backfill
- Laboratory moisture–density (Proctor) curves per ASTM standards
- Earthwork and grading observation with daily field reports
- Final compaction reports for building-department sign-off
Percolation Testing
A percolation test measures how quickly water drains through the soil (the time it takes for the water level in a test hole to drop one inch). County health departments require it before approving residential septic systems, and it informs stormwater and drainage design.
- Perc tests for septic system and leach-field approval
- Infiltration rates for stormwater and drainage design
- Coordination with county environmental health requirements
Drilling & Pier Observation
Hillside homes, decks, and structures on weak soils often bear on drilled piers. We observe drilling operations to confirm each pier reaches competent material at the depth your engineer specified.
- On-site pier and grade-beam drilling observation
- OSHA-certified shoring
- Verification of embedment depth and bearing material
- Field memos and letters for the building inspector's file
Inspections & Consultation
We stay with your project after the report is delivered, through construction, inspections, and final approval.
- Foundation plan review and foundation inspection
- Drainage and grading inspection
- Crushed-rock inspection for garages and driveways
- Final inspection and compliance letters
- Construction meetings and immediate telephone consultation
Not sure which service you need?
Tell us about your home project and we'll scope exactly what your building department requires, nothing more.
Recent work across Northern California
A selection of our recent work, mostly for homeowners: hillside decks and pools, new residences, and the occasional commercial job like a hospital-campus clinic conversion. Every photo below was taken by our crew on the job.
Medical Clinic Remodel: Hospital Campus
Soil and foundation investigation for the remodel of a two-story family practice clinic on the historic San Joaquin General Hospital campus, being converted into a medical training university. Two borings drilled on a rush weekend schedule, with the report delivered the next day.
New Pool on a Terraced Hillside
Geotechnical investigation for a new swimming pool on a sloped, oak-studded lot in the Salinas countryside, followed by a second phase supporting the retaining wall design for the surrounding terraces.
Hillside Deck in the East Foothills
Soil and foundation investigation for rebuilding a multi-level deck on a sloping foothill lot overlooking the Santa Clara Valley. Two borings characterized the silty clay profile to support the new deck's pier foundations.
New Two-Story Home Near the Bay
Soil and foundation investigation for a new two-story residence on a vacant lot overlooking Monterey Bay, characterizing the sandy coastal soils to support the foundation design for new construction.
Backyard ADU Investigation
Soil and foundation investigation for a detached accessory dwelling unit. Our crew set up the tripod rig right in the backyard, drilled, sampled, and was gone the same day with everything the lab needed.
Home Addition Soil Report
Geotechnical investigation for a residential addition on the Peninsula. Drilling tight against the existing house takes care; our portable rig works in spaces a truck-mounted rig can't reach.
Your project could be next
Send us your address and plans. We'll have a fixed-price proposal back to you within 24 hours.
Engineering the foundation of the future
At California Soil Testing Inc., we bridge the gap between architectural vision and geological reality.
Who we are
Since our founding, we have committed ourselves to providing high-accuracy geotechnical intelligence that serves as the backbone for safe, resilient construction. Our focus is residential: the homes, ADUs, additions, decks, and pools that families across Northern California build every day. Based in San Jose, we combine field exploration with our own laboratory analysis to solve the earthwork challenges these projects bring.
We're a family-run firm, and it shows in how we work: same-day quotes, phones answered by the people doing the engineering, and a friendly, straightforward approach to a technical trade. Every report we issue is signed and stamped by a licensed Professional Engineer and built to pass plan check the first time.
Our in-house laboratory, operating in compliance with AASHTO and ASTM standards, means your samples never wait in a third-party queue. That's how we back a 3-week project turnaround guarantee.
At a glance
- Reports signed & stamped by a licensed Professional Engineer (PE)
- In-house laboratory, AASHTO & ASTM compliant
- 3-week project turnaround guarantee
- 24-hour quote & proposal response
- 100% building-department compliance record
- OSHA-certified shoring for drilling operations
- Serving the Bay Area, Monterey County, Santa Cruz, Sacramento & beyond
Accuracy first
Foundations are only as good as the data beneath them. We log, sample, and test with the rigor your structural engineer depends on.
Speed without shortcuts
In-house lab work and same-day proposals keep your permit timeline moving without compromising the engineering.
People you can call
Immediate telephone consultation is part of the service. Questions during construction? You'll reach an engineer, not a queue.
What our clients say
You guys are the best. I called you one day and needed something done quickly. Geo report the next day, which was Saturday. You were out and completed two borings at the old San Joaquin General Hospital building that we're converting into a medical training university. Five stars, ten if I could give it. Excellent price and timing. Thank you!
I'm a GC, and when I need a soil test or anything involving a geotechnical report, I call them.
Thank you! You guys did a great job!
They were very helpful.
Great service. The prices are reasonable and friendly customer service. I highly recommend it.
We needed some recommendations for our foundation and they did a great job helping us. Highly recommend!
Frequently asked questions
The questions homeowners, builders, and architects ask us most.
What is a soil report, and why do I need one?
A soil report (geotechnical investigation report) describes the soil and groundwater conditions on your property and tells your structural engineer how to design a foundation for those conditions: bearing capacity, foundation type, seismic parameters, drainage, and grading criteria.
Most building departments in Northern California require one before they'll issue a permit for new construction, additions, ADUs, and hillside work. It's also simply how you avoid expensive surprises: cracked slabs, settling foundations, and failed retaining walls usually trace back to soil conditions nobody checked.
Do I need a soil report for an ADU?
In most Northern California jurisdictions, yes. A detached ADU is new construction and typically requires a geotechnical report for permit approval. Requirements vary by city and by site conditions, so send us your address and we'll confirm what your building department requires before you spend anything.
How much does a soil report cost?
It depends on the project size, site access, the number of borings required, and your jurisdiction's requirements. A simple ADU or addition costs considerably less than a hillside custom home in a seismic hazard zone.
We provide fixed-price quotes, usually the same day you ask, so there are no surprises. Request a free quote and you'll have a number within 24 hours.
How long does the process take?
We guarantee a 3-week project turnaround from field work to your finished, PE-stamped report. Quotes and proposals go out within 24 hours, usually the same day. If your permit timeline is tight, call us and we'll tell you honestly what's possible.
What happens during the site investigation?
Our crew visits your property and drills borings or excavates test pits, typically a few hours of work for a residential lot. We log the soil profile layer by layer, note any groundwater, and collect samples. The samples then go to our in-house laboratory for testing per ASTM and AASHTO standards. You don't need to do anything to prepare beyond providing access to the site.
What is a liquefaction study, and do I need one?
During an earthquake, loose, water-saturated soil can temporarily lose its strength and behave like a liquid. That's liquefaction,, and it can cause structures to settle or tilt. The State of California maps Seismic Hazard Zones where this risk exists, and if your property falls inside one, your building department will require a site-specific liquefaction evaluation before issuing a permit. We can check your parcel against the hazard maps when you request a quote.
What is a percolation test?
A percolation (perc) test measures how quickly water drains through your soil: specifically, the time it takes for the water level in a test hole to drop one inch. County health departments require perc results before approving a septic system or leach field, and the data also informs stormwater and drainage design.
What is compaction testing, and when is it required?
Whenever soil is placed as fill (under a building pad, behind a retaining wall, in a utility trench) it has to be compacted to the density specified in the grading plan, or it will settle later. We test the fill in the field as it's placed and issue a final compaction report the building department uses to sign off your earthwork.
Will my report be accepted by my building department?
Yes. Every report is signed and stamped by a licensed Professional Engineer and formatted to the requirements of your specific jurisdiction. We maintain a 100% building-compliance record, and if a plan checker has questions, we respond directly. That follow-through is included.
Do you stay involved after the report is delivered?
If you want us to, absolutely. We offer foundation plan review, foundation inspection, pier-drilling observation, drainage and grading inspection, crushed-rock inspection, construction meetings, and final inspection letters, plus immediate telephone consultation whenever questions come up during construction.
Have a question we didn't answer?
Call us. Immediate telephone consultation is part of how we work.
Get your free soil report quote
Fixed pricing and a professional geotechnical scope for your home project within 24 hours, usually the same day.
San Jose headquarters
6455 Almaden Expy, Suite 209
San Jose, CA 95120
HOURS
Monday–Friday, 7 AM – 7 PM
Saturday, 9 AM – 3 PM
Sunday, closed
Service area
Soil reports signed and stamped by a licensed Professional Engineer across the Bay Area and surrounding regions, from the Peninsula and East Bay to Santa Cruz, Monterey County, and Sacramento.
What to expect
1. We reply within 24 hours with fixed pricing and scope.
2. We schedule field work at your convenience.
3. Your PE-stamped report arrives within 3 weeks, guaranteed.