Soil Conditions in Ontario
San Bernardino County sits at the transition from coastal influence to high desert — creating a wide range of soil conditions and seismic considerations. Here's what we typically find.
Deep Alluvial Fan Deposits
Ontario sits on deep alluvial fan deposits transported from the San Gabriel Mountains via Cucamonga Creek and San Antonio Creek. These deposits consist of interbedded sands, gravels, silts, and clays that can extend hundreds of feet below grade. Bearing capacity is generally adequate for conventional foundations but varies with clay content.
Variable Clay Content and Expansion Potential
Portions of Ontario, particularly in the southern and western areas of the city, contain clay-rich soils with low to moderate expansion potential. Expansive soils can cause differential movement in foundations and slabs, requiring moisture conditioning, select fill, or post-tensioned slab designs.
San Jose Fault
The San Jose fault traverses the Ontario area and is a consideration for seismic design. While not as prominent as the San Andreas, it contributes to the regional seismic hazard and must be evaluated in geotechnical reports. Parcels near the mapped fault trace may require fault hazard investigations.
Corrosive Soil Conditions
Sulfate and chloride concentrations in Ontario soils can be elevated, particularly in areas with historically high groundwater or agricultural use. Corrosivity testing is routinely performed to determine the appropriate concrete mix design and protection measures for buried utilities and foundations.
What We Do in Ontario
Soils Reports
Geotechnical investigation and foundation recommendations for building permits.
Learn more →Grading Plans
Precise and rough grading design with drainage and earthwork calculations.
Learn more →Compaction Testing
Field density testing and fill certification for construction.
Learn more →Stormwater / LID / WQMP
WQMP preparation and BMP design for stormwater compliance.
Learn more →Hydrology Reports
Drainage analysis and flood risk assessment.
Learn more →Subsurface Exploration
Drilling, CPT, and test pit programs.
Learn more →Erosion Control Plans
SWPPP and erosion control for grading permits.
Learn more →Street Improvements
Frontage, curb, gutter, and sidewalk design.
Learn more →Utility Plans
Water, sewer, and storm drain design and coordination.
Learn more →Project Coordination
One point of contact managing structural, MEP, surveying, and specialty consultants.
Learn more →We also coordinate with your structural engineer, architect, MEP consultants, and other project team members to ensure our deliverables integrate with the overall design — one point of contact for your geotechnical and civil engineering scope.
What People Build in Ontario
Warehouse & Logistics Facilities
Ontario's proximity to ONT airport and major freeways drives significant warehouse and distribution center construction, requiring large-area geotechnical investigations and slab-on-grade design for heavy floor loads.
Single-Family Residential
New tract homes and custom residences in planned communities, requiring standard geotechnical investigation, grading plans, and stormwater compliance.
Multi-Family & Mixed-Use
Apartment complexes and mixed-use developments near the Ontario Mills area and transit corridors, often requiring deeper exploration programs and podium-style foundation design.
Commercial Retail & Office
Retail and office construction along major corridors including Euclid Avenue, Fourth Street, and Haven Avenue, requiring site-specific geotechnical recommendations.
ADU / Accessory Dwelling Unit
Detached ADUs and garage conversions on existing residential lots, typically requiring a soils report for new foundation construction.
Working With City of Ontario Planning Department
Ontario requires geotechnical reports for new construction and grading permits. The Planning Department coordinates plan check for geotechnical, grading, and civil engineering submittals. Ontario has a well-organized digital submittal process, and review times are generally consistent.
What Makes This Jurisdiction Distinct
Ontario International Airport Land Use Compatibility Plan may impose height, use, and noise insulation requirements on parcels within the influence area
Soils corrosivity testing required — sulfate and chloride levels must be reported for concrete mix design and utility pipe material selection
Expansion index testing required for all foundation recommendations
Projects in the San Jose fault zone may require fault rupture hazard evaluation
The City of Ontario accepts digital plan check submittals. Include the geotechnical report, grading plan, and WQMP as a coordinated package to streamline review.
Common Questions — Ontario
Building in Ontario?
Tell us about your project and we'll send you a fixed-fee proposal — typically within one business day.