Multnomah County is the densest county in Oregon and the most regulated place to dig. Portland sits at the county seat, with Gresham, Troutdale, Fairview, and Wood Village filling out the eastern Multnomah corridor. Excavation work here is shaped by Portland 2025 building codes, BES stormwater requirements, traffic-control overhead on nearly every commercial job, and a subgrade that shifts from Willamette Valley clay west of the river to Columbia River silt-and-sand deposits on the east side and along the Columbia.
Cojo Excavation & Asphalt covers Multnomah County work out of our Hood River HQ and I-84 corridor operations. This guide walks through what Portland-metro conditions mean for site-prep cost, the project mix typical in the area, and what to look for in a CCB-licensed excavation contractor that handles permit-heavy urban work.
Portland and the Permit-Heavy Urban Core
Portland's central city and inner east-side neighborhoods sit on the highest-overhead excavation ground in Oregon. Any project that touches public right-of-way, generates measurable runoff, or alters drainage triggers a permit submittal -- and the city's BES stormwater code (Title 17), street use rules, and tree-protection ordinances all attach to dig plans before any equipment shows up.
The practical implications:
- Most commercial and many residential projects need a stormwater management approach (drywell, sump, planter, or detention) designed and approved before excavation begins.
- Traffic-control plans are required for any work that affects parking or sidewalk access.
- Tree-protection zones add cut and grade restrictions on lots with mature street trees or HRP-designated tree clusters.
- Right-of-way permits and PBOT inspection windows shape the daily schedule.
This is real overhead. Contractors who quote Portland work without naming these costs in writing usually do not survive their first city inspection. See our driveway excavation in Portland work for residential context.
Subgrade -- Willamette Clay and Columbia Silts
West of the Willamette River, Multnomah County sits on classic valley clay loam with pockets of Cascade-foothill basalt as you climb the West Hills. East of the river through Northeast and Southeast Portland, the subgrade transitions into a mix of Willamette silt loam and Columbia River silt-and-sand deposits. Near the Columbia in Northeast and along the Fairview-Troutdale corridor, sandy alluvial soils dominate.
These soil shifts matter for base-prep volume and drainage strategy:
- Clay sites need 6 to 8 inches of compacted crushed-rock base with perimeter and french drains.
- Silt-loam sites compact reasonably well but lose strength when saturated.
- Sandy Columbia-corridor sites drain fast but need geotextile separation to prevent fines migration into base aggregate.
A real Multnomah County quote should name which side of those soil lines a site sits on. Anyone quoting without doing a site walk is guessing.
Gresham, Troutdale, Fairview -- East Multnomah
East of Portland's city limits, Multnomah County stretches through Gresham (population around 115,000), Troutdale, Fairview, and Wood Village. The subgrade here is mostly Columbia silt and Willamette terrace soils. Commercial pad work concentrates along Burnside between 181st and 257th, the Gresham Town Center corridor, and the Troutdale industrial area near I-84 exit 17. Residential work runs from Rockwood-area infill to the Springwater-Corridor adjacent neighborhoods.
Gresham and the smaller east-county cities have their own municipal codes that overlap with Multnomah County rules. Permitting paths differ for sites inside vs outside Portland city limits, which affects timeline and cost.
Wet-Season Strategy
Portland metro gets roughly 43 inches of rain a year, with the wet season concentrated mid-October through April. Pure dry-method excavation on clay subgrades typically pauses December through February in average years. What can still move:
- Utility-trench work in the urban core with dewatering and gravel backfill.
- Storm-drain and combined-sewer work, often easier in wet weather because flow paths are visible.
- Same-week footing excavation paired with covered pour staging.
The peak booking window is May through October, and competent Portland-area crews are typically back-to-back from June through September. February is the right time to lock dates for a July dig in the metro.
Common Multnomah County Project Types
The mix we see across Multnomah County:
- Inner Portland residential driveway, 400 to 1,200 sq ft, valley clay or river silt: Strip 8 to 12 inches, crushed-rock base, drainage tied to BES-approved drywell or sump.
- Commercial pad, downtown or central east-side, 3,000 to 15,000 sq ft: Strip topsoil, base prep, traffic-control plan, BES stormwater management feature integration.
- Gresham / Troutdale commercial pad, 5,000 to 30,000 sq ft: Same scope with lower right-of-way overhead and different stormwater submittal path.
- Utility-trench replacement, 100 to 500 linear feet: Locate, saw-cut, trench, bedding, pipe, compact backfill, surface restoration per right-of-way permit.
- ADU or backyard cottage pad prep: Footing excavation, perimeter drainage, often access-constrained.
For coordination on follow-on scopes, asphalt paving services in Multnomah County, Multnomah County parking lot striping, and concrete curbing services in Multnomah County tie naturally into pad-prep sequences.
Multnomah County Excavation Cost Ranges
Multnomah County pricing reflects the highest permit, traffic-control, and labor overhead in Oregon. Quotes look high on a per-square-foot basis compared to outlying counties because much of the cost is regulatory and logistical, not dirt-moving.
Industry Baseline Range
| Project Type | Typical Range |
|---|---|
| Residential driveway excavation (400 to 1,200 sq ft) | $5,000 to $13,000 |
| ADU or cottage pad prep (300 to 600 sq ft) | $4,500 to $14,000+ |
| Commercial pad prep, per square foot | $6 to $18 |
| Utility trench, per linear foot | $40 to $120 |
| Stormwater drywell or planter, per unit | $1,800 to $6,500 |
| Spoils haul-off, per cubic yard | $55 to $115 |
| Traffic-control package, per day | $850 to $2,500 |
Current Market Reality
2026 Multnomah County pricing lands at the upper end of these ranges for three structural reasons. Permit-and-stormwater overhead has climbed every year for the past five years. Traffic-control crew rates have outpaced general construction inflation. And aggregate disposal at clean-fill and C&D sites within the metro has tightened, with longer hauls to East-County or Clark County, Washington sites adding cost. Quotes well below baseline usually skip line items that will appear on a change order mid-project.
Booking a Multnomah County Site Walk
Cojo Excavation & Asphalt covers Portland, Gresham, Troutdale, Fairview, Wood Village, Maywood Park, and the rest of Multnomah County. We do site walks before we quote, and our scope sheet names soil type, drainage handling, stormwater feature integration, base-rock volume, traffic-control overhead, and permit path. Contact our Portland crew to schedule a walk-through. For the broader range of what we do across Oregon, the excavation services page covers our crew, equipment, and licensing.