Retention Ponds, Swales & Culverts in King County WA
e design and install large-scale stormwater systems that move, store, and treat runoff — and pass inspection.
From underground culverts to vegetated swales and detention ponds, Sandbagger builds infrastructure that meets commercial stormwater requirements in King County and beyond.
Why These Systems Matter
Control More Water, Prevent Flooding, and Stay Compliant
Large developments and public works projects generate massive runoff. Proper stormwater design is essential to:
Meet DOE stormwater treatment standards
Prevent downstream flooding and erosion
Capture and slowly release runoff
Improve water quality through biofiltration
Protect roads, foundations, and utilities
We install these systems with precision — and a deep understanding of drainage flow and code compliance.
Our Capabilities
Stormwater Systems Built to Handle Big Volume
Retention & detention ponds
Excavated basins that store stormwater temporarily or permanently with overflow control.
Bioswales and vegetated swales
Channels designed to slow runoff and filter contaminants through vegetation and soil.
Culverts and under-road drainage
Corrugated steel, concrete, or HDPE pipe installations to convey water under roads, driveways, and access points.
Infiltration systems
Includes pre-treatment, sediment basins, and rock galleries for subsurface discharge.
Emergency overflow and bypass systems
We handle grading, excavation, pipework, vegetation, and stabilization from start to finish.
Trusted on Large Projects
Civil-Grade Drainage by Certified Contractors
DOE and King County stormwater standards
Work with engineer plans or provide design-build
WA CESCL-certified
RainWise and municipal experience
Woman-owned, licensed, and insured
Final inspection and as-built reporting included
ideal For
Large-Scale Drainage for Commercial & Civic Projects
Multi-acre developments
Parking lots and shopping centers
Roadway improvements and culvert replacements
School, city, and county projects
Industrial parks and logistics hubs
Utility or telecom access improvements
Where We Work
Serving King County WA and Surrounding Areas
Seattle
Bellevue
KENT
SHORELINE
RENTON
Federal Way
auburn
TUKWILA
DES MOINES
and surrounding areas
REVIEWS
Contractor Feedback
Developer, Kent WA
Sandbagger excavated and installed a detention pond with emergency overflow for our 12-acre site. Everything worked perfectly.
Municipal Contractor, Shoreline WA
Their culvert installation passed city inspection the first time — fast, clean, no issues.
FAQs
Retention Pond & Culvert FAQs
Are you able to work from stamped engineering plans?
Yes — we frequently install per civil engineer drawings and coordinate with the design team and inspector.
Do you handle permitting?
We can assist with drainage permits and coordinate with city or county departments as needed.
What types of culverts do you install?
Corrugated steel, concrete box, or HDPE — depending on flow volume, load rating, and site needs.
Let’s Build Drainage Infrastructure That Works for the Long Haul
From excavation to final grade, Sandbagger delivers engineered stormwater solutions that perform.