Underground Detention System

Installation

Underground detention systems capture and store stormwater runoff below grade, releasing it at a controlled rate to reduce peak flows, prevent downstream flooding, and protect adjacent properties. In Northern Virginia's dense and rapidly developing landscape, these systems play a critical role in meeting Virginia DEQ standards, local MS4 permit requirements, and Chesapeake Bay watershed goals.

Getting the installation right is essential. Systems built outside of engineered plans and specifications underperform, create compliance exposure and are costly to remediate. Ongoing maintenance is equally important. Sediment accumulation, blocked inlets, and deteriorating components reduce storage capacity and can put a project out of compliance without warning.

From permitting support through installation and into long-term maintenance, Capital Stormwater Services delivers underground detention systems that perform as designed protecting downstream properties, satisfying regulatory requirements and keeping your project in compliance for the long term.

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OUR SERVICES
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Capital Stormwater Services performs new construction installation of underground stormwater detention systems and post-construction best management practices for commercial, residential and public projects across Northern Virginia.

Capital Stormwater Services brings the specialized stormwater knowledge, trained crew, and in-house equipment needed to keep installation moving smoothly from start to finish.

Our foreman operates the excavator. Our crew installs the chambers, pipe, structures, stone, fabric, and system components. The critical work stays under our control, which means fewer delays. No critical work is subcontracted.

All systems are designed to meet site specific hydrology, geothechnical conditions and local regulations. We coordinate with civil engineers and provide installation that follows approved plans and manufacturers specifications.

From proper bedding and geotextile placement to compaction and backfill, our installation practices protect system integrity and ensure long term performance under load.

Stormwater Infrastructure You Can Count On. Installed with Precision. Built to Last.

Underground stormwater detention has become a core requirement of modern development in across Northern Virginia.

As communities grow and impervious surfaces expand, managing stormwater on-site becomes both a regulatory obligation and an engineering challenge. Underground detention systems provide the below-grade storage capacity needed to control peak flow rates, reduce downstream flooding and support water quality goals without sacrificing valuable surface space for parking, green space or future development.

In Northern Virginia's dense and fast-growing corridor, these systems are a cornerstone of compliant site design. Virginia DEQ standards, local stormwater ordinances and Chesapeake Bay watershed requirements all demand that new and redeveloped sites manage runoff effectively. Where surface area is limited and land values are high, underground detention is often the most practical and efficient solution available.

Why Underground Detention

  • Captures and stores stormwater runoff below grade, out of sight and off the surface 

  • Releases stored runoff at a controlled, pre-approved rate to reduce peak flows 

  • Reduces flooding, erosion, and downstream impacts on adjacent properties and infrastructure 

  • Supports compliance with local stormwater ordinances and Virginia DEQ regulations 

  • Preserves valuable surface area for parking, green space, and development

  • Requires scheduled inspection, maintenance, and reporting to sustain long-term performance

UNDERGROUND DETENTION SYSTEM WE INSTALL

We install underground detention systems to project specifications and local stormwater requirements. Done right and on schedule.

HDPE Pipe Detention Systems

High-density polyethylene pipe systems deliver reliable underground stormwater storage with excellent structural integrity, chemical resistance, and long-term durability. Lightweight and adaptable relative to concrete alternatives, HDPE systems are well-suited for linear installations, sites with limited excavation depth and projects requiring efficient mobilization and installation.

Each system is assembled using corrugated or smooth-wall pipe, headers, laterals, fittings, access structures, and engineered stone bedding creating subsurface storage capacity beneath parking lots, access roads, green space and developed sites across Northern Virginia.

  • Available in a wide range of diameters and configurations to meet varying storage volume and site geometry requirements

  • Designed and manufactured for gravity-flow storm sewer and subsurface drainage applications

  • Suitable for both conveyance and detention applications, including controlled-release and retention systems

  • Performs reliably beneath parking lots, access roads and developed surfaces subject to vehicle and traffic loading

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StormTech SC & DC Chamber Systems

StormTech modular chamber systems provide high-capacity underground stormwater storage through an arch-shaped, interlocking design that maximizes subsurface void space while minimizing excavation volume. Lightweight and efficiently staged, chambers are well-suited for sites where storage demand is high, installation windows are tight or surface constraints limit conventional pipe-based approaches.

 StormTech systems are engineered for structural performance across a wide range of soil conditions and loading scenarios and are adaptable to both detention and retention applications depending on site and regulatory requirements.

  • High void ratio delivers maximum storage capacity per cubic yard of excavation

  • Engineered to accept traffic and vehicle loads with proper cover depth and design

  • Fully compatible with filter fabric, stone bedding, and aggregate surround for structural support and water quality integration

  • Modular, interlocking design allows flexible layout configuration to fit irregular sites and varying storage volume requirements

  • Widely specified and accepted by Virginia DEQ and local stormwater review agencies across Northern Virginia

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Inlet & Outlet Control Structures

Inlet and outlet structures manage how stormwater enters, moves through, and discharges from a detention or conveyance system. Custom precast and cast-in-place structures control system hydraulics, provide maintenance access, and ensure the system performs to design intent and regulatory requirements. 

Capital Stormwater Services installs precast concrete manholes, junction boxes, outlet control structures and energy dissipators for stormwater detention, conveyance, and discharge systems. Riser assemblies, orifice plates, trash racks, and related outlet control components are installed, inspected and documented at completion supporting proper system performance and satisfying closeout requirements for engineers, owners and local review agencies. 

  • Precast concrete and cast-in-place structure options to meet site-specific design requirements

  • Weir walls, orifice plates, and flow control devices for regulated stormwater release

  • Manholes, access points, and safety grates for long-term inspection and maintenance access

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Plan Review

We review approved civil plans, hyrology calculations and manufacturer’s specifications to confirm requirements,

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OUR INSTALLATION PROCESS

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Site Preparation & Excavation

Excavation is completed to the required grades with attention to safety and access.

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Bedding & Subbase Preparation

Stone bedding and geotextile are placed to create a stable foundation

System Placement

Chambers or pipes are installed to plan with proper alignment and spacing.

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Structures & Connections

Inlets, outlets. and flow control structures are connected and sealed per design.

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Backfill & Compaction

Backfill is placed in lifts and compacted to meet structural and traffic load requirements.

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Closeout & Documentation

As-built documentation, photos and inspection reports are provided for compliance.

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Plan Review

We review approved civil plans, hyrology calculations and manufacturer’s specifications to confirm requirements,

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OUR INSTALLATION PROCESS

Number 4 inside a green circle
Blueprint or floor plan with a green pencil

Site Preparation & Excavation

Excavation is completed to the required grades with attention to safety and access.

Green circle with the number 3 in white.
A blue toy dinosaur with a small basket on its back holding small balls, positioned above a pile of toy balls.
Blue excavator construction equipment with a bucket on the ground, situated on a pile of dirt or gravel.

Bedding & Subbase Preparation

Stone bedding and geotextile are placed to create a stable foundation

Close-up of a microphone with a blue and gray design.
A metal ring resting on a pile of small spherical objects, with a black background.

System Placement

Chambers or pipes are installed to plan with propoer alignment and spacing.

Green circular sign with the number 5 in white text.
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Structures & Connections

Inlets, outlets. and flow control structures are connected and sealed per design.

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Number six inside a dark green circle on a black background.
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Backfill & Compaction

Backfill is placed in lifts and compacted to meet structural and traffic load requirements.

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Number 7 displayed inside a green circle.
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Closeout & Documentation

As-built documentation, photos and inspection reports are provided for compliance.

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OUR INSTALLATION PROCESS

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Infiltration Trenches

Installation of detention systems that manage runoff and protection downstream communities

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Rain Gardens

Biorentention, rain gardens,swales and other best management practices installed to improve water quality.

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Bioretention Cells

DEQ inspections with detailed reporting to support regulatory compliance and performance.

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Wet/Dry Detention Basins

DEQ inspections with detailed reporting to support regulatory compliance and performance.

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Dry Swales

DEQ inspections with detailed reporting to support regulatory compliance and performance.

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Vegetated Filter Strips

DEQ inspections with detailed reporting to support regulatory compliance and performance.

Expert underground detention installation, BMP maintenance, facility inspections and compliance support for communities, developers, HOAs and commercial properties.From underground systems to ongoing maintenance, we deliver reliable stormwater solutions that protect communities and ensure compliance

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Who We Work With

UNDERGROUND DETENTION INSTALLATION

Installation of detention systems that manage runoff and protection downstream communities

‍ ‍‍ ‍ Learn More ▷

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BIORENTENTION RAIN GARDEN INSTALLATION

Biorentention, rain gardens,swales and other best management practices installed to improve water quality.

‍ ‍‍ ‍ Learn More ▷

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BMP INSPECTION & REPORTING

DEQ inspections with detailed reporting to support regulatory compliance and performance.

‍ ‍‍ ‍ Learn More ▷

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BMP MAINTENANCE

Routine maintenance that keeps stormwater facilitites functioning efficiently and extends their lifespan.

‍ ‍‍ ‍ Learn More ▷

OUR SERVICES

Expert underground detention installation, BMP maintenance, facility inspections and compliance support for communities, developers, HOAs and commercial properties.From underground systems to ongoing maintenance, we deliver reliable stormwater solutions that protect communities and ensure compliance

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Reliable Stormwater Infrastructure Built Right from the Ground Up

UNDERGROUND DETENTION INSTALLATION

Installation of detention systems that manage runoff and protection downstream communities

‍ ‍‍ ‍ Learn More ▷

Sketch of a potted plant with grass and a tall flower with multiple blooms.

BIORENTENTION RAIN GARDEN INSTALLATION

Biorentention, rain gardens,swales and other best management practices installed to improve water quality.

‍ ‍‍ ‍ Learn More ▷

Checklist on a clipboard with three checked items.

BMP INSPECTION & REPORTING

DEQ inspections with detailed reporting to support regulatory compliance and performance.

‍ ‍‍ ‍ Learn More ▷

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BMP MAINTENANCE

Routine maintenance that keeps stormwater facilitites functioning efficiently and extends their lifespan.

‍ ‍‍ ‍ Learn More ▷

WHY CAPITAL STORMWATER

Built Underground. Built to Last.

Our stormwater specific focus means faster mobilization, stronger regulatory knowledge, cleaner documentation and inspection reports that align with County and Virginia DEQ expectations.

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SPECIALIZED SERVICE

Civil engineers, property managers, HOAs, and owners trust Capital Stormwater Services because we specialize in BMP installation, maintenance, inspections and compliance. We manage DEQ permit coordination, BMP documentation, and county inspections from start to finish so compliance is handled and your project keeps moving.

Virginia Class A contractor license. Fully Insured. Ready to work.

Service Area: Fairfax County • Loudoun County • Prince William County • Arlington County • Fauquier County • Culpeper County

CLASS A LICENSED CONTRACTOR

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IN HOUSE EQUIPMENT

With excavation machinery, work trucks, and trailers already in-house, Capital Stormwater Services can mobilize quickly and control the critical work directly, without waiting on subcontractors for the equipment that actually keep a project moving.

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DEQ COMPLIANT INSPECTION REPORTS

Our inspection reports go beyond a checklist. Each one documents BMP performance, identifies deficiencies, and provides a clear compliance record aligned with Virginia DEQ standards and your county's MS4 obligations.

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Ready To Talk About Your Project?
Let’s build smarter, stronger and more sustainable solutions - together.

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