Project Overview
Tucked in one of North Carolina’s fastest-growing regions, the Holly Springs Operations Campus is part of a broader wave of smart, community-driven development reshaping the Triangle area. As new neighborhoods, schools, and commercial projects continue to take shape, infrastructure systems that balance performance, sustainability, and space efficiency are critical to long-term success.
For this municipal site, the project team sought to move away from the limitations of traditional cast-in-place construction to a more versatile precast solution—one that could meet stormwater standards, protect nearby waterways, and support the continued growth of the Holly Springs community.
The CP&P Engineered Products team collaborated closely with the design and construction leaders to rethink stormwater management at the Holly Springs Operations Campus (Phase 1B). Instead of sticking with a difficult, time-consuming cast-in-place system, the team pivoted toward an easier and faster, modular precast application. The final setup included a pair of StormPass sand filters feeding into a StormArc detention system that features an integrated Outlet Control Box with weir wall for built-in flow control.
The goal was to create a watertight, regulatory-compliant underground stormwater solution that delivered both filtration and storage, while keeping things simple for the civil site designer, cost efficient for the owner, and easy to install for the construction crew.
Challenges
A handful of critical design and site-specific challenges made this project unique:
- Space limitations imposed by site conditions
- Need for watertight system validation through water testing, per Holly Springs regulations
- Stormwater filtration volume required large sand filters, tightening shipping limitations
Watch this project unfold in our Case Study Video
Solutions
Engineered Product’s strategy knocked out each hurdle with a custom-engineered, modular approach:
- StormPass Pretreatment Selected – StormPass was selected as the upstream sand filter pretreatment system, fulfilling North Carolina’s preferred filtration methodology and replacing the originally-specified cast-in-place structures. The modular design achieved regulatory compliance and ensured speed, consistency, and ease of installation.
- StormArc Stackable Detention Design – StormArc served as the downstream detention system. Its stackable chambers with connecting arches provided superior volume efficiency versus all other alternative options. The system also incorporated a built-in Outlet Control Box, eliminating the need for a separate flow control structure and therefore reducing labor and materials costs. One of the biggest design advantages was the ability of StormArc to meet the site-specific depth, a feat that would have been far more difficult using cast-in-place. Its modular versatility enabled the team to deliver a detention system tailored to the maximum allowable depth while preserving the total required storage volume.
- Shift Away from Cast-in-Place – Redesigning away from the original cast-in-place concept gave the project team significant benefits. Cast-in-place detention vaults typically require more site preparation, longer labor timelines, and added complexity for forming, curing, and inspection. Pouring the large CIP detention vault would’ve been difficult for the contractor, whereas the modular StormArc system made for easy installation and a more cost-efficient solution overall. The shift to precast offered design versatility, a faster overall timeline, and a streamlined onsite execution.
- Efficient Freight & Delivery – Custom sizing of the sand filters was developed in close collaboration with the Engineer of Record (EoR) to ensure the individual pieces could be transported using standard trailers. Taller pieces would have required drop deck or low boy trailers, limiting the amount of available trucking, introducing additional cost, and creating unnecessary logistical complexity. By identifying an optimal height compatible with conventional trucking, CP&P and the EOR were able to adjust system lengths, accordingly, preserving all required treatment and storage volumes to devise the optimal solution.
- Watertight & Tested – The StormPass sand filters were made watertight with a combination of joint materials, while the StormArc detention system was made watertight with a PVC Liner. Each of these solutions was customized for the specific application and deemed the value engineering solution of choice as well as the optimal solution for the installer.
Results
The final system met all functional, regulatory, and site-specific objectives:
- Efficient stormwater filtration using ASTM C33 sand, as specified in NC
- Seamless detention system integration with built-in flow control
- Rapid installation enabled by modular components and thoughtful, intentional design
- Water testing successfully validated watertightness
The modular design gave the contractor a smoother installation process by avoiding large, complex concrete pours, and it improved the overall construction scheduling by allowing for sequencing of delivery and pre-staged trucking. The project also highlighted how CP&P Engineered Products’ systems can streamline delivery and install without sacrificing performance.
Learn more about Engineered Products stormwater solutions: Storm Flow Information Page
Download the digital case study PDF file here
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