Stormwater Control Retrofits in Holly Springs | NCDOT

Gradient provided NCDOT with enhanced water quality solutions and improved stormwater management in Wake County. Gradient’s comprehensive design capabilities directly benefit municipal clients like Raleigh by upgrading stormwater control measures and delivering innovative, high-performing solutions tailored to community needs.

Overview

NCDOT is working with partners to construct stormwater treatment retrofits within Wake County as part of a settlement associated with the Complete 540 project. NCDOT partnered with the Town of Holly Springs to identify potential retrofit opportunities on two Town owned parcels located in Holly Springs, NC. Stormwater Control Measures (SCMs) at both sites are currently dry detention basins.

Gradient was selected by NCDOT to assist in developing designs for the two stormwater control retrofits, as well as provide construction support services.

Gradient Solution

The Gradient team provided topographic and location surveys and soils investigations for both sites. Gradient conducted hydrologic and hydraulic modeling and developed 30%-level design drawings for the stormwater retrofits.

Current plans are for the existing dry detention basin SCMs to be converted to a submerged gravel wetland and a constructed stormwater wetland.

Due to concerns for hydrology to support stormwater wetland plantings at one of the sites, additional infiltration testing was conducted. Gradient is currently developing 90% construction plans for both retrofits, which will include site and grading plans, planting plans, traffic control plans, sediment and erosion control plans, and appropriate details.

Gradient is also developing Project Special Provisions and construction cost estimates. Gradient will assist with preparing the Bid Proposal Package, support the Division during the letting process, and provide construction/shop drawing review and milestone inspections during construction.

Following construction, Gradient will provide a summary of lessons learned during the design and construction phases of the project.