The Atlantic Wastewater Treatment Plant expansion is the largest single capital improvement project ever completed for the Hampton Roads Sanitation District (HRSD) with an estimated total project cost of $110 M. HRSD selected HDR to provide engineering services for the expansion of the 36-mgd plant to 54 mgd, with provisions for a future expansion to 72 mgd. Treated effluent is discharged through a 1.5-mile outfall and diffuser to the Atlantic Ocean.
HDR evaluated alternative expansion concepts that would provide lowest life-cycle costs and improved service to HRSD. These included:
Four concepts for expansion of the existing headworks structure were developed and evaluated.
The available hydraulic head between the primary clarifiers and secondary clarifiers was limited by existing tank elevations. HDR developed several approaches to address this issue.
The plant employs a labor-intensive dewatered cake handling system. Dewatered cake is conveyed from centrifuges to a storage hopper by a serpentine conveyor. The cake is then hauled from the hopper to a pad for storage until it is land applied by a private contractor. There was not sufficient space in the existing solids handling building to install the proposed gravity belt thickeners. HDR, working with HRSD, developed a concept to relocate the centrifuges to a new building located adjacent to the cake storage pad.
HDR developed a concept of converting two existing biosolids holding tanks to acid-phase digesters.
Extensive geotechnical evaluations are being performed to design the most cost-effective site preparation approach.
HDR prepared the required State level environmental assessment, completed the wetland/stream permitting process, and is assisting with permit condition compliance.