True Grit

NDSD sought to maximize the skills of its own workforce to eliminate traditional consulting and contracting costs. This choice not only saved capital funds, but also significantly lowered the annual cost of grit handling with improved performance and less intensive maintenance.

To understand the effect of the original aerated grit removal system upon the overall WRRF, and any potential future improvements, NDSD established a deliberate, five-step plan:

NDSD surveyed several cost factors when determining the true cost of grit handling. Its aerated-grit chambers — originally installed in the 1980s — were removing roughly 55% of incoming grit. Costs to operate and maintain the grit removal systems were documented to be more than $136,000 a year, including more than $100,000 to drain, clean, and re-seed one of four digesters annually....

Next, NDSD explored new grit removal technologies. The district wanted to retrofit the replacement units into its existing chambers or install these upgrades in another manner requiring minimal construction. NDSD considered two types of systems that could drastically improve grit removal performance and potentially fit within the existing system footprint.

NDSD wanted this project to be an internal design–build project that would allow design, construction, and installation to be completed by its staff without the use of outside consultants or major contractors. This approach, which has been practiced by the management on smaller improvement projects, would maximize the skills of its own workforce, increase personal investment by its O&M...

NDSD approached its board with its project costs as well as a comprehensive plan for the proposed grit removal system upgrade. The Utah Department of Environmental Quality reviewed the proposed plan and concluded that the grit removal upgrade “is a replacement in-kind and does not require a [department of water quality] DWQ construction permit.” With approval by the NDSD Board and the...

Because the new grit removal systems were designed to fit the existing grit chambers and channels as much as possible, most installation work could be conducted by internal district staff without construction contractors. This also meant a relatively quick 16-week construction timeline per unit. Minimal concrete work was conducted by internal staff. There was no interruption to service as one...

NDSD completed the first round of this project in 2018. The first of two original aerated grit chambers was fully converted to the hydraulic forced vortex grit chamber and operational in November 2018. And in October 2019, NDSD staff and the manufacturer completed the installation and commissioning of the second unit.