Best Civil Works/Infrastructure: Little Patuxent Addition Aids in Denutrification
The $92.2-million Little Patuxent Water Reclamation Plant Addition No. 7 helps protect water quality in the Chesapeake Bay by removing excess nutrients while allowing Howard County to meet its wastewater treatment demands through 2030.
The main upgrade included design and construction of new denitrification filters to reduce excessive nitrogen in the wastewater discharges. Other improvements included new influent multi-rake screens and screening compactors.
To meet a February 2012 state-mandated deadline, Howard County chose to use a construction-manager-at-risk delivery to expedite construction and selected a joint venture of Clark Construction Group, Bethesda, Md., and Ulliman Schutte Construction, Miamisburg, Ohio, for the job.
The CM-at-risk method allowed early stages of work to start even while later activities were not formalized. The team delivered the denitrification filter facilities in February 2012, allowing them to operate nearly four months before the enhanced nutrient-removal permit limits went into effect.
The project affected every treatment process at the plant, so maintenance of plant operations (MOPO) procedures had to be considered throughout design and construction to prevent permit violations. Atkins, Calverton, Md., developed detailed MOPO plans for all portions of work to orchestrate shutdowns of and tie-ins to the existing facilities. Plant staff reviewed these plans and provided input on process limitations. The final plans were then included in the contract documents for implementation during construction.
Re-use of existing facilities saved the county more than $5 million and added time for new construction. An abandoned 1-million-gallon aerobic digester was converted to an activated sludge process reactor for industrial waste treatment. A special dissolved-air-floation unit constructed where a future DAF unit will be located allows added treatment capability in the event of process interruptions. The former static primary-sludge fermenters were retrofitted to be continuous-flow fermenters.
Little Patuxent Water Reclamation Plant Addition No. 7 Savage, Md.
Owner: Howard County; Columbia, Md.
CM: Clark/US LLC - Clark & Ulliman Schutte Construction, Joint Venture; Miamisburg, Ohio
Lead Design, Structural, Civil and MEP: Atkins North America Inc.; Calverton, Md.
Submitted by Howard County Bureau of Utilities