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Wastewater Treatment Detailed Design

Client:US Army Corps of Engineers
Location:Baltimore, Maryland


Chester Engineers was contracted by the US Army Corps of Engineers to refine a prior Feasibility Study through the detail design stage level. This project concerns two failing wastewater treatment package plants on a relatively inaccessible island in the Chesapeake Bay by retrofitting the plants to a constructed wetlands method of treatment. The two activated sludge/aeration package plants are currently failing, experiencing salt corrosion and frequent upsets due to system overloading from storm surge flows. The Feasibility Study level defined a preferred alternative solution identifying the constructed wetlands approach as economically and environmentally the optimum next step.

The detailed design during this stage required complete construction documents including specifications, detailed engineering cost estimates, and construction drawings with sufficient detail to allow the construction of the proposed retrofit design.

  • Retrofit or replace existing aeration/settling tanks to above-ground septic tank storage with pumped effluent wetland cell dosing
  • Detailed construction plans and specifications for wetland cell geometry
  • Discharge disinfection and controlled release
  • Hydraulic flow modeling of waste stream
  • Existing surrounding wetland impact minimization
  • Detailed construction estimate using MCACES

Scope of Work

  • Inventory of available hardware and software
  • List of requirements for supplemental hardware and software
  • Report on GIS activities from other Corps of Engineers (COE) Districts within the Great Lakes and Ohio River basins.

Project Constraints

  • Remote location (inaccessible except by watercraft) required design to incorporate long-term minimal maintenance needs in the daily operations of the treatment process
  • Careful control of discharge pollutants required to minimize effects on shellfish harvest in adjacent Chesapeake Bay
  • Salt air/sea spray required attention to long-term corrosion control of construction materials

Results
Detailed design plans and construction documents were developed to retrofit a system of activated sludge aeration treatment to one of primary settling and wetland cell bioremediation that will ultimately reduce the daily operating expenses and will reduce the pollutant discharge to well below the permissible levels in the NPDES permit. Detailed specifications and construction cost estimates were also developed in support of the design and construction bid package.


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