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Cornwell's water treatment design experience ranges from designing new state-of-the-art water treatment facilities to rehabilitating or expanding existing processes and facilities. Many of our designs offer flexibility for potential future regulations, while keeping unit processes easy to operate and cost effective. Our water treatment design experience is summarized in the following pages:

Rapid Mix, Flocculation, Sedimentation -We have extensive experience in optimizing these processes. Our design for the City of Richmond, VA included eight rapid mix units and 32 flocculators for a 140- mgd water treatment plant. Similar designs were performed for the City of Durham, NC and Camden, SC. We have experience with various types of impeller designs, multiple impeller arrangements, and VFD speed controllers to maximize mixing and chemical efficiency. Our experience includes designs of new efficient sedimentation basins and rehabilitation of existing basins. We have incorporated tube settlers and plate settlers in our designs. Our engineers pay particular attention to equal flow distribution throughout all basins via computer models to avoid maldistribution and short circuiting.

Continuous Sludge Collection Systems -Cornwell Engineering Group has designed continuous sludge collection systems in new and existing facilities including for the Charlotte-Mecklenburg Utility Department; the City of Durham, NC; Camden, SC; and several utilities in Virginia. Regardless of the project complexity, we have experienced personnel to develop a cost effective sludge collection system.

  • Filtration -Our design team has designed filter upgrades for the City of Durham including new media, underdrains, controls, and air scour backwash. For the City of Camden, SC, our design included deep bed filters for future GAC, air scour backwash, and filter controls communication with a central SCADA system. We also completed an extensive filter improvement study for the City of Henderson, NC which resulted in the highest approved filtration rate in North Carolina. Typically our filter designs include special features such as influent control weirs, constant level controls, effluent particle counters, and hydraulic constraints to prevent filters from draining.
  • Aqua Ammonia Feed -Cornwell Engineering Group has been designing ammonia feed facilities for water utilities since 1986. For the City of Chesapeake, VA we designed a facility for 9-mgd production. For a 46-mgd water treatment plant in Virginia, we completed an ammonia storage and facility consisting of two 8,000-gal storage tanks, four feed pumps, multiple chemical diffusor and mixing points, instrumentation, and SCADA screens for various operational modes. We also designed an ammonia storage and feed system for a 6-mgd water treatment plant in Camden, SC and performed preliminary design for 150- and 240- mgd water plants in Washington, DC operated by the Corps of Engineers.
  • Chlorine Storage and Feed -Our staff designed several chlorine feed facilities operating in conjunction with ammonia feed systems. For the Appomattox River Water and Sewer Authority in Petersburg, VA we designed a new chlorine gas system with four 2,000-lb/d chlorinators. For the City of Camden, SC we designed a 1,000- lb/d chlorine storage and feed system. We also designed a chlorine scrubber system for the City of Durham, NC at a 30-mgd water treatment plant.
  • Sodium Hypochlorite -After completing six sodium hypochlorite designs, our staff is experienced with the design considerations associated with these projects. We have visited numerous facilities and collected extensive operational data from other utilities that have had good and bad experiences with this chemical. For example, Cornwell Engineering Group designed stage of a sodium hypochlorite storage and feed system for a 22-mgd plant operated by the City of Durham, NC.
  • Miscellaneous Chemical Feed -Cornwell Engineering Group has designed every type of chemical feed system employed by water treatment plants. Our staff is experienced with pumping difficult chemicals such as powdered activated carbon, hydrated lime slurries, polymers, and corrosion inhibitors. We have previously used all types of pumps for chemical feed including diaphragm, peristaltic, progressive cavity, rotary lobe, centrifugal, and plunger. We have also used eductors and carrier water for slurry feed systems. All our designs focus on safety, ease of operation, low maintenance, and reliability.
  • High Service Pumping -Cornwell personnel have completed numerous pump station designs including the use of vertical turbine and split case centrifugal pumps, with and without variable frequency drives. These projects have included related appurtenances including piping, valves, controls, power, and integration with existing SCADA systems. Cornwell personnel have often employed the use of skid-mounted pump systems and modular, prefabricated buildings to minimize construction and start-up time.

In addition to new facilities, Cornwell personnel have been responsible for the modifications to existing structures, pump well cleaning and rehabilitation, intake evaluations, chemical feed systems, and pump troubleshooting.

VFD Design -Cornwell Engineering Group has successfully completed design, construction assistance, and startup assistance for numerous variable frequency drive projects over the past five years. Our experience includes both water and wastewater facilities with sizes ranging from <50 HP to more than 1,000 HP and flows ranging from <0.1 mgd to >10 mgd and includes both low and median voltage drives. A partial listing of recent projects includes: Danville, Virginia

2 @ 90 HP, 480v; 2 @ 700 HP, 480v

Henderson, North Carolina

2 @ 1,000 HP, 4,160v; 2 @ 400 HP, 480v

Niagara Fall, New York

3 @ 1,500 HP, 4,160v; 3 @ 400 HP, 4,160v

Village of Blasdell, New York

2 @ 100 HP, 480v

The Danville project included extensive electrical modifications including transforming the voltage to the high service pump station from 2,300 v to 480v to reduce VFD costs, simplify maintenance and improve the availability of spare parts. All work was complete while maintaining facility operations.

Clearwells -Cornwell staff has experience with conventional cast-in-place concrete tanks and prestressed concrete tanks. In Camden, SC we designed a 1.3-MG prestressed clearwell and 300,000-gal chlorine contact tank. In Fayetteville, NC we completed a major rehabilitation project for a 12-MG clearwell. For the City of Durham, NC, we performed the rehabilitation and baffling for two 1.0-MG clearwells. Clearwell rehabilitation projects have included HDPE membrane liners, urethane coatings, expansion joint repairs, crack repairs, and baffling improvements.

SCADA -We have successfully designed several state-of-the-art SCADA systems utilizing the latest software available for water utilities. Our designs include design of field devices, PLC’s, development of SCADA screens, and computer logic for chemical feed control. Our staff works extensively with the utility’s engineering and operational staffs to develop computer screens that are operator friendly. Many of our designs also include capabilities to view the SCADA screens and plant performance remotely from the utility’s main offices. SCADA systems designed by Cornwell Engineering Group include:

  • Erie County Water Authority, NY
  • City of Camden, SC
  • Rivanna Water and Sewer Authority, VA
  • Roosevelt Roads Water Treatment Plant, Puerto Rico