Opportunity
In 1559, a Spanish settlement near what is now Pensacola was wiped out by a hurricane only a few months after it was founded. The low-lying Pensacola region continues to be vulnerable to severe weather, which demands extremely resilient public utilities.
In 2004, Hurricane Ivan struck Florida, where it caused heavy infrastructure, building, and utility damage and killed 14 people. About a quarter of a mile of the Escambia Bay Bridge in Pensacola collapsed into the bay, and a 15-foot storm surge severely damaged the Main Street Wastewater Treatment Plant, which was built in 1937.
The treatment plant was out of service for three days, prompting discussion of the need to relocate the plant to avoid future outages and environmental damage. The Emerald Coast Utilities Authority (ECUA) received grant money from FEMA for the purpose.
Solution
Beginning in 2002, two years before Hurricane Ivan, Mott MacDonald has provided the ECUA with essential services for making the area’s wastewater treatment system more resilient to damage and outages from storm surges and other extreme weather events.
From 2002 to 2010, Mott MacDonald was responsible for the design, permitting, public bid, and construction administration for the entire project to rehabilitate Lift Station No. 4, an existing regional pump station, and also supported the relocation of the Main Street wastewater facility. Our wastewater services supported the development of a new 22.5 million gallon per day (MGD) process facility. We provided land surveying, design, construction documents, regulatory permitting, and contractor prequalification services.
As a result of these successful collaborations, the ECUA tasked Mott MacDonald to design its three master pump stations — a critical part of the renovated wastewater system for the Pensacola region.
From 2007 to 2010, we provided services including planning, hydraulic analysis, equipment evaluation and selection, design (civil, process mechanical, structural, electrical, and architectural), construction administration, and startup services.
The project included the design of the following three master pump stations:
Government Street Regional Lift Station
As part of the project to relocate the Main Street treatment plant, located in the heart of the downtown historic district, the existing plant was converted into a lift station that pumps wastewater 23 miles north to a new treatment facility.
The pump station has a capacity of 25 million gallons per day (MGD) and features four 500-horsepower submersible pumps, a dual cell wetwell, dual comminutors, dual odour control system, multi-track monorail hoist, protective liners, and dual emergency generators.
Lift Station A (aka Pipeline Road Lift Station)
The head required to pump wastewater the entire distance from downtown to the new treatment plant was beyond the ability of single-stage pumps. Regional Lift Station A was planned in lieu of operating a high-pressure pumping and force main system.
The pump station has a capacity of 38 MGD, with four dry-pit vertical pumps totalling 2,400 horsepower. It features an odour control system with engineered media, variable frequency drive (VFD) operation for energy savings, radar-level sensor, dual emergency generators with dual fuel capability, and two aboveground concrete storage tanks with protective liners.
Lift Station B (aka Morino Road or Guillemard Road Lift Station)
All flows from a major wastewater collection basin had to be diverted and pumped to the new treatment plant. ECUA tasked Mott MacDonald to design Lift Station B in an older section of the city to capture and divert all flows from the affected area. Lift Station features a 1,600-horsepower submersible pump.
Unusual features
Our technical expertise provided the owner with significant advantages and innovations in operations and maintenance that are uncommon among wastewater pumping applications. These included the following:
- Use of HDPE-lined prestressed concrete storage tanks for storage of wastewater with very high levels of hydrogen sulfide (H2S).
- Use of gas phase H2S treatment ahead of engineered media scrubbers to extend the life expectancy of the media
- Use of the geometric shape of the wetwells to provide natural mixing and eliminate the need for mechanical mixers
- Use of the programmable logic controller (PLC) to maintain pumping within the optimum efficiency range for energy efficiency and reduce wear on the pumps
- Use of concrete additive to provide acid resistance to critical concrete structures
- Ability to generate power during peak times to save on energy costs
- Significant sound attenuation requirements, protecting workers and minimizing impact on nearby residents
Challenges
In the course of designing the three master pump stations, we met challenges including these:
- Difficult architectural requirements, including the design of a 5,000-square-foot control building to visually complement the surrounding historic district
- Difficult hydraulic requirements
- Owner-directed requirement for minimal maintenance
- 50-foot-deep excavation in an area with water table near ground surface
- High-amperage electric service entrance and power distribution
- Design of facilities to withstand a Category 5 wind load (189 mph)
- Placement of all equipment beyond reach of a Category 4 storm surge
- Placement of all electrical, motor control centre, and emergency generator equipment beyond reach of a Category 5 storm surge
Outcome
Safety
No recordable injuries were experienced during construction. Mott MacDonald’s design addressed numerous hazardous conditions and allowed safe operations.
Quality
The project received local and regional acclaim for outstanding architectural design and pumping systems design. Our design optimised energy efficiency, reduced wear on the pumps, extended the lifespan of the wastewater system, and helped ensure the system’s resilience in the face of extreme weather conditions. We minimised noise pollution during construction and ensured that facilities would be aesthetically compatible with their surroundings.
Schedule
Projects were accomplished ahead of schedule.
Budget
The project was part of an overall $330M capital programme, both of which were completed under budget.