Blending new technology with existing architecture
Rick Lang, Director of Public Services, City of Allen Park, Michigan
Bill Prevo, Project Manager, Wade Trim, Livonia, Michigan
No one really thought the pumping station would attract much attention when discussions of building it started in the early 1980s. It was expected to work quietly in the background like plumbing or electricity. The concept was pretty simple—pump sanitary flows to keep the sewers operating smoothly and pump extra flows generated by heavy rains into a storage basin so residents' basements wouldn't flood.
The Wayne County Drain Commissioner was undertaking a major pollution control project with four communities in the Ecorse Creek Watershed. The Allen Park pumping station and storage basin facility was one of three facilities designed to keep sewage out of basements and rivers when the sewer system experienced high levels of inflow and infiltration during wet weather. As design progressed, the Allen Park facility attracted more and more public attention as residents resisted spending money to fix the problem. It soon became clear that it would be years before the facility operated silently in the background.
|Facility repairs were undertaken while preserving the bold look of the screw pumps featured in the original, award-winning design (photo shows original construction).|
The idea to create a facility that showcased its engineering strength came during a visit to the pump manufacturer's facility in the Boston area. The facility manufactured enclosed screw pumps, the preferred sanitary pump at the time for a high range of variable flows due to its operational efficiency. The aura of strength created by these pumps was evident during the visit. Large in stature, screw pumps are bold and can't be discretely slipped into a facility. Using screw pumps in the design would make a statement, particularly with the project's prominent location along an interstate.
Conceived on a restaurant napkin, the final design embraced four bright red screw pumps as the central focus of the facility. The 41-foot pumps thrust upward from the wetwell through the glass and aluminum face of the angled, concrete superstructure. The pumping station commands attention and has received plenty of it during the past 25 years. In addition to becoming a local landmark for drivers along I-75, the project was recognized with two architectural and two engineering design awards.
In 2006, pumps started showing signs of their age and the City of Allen Park had to decide whether or not to preserve the station's appearance when undertaking the needed repairs. The decision turned out to be fairly easy—even though the pumps were failing functionally, their visual appeal was still strong. The City decided that the new pumping and instrument and control technology should be architecturally friendly and bring the facility up to current standards.
A thorough evaluation of the 7,200-gpm pumps was performed. Each pump had been designed to pump 2-12 cfs dry-weather flow and up to 50 cfs wet-weather flow. Three pumps were needed to operate the facility with the fourth pump designated as a standby pump. During the evaluation, engineers identified problems with three of the four screw pumps. One pump wouldn't function as a result of pump tube structural failure and bearing damage. Two other pumps showed significant leakage near the bottom bearing and were structurally fatigued; failure was imminent in the near future.
|Five new immersible pumps restored facility capacity and improved operational reliability.|
Keeping the pump station operational during design was critical, particularly since only three pumps were working and two were on the brink of failure. A design-build approach was selected to keep the project on a fast-track. The improvements rapidly introduced a variety of new technologies to the pump station and basin operations fundamentally improving the 25-year-old facility.
Selecting new pumps to blend in with the existing retention facility components and building architecture was a challenge. The brightly painted screw pumps needed to be abandoned but left in place to preserve the architectural appearance. The immersible Hidrostal pump, a new pump technology that uses a screw centrifugal impeller and an immersible motor, was selected. These pumps can operate with as little as 18 inches of influent flow. Five 5,400-gpm Hidrostal pumps, including one for standby, were needed to restore capacity at the facility and meet MDEQ requirements. Popular submersible pumps were evaluated but could not be used due to the lack of depth of the wetwell and invert of the inlet.
|HDPE piping was used because it was cost-effective and easier to install and obtain.|
Another new technology was used in the discharge piping. Normal ductile iron pipe is heavy and hard to work with. High-density polyethylene (HDPE) piping was selected instead because it could be easily installed reducing labor and overall procurement costs. HDPE piping also has a shorter lead time that helped meet the aggressive schedule.
The instrumentation and control system was upgraded to allow for automatic operation of the pumps. New ultrasonic level transducers were installed in the wetwell with new electrical Motor Control Center (MCC) buckets powering each pump. The existing MCC was retrofitted with buckets that fit directly into the MCC. A new Allen-Bradley Programmable Logic Controller (PLC) was installed in a control panel that was mounted on the Main Control Panel (MCP) to allow existing control wiring from the MCC to the MCP to be used. This reduced new conduit and wiring costs on the project. The Allen-Bradley control panel was fitted with a touch-control screen allowing the operators to control the pumps and affiliated discharge valves from the panel in sight of the wetwell.
Technology was taken to the next level with a Human Machine Interface (HMI) control and monitoring system. HMI allows the facility to be remotely operated by an individual or through automated software commands. WonderWare software, a non-proprietary off-the-shelf software package that many local integrators are familiar with, was chosen. The new control and monitoring system has automatic control strategies that have operator-entered set points. These control strategies allow the facility to operate 24/7 during storm events without being manned providing additional operational cost reductions.
|Operations were maintained during installation of the new pumps.|
The sequence of construction allowed for two new pumps to be installed while the existing screw pumps remained in operation. Keeping the facility operational during the construction phase was imperative to avoid backups and illicit discharges. A temporary submersible pump was also installed to allow bypass pumping during the entire construction phase-over process. Temporary piping was installed to allow the temporary pump to back up the existing screw pumps during the construction period, until the new pumps were placed in service. While two screw pumps did fail during construction, operations were not impacted.
The second phase of the project is being undertaken to complete improvements that weren't critical to pump operations. This work focuses on the basin and includes upgrades to the chemical feed system, replacement of the dewatering valve and actuator, replacement of the basin supply fans, and security additions.
New technology was implemented throughout this project to overhaul pump operations. Allen Park's DPW staff sleeps a little more soundly at night knowing the system will perform when an early morning storm hits. Operational costs are also going down providing funds for other public works efforts. The facility's facelift provided tangible benefits to the City without altering the local landscape.
Rick Lang has 37 years of experience working on municipal public works projects and can be reached at (313) 928-4134 or firstname.lastname@example.org. Bill Prevo has 21 years of experience managing construction, startup, testing and maintenance services for wastewater projects. He can be reached at (734) 432-3100 or email@example.com.