Pressure-reducing station solves the problem at a fraction of the time and cost.
HRSD, the regional wastewater treatment utility that serves 18 cities and counties in southeast Virginia, had been experiencing high-pressures in their Williamsburg area force main network during wet weather events. These high pressure events caused operational trouble and, on occasion, resulted in SSOs in the collection system. Since the Regional Wet Weather Management Plan (RWWMP) of HRSD’s Federal Consent Decree to address these SSO issues was still years from finalization, HRSD staff studied the problem to come up with options to mitigate the issue. One option studied was to completely revamp and upgrade a number of pump stations with new pumps, piping and the necessary control equipment to address increased flow and pressures. Another option considered was to install a pressure reducing station (PRS) along the sewer force main system to reduce system pressures and thus increase capacity. After many options were considered, the preferred and the most cost-effective solution that could address the situation was an interim PRS. After HRSD’s procurement staff found the necessary purchasing mechanism to move forward with the solution, the local Xylem branch offered their support and assistance with the design, action plan, purchase, and equipment coordination.
HRSD developed a plan to integrate a pressure-reducing station (PRS) at a strategic location along the force main. Given HRSD’s dedication to regulatory compliance and environmental stewardship, and the need to align with long-term planned upgrades in their network, the new pressure- reducing station was designed and implemented with the Godwin Dri-Prime Backup System (DBS). The Godwin DBS offered pumping equipment to provide additional capacity to handle wet weather flows and pressures and to minimize issues with sanitary sewer overflows (SSOs) during these events.
The short-term need was to get the PRS on-line as soon as possible, on Route 199 near Colonial Williamsburg. The HRSD design engineer provided design specifications to the Xylem team, and Xylem recommended two Godwin diesel-driven, critically silenced CD500M pumps with Final Tier 4 low-emission engines. The fuel supply was provided by two Godwin 250 gallon diesel fuel cubes with double-wall containment to ensure environmental safety. Given the historic sensitivities of neighboring Colonial Williamsburg, the pumps and fuel cubes were also customized to a specific color (Weathered Bark) to comply with County requirements.
Xylem engineers customized the Godwin Advanced PrimeGuard Controller to tie into the HRSD supervisory control and data acquisition (SCADA) system, to activate and control the pumps via local pressure readings. The Xylem team engineered a solution for HRSD that allowed the Godwin DBS pump to automatically maintain a specific designed suction pressure setting by ramping the diesel engine up and down based on measured suction pressure levels. At the end of a wet weather event, the controller would ramp down the RPM’s and stop the DBS pumps.
Based on additional requirements of the procurement conditions from HRSD, the Xylem team customized the pump controls so they could be accessed in three different ways:
Automatic: Pumps turned on/off via pre-set parameters (pressure, flow, or level) with the Advanced PrimeGuard Controller.
Manual: Pumps operated manually on-site, via the Advanced PrimeGuard Controller.
Pass Thru: Pumps operated remotely via the HRSD SCADA system, which was tied in to the Godwin Advanced PrimeGuard Controller.
This future remote control ability will be invaluable during extreme weather events – whether it’s a hurricane or severe snow/ice conditions – when roads are oftentimes closed by local or state authorities, making access to the PRS site impossible. However infrequent these events might be, HRSD considered the Pass Thru capability to be critical as a way to address these specific scenarios.
Additional customized components of Xylem’s unique solution for the Williamsburg PRS included a junction box, to provide access to electrical controls as needed, and an interior work light and exterior working lights at the suction inlets for emergency/night work. In order to ensure remote access to the pump controls even during a long-term power outage event, the system was outfitted with a power inverter, to recharge the remote SCADA controller batteries. Given the possibility for cold weather in their Virginia locale, HRSD required the system to be weatherized. Xylem outfitted the pumps with block heaters and a battery trickle-charger, and the suction lines were set up to drain with pump shut-off.
HRSD also equipped the suction and discharge pipes with heat cables and wrapped them with insulation. Xylem completed delivery of the equipment, and assisted in installation and testing of the project, which included technical and manpower support to the HRSD operations team during the installation and testing process. Xylem also hired and managed the crane service to unload and lower the pumps into position onto the HRSD-constructed concrete pads.
To extend the life of the pumps and to ensure maximum equipment uptime, HRSD technicians are onsite weekly, servicing the pumps to ensure operational readiness should wet weather conditions occur.
Editor's Note: Scranton Gillette Communications and the SGC Water Group are not liable for the accuracy, efficacy and validity of the claims made in this piece. The views expressed in this content do not reflect the position of the editorial teams of Water & Wastes Digest, Water Quality Products and Storm Water Solutions.