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WestLand Resources was selected by Pima County Regional Wastewater Reclamation Department (PCRWRD) to complete upgrades to their largest sewer pump station, the Continental Ranch Regional Pump Station (CRRPS). The original design was completed in the late 80’s and the pump station was put into operation in the 90’s. The pump station consists of a three story building that houses the electrical and controls, the sewer pumps which were shaft driven pumps with the motors on the top floor and the pumps on the bottom floor. Over the years the pump station had problems with pumps clogging, problems with the sewer pigging set up and deterioration in the wet well room. In addition, the pump station did not meet current NFPA 820 codes for a sewer pump station. The pump station has one discharge force main that runs 7-miles to the Tres Rios WRF where it discharges. Future plans called for a second force main. RWRD had WestLand perform an analysis for the upgrades needed and then provide a prioritized report of repairs/upgrades and associated costs. In the end RWRD decided to make all the upgrades.
One initial challenge for the design was that the upgrades had to be done within the existing footprint and connect to existing piping and structures. To help with the design, the entire pump station was scanned with lidar providing a 3-dimensional model to use for a base. This allowed us to see where items and structures were on each floor which was vital as part of the NFPA 820 upgrades were that forced air was needed coming in and leaving the pump station so several new HVAC ducts were needed to run from the roof to the bottom floor.
An issue with the current design were the pumps as they continuously clogged due to the lack of ability to pass solids larger than 1.25”. The motors for the pumps were located on the main floor next to the operators room which made it very loud and a hazard. New dry-pit submersibles were installed to remove the motors and shafts from the top floor and middle floor and opened up area for access and removed the noise hazard for the main floor.
The existing carbon scrubber for odor was equipped with larger blower motors which provided enough capacity to create a negative air pressure in the wet well room which in turn degraded the rating of the other rooms per the NFPA 820 code.
The current pump station met the Arizona Administrative Code (AAC) for redundant power because two substations fed it. RWRD wanted generator back-up and wanted a set up for a bypass system so that they could bring pumps in and hook them up quickly. Due to the cost of back-up generation for pumps of the size at the station (400 HP) the cost would be approximately 1 million. To solve both issues, WestLand designed a permanent bypass pump station that would activate automatically when the main pumps failed.
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