The following projects have progressed over the months of November:

• Clearwell & Backwash Pump Station - CH Nickerson continued backfilling around the Clearwell and assembling precast wall panels for the Pump Station structure, as well as other site and piping work.

• WPF Staff successfully shutdown and restarted the Rapid Sand Filters to allow CH Nickerson to tie into a 48-inch effluent line with a cross and four valves.

The new Clearwell and Backwash Pump Station will replace the existing clearwell and backwash, domestic, and process water pumps. The existing clearwell was originally constructed as a slow sand filter in the 1920's and the roof leaked into the clearwell until we installed the temporary tarp cover. Failure of this clearwell would require the Rapid Sand Filter Plant to be shut down entirely. The existing backwash pumps were installed in the 1970's with the construction of the Rapid Sand Filter Plant and need to be replaced. Parts for these pumps are no longer available should they require repair. This new Clearwell and Backwash Pump Station structure will provide the reliability and redundancy needed for the water treatment process and is the first component of the new water treatment plant.

Rapid Sand Filter Shutdown

CH Nickerson's next step for the Clearwell & Backwash Pump Station project is to install the new piping that will connect the existing Rapid Sand Filters (RSFs) to the new Clearwell and to the new Hydraulic Control Structure. Shown in the figure below, water from the Rapid Sand Filters flows to the existing Clearwell and then out to the system. New piping will direct water from the Rapid Sand Filters to split in two directions to go to the new Clearwell for backwash water storage and to the Hydraulic Control Structure to be sent out to the transmission mains and ultimately to the distribution system. The existing Clearwell will then be disconnected from the system and eventually demolished.

Sketch of Rapid Sand Filters, existing Clearwell, new Clearwell, and associated piping

(by SWSC)

To make the necessary tie-in to the RSF effluent line, the Contractor needed to cut into and install a pipe cross and four valves (pictured below). To be able to cut the effluent line, which is normally always flowing, it first had to be isolated and emptied. This required the rapid sand filters to be shut down and the Clearwell to be drained. The slow sand filters were brought online to maintain our flow of drinking water to the system.

48-inch cross assembly waiting to be installed (photo by AECOM)

The Clearwell normally provides water for carrying disinfection and corrosion control chemicals (chlorine, phosphoric acid, and sodium hydroxide) to the filtered water. Our operators constructed temporary chemical feed systems to continue to dose these chemicals directly into filtered water leaving the slow sand filters.

These temporary chemical systems require refilling every 12 hours. Operators and labor staff filled the chemical systems by raising a tote with a skid-steer and feeding chemical through a flexible hose into the tank.

To transfer the chemicals safely, the Commission's safety and operations staff worked together to develop an SOP and JHA, and gather the PPE needed to keep everyone safe.

Temporary chemical feed systems designed and constructed by Pete Thayer, Alex Roseweir, and Chris Hanechak

(photo by SWSC)

Pete Thayer, Mike Popko, Kristin Monfette, and Dan Candido practicing a chemical transfer with water

(photo by SWSC)

Kristin Monfette and Dan Candido with the portable safety showers that arrived just in time (photo by SWSC)

Transferring chemicals into temporary systems (photo by SWSC)

The Domestic Water Vault, which provides drinking water at the plant, is also fed from the Clearwell. With the Clearwell down, a bulk water hauler transferred water from our transmission mains into the vault. We monitored the system and added chlorine as needed to maintain a good residual. Field Services provided pallets of bottled water for staff to use as well, to help reduce the demand for water from the vault and as a back-up water supply.

Bulk Water Tanker Truck

(photo by SWSC)

Bottled water for on-site staff

(photo by SWSC)

While Commission staff prepared on our end, the Contractor worked to excavate the 48-inch steel effluent line and have it ready for the tie-in.

Excavating the 48-inch Effluent (photo by SWSC)

To shut down the Rapid Sand Filters, each filter had to be backwashed (cleaned) first. After each filter was clean, the influent and effluent valves were all shut. Each valve was locked out for the contractor's safety. The chemical piping systems were flushed and emptied so that they didn't freeze while shut down.

Chris Hanechak closes a filter effluent valve

(photo by SWSC)

Senior Operator Pete Wilson, Steve Hicks, and Kevin Zeneski backwash remaining filter

(photo by SWSC)

The Clearwell was drained by opening an effluent valve that had not been operated since 1974. The valve opened right up! To drain the Clearwell as quickly as possible, pumps were also used to pump water out of the structure. It took less than four hours to drain approximately 1.5 million gallons of water. Once the water was drained below the 48-inch outlet, the contractor was able to safely begin their work without the risk of water flooding back into the pipe.

Dan Deery monitors Clearwell level

(photo by SWSC)

Pumps used to help drain Clearwell

(photo by SWSC)

48-inch outlet into the Clearwell (photos by SWSC and AECOM)

Once the Clearwell was adequately drained, the contractor began cutting through the 48-inch steel pipe. The pipe was 1-inch thick steel with a cement lining and was difficult to cut, requiring a combined effort of saws and torches. It took the contractor about 16 hours (across two days) to cut through the thick pipe, drain the water inside, and install the cross.

Contractor cutting the 48-inch steel pipe

(photo by SWSC)

Pipe segment pulled out of the trench (photo by SWSC)

Lowering the cross assembly in with a crane (drone photo by SWSC)

Installing cross assembly (photo by SWSC)

Once the cross was installed, staff restarted the Rapid Sand Filters and re-acclimated and restored normal service. Operations and labor staff worked hard to stabilize the filters and the chemical feed systems and were able to get the plant running normally before Thanksgiving.

Thank you!

This shutdown was a team effort that could not have been accomplished without each person in Water Operations and many others throughout the Commission stepping up and contributing. Thank you to our Water Operations staff for putting in long hours, and to all of the staff across the Commission who put in the extra effort to support us. Because of your hard work, we were able to continue to accomplish our mission to provide a clean, uninterrupted supply of drinking water to our 250,000 customers.

Commission group photo, September 2022

(drone photo by SWSC)

Men and dog pose behind survey equipment during construction of the water supply system, 1909