Whitehouse, Tyler, Whitehouse

Tyler Whitehouse works for Carollo Engineers and has 15 years of experience performing civil and mechanical planning and design, constructability and...

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About Whitehouse, Tyler

Tyler Whitehouse works for Carollo Engineers and has 15 years of experience performing civil and mechanical planning and design, constructability and design review, and construction services for water and wastewater pumping projects across the U.S. He actively participates in improvements to the Hydraulic Institute standards and currently serves on the 9.6.6 Pump Piping Committee. Tyler enjoys camping with family, golfing, fishing, and cheering his alma mater on, Go Cougs!

Whitehouse, Tyler

Titles from this speaker

Designing a Pump Station Replacement within Tsunami and Sea Level Influenced Zone

Abstract

Purpose: The purpose of this presentation is to provide the attendees with planning and design criteria and solutions when dealing with the design of a sewer lift station within a tsunami and sea level rise impact zone. Background: The City of Bellingham is located approximately 100 miles north of the City of Seattle in Washington State, 20 miles from the Canadian border. The city's Roeder Lift Station is located near the industrial area along Bellingham Bay and serves much of the northern part of the city. The existing lift station was suspected to be operating under reduced reliability conditions during peak storm events. The city contracted with Carollo Engineers to complete an alternatives analysis and design to increase the existing lift station's pumping capacity from approximately 8 million gallons per day (mgd) to 18 mgd. The existing dry-pit/wet-pit station is located on a small city-owned parcel of land surrounded by Port of Bellingham (Port) and Burlington Northern Santa Fe (BNSF) railroad properties. The station's existing 18-inch diameter force main is routed through a city utility easement on Port and BNSF properties including crossing under a BNSF spur track to reach the discharge manhole location. Two lift station retrofit alternatives and one new submersible lift station alternative were evaluated, including installation of a parallel force main alternative. The selected alternative included a new submersible lift station 1,100 feet north of its current location. The lift station design included a combination of variable speed driven non-clog submersible pumps and screw centrifugal pumps in self-cleaning pre-rotation basins with a pumping range of 1 to 18 mgd. Other improvements included 2,500 lineal feet of parallel 14-inch and 28-inch diameter HDPE force mains with trenchless installation beneath the railroad, installation of a 36-inch diameter PVC gravity sewer main and manholes, and miscellaneous 24-inch diameter HDPE water main replacement. Design Challenges: During the planning and design of the sewer lift station replacement, several design challenges came to light. These included the limited property owned by the city and the lack of a viable location near the existing station, the presence of a creek just west of the proposed station location, and issues related to the stations location near Bellingham Bay including tsunami and seal level rise impacts. The first challenge encountered by the design team was the lack of city-owned property near the existing station. Two of the replacement alternatives included retrofitting the existing station infrastructure while a third alternative included constructing a new adjacent station. The lack of property available to the city required relocating the proposed lift station. Further validating the need to relocate the station was the presence of Squalicum Creek approximately 2,000 feet upstream of the proposed station location. The existing gravity sewer crosses the creek before entering the station and the top of the pipe is exposed in the creek bed. The city has future plans to improve the creek which would require lowering the sewer line. An analysis was completed to look at installation of a deeper gravity sewer or installation of an inverted siphon. The two challenges having the greatest impact on the design of the new sewer lift station were sea level rise and tsunami impacts. Based on FEMA mapping, the location of the new lift station is within the 100-year flood plain. The potential impact of flooding became painfully apparent during November 2021 when a major rain event caused significant flooding at the proposed lift station site. Adding to the challenge, the FEMA flood maps do not take into consideration future long-term change due to climate change and the rising sea level. Sea level rise predictions for our project area ranged from 1.1 to 11.7 feet above the base flood elevation. Through multiple modeling efforts the design team settled on a sea level rise impact of 1.5 meters and a 100-year storm event to set the initial water surface elevation used for design. The final challenge impacting the design of the replacement lift station was the fact that the new site was located within the Tsunami Design Zone. With the State's adoption of the International Building Code, we were required to use the Washington Tsunami Design Zone Map to determine whether Risk Category III or IV structures needed to be designed for tsunamis. The tsunami inundation elevation at the project site was identified as 21 feet based on mapping. Ultimately, the impacts related to tsunami inundation controlled the site design and the new station was elevated 9 feet above the existing grade. Status and Conclusions The project was bid for construction in April of 2023 with an engineer's estimate of $18 million including tax. The city received four bids ranging from a low bid of $17.5 million to $21 million. The project is currently under construction with an estimated completion date of Spring 2026. The design of the replacement sewer lift station was impacted by multiple surrounding water bodies which lead to many lessons learned throughout the design. Scour within Squalicum Creek caused exposure of the existing gravity sewer line. Future improvements to the creek impacted the depth of the future sewer upgrade requiring a deeper lift station wet well. This factor required construction of a new lift station and would not allow retrofit of the existing station. The location of the new lift station site and its proximity to Bellingham Bay caused the need to design for sea level and tsunami impact zones. Lessons that were learned during the design included understanding that FEMA flood plain mapping does not take sea level rise into account and that tsunami inundation can have a more significant impact on the final grade of the proposed site. Additionally, the design of the on-site structures themselves relative to the thickness and strength of the structure walls can be affected by the potential for tsunami impact loads. Finally, construction in a historically intertidal zone overlaid by fill required ground improvement design to stabilize the soils before construction could begin.

This paper was presented at the WEF Collection Systems and Stormwater Conference, April 9-12, 2024.

SpeakerWaligorski, Erik

Presentation time

16:15:00

16:45:00

Session time

15:45:00

16:45:00

SessionTidal and Sea Level Rise Impact

Session number11

Session locationConnecticut Convention Center, Hartford, Connecticut

TopicClimate Change Adaptation, Design Storm, Lift Station, Modeling, Resiliency, Sea Level Rise, Stormwater Case Study/Application, Stormwater Management Design And Analysis, Tsunami, Wet Weather

Author(s)

Waligorski, Erik

Author(s)E. Waligorski1, T. Whitehouse1

Author affiliation(s)Carollo Engineers 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Apr 2024

DOI10.2175/193864718825159353

Volume / Issue

Content sourceCollection Systems and Stormwater Conference

Word count13

Description: Installing A Wastewater Pump Station Over An Artesian Groundwater Aquifer With A...

Installing A Wastewater Pump Station Over An Artesian Groundwater Aquifer With A Piezometric Water Head 19ft Above Ground Surface

Abstract

BACKGROUND
Lakehaven Water and Sewer District is located between Seattle and Tacoma in King and Pierce Counties, Washington. The District spans an area of 35 square miles over several small cities including the majority of the City of Federal Way and serves a population of approximately 112,000 people. The District provides water and sewer services, including approximately 350 miles of sewer mainline, 27 pump stations, and two water resource recovery facilities. This project includes the design and construction of a new 9.3 mgd submersible pump station (PS 33B) located on a constrained site surrounded by wetlands, a stream, and challenging subsurface conditions. The new pump station replaces an aged and at-capacity existing wastewater collection system pump station PS33A located approximately 500 feet away. This presentation highlights the unique design and construction elements, including lessons learned, of installing a large collection system pump station on a small site with unsuitable materials, artesian aquifers, and adjacent stream and wetlands.
DESIGN ELEMENTS
The project site for the new pump station is an approximate 95-foot wide by 100-foot long parcel located at the south edge of a busy residential roadway bordered by Hylebos Creek and wetlands to the east and wetlands to the west. Major design components located on the pump station site include a building with separate electrical room, restroom, and generator room, an aboveground diesel fuel tank, a skid-mounted odor control system, electrical transformer, influent sewer manhole, wet well, valve vault, flow meter vault, and ancillary components. The pump station capacity will be provided in two phases. Initially, the pump station will have a capacity of 2.4 mgd and will discharge through the existing 10-inch diameter force main. Ultimately, this pump station will be expanded to a capacity of 9.3 mgd and include 4 total (3 duty, 1 standby) 3.1 mgd pumps. To facilitate this expansion, approximately 9,000 lineal feet of parallel 14-inch and 18-inch diameter force mains will be installed to a new discharge location in the gravity sewer system.
Nine geotechnical borings were performed at the site and identified three different pressurized aquifers within 40 feet of existing grade. The lower aquifer is a significant artesian aquifer encountered at 37 feet below grade. This confined aquifer is known by local hydrogeologists as the Redondo Milton Channel (RMC) and creates a water head extending 19 feet above ground surface if punctured. The subsurface soils from 0 to 30 feet depth include a slightly pressurized middle aquifer followed by an upper aquifer with groundwater at grade. It was also determined that the top 7 feet of soil at the project site were structurally unsuitable and would need to be replaced. In addition, the sloped site topography requires the site to be built up and level, and contained within a 6-foot tall reinforced interlocking block wall around the site perimeter. The most critical design challenge was maintaining global stability of the site by ensuring that the lower aquifer would be protected and not punctured during all phases of construction of the new improvements. Design requirements implemented to protect the lower aquifer included: - Limiting open excavation volumes during removal and replacement of unsuitable soils. - Adding temporary fill to the site extending two feet above proposed grade during installation of the wet well. - Installing the wet well via a 28-step sink-in-place caisson method that included dewatering two upper aquifers, maintaining high water levels inside the caisson, and diver assistance. The installation maintained a minimum design safety factor of 1.5 against puncture of the lower aquifer. Refer to Figure 1.
,b>CONSTRUCTION AND LESSONS LEARNED
Successful installation of the 21-foot deep sink-in-place caisson took approximately 8 weeks, three weeks longer than planned. Challenges and lessons learned along the way included: - Progress of the caisson slowed to four to six inches per day as the caisson reached within two feet of its finished elevation. The pilot holes predrilled along the perimeter walls that were backfilled with pea gravel to facilitate sinking could have been drilled deeper for more efficient sinking production at the final stages. In addition, steel sheets could have been driven on the outside walls simultaneously with the sinking to reduce the amount of material sloughing into the caisson, which also slowed sinking progress. - A water level (higher than the level of groundwater outside the caisson) was maintained inside the caisson during the sinking to add weight as soil was removed to maintain the design safety factor above the lower aquifer. Maintaining this water level proved to be more difficult and required much more water than anticipated. At one stage of caisson sinking, a nearby fire hydrant was required to supply water to the inside of the caisson at a rate up to 100 gpm. To keep water from escaping the project site and eroding the adjacent wetland and stream, a 2-inch and 3-inch submersible pump recirculated water back to the caisson from the upper aquifer at approximately 40 gpm and 225 gpm, respectively. Refer to Figure 2. - Once the caisson was sunk and prepped for sealing with the underwater concrete mud slab, the wood two-by-fours that protected the PVC waterstop in the perimeter of caisson walls had to be removed by the divers; a task planned to be completed in a couple hours. However, since the wood had been underwater for the last six weeks, it had swelled and took the divers over three weeks to chip out. A non-expanding formwork material could have been used or an alternative chamfer design at the waterstop would have facilitated easier removal of the formwork underwater. Refer to Figure 3. The above challenges and lessons learned were specific details that occurred at key stages of the caisson installation. Prior to construction, a pre-installation meeting was held with all involved parties to review the complete caisson installation process. However, the main lesson learned is that for unique, uncommon construction methods such as this, meetings should be held prior to each key stage of installation so the finer details can be discussed, questioned, and hopefully resolved ahead of time.

This paper highlights the unique design and construction elements, including lessons learned, of installing a large wastewater collection system pump station on a small site with unsuitable materials, artesian aquifers, and adjacent to a stream and wetlands. The pump station station's wet well was successfully installed via a 28-step sink-in-place caisson method that included dewatering two upper aquifers, maintaining high water levels inside the caisson, and diver assistance.

SpeakerWhitehouse, Tyler

Presentation time

13:30:00

13:55:00

Session time

13:30:00

15:00:00

TopicIntermediate Level, Collection Systems

Author(s)

Whitehouse, Tyler

Author(s)Tyler Whitehouse1

Author affiliation(s)Carollo Engineers, Seattle, WA1