Cofferdam in Casco Bay

Casco Bay (Lobsters) EXPANDED 

Debbie Reaney & Rick Sadler 

In the Fall of 2016 Maine was in the grips of a drought when a 4-inch storm delivered some temporary but much-needed relief to Portland's streams, wells, and reservoirs. 

Sadly, the storm effects delivered an unhealthy mixture of raw sewage, debris, and polluted runoff to Casco Bay in the form of nearly 69 million gallons (about 261,193,290 L) of stormwater. This nasty mixture flowed into Back Cove, Portland Harbor, and other local waterways as the storm exceeded the capacity of Portland's treatment plants. That is enough stormwater and untreated sewage to fill more than 100 Olympic-sized swimming pools, which, if lined up end to end, would stretch for nearly three miles. 

In the end, Portland reported that 318.4 million gallons (about 1,205,274,544 L) of combined sewage and stormwater overflowed into surrounding waters that October. Thankfully, the waters did not infiltrate sewer backups into area homes, businesses, and streets but it did contribute to Casco Bay pollution. Interestingly, close to 30 years ago, the city was regularly discharging 1.8 billion gallons (about 6,813,738,000 L) of sewage-tainted water into Portland's scenic and economically vital waterways. The 80 percent reduction of this practice over the years illustrates mega strides the city has made but is a reflection on the slow progress everywhere to fixing an underground infrastructure, built generations before environmental regulations were created. 

"This is a legacy problem. It started 100 to 150 years ago when they built the combined sewers," said Mike Riley, coordinator of the Maine Department of Environmental Protection's combined sewer overflow, or CSO (Combined Sewage Overflow), program. ("Millions of gallons of Portland sewage still overflowing into Casco Bay ...") "It took decades to get into this problem and it is going to take decades to get out." 

Compounding those challenges, Portland and coastal cities across the U.S. are trying to fix centuries-old problems while facing uncertainties over future sea level rise and other impacts from climate change. 

"I think Portland has made a considerable amount of progress and has made a considerable amount of investment to address the issue of combined sewer overflows and the treatment of waste," said Sean Mahoney, vice president and Maine director of the Conservation Law Foundation, which sued the cities of Portland and South Portland in 1989 to force federal and state regulators to crack down on the storm-related sewage overflows. 

"Interactive map: see where (and when) Portland's sewers are overflowing" Interactive map: see where (and when) Portland's sewers are overflowing ..., 


As of 2022, Portland is more than halfway through what is now a roughly 45-year project, costing nearly $250 million in hopes of dramatically reducing the amount of raw sewage flowing into local waterways. In addition to violating the federal Clean Water Act and state environmental regulations, those storm-related discharges carry such hidden dangers as E. coli and salmonella that threaten the health of residents who encounter the water, the vitality of Casco Bay's commercial fishing industry and Portland's status as a tourism destination. Currently, over 80% of lobsters sold in the USA come from the adjacent waters of Maine. The state's lobster harvesters bring in more than 100 million pounds (about 45,359,200 kg) of lobster per year, mostly at Casco Bay--an inlet busy with commercial fishing vessels, ferries, cargo ships, and cruise liners. During heavy rainfall, water overpopulates their sewage solutions and the overflow drains into Casco Bay. This issue is exacerbated even further due to climate change. As the climate continues to warm, the Northeast region of the U.S. is expected to see an increased annual rainfall along with more extreme precipitation events. For reference, the decade from 2005 to 2015 was Maine's wettest decade on record, according to the Maine Climate Office


This can cause residents and tourists to contract diseases from consuming these lobsters plus it is harmful to all marine life contaminated by the overflow. A solution was needed to prevent combined sewage overflow (CSO) from entering local waterways and estuaries like Back Cove. Fixing the problem has not been easy and many city residents are feeling the sting during their commutes and in their wallets as the city undertakes massive infrastructure projects to reduce sewage/stormwater discharges in the area. 

To combat this public health hazard, the City of Portland started installing a series of four underground tanks this past summer that will store 3.5 million gallons (about 13,248,935 L) of CSO. The idea behind the massive storage tanks is to capture the first inch of storm runoff which contains the most contaminants, debris, and other pollutants and later treat this "first flush" when the East End Wastewater Treatment Facility has the capacity. H.B. Fleming was a contractor hired to help with this $40 million project. The first step was to build a cofferdam that would create a clean, dry workspace, and support the excavation of the new tanks. This was accomplished by successfully driving steel sheet piling spliced to 100' (feet) length with the ICE® 50B Vibratory Driver Extractor, as exact placement and repositioning is key in situations with underground infrastructures. Additionally, the contractor chose to utilize the ICE® 55-ton dampening solution to help reduce vibrations to the crane.  

Cofferdams are significant when building and repairing structures in or around water due to the high water or saturation/content in soils or from actual bodies of water. It is typically a temporary structure that will form an almost watertight enclosure.  The water/liquid captured inside a cofferdam is pumped out to expose river or seabed surfaces in order to make dry construction of a pier, bridge, and other foundations faster and safer to install. As this is a temporary structure, trickling water will enter the excavation. This is always monitored and usually pumped out periodically.  

Cofferdams are made by driving sheet piling into the ground near a river or seabed to form a close to watertight fence. This allows construction to be done in the "dry", below the waterline, without the need for extra underwater permitting and specialized divers. There is an actual science to professionally installed cofferdams--and vibratory hammers are key. Not only do these hammers embed sheet piling to its required depth but if needed, these hammers can drive sheet piling deeper than originally specified to keep the inside drier and better protected from unpredicted cave-ins. When the job is completed, vibratory hammers make easy work at removing these temporary structures. 

Cofferdams are all around us when creating: 

  1. Foundations 

  1. Bridges and Dams 

  1. Canals 

  1. Boat Ramps 

  1. Shoreline Restoration 

  1. Pipelines 


a. Allows for excavation and construction of structures without specialized underwater installs or divers. 

b. Creates a dry and safer workspace. 

c. Easier inspection of permanent structure. 

d. Vibratory installation allows for underwater installation, repositioning with ease, increased depths at any point necessary, and removal of temporary sheeting with ease. 


The first use of a cofferdam is estimated at 539 BCE where King Cyrus of Persia supposedly used cofferdams as a weapon of war by diverting the Euphrates River with earthen cofferdams to move his army and capture Babylon. Roman engineers built these enclosures to build the foundations of their stone-arch bridges and aqueducts, including cofferdams made of wood pilings in 102 CE to build Trajan's Bridge, which allowed them to cross the Danube River. With 71% of the earth's surface covered in water, and new construction beginning every day, Cofferdams are just as important today as they were in ancient Persia and Rome. 

Today, an engineer decides the best type of cofferdam to use, as it must be sufficient to meet the project requirements. Standard calculations based on known and predicted forces including hydrostatic pressure, soil loads, water currents, waves, frozen water/ice, as well as seismic and accidental loads are used to make the most beneficial choice with a strong emphasis on safety. With workers and equipment inside of what is essentially a deep, dry, well, an emergency response plan should always be in place. There are several potential risks when working inside a cofferdam including a flood event, but rock fissures and shifting soil conditions even vessel traffic can create unsafe conditions within the cofferdam. Any emergency response plan should include dewatering and dewatering backups that are regularly inspected. Another consideration is the impact of cofferdam removal. In some cases, sheet piles are sheared off and the bottoms are left in place to avoid damaging foundation soil that could in turn damage the new structure and must be carefully planned.  

According to the U.S. Environmental Protection Agency 2022 report, more than 800 communities nationwide still use infrastructures with combined stormwater and sewer pipes that result in toxic discharges. An estimated 27 billion gallons (about 102,206,070,000 L) of untreated stormwater and sewage annually from New York City and neighboring communities flow into New York Harbor alone. Meanwhile, the communities in Greater Boston have reduced combined sewer overflow discharges by 98 percent since the late-1980s through a $900 million infrastructure improvement plan. Millions of gallons of Portland sewage still overflowing into Casco Bay ..., 

In Maine, 473.6 million gallons (about 1,792,770,176 L) of untreated stormwater and sewage were discharged into state waterways in 2016 by 25 communities spanning the geographic and demographic gamut from Cape Elizabeth to Calais. Portland's 318.4 million gallons (about 1,205,274,544 L) however, accounted for 67 percent of that total as the combination of stormwater and untreated sewage was passively diverted out of more than 31 overflow sites discharging directly into surrounding waterways. 

This national problem is most acute in older cities in the Northeast and Midwest as city engineers at the time designed "cutting-edge" infrastructure projects around the idea that Mother Nature would "take care of it" by periodically helping flush sewers with stormwater, often into rivers or oceans that will carry the waste away. In a testament to the artisanship of the time, many of the brick-lined sewers laid down by workers 100 or even 150 years ago are still used today in many cities, including Portland. 

According to the EPA, once completed, the Casco Bay Restoration Project will eliminate over 40% of all the CSO that is currently being discharged in the city of Portland, ME; in turn lowering the percentage of pollutants flowing into local waterways. Please note the importance of this project as it resolves over 25% of the entire state's discharge. With that in mind, "Bravo!" to H.B Fleming for working diligently to keep Portland's residents healthy, marine life thriving, and its economy prospering. International Construction Equipment, Inc. (ICE®) is proud to be part of these efforts and will continue to supply innovative equipment to help our clients reduce and stop overflows. We want to enhance the livelihood and safety for the communities in the Casco Bay area and all over the world by supplying the right equipment for every job.  

Learn more about the ICE® 50B and ICE® dampening solutions. 

Media Contact-    
Pollyanna Cunningham, MA, MBA    
Director Marketing, Brand and Media Relations    
ICE® - International Construction Equipment, Inc    
Office - 704-821-8200    
Email -   

Posted in Vibratory Pile Hammers. Tagged as 50B Vibratory Pile Driver, Cofferdam, Enviromental Cleanup, ICEUSA, Sheet Pile.

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