Two significant events took place among the streets of Boston, midway through April 2010. The most widely recognized happening, at least to the general public, was the 114th running of the Boston Marathon on April 19. The other major event, at least in the eyes of the Massachusetts Water Resources Authority (MWRA), was the upgrade of 125 aging manholes in East Boston. This event was more of a sprint than a marathon.
Like many metropolitan areas throughout the Northeast, Boston has been working to rehabilitate its underground sewer system. Decades, if not centuries of deterioration have taken a toll on sewer lines, interceptors, pump stations and manholes. The means of breakdown might range from simple freeze/thaw cycles of brick or concrete infrastructure to more complex corrosion problems caused by microbiological forces. In either case, MWRA is working within its jurisdiction to address underground infrastructure in such a way that the environment is protected from untreated wastewater while repairs are done in an expedient, economical manner.
The East Boston Branch Sewer Relief Project was originally initiated in 2003 to rehabilitate a sewer line that dates back to 1894. Goals of the project were to upgrade an aging regional system by improving treatment capacity and minimizing combined sewer overflows into nearby Boston Harbor and Chelsea Creek.
The first noteworthy upgrade to the system included the insertion of a cured-in-place (CIP) lining in the 5,341-ft main trunk sewer. This was an important milestone for a sewer line that conveys flows from East Boston to the Caruso Pump Station before transfer to the Deer Island Wastewater Treatment Plant.
Work in subsequent years has continued in a joint effort of MWRA and the Boston Water & Sewer Commission. The latest advances concentrated on a network of manholes in a state of disrepair that had been enabling excessive water inflow and infiltration (I&I). Municipal officials, working in conjunction with Jacobs Engineering, reasoned that by eliminating common points of entry for extraneous groundwater and runoff, the sewer system would be free to function as designed rather than succumbing to environmentally damaging overflow conditions. This vantage point was reinforced by a widely cited 2002 study published by Mark G. Wade of Wade & Associates that said as much as 50 percent of measured I&I volume can be traced to dysfunctional manholes.
Project plans called for approximately half of the 125 manholes to be replaced by new pre-cast rings
supplied by Concrete Systems Inc. of Hudson, N.H.
The successful bidder for the East Boston manholes’ coatings work was the Bolton Co. of Rochester, N.H. President Greg Bolton drew upon years of municipal construction experience with a specialty in coatings applications throughout New England as he planned to mobilize for maximum productivity. Keys to Bolton’s plans included usage of appropriate materials and equipment that would enable placement of the specified substrate repair compounds and corrosion resistant lining.
The chosen product for restoring the deteriorated mortar joints and concrete surfaces was Sauereisen SubstrateResurfacer No. F-121. This underlayment is a high-strength, Portland cement-based repair material used as a waterproofing barrier to fill voids in applications where structural integrity may need to be restored as well. For specific areas showing evidence of microbiologically induced corrosion, Sauereisen SewerGard No. 210 polymer lining was specified. This topcoat met criteria for chemical resistance to sulfuric acid, physical strength, low permeability and use in similar environments over the past 20 years. Although the level of corrosion varied in the East Boston manholes, MWRA elected to take a proactive approach in employing a protective lining to further extend the service life of the structures for decades to come.
Aside from the compatibility of the Sauereisen underlayment and topcoat with each other, the materials were both suitable for application with the Bolton Co.’s WIWA Model 410 Thick-Film Mortar Pump. The versatility of such a pump was critical in minimizing mobilization expenses and cleanup time. The WIWA 410 is mobile enough to facilitate access while enabling a high transfer volume.
During the course of the project, Sauereisen representatives Tony Oswald and Rick Thomas visited the jobsite to meet with the Bolton crew and project inspector Miguel Gomes of Kenville Engineering, who had been contracted by Jacobs. A point of discussion was to confirm that standards of surface preparation had been met so that rehab materials would bond and cure appropriately. The high-pressure waterblasting that utilized a force of 5,000 to 7,000 psi thoroughly removed all loose material and surface contaminants.
As application proceeded, the Bolton crew encountered some novel, oval-shaped brick manholes indicating the artistry of the era from which they were originally constructed. Most of the underlayment ranged in application thickness from one-eighth inch to quarter-inch based on the amount of degradation present.
Although several variations of Sauereisen’s SewerGard are available to accommodate different application methods, Bolton had selected the Trowelable grade since their crew was most familiar with that version.
However, the applicators improvised in the placement of the epoxy polymer by pumping it and using a straight-shot nozzle for the early stages of the project. In time, they affixed a rotary-spraying spincast nozzle to their lines which enabled the majority of work to be accomplished from ground level. This further accelerated their production rates and minimized the amount of confined space entry required. Together, the Sauereisen and Kenville personnel expressed approval for each stage of work.
As a means of quality assurance, Bolton’s team operated “spark testing,” or holiday detection equipment, to identify any thin areas or voids in the lining. The typical voltage of 100 volts per millimeter thickness of the coating was used to identify the touch-up areas. Sauereisen’s Glaze version of the SewerGard effectively finished off the project when applied to isolated areas needing additional coverage.
With the project now complete, East Boston will benefit from the effective and efficient job for years to come. Next year, in April 2011, the 115th Boston Marathon can be expected to proceed with thousands of runners, both international and local, pounding the pavement as they do every year. Fortunately for residents of the Greater Boston Area, their East Boston manholes will hold steady, rain or shine, thanks to successful collaboration in the municipal, construction, engineering, and manufacturing sectors.
C. Karl Sauereisen is vice president and director at Sauereisen, Inc.