Combatting H2S Corrosion With 100% Resistant Manhole Lining Technology

October 16, 2024

Aging sewer infrastructure poses significant challenges—and risks—for municipalities across the United States, especially in urban areas where sewer systems have been in place for decades. Many of these systems were constructed using materials today’s engineers recognize as susceptible to corrosion and degradation. As a result, structures like pipes, culverts and manholes continue to deteriorate over time. Manholes in particular often suffer from corrosion and structural degradation due to harsh environmental conditions, especially where hydrogen sulfide (H2S), or sewer gas, is prevalent. H2S corrosion occurs from natural anaerobic activity as bacteria break down waste in enclosed, oxygen-deprived spaces like manholes. This process significantly accelerates the deterioration of concrete and metal structures within manholes.

To combat corrosive elements like H2S, municipalities need an innovative manhole rehabilitation solution to restore structural integrity to 100%. Thankfully, a fully corrosion-resistant manhole lining method exists today, setting a new standard for manhole rehab by enabling what is essentially a manhole replacement without requiring excavation. When a small South Dakota community faced an impending catastrophic sewer infrastructure collapse, HK Solutions Group stepped up to the challenge with our one-of-a-kind Monoform PLUS™ solution primed to strengthen and protect manholes from H2S corrosion.

A South Dakota Community’s Sewer Infrastructure Faced Risk Of Manhole Failure Or Collapse

During a recent project in a small municipality in South Dakota, the challenges of aging sewer infrastructure were immediately apparent to our team at HK. The municipality was grappling with a deteriorating manhole over 40-feet deep that had been previously rehabilitated—unsuccessfully—using a spray-applied epoxy coating. Unfortunately, the initial contractors weren’t able to implement the coating properly, causing more challenges like pinhole leaks. Meanwhile, the affected manhole was still at the mercy of H2S corrosion.

When the manhole coating began to peel off of the walls, it allowed H2S sewer gas to seep between the sprayed coat and the manhole walls. The subsequent sewer gas invasion led to the gradual degradation of the manhole's structural integrity, exacerbating the corrosion of the underlying concrete to the point of exposing the dirt and wire mesh within the structure. The threat of structural failure and collapse was imminent, highlighting the limitations of manhole rehabilitation methods like spray-applied epoxy coating in environments with high levels of H2S.

Vulnerabilities Left Exposed With Spray-Applied Manhole Coating Techniques

The problem with spray-on epoxy manhole coating techniques is their lack of flexibility or forgiveness. For the liner to adhere properly to surface walls, the existing structure must be mostly intact and requires near-perfect application. In the case of the precarious manhole entrenched 40-feet deep and threatening to swallow the nearby businesses, we didn’t have room to make a wrong move. The epoxy coating was already wearing away and positioning the structure for a catastrophic collapse. Our 100% corrosion-resistant manhole lining solution, Monoform PLUS™, proved to be the most effective and cost-efficient method to rehabilitate the failing manhole safely.

What Is The Difference Between Manhole Lining & Coating Solutions?

Manhole coating solutions are typically applied to external surfaces as a protective sealant to prevent corrosion and damage—a temporary fix for problems that will only get worse. Manhole lining solutions, however, provide structural rehabilitation equivalent to a brand new manhole by strengthening the interior structure.

Long-lasting and durable, manhole liners provide unmatched structural integrity for municipalities seeking long-term improvements. Monoform PLUS™ liners represent a significant advancement over coating methods due to their unique design and construction approach. Unlike conventional spray-on epoxy coating applications, our patented Monoform™ solution operates independently of the existing host structure for dependable performance. Traditional methods like excavation aren’t favorable, either, as they present high costs, extensive disruption and high risk to surrounding infrastructure. For projects where H2S corrosion is prevalent, Monoform PLUS™ is the superior solution every time.

Confronting A Heavy Presence Of H2S Sewer Gas & Corrosion With Trenchless Manhole Rehabilitation

Corrosion in manholes is not just a structural concern: it also poses environmental and public health risks. When manholes deteriorate, they can allow inflow and infiltration (I&I), leading to excess water entering the sewer system. This not only increases the treatment burden on wastewater facilities but also raises the risk of untreated sewage overflows, which can contaminate local water bodies and pose serious health hazards.

High volumes of H2S sewer gas and structural depths exceeding 40 feet posed unique challenges that rendered traditional excavation impractical and even irresponsible at the South Dakota job site. Located adjacent to a large car dealership building and its parking lot, excavation would have necessitated digging up the entire corner of the building. This presented a significant risk of structural damage or collapse to the dealership itself and nearby buildings. The potential for a sinkhole was also a concern due to groundwater seepage bringing soil into the manhole over time. Not to mention the financial implications were substantial, with estimates running into multiple hundreds of thousands of dollars solely for digging and associated repairs. Given these risks and costs, traditional dig-and-replace methods were not feasible, highlighting the necessity of trenchless manhole rehabilitation as the only viable solution.

The HK team brought in fans to reduce H2S levels to safe limits, ensuring a secure environment not only for our technicians but also for the dealership employees and patrons as well as those at surrounding businesses. HK effectively stabilized hazardous gasses at the scene and installed corrosion-proof Monoform PLUS™ to prevent further risk of H2S and public health concerns in the community going forward. Traditional methods, such as spray-on manhole coatings or excavation, proved impractical due to environmental risks, structural constraints and escalating costs. By addressing the challenges posed by deteriorating sewer infrastructure in a small municipality, HK’s Monoform PLUS™ exemplified a transformative approach to manhole rehabilitation.

How HK Solutions Group’s Monoform PLUS™ Restored Aging Sewer Infrastructure

Monoform PLUS™ minimizes surface preparation, operates effectively in varied environmental conditions and significantly reduces project timelines and disruptions compared to traditional dig-and-replace methods. The benefits of our manhole lining solution were especially evident in the small South Dakota community, where we completed the entire operation within a compact 8-foot by 8-foot footprint, achieving our goal of efficiency while having a minimal impact on surrounding sewer infrastructure and businesses.

100% Corrosion-Resistance For H2S-Proof Sewer Infrastructure

Utilizing custom ABS plastic forms to create a 3- to 4-inch space between the interior of the existing structure and our liners, we filled the void with a high-strength concrete admixture, reinforced with fiber mesh for durability. To provide robust H2S corrosion resistance, we integrated a 100% corrosion-resistant AGRU Ultra-Grip™ HDPE liner, ensuring a completely sealed and structural lining. Once the concrete set and the forms were removed, the result was a fully structural, stand-alone lining system capable of meeting rigorous load specifications like HS-20 and C-80. Our approach guarantees long-term durability and protection, eliminating reliance on the deteriorating original structure and making it a versatile and reliable solution suitable even under live flow conditions.

Minimally Invasive For Cost-Effective & Efficient Manhole Rehabilitation

To manage high flow rates from the large sewer interceptor line, we designed an internal bypass using a pneumatic plug with a flow-through pipe. Our approach allowed the redirection of flow away from the work area, enabling safe working conditions without putting the costly burden of a shutdown on the municipality. Traditional bypass methods would have been extremely expensive for the municipality, particularly given the interceptor line's critical role in the town's infrastructure. Potential shutdowns would have necessitated extensive bypassing efforts, risking environmental impacts and hazardous H2S exposure if flow redirection was mishandled. The internal bypass was essential for us to repair the bench and invert as required within the manhole before initiating our Monoform PLUS™ process, all with little to no disturbance to the surrounding dealership and community.

Contact HK To Fight Back Against H2S With 100% Corrosion-Resistant Monoform PLUS™

Time and time again, Monoform PLUS™ emerges as a groundbreaking manhole rehabilitation solution through the integration of trenchless technology with advanced materials like the AGRU Ultra-Grip™ HDPE liner and high-strength concrete. By focusing on long-term resilience and cost efficiency, Monoform PLUS™ sets a precedent for municipalities like the South Dakota community grappling with aging infrastructure and environmental hazards. Its successful implementation in a multitude of projects underscores the pivotal role of innovative engineering in creating sustainable urban environments and mitigating risks associated with deteriorating sewer infrastructure. For manhole longevity and performance that resists recurring issues like H2S corrosion, call (515) 283-0500 or contact HK online to learn more about Monoform PLUS™ for your municipal manhole rehabilitation projects.

 

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A variation of this article was originally published as a feature titled “Transforming Manhole Rehabilitation: A Case Study On Advanced Solutions For Corrosion Resistance” in the September 2024 issue of Trenchless Technology magazine.