Your Trusted Experts for Comprehensive I&I Solutions in Sanitary Sewer Manholes
As I&I experts, Epoxytec representatives have the experience and expertise to provide inflow and infiltration (I&I) solutions for sanitary sewer manholes. With decades of experience, Epoxytec’s products are proven to protect against the harsh and harmful effects of I&I.
An Introduction to Inflow and Infiltration (I&I)
Most buried underground assets within the sanitary sewer collection system are concrete, brick, or some form of masonry. A simplified way to visualize concrete within collection systems is to envision it as a buried high-density sponge. Over time, this high-density sponge becomes less dense from corrosion, or fatigued and showing symptoms of cracks and other damage (some hairlines, some more obvious), allowing this substrate to absorb or channel water from the saturated earth surrounding it. Some areas or sections of soil become more saturated than others, usually from a high water table or simply rain and irrigation.
The term inflow and infiltration (I&I) refers to the undesired entry of clean water, originating from stormwater (inflow) and groundwater (infiltration), into sanitary sewer collection systems. This unintentional influx of clean water occurs due to various factors, such as deteriorated concrete, mortar, cracks, faulty seals, joint and connection failures, or other unforeseen areas that result in leaks. The entry points for this water can include manholes, pipes, wet wells, and lift stations. Essentially, all underground assets are vulnerable, particularly those situated within the water table, as they undergo hydrostatic pressure from groundwater infiltration and an inflow of stormwater from heavy rain events that persistently seek pathways for entry. One area that can be tackled to offset I&I contribution is at the manhole.
As infrastructure ages, this condition can be accelerated and compounded by corrosion from hydrosulfuric acid (H2S). The associated costs of excavation, repair, or replacement often become burdensome for municipalities. Utilizing in situ or trenchless solutions for the rehabilitation and lining of collection systems has emerged as a crucial tool for municipalities. This approach is essential in addressing the restoration of aging infrastructure and effectively sealing off the issues related to inflow and infiltration.
I&I is a condition that cannot be ignored, not only from an environmental standpoint, but also because the cost burden grows and becomes unsustainable. The “clean” water entering the system ultimately mixes with sewage and ends up at the treatment plant. Originally, older plants were designed for calculated flow rates and volume based on a projected population growth factor that often did not account for I&I at the rate we see today in many aging, older cities. If this surge of volume continues, many asset owners will end up with a sanitary sewer overflow (SSO) condition, a release of untreated or partially treated sewage from a municipal sanitary sewer. I&I is an environmental problem that must be avoided and also carries a considerable financial impact.
According to the American Society of Civil Engineers (ASCE), the nation’s 16,000+ wastewater treatment plants are currently operating at an average of 81 percent of their design capacities. Additionally, 15 percent of these plants have either reached or exceeded their intended capacity. These statistics shed light on the ongoing challenge posed by I&I, as it persists in pushing these percentages upward. The consequence of this increased strain on treatment plants heightens the risk of SSOs and will necessitate construction expansion of the plant if ignored.
The Rise of I&I Abatement Programs
The ASCE’s “US Infrastructure Report Card” currently assigns a grade of D+ to wastewater infrastructure in the US. However, the ASCE has found that the increased adoption of asset management plans has allowed 62% of surveyed utilities to shift from reactive responses to proactive management of wastewater infrastructure maintenance. This proactive approach is crucial to addressing issues before corrosion takes hold and I&I affects sanitary sewer collection systems.
The US Environmental Protection Agency (EPA) emphasizes the importance of I&I abatement programs as well, outlining minimum goals to achieve comprehensive improvements in wastewater management:
- Reduce Ratepayer Costs: Implement cost-effective I&I reduction projects to decrease the financial burden on ratepayers for treating wastewater.
- Minimize Liability: Mitigate liability arising from pollution and public health risks by eliminating SSOs during storm events.
- Avoid Wastewater Treatment Plant Expansion: Eliminate sufficient I&I to preempt the capital costs associated with expanding wastewater treatment plant capacity in anticipation of a 10% population growth over the next 20 years.
- Avoid Interceptor Expansion Costs: Eliminate sufficient I&I to avoid the capital costs linked to the expansion of interceptors, which will be necessary to support the development of certain neighborhoods.
- Offset Environmental and Regulatory Impact: Eliminate enough I&I to offset the environmental and regulatory impact of sewer system expansion and increased water demand expected over the next 15 years.
These goals underscore the EPA’s commitment to enhancing the efficiency, environmental sustainability, and resilience of wastewater infrastructure while addressing the challenges posed by I&I.
The landscape of mandates has been expanding, accompanied by consent decrees and funding initiatives to address the challenges in wastewater infrastructure. Municipalities are actively pursuing various funding opportunities stemming from federal, state, and local sources intended to bolster their efforts. In addition to external funding, some municipalities are allocating resources from their own annual budgets specifically designated for I&I maintenance. This dual approach, combining external financial support with dedicated internal budgets, reflects a concerted effort to tackle the issues associated with aged and fatigued collection systems comprehensively.
Trenchless Approach to Providing a Targeted Solution
Targeting the sources of contribution and identifying problematic areas, along with determining the factors causing the I&I condition, is the foundation for informed product and solution selection. Is the I&I primarily entering through manholes, pipes, pumping stations, or a combination? Recognizing that not every sewer line requires the same approach ensures that the chosen solutions align with the specific needs of the system.
Fortunately, trenchless methods, featuring innovative and proven lining techniques, can effectively address both EPA mandates and municipal I&I abatement goals.
Over the decades, innovation has given rise to a variety of high-quality and cost-effective trenchless solutions for buried assets, eliminating the need for traditional and more costly dig-and-replace methods. Structural liners are an integral part of these trenchless strategies.
The application of trenchless lining methods goes beyond mere compliance with mandates, offering a holistic and cost-efficient approach to improving the functionality, resilience, and longevity of wastewater infrastructure. Trenchless lining methods, aimed at sealing I&I, not only align with EPA requirements but also offer a range of additional benefits:
- Protects Health and Environment and Reduces SSOs: These methods contribute to protecting public health and the environment from contamination associated with SSOs and other potential hazards.
- Optimizes Taxpayer Funds: Trenchless lining provides a cost-effective solution by addressing I&I issues without the need for extensive and expensive infrastructure replacements.
- Delays Infrastructure Expansion: By reducing the rate of I&I and improving system efficiency, trenchless lining methods can delay the need to expand infrastructure and treatment facilities. This, in turn, alleviates the burden on capacity and associated capital costs.
- Extends Asset Life Cycle: Trenchless liners provide upgraded corrosion protection, extending the life cycle of the infrastructure and reducing the frequency of maintenance and repairs.
Trenchless solutions for vertical structures (such as manholes and lift stations) are not all created equal. Each manhole is unique and therefore finding the right solution should vary depending on the environment, and severity of I&I to name a few factors. Solutions may include cementitious linings, geopolymer concrete, calcium aluminate, epoxy-mortar high-strength, structural polyurethane/ polyurea, foam composite systems bonded polymer lining systems or ultra-high build structural epoxies. Careful consideration should be given to this decision and consulting with an experienced, trained professional can often be the key to a successful I&I mitigation solution.
When addressing inflow and infiltration (I&I), the first critical phase entails a comprehensive condition assessment to gain insights into the impact of corrosion and leaks within the system. Whether proactively managing an I&I abatement maintenance program or reacting to mandates (such as EPA consent decrees), effective planning and execution can only take shape once the relevant data is collected. Understanding which assets contribute the most to I&I, why such occurrences have taken place, and anticipating future challenges is paramount.
Organizations like WEF, AWWA, NASTT, NASSCO, EPA, AASHTO, and AMPP provide guidance on I&I and trenchless lining options, covering standards and education for condition assessment, lining design, and product selection. After a thorough condition assessment, a plan to target specific structures can then be formulated. Some of these structures are discussed in greater detail below.
Distinctions in Underground Buried Assets
Lining methods demonstrate success when using products specifically designed for achieving monolithic watertight sealing for mitigating I&I. When lining both horizontal and vertical structures, should the technologies differ, it is important that they can interface together effectively to deliver seamless monolithic lining in unison.
When evaluating buried collection lining systems, the assessment should consider two main categories of assets: horizontal pipe systems and vertical assets, which include structures like manholes and pump stations.
Each category experiences distinct forces and stresses, often requiring different technologies and performance requirements. Technologies, specifications, surface preparation standards, contractor qualifications, and execution may differ, especially when comparing horizontal pipe lining with vertical structure (manhole and lift station) lining.
In horizontal conditions, for example, liners often need greater strength and wall thickness when the host is deficient due to certain conditions or forces, requiring the liner to bear load and/or resist internal pressure assumptions. With manholes, on the other hand, the directional forces may not be the same and other host assumptions are factored differently. With vertical structures, film thickness is often calculated purely to hold back I&I as the main intention, with consideration at times for low-pressure effective lateral earth stresses when the walls have deteriorated severely.
Numerous manhole rehab and lining options offer benefits based on specific situations:
Zero/Low I&I: For cost-effectiveness, cementitious lining may provide a cost benefit due to its use of inexpensive raw materials and ease of application. And in some cases, where H2S levels are low and I&I abatement is not the main concern, these lining systems can be selected for sewer lines where a full monolithic I&I abatement program or lining job is not necessary and therefore the intent is to simply restore the profile.
High I&I: When manholes necessitate a comprehensive, vacuum-tested, sealed monolithic I&I abatement lining system, advanced technologies may be more suitable. For instance, ultra-high build, high-strength, bonded polymer lining systems are ideal when seeking secure, watertight sealing from manhole to manhole; this approach can integrate seamlessly with CIPP or other pipe lining technologies when choosing certain epoxy-based polymer liners. Here it is imperative to seek a technology that bonds well to avoid the creation of annular space and interfaces, and bonds well to horizontal liners. Because of this requirement, polymer technology is a better choice than cementitious technology. Moreover, due to the advantages of epoxy adhesion over other kinds of polymers (such as polyurethane or polyurea) which may not be sufficient, many epoxy polymer liners, such as Epoxytec CPP, are designed for optimal bonding at their termination to mate or tie-in vertical assets (manholes and lift stations) to horizontal pipes.
Horizontal Pipe Lining
Horizontal pipe lining can be tackled using a variety of proven technologies.
Cured-in-place pipe (CIPP) and pull-in place lining are often the selected for large projects and long lengths of work due to their cost-effectiveness for long runs of pipe. These technologies preserve existing pipe that has been damaged by leaks, cracks, intruding roots, and corrosion.
The pipe bursting method is used on pipes that are severely damaged, for replacing an entire system, or for repairing larger sections of sewer pipeline. The installers begin by placing a “bursting head” at the access point on the one end of the pipe. Hydraulic power is used to drag the head through the pipe. As it makes its way through the system, it breaks the old pipe apart and draws a new seamless pipe behind it.
Sliplining is one of the oldest methods of trenchless rehabilitation of existing pipelines. It is used to repair leaks or restore structural stability to an existing pipeline. It is completed by installing a smaller, “carrier pipe” into a larger “host pipe,” grouting the annular space between the two pipes, and sealing the ends. The most common material used to slipline an existing pipe is high-density polyethylene (HDPE), but fiberglass-reinforced pipe (FRP) and PVC are also common.
Spray-in-place pipe (SIPP) lining is a process where high-build, high-strength applied and bonded polymer systems are utilized to fill dry cracks and surface imperfections, creating a watertight seal once cured. SIPP is an option often sought out for irregular shaped pipe, culverts, or shorter runs when other lining methods may have limitations.
Vertical Lining (manholes, wet wells, lift/pump stations)
The buried forces affecting vertical structures differ, requiring a diverse range of lining solutions. These solutions vary due to distinct conditions and lining intentions, and are distinct from those associated with horizontal pipe lining.
Certain liners aim to prevent hydrogen sulfide (H2S) corrosion as the main design parameter. However, when the project requires more than corrosion protection—specifically, resistance to and mitigation of I&I forces like hydrostatic pressure—a watertight, monolithic high-strength liner is essential.
Vertical manhole lining, though not as high strength as horizontal pipe lining, confronts distinct forces, such as effective lateral earth forces and hydrostatic pressure which are lower pressure forces. This technology is typically applied and bonded to endure these pressures unique to vertical assets.
Applied Polymer Lining – Why Bond Strength Matters
When a true monolithic watertight solution for vertical structures is required, it is important to select a technology that is bonded. Vertical structures would include assets such as manholes, wet wells, and lift stations. Great adhesion is not just limited to how well the liners bond to the host, but also to other system liners which require seamless transition (i.e.- manhole liners to pipe liners).
Bonded systems will reduce risk of an annulus occurring, thereby stopping hydrostatic pressure and water migration with the correct distribution of resistance. In the event of an annulus formation, water pressure undergoes redirection and accumulates at an alternative point. This point tends to exacerbate abnormal pressure, typically manifesting at weakly bonded edge terminations (if a high-bonding material has not been used). Technologies lacking strong adhesion and surface tolerance features are often not designed with an emphasis on optimal bonding, necessitating the implementation of internal seals or end seals at their termination points when remedied later. This should be avoided, as it introduces an additional technology and potential failure mechanism. Instead, select a material with superior edge termination and capability for interface bonding with a variety of construction materials, such as to concrete, clay, brick, steel, PVC, and ductile iron, as well as CIPP. This is the only way to ensure true monolithic sealing with both horizontal and vertical lining fused together over the long term.
Fortunately, bonded systems represent the optimal technology for vertical structures when a comprehensive inflow and infiltration (I&I) mitigation solution is needed. These systems hold back pressure without the risk of annulus formation and exhibit robust bonding capabilities with various construction materials and adjacent pipe lining materials, such as CIPP. Consequently, they deliver a vacuum-verified, true monolithic, watertight system from manhole to manhole.
Various technologies claim to be a bonded system, but it is crucial to delve into the actual bond strength data for a comprehensive evaluation. Ensuring not only high adhesion on both dry and wet conditions, but also compatibility with manhole-specific environments and other construction materials is paramount.
For this type of assessment, testing standards such as those defined by the University of Houston’s CIGMAT program and the US EPA Environmental Technology Verification testing protocol play a valuable role. These entities conduct thorough bond strength tests, not only on dry concrete but also on wet (SSD – Saturated Surface Dry) concrete. Selecting materials with high adhesive properties and favorable surface acceptance helps raise the safety factor to prevent bonding-related failure. Additionally, they extend their assessments to include various substrates like brick, providing a more realistic and comprehensive understanding of how these technologies perform in diverse conditions. This level of testing contributes significantly to validating the effectiveness and reliability of bonded systems in real-world scenarios.
When designing bonded lining systems, the most effective designs commonly incorporate epoxy-amine resins. Epoxy stands out among its counterparts, such as polyurethanes or polyurea, due to its exceptional versatility in navigating manhole environments, in terms of both wet tolerance and optimal substrate acceptance. Additionally, epoxy systems facilitate rapid and efficient self-repairs, with its exceptional ability to tie into itself, and to tie into other materials and liners.
Systems designed with elevated film builds and robust strengths fall under the category of “Ultra-High-Build, High-Strength Epoxy” or simply “Structural Epoxy.” These formulations are frequently specified for diverse applications, including manhole, lift station, and wet well lining systems and SIPP applications, and may also find utility in certain conditions at water treatment plants and wastewater treatment plants when humid or moist conditions cannot be avoided.
Key Attributes of a Fully Sealed Monolithic Solution
Key Attributes of a Fully Sealed Monolithic Solution
When selecting vertical lining technologies requiring a fully sealed monolithic solution from manhole to manhole, consider the following key attributes:
- Adhesion to Various Construction Materials: The liner must exhibit high bond strength to a diverse range of construction materials, including CIPP, clay, brick, concrete, and steel.
- High Film Thickness: The liner should feature a substantial wall thickness, measured as Dry Film Thickness (DFT), to enhance durability and longevity.
- High Flexural and Tensile Strengths: The product must possess elevated flexural and tensile strengths, as compressive strength is less critical for applied and bonded lining applications.
- Vacuum Test Compatibility: The product should be capable of undergoing vacuum testing to ensure a reliable and airtight seal.
- H2S Resistance: The product must exhibit adequate resistance to hydrogen sulfide (H2S), a common corrosive gas found in wastewater environments.
- Repairability and Maintainability: The product should be designed for ease of repair and maintenance without the need for complex equipment, ensuring cost-effective and straightforward upkeep.
- High Bond Strength with Zero Annulus Design Intention: The product must demonstrate high bond strength with respect to the host substrate, and its design should intentionally prevent the formation of an annulus, ensuring a seamless and watertight connection.
- Resistance to Root Intrusion, Hydrostatic Pressure, and Water Infiltration: In the event of small, inadvertent unbonded areas, the product’s “structural” spanned high strength film should resist root intrusion, hydrostatic pressure, and water infiltration, ensuring continued structural integrity and preventing leaks.
Benefits of Applied and Bonded, Ultra-high Build, High strength epoxies
- Zero Annulus Design:
- The epoxy system’s intended design and polymer type advantage prevents the creation of annular space, eliminating any potential redirection of flow channeling to weaker points. This feature enhances the overall integrity of the lining system and prevents vulnerabilities.
- Versatility in Tie-In:
- The system demonstrates compatibility by easily tying into a variety of construction materials, including cured-in-place pipe and other liners. This versatility enhances its applicability in diverse environments and projects, especially when needing to interface and bond with other horizontal lining system to deliver seamless monolithic integration.
- High Repairability and Maintainability:
- An epoxy system facilitates high repairability and maintainability without the need for complex equipment. This attribute allows for efficient and cost-effective upkeep, minimizing downtime and operational disruptions.
- High Surface Tolerance:
- Many epoxy systems exhibit high surface tolerance, enabling effective application and adhesion to different substrate conditions. This characteristic is crucial for ensuring uniform coverage and long-lasting performance.
- Good “Wet” (SSD) Adhesion:
- The epoxy system typically shows good adhesion to wet (saturated surface dry – SSD) surfaces. This is particularly valuable in applications where exposure to moisture or water is commonplace, ensuring reliable performance in wet environments.
- High Flexural and Tensile Strengths:
- A formulated structural epoxy system boasts high flexural and tensile strengths, providing robust resistance to side wall pressures. This strength is essential for maintaining the structural integrity of the lining system, especially in scenarios where pressure variations may occur or unintended spanning is required.
The use of epoxy-amine resins in these systems is the key to their capability to provide durable, long-lasting, structurally sound solutions in challenging and dynamic environments.