A comprehensive reference for terminology used in manhole inspection, rehabilitation, and asset management. Terms are organized alphabetically. Click any term to expand the definition.

A

Acrylamide Grout

A low-viscosity chemical grout used for sealing active infiltration in manholes and pipe joints. Acrylamide grouts penetrate fine cracks and polymerize in contact with water, forming a gel that blocks water passage. Note: Some older formulations contain acrylamide monomer, which is a neurotoxin — newer formulations use acrylate-based chemistries. Always review the SDS and ensure compliance with environmental regulations before use.

Active Infiltration

Water actively entering a manhole structure through defects at the time of inspection, visible as seeps, drips, or flows. Contrasted with staining or deposits indicating historical infiltration. See: Infiltration and Inflow in Manholes.

ASTM

ASTM International (formerly the American Society for Testing and Materials). Develops and publishes consensus technical standards widely used in infrastructure materials specification. Key ASTM standards for manhole rehabilitation include D638 (polyurea tensile properties), C478 (precast concrete manhole specs), and D4258 (concrete surface cleaning).

B

Barrel Section

The cylindrical body section(s) of a manhole between the base slab and the cone/corbel section. The barrel is the primary structural element and the most common location of H2S-driven corrosion damage. Evaluated separately from cone/corbel and bench/invert sections in MACP inspection. See: MACP Inspection Guide.

Bench

The floor surface of the manhole surrounding the invert/flow channel. The bench directs flow from incoming pipes through the invert and into the outgoing pipe. Bench condition is evaluated in MACP inspection, with attention to structural integrity, grease accumulation, and evidence of corrosion.

C

CAC (Calcium Aluminate Cement)

A specialty cement with higher resistance to sulfuric acid attack than ordinary Portland cement (OPC). Produced by fusing limestone and bauxite. CAC-based mortar and coating products are used in H2S corrosive environments where OPC would deteriorate rapidly. See: H2S Corrosion Prevention.

CIPM (Cured-in-Place Manhole Liner)

A structural relining system in which a resin-saturated fabric tube is installed inside the existing manhole barrel and cured using UV light, steam, or ambient temperature. Creates a new structural liner bonded to the existing barrel. See: Rehabilitation Methods Comparison.

CMOM (Capacity, Management, Operations, and Maintenance)

EPA’s framework for managing sanitary sewer collection systems to prevent sanitary sewer overflows (SSOs). CMOM programs require systematic asset management, inspection, and rehabilitation planning. Well-documented manhole rehabilitation programs are a key CMOM deliverable.

Cone/Corbel Section

The tapered transition section of the manhole between the barrel and the frame/cover at the surface. Subject to settlement, cracking, and surface inflow at grade ring joints. A common and often overlooked source of I/I.

CSP (Concrete Surface Profile)

ICRI (International Concrete Repair Institute) standard for describing concrete surface roughness, numbered 1 through 10. Critical for polyurea adhesion — most manhole polyurea systems require CSP 3 or 4 minimum. Achieved by abrasive blasting, hydro-jetting, or mechanical scarification.

F

Frame and Cover

The cast iron, ductile iron, or polymer assembly at the surface that provides access to the manhole. The frame-to-cover interface is a major inflow source in many systems. “Watertight” frame-and-cover assemblies use gasketed or welded designs to eliminate surface water entry.

FRP (Fiberglass Reinforced Polymer)

A composite material consisting of glass fiber reinforcement in a polymer matrix. Used in prefabricated manhole barrel inserts for structural rehabilitation. Excellent corrosion resistance and high strength-to-weight ratio. See: Rehabilitation Methods Comparison.

G

Grade Ring

Precast concrete rings used to adjust the height of the manhole frame to match the road surface elevation. Grade ring joints are a common location for infiltration and inflow. Sealing grade ring joints (mortar, polymer grout, or membrane systems) is often one of the most cost-effective I/I reduction measures.

Gypsum Layer

The calcium sulfate layer formed when sulfuric acid (produced from H2S by bacteria) reacts with calcium hydroxide in Portland cement concrete. Gypsum has very low strength and spalls progressively, exposing fresh concrete to continued attack. The presence of a gypsum layer is a key indicator of H2S-driven corrosion. See: H2S Corrosion Guide.

H

H2S (Hydrogen Sulfide)

A colorless gas with a characteristic “rotten egg” odor at low concentrations, produced by anaerobic decomposition of organic matter in wastewater. H2S is both an atmospheric hazard (toxic at high concentrations, with olfactory fatigue masking the danger) and the driver of biologically-mediated concrete corrosion in manholes. See: Confined Space Safety and H2S Corrosion.

I

I/I (Infiltration and Inflow)

Unwanted water entering the sanitary sewer system. Infiltration is groundwater entering through structural defects below grade; inflow is surface water entering through above-grade defects or connections. Both increase treatment plant loading, reduce system capacity, and can contribute to SSOs. See: I/I Solutions Guide.

ICRI

International Concrete Repair Institute. Develops standards and guidelines for concrete repair, including surface preparation standards widely used in manhole coating specifications.

Invert

The lowest point of the flow channel in the manhole, where wastewater flows from incoming to outgoing pipes. The invert shape is designed to maintain flow velocity and minimize solids deposition. Invert condition is evaluated in MACP inspection.

M

MACP (Manhole Assessment and Certification Program)

NASSCO’s standardized protocol for assessing and scoring manhole condition on a 1–5 grade scale. The industry standard for defensible, comparable condition data used in rehabilitation prioritization, regulatory compliance, and funding applications. See our comprehensive MACP Field Guide.

MACP Grade

The overall condition score assigned to a manhole after MACP inspection, ranging from Grade 1 (light/good condition) to Grade 5 (critical/imminent failure risk). See: MACP Scoring Guide.

N

NASSCO

National Association of Sewer Service Companies. Develops and administers the MACP and PACP inspection standards; trains and certifies inspectors; provides technical guidance for collection system inspection and rehabilitation.

NSF 61

NSF International Standard 61 for drinking water system components. Required for coatings or lining materials used in structures with any potable water contact potential. Always specify NSF 61 compliance explicitly when it applies — never assume.

P

PACP (Pipeline Assessment and Certification Program)

NASSCO’s standardized protocol for assessing sewer pipe condition, analogous to MACP for manholes. PACP and MACP are designed to work together as part of an integrated collection system condition assessment program.

Polyurea

A 100% solids, spray-applied elastomeric coating produced by the reaction of an isocyanate component with an amine-terminated resin. Characteristics include fast cure (seconds to minutes), excellent physical properties (high elongation, tensile strength, and abrasion resistance), moisture tolerance, and long-term resistance to H2S and sulfuric acid. The dominant protective coating system for manhole rehabilitation. See: Rehabilitation Methods.

S

SSO (Sanitary Sewer Overflow)

An overflow of raw or partially treated sewage from the sanitary sewer system at any point other than the designated treatment facility. SSOs are a regulated Clean Water Act violation. Manhole rehabilitation — by reducing I/I and preventing structural failures — is a key strategy in SSO reduction programs.

SRF (State Revolving Fund)

EPA-capitalized state loan (and sometimes grant) programs for water and wastewater infrastructure financing. The Clean Water SRF (CWSRF) is the primary federal financing vehicle for manhole and collection system rehabilitation projects. See: Federal Funding Guide.

T

Trenchless Rehabilitation

Umbrella term for methods of repairing or rehabilitating underground infrastructure without excavation. For manholes, trenchless methods include spray-applied coatings (polyurea, cementitious), cured-in-place liners, FRP inserts, and chemical grouting. See: Trenchless Methods Guide.

This glossary is maintained by the Manhole Recovery editorial team. Terms are updated as standards and practices evolve. If you’d like to suggest an addition or correction, contact us. For more in-depth definitions and technical guidance, visit our Resources page or join the community forum.