Manhole Inspection Best Practices for Municipal Sewer Systems

What MACP® Is and How It Works

Manholes are one of the most accessible and information-rich assets in a collection system, providing direct visibility into structural conditions, infiltration sources, and network performance risks before those problems appear elsewhere in the system. NASSCO’s Manhole Assessment Certification Program (MACP®) is the recognized national standard for turning that visibility into defensible, usable data.

MACP® defines how inspectors document conditions across six manhole components: cover and frame, chimney, cone, wall, bench and channel, and pipe connections. It assigns severity ratings on a 1-5 scale that are calculated separately for Structural and O&M defects. Those ratings flow into standardized deliverables, including the NASSCO Exchange Database file, that integrate directly with asset management platforms and GIS environments.

The standard also defines two inspection levels designed to work together. Level 1 provides rapid condition screening across large inventories. Level 2 delivers the detailed component measurements and defect documentation that rehabilitation planning requires. The most effective programs use both strategically, maintaining broad coverage with Level 1 while directing Level 2 resources toward higher-risk assets, rather than applying the same approach uniformly across every structure.

Common Challenges Organizations Face With Manhole Inspection Programs

Although many organizations perform manhole inspections, they still struggle to translate results into planning decisions.

Common challenges include:

• Inconsistent inspection standards across crews
• Incomplete documentation of structural condition
• Inspection data stored outside asset management systems
• Limited visibility across departments
• Outdated inspection cycles
• Difficulty prioritizing rehabilitation projects

These challenges are rarely caused by a lack of inspection activity. More often, they reflect inspection programs that were built around field collection rather than planning and rehabilitation workflows aligned with NASSCO condition assessment standards.

Organizations working with limited inspection resources often improve inspection coverage and data usability by modernizing how condition assessment information is collected, standardized, and shared across teams. Many are shifting toward sewer inspection software that improve visibility across departments while supporting more consistent infrastructure inspection planning with existing resources. Programs that align inspection standards, workflows, and data storage practices produce more reliable planning outcomes and make better use of existing staff capacity.

Setting an Effective Inspection Frequency

Industry best practice calls for inspecting 20-25% of total manhole inventory annually, a cadence that completes a full inventory cycle every four to five years and keeps condition data current enough to support defensible capital planning. Programs operating below this threshold face a compounding problem: the older the data, the less reliable the priorities derived from it, and the harder it becomes to make the case for rehabilitation investment to leadership and elected officials.

What Should Be Collected During a Manhole Inspection

Inspection programs deliver the most value when field data supports both maintenance operations and capital planning decisions.

A complete inspection record typically includes:

• Structural condition observations
• Operations and maintenance observations
• Frame and cover condition
• Infiltration indicators
• Rim elevation and depth measurements
• Pipe connection observations
• Photographic documentation
• Location verification

Collecting consistent information across the system’s manhole inventory allows organizations to compare structures over time and identify trends that support proactive rehabilitation planning. Inspection data becomes significantly more valuable when it is stored in a format that can be queried, mapped, and shared across departments.

Understanding Condition Grading

MACP® uses a 1-5 condition grading scale applied to individual defect observations. Three aggregate ratings summarize overall structure conditions. The Overall Manhole Rating (OMR) provides a cumulative severity score across all components and is the primary metric for ranking assets in rehabilitation priority lists. The Quick Rating (QR) offers a shorthand summary of the most severe defects for rapid screening. The Manhole Rating Index (MRI) represents average defect severity, useful for comparing structures with very different defect counts over time.

Understanding how these ratings are constructed matters for how programs use them. Sorting by OMR produces a defensible, data-driven rehabilitation priority list. Filtering by structural grade identifies assets that require capital attention regardless of their total defect count. Both are legitimate planning tools, but they answer different questions.

Turning Inspection Data Into Program Decisions

A MACP®-compliant inspection produces structured, standardized data in a format designed to flow directly into asset management systems. The strategic question is whether that data is actually being used to drive decisions, or being filed and forgotten.

When inspection records remain isolated in static reports or contractor databases, their value is limited. When they integrate with GIS and asset management platforms, they support decisions across the entire infrastructure lifecycle.

Programs that operationalize their inspection data use it to rank rehabilitation priorities by condition grade, identify infiltration and inflow sources through O&M coding patterns, establish condition baselines that can be tracked across successive inspection cycles, and feed risk-based asset management frameworks that weigh both likelihood and consequence of failure.

Building a Manhole Inspection Program That Supports Long Term Decisions

Organizations who operate successful manhole programs use MACP® as their defined inspection standard. They maintain consistent inspection cycles across their inventory. They collect repeatable condition data that supports maintenance and engineering workflows. They store inspection results in systems that allow staff to query and analyze asset conditions over time.

Most importantly, they treat inspection programs as part of their broader asset management strategy rather than as isolated field activities.

When inspection data supports planning conversations, budget development, and rehabilitation prioritization, organizations gain a clearer understanding of infrastructure needs and can respond more effectively to long term system risks.