Wet Weather Inspections to Find Inflow and Infiltration (I&I) – Part 1

Unidentified sewer problems and inflow and infiltration (I&I) can result in sewage back-ups, spills, and overflows as well as overall reduced system capacity. Civica specializes in a wide range of field and consulting services including flow monitoring, CCTV inspections, maintenance hole inspections, smoke & dye testing, and other wet-weather inspections to help identify, analyze, and remediate inflow and infiltration, along with their associated system defects.

This article highlights the various reasons for inflow and infiltration, with a focus on wet-weather inspections as a tool to find I&I.

Why Is Inflow and Infiltration a Problem?

Inflow and Infiltration is a problem for a number of reasons, primarily due to the following factors:

• Basement flooding (sewer backup)
• Environmental protection (CSO, SSO, bypass)
• Regulatory compliance
• Costly infrastructure upgrades
• Growth needs (new development)

Inflow and Infiltration Investigation Methods

Inflow and infiltration field inspections are utilized to locate and assess sources of excess water in sanitary sewers, which can cause various capacity problems. Civica utilizes the following inflow and infiltration investigation methods.

Sanitary Sewer Flow Monitoring:

This method features a few key areas such as delineation of flow monitoring catchment areas and proper site selection; installation, maintenance, and calibration of area-velocity meters, flumes and weirs; and data analysis tools used to calculate catchment area KPI’s for prioritization of further field investigations.

Lot Drainage Inventories:

For the lot drainage inventories method, inventories are conducted of potential I&I sources located on private and public lots (downspouts, roof leaders, catch basins, etc.).

Smoke and Dye Testing:

The smoke and dye testing method features investigations that identify potential sources of inflow from both the public and private sides. It also identifies potential cross connections between stormwater drainage features and the sanitary system. Dye testing confirms the hydraulic connection.

Maintenance Hole and CCTV Sewer Inspections:

This involves investigations that identify sources of infiltration within public sewer infrastructure. Video recordings and condition assessments of manholes, mainline sewers, and lateral sewers are used with a focus on defects with infiltration potential.

Wet-Weather Inspections:

Lastly, rapid response maintenance hole and CCTV investigations identify sources of rainfall derived from infiltration during and immediately following rainfall events.

What Is Wet Weather?

Before diving into inflow and infiltration field inspections, it is crucial to first examine what is considered to be wet weather as there is often a misconception about what wet weather inspections entail. To many people, wet weather is only when it is raining. While that is true, there are still instances of what wet weather can mean. Civica considers the following: 

• When it is raining
• Shortly after rain
• During spring snowmelt

Simply, wet weather is when I&I happens and when system capacity is most impacted.

Dry vs. Wet Weather Sewer Inspections

In dry weather conditions, the groundwater table or the antecedent moisture is low. During dry conditions, existing cracks and defects may not be under pressure from groundwater or rapid rainwater infiltration which may prevent technicians from seeing water infiltrating into the pipe.

In wet conditions, there is the presence of water outside the pipe (hydrostatic pressure is acting on the pipe) which will push water into the pipe if there are cracks and/or defects. Defects are not noticeable in dry conditions, which is why dry weather is not the best time to do an inspection to find I&I.

Stay tuned for the second part of this blog that outlines some specific cases of wet-weather inspections that Civica has conducted.

Why Choose Civica? 

Civica is a leader in water resources products, product integration and consulting services, driving innovation and experience to meet your drainage infrastructure management needs.  Stay tuned for part two of the webinar recap, which will take a deeper look into the different case studies in field inspections, the challenges of wet weather inspection, and its testing methods. To perform wet weather inspections, please contact Civica today.

Learn More at – 

Wet Weather Inspections to Find Inflow and Infiltration (I&I) – Part 2

Inflow and Infiltration Inspection Case Studies

Role of Flow Monitoring in Inflow and Infiltration (I&I) (Part 1)

Flow Monitoring and Its Role in Inflow and Infiltration (I&I) (Part 2)

Methodology of Sanitary Maintenance Hole Inflow and Infiltration

New Subdivision Flow Monitoring to Assess Performance of I/I Prevention