Stormwater CenterDesign · Data · Practice

Storm Drain Maintenance

Storm drain maintenance is a fundamental municipal practice involving the inspection, cleaning, and repair of the underground pipe network that conveys stormwater runoff. A proactive maintenance program ensures that the conveyance system, known as a Municipal Separate Storm Sewer System (MS4), functions as designed to prevent flooding. It is also a critical pollution prevention measure that removes accumulated pollutants from the pipes before they can be washed into local rivers, lakes, and streams.

Without regular cleaning, storm drain pipes can become a significant source of pollution. Over time, sediment, trash, leaves, and other debris settle in sections of the pipe with low slopes or sags. These accumulated materials become reservoirs for contaminants such as heavy metals (copper, lead, zinc), hydrocarbons from vehicle traffic, nutrients like phosphorus and nitrogen from fertilizers and organic matter, and bacteria. During heavy rain, high-velocity flows can scour these deposits, mobilizing them and delivering a concentrated pulse of pollution to downstream water bodies.

A well-managed storm drain maintenance program is a core component of MS4 permit compliance for many municipalities. By systematically inspecting the system, removing blockages, and properly disposing of the collected material, communities protect both public infrastructure and water quality. This practice also provides a valuable opportunity to identify and address structural defects or illicit discharges within the system.

How storm drain maintenance prevents pollution

The primary pollution pathway addressed by storm drain maintenance involves the accumulation and subsequent scour of contaminants within the conveyance pipes themselves. Stormwater runoff entering the system carries a variety of pollutants. While the system is designed to transport water, solids and the pollutants attached to them can settle out of suspension wherever water velocity decreases. This commonly occurs in pipes with low gradients, in sags or “bellies” in the pipe line, and upstream of partial blockages.

These deposits do not remain inert. Organic material decomposes, releasing nutrients. Metals and hydrocarbons that were bound to sediment particles can become more mobile. During a large storm, the flow rate and velocity within the pipe increase dramatically. This surge of energy can re-suspend and scour the accumulated materials, flushing them out of the system in a highly concentrated discharge. The result is that the storm drain system, intended only as a conduit, becomes an active source of pollution, degrading the quality of the receiving water body.

Regular cleaning removes these accumulated pollutant stores from the pipes under controlled conditions. By capturing the material with vacuum equipment, the pollutants are removed from the watershed entirely. This preventative action breaks the cycle of accumulation and scour, significantly reducing the pollutant load delivered at the outfall during storm events. Furthermore, clean pipes with full hydraulic capacity reduce the risk of street flooding, which can mobilize additional surface pollutants and cause sanitary sewer overflows.

Recommended practices

A successful storm drain maintenance program is built on a cycle of inspection, prioritized cleaning, and proper material disposal, all tracked within an asset management framework.

Inspection Programs

Systematic inspection is the foundation for prioritizing maintenance efforts. A comprehensive program includes several types of inspection:

  • Routine Manhole and Outfall Inspection: Staff can perform visual inspections of manholes and outfalls to check for signs of blockages, structural damage, or dry-weather flows that might indicate an illicit discharge. These are often done on a rotating basis, with critical locations checked annually.
  • Complaint-Based Inspection: Investigations are triggered by reports of localized flooding or suspected pollution from residents or other municipal departments.
  • Closed-Circuit Television (CCTV) Inspection: A robotic camera is sent through the pipe to provide a detailed view of its internal condition. CCTV is invaluable for precisely locating blockages, identifying structural defects like cracks and offset joints, and confirming suspected illicit connections. While more expensive, it is the most effective way to assess pipe condition and is often used to evaluate high-priority lines or investigate problem areas.

Cleaning Methods

The most common method for cleaning storm drain pipes is hydraulic flushing using specialized equipment.

  • Jetting and Flushing: This method uses a high-pressure water jet to scour the interior of the pipe. A specialized nozzle is propelled up the pipe from a downstream manhole against the flow of water. As the hose is retrieved, the water jets blast sediment, grease, and debris from the pipe walls, and the water flow carries the material back downstream.
  • Downstream Capture: It is absolutely critical that all flushed material is captured at the downstream manhole. Simply flushing pollutants from one pipe segment to the next is not effective pollution prevention. Capture is typically achieved by placing a vacuum hose from a combination truck into the downstream manhole to continuously remove the slurry of water and debris as it is washed down.
  • Equipment: The industry standard is the combination jet-vac truck, which combines a large water tank and high-pressure pump for jetting with a powerful vacuum system and debris tank for material capture. A typical crew consists of two to three trained operators. Jetting is most effective for pipes up to 36 or 48 inches in diameter. Larger culverts may require specialized equipment or manual cleaning methods.
field note

During flushing operations, crews observe that the first pass of the jetter nozzle often dislodges the most visible and concentrated plume of dark, fine sediment. This underscores the importance of having the downstream vacuum system fully engaged before jetting begins to capture this initial, highly contaminated slug of material.

Material Handling and Disposal

The mixture of sediment, debris, and water collected by the vacuum truck must be managed properly. The collected material, or “spoils,” is typically transported to a designated dewatering facility or laydown area. The solids are allowed to settle, and the excess water (decant water) is drained off. The decant water is typically discharged to a sanitary sewer system with prior approval from the wastewater treatment authority. The dewatered solids must be characterized to determine the appropriate disposal method. In most cases, it is classified as non-hazardous solid waste and can be taken to a sanitary landfill. However, material from industrial or high-traffic areas may require testing for contaminants before disposal.

Scheduling and Prioritization

To be cost-effective, cleaning efforts should be prioritized. An asset management system using GIS is the best tool for this. Prioritization should be based on:

  • Inspection Data: Pipes with significant observed sediment accumulation or structural issues.
  • Pipe Characteristics: Low-slope pipes (e.g., less than 1% grade) are more prone to sediment buildup.
  • Maintenance History: Areas with a history of flooding complaints or frequent blockages.
  • Downstream Resources: Pipes that discharge to sensitive water bodies like trout streams or swimming beaches.

Cleaning is most effective when performed during dry periods. Many municipalities focus their cleaning programs in the late summer and early fall to ensure the system has maximum capacity before the onset of winter or a rainy season.

Building a municipal program

A systematic storm drain maintenance program is a requirement of most MS4 permits issued under the Clean Water Act. These permits require municipalities to develop and implement programs to reduce pollutant discharges from their storm sewer systems, and system maintenance is a key component.

An effective program requires a clear institutional framework. This includes having ordinances that grant the municipality the authority to access and maintain the storm drain system, including on private property where necessary easements exist. A comprehensive, up-to-date map and inventory of the system, preferably in a GIS database, is essential for planning, tracking, and reporting on maintenance activities.

Staffing consists of trained equipment operators and supervisors. Crews must be trained in safe equipment operation, traffic control, and confined space entry procedures. They also serve as first responders in the field, and should be trained to recognize and report potential illicit discharges or evidence of illegal dumping. When a suspected spill or illicit discharge is encountered, crews should follow the municipality’s established spill control and notification procedures.

Program costs can be significant, driven by specialized equipment, trained staff, and disposal fees. A combination jet-vac truck can cost over $400,000. Contracted cleaning costs are often priced per linear foot and can range from $3 to $10 or more, depending on pipe size, access, and the amount of material removed. Proactive, scheduled cleaning is almost always more cost-effective than reactive cleaning in response to flooding or system failures.

Effectiveness

Storm drain maintenance is considered a source control and maintenance activity, not a structural best management practice (BMP) with standardized pollutant removal efficiencies. Its effectiveness is measured by the mass of pollutants removed from the system before they can be discharged to a receiving water.

The quantity of pollutants removed can be substantial. Studies have shown that cleaning can remove hundreds to thousands of pounds of solids per mile of pipe. These solids carry with them associated pollutants like phosphorus, nitrogen, and heavy metals. While direct effectiveness percentages are not typically assigned to this practice, the mass of pollutants removed can be tracked and compared to watershed-wide loading estimates, which can be modeled with tools like a Simple Method runoff calculator, to demonstrate the program’s benefit.

Beyond direct pollutant removal, the practice has several other key benefits for water quality and community resilience. It restores the hydraulic capacity of the pipe system, reducing the frequency and severity of localized street flooding. It also provides a critical opportunity for staff to identify and report failing infrastructure or illicit connections, preventing more serious problems in the future.

Frequently Asked Questions

How often should storm drain pipes be cleaned?

There is no single answer, as the ideal frequency depends on local conditions. A common approach is to establish a system-wide cleaning cycle of 5 to 10 years, meaning every pipe is scheduled for cleaning within that timeframe. However, high-priority areas, such as those with flat pipes, significant upstream sediment sources, or discharges to sensitive waters, may be cleaned much more frequently, such as every 1 to 3 years. A good inspection program helps to identify which pipes need cleaning most urgently, allowing resources to be focused where they are most effective.

What is the difference between catch basin cleaning and storm drain cleaning?

The two practices are related but distinct parts of storm sewer maintenance. Catch basin cleaning focuses on removing accumulated sediment and debris from the inlet structures (the grated drains along streets) which are designed with a sump to trap this material. Storm drain cleaning, the topic of this page, addresses the pipes that connect the catch basins and convey the water. While catch basins trap coarse debris, finer sediments can still be carried into the pipes, where they can settle and accumulate over time. A complete program addresses both components of the system.

What happens to the material removed from storm drains?

The material, a slurry of water, sediment, and debris, is vacuumed into a truck and transported to a designated facility. There, it undergoes dewatering, where the solids settle out and the excess water is drained off. The water, known as decant, is typically sent to a sanitary sewer for treatment at a wastewater plant, with permission. The dewatered solids are tested if necessary to ensure they are not hazardous. In most cases, they are classified as municipal solid waste and can be disposed of in a licensed landfill.

How much does storm drain maintenance cost?

Costs vary widely based on whether the work is done by in-house municipal crews or external contractors. Contractor pricing is often based on a per-linear-foot basis and can range from approximately $3 to $10 per foot. Factors influencing the cost include the diameter of the pipe, ease of access to manholes, the amount of material that needs to be removed, traffic control requirements, and local disposal fees for the collected material. Emergency call-outs for blockages are significantly more expensive than planned, preventative maintenance.

Can storm drain flushing cause pollution downstream?

Yes, if performed improperly. The entire purpose of the high-pressure jetting is to dislodge accumulated pollutants. If this material is not captured at the next downstream manhole, the process simply washes a concentrated slug of pollution further down the system and ultimately out into a stream or lake. This is why proper downstream capture, typically using a vacuum truck, is an essential and non-negotiable part of the cleaning process. Without it, the activity can do more harm than good.

What should crews do if they find a strange substance in a storm drain?

Field crews are the eyes and ears of the stormwater program. If they observe unusual colors, odors, oily sheens, or sudsy water during maintenance, they should treat it as a potential illicit discharge or spill. The first step is to ensure their own safety. They should then halt cleaning operations that could spread the substance and immediately report the finding to their supervisor. The supervisor should then initiate the municipality’s formal spill response and illicit discharge detection and elimination (IDDE) plan, which may involve environmental health staff, the fire department, or state environmental agencies.

Does storm drain maintenance help prevent flooding?

Yes, absolutely. This is one of the primary drivers for the practice. Over time, the accumulation of sediment, trash, and root intrusion can significantly reduce the internal diameter of a storm drain pipe, restricting its hydraulic capacity. A pipe that is 50% blocked by sediment can carry much less than half of its original design flow. By removing these obstructions, storm drain maintenance restores the full conveyance capacity of the system, making it much more resilient during heavy storm events and reducing the likelihood of street and property flooding.