image showing staff collecting data from surface water
Staff collecting water data

Municipal operation inspections

Municipal operation inspections help reduce the impacts to stormwater from municipally owned or operated facilities, areas, or stormwater best management practices (BMPs). Staff conducting these inspections can stop pollution before it reaches stormwater, or minimize the impacts if your BMPs have failed or need maintenance.

The municipal separate storm sewer system (MS4) General Permit requires inspections of the following: (MS4 General Permit Part III.D.6.e)

  • Annual inspections of structural stormwater BMPs to determine structural integrity, function, and maintenance needs.
  • At least one inspection every permit term of stormwater ponds and outfalls to determine structural integrity, function, and maintenance needs.
  • Quarterly inspections of stockpiles, and storage and material handling areas identified in the Facility Inventory to determine function and maintenance needs.

During each of these inspections, inspectors must look for evidence of illicit discharges (MS4 General Permit Part III.D.3.c.). All inspections must be documented (MS4 General Permit Part III.D.6.h.(1)), so save any checklists that you are using.

Municipal Operations inspections required by the MS4 General Permit
For a PDF version of this table, click here.

What to inspect When to inspect Why inspect Examples of how-to inspect What to document
Structural stormwater best management practices (BMPs) including green roofs, permeable pavement, infiltration basins or trenches, raingardens, filtration devices, sand filters, hydrodynamic devices, etc. [Part III.D.6.e.(1)] Annually To determine structural integrity, proper function, and maintenance needs
  • Identify clogged, overloaded, and full devices, inlets, or outlets
  • Identify misaligned inlets or outlets/overflow devices
  • Identify materials that are deteriorating and releasing pollution
  • Identify erosion/channelization, sedimentation, soil slides, animal burrows, undercutting, displaced riprap, or other problems
  • For infiltration practices that should be dry (e.g. infiltration basins, filter strips/swales) identify standing water or wet spots
    • If standing water is present, determine if the device is functioning as designed and meeting the 48 hour draw down requirement
  • Identify excess or unwanted vegetation (e.g. long-grass, tree growth)
  • If vegetation is designed to be present (e.g. bioretention basins, filter strips/swales), determine if the vegetation is healthy, is of appropriate size/density, and free of weeds and invasive species
  • Inspection findings and date [Part III.D.6.h.(1)]
  • Dates & description of maintenance [Part III.D.6.h.(3)]
Outfalls where an MS4 discharges to a receiving water, or the discharge permanently leaves the MS4 [Part III.D.6.e.(2)] Once per each permit term To determine structural integrity, proper function, and maintenance needs
  • Identify erosion/channelization, scour, or other problems
  • Identify displaced, damaged, missing, or clogged riprap
  • Identify missing or damaged grates or guards, if applicable
  • Identify cracked, undercut, or spalled aprons, if applicable
  • Identify unwanted vegetation growth or decay, litter or debris, sediment buildup, or animal dens that may obstruct flow of water
  • Inspection findings and date [Part III.D.6.h.(1)]
  • Dates & description of maintenance [Part III.D.6.h.(3)]
Stormwater ponds [Part III.D.6.e.(2)] Once per each permit term To determine structural integrity, proper function, and maintenance needs
  • Identify scour, erosion/channelization, sedimentation, litter, animals burrows, undercutting, displaced riprap or other problems at/around the banks, inlets, or outlets
  • Identify clogged or overloaded inlets or outlets
  • Identify excess or unwanted vegetation (e.g. long-grass, new trees)
  • Identify and record materials within the device that are deteriorating and releasing pollution into the stormwater system
  • Determine if the vegetation looks healthy, is of appropriate size/density, and free of weeds and invasive species
  • Determine if there is evidence of sedimentation or erosion downstream of the outlet
  • Inspection findings and date [Part III.D.6.h.(1)]
  • Dates & description of maintenance [Part III.D.6.h.(3)]
Stockpiles, and storage and material handling areas that are inventoried in the Facilities Inventory [Part III.D.6.e.(3)] Quarterly To determine maintenance needs and proper function
  • Identify leaking, leachate, or runoff
  • Identify undercut, full, clogged, ripped, broken, misplaced, askew, or other BMP maintenance needs
  • Install additional BMPs, such as secondary containment, impervious cover, runoff collection areas as needed
  • Inspection findings and date [Part III.D.6.h.(3)]
  • Dates & description of maintenance [Part III.D.6.h.(3)]
Illicit discharges (Part III.D.3.c.&f.) During the structural stormwater BMP; outfall; pond; and stockpile and storage and materials handing inspections To identify and eliminate illicit discharges to the MS4
  • Identify and characterize any dry weather flow
  • Describe the material (color, odor, sheen, froth, etc.), its effects (e.g. corrosion, pipe etching), or, if appropriate, analyze chemically
  • Investigate potential upstream sources that may be contributing non-stormwater flow
  • Record clear, unpolluted dry weather flows. If present, the discharge may be coming from unregulated sources
  • Inspect areas that you've identified as priority areas likely to have illicit discharges (e.g. business/industrial areas, where illicit discharges have been identified in the past)
Dates and locations of IDDE inspections conducted [Part III.D.3.h.(1)]
Construction activity At the frequency identified in the Construction Site Inspection procedure for your MS4 To prevent and minimize erosion to reduce the amount of sediment from entering your MS4
  • Inspect for items required by the MPCA construction stormwater permit and your regulatory mechanism, some examples include:
    • Are erosion and sediment control and vehicle tracking BMPs effective, in good working condition, and able to perform their intended function?
    • Are soils stabilized where needed?
    • Do pipe outlets have energy dissipation?
    • Are inlets protected?
    • Are solid and hazardous wastes contained, stored, and properly disposed of?
    • Is the contractor conducting the required site inspections?
    • Is the permanent stormwater BMP designed appropriately and protected?
    • Are temporary sedimentation basins used and with BMPs?
    • Is dewatering discharging to a sediment basin or preventing nuisance conditions?
  • Identify any potential pollution problems related to stormwater runoff or infiltration into the groundwater
  • Determine if any additional BMPs may be appropriate
Checklist or other written means to document what was inspected for [Part III.D.4.h.(1)]

Resources

Fact sheets and guidance documents

Checklists and templates

BMP inspection checklists

Pond inspection checklists

Outfall inspection checklists

This page was last edited on 12 February 2018, at 15:57.

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