Stormwater 101: Underground Inspection

December 19, 2014

DEP’s Stormwater Facility Maintenance Program is responsible for inspecting and ensuring maintenance of all public and private stormwater management facilities within Montgomery County.  DEP Planning Specialist Audra Lew guest blogs about the important role the inspectors play in the County:

What are stormwater management facilities?

The Department of Environmental Protection (DEP) stormwater management (SWM) facility inspectors are responsible for monitoring the effectiveness and functioning of all stormwater facilities in the County. The inspectors are responsible for both above ground and underground stormwater management structures.


Dry pond

Dry ponds and sand filters are two types of above ground stormwater management structures.


Ponds and sand filters are the most common above ground features.  As far as underground features, you may never see those save for manholes and inlets in parking lots.  The purpose of the SWM facilities is to collect the “first flush” of stormwater, usually contaminated with street pollutants (oils, grit, detergents, deicers, etc.), fertilizers, and pet waste from lawns. The facilities retain large volumes of this stormwater, allowing some of the pollutants to settle or filter out before reaching our streams and rivers.


underground stormwater facility

One example of parking lot manholes and an inlet that lead to an underground stormwater facility.


The role of inspectors

Using mobile technology, DEP SWM facility inspectors work throughout the county to inspect the more than 7,000 SWM facilities. The photos below capture an hour in the life of Inspector Rick Watson as he checks an underground structure at a county facility. Based on the inspection results, this structure has collected too much sediment and will need cleaning. The county’s SWM facility maintenance contractor will be tasked to clean the facility to the inspector’s satisfaction.

Clean, functioning SWM structures are key to healthy local creeks, streams, rivers and ultimately the Chesapeake Bay.  For more information on the SWM Facilities Inspection Program and how you can help the county manage stormwater, please visit


Using mobile technology to locate SWM facilities

Inspector Watson utilizes mobile technology to locate the stormwater management facility, examine plans, and record results.


Looking for trash and sediment buildup

Inspector Watson documents his findings with photos. He is looking for trash and sediment build up as well as structural damage that may decrease the functionality or safety of the facility.


Using special tools to measure sediment levels

Inspector Watson uses a clear tube with depth measurement markings to evaluate the level of sediment inside the facility.


Sediment levels show this facility needs to be cleaned

Based on his findings of sediment build-up, Inspector Watson will task the County’s maintenance contractor to clean this facility.


Guest blog by Audra Lew, Stormwater Facility Maintenance Program Planning Specialist, DEP

4 comments on "Stormwater 101: Underground Inspection"

  1. Audra Lew says:

    Here’s a link to a page containing fact sheets describing common types of SWM structures in the County:

  2. I just wanted to thank you for helping me learn more about stormwater. It’s so interesting that the inspectors use a clear tube to be able to evaluate what the sediment level is like. I’m kind of interested to learn more about how much sediment should be built up before you can clean it, or how much is a normal amount.

    1. jjones says:

      Thanks Taylor for your comment! We’ll forward your question to our stormwater facility maintenance folks who are best equipped to answer your question. You can send any other questions to

    2. jjones says:

      I spoke to Inspector Watson who said,

      “sediment measurement are as follows:

      0″ inches to 2″ inches is considered clean or passed and no maintenance (cleaning) is required.

      2″ inches and above is considered dirty or failed and Maintenance (cleaning) is required.”

      We hope this helps!

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