This document provides information from a training on privately maintained stormwater management facilities held by Fairfax County, VA. The training covered the inspection and maintenance of various below ground stormwater best management practices (BMPs) such as underground detention vaults, sand filters, and manufactured devices. Common deficiencies like debris accumulation and structural damage were shown and remedies like cleaning and repair/replacement were discussed. Safety protocols around confined space entry were also emphasized.

1. A Fairfax County, VA, publication
Department of Public Works and Environmental Services
Working for You!
Stormwater Maintenance Awareness Training
For privately maintained stormwater management facilities
Maintenance and Stormwater Management Division (MSMD)
Winter 2018

2. Stormwater Maintenance Awareness Training
MSMD/DPWES
Course Schedule
AM session (includes two short breaks)
– History of SWM and regulations
– County inspection basics
– The inspection report and MAR
– Common SWM/BMP types
• Common maintenance items-General
– Common SWM/BMP types, deficiencies, and remedies
• Above Ground Facilities
12:00-1:00 PM Lunch
PM session (includes two short breaks)
– Common SWM/BMP types, deficiencies, and remedies
• Below Ground Facilities
• Vegetative Practices
– Closing remarks/questions
2
NOTE: All pictures, unless noted, are the property of Fairfax County.

3. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-General Safety
3
The County’s private inspection program does NOT allow
for Confined Space Entry!
Please ensure you are properly certified, have the proper
entry permits, and are appropriately equipped before
entering any applicable confined space!

4. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-General Safety
4
The County’s private inspection program does NOT
allow for Confined Space Entry!
Please ensure you are properly certified, have the
proper entry permits, and are appropriately equipped
before entering any applicable confined space!
In the event that CSE is necessary
for proper facility maintenance
• Any confined space entry must
be conducted by personnel
with proper training and
equipment

5. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
• An underground basin which
temporarily stores stormwater runoff
• Control structure
• Inflow
• Detention structure
• Outfall
5
Picture: Georgia Stormwater Management Manual 3.4-15, figure 3.4.3-1 “Example Underground Detention Tank System”
UNDERGROUND DETENTION
COMPONENTS

6. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
• Detention Pipe/Vault Types:
– Corrugated Metal Pipe (CMP)
– Concrete pipe
– Box culvert
– HDPE (High-density Polyethylene)
– Large concrete vault
6
NOTE: Some of these photos may show deficiencies as well as pipe/vault types.

7. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
• Control Weir & Orifice Types:
– Concrete
– CMP Half-Round
– Multiple orifices
7
NOTE: Some of these photos may show
deficiencies as well as control
weir/orifice types.

8. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
• “TRUGS”
Some UGs include underground trenches, composed of a perforated pipe
within an aggregate bed or a plastic modular structure, both meant to
incorporate groundwater infiltration capabilities into the facility.
8
Perforated pipe with aggregate bed design examples:
Modular, stackable design
Perforated CMP Concrete with drilled holes
NOTE: Some of these photos may show deficiencies as well as TRUG design types.

9. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
Routine Deficiencies Observed
Pipes (Sediment/Debris Accumulation)
9
Debris and sediment accumulation inside pipes

10. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
Pipes (Damage and Deterioration)
10
Damage and/or deterioration inside pipes

11. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
Pipes (Damage and Deterioration, Continued)
11
Spalling and exposed rebar Spalling and deterioration of control
structure’s outflow pipe

12. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
Pipes (Damage and Deterioration, Continued)
12
Patching brick work around pipes…

13. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
Control Structure (Sediment/Debris Accumulation and Concrete Damage)
13
Trash/debris/sediment in
control structure
Standing water after several
dry weather days indicates a
flow blockage
Deterioration and
spalling around
control structure

14. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
Orifice Blockage and Missing Components
14
Downstream view of orifice
blockage
Upstream views of orifice
blockages

15. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
Trash Rack and Orifice Plate
(Blockages, damage, missing components, etc.)
15
Sediment build-up, looking
upstream through the orificePonded water suggests a possible
orifice blockage
Debris blocks trash rack

16. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
• Common Remedies
– Remove all flow blockages as well as any additional trash, debris, and
accumulated sediment
• Special attention should be given, as required, to a thorough
vacuum and Hydrojet of the interior of structure
– Repair/replace any damaged/missing components
• Components vary by facility type and design, and they can range
from parts to structural to environmental materials (see prior noted
examples)
– Check plans for specific facility requirements
– Rebuild/stabilize any areas with erosion, cave-ins, and bare spots:
• Cave-ins require additional investigation to determine cause and
prevent re-occurrence
16

17. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
• Common Remedies
– Repair/replace any damaged/missing components (continued)
• For damaged/misaligned pipes:
– Reinforce/repair, if possible (Internal bands and gaskets)
– Slip-line pipes when possible
– Excavate and replace/reseal, if first two options are not possible
– Obtain appropriate Confined Space Certification for applicable systems
17

18. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
• Provide water quality control by
filtering stormwater through a
gravel and sand bed
18
• Different sand filter types and
components:
– D.C. Sand Filter (In-Line)
– Delaware Sand Filter (Side-by-Side)
– Austin Sand Filter (Above-Ground)
Filter chambers in
good condition
D.C. SAND FILTER

19. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
19
Filter chambers in good
to moderate condition
Sediment
Chamber
Clearwell
Filter
Chamber
Delaware Sand Filter
SAND FILTER COMPONENTS

20. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
• Gravel riprap
• Sand
• Cleanouts
20
Austin Sand Filter
SAND FILTER COMPONENTS
• Perforated underdrain
• Geotextile fabric
• Outfall pipe

21. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
Routine Deficiencies Observed
Sedimentation and Filter Chambers (Trash/debris accumulation)
21
Debris in the Sedimentation Chamber
Trash and sediment accumulation in the
Filter Chamber - If a filter chamber is still
holding water after three days of dry
weather, it is likely clogged or blocked.

22. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
Dewatering Valves (open or missing)
22
Dewatering valves must remain CLOSED, except during maintenance
activities or the facility will be non-functional.
Valve not fully closed One of the valves has
fallen off and is lying on
the chamber floor

23. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
Dewatering Valves/Confined Space
What are some of the safety
concerns and improper practices
shown in this picture?
23

24. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
Filter Media (Uneven)
24
These photos are all from the same sand filter facility.

25. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
• Common Remedies
– Remove all flow blockages as well as any additional trash, debris, and
accumulated sediment
• Special attention should be given, as required, to a thorough
vacuum and Hydrojet of the interior of structure
• Do not Hydrojet the filter chamber
– Removal/replacement of top layer of filter bed may be required
– Repair/replace any damaged/missing components
• Components vary by facility type and design, and they can range
from parts to structural to environmental materials (see prior noted
examples)
– Check approved site plans for specific facility requirements
25

26. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
• Common Remedies
– Repair/replace any damaged/missing components (continued)
• For damaged/misaligned pipes:
– Reinforce/repair, if possible (Internal bands and gaskets)
– Slip-line pipes when possible, as this may be most cost effective
– Excavate and replace/reseal, if first two options are not possible
– Rebuild/stabilize any areas with erosion, cave-ins, and bare spots:
• Cave-ins require additional investigation to determine cause and
prevent re-occurrence
– Obtain appropriate Confined Space Certification for applicable systems
– Maintenance for Austin sand filters may be similar to that for a dry pond
26

27. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
• A pre-fabricated stormwater treatment structure utilizing one or more of
the following to remove pollutants from stormwater runoff:
– Settling
– Filtration
– Absorptive/adsorptive materials
– Vortex separation
– Vegetative components
• There are many kinds of MBs, which fall into two types:
– Non-proprietary (public-domain)
– Proprietary (patented or factory-made*)
• Follow manufacturer’s maintenance recommendations, which may
require the contractor to be certified to perform the maintenance
27
* Note proprietary MBs are attributed (to the extent possible) to the patent holder as identified at the time of training material
preparation. The following examples are commonly available/utilized technology. The inclusion of these products as examples for
training purposes does not constitute any real or implied endorsement of these products by Fairfax County.

28. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Example of a non-proprietary MB: Oil-Grit Separator
28
Picture: US Department of Transportation, Stormwater Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring, Fact Sheet:
Oil/Grit Separator Units”, https://www.environment.fhwa.dot.gov/ecosystems/ultraurb/3fs12.asp

29. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Example of a proprietary MB: StormFilter
(Plan Detail for MB0173)
29
InletBay
Cartridge Bay
OutletBay
www.conteches.com

30. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
30
ABOVE: StormFilter cartridge
RIGHT: 33+ cartridges during
installation
www.conteches.com
STORMFILTER COMPONENTS

31. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
31
Energy dissipater or level spreader is
located at the upstream end of the
cartridge bay
www.conteches.com
STORMFILTER COMPONENTS

32. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
32
Flow spreader
www.conteches.com
Underdrain pipes
STORMFILTER COMPONENTS

33. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
33
StormGate directs low flows toward the
StormFilter while allowing higher flows to bypass
StormGate
www.conteches.com
STORMFILTER COMPONENTS

34. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Example of a proprietary MB: Vortech Stormwater Treatment System
34
Hydrodynamic Separation
www.conteches.com

35. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Example of a proprietary MB: Stormceptor
35

36. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Example of a proprietary MB: Downstream Defender
36
Hydrodynamic
Separation
http://www.hydro-int.com/us/products/
downstream-defender

37. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Example of a proprietary MB: StormTreat System
37
www.stormtreat.com
Bio-Media Filtration

38. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Routine Deficiencies Observed
Accumulated Trash/Debris/Grit/Sediment/Floatables
38
Collected grit, sediment, and
floatable debris in the Oil/Grit
Separator
Regular maintenance is required to
remove collected materials like these
Trash, sediment, and debris in the StormFilter

39. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Spalling/Deterioration/Damage to Components
39
Spalling and exposed rebar around pipe
end, inside chamber looking downstream
toward outfall

40. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Common Remedies
• Proprietary MBs
– Follow Manufacturers Guidance/Recommendations
• Non-Proprietary MBs
– Remove all flow blockages as well as any additional trash, debris,
and accumulated sediment
• Special attention should be given, as required, to a thorough
vacuum and hydrojet of the interior of structure
– Repair/replace any damaged/missing components
• Components vary by facility type and design, and they can
range from parts to structural to environmental materials (see
prior noted examples)
– Check plans for specific facility requirements
40

41. Stormwater Maintenance Awareness Training
MSMD/DPWES
Below Ground Facilities-Manufactured BMPs (MB)
Common Remedies
• Non-Proprietary MBs (continued)
– Repair/replace any damaged/missing components (continued)
• For damaged/misaligned pipes:
– Reinforce/repair, if possible (internal bands and gaskets)
– Slip-line pipes when possible, as this may be most cost effective
– Excavate and replace/reseal, if first two options are not possible
– Rebuild/stabilize any areas with erosion, cave-ins, and bare spots:
• Cave-ins require additional investigation to determine cause and
prevent re-occurrence
– Cut back overgrown vegetation around facility structures to facilitate
access and proper function
– Obtain appropriate Confined Space Certification for applicable systems
41

42. Additional Information
For additional information, please contact
MSMD/DPWES 42
Todd Nelson
703-877-2800, TTY 711
www.fairfaxcounty.gov/publicworks