Stormwater Maintenance Awareness Training, Part II: Above Ground Facilities, October 6, 2015

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)
Fall 2015

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 issues-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
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NOTE: All pictures, unless noted, are the property of Fairfax County.

3. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
• Wet Ponds (WP) and Dry Ponds (DP) are both depressed basins
providing temporary storage for stormwater runoff.
– WP are designed to have a permanent pool.
– DP basins are designed to usually be dry, except when handling
runoff.
• Some DP basins may have permanent wet features, including deep cells,
micropools, or sediment forebays.
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4. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
WET POND COMPONENTS Profile of a typical WP
Plan view of WP with sediment
forebay and WL
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Pictures: VDEQ Stormwater Design Specification No. 14, Wet Pond, Version 1.9, 3/1/11, Figure 14.1 “Wet Pond Design Schematics”

5. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
Deficiencies Requiring Action:
Algae/Turbidity (WP only)
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Trash rack crushed/damaged,
requires replacement
BELOW: High turbidity caused by suspended
materials (soil, sediment, microbes, etc.) can
harm aquatic life, create clogging concerns,
and cause build-up.
ABOVE: Algal bloom and growth can create
significant water quality issues, impacting
plant and wildlife, as well as creating visual and
odor concerns.

6. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
Water level inconsistent with plans (WP only)
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s

7. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
DRY POND COMPONENTS - Under the new Virginia SWM regulations,
Extended Detention Ponds constructed after July 1, 2014 must include, at a
minimum, the following components:
• Sediment Forebay
• Micropool
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Pictures: VDEQ Stormwater Design Specification No. 15, Dry Pond, Version 1.9, 3/1/11, Figure 15.1 “Typical Extended Detention Pond Details”

8. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
DRY POND COMPONENTS - Dry Ponds constructed prior to July 1, 2014
are likely to have a simpler profile:
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LEFT Picture: Page 62, http://www.novaregion.org/DocumentCenter/Home/View/1679

9. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
Deficiencies Requiring Action (continued):
Trickle Ditches (DP only)
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TOP RIGHT: Erosion and
trenching along the trickle
ditch, with some overgrown
vegetation
BOTTOM RIGHT: Significant
spalling and deterioration of
concrete in trickle ditch
TOP LEFT: Obstruction or
blockage in trickle ditch
BOTTOM LEFT: Trickle ditch
with some significant sediment
and debris accumulation

10. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
Dam/Berm - Erosion and Failure
NOTE: Remaining slides apply to both WP and DP
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BELOW: Erosion of the dam face has led to significant
piping (formation of water channels throughout
embankment interior) and blockage, requiring immediate
attention
RIGHT: (Both pictures are from same site) Significant
erosion and sloughing of the dam/berm, requiring
immediate attention as this can lead to dam failure with
increasing area damage

11. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
Dam/Berm - Cave-Ins and Animal Holes
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LEFT: Dam/berm cave-ins,
possibly caused by pipe joint
separation, seepage, and/or
problems with the interior
dam fill
RIGHT: Animal holes on top
and side slope of dam/berm

12. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
Vegetation & Trash/Debris Accumulation
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RIGHT BOTTOM: Sediment accumulation and
debris reduces the holding capacity of the pond
and its ability to treat the designed volume of
stormwater runoff.
BELOW: Large appliance dumping and
other trash/debris accumulation from
upstream can critically impact facility
function & create problems downstream.
RIGHT TOP: The riser structure has
overgrown vegetation around it.

13. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
Trees and Woody Vegetation on Dam/Berm
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Back
Face
Control
Structure
No trees or woody vegetation should be on
any side of the dam/berm embankment
(face, back, top, etc.)
*Check site plans for specifics.
Pond
Floor

14. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
Riser/Trash Rack
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Significant sediment & debris
accumulation and trash rack
damage-requires cleaning and
trash rack replacement
Trash rack & low-flow orifice
plate, if required by site plans,
must be installed flush with
the riser structure, with no
gapping. Here, debris must be
cleared, then low-flow orifice
plate & trash rack properly re-
installed. Missing low-flow
orifice plates are a common
issue.
Inside riser blockage

15. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
Outfalls
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Undermining below outfall pipe (can be related to
separation at last joint of PSP, etc.)
Downstream blockage or impending blockage
within 20 feet of outfall structure (potential
back up and impact to water flow from the
PSP)
Erosion at curb cut inflow area,
needs repair

16. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
• Common Remedies
– Algal bloom, turbidity, and water level inconsistent with plans (WP only)
• Investigate and resolve cause(s), if at all possible
– Remove all flow blockages as well as any additional trash, debris, and
accumulated sediment
– Repair/replace any damaged/missing components
• Components vary by facility type and design, and they can range
from parts (trash racks, well caps, etc.) to structural (walls, concrete,
etc.) to environmental materials (soil, gravel, etc.)
– Check approved site plans for specific facility requirements
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17. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
• 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 more 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
• Fill-in/stabilize any animal holes, per plan maintenance guidelines,
to discourage occupancy and re-occurrence
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18. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Ponds (WP, DP)
• Common Remedies
– Cut back overgrown vegetation around facility structures to facilitate
access and proper function (WP/DP/WL have special requirements, as
noted below)
• Remove all trees and woody vegetation from the entire dam
embankment: face, back, top, etc.
– Check plans for a ‘Planting Plan’ which may have allowed
plantings on the dam embankment
• Remove overgrown vegetation
– Within 10’ of control structure
– Within 5’ of all other structures
– Within inflow/outlet channels
– Other areas, as needed, for facility access
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19. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Wetlands (WL)
• Shallow depressions that receive
stormwater for water quality
treatment by providing an ideal
environment for:
– Long residence time
– Gravitational settling
– Biological uptake
– Microbial activity
• Stormwater management benefits:
– Nutrient load removal and
reduction
• Nitrogen
• Phosphorus
• Sediment
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– Runoff volume reduction
– Channel protection
– Flood mitigation
Properly Functioning Example:

20. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Wetlands (WL)
• Inflow
• Forebay
• Weir wall
• Permanent pool
• Low flow orifice
• Riser
• Embankment
• Outfall
• Emergency spillway
• Micro-topographic features
• Tree peninsulas
• High and low marshes
• Micropools
• Deep pools
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Picture: VDEQ Stormwater Design Specification No. 13, constructed Wetlands, Version 1.9, 3/1/11, Figure
13.1 “Plan and Cross Sections of Constructed Wetland Level 1 and Level 2 configurations”

21. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Wetlands (WL)
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Picture: VDEQ Stormwater Design Specification No. 13, constructed Wetlands, Version 1.9, 3/1/11,
Figure 13.1 “Plan and Cross Sections of Constructed Wetland Level 1 and Level 2 configurations”

22. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Wetlands (WL)
Deficiencies Requiring Action
• Clogging of pipes from sediment, vegetation and debris
– If low flow orifice is clogged, it can result in a rapid change in
wetland water elevations.
• Sedimentation accumulations in forebays and micropools
• Erosion and braiding (channel separation and intermixing,
sometimes with formation of deposited bars or islands)
• Vegetation Issues
– Growth over access points
– Invasive species
– Dead, dying, missing vegetation
– Bare spots
– Trees and woody vegetation on dam embankment
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23. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Wetlands (WL)
• Common Remedies
– Remedies are the same as for WP/DP (please refer to slides 16-18)
– Additional vegetative concerns specific to wetlands:
• Remove any non-spec vegetation, especially if it impacts the health
and function of the facility, as designed
• Replace/replant any dead, dying, or missing wetland vegetation per
approved site plans
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24. Stormwater Maintenance Awareness Training
MSMD/DPWES
Above Ground Facilities-Rooftop Detention (RT)
• For more information call 703-877-2800 TTY 711
• Maintenance and Stormwater Management
• Department of Public Works and Environmental Services
• Fairfax County, Va.
• www.fairfaxcounty.gov
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