Stormwater Maintenance Awareness Above Ground Facilities parts 1 and 2

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

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)
• Below Ground Facilities
• Vegetative Practices
– Closing remarks/questions
2
NOTE: All pictures, unless noted, are the property of Fairfax County.

MSMD/DPWES
Above 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!

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.
4

MSMD/DPWES
WET POND COMPONENTS Profile of a typical WP
Plan view of WP with sediment
forebay and WL
5
Pictures: VDEQ Stormwater Design Specification No. 14, Wet Pond, Version 1.9, 3/1/11, Figure 14.1 “Wet Pond Design Schematics”

MSMD/DPWES
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
6
Pictures: VDEQ Stormwater Design Specification No. 15, Dry Pond, Version 1.9, 3/1/11, Figure 15.1 “Typical Extended Detention Pond Details”

MSMD/DPWES
DRY POND COMPONENTS - Dry Ponds constructed prior to July 1, 2014
are likely to have a simpler profile:
7
LEFT Picture: Page 62, http://www.novaregion.org/DocumentCenter/Home/View/1679

MSMD/DPWES
Routine Deficiencies Observed:
Algae/Turbidity (WP only)
8
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.

MSMD/DPWES
Water level inconsistent with plans (WP only)
9
s

MSMD/DPWES
Trickle Ditches (DP only)
10
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

MSMD/DPWES
Dam/Berm - Erosion and Failure
NOTE: Remaining slides apply to both WP and DP
11
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

MSMD/DPWES
Dam/Berm - Cave-Ins and Animal Holes
12
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

MSMD/DPWES
Vegetation & Trash/Debris Accumulation
13
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.

MSMD/DPWES
Trees and Woody Vegetation on Dam/Berm
14
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

MSMD/DPWES
Riser/Trash Rack
15
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

MSMD/DPWES
Outfalls
16
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

MSMD/DPWES
• 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
17

MSMD/DPWES
• 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
18

MSMD/DPWES
• Common Remedies
– Cut back overgrown vegetation around facility structures to facilitate
access and proper function (WP/DP 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 25’ radius of channels
– Within 10’ from the heel of dam, 10’ from toe of dam
– Within inflow/outlet channels
– Other areas, as needed, for facility access
19

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
20
– Runoff volume reduction
– Channel protection
– Flood mitigation
Properly Functioning Example:

MSMD/DPWES
• 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
21
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”
WETLAND COMPONENTS

MSMD/DPWES
22
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”

MSMD/DPWES
Routine Deficiencies Observed:
• 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
23

MSMD/DPWES
24
Erosion on the main pool floor
Damaged wetland
habitat vegetation
Sediment and debris in upstream inflows
Sediment
accumulation in
forebays

MSMD/DPWES
• 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
– Cut back overgrown vegetation around facility structures to facilitate access and
proper function (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
25

MSMD/DPWES
Above Ground Facilities
We will finish up Above Ground Facilities
after a short
BREAK…
26

MSMD/DPWES
Course Schedule
AM session (includes two 15 minute breaks)
– History of SWM and regulations
– County inspection basics
– The inspection report and MAR
– Common SWM/BMP types
• Common maintenance items-General
• Above Ground Facilities (the rest of the story….)
12:00-1:00 PM Lunch
PM session (includes two 15 minute breaks)
• Below Ground Facilities
• Vegetative Practices
– Closing remarks/questions
28
NOTE: All pictures, unless noted, are the property of Fairfax County.

MSMD/DPWES
Above Ground Facilities-Infiltration Trenches (TR)
Provides some quantity control & treats runoff through filtration/infiltration
29
May be designed to treat surface
runoff or piped drainage (downspouts)

MSMD/DPWES
Properly Functioning Examples: (Typical single-family residential lot facilities)
30
LEFT: Picture shows a gravel infiltration trench
with a cleanout and observation well, during a
soil probe test. A soil probe is pushed into the
underlying gravel layer to determine the topsoil
depth and confirm facility is “per design”.
Sod cover

MSMD/DPWES
• Topsoil and sod cover
(optional)
• Observation well with
metal cap with lock
• Overflow berm
• Pea gravel or river stone
• Filter fabric layer
• Aggregate (1.5 in. – 3.5 in.
diameter)
• Sand bed (6-8 in. deep)
• Perforated underdrain
(optional)
31
Picture: VDEQ Stormwater Design Specification No. 8, Infiltration Practices, Version 1.9, 3/1/11
INFILTRATION TRENCH COMPONENTS

MSMD/DPWES
Sediment Accumulation & Curb Cuts
32
TOP LEFT: Some debris
and sediment on
surface at curb cut
BOTTOM LEFT: Curb
cut blocked (remove
wheel stop)
TOP RIGHT: Surface
debris & sediment
accumulation
BOTTOM RIGHT:
Sediment
accumulation in gravel
bed
Routine Deficiencies Observed

Plantings & Overgrown Vegetation
33
Downed tree limb with deep-
rooted/overgrown vegetation
Overgrown vegetation within
the limits of a gravel bed
trench may indicate sediment
accumulation, as plants do
not tend to grow in clean
gravel.
Unauthorized plantings
MSMD/DPWES

MSMD/DPWES
Turf Covered TRs
34
Some trenches may have turf and topsoil,
covering the gravel bed; however, turf is not
automatically acceptable. ALWAYS refer to the
approved site plan!
• A soil probe test checks the gravel layer
(refer to slide 4).
• Water usually reaches the gravel bed
through underground PVC pipes connected
to the roof drain downspouts.
Common issues include:
• Missing underground gravel beds
• Disconnected roof downspouts draining
overland instead of via an underground
pipe
• Bare spots/exposed soil in turf covering
• Missing berms or observation wells

MSMD/DPWES
Cleanouts/Observation Wells
35
Other common issues:
• Caps stuck/not removable
• Clogged cleanouts
• Presence of standing water in the cleanout
Broken/damaged well cap Missing cap

MSMD/DPWES
• Common Remedies
– Standing water after 48 hours:
• Underdrain may need to be flushed and re-checked
• Special attention should be given, as required to gravel beds
(surface and within gravel pores) and may require
removal/replacement of clogged sections of gravel
• Fully remove any plants growing in the accumulated sediments
– Full removal includes eliminating roots and supporting
soil/sediment from the gravel bed, as spraying weed killer is not
a sufficient treatment solution
– Rebuild/stabilize any areas with erosion, cave-ins, and bare spots:
• Cave-ins require additional investigation to determine cause and
prevent re-occurrence
36

MSMD/DPWES
• Common Remedies
from parts to structural to environmental materials (see prior noted
examples)
• 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
– Cut back overgrown vegetation around facility structures to facilitate
access and proper function
37

MSMD/DPWES
Above Ground Facilities-Permeable Pavement (PP)
• Alternative paving surface which
treats runoff through filtration
(voids in paved surface), temporary
storage (underlying stone
reservoir), and infiltration
– Includes permeable pavement,
pervious concrete, porous
asphalt, and permeable pavers
– PP promotes a high degree of
runoff volume reduction &
nutrient removal
– Primarily used on commercial,
institutional, & residential sites
38
Properly Functioning Examples:

MSMD/DPWES
• Observation well
• Perforated underdrain
• Geotextile (optional)
• Bedding Course
• Aggregate base
• Uncompacted subgrade
soil
• Permeable joint
material (for PICP)
39
PERMEABLE PAVEMENT COMPONENTS

MSMD/DPWES
40
Picture: VDEQ Stormwater Design Specification No. 7, Permeable Pavement, Version 1.8, 3/1/11, Figure 7.1 (as noted)
PERMEABLE PAVEMENT COMPONENTS

MSMD/DPWES
Pervious Layer
41
Sediment/Silt
Weeds/overgrown
vegetation
Deterioration &/or cracks
in pervious layer

MSMD/DPWES
Pervious Layer
42
Asphalt Sealed Pavers Clogged

MSMD/DPWES
Outfall Structure/Underdrain
43
Damaged underdrains
Clogging and/or a potential
blockage in the outfall
structure/underdrain
Blockage in the underdrain

MSMD/DPWES
• Common Remedies
• Perform a thorough restorative vacuum sweep of paved surface
• Investigate the causes of any blockages to prevent re-occurrence, if
at all possible.
from parts to structural to environmental materials (see prior noted
examples)
• Specific to this facility type: any damaged, cracked, or failing pavers
or paved sections
44

MSMD/DPWES
• Common Remedies
– Rebuild/stabilize any areas of erosion:
• Adjoining land erosion can silt in permeable pavement
– Remove vegetation in permeable pavement to facilitate proper function
• Remove any non-spec vegetation, especially if it impacts the health
and function of the facility, as designed.
– Sealed permeable pavement requires a complete replacement
45

MSMD/DPWES
Above Ground Facilities-Rooftop Detention (RT)
• Designed to slow the flow from the
roof through short-term ponding
on the roof surface
46
Properly Functioning Examples of
Rooftop Detention Devices:
Ring with
1” holes
Slotted square
detention
device
Adjustable
detention
device
Custom
devices

MSMD/DPWES
• Roof drain
• Debris cage
• Detention cage
• Parapet wall
• Scupper
• Roof access (varies)
47
ROOFTOP DETENTION COMPONENTS

MSMD/DPWES
Properly Functioning Examples:
Scuppers convey emergency overflow off rooftop
48

MSMD/DPWES
Scuppers and Adjustable Detention Devices
49
Scupper not providing proper
water detention because it is
level with roof
Adjustable detention
device opened too
wide
Detention
device and
debris cage
missing
Debris cage is
damaged and
detention device
missing
Incorrect number of drains and/or
scuppers (usually too many)

MSMD/DPWES
Parapet Walls, Vegetation, and Detention Devices
50
Parapet wall missing
Debris Ponding Sediment
Tree growing on roof surface

MSMD/DPWES
• Common Remedies
• Components vary by facility type and design, and they can range from
parts to structural to environmental materials (see prior noted
examples)
– Remove ANY vegetation around facility structures and on rooftop
– Provide required detention flow rate
• Replace any missing or damaged detention devices and debris cages
• Re-adjust detention devices, as needed
• Raise scuppers that are too low or provide detention at the scupper
• Repair or install any missing parapet walls
• Recalculate the flow based on the actual number of drains to attain the
prescribed detention
51

MSMD/DPWES
Above Ground Facilities
LUNCH!
Please be back & ready to start at 1:00 PM
52

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Stormwater Maintenance Awareness Above Ground Facilities parts 1 and 2