Contractor Awareness Training Below Ground Facilities 2016

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)
Spring 2016

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
2
NOTE: All pictures, unless noted, are the property of Fairfax County.

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!

MSMD/DPWES
Below Ground Facilities-Underground Detention (UG)
• An underground basin which temporarily stores stormwater
runoff
• Key components include:
– Control structure
– Inflow
– Detention structure
– Outfall
4
Picture: Georgia Stormwater Management Manual 3.4-15, figure 3.4.3-1 “Example Underground Detention Tank System”

MSMD/DPWES
• Detention Pipe/Vault Types:
– Corrugated Metal Pipe (CMP)
– Concrete pipe
– Box culvert
– HDPE (High-density Polyethylene)
– Large concrete vault
5
NOTE: Some of these photos may show deficiencies as well as pipe/vault types.

MSMD/DPWES
• Control Weir & Orifice Types:
– Concrete
– CMP Half-Round
– Multiple orifices
6
NOTE: Some of these photos may show
deficiencies as well as control
weir/orifice types.

MSMD/DPWES
• “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.
7
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.

MSMD/DPWES
Deficiencies Requiring Action
Pipes (Sediment/Debris Accumulation)
8
Debris and sediment accumulation inside pipes

MSMD/DPWES
Pipes (Damage and Deterioration)
9
Damage and/or deterioration inside pipes

MSMD/DPWES
Pipes (Damage and Deterioration, Continued)
10
Spalling and exposed rebar Spalling and deterioration of control
structure’s outflow pipe

MSMD/DPWES
Pipes (Damage and Deterioration, Continued)
11
Patching brick work around pipes…

MSMD/DPWES
Control Structure (Sediment/Debris Accumulation and Concrete Damage)
12
Trash/debris/sediment in
control structure
Standing water after several
dry weather days indicates a
flow blockage
Deterioration and
spalling around
control structure

MSMD/DPWES
Orifice Blockage and Missing Components
13
Downstream view of orifice
blockage
Upstream views of orifice
blockages

MSMD/DPWES
Trash Rack and Orifice Plate
(Blockages, damage, missing components, etc.)
14
Sediment build-up, looking
upstream through the orificePonded water suggests a possible
orifice blockage
Debris blocks trash rack

MSMD/DPWES
Above 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
15

MSMD/DPWES
Above 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
16

MSMD/DPWES
Below Ground Facilities-Sand Filters (SF)
• Provide water quality control by
filtering stormwater through a
gravel and sand bed
17
• Components of different sand filter
types:
– 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

MSMD/DPWES
• Components of Different Sand Filter Types:
18
Filter chambers in good
to moderate condition
Sediment
Chamber
Clearwell
Filter
Chamber
Delaware Sand Filter

MSMD/DPWES
• Components of Different Sand Filter Types:
19
Austin Sand Filter

MSMD/DPWES
Deficiencies/Conditions Requiring Action
Sedimentation and Filter Chambers (Trash/debris accumulation)
20
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.

MSMD/DPWES
Dewatering Valves (open or missing)
21
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

MSMD/DPWES
Dewatering Valves/Confined Space
What are some of the safety
concerns and improper practices
shown in this picture?
22

MSMD/DPWES
Filter Media (Uneven)
23
These photos are all from the same sand filter facility.

MSMD/DPWES
Above Ground Facilities-Sand Filters (SF)
• Common Remedies
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
examples)
– Check approved site plans for specific facility requirements
24

MSMD/DPWES
Above Ground Facilities-Sand Filters (SF)
• Common Remedies
– Reinforce/repair, if possible (Internal bands and gaskets)
– Slip-line pipes when possible, as this may be most cost effective
– Maintenance for Austin sand filters may be similar to that for a dry pond
25

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
26
* 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.

MSMD/DPWES
Example of a non-proprietary Oil-Grit Separator:
27
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

MSMD/DPWES
• StormFilter Components (Plan Detail for MB0173)
28
InletBay
Cartridge Bay
OutletBay
www.conteches.com

MSMD/DPWES
• StormFilter Components
29
ABOVE: StormFilter cartridge
RIGHT: 33+ cartridges during
installation
www.conteches.com

MSMD/DPWES
30
Energy dissipater or level spreader is
located at the upstream end of the
cartridge bay
www.conteches.com

MSMD/DPWES
31
Flow spreader
www.conteches.com
Underdrain pipes

MSMD/DPWES
32
StormGate directs low flows toward the
StormFilter while allowing higher flows to bypass
StormGate
www.conteches.com

MSMD/DPWES
• Proprietary MB-Vortech Stormwater Treatment System
33
Hydrodynamic Separation
www.conteches.com

MSMD/DPWES
• Proprietary MB-Stormceptor
34

MSMD/DPWES
• Proprietary MB-Downstream Defender
35
Hydrodynamic
Separation
http://www.hydro-int.com/us/products/
downstream-defender

MSMD/DPWES
• Proprietary MB- StormTreat System
36
www.stormtreat.com
Bio-Media Filtration

MSMD/DPWES
Deficiencies/Conditions Requiring Action
Accumulated Trash/Debris/Grit/Sediment/Floatables
37
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

MSMD/DPWES
Spalling/Deterioration/Damage to Components
38
Spalling and exposed rebar around pipe
end, inside chamber looking downstream
toward outfall

MSMD/DPWES
• Common Remedies
• Proprietary MBs
– Follow Manufacturers Guidance/Recommendations
• Non-Proprietary MBs
vacuum and hydrojet of the interior of structure
examples)
– Check plans for specific facility requirements
39

MSMD/DPWES
• Common Remedies
• Non-Proprietary MBs (continued)
– Reinforce/repair, if possible (internal bands and gaskets)
– Slip-line pipes when possible, as this may be most cost effective
– Cut back overgrown vegetation around facility structures to facilitate
access and proper function
40

MSMD/DPWES
Above Ground Facilities-Rooftop Detention (RT)
We will finish up with Vegetative
Practices after a short
BREAK…
41

Contractor Awareness Training Below Ground Facilities 2016

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Contractor Awareness Training Below Ground Facilities 2016