A Fairfax County, VA, publication

Department of Public Works and Environmental Services

Working for You!

Stormwater Maintenance Awareness TrainingFor privately maintained stormwater management facilities

Maintenance and Stormwater Management Division (MSMD)

Spring 2016

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Stormwater Maintenance Awareness Training

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Course ScheduleAM 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/questionsNOTE: All pictures, unless noted, are the property of Fairfax County.

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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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Above Ground Facilities-Ponds (WP, DP)

WET POND COMPONENTS Profile of a typical WP

Plan view of WP with sediment forebay and WL

Pictures: VDEQ Stormwater Design Specification No. 14, Wet Pond, Version 1.9, 3/1/11, Figure 14.1 “Wet Pond Design Schematics”

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Above Ground Facilities-Ponds (WP, DP)Deficiencies Requiring Action:Algae/Turbidity (WP only)

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.

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Above Ground Facilities-Ponds (WP, DP)Water level inconsistent with plans (WP only)

s

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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

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

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Above Ground Facilities-Ponds (WP, DP)

DRY POND COMPONENTS - Dry Ponds constructed prior to July 1, 2014 are likely to have a simpler profile:

LEFT Picture: Page 62, http://www.novaregion.org/DocumentCenter/Home/View/1679

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Above Ground Facilities-Ponds (WP, DP)Deficiencies Requiring Action (continued): Trickle Ditches (DP only)

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

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Above Ground Facilities-Ponds (WP, DP)Dam/Berm - Erosion and FailureNOTE: Remaining slides apply to both WP and DP

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

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Above Ground Facilities-Ponds (WP, DP) Dam/Berm - Cave-Ins and Animal Holes

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

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Above Ground Facilities-Ponds (WP, DP)Vegetation & Trash/Debris Accumulation

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.

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Above Ground Facilities-Ponds (WP, DP)Trees and Woody Vegetation on Dam/Berm

Top

of D

amBackFace

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

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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

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Above Ground Facilities-Ponds (WP, DP)Outfalls

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

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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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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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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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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

– Runoff volume reduction– Channel protection– Flood mitigation

Properly Functioning Example:

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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 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”

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Above Ground Facilities-Wetlands (WL)

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”

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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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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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Above Ground Facilities-Rooftop Detention (RT)

We will finish up Above Ground Facilitiesafter a short

BREAK…