feb 11 2014 public meeting show
DESCRIPTION
February 11, 2014 public meeting presentation for three proposed stormwater facility management projects off of Cabin Branch of Great Seneca Creek. (powerpoint file)TRANSCRIPT
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Cabin Branch Stormwater Management
Retrofit Projects
Quail Valley Pond #1Quail Valley Pond #2
Strawberry Knoll Facility
Concept Design PresentationFebruary 11, 2014
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Today’s Agenda
Sources of Water on Earth
Montgomery County background
What is a Watershed & Runoff?
Intro to Stormwater
What the County is Doing to Protect Our Streams
Goals of the Project
Proposed Pond Retrofit
Questions/Comments
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Sources of Water
About 97% is salt water About 2% is frozen Only 1% is available for drinking water
Across the country, most potable water is from groundwater In Maryland, most is from surface water
Potential for greater impacts from runoff in Maryland
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Montgomery County, MD 500 sq. miles 970,000 people
Second only to Baltimore City within Maryland in average people per square mile
184 languages spoken
About 12% impervious surface overall About the size of Washington DC
Over 1,500 miles of streams Two major river basins:
Potomac Patuxent
Eight local watersheds
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District of Columbia
Impervious: Not allowing water to soak through the ground.
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What is a Watershed? A watershed is an area
from which the water above and below ground drains to the same place.
Different scales of watersheds: Chesapeake Bay Eight local watersheds Neighborhood (to a storm
drain)
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What is Runoff?Water that does not soak into the ground becomes
surface runoff. This runoff flows over hard surfaces like
rooftops, driveways and parking lots collecting potential
contaminants and flows:
• Directly into streams
• Into storm drain pipes, eventually leading to streams
• Into stormwater management facilities, then streams
Two Major Issues:Volume/Timing of Runoff
Water Quality6
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What is the County doing toprotect our Streams?
Must meet regulatory requirements Federal Clean Water Act permit program MS4 = Municipal Separate Storm Sewer System
Applies to all large and medium Maryland jurisdictions County programs
Restore our streams and watersheds Add runoff management
Meet water quality protection goals Reduce pollutants getting into our streams
Educate and engage all stakeholders Individual actions make a difference
Focus on watersheds showing greatest impacts
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MS4 Permit: What is it? Montgomery County is responsible for:
• What goes into our storm drain pipes
• What comes out of them
• What flows into the streams
Requires additional stormwater management for 20 percent of untreated impervious surfaces (4,292 acres = 6.7 square miles). That’s about three times the size of Takoma Park.
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Overall Goals of the Project
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Provide water quality treatment and downstream channel protection to meet MS4 program requirements.
Improve ecological value of existing stormwater management facilities.
Improve existing landscaping and plant diversity of existing facilities.
Upgrade existing facilities to comply with safety and design standards.
Utilize existing open space to provide stormwater management.
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Project Location
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CabinBranch
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Quail Valley Pond # 1SWM Retrofit
Project Overview
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Drainage Area 9.24 acre drainage
area to pond
51% impervious
Land cover includes roadway, sidewalks, manicured lawns/landscaping.
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Constructed in the early 1980s
Fully developed drainage area
Does not provide water quality functions
High groundwater exists in bottom of facility
Does not meet current safety and design standards (materials and conveyance)
Sinkholes have recently developed in embankment
Maintenance access is inadequate
Minor sediment deposition from upstream erosion
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Existing Conditions
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Existing Quail Valley Pond # 1
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View of facility from Centerway Rd Bottom of facility showing base flow
Existing substandard riser. Sinkhole resulting from riser degradation.
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Grade bottom of pond and eastern bank.
Create a 3.5’ deep wet pool.
Remove and replace existing riser and outflow pipe.
Reconstruct portion of existing embankment.
Remove small diameter trees within limits of work.
Provide access path for maintenance.
Re-vegetate pond and plant additional trees.
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Retrofit Design Details
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Proposed Pond Retrofit
Plan View
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Proposed Pond Retrofit
Profile
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Quail Valley Pond # 2SWM Retrofit
Project Overview
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Drainage Area 48.9 acre drainage
area to pond
24% impervious
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Constructed in the early 1980s
Fully developed drainage area
Dry detention pond constructed in a stream valley
Very few ecological or water quality benefits
Good condition, but riser is nearing end of service life
Maintenance access is inadequate
Minor sediment deposition from upstream erosion
Degradation and incision of downstream channel
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Existing Conditions
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Existing Quail Valley Pond # 2
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Enlarge the storage volume to treat 50% of the
Water Quality Volume (WQv)
Add a sand berm to increase infiltration
Grade an additional storage basin in existing open
space adjacent to stream banks
Safely pass larger storms, including the 100-year
storm
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Retrofit Design Details
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Install a forebay at the top of the pond to improve
maintenance
Remove existing risers and replace with cobble riffle
structures
Restore downstream channel using step pools
Revegetate pond with native plants
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Retrofit Design Details
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Proposed Pond Retrofit
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Profile of Proposed Retrofit
Proposed Pond Retrofit
Cross-Section of Proposed Retrofit
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Stormwater Pond RetrofitDuring Construction
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Stormwater Pond RetrofitWithin 1 Year After Construction
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Stormwater Pond RetrofitWithin 5 Years After Construction
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Strawberry KnollUnderground SWM Facility
Project Overview
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Drainage Area 20.5 acre drainage
area to facility
37% impervious
Land cover includes roadway, sidewalks, manicured lawns, open space, and landscaping.
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Parcel is owned by the Flower Hill Central Corporation
Parcel provides open space for Flower Hill Community
Two stormdrain systems connect under open space
Flow in existing stormdrain is not treated for Water Quality or Channel Protection
Space is available on site to provide an SWM facility
Site is accessible from Strawberry Knoll Road
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Existing Site Conditions
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Existing Open Space
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Location of Proposed SWM Facility. Open space south of proposed facility.
Location of proposed construction and maintenance access.
Existing inlet which SWM system will connect to.
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Underground gravity driven treatment system.
Three components: pretreatment, storage, and
treatment.
Pretreatment simplifies and reduces the need for
maintenance.
Storage System stores stormwater until filtered.
Filter replaces natural functions depleted with development.
Provide stable vegetated access path for future
maintenance.
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SWM Design Details
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Proposed SWM Design
Plan View
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Proposed SWM Design
Profile
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Grass Pavers
UrbanGreen Grass Paver Detail
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Stormwater Treatment
Vortechs Pretreatment System Stormfilter System
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Underground SWM FacilityDuring Construction
Storage system being installed Watertight joint being sealed
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Quail Valley Pond # 1 Construction Access
Access from Centerway Road
Tree removal and grading
Tree protection where needed
Mulch placed on path and removed after construction
Access will be stabilized to prevent sediment transport to Centerway Road
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Quail Valley Pond # 2 Construction Access
Access from CenterwayRoad
Clear width will likely require tree removal and grading
Tree protection where needed
Mulch placed on path and removed after construction
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Strawberry Knoll Construction Access
Access from Strawberry Knoll Road
Access will be stabilized to prevent sediment transport to Strawberry Knoll Road
Curb ramp and grass pavers will be provided at final stages of construction.
Location of proposed construction and maintenance access.
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Construction Access (Example)
During Construction After Construction
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Reforestation
Attractive native trees and shrubs will be planted within the project area
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Schedule
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Public meeting to discuss 30% designs 2/11/2014
60% design – Summer 2014
90% design – Winter 2014
Permits issued – Spring 2015
Construction – Summer 2015
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Darian Copiz, Montgomery County Department of Environmental Protection240-777-7774 / [email protected]/watershedrestoration
Click on “Stream Restoration” and “Stormwater Pond Retrofits”
Questions/Comments?