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Watershed Restoration Program and Purpose of the Spring Street/ Ballard Street Stormwater Project

October 20, 2011 Jennifer St. John, Watershed Planner John Hollister, Engineer


Agenda 

Introductions



Project Overview



Project Tasks and Goals



Stormwater Management Retrofit Assessment



Storm Drain Analysis



Questions/Discussion


Project Overview  

Spr ing St Are reet a



Located in the Rock Creek Watershed Study Point is located behind the existing Post Office, east of the railroad tracks Drainage Area to Study Point = 28.2 acres

t in o yP d u St


Overall Project Tasks 

Stormwater Management Retrofit Assessment 



Identify opportunities for Stormwater Management Retrofits

Storm Drain Analysis


Effects of Urban Runoff 



Impervious (hard surfaces) = Increased runoff & pollutants

Reduced groundwater recharge (infiltration)



 

Storm drain systems convey heated, dirty water directly to streams



Increased storm flows & decreased base flows

Streams eroded, incised

Infrastructure threatened



Degraded aquatic habitat & water quality


Proposed Stormwater Management Project Goals 

Maximize stormwater management to improve conditions in Rock Creek, the Potomac River & the Chesapeake Bay



Improve water quality treatment



Encourage infiltration of runoff from parking lots, roadways and other impervious surfaces



Fulfill requirements in the County’s National Pollutant Discharge Elimination System (NPDES) permit


Montgomery County’s (NPDES) Permit National Pollutant Discharge Elimination System 

Montgomery County’s Municipal Separate Storm Sewer System (MS4) NPDES Permit (issued in 2010) Requires: 





New stormwater management for 20% of existing impervious area that is currently unmanaged (~ 4,100 acres). Identify pollution sources and improve water quality in all county watersheds Increase use of Environmental Site Design (ESD), or Low Impact Design (LID)    

Variety of small-scale practices to capture stormwater runoff close to the source Slows rate and reduces volume of runoff Allows stormwater to soak into the ground, replenishing ground water Filters out pollutants

Bioretention

Pervious Pavers

Curb Extension


Stormwater Management 

Maryland Department of the Environment (MDE) has set forth a unified approach to stormwater management throughout the entire state. 



Water Quantity • Control runoff from small storms to prevent downstream erosion Water Quality • Treat the first inch of runoff to remove pollutants


Stormwater Management Retrofit Assessment 

Study Area = 28.2 acres 



Limitations to possible facilities 

 



Dense Urban Area

Existing infrastructure and utilities Limited open space Parking requirements

Small water quality facilities possible  

Low Impact Development Provides small % of required treatment


Examples of Potential Stormwater Management Facilities Underground Water Quality Structure 

Consists of a storage pipe and filtering chamber located underground.

Swale with Infiltration • Stone trench underground to provide infiltration


Examples of Potential Stormwater Management Facilities Bioretention

Curb Extensions


Examples of Potential Stormwater Management Facilities Water Quality Inlets

Inlet Modifications • Modifications capture trash and prevent it from being carried to downstream channels


Storm Drain Analysis

26.2ac

28.2ac Limits of Storm Drain Analysis


Storm Drain Analysis  

Verified storm drain capacity Performed inspection of pipe located under railroad tracks 



Pipe changes from a concrete pipe to a stone box culvert

Modeled large storm events through the stone box culvert 

Stone box culvert is the limiting factor


Estimated Floodplain 

Approximate limits of flooding 

Based on aerial topography


Questions/Discussion


Spring/Ballard Street Proposed Stormwater Controls