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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



Project Overview

Project Tasks and Goals

Stormwater Management Retrofit Assessment

Storm Drain Analysis


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


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


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


Spring/Ballard Street Proposed Stormwater Controls  

Spring/Ballard Street Proposed Stormwater Controls