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From page 1... ... 1 1.1 Motivation and Objectives State departments of transportation (DOTs) and county and city transportation departments routinely design, construct, and maintain highway drainage systems to ensure safe driving conditions and to prevent downstream flooding. Read the entire page →
From page 2... ... 2evolve. More recently, environmental regulations increasingly require retrofit treatment BMPs for previously constructed highway facilities. Read the entire page →
From page 3... ... 3 impacts of runoff from existing highway facilities. A BMP retrofit can entail: • Modification and enhancement of existing BMPs and infrastructure; • Construction of stand-alone treatment/flow control BMPs for existing highway facilities; and • Construction of retrofit BMPs in association with highway improvement projects, for example, highway-widening projects that include BMPs to treat existing and added travel lanes. Read the entire page →
From page 4... ... 4Retrofit Consideration Retrofit Constraints Mitigation Potential Implications Limited ROW • ROW too small for aboveground BMPs • Available ROW has planned uses such as future highway expansion • Available ROW has poor configuration or location, limited access • Adjacent land costs are high • Select alternative locations • Locate BMPs underground • Adapt BMP design or type to fit within available ROW • Use proprietary small-footprint BMPs • Coordinate retrofits with future projects • Greater design and construction costs • More maintenance requirements and costs for underground BMPs • Reduced treatment performance • Project delays Obstructions • Buried utilities • Building foundations • Landfills/contaminated soils • Historic structures • Archeological finds • As-built drawings are not available or unreliable • Select alternative location • Adapt/change BMP design • Dig additional test pits to identify obstructions • Remove obstruction at additional cost • Greater design and site characterization costs • Greater construction costs • Project delays and change orders • Longer construction period Topography • Below-grade highway sections • Roadway crowned to drain away from candidate locations • Available ROW has steep slopes, rocky, and uneven terrain • Insufficient head in flat terrains • Select alternative location or retrofit design • Re-grade/excavate/fill as needed • Construct retaining walls • Modify existing drainage system • Modify roadway crown • Greater design and construction costs • Longer construction period Soil and groundwater conditions • Compacted soils with low permeability • Shallow groundwater • Overly wet soils/hydric soils • Unknown or non-engineered fill • Soil or groundwater contamination • Select alternative location or retrofit design • Amend soils at additional cost • Install dewatering systems • Excavate and dispose unsuitable or contaminated soil • Increased design and construction costs • Construction delays and change orders to address unexpected conditions • Longer and more complicated construction Connection to existing drainage system • Piped and underground systems • Difficult to tie in BMPs due to insufficient head, conveyance capacity, and location • Select alternative location or retrofit design • Use pumps to compensate for elevation issues at additional cost • Reconfigure existing conveyances • Greater costs for design, construction, and ongoing operation Construction • Space and connectivity constraints • Obstructions, depth, confined-space issues • Limited space for construction staging • Longer distance from import/export sites • Lane closures due to limited space or retrofit design • Traffic delays due to high volume or lane closure • Select alternative location • Modify BMP design • Develop designs that eliminate required lane closures, minimize connectivity issues, require no proprietary materials • Schedule construction for offpeak hours/seasons • Reuse exports on site • Greater construction costs • Longer construction periods because of traffic impacts and traffic control • Potential construction delays and change orders to address unexpected conditions • Worker and public safety concerns due to limited space and large traffic volume BMP treatment performance • Large flowrates, runoff volumes, and pollutant loadings • Space constraints limit BMP options and capacity • Compacted soils restrict use of infiltration BMPs • Little potential for runoff capture and reuse • Cold climate–related effects on pollutant loadings and BMP sizing • Select alternative location • Modify BMP design and sizing • Include operational and design enhancements • Provide pretreatment • Use treatment trains • Greater project costs • Target pollutants not mitigated Maintenance burden • Impacts to traffic • High maintenance frequency • Need for specialized equipment or materials • Safety issues for road crews and drivers • Maintenance access requires lane closures or traffic impacts • Vegetation maintenance • Select alternative location • Select alternative BMP types • Modify BMP design • Schedule maintenance at off-peak hours/seasons at additional cost • Potentially excessive maintenance requirements and costs • Diminished treatment performance if maintenance needs are not met Table 1.2. Constraints and challenges of BMP retrofits for ultra-urban highways. Read the entire page →
From page 5... ... 5 ROW for siting aboveground retrofit BMPs. The lack of adequate surface area requires retrofit designers to seek alternative locations or to develop designs that can fit within the available ROW including consideration of underground BMPs. Read the entire page →
From page 6... ... 6measures, and costly proprietary materials. As a result, BMP maintenance requirements and costs can dictate BMP selection. Read the entire page →
From page 7... ... 7 ization supports the development of sensible treatment objectives and effective retrofit solutions. A summary of common highway pollutants and conditions of concern and their characteristics is provided in Table 2.1. Read the entire page →

From page 1...

... 1 1.1 Motivation and Objectives State departments of transportation (DOTs) and county and city transportation departments routinely design, construct, and maintain highway drainage systems to ensure safe driving conditions and to prevent downstream flooding.

Read the entire page →

From page 2...

... 2evolve. More recently, environmental regulations increasingly require retrofit treatment BMPs for previously constructed highway facilities.

Read the entire page →

From page 3...

... 3 impacts of runoff from existing highway facilities. A BMP retrofit can entail: • Modification and enhancement of existing BMPs and infrastructure; • Construction of stand-alone treatment/flow control BMPs for existing highway facilities; and • Construction of retrofit BMPs in association with highway improvement projects, for example, highway-widening projects that include BMPs to treat existing and added travel lanes.

Read the entire page →

From page 4...

... 4Retrofit Consideration Retrofit Constraints Mitigation Potential Implications Limited ROW • ROW too small for aboveground BMPs • Available ROW has planned uses such as future highway expansion • Available ROW has poor configuration or location, limited access • Adjacent land costs are high • Select alternative locations • Locate BMPs underground • Adapt BMP design or type to fit within available ROW • Use proprietary small-footprint BMPs • Coordinate retrofits with future projects • Greater design and construction costs • More maintenance requirements and costs for underground BMPs • Reduced treatment performance • Project delays Obstructions • Buried utilities • Building foundations • Landfills/contaminated soils • Historic structures • Archeological finds • As-built drawings are not available or unreliable • Select alternative location • Adapt/change BMP design • Dig additional test pits to identify obstructions • Remove obstruction at additional cost • Greater design and site characterization costs • Greater construction costs • Project delays and change orders • Longer construction period Topography • Below-grade highway sections • Roadway crowned to drain away from candidate locations • Available ROW has steep slopes, rocky, and uneven terrain • Insufficient head in flat terrains • Select alternative location or retrofit design • Re-grade/excavate/fill as needed • Construct retaining walls • Modify existing drainage system • Modify roadway crown • Greater design and construction costs • Longer construction period Soil and groundwater conditions • Compacted soils with low permeability • Shallow groundwater • Overly wet soils/hydric soils • Unknown or non-engineered fill • Soil or groundwater contamination • Select alternative location or retrofit design • Amend soils at additional cost • Install dewatering systems • Excavate and dispose unsuitable or contaminated soil • Increased design and construction costs • Construction delays and change orders to address unexpected conditions • Longer and more complicated construction Connection to existing drainage system • Piped and underground systems • Difficult to tie in BMPs due to insufficient head, conveyance capacity, and location • Select alternative location or retrofit design • Use pumps to compensate for elevation issues at additional cost • Reconfigure existing conveyances • Greater costs for design, construction, and ongoing operation Construction • Space and connectivity constraints • Obstructions, depth, confined-space issues • Limited space for construction staging • Longer distance from import/export sites • Lane closures due to limited space or retrofit design • Traffic delays due to high volume or lane closure • Select alternative location • Modify BMP design • Develop designs that eliminate required lane closures, minimize connectivity issues, require no proprietary materials • Schedule construction for offpeak hours/seasons • Reuse exports on site • Greater construction costs • Longer construction periods because of traffic impacts and traffic control • Potential construction delays and change orders to address unexpected conditions • Worker and public safety concerns due to limited space and large traffic volume BMP treatment performance • Large flowrates, runoff volumes, and pollutant loadings • Space constraints limit BMP options and capacity • Compacted soils restrict use of infiltration BMPs • Little potential for runoff capture and reuse • Cold climate–related effects on pollutant loadings and BMP sizing • Select alternative location • Modify BMP design and sizing • Include operational and design enhancements • Provide pretreatment • Use treatment trains • Greater project costs • Target pollutants not mitigated Maintenance burden • Impacts to traffic • High maintenance frequency • Need for specialized equipment or materials • Safety issues for road crews and drivers • Maintenance access requires lane closures or traffic impacts • Vegetation maintenance • Select alternative location • Select alternative BMP types • Modify BMP design • Schedule maintenance at off-peak hours/seasons at additional cost • Potentially excessive maintenance requirements and costs • Diminished treatment performance if maintenance needs are not met Table 1.2. Constraints and challenges of BMP retrofits for ultra-urban highways.

Read the entire page →

From page 5...

... 5 ROW for siting aboveground retrofit BMPs. The lack of adequate surface area requires retrofit designers to seek alternative locations or to develop designs that can fit within the available ROW including consideration of underground BMPs.

Read the entire page →

From page 6...

... 6measures, and costly proprietary materials. As a result, BMP maintenance requirements and costs can dictate BMP selection.

Read the entire page →

From page 7...

... 7 ization supports the development of sensible treatment objectives and effective retrofit solutions. A summary of common highway pollutants and conditions of concern and their characteristics is provided in Table 2.1.

Read the entire page →

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