Guidelines for Evaluating and Selecting Modifications to Existing Roadway Drainage Infrastructure to Improve Water Quality in Ultra-Urban Areas (2012) / Chapter Skim
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24 This section describes BMP options for ultra-urban highway retrofit applications. The available approaches include traditional non-proprietary BMPs such as detention basins, and a variety of proprietary BMPs that have been developed and adapted specifically for space-constrained environments.
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25 traffic areas. Frequent inspection, if required, can be costly to the point that they are cost prohibitive (Caltrans, 2004)
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26 4.2.3 Sumped Inlet Structures Types of Devices: Deep sumped catch basins are inlet structures with enlarged sediment storage capacity. The outlets may include inverted elbows or hoods to help trap floatables.
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27 Figure 4.1. Two examples of catch basin inserts.
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28 catch basins provided there are no space and connectivity restrictions. Performance: Sumped catch basins target removal of easily settleable coarse solids.
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29 Figure 4.3. Three examples of proprietary catch basin devices.
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30 Applicability for Ultra-Urban Highway Retrofits: Catch basin filtration BMPs are applicable for ultra-urban highway retrofits when: • Space and/or budgetary constraints are restrictive and alternative retrofit options are not practical or cost effective; • Sediment and particulate-bound POCs are the primary target pollutants; and • There are adequate maintenance capabilities and safe maintenance access. 4.3 Gross Solids Removal Device Retrofits Urban centers and urban highways are sources of trash and debris.
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31 Area and Head Requirements: Footprint requirements for GSRDs are design dependent but, in general, space requirement are small. Some designs can be retrofit into existing inlets and outlets with no added space requirements.
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32 debris, vactoring of accumulated sediments in sumped facilities, and replacement of trash nets with truck-mounted cranes. Applicability for Ultra-Urban Highway Retrofits: GSRDs are applicable in ultra-urban highway retrofits when: • Trash and debris are the primary target pollutant; • GSRDs are used as pretreatment for other BMPs; and • There are adequate maintenance capabilities including maintenance access.
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33 example devices, which represent a small cross section of available systems. Area and Head Requirements: Hydrodynamic systems are small-footprint, underground structures with minimal space requirements.
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34 particulates and little to no effectiveness for dissolved pollutants and flow attenuation (USEPA, 1999a; Barbaro and Kurison, 2005; Roseen et al., 2006)
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35 • Space constraints are restrictive and alternative surface locations are not feasible or cost effective; • Coarse sediment and gross solids are the primary target pollutants; • They are used as pretreatment for other BMPs; and • There are adequate maintenance capabilities and maintenance access. 4.5 Oil-Water Separation Retrofits Oil-water or oil-grit separators are chambered tanks that are designed to remove gross pollutants and solids by sedimentation and to trap floatables, specifically including freephase oils and grease.
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36 series of oil-attracting coalescing plates in the main chamber. Larger oil-water separators contain a sludge scraper that continually removes the captured settled solids into a sludge pit.
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37 constructed offline (Smith, 2002)
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38 Consideration Attributes Target Constituents • Flow attenuation, trash and debris, sediment and associated pollutants Types of Facilities • Surface detention basins, multiple configurations • Underground vaults, pipes, cisterns Unit Operations • Primary processes: sedimentation and screening • Minor processes: infiltration, filtration, sorption, degradation, transformations Area Requirement • Surface facilities: 2% to 4% of the tributary watershed, larger for wet basin and wetlands • Subsurface facilities: 0.5% to 1% of the tributary watershed Head Requirement • Low to moderate; ~ 1 to 4 ft Online/Offline • Usually online, offline designs may improve sediment capture Maintenance Requirement • Regular inspection • Routine sediment and trash removal • Vector control • Vegetation management Performance • Generally effective treatment for gross solids, sediment, and particulate-bound POCs. Many design factors influence treatment effectiveness including storage volume, detention time, hydrodynamic characteristics, permanent wet pool volume, infiltration pathways, inclusion of vegetation • Generally less effective treatment performance for dissolved POCs.
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39 Area Requirements: The space requirements for surface detention ranges from 2% to 10% of the tributary area, which is the primary drawback for ultra-urban applications. Space requirements are smallest for detention facilities and largest for wet basins and wetlands (Table 4.7)
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40 requirements. Routine requirements are inspection, trash and litter pickup, removal of obstructions at inlets and outlet, vector control, and vegetation management if applicable.
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41 good flow attenuation and general water quality treatment performance; (3) they have relatively low cost; and (4)
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Material Example Advantages Disadvantages Concrete Pipe • Standard materials, widespread availability • Many sizes and shapes • High strength, high load-bearing capacity • Very rigid, fill not required to ma intain rigidity • Requires minim al fill above structures • Will not float • Good corrosion resistance • Long-term durability and less chance of failure • Reduced repair and replacement needs promote sustainability • Flexible design, adaptable to site configurations and connectivity to existing conveyances • Many vendors with a variety of modular sy stems and very flexible design; they are pre-engineered and eas y to inst all • Suitable for linear highway environments with small catchments • Requires more excavation than rectangular-shaped vaults • Heavy, requires moving equipment. More difficult to work with than alterative materials • More costly than alternative materials Prefabricated Concrete Vaults • Similar advantages to concrete pipes • Potentially, less excavation than circular pipes • More compact than pipes; may be more suitable for highly constrained highway environments • More adaptable to irregular-shaped spaces and depths • Vendors have developed a variety of modular designs that are adaptable to site conditions; pre-engineered, easy to install • Heavy, requires moving equipment • More costly than alternative materials Table 4.8.
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Corrugated Metal Pipes • Standard materials, widespread availability • Many sizes and shapes • Lightweight and longer lengths than concrete pipes; easier to work with and less costly to install • Lower cost com pared to concrete • Good durability, but less than concrete • Rigid, can withstand some shifting without breaking • Requires minim al fill above structures • Vendors have developed modular s y stems with flexible designs; they are pre-engineered and easy to install • Good alternative to concrete pipes in linear, space- constrained highway environments. • Susceptible to corrosion; may require coatings • Concerns about deformation if improperly installed • Requires fill to maintain rigidity Corrugated High-Density Poly ethy lene Pipe & Tanks • Extremely lightweight and eas y to work with; can reduce installation costs • Durable and corrosion resistant • Plastic tanks are available in a variety of sizes • Some are made with recycled ma terial supporting sustainability goals • Vendors have developed modular s y stems with flexible designs; they are pre-engineered and easy to install • Good alternative to concrete/metal pipes in linear, space- constrained highway environments.
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44 Figure 4.8. Two examples of proprietary underground detention systems.
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45 • Sediments and associated pollutants are the primary target pollutant. 4.6.3 Enhancements for Detention Retrofits Retrofit designers may consider several structural and operational enhancements to increase performance of detention retrofits.
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46 Perforated riser outlets improve sediment capture by permitting multiple drawdown rates over different stages of the basin. This allows for slower drawdown rates for the lower portion of the basin, providing more effective sediment capture for smaller storms.
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47 installations. The options for media filtration retrofits can be divided into three broad categories: • Standard sand filter systems, • Non-proprietary media filter drains with engineered media mixtures, and • Proprietary underground stormwater filtration systems.
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48 Figure 4.11. Three examples of sand filter configurations: Austin sand filter (top)
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49 • Delaware sand filters. Delaware sand filters are underground filter systems with long narrow configurations that are suitable as perimeter filters along parking lots and highway shoulders.
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50 4.7.3 Non-Proprietary Media Filters with Amended Soils Use of Soil Amendments. Media amendments to sand filters or specially designed media mixtures are used to improve treatment performance over sand media alone.
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51 Multi-Chambered Treatment Train Multi-Chambered Treatment Train Design: The MultiChambered Treatment Train (MCTT) is a three-stage treatment system.
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52 depending on site conditions and performance requirements. Hydraulic head requirements can be high with a minimum of about 3 to 10 ft or more depending on design.
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53 underground vaults are also widely used. Most systems incorporate sedimentation for pretreatment, but some designs integrate hydrodynamic separators for pretreatment.
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54 preclude some designs and media mixes from providing better or very good performance, as for example, some systems have received enhanced treatment certification by the Washington State Department of Ecology. Underground systems, like the surface systems, are not designed to provide flow attenuation or volume reduction.
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55 Filter Fabric Use of filter fabric in sand traps has shown effective filtration for sediments without significant clogging and loss of permeability (Caltrans, 2006)
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56 Studies suggest bioretention facilities can perform well in cold climates when properly designed (UNH, 2009b)
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57 • Drainage patterns and topography are suitable; and • There is safe maintenance access. 4.8.2 Potential Enhancements for Vegetative Filtration Retrofits Check Dams Check dams are used in swales to promote ponding and infiltration when the longitudinal slopes are large (> 3% to 5%)
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58 surface dimension; an improved sinkhole; or a subsurface fluid distribution system (an infiltration system with piping to enhance infiltration capabilities)
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60 Space and Head Requirements: Space requirements for infiltration basins and infiltration trenches are about 2% to 4% of the tributary drainage areas. Basins are suited for vacant areas in interchanges with flat topography, and linear trenches can be located in vacant ROW along shoulders and ramps.
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61 Applicability for Ultra-Urban Highway Retrofits: Infiltration retrofits potentially deliver appealing receiving water benefits including highly effective treatment, flow attenuation, and volume reduction. However, siting constraints in ultraurban environments are very restrictive, and there can be high costs and maintenance requirements.
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62 the mix can improve strength and durability without substantially reducing permeability; however. this approach requires additional research/testing.
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63 such applications would be difficult due to irregular slopes, underground obstructions and utilities, and irregular and compacted soils in ultra-urban settings that would challenge the feasibility of this approach. • Permeable asphalt shoulders: As an alternative to using permeable asphalt across the entire roadbed, WSDOT (1997)
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64 potential to contaminate high-quality groundwater resources from hazardous material spills. Studies and reports on PAOs indicate good treatment performance.
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65 tional maintenance requirements. Gunderson (2008)
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66 pollutants, dioxin is an example, may also be of concern to the extent that advanced treatment is required. Treatment approaches that use chemical dosing to promote flocculation have been studied and tested by DOTs for enhanced treatment of fine particulates (Li and Kegley, 2005; Bachand et al., 2006; McGowen et al., 2009)
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67 Source Description Reference/Lin k Caltrans Retrofit Pilot Stud y -- a multi-year study of stand - alone BMP retrofits of highway facilities • Caltrans (2004) • http://www.dot.ca.gov/hq/env/stormwater/special/ne wsetup/_pdfs/new_technology/index.htm Statewide Stormwater Program -- conducts a wide variety of BMP research and assessments http://www.dot.ca.gov/hq/env/stormwater/ BMP technology report -- a biannual report on BMP technologies and assessment of new technologies Caltrans (2010)
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68 Source Description Reference/Lin k Street Sweeping Studies for Source Control and Maintenance USGS study evaluating the effectiveness of different sweeping strategies http://wi.water.usgs.gov/non-point/bqy26/index.html USGS study presenting street sweeping data including mass and particle size distribution http://wi.water.usgs.gov/pubs/ofr-03-93/ofr-03-93.pdf Wisconsin Department of Transportation study on the effectiveness of high efficiency sweepers http://wisdotresearch.wi.gov/wp-content/uploads/04- 04sweeperstudy-b.pdf Metro Washington report on the state of practice of street sweeping and policy directions and implications regarding street sweeping for water quality improvement http://www.pca.state.mn.us/index.php/view- document.html? gid=13933 Low Impact Development, Green Streets USEPA summaries of Green Street and Low Impact Development initiatives • http://www.epa.gov/owow_keep/podcasts/greenstreet susa.html • http://water.epa.gov/polwaste/green/ Low Impact Development Center, Green Streets • http://www.lowimpactdevelopment.org/ • http://www.lowimpactdevelopment.org/greenstreets/ Selected municipalities • http://www.portlandonline.com/bes/index.cfm ?
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