Stormwater Infiltration in the Highway Environment: Guidance Manual (2019) / Chapter Skim
Currently Skimming:
Pages 15-60
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 15... ...
15 C H A P T E R 2 This chapter provides guidance to support decisions about infiltration approaches. The chapter supports the first two steps of the overall infiltration and assessment and decision- making framework: (1)
|
From page 16... ...
16 Stormwater Infiltration in the Highway Environment: Guidance Manual 2.1 Establishment of Infiltration Objectives Planning and design teams should begin with an evaluation of the underlying objectives associated with infiltration. This can inform selection of BMP strategies and guide the level of effort of infiltration investigations in subsequent steps.
|
From page 17... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 17 • Infiltration is being considered for flow control to reduce flooding and protect streams, but this could also be achieved by an extended-detention basin (flow-duration control)
|
From page 18... ...
18 Stormwater Infiltration in the Highway Environment: Guidance Manual as ET or harvest and use) within the site constraints, but the project is not required to achieve a certain minimum level of infiltration to comply.
|
From page 19... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 19 2.1.3 Implications of Infiltration Objectives on Subsequent Steps The applicable infiltration objectives have several implications on subsequent steps: • The project team can use an understanding of infiltration objectives to determine how rigorously and aggressively the project should pursue the assessment of infiltration feasibility. In other words, what is the burden of proof that infiltration assessments will need to support?
|
From page 20... ...
20 Stormwater Infiltration in the Highway Environment: Guidance Manual • As outlined in Figure 2, the project team should combine the results of preliminary feasibility analyses with the established infiltration objectives to help make preliminary decisions about infiltration strategies for the project. Section 2.3 provides guidance for integrating Steps 1 and 2 into preliminary decision-making.
|
From page 21... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 21 Groundwater and Geotechnical Feasibility. Can water be infiltrated without introducing undesirable consequences or elevating risks to infrastructure or the environment?
|
From page 22... ...
22 Stormwater Infiltration in the Highway Environment: Guidance Manual Connection to Receiving Water. Create a map to show the connection from the project site to each outfall location based on existing drainage infrastructure, including the following information: • Receiving waterbody name • Location of existing or new outfalls • Proximity of project to existing or new outfalls • Land ownership and space availability along flow path Characteristics of Receiving Water.
|
From page 23... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 23 objectives apply to different parts of the project based on different receiving waters and their specific conditions and regulatory status. Environmentally Sensitive Areas.
|
From page 24... ...
24 Stormwater Infiltration in the Highway Environment: Guidance Manual Highway Type Opportunities for Infiltration Constraints on Infiltration Ground-level highways • Infiltration BMPs can be integrated into vegetated conveyances present in the typical cross section. • Wide shoulders and long stretches allow for flexibility in practice selection and siting.
|
From page 25... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 25 New Projects. These types of projects include construction of new roadways.
|
From page 26... ...
26 Stormwater Infiltration in the Highway Environment: Guidance Manual While infiltration capacity, groundwater quality, and geotechnical issues are addressed in separate sections, the following information may be useful to include on a topographic map: • Known soil and groundwater contamination from state environmental agency or other applicable data source • Known areas of sanitary sewer inflow and infiltration issues from local sewerage agency • Groundwater elevation data (either available contour maps or well data) , potentially available from a local government or groundwater management agency • Soil type(s)
|
From page 27... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 27 minimum geometric design standards are related to safety (e.g., site distance, stopping distance, design speed, etc.) and serviceability (e.g., land widths, overpass heights, etc.)
|
From page 28... ...
28 Stormwater Infiltration in the Highway Environment: Guidance Manual NCHRP Report 802: Volume Reduction of Highway Runoff in Urban Areas can be used to help assess these options. • Centralize operation and maintenance activities.
|
From page 29... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 29 The project team should consider the following factors when selecting methods for preliminary infiltration assessments. Results of Other Groundwater and Geotechnical Investigations.
|
From page 30... ...
30 Stormwater Infiltration in the Highway Environment: Guidance Manual Fill Conditions. If BMPs will be installed in fill conditions, in situ measurements are not possible until grading has been completed.
|
From page 31... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 31 In addition to characterizing current conditions, the project team may also need to consider future rise in the groundwater table, such as from sea level rise, wider spread use of infiltration in the vicinity of the project, nearby water impoundments, or other factors. Groundwater level rise that could potentially interfere with BMP operation in the future could influence feasibility determinations.
|
From page 32... ...
32 Stormwater Infiltration in the Highway Environment: Guidance Manual Interpret Results of Infiltration Capacity Rate Assessment The primary objective for preliminary site investigations is to determine the semi-quantitative infiltration capacity at potential BMP locations within a project site. Table 7 provides general guidance for interpreting preliminary assessments.
|
From page 33... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 33 • Location of BMP opportunity areas (Section 2.2.2) • Locations of infiltration testing conducted at the project site • Boring log locations and results relevant to infiltration feasibility determination • Raw results and professional interpretation of infiltration test results • Categorization of areas into infiltration feasibility classes (see Table 7)
|
From page 34... ...
34 Stormwater Infiltration in the Highway Environment: Guidance Manual Proposed Fill Conditions. Compacted fills have important influence on infiltration feasibility.
|
From page 35... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 35 the proposed roadway cross section and adjacent infrastructure or utilities to determine if the mound would contribute to geotechnical issues. Figure 4 shows a subset of an example output from the Groundwater Mounding Assessment Tool.
|
From page 36... ...
36 Stormwater Infiltration in the Highway Environment: Guidance Manual Summarize Planning-Level Findings Investigations of soil and geological properties at the preliminary planning stage should be only as detailed as needed to support site layout planning and initial selection of BMP strategies. Using results from these investigations, the project team can overlay soil and geological features on the physical constraints map to identify areas where (1)
|
From page 37... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 37 • What is the separation to private or public water wells? Do these wells draw from a shallow unconfined aquifer or a deeper confined aquifer?
|
From page 38... ...
38 Stormwater Infiltration in the Highway Environment: Guidance Manual approaches to protect groundwater quality, including pretreatment, spill containment, separation distance, or other approaches. In general, accidental contaminant spills, such as solvents or petroleum products, are the principal concern for groundwater quality protection in these areas.
|
From page 39... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 39 Sensitive surface waters may have water quality standards considerably lower than drinking water standards. For example, the drinking water MCL for copper is 1 mg/L, but toxicity-based standards (for fish and other aquatic biota)
|
From page 40... ...
40 Stormwater Infiltration in the Highway Environment: Guidance Manual 2.3 Selection of Preliminary Infiltration Approach 2.3.1 Overview This step guides users in selecting a preliminary infiltration approach that aligns with the established infiltration objectives (Section 2.1) and the preliminary infiltration feasibility (Section 2.2)
|
From page 41... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 41 apply, but all conditions in Section 2 apply, then the rating is "marginal." If any criteria in Section 3 apply, then the rating is "infeasible." 2.3.3 Identification of Tentative Infiltration Approach To support tentative decision-making, the project team should review the feasibility findings summarized with the infiltration objectives established in Section 2.1: • Where conditions are clearly favorable for infiltration, the decision to proceed with an infiltration approach may be obvious, regardless of infiltration objectives. Infeasible: Any condition in Section 3 is met.
|
From page 42... ...
42 Stormwater Infiltration in the Highway Environment: Guidance Manual • If infiltration is clearly infeasible, then the stringency of infiltration objectives may not be relevant for making decisions about infiltration. Regardless of the level of stringency, infiltration should not be used.
|
From page 43... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 43 • For the site areas where infiltration could be implemented, which BMPs are applicable or suitable (considering location, geometry, and size of available space)
|
From page 44... ...
44 Stormwater Infiltration in the Highway Environment: Guidance Manual Screening Condition Potential BMPs and BMP Adaptations Best Suited to Infiltration Screening Conditions1 Track 1a – Favorable Infiltration Conditions • Select BMPs to provide Full Infiltration. • Confirm planning-level feasibility findings.
|
From page 45... ...
Geometric Siting Opportunity BM P 01 V eg et at ed C on ve ya nc e BM P 02 D is pe rs io n BM P 03 M ed ia F ilt er D ra in BM P 04 P er m ea bl e Sh ou ld er s BM P 05 B io re te nt io n w /o U nd er dr ai ns BM P 06 B io re te nt io n w ith U nd er dr ai ns BM P 07 In fil tra tio n Tr en ch es BM P 08 In fil tra tio n Ba si ns BM P 09 In fil tra tio n G al le rie s Narrow Medians X X X X X X Wide Medians X X X X X X X X X Shoulders including breakdown lane and area within the clear zone (less than approx.15% or 6H:1V) X X X X X X Shoulders outside of the clear zone (less than approx.15% or 6H:1V)
|
From page 46... ...
46 Stormwater Infiltration in the Highway Environment: Guidance Manual Part 1: Screening of Project Geometric Design Features and BMP Siting Opportunities Instructions: 1. Enter Y (for Yes)
|
From page 47... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 47 (continued on next page) Part 2: Screening of Overall Project Attributes Instructions: 1.
|
From page 48... ...
48 Stormwater Infiltration in the Highway Environment: Guidance Manual Key for Table 13 (Part 3) Headings User Input Guidance Part 3: Other Project-Specific Factors Instructions: 1.
|
From page 49... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 49 Part 4: Summary of Applicability and Suitability Screening Instructions: 1. Review results of Parts 1 through 3.
|
From page 50... ...
50 Stormwater Infiltration in the Highway Environment: Guidance Manual Figure 8. Example Phoenix, Arizona, freeway with sparsely vegetated shoulders.
|
From page 51... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 51 reinforced concrete features. For infiltration in cold climates, project teams should consider whether infiltrated water would pose elevated corrosion risks to steel culverts, steel structures, or other intrastate containing steel (either external or as internal reinforcement)
|
From page 52... ...
52 Stormwater Infiltration in the Highway Environment: Guidance Manual Category of BMP Characteristic Properties Example Opportunities and Constraints Related to Geotechnical Issues1 Opportunities Constraints Direct infiltration into roadway subgrade Example: BMP 04 Permeable Pavement loading ratio2 Road subgrade Relatively low has important structural considerations, particularly for flexible pavement design. Broad footprint of permeable pavement may allow infiltration in relatively impermeable and compacted soils.
|
From page 53... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 53 Category of BMP Characteristic Properties Example Opportunities and Constraints Related to Geotechnical Issues1 Opportunities Constraints Basins Example: BMP 05 and 06 Bioretention (more centralized variation) BMP 08 Infiltration Basins BMP 09 Infiltration Galleries Typically located in more centralized locations Typically have a relatively high loading ratio Typically, effective water storage depth is between 12 in.
|
From page 54... ...
54 Stormwater Infiltration in the Highway Environment: Guidance Manual BMP Relative Risk of Groundwater Impacts1 Key Characteristics Influencing Ranking BMP 01 Vegetated Conveyance L More limited infiltration, shallower ponding, and soil filtration of infiltrating runoff BMP 02 Dispersion L Shallower ponding, high soil contact ratio, amended/organic/biologically active soils BMP 03 Media Filter Drain L Shallow ponding, specialized media with high treatment capacity BMP 04 Permeable Shoulders M Can have a relatively small footprint area, some pretreatment provided in base material but additional pretreatment not practical, can infiltrate water below organic soil strata BMP 05 Bioretention without Underdrains L to M Provide treatment for most constituents within media, can have relatively small footprint and deeper infiltrating surface BMP 06 Bioretention with Underdrains L Provide treatment for most constituents within media, infiltrate less water than bioretention w/o underdrain BMP 07 Infiltration Trenches M to H Deeper profile typically below surface soil strata, pretreatment options may be limited BMP 08 Infiltration Basins M Deeper profile and typically smaller tributary area ratio but soil can be amended to improve water quality. BMP 09 Infiltration Galleries M to H Deeper profile typically below surface soil strata, pretreatment may not address all pollutants of concern.
|
From page 55... ...
Planning Framework for Early Decision-Making and Tentative BMP Selection 55 Potential Safety Consideration B M P 0 1 V eg et at ed C on ve ya nc e B M P 0 2 D is pe rs io n B M P 0 3 M ed ia F ilt er D ra in B M P 0 4 P er m ea bl e S ho ul de rs B M P 0 5 B io re te nt io n w /o U nd er dr ai ns B M P 0 6 B io re te nt io n w ith U nd er dr ai ns B M P 0 7 In fil tr at io n T re nc h B M P 0 8 In fil tr at io n B as in B M P 0 9 In fil tr at io n G al le rie s Limitations on side slopes and berms within the clear zone, including check dams, etc. X X X X X X X Limitations on drainage structure design within the clear zone (e.g., pipe inlets and outlets flush to slope)
|
From page 56... ...
56 Stormwater Infiltration in the Highway Environment: Guidance Manual Corrective Maintenance Activities B M P 0 1 V eg et at ed C on ve ya nc e B M P 0 2 D is pe rs io n B M P 0 3 M ed ia F ilt er D ra in B M P 0 4 P er m ea bl e S ho ul de rs B M P 0 5 B io re te nt io n w /o U nd er dr ai ns B M P 0 6 B io re te nt io n w ith U nd er dr ai ns B M P 0 7 In fil tr at io n T re nc he s B M P 0 8 In fil tr at io n B as in s B M P 0 9 In fil tr at io n G al le rie s Re-grading to maintain level spread function X X Re-grade to remove sediment or fix erosion X X X X Repair berms, inlets, outlets, or other structures X X X X X X X X Cleaning of underdrain pipes X X X Decompaction/reamendment X X X X Partial removal of surface material to remediate clogging or pollutant buildup X X X X X X Complete replacement of system components X X X X X X Re-seeding to provide needed coverage X X X X Significant re-vegetation to provide needed coverage X X X X X Remediate contamination from acute or chronic loadings (oil, gas, or other contaminants) X X X X X X X X X X = Potentially applicable.
|
From page 57... ...
BMP Capital Costs – New Roadway or Major Redevelopment Capital Costs – Retrofit Projects or Minor Redevelopment O&M and Replacement/ Reconstruction Costs Effective Life Span BMP 01 Vegetated Conveyance Low to Moderate Can typically be easily incorporated into grading plans for non-ultra-urban settings. Provides conveyance function that can offset need for pipes and structures.
|
From page 58... ...
BMP Capital Costs – New Roadway or Major Redevelopment Capital Costs – Retrofit Projects or Minor Redevelopment O&M and Replacement/ Reconstruction Costs Effective Life Span BMP 04 Permeable Shoulders with Stone Reservoirs Low to Moderate Assumes new development or lane additions in which the cost of permeable pavement offsets traditional pavement costs that would have been used. High Cost to add permeable shoulders to an existing roadway are much greater than building these as part of a new roadway.
|
From page 59... ...
BMP 08 Infiltration Basin Moderate Assumes no acquisition costs for land. Assumes potential additional excavation and infrastructure to convey water to centralized location.
|
From page 60... ...
60 Stormwater Infiltration in the Highway Environment: Guidance Manual An infiltration feasibility exhibit can also be useful to document preliminary BMP selection and siting. Potential content of this exhibit includes the following: • Topographic and drainage feature elements (Section 2.2.2)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.