Stormwater Infiltration in the Highway Environment: Guidance Manual (2019) / Chapter Skim
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Pages 99-109
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99 C H A P T E R 5 This chapter presents case studies of how local agencies and project proponents have approached selection and design of infiltration BMPs. Each case study presents the highlights of the process that was used and the decisions that were made.
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100 Stormwater Infiltration in the Highway Environment: Guidance Manual 5.1.3 Sizing and Design Approach Applicable BMP section and sizing standards for stormwater BMPs are described in the HRM. These standards require infiltration of 91% of long-term runoff volume if infiltration rates exceed 0.3 in./h.
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BMP Selection and Sizing Case Studies 101 estimates that fell below the thresholds. At any given point along the embankment, it is possible that infiltration rates would be below the 0.3 in./h threshold.
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102 Stormwater Infiltration in the Highway Environment: Guidance Manual to be infeasible. Biofiltration is the second priority but can require larger facilities and be more expensive to construct.
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BMP Selection and Sizing Case Studies 103 The stormwater management approach described in project environmental documents was based on these findings. Additionally, project environmental documents identified the need for subsequent investigations to confirm or refine infiltration feasibility.
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104 Stormwater Infiltration in the Highway Environment: Guidance Manual Figure 23. Example borehole log from borehole percolation test.
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BMP Selection and Sizing Case Studies 105 2. A valve was proposed to be installed at the underdrain outlet of Facility A as a means of providing adaptability for potential design or operation revisions.
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106 Stormwater Infiltration in the Highway Environment: Guidance Manual for Full Infiltration, allowing compliance with the overall water quality requirement to be demonstrated without fully relying on infiltration.
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BMP Selection and Sizing Case Studies 107 5.3.2 Key Lessons Learned SPU used this project as an opportunity to learn how to improve practices and has published articles and presentations to transfer these findings to other organizations. Examples of lessons learned included the following: • Geotechnical testing was not conducted early enough in the process.
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From page 108... ...
108 Stormwater Infiltration in the Highway Environment: Guidance Manual • The investigation period occurred during the summer, and geotechnical recommendations did not account for groundwater mounding and perched groundwater conditions that can form in the soil types present at the sites. Recommendations conducted over an abbreviated period should have been interpreted with a greater implied uncertainty.
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From page 109... ...
BMP Selection and Sizing Case Studies 109 Step 1c and Step 2. Infiltration Approach and Planning Track.
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