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From page 75... ... Appendix C Infiltration Testing and Factors of Safety in Support of the Selection and Design of Volume Reduction Approaches (White Paper #1) 1 Introduction .................................................................................................................................... Read the entire page →
From page 76... ... 1 Introduction Characterization of potential infiltration rates is a critical step in evaluating the degree to which infiltration can be used to reduce stormwater runoff volume. There are numerous methods for measuring or estimating infiltration rates of soils; however not all methods are equally applicable to stormwater facility siting and design. Read the entire page →
From page 77... ... 2 Role of Infiltration Testing in Different Stages of Project Development In the process of planning and designing infiltration facilities, there are a number of ways that infiltration testing or estimation factors into project development. At the project planning phases, a designer faces the questions: Where within my project area is infiltration potentially feasible? Read the entire page →
From page 78... ... can be useful for early identification of fatal flaws that may not be caught using desktop methods. At the planning phase, it is generally recommended that screening for other feasibility factors, such as groundwater contamination, depth to groundwater, setbacks from wells and structures, and other criteria be applied first, before identifying potential areas for infiltration testing. Read the entire page →
From page 79... ... footprint) Read the entire page →
From page 80... ... proponents regarding site assessment to support BMP selection. For example, a designer may still be interested in determining where infiltration is feasible, but the proponent would not be required to demonstrate that they have adequately assessed infiltration opportunities before moving on to other noninfiltration BMP options. Read the entire page →
From page 81... ... Table 1. Selected State and Local Government Approaches to Infiltration Testing Jurisdiction Planning Phase Requirements Design Phase Requirements Safety Factors Orange County, CA Small projects may rely solely on regional NRCS soils maps and data that are already available for the project, such as geotechnical investigations, groundwater maps, etc. Read the entire page →
From page 82... ... Jurisdiction Planning Phase Requirements Design Phase Requirements Safety Factors Caltrans1 In this study, screening for potential locations with suitable infiltration rates consisted of the following steps: • Conduct desktop analysis, including NRCS Soil Survey hydrologic soil groups and clay content. • Characterize subsurface lithography and depth to groundwater using boreholes; collect continuous cores. Read the entire page →
From page 83... ... Jurisdiction Planning Phase Requirements Design Phase Requirements Safety Factors Wisconsin (including WisDOT) Allows use of desktop resources based on soil texture to evaluate infiltration potential. Read the entire page →
From page 84... ... Jurisdiction Planning Phase Requirements Design Phase Requirements Safety Factors Western Washington (including WSDOT) Specific criteria for planning phase assessment are not included in the Manual. Read the entire page →
From page 85... ... 4 Guidance for Selecting Infiltration Testing Methods In order to select an infiltration testing method, it is important to understand how each test is applied and what specific physical properties the test is designed to measure. Infiltration testing methods vary considerably in these regards. Read the entire page →
From page 86... ... 4.1 Desktop Approaches and Data Correlation Methods This section reviews common methods used to evaluate infiltration characteristics based on desktopavailable information available, such as GIS data. This section also introduces methods for estimating infiltration properties via correlations with other measurements. Read the entire page →
From page 87... ... Philips and Kitch (2011) found that this method did not consistently align with direct measurements. Read the entire page →
From page 88... ... 4.2.2 Open Pit Falling Head Test This test is similar to the Simple Open Pit Test, but covers a larger footprint, includes more specific instructions, returns more precise measurements, and generally should be overseen by a geotechnical professional. Nonetheless, it remains a relatively simple test. Read the entire page →
From page 89... ... 4.2.4 Single Ring Infiltrometer Test The single ring infiltrometer test is not a standardized ASTM test, however it is a relatively wellcontrolled test and shares many similarities with the ASTM standard double ring infiltrometer test (ASTM 3385-09) Read the entire page →
From page 90... ... infiltration rate than double ring infiltrometer and borehole percolation tests (Philips and Kitch 2011) Read the entire page →
From page 91... ... be biasing results at the strata where testing is conducted. This boring should also be extended below the depth of the test, following the completion of the test. Read the entire page →
From page 92... ... "Havg" is the average height of water in the hole over the time interval, measured from the bottom of the hole, inches "Δt" = test interval, minutes "r" is the test hole radius, inches "It" is the resulting infiltration rate, inches per hour. When the ΔH is more than 25 percent of the Havg, more detailed equations may be necessary. Read the entire page →
From page 93... ... Table 2. Summary Matrix of Infiltration Rate Estimation and Testing Methods Test Spatial Scale Dimensionality Vertical Strata Suitable for Planning-Level Screening Suitable for Design Infiltration Rate Estimation Methods NRCS Soil Survey Maps Geographic/ landscape scale (regional maps) Read the entire page →
From page 94... ... Test Spatial Scale Dimensionality Vertical Strata Suitable for Planning-Level Screening Suitable for Design Infiltration Testing Methods Simple Open Pit Test Point measurement (~4 sq-ft) Has a greater component of horizontal flow than expected in most BMPs. Read the entire page →
From page 95... ... Test Spatial Scale Dimensionality Vertical Strata Suitable for Planning-Level Screening Suitable for Design Smaller-scale Pilot Infiltration Test (PIT) Smaller-scale extensive measurement (~20 to 32 sq-ft) Read the entire page →
From page 96... ... 5 Specific Considerations for Infiltration Testing The following subsections are intended to address specific topics that commonly arise in characterizing infiltration rates. 5.1 Hydraulic Conductivity versus Infiltration Rate versus Percolation Rate A common misunderstanding is that the "percolation rate" obtained from a percolation test is equivalent to the "infiltration rate" obtained from tests such as a single or double ring infiltrometer test which is equivalent the "saturated hydraulic conductivity". Read the entire page →
From page 97... ... safety to borehole methods to account for the inherent uncertainty in these measurements and conversions. If the bottom of a BMP (infiltration surface) Read the entire page →
From page 98... ... compaction (such as by movement of machinery, placement of fill, stockpiling of materials, and foot traffic) can be difficult to avoid in some parts of the project site. Read the entire page →
From page 99... ... study provide requirements for the number of infiltration tests they require. The number of infiltration tests specified varies considerably by jurisdiction and is generally a matter that is left to the discretion of the designer and plan reviewer. Read the entire page →
From page 101... ... • Soil assessment methods – the site assessment extent (e.g., number of borings, test pits, etc.) and the measurement method used to estimate the short-term infiltration rate. Read the entire page →
From page 102... ... • Expected influent sediment loads and the level of pretreatment – Sediment loading to the infiltration system is a major factor in the rate at which infiltration rates decline and the potential for failure of the facility increases. For areas with expected sediment in runoff, well designed pretreatment should be included to reduce the probability of clogging from high sediment loading. Read the entire page →
From page 103... ... Table 4. Design-Related Considerations for Infiltration Facility Safety Factors Consideration High Concern – 3 points Medium Concern – 2 points Low Concern – one point Compaction during construction Construction of facility on a compacted site or increased probability of unintended/ indirect compaction. Read the entire page →
From page 104... ... Note: The minimum combined adjustment factor should not be less than 2.0 and the maximum combined adjustment factor should not exceed 9.0. Worksheet 1 provides a form for documenting this method. Read the entire page →
From page 105... ... Worksheet 1: Factor of Safety and Design Infiltration Rate Worksheet Factor Category Factor Description Assigned Weight (w) Factor Value (v) Read the entire page →
From page 106... ... 7 References ASTM International. Read the entire page →
From page 107... ... Hinman, C Read the entire page →
From page 108... ... Washington State Department of Ecology (2012) Read the entire page →

From page 75...

... Appendix C Infiltration Testing and Factors of Safety in Support of the Selection and Design of Volume Reduction Approaches (White Paper #1) 1 Introduction ....................................................................................................................................