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Design infiltration rate (view source)

Revision as of 22:03, 6 May 2020

2,710 bytes added ,  4 years ago
→‎Sampling
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It does not relate to the hydraulic conductivity or permeability of filter media or planting media used within vegetated BMPs.  
 
It does not relate to the hydraulic conductivity or permeability of filter media or planting media used within vegetated BMPs.  
 
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{{TOClimit|2}}
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The design infiltration rate (''f''') is used in all sizing calculations for [[bioretention]] and [[bioswales]], [[dry ponds]], [[infiltration trenches]] and [[infiltration chambers|chambers]], and [[exfiltration trenches]]. It is related to, but not synonymous with 'permeability', 'field hydraulic conductivity' (''K<sub>fc</sub>''), or 'saturated hydraulic conductivity' (''K<sub>sat</sub>''). Before application a safety correction factor (''SCF'') is incorporated into the figure, depending upon the source of the raw data, and the risk of failure of the finished practice.
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The design infiltration rate (''f''') is used in all sizing calculations for [[bioretention]] and [[bioswales]], [[dry ponds]], [[infiltration trenches]] and [[infiltration chambers|chambers]], and [[exfiltration trenches]]. It is related to, but not always synonymous with 'permeability', 'field hydraulic conductivity' (''K<sub>fc</sub>''), or 'saturated hydraulic conductivity' (''K<sub>sat</sub>''). Before application a safety correction factor (''SCF'') is incorporated into the figure, depending upon the source of the raw data, and the risk of failure of the finished practice.
    
{{textbox|It is highly recommended that testing be conducted on site.}}
 
{{textbox|It is highly recommended that testing be conducted on site.}}
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*[[Permeameter]]
 
*[[Permeameter]]
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*Double ring infiltrometer
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*[[Double ring infiltrometer]]
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*Cased borehole ([[percolation test]])
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*[[Percolation test]]
 
|
 
|
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*[[Grain size analysis]] (Hazen)
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*[[Grain size analysis]] (Hazen method)
 
|
 
|
 
*Single ring infiltrometer
 
*Single ring infiltrometer
 
*Soil textural classification   
 
*Soil textural classification   
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|}
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==Becoming familiar with the different measurement practices==
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STEP have produced a free online module to provide some basic information on infiltration test methods. Access it [https://sustainabletechnologies.ca/events/design-infiltration-rate-e-learning-course/ '''HERE''']
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==Safety correction==
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To apply conservatism, the measured or calculated infiltration rate may be divided by a value between 2 and 3 before use in design calcualtions<ref>Design criteria for infiltration. (2018, February 14). Minnesota Stormwater Manual, . Retrieved 00:16, March 14, 2018 from https://stormwater.pca.state.mn.us/index.php?title=Design_criteria_for_infiltration&oldid=35583.</ref>
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{| class="wikitable"
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|+ Selecting a safety factor
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|-
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! Lower value (closer to 2)
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! Higher value (closer to 3)
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|-
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|Catchment < 100 m²
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|Catchment > 100 m²<ref>Ballard, B. W., Wilson, S., Udale-Clarke, H., Illman, S., Scott, T., Ashley, R., & Kellagher, R. (2015). The SuDS Manual. London.</ref>
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|-
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|Permeameter or percolation test on site
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|Double ring infiltrometer test on site, or grain size analysis used <ref>San Francisco Public Utilities Commission. (2017). Determination of Design Infiltration Rates for the Sizing of Infiltration‐based Green Infrastructure Facilities. Retrieved from http://sfwater.org/modules/showdocument.aspx?documentid=9681</ref>
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|-
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|Loamy or sandy soil texture
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|Clayey soil texture<ref>CRC for Water Sensitive Cities. (2015). Adoption Guidelines for Stormwater Biofiltration Systems: Appendix C - Guidelines for filter media in stormwater biofiltration systems.</ref>
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|-
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|No variation in geologic formation, soil texture or soil bulk density within 1.5 metres below the proposed bottom elevation of the practice.
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|Variation in geologic formation, soil texture or soil bulk density within 1.5 metres below the proposed bottom eleation of the practice observed.
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|-
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|No nearby sensitive receptors
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|Sensitive receptors in near proximity (e.g. septic systems, building foundations).
 
|}
 
|}
    
==Planning for testing==
 
==Planning for testing==
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===Background Evaluation===
 
===Background Evaluation===
 
Prior to performing testing and developing a detailed site plan, existing site conditions should be inventoried and mapped including, but not limited to:
 
Prior to performing testing and developing a detailed site plan, existing site conditions should be inventoried and mapped including, but not limited to:
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#Surficial geology and underlying stratigraphy;
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*Surficial geology and underlying stratigraphy;
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#Watercourses (perennial and intermittent), waterbodies, wetlands and floodplains;
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*Watercourses (perennial and intermittent), water bodies, wetlands and floodplains;
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#Small headwater drainage features;
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*Small headwater drainage features;
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#Topography, slope, and drainage patterns;
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*Topography, slope, and drainage patterns;
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#Existing land cover and land use;
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*Existing land cover and land use;
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#Natural heritage conservation areas; and
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*Natural heritage conservation areas; and
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#Other man-made features or conditions that may impact design such as existing nearby structures (buildings, infrastructure, etc.).
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*Other man-made features or conditions that may impact design such as existing nearby structures (buildings, infrastructure, etc.).
      
A sketch plan or preliminary layout plan for the proposed development should be evaluated, including:
 
A sketch plan or preliminary layout plan for the proposed development should be evaluated, including:
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#The preliminary grading plan and areas of cut and fill;
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#The location and water surface elevation of all existing, and location of proposed water supply sources and wells;
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#The location of all existing and proposed on-site wastewater (septic) systems;
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#The location of other features of note such as utility rights-of-way, water and sewer lines, etc.;
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#Existing data from borehole, well and geophysical testing; and
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#Proposed location of development features (buildings, roads, utilities, etc.).
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*The preliminary grading plan and areas of cut and fill;
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===Sampling===
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*The location and water surface elevation of all existing, and location of proposed water supply sources and wells;
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[[File:Test_pit.jpg|thumb|Infiltration testing should be carried out at relevant stages down through the profile of a test pit.]]
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*The location of all existing and proposed on-site wastewater (septic) systems;
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The number of test pits or soil borings varies depending on site conditions and the proposed development plan. General guidelines are as follows:
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*The location of other features of note such as utility rights-of-way, water and sewer lines, etc.;
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*Existing data from borehole, well and geophysical testing; and
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*Proposed location of development features (buildings, roads, utilities, etc.).
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==Safety correction==
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The measured or calculated infiltration rate must be divided by a value 2 or 3 before use in design<ref>Design criteria for infiltration. (2018, February 14). Minnesota Stormwater Manual, . Retrieved 00:16, March 14, 2018 from https://stormwater.pca.state.mn.us/index.php?title=Design_criteria_for_infiltration&oldid=35583.</ref>
   
{| class="wikitable"
 
{| class="wikitable"
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|+ Selecting a safety factor
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! BMP footprint (m²)
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! Test pit
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! Borehole
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|-
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| < 50 || 1 || 1
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|-
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|rowspan = 2| 50 – 900 || 1 || 2
 
|-
 
|-
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! 2
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| 2 || 0
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! 3
   
|-
 
|-
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|Catchment < 100 m²
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| rowspan = 2|> 900 || 1 every 450 m² || 2 every 450 m²
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|Catchment > 100 m²<ref>Ballard, B. W., Wilson, S., Udale-Clarke, H., Illman, S., Scott, T., Ashley, R., & Kellagher, R. (2015). The SuDS Manual. London.</ref>
   
|-
 
|-
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|Permeameter or Percolation test on site
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| 2 every 450 m² || 0
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|Double ring infiltrometer test on site, or Grain size used <ref>San Francisco Public Utilities Commission. (2017). Determination of Design Infiltration Rates for the Sizing of Infiltration‐based Green Infrastructure Facilities. Retrieved from http://sfwater.org/modules/showdocument.aspx?documentid=9681</ref>
   
|-
 
|-
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|Loamy or sandy soil
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| Linear  || 1 every 450 m² || 1 every 50 m
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|Clayey soil<ref>CRC for Water Sensitive Cities. (2015). Adoption Guidelines for Stormwater Biofiltration Systems: Appendix C - Guidelines for filter media in stormwater biofiltration systems.</ref>
   
|}
 
|}
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* Tests must be conducted within 10 metres of the infiltration practice footprint area.
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* Tests should be performed within 48 hours of a rain event, when the soil is already near, or at field capacity.
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* Test locations should be spaced equidistant from one another.
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* Make a minimum of seven (7) measurements (i.e. tests) for each test location (i.e., each test pit or borehole).
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* An additional round of tests should be conducted at 1.5 metres depth below the proposed bottom elevation of the practice if there is significant variation in geologic formation, soil texture or bulk density compared to conditions at the proposed bottom elevation.<br>
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* To calculate the median infiltration rate of the native soil at the depth tested, discard the highest and lowest values obtained from each test location and calculate the median from the remaining measurements.
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'''The recommendations above are guidelines'''
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Keep in mind that excessive testing and disturbance of the site prior to construction is not recommended.<ref>Christopher B. Burke Engineering LLC. (2009). Soil Infiltration Testing Protocol SOIL INFILTRATION TESTING PROTOCOL Purpose of this Protocol Who Should Conduct Testing. Retrieved from https://www.in.gov/ocra/files/Appendix%20F%20-%20Soil%20Infiltration%20Testing%20Protocol.pdf</ref>
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[[Category:Infiltration]]
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