Table 4 - 48: Soils Report Requirements by BMP shows the necessary components of a soils report organized by BMP.
Table 4 - 48: Soils Report Requirements by BMP BMP L602 - Downspout Full Infiltration – Includes BMP L602a - Downspout Infiltration Trenches and BMP L602b - Downspout Infiltration Drywells A soils report is required to design downspout full infiltration facilities. A soils report is also required if citing that downspout full infiltration is not feasible due to subsurface characteristics. The soils report shall be based on site specific subsurface explorations. The soils report shall be prepared by a Washington State Licensed Professional Engineer, Washington State Licensed Professional Geologist, a Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America, Washington State Licensed On-Site Wastewater Treatment System Designers, or other suitable trained persons working under the professional. The soils report shall be based on site specific explorations and: Classify the underlying soils of the project site. Identify the NRCS series of the soil and the USDA textural class. The USDA textural class is needed to size the facility. Use soil borings, soil test pits, or published USDA/NRCS soil surveys to classify the soil. Soil surveys cannot be used as the sole means of classifying soils for design purposes. Soil surveys are available here: https://websoilsurvey.nrcs.usda.gov/app/HomePage.htm Currently USDA has not published soil information in the City limits. If published information becomes available it may be used. Prepare detailed logs for each boring or test pit and a map showing the location of the boring or test pit. Borings or test pits shall be taken at the location of the proposed downspout full infiltration system. Soils logs must include: • The boring or pit must be at least 4 feet deep (from proposed grade) and at least one foot below expected bottom elevation of the infiltration facility. Identify the hydraulic restriction layer (groundwater, low permeability layer, bedrock, etc.). Testing with a monitoring well or an excavated pit must extend to a depth at least 1 foot below the estimated bottom elevation of the infiltration facility. Perform analyses during the wet season (December 1 - April 1). The hydraulic restriction layer may be identified by: A soils report is required to design a rain garden. A soils report is also required if citing that a rain garden is not feasible due to subsurface characteristics. The soils report shall be based on site specific subsurface explorations. The soils report shall be prepared by a Washington State Licensed Professional Engineer, Washington State Licensed Professional Geologist, a Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America, Washington State Licensed On-Site Wastewater Treatment System Designers, or other suitable trained persons working under the professional. The soils report shall be based on site specific explorations and: Classify the underlying soils of the site. Use soil borings, soil test pits, or published USDA/NRCS soil surveys to classify the soil. Soil surveys cannot be used as the sole means of classifying soils for design purposes. Soil surveys are available here https://websoilsurvey.nrcs.usda.gov/app/HomePage.htm. Currently USDA has not published soil information in the City limits. If published information becomes available it may be used. Prepare detailed logs for each boring or test pit and a map showing the location of the boring or test pit. Borings or test pits shall be taken at the location of the proposed rain garden. Soils logs must include: • The boring or pit must be at least 4 feet deep (from proposed grade) and at least one foot below expected bottom elevation of the rain garden. Identify the hydraulic restriction layer (groundwater, low permeability layer, bedrock, etc.). Testing with a monitoring well or an excavated pit must extend to a depth at least 1 foot below the estimated bottom elevation of the rain garden. Perform analyses during the wet season (December 1 - April 1). ◦ The hydraulic restriction layer may be identified by: ◦ Soil evidence of groundwater such as mottling ◦ Reliable site historical data Identify the native soil infiltration rate. Use either of the following methods to determine the native soil infiltration rate. It is not necessary to identify the native soil infiltration rate for determining infeasibility if other subsurface characteristics such as high groundwater preclude the use of a rain garden. Small Scale Pilot Infiltration Test (PIT) per Appendix A - Appendix A Determining the Design Infiltration Rate Soil Grain Size Analysis per Appendix A - Appendix A Determining the Design Infiltration Rate. This method is only allowed if subsurface is underlain with soils not consolidated by glacial advance. A soils report is required if citing that perforated stub-outs are not feasible due to subsurface characteristics. The soils report shall be based on site specific subsurface explorations The soils report shall be prepared by a Washington State Licensed Professional Engineer, Washington State Licensed Professional Geologist, a Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America, Washington State Licensed On-Site Wastewater Treatment System Designers, or other suitable trained persons working under the professional. The soils report shall be based on site specific explorations and: Classify the underlying soils of the site Use soil borings, soil test pits, or published USDA/NRCS soil surveys to classify the soil. Soil surveys cannot be used as the sole means of classifying soils for design purposes. Soil surveys are available here: https://websoilsurvey.nrcs.usda.gov/app/HomePage.htm Currently USDA has not published soil information in the City limits. If published information becomes available it may be used. Prepare detailed logs for each boring or test pit and a map showing the location of the boring or test pit. Borings or test pits shall be taken at the location of the proposed bioretention facility. Soils logs must include: • The depth must extend a minimum of 5 feet below the estimated bottom elevation of the bioretention facility. Assess soil stratigraphy for low permeability layers, highly permeable sand/gravel layers, depth to groundwater, and other soil structure variables necessary to assess subsurface flow patterns. Obtain soil samples for laboratory testing from each soil stratum within 3.0 times the maximum design water depth below the base of the bioretention (but not less than 3 feet below the base of the infiltration facility). Soil characteristics for each soil unit shall include: • Grain size distribution (if using the Grain Size Analysis Method for Determining Infiltration Rates) • Variations in nature of stratification Identify the hydraulic restriction layer (groundwater, low permeability layer, bedrock, etc.). The hydraulic restriction layer may be identified by: Soil evidence of groundwater such as mottling Testing with a monitoring well or an excavated pit must extend to a depth at least 1 foot below the estimated bottom elevation of the bioretention facility for facilities that serve a contributing area that is less than: 5,000 ft2 of pollution generating impervious surface, or 10,000 ft2 of impervious surface, or Testing with a monitoring well or an excavated pit must extend to a depth at least 3 foot below the estimated bottom elevation of the bioretention facility for facilities that serve a contributing area that meets or exceeds: 5,000 ft2 of pollution generating impervious surface, or 10,000 ft2 of impervious surface, or Perform analyses during the wet season (December 1 - April 1). If the general site assessment cannot confirm that hydraulic restricting layer will be greater than 3 feet below the bottom of the bioretention facility (for facilities serving contributing areas that meet or exceed 5,000 ft2 of pollution generating impervious surface, or 10,000 ft2 of impervious surface, or ¾ acre of pervious surface), place monitoring wells or excavated pits strategically to assess depth to groundwater. Monitoring with a continuously logging sensor between December 1 and April 1 provides the most thorough information. Special considerations are necessary for highly permeable gravel areas (>4 inches per hour) which may not show signs of high groundwater. Exercise sound professional judgment. Only for projects required to comply with Minimum Requirements #1-9: If onsite infiltration might result in shallow lateral flow, assess the locations where interflow will surface. Place groundwater monitoring wells to determine gradient and flow. Identify the native soil infiltration rate using methods outlined in Appendix A - Design Infiltration Rate Steps. It is not necessary to identify the native soil infiltration rate for determining infeasibility if other subsurface characteristics such as high groundwater preclude the use of a bioretention facility. Small bioretention facilities that receive stormwater from less than 10,000 square feet can use one of the following to determine the native soil infiltration rate: Small Scale Pilot Infiltration Test (PIT) per Appendix A - Design Infiltration Rate Steps. Soil Grain Size Analysis per Appendix A - Design Infiltration Rate Steps. This method is only allowed if subsurface is underlain with soils not consolidated by glacial advance. The rate determined can be based on one test pit or boring. Large bioretention facilities that receive stormwater from 10,000 square feet or more can use one of the following to determine the native soil infiltration rate: Large Scale Pilot Infiltration Test (PIT) per Appendix A - Appendix A Determining the Design Infiltration Rate. Multiple Small Scale Pilot Infiltration Tests (PIT) per Appendix B - Appendix B Soils Reports. • Tests must occur at several locations approximately every 5,000 square feet. Soil Grain Size Analysis per Appendix A - Appendix A Determining the Design Infiltration Rate This method is only allowed if subsurface is underlain with soils not consolidated by glacial advance. The rate determined must be based on information obtained from more than one test pit or boring. Long, narrow bioretention facilities (such as those following the right of way) have the following options for determining the native soil infiltration rate: Small Scale Pilot Infiltration Test (PIT) per Volume 4 - Appendix A -Determiningthe Design Infiltration Rate. • Tests must occur every 200 feet. Soil Grain Size Analysis per Volume 4 - Appendix A -Determining the Design Infiltration Rate. • This method is only allowed if subsurface is underlain with soils not consolidated by glacial advance. • The rate determined shall be based on a boring or test pit taken every 200 feet. If subsurface characteristics across the project site indicate consistent soil characteristics and depths to seasonal high groundwater conditions or hydraulic restriction layer, the number of test locations may be reduced to a frequency recommended by the Washington State Licensed Professional Engineer or Washington State Licensed Professional Geologist, or Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America. 5. A groundwater mounding analysis is required to determine the final native infiltration rate for bioretention facilities that will serve contributing areas greater than 1 acre and where there is less than 15 feet from the bottom elevation of the facility to the seasonal high groundwater. MODRET or an equivalent model shall be used. A soils report is required if citing that perforated stub-outs are not feasible due to subsurface characteristics. The soils report shall be based on site specific subsurface explorations The soils report shall be prepared by a Washington State Licensed Professional Engineer, Washington State Licensed Professional Geologist, a Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America, Washington State Licensed On-Site Wastewater Treatment System Designers, or other suitable trained persons working under the professional. The soils report shall be based on site specific explorations and: Classify the underlying soils of the site. Classification is not needed if it is determined that there is a hydraulic restriction layer that deems a perforated stubout infeasible. Use soil borings, soil test pits, or published USDA/NRCS soil surveys to classify the soil. Soil surveys cannot be used as the sole means of classifying soils for design purposes. Soil surveys are available here: https://websoilsurvey.nrcs.usda.gov/app/HomePage.htm Currently USDA has not published soil information in the City limits. If published information becomes available it may be used. Prepare detailed logs for each boring or test pit and a map showing the location of the boring or test pit. Borings or test pits shall be taken at the location of the proposed downspout full infiltration system. Soils logs must include: • The boring or pit must be at least 4 feet deep (from proposed grade) and at least one foot below expected bottom elevation of the infiltration facility. Identify the hydraulic restriction layer (groundwater, low permeability layer, bedrock, etc.). Testing with a monitoring well or an excavated pit must extend to a depth at least 1 foot below the estimated bottom elevation of the infiltration facility. Perform analyses during the wet season (December 1 - April 1). The hydraulic restriction layer may be identified by: A soils report is required to design permeable pavement. A soils report is also required if citing that permeable pavement is not feasible due to subsurface characteristics. The soils report shall be based on site specific subsurface explorations. The soils report shall be prepared by a Washington State Licensed Professional Engineer, Washington State Licensed Professional Geologist, a Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America, or other suitable trained persons working under the professional. The soils report shall be based on site specific explorations and: Classify the underlying soils of the site. Use soil borings, soil test pits, or published USDA/NRCS soil surveys to classify the soil. Soil surveys cannot be used as the sole means of classifying soils for design purposes. Soil surveys are available here: https://websoilsurvey.nrcs.usda.gov/app/HomePage.htm. Currently USDA has not published soil information in the City limits. If published information becomes available, it may be used. Prepare detailed logs for each boring or test pit and a map showing the location of the boring or test pit. Borings or test pits shall be taken at the location of the proposed permeable pavement. Soils logs must include: • The depth must extend a minimum of 5 feet below the estimated bottom elevation of the lowest subgrade layer. Assess soil stratigraphy for low permeability layers, highly permeable sand/gravel layers, depth to groundwater, and other soil structure variables necessary to assess subsurface flow patterns. Obtain soil samples for laboratory testing from each soil stratum within 3.0 times the maximum design water depth below the base of the permeable pavement (but not less than 3 feet below the base of the infiltration facility). Soil characteristics for each soil unit shall include: • Grain size distribution (if using the Grain Size Analysis Method for Determining Infiltration Rates) • Variations in nature of stratification • Cation exchange capacity (needed to determine if underlying soils can provide treatment) • Percent organic content (needed to determine if underlying soils can provide treatment) Identify the hydraulic restriction layer (groundwater, low permeability layer, bedrock, etc.). The hydraulic restriction layer may be identified by: Soil evidence of groundwater such as mottling Testing with a monitoring well or an excavated pit must extend to a depth at least 1 foot below estimated bottom elevation of the lowest subgrade layer. Perform analyses during the wet season (December 1 - April 1). If the general site assessment cannot confirm that hydraulic restricting layer will be greater than 1 foot below the bottom of the permeable pavement subgrade, place monitoring wells or excavated pits strategically to assess depth to groundwater. Monitoring with a continuously logging sensor between December 1 and April 1 provides the most thorough information. Special considerations are necessary for highly permeable gravel areas (>4 inches per hour) which may not show signs of high groundwater. Exercise sound professional judgment. Only for projects required to comply with Minimum Requirement #1-9: If onsite infiltration might result in shallow lateral flow, assess the locations where interflow will surface. Place groundwater monitoring wells to determine gradient and flow Identify the native soil infiltration rate using methods outlined in Appendix A - Appendix A Determining the Design Infiltration Rate. It is not necessary to identify the native soil infiltration rate for determining infeasibility if other subsurface characteristics such as high groundwater preclude the use of permeable pavement. Projects can use one of the following to determine the native soil infiltration rate: Small Scale Pilot Infiltration Test (PIT) per Volume 4 - - Appendix A Determining the Design Infiltration Rate. • Perform test for every 5,000 ft2 of permeable pavement and at least one per project site. • For residential developments, perform a test on every lot. • For linear projects or linear portions of a project, complete a test for every 200 feet of linear surface (roadway or sidewalk) Soil Grain Size Analysis per Volume 4 - Appendix A - Appendix A Determining the Design Infiltration Rate. This method is only allowed if subsurface is underlain with soils not consolidated by glacial advance. The rate determined can be based on one test pit or boring. • For residential developments, a test pit or boring must be completed on each lot. • For linear projects or linear portions of a project the rate determined shall be based on a boring or test pit taken every 200 feet. If subsurface characteristics across the project site indicate consistent soil characteristics and depths to seasonal high groundwater conditions or hydraulic restriction layer, the number of test locations may be reduced to a frequency recommended by the Washington State Licensed Professional Engineer, Washington State Licensed Professional Geologist, or Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America. 5. A groundwater mounding analysis is required to determine the final native infiltration rate for permeable pavement with contributing areas greater than 1 acre and where there is less than 15 feet from the bottom elevation of the facility to the seasonal high groundwater. MODRET or an equivalent model shall be used. A soils report is required to design an infiltration trench, infiltration basin, or drywell. The soils report shall be based on site specific subsurface explorations. The soils report shall be prepared by a Washington State Licensed Professional Engineer, Washington State Licensed Professional Geologist, a Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America, or other suitable trained persons working under the professional. If subsurface characteristics across the project site indicate variable soil characteristics and depths to seasonal high groundwater conditions or hydraulic restriction layer, the number of test locations shall be increased to a frequency recommended by the Washington State Licensed Professional Engineer or Washington State Licensed Professional Geologist, or Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America. If subsurface characteristics across the project site indicate consistent soil characteristics and depths to seasonal high groundwater conditions or hydraulic restriction layer, the number of test locations may be reduced to a frequency recommended by the Washington State Licensed Professional Engineer or Washington State Licensed Professional Geologist, or Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America. Subsurface exploration does not need to be extended lower than 2 feet below the groundwater table. The soils report shall be based on site specific explorations and: Classify the underlying soils of the site. Use soil borings, soil test pits, or published USDA/NRCS soil surveys to classify the soil. Soil surveys cannot be used as the sole means of classifying soils for design purposes. Soil surveys are available here: https://websoilsurvey.nrcs.usda.gov/app/HomePage.htm Currently USDA has not published soil information in the City limits. If published information becomes available it may be used. Prepare detailed logs for each boring or test pit and a map showing the location of the boring or test pit. Borings or test pits shall be taken at the location of the proposed infiltration facility. Soils logs must include: • The depth shall be a minimum of 5 times the maximum design depth of ponded water below the base of the infiltration facility (but not less than 10 feet below the base of the infiltration facility). Assess soil stratigraphy for low permeability layers, highly permeable sand/gravel layers, depth to groundwater, and other soil structure variables necessary to assess subsurface flow patterns. Obtain soil samples for laboratory testing from each soil stratum within 2.5 times the maximum design water depth below the base of the infiltration facility (but not lessInfiltration basins serving 10 acres or more shall obtain samples on layers to 50 feet below the base of the infiltration facility (samples are not needed more than 10 feet below the water table). • For infiltration basins and drywells, obtain samples from at least one test pit or boring per 5,000 ft2 of infiltrating BMP surface area (in no case less than two per infiltration basin or drywell). For infiltration trenches, obtain samples from at least one test pit or boring per 200 feet of trench length (in no case less than 2 per trench). Soil characteristics for each soil unit shall include: • Grain size distribution (if using the Grain Size Analysis Method for Determining Infiltration Rates) • Percent clay content (type of clay if known) • Variations in nature of stratification • Cation exchange capacity (CEC) Identify the hydraulic restriction layer (groundwater, low permeability layer, bedrock, etc.). The hydraulic restriction layer may be identified by: Soil evidence of groundwater such as mottling Information obtained from nearby wells (for depth to groundwater) Testing must extend to a depth at least 10 feet below the estimated bottom elevation of the infiltration facility. Perform analyses during the wet season (December 1 - April 1). If the hydraulic restriction layer is groundwater, establish the gradient, direction of flow, and seasonal variations. If onsite infiltration might result in shallow lateral flow, assess the locations where interflow will surface. Place groundwater monitoring wells to determine gradient and flow. than 10 feet below the base of the infiltration facility). Place at least 3 monitoring wells or 3 hydraulically connected surface or groundwater features to establish the direction of flow and gradient. Monitoring wells must extend to a depth at least 10 feet below the estimated elevation of the infiltration facility. If it is determined by the site assessment that gradient and flow direction are not critical (low risk of impacts), 1 monitoring well may be used. The use of less than 3 wells must be substantiated in the soils report. • Monitoring through at least one wet season is required unless substantially equivalent historical data regarding groundwater levels is available. A groundwater mounding analysis is required to determine the final native infiltration rate for infiltration facilities that will serve contributing areas greater than 1 acre and where there is less than 15 feet from the bottom elevation of the facility to the seasonal high groundwater table. MODRET or an equivalent model shall be used. Identify the native soil infiltration rate using methods outlined in Volume 4 - Appendix A - Appendix A Determining the Design Infiltration Rate. The Small Scale Pilot Infiltration Test may only be used: Where infiltration facilities that receive stormwater from less than 1 acre. Where subsurface characterization suggests a uniform subgrade a the subsurface shows high infiltration rates making the Large Scale PIT Test difficult The Soil Grain Size Analysis can only be used if the subsurface characterization suggests that the project site is underlain with soils not consolidated by glacial advance. The soils report shall be based on site specific subsurface explorations. The soils report shall be prepared by a Washington State Licensed Professional Engineer, Washington State Licensed Professional Geologist, a Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America, or other suitable trained persons working under the professional. The soils report shall be based on site specific explorations and: Classify the underlying soils of the site. Use soil borings, soil test pits, or published USDA/NRCS soil surveys to classify the soil. Soil surveys cannot be used as the sole means of classifying soils for design purposes. Soil surveys are available here: https://websoilsurvey.nrcs.usda.gov/app/HomePage.htm. Currently USDA has not published soil information in the City limits. If published information becomes available, it may be used. Prepare detailed logs for each boring or test pit and a map showing the location of the boring or test pit. Borings or test pits shall be taken at the location of the proposed CAVFS. Soils logs must include: • The depth must extend a minimum of 5 feet below the estimated bottom elevation of the lowest subgrade layer. Assess soil stratigraphy for low permeability layers, highly permeable sand/gravel layers, depth to groundwater, and other soil structure variables necessary to assess subsurface flow patterns. Obtain soil samples for laboratory testing from each soil stratum within 3.0 times the maximum design water depth below the base of the CAVFS (but not less than 3 feet below the base of the infiltration facility). Soil characteristics for each soil unit shall include: • Grain size distribution (if using the Grain Size Analysis Method for Determining Infiltration Rates) • Variations in nature of stratification • Cation exchange capacity (needed to determine if underlying soils can provide treatment) • Percent organic content (needed to determine if underlying soils can provide treatment) Identify the hydraulic restriction layer (groundwater, low permeability layer, bedrock, etc.). The hydraulic restriction layer may be identified by: Soil evidence of groundwater such as mottling Testing with a monitoring well or an excavated pit must extend to a depth at least 1 foot below estimated bottom elevation of the lowest subgrade layer. Perform analyses during the wet season (December 1 - April 1). If the general site assessment cannot confirm that hydraulic restricting layer will be greater than 1 foot below the bottom of the CAVFS subgrade, place monitoring wells or excavated pits strategically to assess depth to groundwater. Monitoring with a continuously logging sensor between December 1 and April 1 provides the most thorough information. Special considerations are necessary for highly permeable gravel areas (>4 inches per hour) which may not show signs of high groundwater. Exercise sound professional judgment. Only for projects required to comply with Minimum Requirement #1-9: If onsite infiltration might result in shallow lateral flow, assess the locations where interflow will surface. Place groundwater monitoring wells to determine gradient and flow Identify the native soil infiltration rate using methods outlined in Volume 4 - Appendix A - Appendix A Determining the Design Infiltration Rate. It is not necessary to identify the native soil infiltration rate for determining infeasibility if other subsurface characteristics such as high groundwater preclude the use of CAVFS. Projects can use one of the following to determine the native soil infiltration rate: Small Scale Pilot Infiltration Test (PIT) per Volume 4 - Appendix A - Appendix A Determining the Design Infiltration Rate. • Perform test for every 5,000 ft2 of contributing hard surface area and at least one per project site. • For residential developments, perform a test on every lot. • For linear projects or linear portions of a project, complete a test for every 200 feet of linear surface (sidewalk, walkway, or trail) Soil Grain Size Analysis per Volume 4 - Appendix A - Appendix A Determining the Design Infiltration Rate. This method is only allowed if subsurface is underlain with soils not consolidated by glacial advance. The rate determined can be based on one test pit or boring. • For residential developments, a test pit or boring must be completed on each lot. For linear projects or linear portions of a project the rate determined shall be based on a boring or test pit taken every 200 feet. If subsurface characteristics across the project site indicate consistent soil characteristics and depths to seasonal high groundwater conditions or hydraulic restriction layer, the number of test locations may be reduced to a frequency recommended by the Washington State Licensed Professional Engineer, Washington State Licensed Professional Geologist, or Certified Professional Soils Scientist (CPSS) certified by the Soil Science Society of America. 5. A groundwater mounding analysis is required to determine the final native infiltration rate for CAVFS with contributing areas greater than 1 acre and where there is less than 15 feet from the bottom elevation of the facility to the seasonal high groundwater. MODRET or an equivalent model shall be used.