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Applications to Stormwater Management Presented by: Mr. Brian Oram, PG, PASEO Wilkes University GeoEnvironmental Sciences and Environmental Engineering Department Wilkes - Barre, PA 18766 570-408-4619 http://www.water-research.net Nearly 50% of Soil is Space or Space Filled with Water • Water – 25+ % • Air – 25 + % • Pore Space Makes Up 35 to 55 % of the total Soil Volume • This Space is called Pore Space Therefore, soil can be used as a storage system, treatment system, and transport media. Soil Properties Critical To Stormwater Management • Soil Texture • Porosity and Pore Size • Water Holding Capacity • Bulk Density • Aggregate Stability • Infiltration Capacity • Hydraulic Conductivity !!! Just to Name a Few Properties !!!! Types of Pores Macropores (> 1,000 microns)-Large Mesopores (10 to 1,000 microns)- Medium Micropores (< 10 microns)- Small Source: http://www2.ville.montreal.qc.ca Key Points on Soil Pores Under gravity, water drains from macropores, where as, water is retained in mesopores and micropores, via matrix forces. Coarse-textured horizons (e.g., sandy loam) tend to have a greater proportion of macropores than micropores- but they may not have more macropores than finer textured soils. Soils with water stable aggregates tend to have a higher percentage of macropores than micropores. Proportion of micropores tends to increase with soil depth, resulting in greater retention of water and slower flow of water with depth. Water Holding Capacity Available Water Capacity Textural Class (Inches/Foot of Depth) Coarse sand 0.25–0.75 Fine sand 0.75–1.00 Loamy sand 1.10–1.20 Sandy loam 1.25–1.40 Fine sandy loam 1.50–2.00 Silt loam 2.00–2.50 Silty clay loam 1.80–2.00 Silty clay 1.50–1.70 Clay 1.20–1.50 Please Do Not Use Sand in a Bio-Retention System ! Bulk Density, Porosity, and Texture Porosity Textural Class Bulk Density (Mg/m³) (%) Sand 1.55 42 Sandy loam 1.4 48 Fine sandy loam 1.3 51 Loam 1.2 55 Silt loam 1.15 56 Clay loam 1.1 59 Clay 1.05 60 Aggregated clay 1 62 Sands – Tend to have higher bulk density and lower permeability Please do not use sands in Bio-Retention systems! How can a silt loam have more macropores than sand? Answer: More Water Stable Structures Source: Brady, Nyle, C. “ The Nature and Properties of Soils” (1990). Better Structural Development More Macropores Source: Brady, Nyle, C. “ The Nature and Properties of Soils” (1990). Water Stable Aggregates I Aggregates on left are more water stable, i.e., aggregate stays together and do not separate into the its components, i.e., three soil separates. Water Stable Aggregates Water Stable Aggregates – II The Classic Photo Source: Brady, Nyle, C. “ The Nature and Properties of Soils” (1990) Great Desk Reference Text !!!! Permeability Inches Class Ksat Class per hour Material Massive, Rock, Impermeable Very Low <0.001417 Fragipan 0.001417 Massive, Rock, to Fragipan, Very Slow Low <0.0147 clayey Very Slow to 0.01417 Moderately Moderately to clay, silty clay, Slow Low <0.1417 clay loams Moderately 0.1417 silt, silt loam, Slow to Moderately to loam, fine Moderate High < 1.417 sandy loam Moderate to 1.417 to loamy sand to Rapid High < 14.17 medium sand coarse sand, Rapid Very High > 14.17 gravel General Guide – To Ksat and Material Hydrologic Soil Terms •Infiltration - The downward entry of water into the immediate surface of soil or other materials. •Infiltration Flux (or Rate)- The volume of water that penetrates the surface of the soil and expressed in cm/hr, mm/hr, or inches/hr. The rate of infiltration is limited by the capacity of the soil and rate at which water is applied to the surface. It is a volume flux of water flowing into the profile per unit of soil surface area (expressed as velocity). •Infiltration Capacity (fc)- The amount of water per unit area of time that water can enter a soil under a given set of conditions at steady state. •Cumulative infiltration: Total volume of water infiltrated per unit area of soil surface during a specified time period. Horton Equation, Philip Equation, Green- Ampt Equation Infiltration Rate Infiltration Rate (Time Dependent) Steady Gravity Induced Rate Infiltration with Time Initially Final Infiltration Capacity High Because of a Combination of (Equilibrium)- Infiltration Capillary and Gravity Forces Approaches q - Flux Density f = fc +(fo-fc) e^-kt fc does not equal K Infiltration Rate Decreases with Time 1) Changes in Surface and Subsurface Conditions 2) Change in Matrix Potential and Increase in Soil Water Content and Decrease in Hydraulic Gradient 3) Overtime - Matrix Potential Decreases and 4) Reaches a steady-state condition Gravity Forces fc – final infiltration rate Dominate - Causing a Reduction in the Infiltration Rate Infiltration Rate Function of Slope & Texture Source: Rainbird Corporation, derived from USDA Data (Oram,2004) Infiltration Rate Function of Vegetation Source: Gray, D., “Principles of Hydrology”, 1973. Infiltration Rate Function of Horizon A, B, Btx, Bt, C, R C/R Testing - Areas Fractured Rock Source: On-site Infiltration Testing - Mr. Brian Oram, PG (2003) and FX. Browne, Inc. (Lansdale, PA) Infiltration (Compaction/ Moisture Level) Site Compaction – Can Significantly Reduce Surface Infiltration Rate Rain Drop Impact Bare Soil Destroys Soil Aggregates Disperses Soil Separates Seals Pore Space Aids in Loss of Organic Material Creates a Surface Crust Source: (D. PAYNE, unpublished) http://www.geographie.uni-muenchen.de Percolation Rate Percolation Rate Percolation -Downward Movement of Water through the soil by gravity. (minutes per inch) at a hydraulic gradient of 1 or less. Used and Developed for Sizing Small Flow On-lot Wastewater Disposal Systems. On-lot Disposal Regulations (Act 537) has preliminary Loading equations, but for large systems regulations typically require permeability testing. Also none as the Perc Test, Soak-Away Test (UK) Not Directly Correlated to or a Component of Unsaturated or Saturated Flow Equations Comparison Infiltration to Percolation Testing 4.5 4 Infiltraton Test 3.5 Percolation 3 Testing Over Percolation Test Rate (in/hr) Estimated 2.5 Infiltration 2 Rate by 40% to 1.5 over 1000% * 1 0.5 0 1 2 3 4 5 6 7 8 9 10 Trail Source: On-site Soils Testing Data, (Oram, B., 2003) Hydraulic Conductivity Darcys Law- Saturated Flow Vertical or Horizontal Volume of discharge rate Q is proportional to the head difference dH and to the cross-sectional area A of the column, but it is inversely proportional to the distance dL of the flow path and coefficient K is called the hydraulic conductivity of the soil. The average flux can be obtained by dividing Q with A. This flux is often called Darcy flux qw . Flux Density or Hydraulic Conductivity (Ksp) Flux Density (q): The volume of water passing through the soil per unit cross- sectional area per unit of time. It has units of length per unit time such as mm/sec, mm/hour, or inches/ day (q = -K(ΔH/L )) Actually the term is volume/area/time= q = Q/At Hydraulic Conductivity (Ksp) quantitative measure of a saturated soil's ability to transmit water when subjected to a hydraulic gradient. It can be thought of as the ease with which pores of a saturated soil permit water movement . Side by Side (Pagoda, J, 2004) Testing Methods Goals of the Field Method • Field Measurement of the Flux Density (qw) and calculate hydraulic conductivity – qw = Ksp (dh/dl) • Field Measurement of Hydraulic Conductivity (Ksp) Infiltrometer Single Rings Infiltrometers Cylinder - 30 cm in Diameter- Smaller Rings Available. Drive 5 cm or more into Soil Surface or Horizon. Water is Ponded Above the Surface- Typically < 6 inches. Record Volume of Water Added with Time to Maintain a Constant Head. Measures a Combination of Horizontal and Vertical Flow ASTM Double Rings Infiltrometers Outer Rings are 6 to 24 inches in Diameter (ASTM - 12 to 24 inches) Mariotte Bottles Can be Used to Maintain Constant Head Rings Driven - 5 cm to 6 inches in the Soil and if necessary sealed Very Difficult to Install and Seal – ASTM Double Rings in NEPA Potential Leaking Areas Significant Effort is Needed to Install and Seal Units ASTM requires documentation of the Depth of the Wetting Front Other Double Rings Small Diameter 6” and 12” Double Ring 3” and 5” Double Ring in Flooded Pit Infiltration Data- Double Ring Test Note: Ring Diameter – 26 cm (Oram 2005) Cumulative Infiltration Infiltration Rate –cm/hr (cm) Steady-State Rate (slope) 0.403 cm/hr Fc = Ultimate Infiltration Capacity (approx.0.47 cm/hr) Estimated Methods- Based on Grain Size C- Factor Hazen Method Very Fine 40 - 80 Applicability: sandy Sand, poorly sediments Sorted • K = Cd10 2 Fine Sand with 40 - 80 fines • d10 is the grain diameter Medium Sand, 80 - 120 for which 10% of distribution is finer, Well Sorted "effective grain size" - Coarse Sand, 80 - 120 where D10 is between 0.1 Poorly Sorted and 0.3 cm Coarse sand, 120 - 150 • C is a factor that well depends on grain size Sorted, clean and sorting Guelph and Amoozegar Borehole Permeameters $ 1500 each Field Testing (Oram, 2000) Photo Source:http://www.usyd.edu.au Measuring Hydraulic Conductivity 12-inch/ 6-inch Double Ring Constant or Falling Head Permeameter- Homemade - $ 15.00 Side by Side Testing Mr. Brian Oram and Mr. Chris Watkins, 2003. Constant Head Borehole Permeameters Talsma Permeameter- Could be Homemade $ 50.00 Retail ($ 300.00) Modified Amoozegar- Could be Homemade – $30.00- Retail ($ 200.00) Side by Side Testing by Mr. Brian Oram and Mr. John Pagoda, 2004 Measuring Infiltration Rate to Estimate / Calculate the Flux Density • Infiltrometers- Yes ! – Single ring- May Not Be Advisable – Multiple tests required – Double ring- Yes ! - May be difficult in rocky and stony areas (i.e., Most of the Poconos !) – Smaller Double Ring in Flood Pit – Yes ! • Flooded Infiltrometers – Yes ! • Adoption of a Strict Double Ring ASTM Method – Likely not appropriate, but method should be used as a guide by professionals. • Cased Borehole Permeability Test – ASTM Method– Yes ! (Minimum diameter casing 4 inches) with bentonite packing of annular space – Maximum Pipe Height is a function of soil conditions. My Recommendation and Opinion ! Please Do NOT Use a Conventional Percolation Rate or Percolation Test for Developing Engineering Design ! Percolation Testing • Does not directly measure permeability or a flux velocity. • Has been used to successfully design small flow on-lot wastewater disposal systems, but equations and designs have a number of safe factors. • Results may need to be adjusted to take out an estimate of the amount of horizontal intake area. • Without Correction Percolation Data over-estimated infiltration rate data by 40 to over 1000 % with an adjustment for intake area error could be reduced to 10 to 200% (Oram, 2003) , but infiltration rate can overestimate saturated permeability by a factor of 10 or more (Oram, 2005). • May need to consider the use of larger safety factors and equations similar to sizing equations used for on-lot disposal systems. Safety factors of 50% reduction may not be enough !! • Borehole Permeability Testing can be a Suitable Method. • Falling Head , Constant Head, and Quasi Constant S Head Methods would be suitable. U M • Permeability Data for Specific Site should be calculated M using Geometric Average. A • Equations and Methods Based on Darcy’s Law and the R result is a value for Ksp or qw. Y • Do not recommend estimating permeability based on particle size distribution – Ok for preliminary desktop evaluations if data is available – Not for Final Design ! • Laboratory permeability testing is possible, but it may be difficult to get a representative sample and account for induced changes. May be Ok for Preliminary Evaluations. What NOW ? The Hydrologic Cycle Discharge Zone Recharge Zone Where is the Project Site ? Save Your Client – Money None Structural Development Practices • Maintain Soil Quality and Maximize the Use of Current Grading to Minimize Loss of O, A, and upper B horizons. • Minimize Compaction, Maximize Native Vegetation, and Use Good Construction Practices • Consider Hydrological Setting and Existing Hydrological Features in Site Design and Layout Answer: New Development/ Construction Practices and New and Updated Ordinances and Planning Documents ! Infiltration System Approach Individual Infiltration BMP Units Soil: Tunkhannock Series Soil had stratified sand and gravel lenses Water Table > 8 feet Open Voids (Gravel and Cobbles) 3 to 6 feet Ksp Field Measured 1 to 10+ inches per hour Reported Permeability > 6 inches per hour Design Used a Ksp of 0.5 inch per hour (50% reduction) Note- A few sections of the site had permeability of 0.1 inch per hour Infiltration Unit Configuration Installed: Sump and Grass Swale Prior to Unit and Geotextile within unit to capture large organic material Concrete – Open bottom perforated tank not filled with gravel for storage. Conceptual Design by: Malcolm Pirnie (Scranton, PA) and Brian Oram (October 2004), Anticipated Installation 2007. Sizing Calculations- Areas 0.5 in/hr • Impervious Area Roof and Driveway– 3500 ft2 • Design Storm – 1.3 inch • Volume of Water to Recharge- 2840 gallons (379 ft3) • Design Loading- Based on Field Measured Soil Permeability- 0.5 inch per hour or 0.5 in3/in2.hour = 7.481 gpd/ft2 • Minimum Recharge Period – 72 hours (PADEP Recommended) • Recharge Volume per day – 945 gpd • Minimum Recharge Area- (945 / 7.481) =126 ft2 • Internal Tank Storage – 3 ft * 8 ft perforated Concrete Tank, plus 3+ foot perimeter and subsurface aggregate storage to generate a minimum surface area of 150 ft2. • Additional Gravel Layer was added to Meet System Storage Requirement. Primary Limiting Factor is Not Recharge Capacity but Providing Detention Storage or Storage in the System ! Sizing Calculations- Areas 0.1 in/hr • Impervious Area Roof and Driveway– 3500 ft2 • Design Storm – 1.3 inch • Volume of Water to Recharge- 2840 gallons (379 ft3) • Design Loading- Based on Field Measured Soil Permeability- 0.1 inch per hour or 0.1 in3/in2.hour =1.49 gpd/ft2 • Minimum Recharge Period – 72 hours (PADEP Recommended) • Recharge Volume per day –945 gpd • Minimum Recharge Area- (945 / 1.49) =634 ft2 (over 18 % of impervious) • Recommended Changing the Recharge Period to 7 days to Reduce Infiltration Area to 270 ft2, but providing a system with 100 % detention storage. (7 % of impervious) • This could not be approved and the project implemented a bioretention/ recharge design Primary Limiting Factor is Area Requirement Caused by Recharge Period and not Recharge Capacity or Storage in the System ! Bio-Retention Systems Image Source: http://www.co.monroe.in.us Bio-Retention Concept Sump and Grass Swale Prior to Unit and a By-pass Berm Structure for large runoff events. System has a controlled discharge that maintains a discharge elevation that this consistent with natural water table conditions. Vegetation – Native Seed Mix Soil Media – Native Soil from Site Modified to either a loam texture with 2 to 5 % organic material; covered with compost/mulch layer (on-site source). Washed Stone at the Base of the Unit. Sizing based on detention storage requirements and flow routing. Conceptual Design by: Malcolm Pirnie (Scranton, PA) and Brian Oram (2004) Evaluating Recharge Capacity •Step 1: Desktop Assessment - GIS Review Published Data Related to Soils, Geology, Hydrology •Step 2: Characterize the Hydrological Setting •Where are the Discharge and Recharge Zones? •What forms of Natural Infiltration or Depression Storage Occurs? •How does the site currently manage runoff ? •What are the existing conditions or existing problems? Evaluation Recharge Capacity •Step 3: On-Site Assessment Deep Soil Testing Throughout Site Based on Soils and Geological Data Double Ring Infiltration Testing or Permeability Testing to calculate qw and provide estimate of loading rates? How does the water move through the site ? •Step 4: Engineering Review and Evaluation (meet with local reviewers and PADEP) •Step 5: Additional On-site Testing •Step 6: Final Design and Final BMP Selection How Can We Use Site Conditons ? Surface Boulders Created 3 feet Surface Natural Depression Storage Boulders Areas that appeared to range in width from 5 to 25 feet. Natural Depression Storage System – New Potential BMP ! Use Of Manufactured Soils Manufactured soils are loosely defined as soil amendment products comprised of treated residuals and various industrial by-products, such as foundry sand and coal ash. •Use of Organic By-Products – Compost – Organic Soil and Mulch • Recycling of Industrial By-Products and Wood Products •Improving Quality Structural Stability and Nutrient Content of Unconsolidated Materials with Poor Soil Quality • Use of Fly Ash, Incineration Ash, Recycling Remediated Soil/Unconsolidated Material, Spent Foundry Sands • Use of Soil Conditioners • Use of Dredge Materials and Sediment I did not say these were off the shelf or easy options ! Artificial Soil Quality Improvement Aggregate Stability- Using a Polymer No Soil Conditioner Less Soil Conditioner Source: Brady, N. C., 1990 Interested – Get Involved and Stay Informed? • Stormwater Manual Oversight Committee Website – Keywords in Google: (stormwater committee PA- 1st Site) • Meets at the Rachel Carson Building – First Floor Conference Room • Next Meetings April 25, 2006, May 23, 2006, and June 27, 2006. • Download- Current Manuals, Discussions, and Meeting Minutes Soils, Groundwater Recharge, and On-site Testing Presented by: Mr. Brian Oram, PG, PASEO Wilkes University GeoEnvironmental Sciences and Environmental Engineering Department Wilkes - Barre, PA 18766 570-408-4619 http://www.water-research.net PADEP in the Field Darcy Equation- What is Delta H?
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