MN Clean Water Summit UMN Arboretum, MN 13Sep12 Low Impact Development and the Importance of Soil Bill Hunt, Ph.D., PE, D.WRE Associate Professor & Extension Specialist North Carolina State University
The Real Reason I m Happy to Be Here
Outline Soil Importance on Defining the Target Condition Underlying Soils & Infiltration by SCMs Utilizing Soil / Media to Sequester/ Mitigate Pollutants Phosphorus, Temperature, + MediaDepths Minimizing Compaction Impacts to Maximize Infiltration
Low Impact Development Reduce impervious surfaces Retain runoff on-site Promoting infiltration and evapotranspiration Soils were recognized by the Founding Fathers
Early on LID First Step How to Lay Out your site? Where to location your practices? Is ideally based on
Courtesy of Todd Houser, Cuyahoga S&W Your Soils!
e.g., Cuyahoga County Soils & LID Loamy Sand & Sand (5.8%) Infiltration, if well drained Wet or dry BMP depending on drainage class Well Drained Soils (12.6%) Dry BMPs Moderately Well Drained (11.2%) 1.5-3 ft. November to May most years Shallower Wet Deeper Dry with Liner Somewhat Very Poorly Drained (76.2%) 0.5 1 ft. November to June most years Wet BMPS Slippage Prone (5.8%) Stay Away Urban Complexes (49.9%) Highly Variable KSU Courtesy of Todd Houser, Cuyahoga S&W 4(/ 22
Goals of Low Impact Development Reduce impervious surfaces Retain runoff on-site Promoting infiltration and evapotranspiration Replicating pre-development hydrologic conditions as closely as possible Amounts of Each Depending upon Underlying Soil - Davis, 2005
Primary Goal of LID Design each development site to protect, or restore, the natural hydrology of the site so that the overall integrity of the watershed is protected. This is done by creating a hydrologically functional landscape.
What is the Target Condition? In North Carolina, Coweeta Coweeta is a US Forest Service Research Station
Establishing Target Condition Coweeta Hydrologic Laboratory Forested Mountain Watersheds Longest Term Hydrologic Record (Runoff, Infiltration, and ET) in the World for a forest site Records used for this study were 37 and 50 years old Rain Shed Mountain Region Annual Precipitation in excess of 1500 mm (60 inches) Drawback: Coweeta Wetter than any major city in NC Data From Swift, LW, G.B. Cunningham, J.E. Douglass. 1987. Climatology and Hydrology. Forest Hydrology and Ecology at Coweeta. Eds: W.T. Swank and D.A. Crossley. Springer Verlag. New York, NY, pp 35-57.
Establishing Target Condition Annual Hydrologic Fate Average Amount Percent of Total Precipitation Precipitation 1770 mm (70 in) 100% Runoff 80 mm (3 in) 5% Evapotranspiration 890 mm (35 in) 50% Infiltration 800 mm (31 in) 45% Shallow Interflow 770 mm (30 in) 44% Deep Seepage 30 mm (1 in) 2% All values rounded to the nearest 10 mm or 1 in. Infiltration is the sum of Shallow Interflow and Deep Seepage
Santee Experimental Forest (Coastal Plain South Carolina) Experimental Data (Amatya et al., 2006) Evapotranspiration Infiltration + Runoff 77% 23% Coastal plain region, undisturbed woods, sandy soils 30+ years of experimental data
Why the Difference? Sandier Soil Systems + flatter landscapes + higher water table systems = MORE ET Underlying SOILS! Soils impact what your HYDROLOGIC TARGET CONDITION is
Outflow Volume (m^3) Example of Target Condition Variation 140 120 100 Landscape Outflow Comparison Detention: to Curve Number NC North Carolina Grassed Cell NC Grassed Cell Pavement Woods B (CN 55) Woods C (CN 70) Regression (CN 79) 80 60 40 20 0 0 1 2 3 4 5 6 7 www.bae.ncsu.edu/stormwat Rainfall (cm)
So, how well do SCMs Convert Runoff to Infiltration? www.bae.ncsu.edu/stormwat
Answer: It depends (in part) on Underlying Soil www.bae.ncsu.edu/stormwat
www.bae.ncsu.edu/stormwat Improving Infiltration
Water Balance Brown & Hunt, JEE 2011
Reduced Performance in Clayey insitu Soils Rocky Mount (sand): Upper Coastal Plain Greensboro (clay): Piedmont Graham: (N) loamy-clay & (S) sandy-loam Site We Bring Engineering to Life # Events Monitored # Events w/ Outflow Media Depth (m) IWS Depth (m) RM Grass 78 5 0.9 0.6 RM Mulched 78 4 0.9 0.6 Greensboro 1 63 18 1.2 0.6 Greensboro 2 63 40 1.2 No IWS Graham (N) 40 34 0.6 0.3 Graham (S) 40 22 0.9 0.6
Ritter Field Stormwater Wetland (River Bend, NC)
Outflow (m3) Runoff Reduction by Storm 10000.0 1000.0 100.0 Line if Outflow Volume= Inflow Volume 10.0 1.0 1.0 10.0 100.0 1000.0 10000.0 Inflow (m3) Lenhart and Hunt. JEE. 2011
Wetlands are not supposed to reduce runoff volumes this much! Why is this wetland so good at infiltrating? Design Element Value Watershed Size 115 ac Wetland Size 0.34 ac Watershed Curve Number 55 Underlying Soil at Wetland Appling Fine Sand
er Field Stormwater Wetland: y is it so (relatively) small? Design Element Value Watershed Size 115 ac Wetland Size 0.34 ac Watershed Curve Number 55 Underlying Soil at Wetland Appling Fine Sand
Determining Volume: Using NRCS Methods NRCS Curve Number Method SA = Volume (V) Ponding Depth Depth (D) V = Runoff Depth (Q*) Watershed Area (A) Q = (P 0.2 S) 2 (P +0.8 S) P= Precipitation Depth; S = Initial Abstraction S = 1000/CN - 10 CN = Curve Number
Key Mid-term Take Home Points Underlying Soils impact performance of a Stormwater Control Measure E.g., SCMs over sandy soil will infiltrate (sometimes much) more than those over clays Underlying Soils have major factor in size of practice (& therefore cost) Sandy Watersheds can have much smaller SCMs than Clayey Watersheds
Watershed Soils & SCM effectiveness
Bacteria Pollution Stormwater is a transport mechanism for bacterial pollution Urbanization can lead to increased pathogen loads to surface waters Pet waste, sewer overflow, sewer leakage Leads to 50,000 acres of Shellfish closures in NC each year.
Charlotte Wet Pond Piedmont Clays Watershed = 48.6 ha CN = 75
Wilmington Wet Pond Coastal Plain Sands
Charlotte (Clay) Wet Pond E.Coli Hathaway and Hunt. JIDE. 2012
Sand Underlying Soil Pond E.Coli Hathaway and Hunt. JIDE. 2012
Why? Pathogen Indicator Species travel (in part) on sediment Coarser sediment = better trapping efficiency for TSS And therefore for E.Coli Hathaway and Hunt. JIDE. 2012
Fill Soils/ Media & SCM Effectiveness
Greensboro Bioretention
3 2.5 TP Removal/Sequestration Mass (Kg) Greensboro 2 1.5 1 In Out 0.5 0 TN NO3-N TKN TP Hunt et al. JIDE. 2006
Chapel Hill Cell, C1 STP/WS = 0.14 Conventional Drainage We Bring Engineering to Life
0.8 TP Removal/ Sequestration Chapel Hill 0.6 Mass (Kg) 0.4 0.2 In Out 0 TN NO3-N TKN TP Hunt et al. JIDE. 2006
Results of Early Research Relationship between P-Index (Soil Test P) and TP outflow load. Greensboro Chapel Hill TP +240% - 65% P-Index 85-100 4-12 P-Index 50-100: High P-Index 0-25: Low (Hunt 2003) Hunt et al. JIDE. 2006
Blame it on the Media Phosphorus Index (P- Index) is a measure of how much phosphorus is already in the soil media. Low P-Index: Can capture more phosphorus High P-Index: Soil is saturated with phosphorus Very High: > 100 High: 50-100 Medium 25-50 Low: 0-25
Enter the NC Standard Fill Media 85% Sand 10% Fines (Silt + Clay) 5% Organic Matter + Low P-Index 10 to 30 Time to test it
Mecklenburg Co. Hal Marshall Bioretention Cell (2004-2006) Soil 80% Mason Sand 20% Fines + Compost P-Index = 6 4 ft (1.2 m) Depth
[TP] in mg/l TP - Charlotte, NC (2004-2006) Concentration Red. = 31%; Load Reduct. 50% 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1/1/04 7/1/04 12/30/04 6/30/05 12/29/05 Date TP-In TP-Out Hunt et al., JEE. 2008
Effluent Concentration vs. P-Index Site P-Index Depth (in) Outflow (mg/l) C-1 6 48 0.13 L O W L-1 1-2 30 0.16 L-2 1-2 30 0.18 G-1 35-50 48 0.57 G-2 85-100 48 1.85
Take Home Message Your composition of Fill Soil / Media Matters Be careful of what you add or incorporate
Sometimes the Question isn t What type?, it s How much?
Depth of Fill Soil/ Media Matters!
Oil/Grease Removal Effciency, % Results: Oil and Grease 100 80 60 40 20 0 0.1 1 10 Infiltration Rate, cm/min 100% O/G removal. Type of Media has no impact. Hsieh & Davis J. Environ. Engg. 2005
Accumulation - PAH CP Top Crust (1-2 mm) Top Loose Gravel In 0 to 10 cm In 10 to 20 cm In 20 to 30 cm In 30 to 41 cm In 41 to 51 cm Mid 0 to 10 cm Mid 10 to 20 cm Mid 20 to 30 cm Mid 30 to 41 cm Diblasi, Li, Davis & Ghosh, Environ. Sci Technol., 2009 0 5 10 15 20 25 PAH Concentration ( g/g dry) Accumulated PAH are found in upper layers of sediment in bioretention facility. Very little PAH compounds have migrated deeper into the cell media
Depth (cm) Zinc concentrations decrease with distance from the inlet and media Jones & Davis, in preparation Depth and distance - Zinc 3 2 1 0 5 4 5 10 15 20 Original BSM Solid = Organic Empty = BSM 0 50 100 150 200 250 300 Total Zinc (mg/kg)
% Removal Nitrate with Depth 100 80 60 40 20 0-20 -40-60 0 20 40 60 80 100 120 140 c. Nitrate Bioretention Depth (cm)
Different Pollutants Different Fill Soil/ Pollutant Media Depths Recommended Media Depth (ft) References TSS, PAH s <1 ft Li et al. (2008); DiBlasi et al. (2009) Metals 1 ft Li and Davis (2008); DiBlasi et al. (2009); Phosphorus 1.5-2.0 ft Hsieh et al. (2007); Hatt et al. (2009b); Nitrogen 3 ft Kim et al. (2003); Passeport et al. (2009) Hunt et al. JEE. 2012
Coldwater Ecosystems Have Economic Value Criteria Salmonid incipient lethal temperature NC trout upper avoidance Temp. 25 C (77 F) 21 C (70 F) 2007 in AK 2008 in NC ~$1 2002 billion in MN total Over 92,700 anglers = economic $150 million output $174 million total supported in direct sales 11% of supported economic output regional 3000+ jobs jobs Reference: Bartholow, 1981; Responsive Mgmt, 2009; Gartner et al., 2002; Wegge et al., 2012
Avg. Temperature ( C) Jones & Hunt, JIDE. 2010 30 4-8 o C Increase 25 20 15 10 5 0 May June July August September October Runoff Conc. Inlet Metal Inlet Effluent
Jones & Hunt, JEE. 2009
Take Home Points: Fill Soils Fill Soils/ Media Selection and Depth is hugely important in TP and TN performance Fill Soils/ Media PRESENCE is equally important to tame temperatures
Improving Infiltration Capacity of Soils LID really is predicated on getting some runoff (at least temporarily) into the ground We want to encourage this.
Wilmington, NC (Anne McCrary) Permeable Concrete Study Loamy Sand Soil Coastal NC Undisturbed K ~ 1-2 in/h Water table > 1 m from surface Day Use Recreation (40 ADT)
Runoff (in) Permeable Concrete Wilmington NC 4.00 3.50 3.00 2.50 2.00 1.50 1.00 Pavement Storage Infiltration Rate LESS THAN 0.1 in/hr INFILTRATION 0.50 0.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 We Bring Engineering to < 12 hour Rainfall (in) Life Runoff from an Impermeable Lot Runoff from Permeable Concrete Lot
In Situ Soil Compaction Associated with Initial In Situ Soil Infiltration is INVARIABLY reduced when permeable pavements (& other practices) are installed. Lot Construction www.bae.ncsu.edu/stormwat
Tyner et al. (2009): Trenching the Subsoil
Ripping the Subsoil - Tyner et al. (2009)
Permeable Pavement Design IWS - Shallow IWS - Deep Conventional
Milimeters Hydrology Total Rainfall Total Outflow from Underdrains 1000 900 8 Outflow 77% 0100% Outflow 1 99.5% Outflow 800 Reduction Events Reduction Events Reduction Event 700 600 500 400 300 200 100 0 CONVENTIONAL DEEP IWS SHALLOW IWS
Same is True with Bioretention Construction impact on bottom layer
How are BRC s constructed? Bioretention Backhoe w/ arm Scoop out soil & replace w/ sandy media www.bae.ncsu.edu/stormwat
Construction Impacts Bioretention Bucket contact with bottom layer Compaction & Smearing using conventional scoop technique decreased infiltration rates www.bae.ncsu.edu/stormwat
Innovative Construction Technique Less intensive bucket contact when excavating final 1 ft of subsoil Rake method Scarify surface with teeth on bucket
Tested Excavation Technique Scoop vs. Rake For final 9-12 of excavation, depth most affected by compaction
Clay vs. Sand 2 Sites Varying Soil Type 1)Piedmont (clay): Raleigh 2)Coastal Plain (sand): Nashville www.bae.ncsu.edu/stormwat
And Antecedent Moisture Condition Dry vs. Wet Effects of excavating right after a large rain or if it rains before cell is filled
Compaction Scout SC-900 soil cone penetrometer < 1 minute per test
Nashville (Sand) Wet Cell
Infiltration Double Ring Infiltrometer Prevents divergent flow in middle ring record rate of infiltration from inner ring ~ 90 minutes per test
Average Infiltration
Sat. Hydraulic Conductivity Collect soil cores and run constant head saturated conductivity test
Nashville Results Average change in performance using rake vs. scoop method Site Type K Sat Infiltration "Dry" / (Loamy-Sand) "Wet" / (sand) Performance Increase Rake Performance Increase Rake Bulk Density 84% 123% -2.4% 172% 42% -3.8% Notes: n = 6 n = 3 n = 6
Take Home Point How you Treat your soil during construction makes a big difference in how well your SCM / LID Site is going to Perform Be nice to your soils!!!
Summary Soils are an Integral Component of Low Impact Development Establishing the Reference Hydrologic Condition Set the Infiltration Capacity of SCMs Influence the Pollutant Removal Ability Fill Soils/ Media Selection is critical for the capture of several pollutants We can do a lot to make soils work for us. And to overcome negative impacts of construction
Parting Thought: Know Soils Know LID No Soils No LID
Questions? Please Ask!