Quantifying the Effectiveness of Soil Amendments in Compact Urban Soils By Nick Olson
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Soil Compaction Residential and commercial developments requires large equipment to grade and stabilize the soil. Reduced Pore Volume Hard Pan Layers Poor Infiltration Poor Plant Growth Maple Lakes Park, City of Maple Grove
Measuring Soil Compaction Saturated Hydraulic Conductivity Darcy's Law : f = q = K sat h z Soil Bulk Density ρ Bulk = Dry Mass of Solids Volume of Soil Soil Strength Penetration Resistance = Force Area cone
Previous Research Study Description Area Tested: Soil Disturbance Soil Type Infiltration Rate Bulk Density Soil Strength [cm/hr] [g/cm 3 ] [MPa] Gregory et al. (2006) Study on urban soil compaction in North Central Florida 2 Naturally Wooded Lots 1 Planted Lot Undisturbed Sandy 73.3 1.34 Max: 1.07 to 1.91 Construction Vehicle Traffic Sandy 17.8 1.49 Max: 1.97 to 3.74 In Wheel Ruts Dump Truck Sandy 2.3 1.68 n/a Back Hoe Sandy 5.9 1.61 n/a Pickup Sandy 6.8 1.61 n/a Ocean County Soil Conservation District (2001) Study on soil infiltration rates on modified and compacted sites Woods Undisturbed Mostly Sandy Loam 38.1* 1.42 n/a Single House Somewhat Disturbed (not specified) Loamy Sand 18.03* 1.67 n/a Subdivision Lawn 1 Disturbed (not specified) Loamy Sand 0.36* 1.79 n/a Subdivision Lawn 2 Disturbed (not specified) Loamy Sand 0.08* 2.03 n/a Athletic Field Disturbed (not specified) Loamy Sand 0.03* 1.95 n/a * Measurement of Ksat
Soil Amendment: Tillage Tilling is a common practice used in agriculture to break up the soil and improve infiltration and growing conditions for plants + Pros Breaks surface seal Break hardpan layers Improves infiltration (Spoor, 2006) - Cons Pore Continuity Disturbed Benefit degrades Equipment size
Soil Amendment: Compost Addition Compost addition involves adding organic matter to the soil to create more aeration and provide nutrients. Different lifts may be created. + Pros Decreases bulk density Increase water holding capacity May provide a longer term solution than tillage alone (image by denvergov.org) - Cons Material availability Nutrient leaching Amount needed
Research Objectives How much does tilling improve infiltration? How much does compost addition improve infiltration? At what level of soil compaction does infiltration become hindered? When should remediation be applied? How practical is remediation in an urban setting?
Clifton E. French Regional Park Site info Site of old Hwy. 36 Formerly inhabited Lagoon fill Problems Poor tree growth Poor turf Soil Type 0-24 Loam, Clay Loam > 24 Organic Material
Lake Minnetonka Regional Park Site info Next to constructed swim pond Has been renovated before Highly used area Problems Poor tree growth Poor turf Soil Type 0-12 Loam > 12 Clay Loam
Maple Lakes Park Site info New development (< 10 year old) Formerly sand/gravel pits Highly used area Problems Assumed to be compact Soil Type 0-36 Silty/Sandy Clay
Research Modus Operandi Summer 2008 Initial Assessment Visual Observations Measured Ksat using Modified Philip-Dunne Infiltrometer (MPD) Measured Soil Bulk Density with Drive Cylinder Right: The MPD device was designed at St. Anthony Falls Laboratory by Rebecca Nestingen. The MPD is easily transported and uses a minimal amount of water (Nestingen, 2007).
Can get several MPD measurements at once ~100-150 measurements per site
Research M.O. Fall 2008 Tilled plot Tilled plot with compost Control } Treated Plots
Soil Remediation Subsoiler Deep Tillage: 22-24 12 rip spacing Ripped one direction Spading Depth: 16-18 Helps level surface after tilling (both treated plots) Mixed 3 of compost in soil (compost plot only)
Research M.O. Summer 2009 MPD measurements Measured Soil Strength with Penetrometer Bulk Density Measurements Spring/Summer 2010 MPD measurements French Reg. Park & Maple Lakes Park only Hand held penetrometer. Photo by Eijkelkamp
Results- French Regional Park (YR 1)
YR 1 Results High Variability 3 orders of magnitude difference in Ksat values Plots established in NE area
Results- French Regional Park (YR 2) The control plot increased in saturated conductivity between years. Treated plots must be compared to control plot within the same season and not between years
YR 2 Results Ratio of Saturated Hydraulic Conductivity Till/Control Compost/Control 0.6* 1.5* *Means are not statistically different
Results- French Regional Park (YR 3, Spring) Ratio of Saturated Hydraulic Conductivity Till/Control Compost/Control 0.5 1.2* *Means are not statistical different
Results- French Regional Park (YR 3, Summer) Ratio of Saturated Hydraulic Conductivity Till/Control Compost/Control n/a 2.7
Results- Lake Minnetonka Regional Park (YR 1)
YR 1 Results High Variability 3 orders of magnitude difference in Ksat values Plots established in SW area
Results- Lake Minnetonka Regional Park (YR 2)
YR 2 Results Ratio of Saturated Hydraulic Conductivity Till/Control Compost/Control 1.2* 3.0 *Means are not statistically different
Results- Maple Lakes Park (YR 1)
YR 1 Results Low Variability 2 orders of magnitude difference in Ksat values Whole site was used
Results- Maple Lakes Park (YR 2)
YR 2 Results Ratio of Saturated Hydraulic Conductivity Till/Control Compost/Control 2.3 5.7
Results- Maple Lakes Park (YR 3) Ratio of Saturated Hydraulic Conductivity Till/Control Compost/Control 2.1 5.5
Clifton E. French Regional Park Soil Strength [MPa] 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0-6" 6-12" Depth 12-18" Control Till Compost 18-24" 24-30"
Maple Lakes Park Soil Strength [MPa] 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0-6" 6-12" Depth 12-18" Control Till Compost 18-24" 24-30"
Green-ampt Model If the rainfall intensity, i(t), is greater than or equal to Ksat, then there is a potential for the rainfall to pond on the surface of the soil. If the depth of infiltrated water, F(t=t), is less than the depth of rainfall during a time interval of a certain rainfall intensity then runoff will be generated. ψ θ f (t) = K sat F(t) +1 K sat t = F(t) ψ θ ln 1+ F(t) ψ θ
Green-ampt Model Average: 61.6% 29.5% 9.1%
Discussion & Conclusions How much does tilling a soil improve infiltration? -Tilling reduced the bulk density and strength of the soil -Little to no effect on Ksat. -Tilling may have destroyed connected pathways in the soil at Lake Minnetonka and French Regional Park. -Tilling was beneficial at Maple Lakes Park, a newer development. How much does compost improve soil infiltration? -Compost improved the saturated hydraulic conductivity by 2.7 to 5.7 times. -The longevity of compost addition is yet to be determined.
Discussion & Conclusions At what level of soil compaction does infiltration become hindered? It was hard to determine when compaction affects infiltration. This was due to the high level of soil variability (within the site and between years). There was no correlation between Ksat, soil bulk density and soil strength. When should remediation be applied? The most practical time to apply soil remediation techniques is right after a site has been graded and/or compacted. This will reduce the amount of obstacles (i.e. trees, utility lines, etc).
Benefits of Compost Increase groundwater recharge Reduce volume of water for lawn maintenance. Reduce pollutant loading. P8 model adjustments Reduce runoff Less stormwater infrastructure
Discussion & Conclusions Size & Proximity of Remediation Sites Could get bulk rates Transportation costs Availability Increased market would likely reduce costs New developments No turf reestablishment Less obstacles = more amendable area
Thank you to Undergraduate Research Assistants: Lanre Adekola Jimmy Crist Monica He John Farmer Eric Johnson Greta Schmalle Three Rivers Park District: John Barten Randy Lehr Marylee Murphy Brian Vlach Especially These Guy!
Thank you! Nick Olson nolson@wenck.com
Discussion & Conclusions: Cost Compost Amendment Existing Development Activity Units Cost/Unit Total Cost Acres Amended Cost/Acre Cost/Lot (0.06 acre of lawn) Amendments (hrs) 15 $70 $1,050 0.074 $14,189 $936 Intersite Travel (hrs) * 6 $70 $420 0.074 $5,676 $140 Compost (yards) 84 $13 $1,092 0.074 $14,757 $974 Compost Mobilization (site) * 3 $260 $780 0.074 $10,541 $260 Turf Establishment (hrs) 15 $35 $525 0.074 $7,095 $468 Total $52,257 $2,779 Till Amendment Amendments (hrs) 15 $70 $1,050 0.074 $14,189 $936 Intersite Travel (hrs) * 6 $70 $420 0.074 $5,676 $140 Turf Establishment 10 $35 $350 0.074 $4,730 $312 Total $24,595 $1,389 Estimates were provided by Randy Lehr (TRPD)