John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Two Example Ground Water Mounding Situations John L. Nieber Department of Biosystems and Agricultural Engineering University of Minnesota
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Model Evaluation of Auxiliary Drainage for On- Site Septic Systems John L. Nieber and David M. Gustafson Biosystems and Agricultural Engineering Dept. James L. Anderson Soil, Water and Climate Dept. Originally presented at the 8 th National Drainage Symposium American Society of Agricultural Engineers Orlando, Florida March 1998
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum What are Auxiliary Drainage Systems for On-Sites? Drainage system used to lower water table when the water table is higher than allowed by health code (Minnesota requires a 3’ separation distance) Viable (hopefully) alternative to use of mound designs Significantly less expensive than mound designs
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Are Auxiliary Drainage Systems Effective? Field experiments are being conducted for various soil and climate conditions to test this question (in Minnesota and elsewhere) Some modeling has been done; mostly with Boussinesq equation formulations
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Objectives of Current Study Experimentally test effectiveness of an auxiliary drainage system on the performance of an on-site system located in east-central Minnesota Test a model of water flow in the soil at the experimental site and compare measured water table levels with simulated water table levels
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Experimental Site Located near Waverly, Minnesota; in the east-central part of the state For a private home with family of four Septic system designed for 450 gpd Water table within 1-2 feet of disposal trench prior to placement of auxiliary drainage system
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Trenches Tile drain Solid pipe to county ditch Piez. #5 Piez. #6 Piez. #3 Piez. #4 Piez. #1 Piez. #2 Well # m 30.5 m 3.1 m3.1 m 1,000 gal septic tank Drop boxes Home
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum 0.45 m 4.0 m 1.56 m 0.95 m V V Piezometers Rainfall/ET Boundary Drain Tile Wastewater Trenches Natural Boundary
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Field Site Location
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Field Site Location
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Day since January 1, D a i l y R a i n f a l l ( m m ) Winter 95/96 Winter 96/9 7
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Days since January 1, W a t e r T a b l e D e p t h ( m ) Winter 95/96 Winter 96/97 Piezometers between trench; average Piezometers next to drain; average Piezometer #7 Depth required Minnesota code
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Simulation Model Based on dual-porosity concept for variably saturated porous media Equations for each pore domain (matrix and macropores) described by a Richards’ equation; these equations are coupled Considers plant transpiration, vapor movement in the soil and soil evaporation Finite element solution in two-dimensions
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Volumetric Water Content (m 3 / m 3 ) C a p i l l a r y P r e s s u r e ( m ) Ap Horizon Ab Horizon Bt Horizon Bk Horizon C Horizon
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum 1E-71E-61E-51E-41E-31E-21E-11E+01E+1 Unsaturated Hydraulic Conductivity (m/day ) C a p i l l a r y P r e s s u r e ( m ) Ap Horizon Ab Horizon Bt Horizon Bk Horizon C Horizon
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Days since January 1, W a t e r T a b l e D e p t h ( m ) Winter 95/96 Winter 96/97 Piezometer between trenches Piezometer next to drain Depth required Minnesota code Without Evapotranspiration
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Days since January 1, W a t e r T a b l e D e p t h ( m ) Winter 95/96 Winter 96/97 Piezometer between trenches Piezometer next to drain Depth required Minnesota code With Evapotranspiration
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Days since January 1, W a t e r T a b l e D e p t h ( m ) Winter 95/96 Winter 96/97 Piezometers between trench; average Piezometers next to drain; average Piezometer #7 Depth required Minnesota code Measured
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Limitations The State Code ignores the unsaturated part of the profile; impact will depend on soil type We considered only flow in the soil matrix; macropore flow may be important for some conditions Did not examine chemical transport and transformations
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Ground Water Mounding Beneath a Stormwater Basin Study conducted in Washington Co. by Emmons & Olivier Associates Results presented here are from a report to the MPCA and also from the M.S. thesis (May 2005) of Jennifer Olson.
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum CD-P85 Natural infiltration basin 30 acres in extent 29 feet deep Outwash material 7 wells Pump station links CD-P85 with City stormwater system
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Topographic characteristic of CD-P85
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum X-section through CD-P85
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Sample infiltration curves for CD-P85
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Monitoring well locations near CD-P85
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Water levels during 2002 in CD-P85
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Water levels in monitoring wells near CD-P85 Note the two scales for water levels
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Models Used for Simulations Hantush mounding model – simple analytical model, most common ground water mounding equation Multi Layer Analytic Element Model (MLAEM) – has been used at this site in past, regional flow model in TCMA FEMWATER – unsaturated/saturated flow model, recommended in literature for complex systems
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Model Input Identical parameters used when applicable Measured parameters –Recharge area, recharge rate, duration (transient vs. steady state models), depth to water table, saturated thickness, initial ground water elevation, bedrock elevation, nearby lake elevations Literature value (unknown) parameters –Saturated hydraulic conductivity (calibrated model, slug test) –Porosity (effective and fillable) –Unsaturated flow characteristics Used first dataset (July 2002) to determine unknown parameters
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Model Input (July event)
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum MLAEM
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Hantush Equation
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Hantush
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum FEMWATER
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Initial Model Result Comparison
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Model Selection Sum of square differences MLAEM model – closest to observed values –Unable to calibrate porosity and Ksat to desired accuracy – steady state Hantush model – second best –Calibration parameters include Ksat and porosity – most variable and unknown parameters
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Calibrated Model (Hantush)
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Some WSAS Mounding Effects Analysis performed with COMSOL MP3.2 Finite Element Solution of the Richards Equation
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Vertical section showing five leach trenches and a perching layer
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum 120 gallons/day/foot; K s = 2.8 feet/day K perch layer = 0.28 feet/day
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum 120 gallons/day/foot; K s = 2.8 feet/day K perch layer = 0.28 feet/day
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum 18 gallons/day/foot; K s = 2.8 feet/day K perch layer = feet/day
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum 7 gallons/day/foot; K s = 2.8 feet/day K perch layer = feet/day
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum 246 gallons/day/foot; K s = 2.8 feet/day K perch layer = 2.8 feet/day
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum 175 gallons/day/foot; K s = 2.8 feet/day K ellipses = 0.28 feet/day
John L. Nieber Biosystems and Ag. Eng. Feb. 21, 2006 GW Mounding Forum Summary Low perm layers do not need to be continuous to affect septic infiltration rate Perm of low perm layer (ft/day) Infiltration (gal/ft/day) ellipses175