Download presentation
Presentation is loading. Please wait.
Published byElfreda Butler Modified over 9 years ago
1
Simulation of Short Circuit Flow Paths and Transient Conditions to Understand Vulnerability of Public Supply Wells to Contamination in the High Plains Aquifer, York, Nebraska Brian Clark Matt Landon Leon Kauffman George Hornberger 4/12/2005
2
Take-Home Messages Wellbores drilled through confining units can act as “short circuits” Transient stresses provide opportunities for pulses of flow Combination of transient stresses and wellbores through confining units can allow contaminants to lower layers
3
Study Background USGS National Water-Quality Assessment (NAWQA) program
4
Study Background USGS National Water-Quality Assessment (NAWQA) program NAWQA topical study: Transport of Anthropogenic and Natural Contaminants (TANC) to public supply wells
5
Study Background USGS National Water-Quality Assessment (NAWQA) program TANC goal: determine controls on movement of contaminants to public supply wells
7
Study area
8
Potential contaminant sources RCRA, LST, NPDES Water / wastewater Landfill / livestock Superfund !. !. !. !.
9
Study area Recharge zones
10
Study area Recharge zones Multi-node pumping wells
11
Study area Recharge zones Observation wells FP5 FP4 FP3 FP1
12
Study area Recharge zones Transect FP5 FP4 FP3 FP1
13
Hydrogeology unconfined sand upper confined sand Electrical Resistivity logs Well screens
14
Confined and unconfined water-levels many wells are commonly screened in unconfined and confined layers Date
15
Model discretization unconfined sand upper confined sand
16
Model discretization
17
Specific yield 0.2 to 0.25 upper confined sand HK values0.315m/d Specific Storage 1 x 10 -4 7 x 10 -7 per meter Fine coarse
18
Transient stresses Simulation time –Sept 1944 to Sept 2004 Seasonal stress periods –Irrigation pumpage off during winter
19
Transient stresses Multi-node wells allow flow through wellbores Halford, K.J. and Hanson, R.T., 2002
20
Hydrograph comparison Simulated Observed unconfined
21
Hydrograph comparison Simulated Observed confined
22
Hydrograph comparison Simulated Observed confined
23
Hydrograph comparison Simulated Observed confined
24
Hydrograph comparison Simulated Observed unconfined
25
Hydrograph comparison Simulated Observed unconfined
26
YEARMEANMINMAXRMS MEAN ABS COUNT 19640.08-2.331.541.471.206 1974-0.07-2.881.421.290.959 19840.10-2.182.531.421.0010 19940.15-2.601.751.311.0712 2004-0.26-3.122.971.130.7643 Residual Statistics all units in meters Residuals = observed minus simulated
27
Transport model sub-grid 13 layers (2-14) Version of GWT to support MNW 61 rows 122 columns Age & CFC boundary by layer observation wells
28
Simulated age animation 100 90 80 70 60 50 40 30 20 10 0 Age, in years Cross-sectional view
29
Simulated age animation 100 90 80 70 60 50 40 30 20 10 0 Age, in years Map view cutaway
30
Age of water vs depth below water table (unconfined wells only) (measured= tritium-helium ages)
31
CFC concentration vs depth below water table (confined wells only)
32
Conclusions Wellbores drilled through confining units act as “short circuits” for flow Simulated transient stresses provide pulses of flow Transient stresses and wellbores through confining units allow flow and contamination to lower layers
33
Contact information Brian Clark - brclark@usgs.gov Matt Landon – landon@usgs.gov Leon Kauffman – lkauff@usgs.gov George Hornberger – gzhornbe@usgs.gov 4/12/2005
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.