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Groundwater Modeling Hydrogeology 127 Kent E. Parrish, P.G

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Title: Groundwater Modeling Hydrogeology 127 Kent E. Parrish, P.G


1
Groundwater Modeling
  • Hydrogeology 127
  • Kent E. Parrish, P.G., C.Hg
  • November 30, 2010

2
Introduction
3
Lecture Outline
  • Groundwater Pollution
  • What Is A Model?
  • Modeling Axioms
  • Guiding Thoughts and Protocol
  • Governing Equations
  • Practical Applications and Examples
  • Model Documentation
  • Concluding Remarks

4
Groundwater Pollution
4
5
Pollutant Types
  • Point Source small-scale, identifiable source,
    reasonably well-defined plumes.
  • Nonpoint Source larger-scale, many smaller
    sources, usually diffuse plumes.

5
6
Pollutant Classes
  • Metals - Arsenic, copper, uranium
  • Nonmetals Acids, Phosphate, radium
  • Organics Detergents, gasoline, PCB
  • Organisms Giardia lamblia, Salmonella sp.

6
7
Fate and Transport in Porous Media
  • Advection - moves at same rate as groundwater
  • Dispersion - tortuous flow paths in porous medium
  • Retardation adsorption and reaction
    (degradation)

7
8
Groundwater Models
9
What is a Model?
  • A Model Is Any Device That Represents An
    Approximation Of A Field Situation (Anderson and
    Woessner, 1992, p. 2).

10
What is a Model?
  • It is an Imperfect Tool

11
What is a Model?
  • Its Purpose Is To Predict The Value Of A
    Particular Variable Or Set Of Variables

12
What is a Model?
  • A Flow Model Predicts Groundwater Heads
  • A Contaminant Fate and Transport Model Predicts
    Changes In Contaminants and Their Concentrations

13
Modeling Axioms
  • There Should Be No Such Thing As A Model For an
    Area, Only For A Specific Problem

A model should be designed to achieve a specific
objective or set of objectives. No one,
all-inclusive model exists for an area.
14
Modeling Axioms
  • Do Not Use A Model For A Purpose Other Than That
    For Which It Was Intended

Rather, change the model to solve the new
problem.
15
Modeling Axioms
  • No One Understands The Compromises Made During
    Development, Nor The Nuances Of A Model Better
    Than The Developer

Consequently, a model should not be developed by
one party and then used by another.
16
Modeling Axioms
  • Changing Software Without Updating And Revising A
    Model (Starting With The Conceptual Model) Gains
    Little Beyond The Ability To Use Different
    Software

The confidence in a model and its predictions
will not be significantly increased by a software
change alone.
17
Guiding Thoughts
  • Plan Think Through The Steps And Decisions To
    Build The Model
  • Keep It Physically-Based In Reality
  • Seek And Use Stakeholder Advice
  • Define The Questions To Be Answered By The Model

18
Guiding Thoughts
  • Develop Modeling Objectives
  • Understand Expectations
  • Conduct Technical Working Meetings (Early and
    Often)

19
Questions
  • On Which Contaminants Should The Model Focus?
  • Can An Action Reach Conclusion In A Reasonable
    Time?

20
Questions
  • Can An Action Be Improved Or Revised To Shorten
    Its Life Cycle?
  • What Would Be The Potential Effect(s) Of Reducing
    The Level Of Effort On An Action? Of Increasing
    The Level Of Effort?

21
Modeling Protocol
  • Establish A Purpose For The Model
  • Develop A Conceptual Model
  • Select The Governing Equation And A Computer Code
  • Design The Model (Conceptual and Numerical)
  • Calibrate The Model

Anderson and Woessner, 1992
22
Modeling Protocol
  • Perform Calibration Sensitivity Analysis
  • Perform Model Verification
  • Run Model to Predict Outcomes
  • Perform Predictive Sensitivity Analysis
  • Present Model Design and Results

Anderson and Woessner, 1992
23
Modeling Protocol
  • Conduct Post-audits
  • Revise Model Based On Post-audit Results

Anderson and Woessner, 1992
24
Governing Equations
25
Flow Equation
Harbaugh, A et al., 2000
26
Fate and Transport Equation
Zheng and Wang, 1999
27
Common Types of Numerical Models
  • Finite Difference
  • Finite Element
  • Stochastic

28
Common Types of Numerical Models
Wang and Anderson, 1982
29
Common Types of Numerical Models
Wang and Anderson, 1982
30
Common Types of Numerical Models
Wang and Anderson, 1982
31
Common Types of Numerical Models
Wang and Anderson, 1982
32
Practical Applications
33
Developing a Conceptual Model
  • Regional Geologic Formations
  • Alluvial and Fluvial Deposits from the Sierra
    (Modesto and Riverbank Formations) About 150 Feet
    Thick in Center of Basin
  • Discontinuous lenses of Fluvial Sand and Silt
    with Clay and Gravel (Laguna Formation). About
    400 to 1,000 Feet Thick.
  • Indurated Andesitic Sand to Sandstone with
    Conglomerate, Siltstone, and Claystone (Mehrten
    Formation). About 400 Feet to 600 Feet Thick.

34
Developing a Conceptual Model
Conceptual Depositional Environment
35
Developing a Conceptual Model
Local Geologic Model
36
Developing a Conceptual Model
  • Regional Hydrogeology
  • Located in the San Joaquin River Groundwater
    Basin/East San Joaquin Subbasin
  • Sources of Groundwater Recharge
  • Infiltrating Rainwater
  • Losses from Rivers and Sloughs
  • Deep Percolation of Irrigation Water

37
Developing a Conceptual Model
Hydrogeologic Features
38
Developing a Conceptual Model
Multiple Sources of Contaminants Reaching
Groundwater
www.orcbs.msu/edu/
39
Developing a Conceptual Model
Schematic
40
Developing a Conceptual Model
Numerical Model Grid
41
Practical Examples
42
Practical Examples
  • Conceptual Model Film Loops
  • Particle Tracking
  • Transport Film Loops

43
Uncertainty
44
Sources of Uncertainty
  • Water Level, Flow and Chemical Measurement Errors
  • Input Parameter Errors
  • Outside Influences (Extraneous Pumping)
  • Mathematic Approximations of Model Code
  • Aquifer and Aquitard Heterogeneities

45
Model Documentation
46
Example Report Outline
  • Title
  • Introductory Material
  • Hydrogeologic Setting and Conceptual Model
  • Model Design, Calibration and Sensitivity
    Analysis
  • Results
  • Model Limitations
  • Disclaimer
  • Summary, Conclusions, and Recommendations

47
Concluding Remarks
48
Summary
  • All Models are Wrong
  • Must Use Professional Judgment
  • Identify Uncertainties and Acknowledge Them
  • Always Maintain Your Ethics

49
References
  • Anderson, M.P. and W.W. Woessner, 1992. Applied
    Groundwater Modeling Simulation Of Flow And
    Advective Transport. Academic Press. San Diego,
    California. 381 p.
  • Harbaugh, A., E. Banta, M. Hill, and M. McDonald,
    2000, MODFLOW-2000, The U.S. Geological Survey
    Modular Ground-Water Model User Guide to
    Modularization Concepts and the Ground-Water Flow
    Process. U.S. Geological Survey Open-File Report
    00-92. 121 p.
  • McDonald, M. and A. Harbaugh, 1988. A Modular
    Three-Dimensional Finite-Difference Ground-Water
    Flow Model. U.S. Geological Survey. Techniques of
    Water-Resources Investigations. Book 6. Chapter
    A1. 586 p.

50
References
  • Mercer, J. and C. Faust, 1980a. Ground-Water
    Modeling An Overview. Ground Water v. 18. n. 2.
    p. 108-115.
  • Wang, H and M. Anderson. 1982. Introduction to
    Groundwater Modeling. Finite Difference and
    Finite Element Methods. Academic Press. San
    Diego, CA. 237 p.
  • Zheng, C. and P. Wang, 1999. MT3DMS A Modular
    Three-Dimensional Multispecies Transport Model
    for Simulation of Advection, Dispersion, and
    Chemical Reactions of Contaminants in Groundwater
    Systems, Documentation and Users Guide. U.S.
    Army Corps of Engineers. Engineer Research and
    Development Center. Washington, D.C. 169 p. Plus
    Appendixes.

51
Developing a Conceptual Model
52
Developing a Conceptual Model
53
Developing a Conceptual Model
54
Developing a Conceptual Model
55
Developing a Conceptual Model
56
Developing a Conceptual Model
57
Developing a Conceptual Model
58
Developing a Conceptual Model
59
Developing a Conceptual Model
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