Introduction to Groundwater Geochemistry Reaction Modeling (short course #292)

Date: December 6-7, 2018
Location: Las Vegas, Nevada
CEUs: 1.5
Education level: Intermediate*


This two-day short course will provide you an introduction to the important geochemical processes that affect groundwater composition and methods for developing reasonable conceptual models using site-specific data. Conceptual models will also be combined with an equilibrium modeling code to produce a geochemical model of a site.

The geochemical processes that affect the composition of natural groundwater and the movement of groundwater contaminants include a wide variety of solid phase/water and gas interactions in the subsurface. It is oftentimes impossible to predict the impact of these interactions on groundwater composition without a realistic conceptual geochemical model of the system and a means to calculate the interdependent chemical reactions.

This course will strengthen your understanding of the fate and transport of groundwater contaminants, and provide you with techniques and software for using site data to develop geochemical models for a given site. In addition to site understanding, geochemical models can be used in a predictive mode for evaluating natural attenuation of contaminants and designing in situ and ex situ remediation methods.

You will receive an introduction to groundwater geochemistry and chemical reaction modeling using PHREEQCI (free, widely used USGS code) for natural and contaminated systems. Emphasis will be placed on inorganic reaction modeling involving major ions and trace metals. Each session will include a discussion of an important geochemical process (such as mineral dissolution/precipitation, oxidation/reduction, or adsorption/desorption) and a demonstration of modeling the process with PHREEQCI. Practice sessions will integrate examples presented in lectures into realistic problems to provide valuable experience in modeling at specific sites.

Additional information

You should bring with you

You should bring a laptop computer to the class to work class examples independently and along with the instructor. Prior to the class, you should download the PHREEQCI Windows version and its accompanying files from the USGS website at

You will receive

At the class, you will receive a comprehensive handout covering the discussion topics and guidelines for setting up, running, and interpreting each class example.

Learning objectives

In this course, you will learn about:

  • Chemical reactions and the groundwater geochemical system
  • Chemical equilibrium calculations
  • Ion speciation calculations
  • Gas phase equilibrium
  • Carbonate system
  • Mineral equilibria
  • Mass transfer modeling
  • Oxidation/reduction modeling
  • Adsorption/desorption processes
  • Surface complexation modeling
  • One-dimensional contaminant fate and transport modeling.

Who should attend?

  • Geochemists
  • Hydrogeologists
  • Engineers
  • Project managers
  • Regulators.

*Note regarding education level

To benefit the most from this intermediate-level course that will be presenting relevant concepts in aqueous geochemistry as background material, you should possess a basic understanding of chemistry, and be knowledgeable in the topics covered in the NGWA courses, “Fundamentals of Groundwater Geochemistry” and “Applications of Groundwater Geochemistry.”


Day 1

8:00 a.m. Session 1: Basic aquifer geochemistry — refresher
  • Aquifer geochemical system
  • Geochemical processes (ion speciation, gas equilibrium, mineral, redox, adsorption)
  • Data collection

10:00 a.m. Break

10:15 a.m. Session 2: Introduction to PHREEQCI

  • Input preprocessor (normal options)
  • Input files
  • Concentration and activity (ionic strength)
  • Databases
  • Ion speciation calculations
  • Output files

12:00 p.m. Lunch (on your own)

1:00 p.m. Session 3: Gas equilibrium and the carbonate system

  • Dissolved oxygen and Eh
  • Carbon dioxide, inorganic carbon speciation, and pH
  • PHREEQCI example problem

2:45 p.m. Break

3:00 p.m. Session 4: Mineral equilibrium and solubility

  • Saturation index
  • Solubility = f (temp, pH, Eh, solution complexation, ionic strength)
  • Reactive minerals (primary minerals, weathering products, analysis)
  • PHREEQC example problem

5:00 p.m. Course adjourns for the day

Day 2

8:00 a.m. Session 5: Redox reaction modeling

  • Redox reactions (pyrite oxidation, Fe(OH)3 reduction)
  • Redox potential (Eh and pe)
  • PHREEQC redox options and examples
  • Redox modeling (Fe, Mn, As)

10:00 a.m. Break

10:15 a.m. Session 6: Adsorption/desorption

  • Adsorption isotherms (linear (Kd) and nonlinear)
  • Ion exchange and surface complexation reactions
  • Adsorption/ion exchange affinity and capacity
  • Arsenic adsorption onto HFO (example with and without initial solution equilibration)
  • Ion exchange example using PHREEQCI

12:00 p.m. Lunch (on your own)

1:00 p.m. Session 7: One-dimensional transport with chemical reactions

  • Arsenic release and natural attenuation
  • Initial conditions
  • Low Eh generated by organics, high As and Pb plume development
  • Natural attenuation along a flowpath
  • Example of one-dimensional transport simulation in PHREEQCI

3:45 p.m. Break

4:00 p.m. Session 8: Modeling applications

  • Review of other examples in the PHREEQC user’s guide
  • Course participant “real world” problems
  • Course summary and wrap-up

5:00 p.m. Course adjourns

Fees and registration
We're sorry, but this short course is sold out.
Venue and accommodations


Las Vegas Convention Center
3150 Paradise Road
Las Vegas, Nevada 89109
(702) 892-0711


Westgate Las Vegas Resort & Casino
3000 Paradise Road
Las Vegas, Nevada 89109
(800) 732-7117
(702) 732-5111

Accommodations: NGWA has secured a limited block of rooms on a first come, first served basis at the group rate of $69 per night, plus applicable resort fees and taxes. This rate is valid until the November 9, 2018 cutoff date, unless our room block has been filled before that date. To receive this group rate mention group name "SNGW8R" when making your reservations. Book your room online at or call (800) 635-7711 and provide the group code SNGW8R. For guest check-in and checkout times, please contact the hotel directly.