Groundwater Quality

and Geochemistry

Environmental Professionals'

Organization of Connecticut

April 28, 2017

Course Instructor:

Stephen P. Garabedian, Ph.D.

1. Introduction

What are the geochemical principles on which the

fate and transport of organics and metals are based?

What are typical background concentrations of

organics and metals in New England aquifers?

What are the geochemical conditions in which the

fate and transport of organics and metals in

groundwater can be interpreted?

“Concepts, Facts, and Case Studies”

Focus Questions:

Course Outline

1. Introduction

2. Principles of Aqueous Geochemistry

3. Principles of Organic Geochemistry

4. Groundwater Geochemistry

5. Case Study: Cape Cod Sewage Plume

6. Organics - Hydrocarbons

7. Solvents

Course Outline contd.

8. Metals - Zinc

9. Cadmium

10. Chromium

11. Arsenic

12. Lead

13. Mercury

14. Arsenic Plumes

15. Summary and Assessment

Overview

The geochemical conditions for the fate and

transport of organics and metals in ground-

water systems are the result of interactions

between solids, liquids, gases, and microbial

populations.

These interactions are strongly

influenced by, and in turn

affect, man-made conditions

(e.g. contamination).

Overview contd. The primary factors influencing the occurrence

and concentrations of organics and metals are:

1) sources (natural or man-made),

2) water chemistry (major ions/gases, pH),

3) adsorption reactions (surface chemistry),

4) oxidation-reduction (redox) reactions,

5) precipitation-dissolution (mineral) reactions.

- Often these factors are not in hydrologic or

chemical equilibrium, and concentrations can

and will change over space and time.

Some Major Classes

of Groundwater Pollutants

- Pathogens: (Bacteria, Viruses, Protozoa)

- Major/Minor Ions (e.g. NaCl, Fluoride, Iron)

- Sewage, Fertilizers, and Nitrate (Methemoglobinemia)

- Pesticides (e.g. Insecticides, Herbicides, Fungicides)

- Industrial Chemicals (e.g. Plasticizers, PCBs)

- Hydrocarbons (e.g. Crude Oil, BTEX, MTBE)

- Volatile Organic Compounds: (e.g. PCE, TCE)

- Metals (e.g. Chromium, Arsenic)

- Radioactive Materials (e.g. Radon, Uranium)

- Leachates (e.g. Landfills, CAFO, Mine Tailings)

Periodic Table with

Carbon in green, Metals* in red

Major Elements in yellow

*As, Cd, Cr, Hg, Pb, Zn; and Fe

References and Acknowledgments

- Please Note References in Appendix

- Acknowledgment and grateful thanks to my many colleagues at the USGS, particularly Denis LeBlanc and Doug Kent

Next

Aqueous Geochemistry