2. Water quality issues – ‘natural’ controls Acidity – low pH due to infiltration of acidified precipitation; acids from mine drainage; pyrite oxidation acid groundwater limited (generally) to shallow aquifers where buffering is limited; short residence time low pH water can leach metal plumbing and mobilize metals; corrosive

3. Hardness: elevated Ca, Mg and CO3; generally found in areas with carbonate rock aquifers or sediments containing carbonate minerals calcite and/or dolomite hardness reduces effectiveness of soap and detergents solid carbonate precipitates as scale in pipes and boilers may call for ‘softening’ of water using cation exchange which elevates Na levels in water – problem for hypertensives

4. Salinity: Aquifers containing soluble salts halite, gypsum; also saltwater incursion in aquifer Salinity exceeding 1500 ppm may cause illness Desalinization using membrane filters or distillation may be required

5. Fe and SO4/H2S: Commonly caused by dissolution of pyrite from aquifer. Marine shale a common source. H2S causes odors; bacteria oxidize to SO4 Fe oxidizes to ferric state and precipitates causing staining Treatment involves use of strong oxidizing agent (KMnO4) and filtration

6. Other water quality parameters: Eh Dissolved Oxygen Biological Oxygen Demand Chemical Oxygen Demand Bacterial and Viral Counts Turbidity Color Taste Odor

10. DNAPL LNAPL

19. Pumping to produce cone of depression and ‘capture’ plume. “Pump and Treat” - the most common approach to remediation.

20. Heavier components of LNAPL will stick to particles in aquifer.

21. Multiple pumping wells may induce areas of stagnation in groundwater system, slowing extraction of contaminants.

23. Chemical agents such as detergents may enhance the rate of removal of adsorbed contaminants.

24. Air sparging

25. Enhanced bioremediation involves injection of nutrients, oxygen and sometimes bacterial cultures, to increase the rate of biodegradation.

26. Hydrogen peroxide acts as a source of oxygen for enhanced bioremediation systems.

27. c and d illustrate the use of reactive barriers. Iron filings or steel wool are often used to enhance the rate of reaction.