Most numerous Western USA related to recent igneous activity within this region By-products of hot springs - material precipitated from ions in solution (e.g. Siliceous sinister or geyserite (precipitation of dissolved silica), calcium carbonate (travertine and calcareous tufa), sulfur - e.g. Rotten Egg Springs, Nevada 26 CHAPTER 11 GROUNDWATER PROBLEMS ASSOCIATED WITH GROUNDWATER Excessive Groundwater Withdrawal - depletion due to over pumping (e.g. intense irrigation) or drought 1) subsidence - compaction of aquifer material due to removal of water from pores spaces most important in fine-grained unconsolidated sediments (subsidence is irreversible e.g. Mexico City built on lake bed) New Mexico 27 CHAPTER 11 GROUNDWATER PROBLEMS ASSOCIATED WITH GROUNDWATER 2) salt water contamination - significant in Coastal areas (results in changes in water chemistry and increase in dissolved solids 25 CHAPTER 11 GROUNDWATER GROUNDWATER CONTAMINATION Human Activities point source pollution - landfills, dumps, hazardous waste disposal sites, USTs, mines, septic tanks, broken sewer systems, barn yard waste etc. non-point source pollution - agricultural fertilizers and pesticide, highway salt application 29 CHAPTER 11 GROUNDWATER NATURAL METHODS OF GROUNDWATER PURIFICATION 1) mechanically filtered 2) destroyed or changed by chemical reaction (e.g. oxidation) 3) assimilation by microorganisms (biodegradation) 30 CHAPTER 11 GROUNDWATER EROSION BY GROUNDWATER - erosion by solution - most important in limestone (karst) terrain Dissolution reaction: CO2 + H2O = H2CO3 H2CO3 = H+ + HCO3- CaCO3 + H+ + HCO3- = Ca2+ + 2HCO3- 31 CHAPTER 11 GROUNDWATER EROSION BY GROUNDWATER - groundwater percolates through cracks/fractures in limestone dissolving it to form solution 
(numerous Western USA; related; to recent igneous activity within this region By-products of hot springs) (subsidence; is; irreversible) (Ca2+ + 2HCO3- 31 CHAPTER 11 GROUNDWATER EROSION BY GROUNDWATER - groundwater percolates through cracks/fractures in limestone; dissolving; it)
numerous Western USA subsidence Ca2+ + 2HCO3- 31 CHAPTER 11 GROUNDWATER EROSION BY GROUNDWATER - groundwater percolates through cracks/fractures in limestone
related is dissolving
to recent igneous activity within this region By-products of hot springs
irreversible
it