ES 106 2006 April 21 Groundwater Exploitation and Pollution Wells A Draw water from aquifer B Zone of saturation may be depressed due to withdrawal 1 drawdown of water table a cone of depression b may refill seasonally with recharge c may be permanent if aquifer compresses C artesian flow 1 hydraulic pressure is above water table a flowing artesian above well head b non flowing artesian rises upon intersection of water table II Groundwater concerns A Withdrawal exceeds recharge in many areas 1 mining a non renewable resource 2 water tables in some areas drop 1 meter per year 3 may not ever recharge if aquifer has compressed a overlying land packs grains after water leaves void space b land subsidence several meters in some areas B Contamination 1 organic leachate a sources 1 septic tanks 2 farm wastes 3 sewage system failure b removal 1 natural filtering by sand and gravel 2 oxidation by chemicals and assimilation by organisms 3 if aquifer has proper characteristics mostly optimal porosity 2 other pollution sources road salt fertilizer pesticide leaking underground tanks pipelines landfills impoundment ponds a Denver pesticide production b Minneapolis wood preservatives c Potato production aldecarb antifungal compound 3 Nitrates from fertilizer blue baby syndrome impaired hemoglobin 4 VOC solvents spilled discarded buried storage leaking persistent C Cleanup of groundwater costly difficult mixed rate of effectiveness III Drinking water standards A Established by EPA 1 milligrams per liter is parts per million 2 parts per billion is milligrams per 1000 liters B dilution is a poor solution to pollution I IV Sewage treatment methods A primary treatment settling ponds removes solids B secondary treatment aerobic bacteria metabolize organic matter 1 sand and gravel filter bed 2 aeration encourages aerobic bacteria activity C advanced treatment filtration 1 activated carbon charcoal removes solvents pesticides metals 2 reverse osmosis removes most impurities D chlorine kills bacteria not viruses V Geologic work of groundwater A Dissolves rock limestone more common than salt gypsum B Caverns 1 groundwater dissolved limestone along cracks bedding planes 2 calcium ions bicarbonate ions carbonate ions flushed away 3 depositional features in caverns from these ions re precipitating a dripstone features 1 stalactites on ceiling 2 stalagmites on ground 3 columns joined stalactites and stalagmites 4 soda straws angel wings cave pearls b formation due to loss of dissolved CO2 changing pH of water C Karst terrain usually limestone land area with solution collapse of underground openings can be on salts also 1 sinkholes collapsed caverns a Florida Kentucky Indiana New Mexico b Gradual dissolution sudden collapse c Enhanced by removal of groundwater 1 Exploitation for municipal industrial agricultural purposes 2 Mitigation of swampland for development 2 typical features of karst terrain a sinkholes b disappearing streams lack of through flowing streams c steep sided solution valleys d haystack buttes common in southeastern Asia
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