14.6 Environmental Problems

What threatens groundwater? How does this affect the land?

overuse threatens supply, withdrawal causes subsidence

Why is groundwater a nonrenewable resources?

amount of water recharging is significantly less than water being dicharged/withdrawn

Why is groundwater considered mined?

not renewing itself, using up a resource in finite supply on this time scale

What is happeneing to the Highplains/Ogallala Aquifer?

agricultural & irrigation depend on groundwater, which ths quifer provides 30% of irrigation water

little recharge because evaporation is high, but precipitation is only modest

intense irrigatkion usage

How does prolonged drought affect groundwater?

amount of water in lakes & reservoirs severely depleted, so increased groundwater use

60% of state needs met by groundwater in CA

What happens when water is pumped from wells faster than recharge?

the ground sinks, subsidence

important for areas underlain by thick, unconsolidated sediment

water is withdrawn, water pressure drops, weight of the ground transfers onto sediment & packs them tightly together, ground subsides

What happened in San Joaquin Valley CA?

9meters of subsidence due to overpumping groundwater and loose sediment underlying

What happened in Mexico city?

built on former lake bed, water withdrawn by pumping, 6-7 meters of subsidence

Why is saltwater contamination an environmental problem?

excessive groundwater withdrawal causes saltwater to be drawn into wells, which contaminates the freshwater supply

What is the relationship between freshwater and salty groundwater?

freshwater less dense, floates on saltwater like a lens

the depth of freshwater below sea level is 40 times greater than the elevation of water above sea level

excessive pumping lowers water table, bottom of fresjwayer zone rises 40x that amount

Saltwater intrusion/contamination

elevation of saltwater high enough to be drawn into wells & contaminate freshwater supply

problem near the coasts, especially urbanized costal areas: decrease in infiltration from roads = lack of recharge

How do you correct saltwater intrusion?

network of recharge wells, pump wastewater back into groundwater system

recharge basins to collect surface drainage, allow it to seep into the groun

What is a common source of groundwater contamination?

sewage from septic tanks, broken sewer systems, and farm waste

How can groundwater system purify sewage water?

hardmful bacterial mechanically filtered through sediment, destroyed by chemical oxidation, assimilated by other organisms

aquifer must be of correct composition

What happens to sweage water if the aquifer is very permeable with large pores or highly fractured?

contaminated water travels long distances without being filtered & cleansed

too rapid flow, no purification

What happens when the aquifer is compsoed of sand or permeable sandstone?

water purified after traveling only a few dozen meters, openings large enough to permit water movement, but very slowly

How can sinking a well lead to groundwater pollution problems?

the cone of depression locally increases or reverses slope of the water table

What are other pollution sources?

highway salt, fertilizers, pesticides, leakage from pipelines/storage tanks/landfills/holding ponds

what are hazardous pollutants?

flammable, corrosive, explosive, toxic

How can landfills pollute groundwater?

contaminants, rainwater dissolved materials & can reach water table

same issue with holding ponds

What is the main issue with sourcing groundwater pollution?

groundwater moves slow, pollution goes undetected, mostly detected only after people have become ill, removal of the source doesn’t solve problem immediately

What are the sollutions to groundwater contamination?

abandon the water supply after removing contaminant

gradual flushing away of pollutants

pump & treat polluted water

prevention is most important