groundwater

Question 1

sinkholes

Answer 1

groudnwater dissolved away limestone bedrock forming a cavern that collapsed inward
sinkholes fill with groundwater, forming lakes

Question 2

groundwater is:

Answer 2

• major component of hydrologic cycle
• source of water
• largely hidden from view , poorly understood reservoir

Question 3

how do groundwater reservoirs form?

Answer 3

precipitation enters subsurface via infiltration. infiltrated water adds to soil moisture and groundwater. some infiltrated water percolates to deeper level and slowly flows in subsurface for months to 1000s of years before returning to surface

Question 4

porosity

Answer 4

primary: originally formed with the material.
secondary: develops later through fracturing, faulting, dissolution

Question 5

permeability and impermeability

Answer 5

perm: allows water to flow readily due to pore interconnectedness. enhanced by large and straight flow paths
imperm: prevents water flow and can act as seal or cap layer trapping water in permeable materia;

Question 6

aquifers and aquitards

Answer 6

aquifer: sediment or rock that transmits water easily
aquitard: impermeable or low permeability sediment or rock that hinders water flow

Question 7

unconfined vs confined

Answer 7

unconfined: aquifer that intersects the surface, in contact w atmosphere so easily contaminated
confined: aquifer beneath aquitard, isolated and less susceptible to pollution

Question 8

water table

Answer 8

subsurface boundary
above water table: pores mostly filled with air (unsaturated)
below water table: pores filled with water (saturated)
capillary fringe separates the two zones

Question 9

depth of water table

Answer 9

it is variable
humid: water table closer to surface
arid: deeper down
position changes with rainfall
where watertable intersects the surface, you see lakes, streams, or sea
ponds dry up if water table falls below pond bottom

Question 10

water table topography

Answer 10

sloping surface
high where land is high
low where land is low
water flows from higher elevations to lower elevations
HOWEVER: distance between watertable and surface is greater on hill than in the valley

Question 11

groundwater flow

Answer 11

flows under influence of gravity
straight downward in unsaturated zone, more complicated in saturated zone
occurs on a variety of scales: local, intermediate, regional

Question 12

hydraulic head

Answer 12

potential energy driving flow. due to elevation above sea level and pressure exterted by weight of overlying water
flow moves from high to low hydraulic head
flow paths are not straight lines

Question 13

recharge vs discharge

Answer 13

recharge areas: infiltration
flow is directed downward
found in topographic uplands
discharge areas: where groundwater exists the subsurface
flow directed upward and in topographic lows

Question 14

how is groundwater obtained?

Answer 14

wells: holes excavated or drilled to obtain water
springs: natural groundwater outlets

Question 15

cone of depression

Answer 15

tapping subsurface water reservoirs results in depleting them if recharge not fast or abundant enough
local depression at zone of extraction, steepest near well, flattens with distance
cones of depression can interfere, process is additive

Question 16

springs

Answer 16

locations of natural groundwater discharge
yield fresh, clear, clean water without drilling

Question 17

where are springs formed?

Answer 17

• where water bearing fractures intersect the surface
• where a fault separates impermeable rock layers
• where vertically flowing water encounters impermeable layer

Question 18

hot springs

Answer 18

groundwater discharges hot water - 30 to 104 celsius
waters are high in dissolved minerals
develop where deep groundwater surfaces along faults
develop in geothermal regions (shallow magma)
hot water rises and then replenished with cold water from surface

Question 19

groundwater problems

Answer 19

cannot be replenished quickly
threatened by mismanagement overuse and pollution
potential grounwater depletion and drainage
lowering of the watertable

Question 20

saline intrusion

Answer 20

renders water unpotable
pumping of groundwater causes salt boundary to rise and potentially enter the pumping well

Question 21

pore collapse and land subsidence

Answer 21

sediment grains compress and pore space (previously filled with water) collapses
land surface cracks and sinks
irreversible

Question 22

age of groundwater

Answer 22

its old age is preferred because pre-dates contaminating activities
filtering effect of porous material and clay minerals remove particulates and dissolved ions

Question 23

unwanted substances in groundwater

Answer 23

from contact with soil, can pick up bad minerals
iron and manganese cause taste and odor problems
hydrogen sulfide as well

Question 24

groundwater contamination (6)

Answer 24

sanitary wastes
agricultural wastes
toxic chemicals
petroleum storage
landfill leachate
mining wastes

Question 25

groundwater excess

Answer 25

rising water table may initiate slope failures
adds weight to material
increase in pore pressure decreases material strength

Question 26

acidic groundwater

Answer 26

caves develop when groundwater dissolves limestone
groundwater weakly acidic
CO2 reacts with water to form carbonic acid which interacts with limestone to dissolve rock

Question 27

caves

Answer 27

cave networks develop when limestone bedrock and abundant freshwater interact. caves grow as joints

Question 28

speleothems

Answer 28

formed from formation of dripstone when groundwater degasses CO2
stalactites hang down
stalagmites point up