Hydrogeology Final SP25

transmissivity and hydraulic conductivity are important aquifer properties. what is the standard unit gradient for these aquifer properties?

1 ft/ 1 ft

the average salinity of marine water is 35 ppt. Based on the figure to the right, what is the salinity of water beneath the continental shelf 120 km offshore of new jersey at depth of 200 meters

15 ppt add image

in region indicated by arrow on map to the right, what is a source of significant quantities of ground water

intergranular porosity in highly weathered granite

___ has been out of contact with the atmosphere for a geologically significant amount of time. It can be thought of as "fossil water trapped in the pores of sediment at the time of deposition". Later, it might migrate through the rocks as saline groundwater

connate water

what is the only source of freshwater on Nantucket island, cape cod, and marthas vineyard coastal areas

pleistocene unconsolidated glacial outwash

deep gw from arabian desert has yielded ages from 20,000-30,000 years. This water dating to 20,30-000 years was recharging aquifers of the region during an interval of the humid climate that existed in the region around the time of the _

wisconsinan ice age

gw is from pore to pore via pore throats. in intergranular porosity, pore throats are typically smaller in diameter than pores they connect. Studies have shown, however, that even fine clays have pore throats that are larger than water molecules. Nonetheless, flow is greatly retarded because of _ in clays

the tortuosity of the flow paths

for a rock or unconsolidated material with fabric shown in figure to right, which direction will have lowest hydraulic conductivity

A add pic

is a function of the properties of a porous material, as well as, the properties of the fluid being transmitted

hydraulic conductivity

in blue ridge province of appalachian mountains _ are vitally important because they potentally contain and can transmit large quantities of water to residential and municipal wells

thrust faults

in areas of WV bordering ohio river, GW circulation in the drainage basin is from recharge areas in the hills to discharge areas in the valleys. The mean altitude of the water table is much higher under the hills, and saltwater is found at lesser depths beneath the _

valleys

specific yield is a measure of the amount of water that will drain from a geologic material due to gravity. Which of the following will generally have lowest specific yield?

clay

GW reserves in counties of WV that border the Ohio River are contained in two aquifer systems. Which of the following is the aquifer system capable of yielding wells that can sustain pumping rates of hundreds gallons/minute?

quaternary alluvium

an aquifers ______ will be different for “fresh water” vs “brine” or cold water vs warm water, or water vs oil.

hydraulic conductivity

at what depth range is salty GW commonly encountered beneath the major stream valleys in the western half of WV?

100-300 ft

what two phenomena control the specific retention of aquifers dominated by intergranular porosity?

surface tension and adhesion to/of mineral grain surfaces

which of the following would have the lowest rational equation C value-

a) residential suburbs

b) flat lawn, sandy soil

c) downtown business area

d) roofs

b) flat lawn, sandy soil

In appalachian plateaus region, claystones are aquitards and create perched zones in ______ and hydrologically connected overlying sandstones. Where perched zones intersect land surface, springs flow from hillsides.

coal beds

what is required for artesian GW systems

confined, inclined aquifer

on the appalachian plateau in WV, the yield of water from wells that tap the consolidated rock units in the minor tributary basins of the Ohio River is typically low. The mean yield is about 8 gal/min. Most of this GW is withdrawn from secondary permeability features such as ________ in the sedimentary rocks

bedding plane parting and fractures

______ aquifers (shown on map) are especially important in midwest states such as Ohio. These aquifers are very susceptible to contamination due to their high permeability as reflected by their yield in excess of 500 gal/min

buried valley

in the chicago area GW was used as the sole source of drinking water during the period 1864-1980. Pumping during this period lowered the water table by nearly ____ ft

900

extensive areas of fresh GW aquifers have been contaminated by vertical migration of artesian salty GW. In Fayette County WV, how did salty GW migrate into freshwater aquifers?

through unplugged test bores and improperly abandoned wells

the figure to the right shows various arrangements and configurations of ________

monitoring wells.

at 20 degrees C, the hydraulic conductivity on a rock or sediment will be highest for which of the following liquids?

gasoline

which of the following is the GW ownership rule used in WV. It limits landowners to beneficial use in connection with the land above, such that one landowners use should not deprive neighboring landowners from groundwater to meet their needs.

reasonable use

what is the aquifer property that describes the ability of the entire thickness of an aquifer to yield water

transmissivity

in most areas of the western half of WV, at depths of 1,000-5,000 ft, highly concentrated brines containing 30,000-100,000 mg/l of total dissolved solids are encountered. What is the source of these brines?

derived from sea water trapped in the original rock-forming sediments

what do the various colored areas on the map depict?

areas where GW withdrawal rates exceed recharge rate

what is the elevation of the Fries Fault at the field site

400 m

freshwater found in deep confined aquifers can extend beneath the sea floor many miles to offshore areas beneath broad continental shelves (True or False?)

True

below is classic formula for determining the porosity of an aquifer. However, it is very difficult to directly measure the volume of pores. Which of the properties listed below can be used in combination with the practical formula to determine porosity?

a)transmissivities

b)specific yields

c)bulk densities

e)pore throat diameters

c) bulk densities

________ of the aquifer exerts fundamental control on the general shape of the __________ as shown in cross section view here.

Transmissivity, Shape of the cone of depression

low transmissivity equals what type of cone shape?

steeper and deeper cone

high transmissivity equals what type of cone shape?

broader and shallower cone

Characteristics of cone of depression for a fully penetrating well

(flow lines, equipotential lines, and flow net)

flow lines are parallel
and horizontal and
equipotential lines are
vertical and parallel; flow
net comprised of rectangle

Characteristics of cone of depression for a partially penetrating well

(flow lines, equipotential lines, and flow net)

flow lines curved and converge toward the well, whereas equipotential lines are curved and subvertical; flow net comprised of non rectangular shapes

drawdown depends on what 5

things?

pumping rate, transmissivity, storativity, distance from pumping well, and time.

the Thies well function depends on what 4 things?

transmissivity, storativity, distance from pumping well, and time

Leaky Confined Aquifer:

bounded on top by aquitard and an unconfined aquifer (source bed); water table in source bed initially horizontal and does not change during pumping (except at cone of depression); flow through aquitard is vertical. *no water derived from storage in confining unit*

What are the two types of hydrogeologic boundaries?

barrier boundaries, and recharge boundaries

Barrier boundaries

-areas where aquifer terminates against impermeable material

-part of the cone of depression adjacent to barrier boundary experiences greater drawdown

Recharge boundaries

• Areas where aquifer is replenished

• Part of cone of depression adjacent to recharge boundary experiences less drawdown

Parkersburgs water supply is GW pumped from 5 ______ collector wells, 3 of which are located along the ___ bank of the ohio river. The other 2 are located on ___ Island

radial, east, neal

The flow of GW through aquifers is the focus of which law?

Darcys Law (of GW flow)

_____ is the most important contribution to present day understanding of GW flow and provides an accurate description of the flow of GW in almost all hydro environments

Darcys Law

Darcys Law Formula

Q=KiA

Q: rate of gw flow

K: hydraulic conductivity

i: hydraulic gradient

A: cross sectional area of flow

GW flow path slope (rise/run) calculation

i=dh/L

dh: diff in hydraulic head

L: flow length

Darcys Law holds for almost all flow types except for

turbulent flow

GW flow is characteristically laminar except: (hint-2 things)

• along STEEP gradients in the immediate vicinity of high volume pumping wells

• and where flow is through large openings such as solution cavities or open fractures

Determinations of the velocity of GW flow through porous material must take into account that flow is _________. Thus effective porosity must be incorporated into calculation of average linear flow velocity

pore to pore