FATE POLLUTANTS

MIDTERM 1

Contaminant sources

accidental fuel spills, leak from hazardous waste site

Types of contaminants

LNAPLS, DNAPLS, lead, chloride(road salts)

LNAPLS

less dense than water, floats on top of water table

DNAPLS

denser than water, sinks through water table

Contaminants that are harder to remediate

DNAPLS(sink), metals(absorbs)

Surface water-GW interactions

Two way exchange of water and the groundwater system

Gaining stream

gains water, water table above stream

Losing stream

loses water, water table below stream

Vadose zone (unsaturated)

area between land surface and water table, contains air and water

Saturated zone

Pores filled with water, where groundwater flows

Water table

Upper surface of saturated zone, fluctuates

Capillary zone

water held by surface tension, above water table

Unconfined aquifer

No confining layer, saturated zone open to surface

Confined aquifer

Confining layer on top that restricts water flow

Impervious actually means…

confining

Conservative tracer

solute movement, non reacting, used to measure dispersion, no sorption

Step input

Continuous, long duration, zero to a high concentration

Example of step input

leaky pipe

Pulse input

Short duration, zero to concentration to zero

Example of pulse input

A spill

Transport phenomena

Diffusion, advection, and mechanical dispersion

diffusion

random molecular motion, no bulk flow, high to low concentration

advection

movement with fluid

mechanical dispersion

mixing due to fluid movement

Groundwater flow parameters

water flows downhill, hydraulic gradient

Isotropic

Same in all direction Kx = Ky = Kz

Anisotropic

Different in different directions, where Kx ≠ Ky.

Heterogeneous 

K changes, K(x,y,z) = varies

Homogenous

Same in all locations K(x,y,z) = constant

Hydraulic head

at the water table, pressure = 0

Porosity

= Vvoids/Vtotal

If a well is not pumping..

Hydraulic head is the same at all depths

ADE first type

Step change (column tracer test)

ADE second type

Continuous injection (leakage into aquifer)

Peclet number

advection/diffusion = Vx*L/DL

Hydraulic conductivity

ability to transmit water through pore spaces

High hydraulic conductivity

easier to transmit water, large grain size:well sorted