I Solute and Contaminant Transport Flashcards
advection
mass transport simply due to the flow of water in which the mass is dissolved
change in conc over time is
the pore velocity
contaminant plumes in the direction of flow
get broader and spread by diffusion
Fick’s law qd
diffusive flux M/L^2/T
Fick’s law Dw
molecular diffusion co in free water L^2/T
tortuosity
dist a molecule must travel divided by the shortest dist between those points
diffusion alone can not account for
the transport of chemical mass, as more spread than predicted
mechanical dispersion
mixing that happens because the porous media forces some solute molecules to move faster than others (shorter pathways)
longitudinal dispersion is bigger than
transverse dispersion
molecular diffusion depends
solely on a concentration
gradient to operate, is
dominant at lower velocities
mechanical dispersion
depends
on advection to
operate and dominates at
higher velocities
mechanical dispersion alpha
dispersivity
dispersivity
mixing parameter L
matrix diffusion
if GW flow is slow,
solutes diffuse into lower permeability zones
as conc in the transmissive zone reduce, solutes diffusion back out
causing long extended tail of conc
mean its very hard to clean up contaminates
Differential conduit recharge
Occurs under rapid flow conditions
driven by differences in pressure
between the conduit and the
adjacent matrix
conservative contaiminants
does not react with
soil / aquifer solids, transport
controlled simply by dispersion
and advection
reactive contaminants
sorbed into mineral grains
as well as organic matter, and change in concentration due to reactions or radioactive decay
LNAPL light non aqueous phase liquids
Lighter than water so plume forms at water table
migrates down hydraulic grad
DNAPL Dense non aqueous phase liquids
denser than water so sinks and pools at base of aquifer
migrate down the dip of aquifer
radioactive decay
Radionuclides entering the groundwater system which are cations are subject to
retardation on soil surfaces
they undergo radioactive decay which reduces radionuclide concentration in BOTH dissolved and sorbed phases
sorption processes include
absorption and adsorption
cation exchange -attraction between clay and cation minerals
chemisorption
colloid
large particle that doesn’t settle
Partition Coefficient
estimates contaminant retardation
partitioning of contaminant between solid and aqueous phase
Ai for Partition coefficient
mass of absorbate sorbed
Ci for Partition coefficient
mass of absorbate in solution
partition coefficient (Kd) is small means
contaminant is very mobile
Kd (partition coe) is large means
contaminant is immobile
partition coe parameters
varies greatly between contaminants
sensitivity of contaminant to changing conditions not addressed
only valid conditions measured in
diffuse sources
waste water, pesticides and fertilizers
much more difficult to deal with as over a larger area
fully quantitative tracer tests requires accurate messurement of …
amount (mass) of tracer injected,
discharge from the spring or aquifer during the test, and
concentration or total mass of tracer in the discharging water.
