Hydrology BC ENV 3025

Groundwater transport

(Fig)(Fig)(Fig)(Fig)(Fig)

Advection

groundwater flow velocity v can be calculated from Darcy's law
according to Darcy's law, a contaminated parcel of water would not change its shape during transport in a horizontal flow regime (Fig)
However, if you take a liter of a salt solution for example and release it in the aquifer, after a while the contaminant will have spread out and not any more confined to 1 liter

Dispersion

spreading of a contaminant can be explained by `dispersion'
variability of the flow velocity on the pore/grain scale (Fig) and on the aquifer scale (Fig) can explain the spreading of the plume

Adsorption

certain solutes interact with the solid phase and are temporarily adsorbed on the surface
results in a retardation of the contaminant
example: certain organic contaminants, Cs-137
demonstration with the model: separation of yellow and blue plume

Decay

radioactive decay or microbial activities remove contaminants
example: conversion from nitrate to nitrogen gas

Everything working together

random walk model

all above processes affect the spreading of contaminants in groundwater (Fig)
transport of contaminants is more complicated when it does not dissolve in groundwater (Fig)
example: hydrocarbons floating on the watertable in Brooklyn/Queens
groundwater remediation (model demonstrations)

remove the source of the contaminant
let the aquifer flush out the contaminant naturally
pump and treat
bioremediation

Student excercise: the 'groundwater model' (Fig)

play with sandtank model, consider the following questions:

inject dyes into all three injection wells, do you see any correlations between geology and spreading of the plume?
what interactions are there between surface waters and groundwaters and between the two aquifers?
do you see evidence for adsoption?
what is your most efficient remediation option?
do something interesting with the model

Other concepts to explore:

water quality can vary in the aquifers
pollutants travel with the groundwater
dispersion, inhomogeneities, adsorption
wells can cause groundwater pollution
contaminated groundwater can pollute surface water and vice versa
leakage through confining beds
capillary action may cause upward movement of water