Groundwater sources pathways and impacts Flashcards
What is groundwater?
Groundwater is the result of rain or snow melt that percolates into the ground. The water that is not absorbed by plants continues to move down through the soil via gravity. This water continues down filling the pores between porous rocks (Aquifers). Once the pores are filled the area becomes saturated. This stored water moves very slowly though aquifers and is an important supply of water.
What is the water table?
The water table is the top of the saturate zone, the boundary between saturated and unsaturated zones. It may move up and down depending on the extent of water entering the land. Important to know the limit of water tables for buildings and development - flooding.
What is an aquifer?
An aquifer is an area of porous rock, through which groundwater can travel
What are the advantages of groundwater?
can be used as and when needed (useful in arid regions), unlike reservoirs you do not require a large space for them, reservoirs may often be located far from where the water is needed groundwater is not, less susceptible to pollutants than surface water.
What are the issues for groundwater concerning pollution?
Groundwater moves very slowly through aquifers and once polluted it becomes very difficult to clean up and restore to previous state.
Urban - industrial sources; gas works, leaking tanks etc
rural - agriculture; fertilizer/pesticide etc
Why is groundwater important?
97% of water on earth is saline. of the remaining 3%, 87% is stored in ice, 12% in groundwater and 1% is surface waters.
Groundwater acts as an important national resource, holding 20X more water than surface reservoirs, supplying 3/4 of water in SE England.
It also has significant ecological importance providing the water for many wetland, lakes and river systems.
what are the point and non point sources of pollution affecting groundwater?
point - smaller scale identifiable source - leaking tanks, disposal ponds, landfills/cemetery, sewage sludge, petrochemical industries with well defined plumes.
Non point - larger discrete sources - herbicides, pesticides, surface run-off, peterochemicals, acid mine drainage, conifer plantations with less well defined plumes
What effects the shape and distribution of a pollutant plume?
reactions within the ground, transport speeds, solubility etc
How does petroleum leakage move within groundwater.
Petrochemicals are immiscible with water, light contaminants therefore move over the surface of the groundwater in the direction of water flow whilst heavy contaminants sink down to the bottom of the aquifer until they meet an impermeable surface (Clay) and then run in the direction of the sloping land.
How does nitrogen behave as a contaminant?
Nitrogen has many different forms, its principle form entering the ground is as a nitrate. Is very soluble and therefore mobile throughout groundwater. In oxidising systems nitrate will move with little retardation or modification. in reducing systems nitrates may be undergo de-nitrification. desirable from water quality point of view.
Farmers are now being payed to modify land use practices.
what is the most important factor when determining the toxicity of metals in groundwater?
the form of metals - redox conditions
adsorption and ppt reactions causes fronts of these element to move very slowly.
What controls the plume of non reactive compounds?
advection and hydrodynamics of system
What controls the plume of reactive compounds?
various process such as - chemical ppt, sorption, microbial/redox reactions, radioactive decay.
