Summary Notes - Final Exam - ENVB 210
Week 6 - Soil Water, Removal, & Contamination
•Groundwater use = 30% = stream water + inﬁltration!
•Flow always wet => dry, high => low elevation!
•Rates of ﬂow depend on elevation !+ permeability!= 30-150 cm/day = 5yrs/2km (clays slower)
•River ﬂow comparison - twig moves downstream at 30-60 cm/second - 1hr for 2km!
•Mill tailings in mining areas!
•Land spreading of sludge
•Runoff of salt from roads and highways!
Non-Point (distributed sources)!
•Fertilizers on agricultural land!
•Pesticides on agricultural land and forests!
•Contaminants in rain, snow, and dry
Pollution Plume in groundwater - liquids from solid wastes//leaking liquid pollutants
•percolate through soil, simultaneously releasing into the gas-phase
•H2O soluble pollutants disperse at capillary fringe
•Insoluble pollutants form pollutant lens: ﬂoats above water table OR moves down!(high d)
Unconﬁned//Shallow Aquifer: Separated by impermeable layer!(low hydraulic conductivity)
Subsidence due to water removal
•Opposing water pressure reduced by excessive pumping/withdrawal
•Upper layers dry out, compress and compact due to downward force of gravity
•Reduced pore size - permanent condition, rewetting the soil does not cause it to go back up!
•Lessens total storage capacity of the aquifer system!
•Severe cases (extensive ground water mining) may case crack in ground => EARTH FISSURE
Salt Water Intrusion into Coastal Wells!
•Sea water depth: overlying column of fresh groundwater = column of heavier sea water!
•If sea level = constant + uniform recharge from rainfall, interface would be motionless
•Neither element is constant + humans use groundwater
•Edge of land and water is porous - if excess water is drawn, salt water intrudes
•Factors of Salt water intrusion:
-sea level rise//decrease in recharge
-subsidence//increase in pumping!
Problems in the Prairies: said to become drier - need more irrigation. To estimate the salinity in
western Canada is difﬁcult!because salts move with precipitation up and down the soil proﬁle!
•Excess water in holding capacity raises water table causing groundwater to ﬂow downslope!
•Groundwater ﬂowing over salts in bedrock deposits dissolves and transports the salts
•If water is (~2m) to the soil surface, capillary action and evaporation draw up the saline water
•Water evaporates, leaving the salts behind => gradually accumulate to form saline seep