1. GROUND WATER CONTAMINATION

2. IMPORTANCE OF GROUND WATER Approximately 99 percent of all liquid fresh water is in underground aquifers At least a quarter of the world’s population draws its water from these groundwater supplies Ground water provides the largest source of usable water storage in the United States. – Underground reservoirs contain far more water than the capacity of all surface reservoirs and lakes, including the Great Lakes

3. Septic tank leakage water table Infiltration of fertilizers and pesticides Accidental fuel spill Municipal water well Pond Leakage from hazardous waste site Industrial site Farmer house McDonald’s & gas Leaking petroleum tank Ocean Saline water Mechanisms of ground water contamination

4. PROPERTIES OF GROUND WATER Soil properties –Porosity –Volumetric water content Hydraulic properties of soils –Soil water pressure

5. PROPERTIES OF GROUND WATER p>0 Intermediate zone Tension saturated zone Soil profile –Vadose zone Root zone Intermediate zone Tension saturated zone –Ground water zone Root zone Ground water

6. PROPERTIES OF GROUND WATER Darcy’s Law –Q proportional to A –Q proportional potential  H –Q inverse proportional to distance L

7. DARCY’S LAW IN VERTICAL COLUMNS Hydraulic conductivity, K, is function of 

8. VERTICAL TRANSPORT IN THE UNSATURATED ZONE Continuity and Darcy’s law used to determine the 1-D vertical flow –h is the soil pressure –After algebraic manipulations the Richards Equation is obtained

9. 3-D TRANSPORT IN THE SATURATED ZONE Mass conservation –M in -M out =Accumulation dy dz dx z x y

10. 3-D TRANSPORT IN THE SATURATED ZONE (ctd) –After algebraic manipulations –Assumptions  =constant Darcy’s law applies –The transient flow equation becomes

11. 2-D STEADY STATE FLOW –Time derivative is zero –If K x =K y then –The boundary conditions may be Dirichlet: h=f(s) on  1 Neuman  h/  x=g(s) on  2 Mixed :  (s)  h/  x+  (s)h=u(s) on  3  1  3  2

12. 2-D STEADY STATE FLOW (Example) –Boundary conditions –The discretization of the transport equation yields i,j-1 i+1,j i-1,j i,j+1

13. WRAP-UP Ground water is an important resource There are various mechanisms of ground water contamination The physical laws needed for ground water modeling include –Darcy’s law –Mass continuity Numerical methods for solving ground water equations may be readily derived