1. Department of Civil & Environmental Engineering
ENVE3503
Environmental
Engineering
Groundwater
Supply
Dr. Martin T. Auer
Michigan Tech
Department of Civil & Environmental Engineering

2. Drinking Water Sources
Approximately two-thirds of the population of the U.S. receives its supply from surface waters. However, the number of communities supplied by groundwater is four times that supplied by surface water. This is because large cities are typically supplied by surface waters and smaller communities use groundwater.

3. Domestic Wells

4. An Aquifer water table water table well vadose zone capillary fringe
unconfined aquifer
water table
impermeable layer

5. Unconfined Aquifer manometer water table –
re-charge
well
water table –
piezometric surface where water pressure equals atmospheric pressure
Unconfined
Aquifer
manometer

6. Confined Aquifer = f (K) piezometric surface aquiclude Confined
re-charge
confining
layer
piezometric
surface
= f (K)
piezometric
surface
Confined
Aquifer
aquiclude

7. Comparison Unconfined Aquifer Confined Aquifer = f (K) water table
re-charge
well
Unconfined Aquifer
confined
aquifer
re-charge
piezometric
surface
= f (K)
Confined Aquifer
confining
layer

8. Cone of Depression
cone of depression
aquaclude = impermeable layer

9. Effect of Pumping Rate
drawdown
radius of influence

10. Effect of Multiple Wells

11. Effect of Pumping Rate

12. Porosity and Packing
Small soil particles pack together more closely than large particles, leaving many small pores.
Large soil particles pack together less closely, leaving fewer, but larger, pores.
A given volume of spherical solids will have the same porosity, regardless of the size of the particles. The significance of porosity lies in role of surface tension (higher for small pores) in retaining water and frictional losses in transmitting water.
Most soils are a mixture of particle sizes. Poorly sorted soils (greater range of particle sizes) will have a lower porosity, because the smaller particles fill in the "gaps“.

13. Porosity of Specific Soils
Clays are small soil particles and thus one would expect tight packing. However, the net negative charge of clay particles separates them, resulting in a higher porosity than for a sphere of equivalent volume.
Silts are intermediate in size between clays and sands and are irregular in shape. This irregularity leads to poorer packing than for spherical particles of similar volume and thus a higher than expected porosity.
Sands are large particles, more regular in shape than silts and thus having a porosity similar to that expected for spherical particles.

14. Porosity Values Material Porosity (%) Comment Clay 55 negative charge
The net effect of the physicochemical properties of clay, silt and sand particles is that the porosity and thus water content tends to decrease as particle size increases.
Material
Porosity (%)
Comment
Clay 55
negative charge
Loam (silts) 35
irregular shape
Coarse sand 30
regular shape
soil particles
pores

15. Specific Yield
This is the amount of water, expressed as a %, that will freely drain from an aquifer

16. Specific Yield Material Porosity (%) Sp. Yield (%) Clay 55 3 Loam 35 5
Having a lot of water does not mean that an aquifer will yield water. Surface tension effects, most significant in soils with small pores, tend to retain water reducing the specific yield.
Material
Porosity (%)
Sp. Yield (%)
Clay 55 3
Loam 35 5
Coarse sand 30 25
A better expression of the water available for development in an aquifer is the ratio of specific yield to porosity.
Material
Ratio of Specific Yield : Porosity
Clay
0.05
Loam
0.14
Sand/Gravel
0.83

17. Hydraulic Gradient
Darcy’s Law
hydraulic
conductivity

18. Hydraulic Conductivity (a.k.a. coefficient of permeability)
K = m3·m-2·d-1 = m·d-1

19. Hydraulic Conductivity
Determining
Hydraulic Conductivity
An extraction well (E) is pumped at a constant rate (Q) and the drawdown (S) is observed in two monitoring wells (M) located at a distance (r) from the extraction well.
Determination of Hydraulic Conductivity H M2 M1 E S1 S2 h1 h2
h = H - s r1 r2
Hydraulic conductivity (m3∙m-2∙d-1) is then calculated by solving Darcy’s Law to yield:

20. Estimating Well Production
At maximum drawdown, conditions at r1 (the well radius) are s1 = H and h1 = 0 and conditions at r2 (the edge of the cone of depression) are s2 = 0 and h2 = H. H E S1 S2 h1 h2
h = H - s r1 r2
And the maximum pumping rate (m3∙d-1) is calculated using the equation below: