Methods for determining hydraulic conductivity + Tracer methods

Why are hydraulic properties of groundwater important?

• Slope stability and seepage (Versickerung) control

• planning of control and monitoring measures for geotechnical projects

• Drainage for open pit mines

• Effects of seepage water from mine tailings

• Barrier wells and control barriers (for conatminated groundwater)

• Environmental impact assessment

• planning of suitable drinking water wells or site for landfills

What methods exist to determine groundwater properties?

• calculated from the grain size curves

• laboratory methods

• field methods

How does the grain size curve function?

e.g. d10 is the grain diameter at which 10% of the sample is finer than the respective grain size value

What is considered when calculating hydraulic properties from the grain size curve?

considering:

• packing type (how much space is between the graines?)

• Uniformity coefficient C_u=d₆₀/d₁₀​​ → how uniform is the sample?

• Coefficient of curvature C_c = (d₃₀² / d₆₀*d₁₀)

  • Soils are considered uniform if C_u < 4 and C_c between 1-3

  • lower uniformity → higher dispersivity

• Temperature

  • increase of T leads to decrease of viscosity, which again leads to increase of k_f

Formulas to calculate the hydraulic conductivity from grain size curve.

Kozeny formula

• good for homogenous material e.g. river sand

• Takes porosity, grain shape factor (r), and viscosity into account

Therzagi formula

• used for very fine clay

Beyer & Schweiger formula

• can be used for everything

• includes the uniformity coefficient C_U

Hazel formula

• only used for fine, uniform material C_U < 4

Labaroty methods - Porosity

Sand: 0.26-0.43

Organic clay: 0.5-0.75

→ clay has much more pores altough much smaller than sand and hence porosity is larger (porosity ≠ permeability)!!

Laboratory method - Permeameter

Difference between Permeability (K) vs. Hydraulic Conductivity k_f

• K [m²] only depends on the material

• k_f [m/s] depends on material and fluid flowing through it

Why do we need tracer tests? What are fields of application?

to determine…

• source of water

• subsurface flow paths

• flow directions

• flow velocity

• catchment areas

• residence times

• mixing processes (e.g. with surface water)

• discharge rates

• contaminant transport processess

applications:

• Fractured, pore, and karst aquifers

• Unsaturated (vadose) and saturated zone

• Rivers, streams, lakes, glaciers

• Column tests in the laboratory

Explain the transport mechanisms in the soil.

• Advection

  • mass transport with water flow

• Dispersion

  • mass transport due to velocity fluctuations

• Diffusion

  • mass transport due to concentration gradient

• Reactions (chemical/biological processes)

What types of tracer tests do you know?

Simple tracer test

• to characterize flow paths

• 1 input location, 1 tracer, 1 or more sampling sites

Combined tracer test

• to determine boundaries of catchment area

• with different tracers at different input points

Comparative tracer test

• simultaneous introduction of different tracers at one input location

Repeated tracer test

• same test setup at different discharge conditions

What types or tracers do you know?

Artificial

• uranine, bromide

• colloidal tracers (mimic microorganisms or particles in groundwater e.g. bacteriophages or spores)

• DNA based tracers (free or encapsulated)

Natural

• isotopes

• Salt NaCl

• chemical tracers e.g. PFAS

• Pharamceuticals…

Other classification of Tracers

• fluorescent tracers (Uranine)

• Salt tracers

• chemical tracers

• stable and radioactive isotopes (e.g. Deuterium)

Fluorescent tracer

• organic substance containing aromatic groups and exhibiting the optical property of fluorescence

• good: very low detection limit

• bad: can sorb especially to gravel

What is the transport of pathogenic Viruses in Groundwater depending on

• water saturation

• flow rate

• ionic strength and pH