Groundwater Contamination Lab

Investigate how contaminants migrate through groundwater in different soil types. Compare plume spread in sand, clay, and gravel. Experiment with extraction wells to study remediation strategies. Collect data, form hypotheses, and draw conclusions about contaminant transport.

Guided Experiment: Soil Permeability and Contaminant Spread

Hypothesis

Setup

Run Experiment

Analyze

Conclude

How will the soil type (sand vs clay vs gravel) affect the speed and extent of contaminant plume migration through groundwater?

Write your hypothesis in the Lab Report panel, then click Next.

Aquifer Cross-Section

Controls

Soil Type

Presets

Hydraulic Conductivity10 m/day

Porosity0.35

Hydraulic Gradient0.010

Source Concentration100 mg/L

Dispersivity5.0 m

Time30 days

Enable Extraction Well

Results

v_s = \frac{K}{n} \cdot \frac{dh}{dl}

Seepage velocity = 0.2857 m/day

Darcy Velocity

0.1000 m/day

Specific discharge

Seepage Velocity

0.2857 m/day

Actual pore velocity

Plume Distance

8.6 m

Center of mass

Peak Concentration

0.587 mg/L

At plume center

Plume Length

27.1 m

Along flow direction

Plume Width

11.7 m

Perpendicular spread

Concentration Profile (Centerline)

Data Table

(0 rows)

#	Trial	Soil Type	K(m/day)	Porosity	Gradient	Time(days)	Plume Dist.(m)	Peak Conc.(mg/L)

Hypothesis

0 / 500

Observations

0 / 500

Conclusions

0 / 500

Reference Guide

Groundwater Flow

Groundwater flows through pores in soil and rock. The speed depends on the hydraulic conductivity (K) and the hydraulic gradient (dh/dl).

v_s = \frac{K}{n} \cdot \frac{dh}{dl}

Seepage velocity ( $v_s$ ) is the actual speed water moves through pores. It equals the Darcy velocity divided by porosity ( $n$ ). Sandy soils with K = 10 m/day flow much faster than clay with K = 0.001 m/day.

Advection and Dispersion

Contaminants move by two mechanisms. Advection carries the plume with the flowing groundwater at seepage velocity. Dispersion spreads the plume due to variable flow paths through pores.

D_L = \alpha_L \cdot v_s, \quad D_T \approx 0.1\, D_L

The dispersion coefficient ( $D_L$ ) depends on dispersivity ( $\alpha_L$ ) and velocity. Longitudinal dispersion (along flow) is about 10 times greater than transverse (perpendicular).

Gaussian Plume Model

The 2D Gaussian solution describes how concentration varies in space and time from an instantaneous point source.

C = \frac{C_0}{4\pi t\sqrt{D_L D_T}}\, e^{-\frac{(x-v_s t)^2}{4D_Lt} - \frac{y^2}{4D_Tt}}

The center of mass travels at $v_s \cdot t$ meters. Peak concentration decreases as $1/t$ due to spreading. The plume width grows proportional to $\sqrt{t}$ .

Pump-and-Treat Remediation

Pump-and-treat systems extract contaminated groundwater through wells, treat it at the surface, and either discharge or reinject the clean water.

The capture zone of an extraction well depends on pumping rate relative to the natural groundwater flow. A well must pump fast enough to reverse the local flow direction and capture the plume.

Effectiveness depends on well placement (ideally downgradient of the plume), pumping rate, and soil properties. Clay soils are harder to remediate because contaminants diffuse into low-permeability zones and slowly release back.