Calculator Inputs
Example Data Table
| Scenario | C₀ mg/L | x m | t days | K m/day | i | n | αL m | Kd L/kg | Half life days |
|---|---|---|---|---|---|---|---|---|---|
| Sand aquifer | 100 | 120 | 365 | 2.5 | 0.003 | 0.28 | 8 | 0.4 | 730 |
| Fast gravel flow | 80 | 150 | 300 | 8 | 0.004 | 0.32 | 12 | 0.1 | 500 |
| Sorbing compound | 60 | 90 | 900 | 1.2 | 0.002 | 0.25 | 5 | 1.8 | 1200 |
Formula Used
The calculator applies a simplified one dimensional advection, dispersion, retardation, and decay approach.
Darcy flux: q = K × i
Pore water velocity: v = q / n
Retardation factor: R = 1 + (ρb × Kd) / n
Retarded velocity: vr = v / R
Dispersion coefficient: D = αL × v + Dm
First order decay constant: λ = ln(2) / half life
Retarded travel time: tt = x × R / v
Relative concentration: C / C₀ = 0.5 × erfc((x - vt / R) / (2√(Dt / R))) × e^(-λt / R)
Predicted concentration: C = C₀ × relative concentration
Mass flux estimate: J = q × C × 1000
How to Use This Calculator
- Enter the source concentration in milligrams per liter.
- Add the receptor distance measured along groundwater flow.
- Enter the elapsed transport time in days.
- Provide hydraulic conductivity, gradient, and effective porosity.
- Add dispersivity and molecular diffusion for plume spreading.
- Enter bulk density and distribution coefficient for sorption.
- Use half life to include first order decay.
- Press the calculate button and review the result section.
- Download the CSV or PDF for reports and records.
Groundwater Contaminant Transport Planning
Groundwater contamination moves through pores, fractures, and layered aquifer materials. A transport calculator helps turn field measurements into practical estimates. It links flow speed, dispersion, sorption, and decay in one place. The result is not a permit decision by itself. It is a screening tool for planning, comparison, and documentation.
Why Transport Estimates Matter
Many sites have wells, tanks, spills, or landfills near useful water sources. A dissolved plume can arrive slowly, but it may still create long term exposure. Distance alone does not explain risk. Hydraulic gradient, porosity, and aquifer texture also control arrival time. Strong sorption can slow some chemicals. Rapid decay can lower concentration before a receptor is reached.
Core Physics Behind the Tool
The calculator uses Darcy flow to estimate seepage velocity. It then applies a retardation factor for reversible partitioning between water and solids. Longitudinal dispersion spreads the plume around the average travel front. First order decay reduces dissolved mass with time. Together, these terms give a simplified one dimensional concentration estimate at a selected distance and time.
Inputs That Need Care
Good inputs produce better screening results. Hydraulic conductivity should represent the active flow zone. Gradient should come from water level data. Effective porosity should match the geologic material. Dispersivity is scale dependent, so larger distances often need larger values. Bulk density and distribution coefficient control retardation. Half life should reflect site chemistry, oxygen conditions, and temperature.
Using Results Responsibly
Use the output to compare scenarios, design monitoring, and discuss uncertainty. Review the retarded travel time, predicted concentration, relative concentration, and mass flux together. A small concentration may still matter for very low regulatory limits. A short travel time may demand faster sampling. Always compare calculator findings with site maps, well logs, lab results, and professional judgment.
Practical Next Steps
Run conservative and realistic cases. Keep a record of every assumption. Export the result for reports. Update the model when new sampling data arrives. For complex sites, use calibrated numerical groundwater software and expert review. Document the selected units carefully. Share tables with reviewers before field work. Recheck sensitive inputs after storms, pumping changes, or seasonal shifts, because groundwater gradients can change and plume direction may also shift quickly onsite.
FAQs
What does this calculator estimate?
It estimates groundwater plume movement, concentration reduction, retardation, dispersion, decay, and approximate arrival time at a selected receptor distance.
Is this suitable for final regulatory modeling?
No. It is a screening calculator. Use professional site investigation, calibrated models, and regulatory guidance for final compliance decisions.
What is hydraulic conductivity?
Hydraulic conductivity describes how easily water moves through aquifer material. Sand and gravel usually have higher values than clay.
Why is porosity important?
Effective porosity controls actual pore water velocity. Lower effective porosity usually increases seepage velocity for the same Darcy flux.
What does retardation mean?
Retardation means the contaminant moves slower than groundwater because some mass partitions onto aquifer solids.
What does dispersivity do?
Dispersivity spreads the plume around the average flow path. Higher dispersivity can cause earlier low concentration arrival.
How should half life be selected?
Use site specific studies when possible. Half life can change with oxygen level, temperature, microbial activity, and contaminant chemistry.
Why export CSV and PDF files?
CSV files support spreadsheets and further analysis. PDF files help preserve a simple report for project records and review.