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EPA On-line Tools for Site Assessment Calculation

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Calculator List This page groups the calculators by function. Common instructions, example problems and detailed references follow on subsequent pages of this guide.

Formulasfor calculating quantities used for site data manipulation, model input parameters, and for flow and transport phenomena.

Site Data Preparation: the Hydraulic Gradient is calculated in three ways depending on the source of site information with the distance between two, three or more wells. These calculations can also be done by applying a scaling factor to convert directly between measurements made on a map: two or three wells.
Vertical gradients are calculated from adjacent wells with screens at differing depths.

The moisture content in a soil sample.

Model Input Parameters: Solubility, Vapor Pressure, Henry's Constants for petroleum hydrocarbons estimated from the SPARC Performs Automated Reasoning in Chemistry (SPARC) calculator, Henry's Law Constants for a variety of chemical types, Retardation Factor, Estimated Longitudinal Dispersivity, Estimated Diffusion Coefficients.

Flow and Transport Phenomena: Ground water flow estimated from Darcy's Law and the Seepage Velocity

Dissolution of chemicals from fuels: Effective Solubilities, approximation of Temperature-Dependent Effective Solubility and Mass Distribution.


Models Simple models to answer various questions about sites and to design site characterization strategies:

How much plume diving might occur because of locallized recharge patterns? Run plume diving. How much borehole concentration averaging can occur because of screen placement?

How does plume length vary with source concentration? Use Steady State Plume Length.

What is the first arrival time, peak concentration and breakthrough curve for a contaminant? Try One-Dimensional Transport from a Continuing or Pulse Source , or One-Dimensional Transport with Fuel Source.

How much variation in model results is introduced by input parameter uncertainty? To see results of an approach to this problem use the concentration uncertainty calculator and read our paper.

Three-Dimensional "Domenico" models: Steady-State, Centerline model , Unsteady three-dimensional model

Do contaminated vapors impact residences? Two approaches are demonstrated using the Johnson-Ettinger model:
  • Constrained modeling with two parmaters explicitly considered variable/unknown: depth to source and moisture content "Johnson-Ettinger" back calculation or forward calculation model.
  • Generalized uncertanty modeling with all parameters considered variable/unknown.Uncertainty Model New


Unit Conversion Factors
Hydraulics: Flow Rates , Hydraulic Conductivity
Chemical & Biological: Half Lives and Rate Constants , Henry's Law Constants , Indoor Air Concentrations
Time: Dates to Sequential Times
Position: Lat-Long to distance degrees-minutes-seconds , decimal degrees
Thermodynamics: Fahrenheit to Celsius

Scientific Demos: Darcy Flow in a Laboratory Column , Unsteady Mass Balance , Flow in a One-Dimensional Aquifer
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