![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
The OnSite on-line Calculators for Subsurface Contaminant Transport Site Assessment
EPA has developed a suite of on-line calculators called "OnSite" for assessing transport of MTBE and other environmental contaminants in the subsurface. The calculators are available on the Internet at http://www.epa.gov/athens/onsite/, and are divided into four categories:
- Parameter Estimates
- Hydraulic gradient
- Moisture content in a sample
- Retardation factor
- Henry's constants
- Estimated longitudinal dispersivity
- Darcy's Law
- Seepage Velocity
- Effective solubility from fuels
- Multiphase mass distribution
- Simple Transport Models
- Plume diving
- Steady plume length
- One-dimensional transport from a pulse, continuing, or fuel source
- "Domenico" models: steady state centerline, unsteady
- Unit Conversions
- Flow rates
- Hydraulic conductivity
- Half lives/rate constants
- Henry's Law constants
- Dates/sequential times
- Latitude-longitude to distance
- Scientific Demos
- Darcy flow in a laboratory column
- Unsteady mass balance
- Flow in a one-dimensional aquifer
- Borehole concentration averaging
NOTE: The four most important calculators that address MTBE are the retardation factor, effective solubility, transport from a pulse source, and transport from a fuel source. These allow MTBE to be the selected chemical (note chemical selection boxes).
Purpose of OnSite: The purpose of these calculators is to provide methods and data for common calculations used in assessing impacts from subsurface contamination. Parameter estimates are included in OnSite for the convenience of experienced personnel, the education of inexperienced personnel, and for the potential to provide consistency among a diverse user community. The simple transport models were developed for two purposes: to demonstrate concepts of ground water flow and contaminant transport and to calculate concentrations given a set of input parameters. Unit conversions were provided for unit sets unique to subsurface transport calculations. These were intended to facilitate the correct application of transport formulas, because some of the units and conversions included are unfamiliar to many people. The scientific demos were outgrowths of modeling courses, where general concepts of transport need to be introduced.
History: Since their inception in 1998 the calculators have been used by several state agencies, EPA Regional Offices and private consulting firms. From the web logs we know that there has been a steady increase in usage of the site and that the most commonly-used calculators are the estimators for effective solubility, the retardation coefficient, plume diving in aquifers, estimation of hydraulic gradients, seepage velocity and moisture contents. In November of 2002, web site usage went above 15000 per month for the first time.
Computer Details: The calculators are implemented in either JavaScript or Java. JavaScript is well suited for a simple calculation that does not require a graphical output. Java was used to create applets for calculations with complex inputs or the need for graphical output. In either case all calculation is performed on the end-user's computer. No information that is entered into any OnSite calculator is collected by EPA. EPA does, however, accumulate statistics on the number of times pages are accessed, browsers used, user's domain names (.com, .edu, .gov, etc), and similar generalized information (see http://www.epa.gov/epafiles/usenotice.htm for details)
Ideas for new calculators are developed from suggestions from users and in response to requests for information. These have come from State Agencies, EPA Regional and Program Offices and the private sector. Contact Dr. Jim Weaver at weaver.jim@epa.gov to discuss these concepts or suggest new ideas.