The OnSite On-line Calculators
For Subsurface Contaminant
I Transport Site Assessment
Office of Research
and Development
National Exposure
Research Laboratory
The U.S. Environmental Protection Agency (EPA) has developed a suite of
on-line calculators called "OnSite" for assessing transport of 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:
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
1) Parameter Estimates 3)
Hydraulic gradient
Moisture content in a sample
Retardation factor
Henry's constants
Estimated longitudinal dispersivity
Darcy s Law
Seepage Velocity 4)
Effective solubility from fuels
Multiphase mass distribution
2) Simple Transport Models
Plume diving
Steady plume length
One-dimensional transport from a
pulse, continuing, or fuel source
"Domenico" models: steady state
centerline, unsteady
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 conve-
nience of experienced personnel, the education of inexperienced personnel,
and for the potential to provide consistency among a diverse user commu-
nity. 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 formu-
las, 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.
A focus of some of the methods is on simple calculations, such as the re-
tardation factor. Ideally there would be nearly universal ability to perform
this calculation, but interaction with various client groups showed this not
to be the case. Even for experienced analysts, the availability of a prepack-
aged calculation is viewed as a convenience. Beyond obvious labor savings,
"convenience" facilitates correct application of the principles and ultimately
more scientific decision making. Web site usage statistics show that even the
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The OnSite On-line Calculators
simple calculators are used commonly. A somewhat
different class of calculation is represented by the
effective solubility calculator. This calculator deter-
mines concentrations of chemicals in equilibrium
with various fuels. In contrast to the retardation
factor, the formula itself is much less well-known,
and the required input data are not commonly
available. In this case the calculator provides a
unique resource to the community as the ability
to calculate this quantity is not expected to be
widespread.
Unique concepts were introduced through the
calculators, primarily to the underground storage
tank community. The premier example of this
concerns the effect of rainwater infiltration on
contaminant plumes. Research conducted at con-
taminated sites showed that plumes were pushed
downward, rather than diluted. Development
and testing of assessment methodologies provided
software for predicting this behavior. Providing
an on-line calculator (plume diving) placed this
technology directly into the hands of the Leak-
ing Underground Storage Tank community. The
calculators allow estimation of the amount of verti-
cal displacement of the plume (plume diving) and
show the effects on measured concentrations of
placing well screens in the wrong vertical position
(average borehole concentration).
History: Since their inception in 1998 the calcula-
tors 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 June of 2002, web site usage went above 10,000
per month for the first time.
Computer Details: The calculators are imple-
mented 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 cal-
culation 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 sug-
gestions from users and in response to requests for
information. These have come from State Agen-
cies, EPA Regional and Program Offices and the
private sector.
Reset
F Label Drawing ?
Select Parameters'
Site • EaslPatchogue
Depth of Top ofScreen |65 Ofi
Screen Length
I Ignore Conductivity Variation ?
Formation Data Well
Concentrations.,
Range of Measured Values
Estimated Borehole Concentration =
(120 ug/l to 6400 0 ug/l)
1335.0 us/l
The Average Borehole Concentration calculator that is illustrating
the concentration that would be seen in a well with a 10 loot long
screen located 65 feet below the ground surface. The maximum peak
concentration nearby this well was 6400 ug/l, but the effect of borehole
averaging was to reduce the observed concentration to 1335 ug/l.
For More Information,
Contact:
Jim Weaver, weaver.jim@epa.gov
U.S. Environmental Protection Agency
Athens, GA 30605-2700
706-355-8329
http://www.epa.gov/athens/onsite
NERL Web Site Announcement
November 2001
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