United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Las Vegas NV 89114
Research and Development
EPA-600/S4-83-030 Aug. 1983
Project Summary
Guidelines for Field Testing
Aquatic Fate and Transport
Models: Final Report
Stephen C. Hern, George T. Flatman, Wesley L Kinney, Frank P. Beck, Jr.,
James E. Pollard, and Alan B. Crockett
These guidelines have been written
for the Office of Pesticides and Toxic
Substances (OPTS) U.S. EPA as an aid
in field validation of aquatic fate and
transport models. Included are discus-
sions of the major steps in validating
models and sections on the individual
fate and transport processes: biotrans-
formation, oxidation, hydrolysis, pho-
tolysis, ionization, sorption, biocon-
centration, volatilization, and physical
transport. For each process, the fol-
lowing information is provided: a gen-
eral description of the process, a list
and discussion of environmental fac-
tors affecting the process, a list of the
priority pollutants for which the process
is important, a list of model-specific
environmental inputs, and field methods
for collecting these input data.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory. Las Vegas. NV, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Aquatic fate and transport models have
been developed which predict the fate and
concentration of chemicals released into
natural waters. These models may be
based upon either an empirical approach
or a theoretical approach that considers
transport and fate processes. Empirical
models, which are based on extensive
field observation, are usually calibrated to
specific existing sites and chemicals and
provide no rational basis for making pre-
dictions outside their range of prior ob-
servation. Thus, models of this type are
generally not suited to predicting the fate
of new chemicals and are not considered
in these guidelines.
The theoretical approach is based upon
an understanding of environmental fate
and transport processes, including bio-
transformation, hydrolysis, oxidation, pho-
tolysis, ionization, sorption, volatilization,
bioconcentration and physical transport
This type of model is considerably more
versatile, since it is designed to predict
environmental fate and pollutant concen-
trations based upon degradation rate con-
stants and relatively simple chemical and
environmental input data. Therefore, the-
oretical models can be applied to chem-
icals which have not yet been introduced
into the environment Such models are of
considerable interest to the U.S. EPA and,
in particular, the OPTS.
Guidelines
The guidance provided consists of a
beginning section which addresses the
steps in validation. Subsequent sections
cover the environmental fate processes
and field methods for collecting environ-
mental input and output data. The major
steps in the field validation process are
outlined in Table 1.
Validation of a model is defined in this
report as a comparison of model results
with numerical data derived from obser-
vations of the environment. Complete
model validation requires testing over the
full range of conditions for which pre-
dictions are intended. At a minimum, this
requires a series of validations in various
aquatic environments (streams, lakes,
estuaries) with chemicals that typify the
major fate and transport process. Vali-
-------
Table 1. Steps in Field Validation of Aquatic Fate and Transport Models
Step 1. Identify Model User's Needs: The first step in field validation is to obtain a clear
understanding of the model user's needs and how the model would be used.
Step 2. Develop Acceptance Criteria for validations: The potential model user should provide
criteria against which the model is to be judged.
Step 3. Examine the Model: This step involves a detailed examination of the model to precisely
define input data requirements, output predictions and model assumptions.
Step 4. Evaluate the Feasibility of Field Validation: It may not be feasible to attempt field
validation for some models, and the validator should consider this possibility.
Step 5. Determine Validation Scenario: There are many different approaches to field validation
and a scenario should be identified or approved by the potential model user.
Step 6. Plan and Conduct field validations by performing the following steps:
Step 6a. Select a Site and Compound(s): There are many factors to consider in selecting
a site and compound(s).
Step 6b. Collect Preliminary Data and conduct Sensitivity Analyses: Preliminary data
are required to conduct a sensitivity analysis and determine the most important
input variables.
Step 6c. Develop a Field Study Design: Development of a detailed field sampling plant for
the specific model compound and site.
Step 6d. Conduct Field Study: Implementation of the field plan not addressed in these
guidelines.
Step 6e. Analyze Samples: The document does not provide specific guidance on
analytical methods and quality assurance procedures but references are
provided.
Step 6f. Compare Model Performance with Acceptance Criteria: Graphical and
statistical comparison.
input parameters. The report also briefly
covers the collection of input loading data,
field sampling for predicted model out-
puts, and quality assurance. Experience
gained during field validation of the EXAMS
model was used to modify and improve
this document The guidance provided by
this document was constructed for simpli-
fied aquatic fate and transport models, e.g.
EXAMS. However, the steps in field
validation and many of the environmental
measurement techniques would apply to
all aquatic fate and transport models.
dated models are useful in the regulatory
process because they withstand scientific
scrutiny and are defensible in courts of
law.
Much of the information presented in
the first section relates to the identification
of potential problems associated with field
verification of models. Where possible,
solutions or approaches have been sug-
gested, but many problems are specific to
a site, compound, or model and have to be
dealt with individually. An example of the
type of information important in Site and
Compound Selection Criteria, is depicted
in Table 2.
Subsequent sections of this report deal
individually with environmental fate and
transport processes. For each process, the
following information is given: a general
description of the process, a list and dis-
cussion of environmental factors affecting
the process, a list of the priority organic
pollutants for which the process is important
a list of model-specific environmental in-
puts and, finally, field methods for collecting
the model input data Environmental inputs
to several models are listed in Table 3. In
addition. Table 3 includes parameters
which can be important to a specific pro-
cess but are not currently required model
Table 2. Compound and Site Selection Criteria
Compound Factors
Analytical methods
Compound inputs
Environmental Fate
Compound Toxicity
Source
Site Factors
Traceable
- Methods must exist for quantifying the input loadings to the model and the concentration of the compound in environmental
media.
- The availability of compound specific inputs such as aqueous solubility, degradation rate constants is a factor in selecting
compounds.
- The predicted half-life of the compound by each fate and transport process must be considered relative to the time which the
compound can be followed. Ideally, the compound should be tracked through several half-lives.
- The least toxic compound representative of a given process should be selected.
- Select compounds that exist in concentrations that can be tracked in aquatic systems. Although many compounds have been
detected in effluents, relatively few, have been found in easily detectable levels in receiving waters.
- The compound of interest must be present in sufficiently high levels to be traced for considerable time or distance. Factors
influencing traceability include input load, water body size, flow rate, half-life, mixing and dilution.
Ability to collect - The collection of most site specific model input data presents no unusual problems. However, particular consideration should
data be given to mixing, flow sediment transport ground water movement weather, season, size of the water body and access.
Historical site - If historical data are available, they can be used to conduct preliminary sensitivity analyses. Depending upon the amount and
data type of data, it may not be necessary to conduct a preliminary sampling study.
Input loadings - The pollutant load to the system must be known. The accuracy of these data will depend upon the types and number of
sources, their relative loading, and their variability.
Analytical problems - Chemicals found in the water body to be studied may interfere with analyzing for the compound of interest. Samples or
environmental media should be analyzed prior to any major field effort
-------
Table 2.
(Continued)
Model assumptions
Type
Simplicity
- Conditions at the site should not violate model assumptions. Proper site and compound selection offers an opportunity to
design around some model assumptions.
- Compounds with short or long half-lives can easily be studied in small, well-mixed pounds. Rivers or streams are best suited to
test the degradation or transport of short lived compounds. Long lived compounds should only be used to test physical
transport and bioconcentration processes. It is usually impossible to track long lived compounds through several half-lives in
rivers or streams.
- Generally, the simpler the site in terms of the amount of data that must be obtained, the more cost effective the validation
effort. Multiple sources may significantly increase expense of collecting data, increase input data and complicate data
interpretation.
Table 3. Environmental Inputs by Process, to Aquatic Fate and Transport Models
Biotransformation
Temperature (C)
Total Bacteria Pop. (Cells/ml) or (Cells/100 g dry sed.)
Active Degrading Pop. (% of Total)
Nutrients C/N. P (mg/lj
Acclimation State
PH (pH Units)
Dissolved Oxygen (mg/l)
Hydrolysis
POH (pH Units)
PH fpH Units)
Temperature (C)
Oxidation
Temperature (C)
Oxidant Concentration (moles/1)
Reaeration (cm/hr)
Suspended Paniculate (mg/l)
Dissolved Oxygen (mg/l)
Dissolved Organic Carbon (mg/l)
Photolysis
Depth (m)
Chlorophyll (mg/l)
Latitude (degrees)
Cloudiness (tenths)
Dissolved Organic Carbon (mg/l)
Suspended Sediment (mg/l)
Spectral light intensity at surface
Altitude (m)
Temperature (C)
Time of Day (24 hr time)
lonization
POH (pH Units)
PH (pH Units)
Temperature (C)
Total Dissolved Solids (mg/l) Ionic Strength
Volatilization
Temperature (C)
Compartment Dimensions, area and volume
Mixing Reaeration Rate (cm/hr)
Wind (m/s)
Slope (m/m)
Water Velocity (m/s)
Sediment Sorption
Organic Carbon Content (% of dry sediment)
Percent Water of Benthic Sediment
(100 FreshWt.)
( Dry Wt. )
Bulk Density Benthic Sed. (g/cc)
Suspended Sediment (mg/l)
Compartment Dimensions ft Areas
Cation Exch. Cap. (meg/100 g dry sediment)
Anion Exch. Cap. (meg/100 g dry sediment)
Particle Size (mm)
PH of Sediment (pH Units)
Bioconcentration
Total Biomass (mg/l or g/m2)
Planktonic Biomass (fraction of total)
Fish (g/m3)
Water Bugs (g/m3)
Zooplankton (g/m3)
Phytoplankton (g/m3)
Paniculate Organic Matter (g/m3)
Floating Particulates Organic Matter (g/m3)
Floating Macrophytes (g/m3)
Dissolved Organic Matter (g/m3)
Zoobenthos (g/m3)
Chlorophyll a (mg/l)
Fish by species (g/m3)
Fish by Age or Size Class (g/m3)
Periphyton (g/m3)
Zoobenthos by Functional Group (g/m3)
Temperature (C)
Dissolved Oxygen (mg/l)
Macrophytes, Rooted (g/m3)
Physical Transport
Evaporation-(mm/month)
Interflow (m3/hr)
NFS Sediment Load (kg/hr)
NFS Water Load (m3/hr)
Percent Water of Bottom Sed.
(100 x fresh/dry Wt. sed.)
Rainfall (mm/month)
Suspended Sediment (mg/l)
Bulk Density Bottom Sed. (g/cc) Stream Inflow (m3/hr)
Stream Borne Sediment Inflow (kg/hr)
Compartment Volume (m3)
Eddy Diffusivity (m2/hr) Cross Section Area for Dispersive
Exchange (m2)
Surface Area (m2) Dist Between Compt Centers (m)
Compartment Dimensions L W, H (m)
Sediment Bed Load (kg/hr)
Planktonic Biomass (mg/l)
Water Velocity (m/s)
Dissolved Organic Carbon (mg/l)
Bed Load by Part. Size
Classes (%)
Total Organic Carbon (mg/l)
-------
The EPA authors Stephen C. Hern (also the EPA contact, see below). George T.
Flat/nan. Wesley L. Kinney. and Frank P. Beck, Jr., are with the Environmental
Monitoring Systems Laboratory. Las Vegas, NV 89114; James f. Pollard is
with the University of Nevada, Las Vegas, NV 89154; and Alan B. Crockett is
with EG&G Idaho. Inc., Idaho Falls. ID 83415.
The complete report, entitled "Guidelines for Field Testing Aquatic Fate and
Transport Models: Final Report," (Order No. PB 83-222 760; Cost: $19.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
Stephen C. Hern can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas, NV 89114
4US GOVERNMENT PRINTING OFFICE. 1983-659-017/7160
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
2
lON AGENCY
------- |