**FIRST**

**(F)QPA (I)NDEX (R)ESERVOIR (S)CREENING (T)OOL**

ENVIRONMENTAL FATE AND EFFECTS DIVISION

OFFICE OF PESTICIDE PROGRAMS

U.S. ENVIRONMENTAL PROTECTION AGENCY

TIER ONE SCREENING MODEL

FOR DRINKING WATER PESTICIDE EXPOSURE

VERSION 1.1.1

March 26, 2008

![](media/image1.png){width="1.0576388888888888in"
height="1.0291666666666666in"}

USERS MANUAL

# Background for Tiered Modeling System Approach

When developing risk assessments under the Food Quality Protection Act
(FQPA), the Environmental Fate and Effects Division (EFED) of USEPA\'s
Office of Pesticide Programs (OPP) uses a tiered system of exposure
modeling to estimate the concentrations of pesticides in drinking water.
This tiered system is designed to minimize the amount of analysis that
is required to evaluate any given chemical. Each of the tiers is
designed to screen out pesticides by requiring higher, more complex
levels of investigation only for those that have not passed the next
lower tier. Each tier screens out a percentage of pesticides that are
not expected to exceed a level of concern and that will not require a
more rigorous review prior to registration or reregistration.

The first two tiers of drinking water exposure modeling are based upon
the characteristics of a drinking water reservoir located in Shipman,
Illinois (the *Index Reservoir*). This reservoir is representative of a
number of reservoirs in the Midwest that are vulnerable to pesticide
contamination. Thus, the index reservoir scenario represents an
upper-end exposure site for pesticide residues found in drinking water
derived from surface water. (Hetrick, et.al, 1998). Pesticide
concentration values estimated using this scenario should be exceeded
only rarely in the source water at the intake pipe of a community water
supply (CWS) systems in the United States. The first tier, which is
based on a few basic chemical parameters and pesticide label application
information, is designed as a coarse screen and provides conservative
estimates of pesticide concentrations in drinking water. 'Passing' a
given assessment tier indicates that there is a low possibility of risk
to human health. 'Failing' an assessment tier, however, does not mean
the chemical is likely to cause health problems, but that the assessment
should continue on to the next higher assessment tier.

## Description of FIRST

OPP uses the Tier 1 model, **[F]{.underline}**QPA
**[I]{.underline}**ndex **[R]{.underline}**eservoir
**[S]{.underline}**creening **[T]{.underline}**ool (**FIRST**), to
estimate both acute and chronic potential pesticide concentrations in
untreated drinking water. The 'FIRST' program is a metamodel of the more
complex Tier II simulation using the linked PRZM3 (Carsel et. al., 1997)
and EXAMS 2.97.7 (Burns et.al., 2000) models. Being a metamodel, FIRST
requires less time and effort to complete. FIRST considers the most
salient features used in the PRZM/EXAMS Tier II simulations including
the percentage of the watershed that is cropped (percent cropped area -
PCA), spraydrift, sorption of pesticide to field soil and to reservoir
bottom sediment, incorporation of the pesticide at the time of
application, degradation of pesticide in the soil, and degradation of
pesticide within the water body.

## Effect of Kd On Concentration

This Tier 1 program assumes that up to 8% of the pesticide applied to a
427-acre (172.8 hectare) watershed (i.e., the Shipman watershed) is
washed into the reservoir by one large storm. The actual amount, which
appears as the dissolved concentration estimate, is a function of the
equilibrium partition coefficient (K~d~) or the organic carbon
normalized equilibrium partition coefficient (K~oc~). These parameters
describes the equilibrium partitioning of a pesticide between the sorbed
(to soil) phase and the dissolved (in water) phase

The impact on the system of changing the partition coefficient was
determined through sequentially increasing the K~d~ value within
PRZM/EXAMS simulations and then recording the resulting instantaneous
EXAMS reservoir concentration for each value. This procedure produced a
series of dissolved pesticide concentration values as a function of
K~d~. A dissolved vs. sorbed relationship to K~d~ was established and
programmed into FIRST.

The value of the K~d~ parameter in the EXAMS program controls not only
the final equilibrium partitioning of the chemical between the dissolved
and sorbed phases, but also determines the relative rate of approach to
equilibrium. In a non-infinite system (like the EXAMS reservoir), as
K~d~ increases, the rate that a pesticide approaches equilibrium between
the sediment and the water column increases. For very high K~d~ values
(1,000 mL/g or more), the equilibrium is essentially reached within the
first day, while for lower values (1.0 mL/g or less), an equivalent
relative uptake may take almost a year. Each K~d~ value is used to
calculate a pseudo sediment-uptake rate. Sediment uptake within the
reservoir occurs simultaneously with abiotic chemical and biological
degradation.

## Degradation

Degradation in the reservoir is calculated in order to estimate annual
average concentration values for chronic exposure assessment.
Degradation over time is estimated by first-order degradation. The model
considers aerobic aquatic metabolism, abiotic hydrolysis, and aquatic
photolysis. Biological and abiotic degradation of the spray drift
applications (see below) in the reservoir begins immediately.
Degradation of the pesticide reaching the reservoir via runoff begins
two days later (on the day it reaches the reservoir).

## Application Methods

With FIRST, the user can also simulate application by aerial spray, air
blast spray, ground spray or broadcast application of granular material.
For aerial application the program assumes that there is sixteen percent
spray drift directly into the reservoir with 95% landing on the field
(application efficiency). For air blast application to orchards, groves,
and vineyards, FIRST assumes 6.3% spray drift directly into the
reservoir with 99% landing on the field. For ground spray, FIRST assumes
that 6.4% goes directly to the reservoir with 99% being deposited on the
field. For granular broadcast application, 100% application efficiency
is assumed with no pesticide drifting directly to the stream or
reservoir. **NOTE: The application efficiency values and the spray drift
values do not add up to 100% because the application efficiency is a
percentage deposited on each hectare of the watershed and the spray
drift value is a percentage of the application rate.**

The program also accounts for those pesticides which are incorporated at
the time of application. Incorporation reduces the mass of pesticide
available to runoff by a factor equal to the depth of incorporation in
inches up to a maximum of six inches.

## Washout of Pesticide from the Reservoir

FIRST assumes that flow from the watershed is sufficient for two full
reservoir turnovers each year. In other words, the annual flow through
the reservoir is equal to twice the reservoir volume of approximately
144,000 cubic meters. This volume is equivalent to a flow of
approximately 33 cubic meters per hour (EXAMS parameter STFLO) through
the reservoir. The reduction in pesticide concentration as a result of
this flow is related to the partition coefficient (K~d~) of the
chemical. At a K~d~ of 1.0 ml/g or less, the PRZM program simulation
shows an approximate 2.5% reduction of the peak concentration and a 30%
reduction of the annual average concentration. The reduction is greatest
at a K~d~ of 10 ml/g with a 7% reduction of the peak concentration and a
35% reduction of the annual average concentration. Above a K~d~ of
10,000 ml/g, there is no reduction as a result of flow. This reduction
is programmed into FIRST.

# Limitations of FIRST for Drinking Water Exposure Assessments

The FIRST program does not consider the impact of water treatment
processes. Removal and transformation of most pesticides by water
treatment processes is difficult to predict on a consistent basis
because it can vary significantly from CWS to CWS and from day to day in
the same CWS. If consistently high removal across most CWS systems has
been documented for a specific pesticide, FIRST will overestimate
concentrations in drinking water to the extent that removal by treatment
is not estimated by the FIRST model.

FIRST is designed to yield concentration values which exceed those
predicted by the higher-tiered, linked PRZM and EXAMS models for all but
the most extreme sites, application patterns, and environmental fate
properties. PRZM/EXAMS predictions may exceed FIRST predictions under
the following circumstances:

> \(1\) Applications to crops in managed environments known to produce
> excessive runoff (e.g., crops grown over plastic mulch).
>
> \(2\) Applications at sites with hydrologic group D soils which also
> receive excessively high rainfall (e.g., EFED sweet potato scenario in
> southern Louisiana).
>
> \(3\) Multiple applications over a window of 30 days or longer in
> exceptionally high rainfall areas (e.g., far southeastern U.S.). In
> each of these cases, FIRST will usually exceed PRZM/EXAMS estimated
> peak concentrations values, but will not always exceed the annual
> average concentration values. Even when FIRST values do exceed
> PRZM/EXAMS values, the exceedance is not expected to be more than a
> factor of 2.
>
> \(4\) For applications of chemicals with half-life values of 5 days or
> less at exceptionally high runoff sites, the PRZM/EXAMS concentrations
> values may exceed both the FIRST peak and annual average values by a
> factor of 2. Allowing these few exceedances for extreme conditions
> makes FIRST a reasonable predictive tool for the rest of the country.

# Running FIRST

The following description provides the screen images that the FIRST
model produces, with an \"\-\--\>\" at each point where the user needs
to provide input. Instructions for entering data and using the program
are shown in bold text.

**Begin by creating a \'FIRST\' subdirectory at the desired location and
coping the program \'FIRST.EXE\' to that subdirectory. The program can
be run under any Windows environment. To run FIRST, go to the program
and click on FIRST.EXE. This will lead to the following opening
screen:**

FIRST

(F)QPA (I)NDEX (R)ESERVOIR (S)CREENING (T)OOL

ENVIRONMENTAL FATE AND EFFECTS DIVISION

OFFICE OF PESTICIDE PROGRAMS

U.S. ENVIRONMENTAL PROTECTION AGENCY

TIER ONE SCREENING MODEL

FOR DRINKING WATER PESTICIDE EXPOSURE

VERSION 1.1.1

March 26, 2008

THIS IS A PROGRAM TO ESTIMATE TIER ONE, ACUTE AND CHRONIC

CONCENTRATION VALUES FOR PESTICIDES IN DRINKING WATER BASED

UPON AN INDEX RESERVOIR LOCATED IN SHIPMAN, ILLINOIS

THE PROGRAM IS USED TO ESTIMATE CONSERVATIVE EXPOSURE

VALUES FOR PESTICIDES IN ANY AREA OF THE UNITED STATES

PLEASE ENTER A RUN NUMBER TO CONTINUE ‑‑‑\>

The run number is a bookkeeping aid to allow the user to keep track of
multiple consecutive runs; any integer may be entered. This number will
appear on the output screen and in the output file to identify each run
of the program. The run number is not used for any calculation.

ENTER AN OUTPUT FILE NAME ‑‑‑\>

**The choice of a name for the output file is up to the user. Typical
output files names would be: Metolachlor_Corn.TXT or CAPTAN_Tomato.TXT.
If the same output file name is used in successive runs, the new output
file will write over the old file and the old one will be lost. To save
an older output file, give each new file a new, different name. The
output file will be stored in the same directory in which the FIRST
program is located. To insert a FIRST output file into with a
word-processed report (i.e. MSWord^®^ or WordPerfect®),** set the font
to *Courier* to maintain the needed spacing between alphabetic and
numeric characters.

PLEASE ENTER THE CHEMICAL NAME ‑‑‑\>

**Use either the common or chemical name. The structure is optional; use
whatever is the most easily understood. This name will become part of
the output file.**

PLEASE ENTER THE CROP NAME \-\--\>

**Enter the name of the crop. The name specified is used only for
documentation purposes, and is not currently checked against a database
of possible values.**

THE PROGRAM ASSUMES THAT RAINFALL AND RESULTING RUNOFF ARE

SUFFICIENT TO REMOVE UP TO 8 % OF THE PESTICIDE

FROM THE PORTION OF THE 427 ACRES (172.8 HECTARES) OF

FIELDS IN THE RESERVOIR WATERSHED WHERE THE CROP IS GROWN

THE PORTION OF THE CHEMICAL THAT IS REMOVED FROM THE FIELDS

IN THIS WAY, FLOWS INTO THE RESERVOIR AND IS DISSOLVED IN

THE RESERVOIR WATER

THE CHEMICAL CONCENTRATION IN THE RESERVOIR REPRESENTS THE

PART THAT IS DISSOLVED AND NOT BOUND TO FIELD SOIL OR TO

RESERVOIR BOTTOM SEDIMENTS

THE FOLLOWING INFORMATION SHOULD BE TAKEN FROM THE MOST

CURRENT, ACCEPTED LABEL FOR THE USE SITE IN QUESTION

PLEASE ENTER APPLICATION RATE (IN POUNDS a.i. PER ACRE)\-\--\>

**In most cases, this will be the maximum rate permitted by the label.
Situations may also arise when it is desirable to use an average or
typical application rate or some other rate less than the maximum
rate**. **To use a rate in units of kilograms per hectare, enter a value
of "zero" (0) at the prompt, and you will be asked for a metric rate.**

ENTER MAXIMUM NO. OF APPLICATIONS PERMITTED PER YEAR‑‑‑\>

**The maximum number of applications or maximum pounds of pesticide is
included in most labels. If the maximum annual mass is given on the
label, divide this by the application rate to find the number of
applications. A situation may also arise when it is desirable to use an
average or typical number of applications. If the number of applications
entered is greater than one, the following will be requested:**

ENTER INTERVAL BETWEEN APPLICATIONS (DAYS) \-\--\>

**Use the minimum interval permitted by the label or the typical
interval in practice in the area of use, whichever is most appropriate.
If not specified on the label, the interval may be available directly
from the chemical manufacturer or from county extension agents in use
areas. The source of the data should be documented.**

THE AMOUNT OF PESTICIDE IN THE WATERSHED AVAILABLE FOR

WASHOFF BY RAINFALL INTO THE RESERVOIR IS DEPENDENT ON

ON EXTENT OF THE WATERSHED ON WHICH THE CROP IS GROWN.

THE PROGRAM REPRESENTS THIS AREA BY A PERCENT CROPPED AREA

(PCA) FACTOR FOR THE CROP AS FOUND IN THE FOLLOWING LIST:

CORN 0.46 CORN‑SOY 0.83 CORN‑SOY‑WHEAT 0.83

SOYBEANS 0.41 CORN‑WHEAT 0.56 CORN‑SOY‑COTTON 0.83

WHEAT 0.56 CORN‑COTTON 0.46 SOY‑WHEAT‑COTTON 0.58

COTTON 0.20 SOY‑ WHEAT 0.56 SOYBEANS‑COTTON 0.49

WHEAT‑COT 0.20

ALL OTHER 0.87

PLEASE ENTER THE APPROPRIATE PCA FACTOR (DECIMAL) ‑‑‑\>

**Enter the decimal value corresponding to the percent of the area of
the index watershed in which the crop is grown. This value is a maximum
value from remotely sensed data.**

**The program assumes the pesticide degrades in the field by the aerobic
soil metabolism rate after one application and between multiple
applications. The actual amount of available pesticide that is washed
from the field into the reservoir depends upon the number of
applications. For a single application, it is the amount remaining after
two days (zero days for pesticides for which the label specifies
application prior to rainfall or irrigation). For more than one
application, it is the amount in the field after the last application,
assuming degradation of previous applications for the length of time
each was in the field.**

**The next input requested is the equilibrium partition coefficient for
the chemical:**

THE DISSOLVED PESTICIDE CONCENTRATION IN THE RESERVOIR IS

CALCULATED BY SUBTRACTION OF THE PORTION OF THE CHEMICAL

THAT IS BOUND TO FIELD SOIL, TO FIELD ORGANIC MATTER, OR

TO RESERVOIR BOTTOM OR SUSPENDED SEDIMENT.

THIS BOUND FRACTION IS ESTIMATED BY USE OF THE SOIL/WATER

EQUILIBRIUM PARTITION COEFFICIENT (Kd) OR THE ORGANIC

CARBON NORMALIZED SOIL/WATER EQUILIBRIUM PARTITION

COEFFICIENT (Koc).

SEE THE FIRST PROGRAM USERS MANUAL FOR THE APPROPRIATE Kd

OR Koc VALUE TO USE.

TO USE A Kd VALUE, PLEASE ENTER IT HERE. TO USE A Koc

VALUE, PLEASE ENTER ZERO (0) ‑‑‑\>

**Sorption and desorption (pesticide binding to soil) tests are
performed on soils of different textural classes, pH's, and organic
matter contents. Either the soil/water partition coefficient (Kd) or the
organic carbon normalized soil/water equilibrium partition coefficient
(Koc) can be used to estimate the dissolved and the adsorbed fraction
for any chemical. To use a Kd value, choose the lowest of the Kd values
that was measured on a non‑sand texture soil (not sand, coarse sand,
fine sand, sandy loam or loamy sand). This will result in a realistic
yet conservative water column exposure value. If an appropriate value
for Kd is available, enter it here. If not, enter a value of zero (0) at
the prompt and you will be asked for a Koc value:**

PLEASE ENTER THE APPROPRIATE Koc VALUE \-\--\>

**The organic carbon normalized, soil/water equilibrium partition
coefficient (Koc) may also be used in lieu of the Kd value. The Koc of
choice, when two or more are available, is the lowest Koc value measured
on a non‑sand texture soil (see above). When in question, the actual
number to be used should be decided in discussion with EFED
environmental fate scientists. The Kd / Koc conversion is based on an
organic matter content of 2 % and an organic carbon content of 1.16 %.
If neither the Kd nor the Koc is available, use 0.35 times the Kow
value.**

THE DISSOLVED PESTICIDE CONCENTRATION IS ALSO REDUCED

BY DEGRADATION IN THE FIELD PRIOR TO A RAINFALL/RUNOFF

EVENT - THE PROGRAM ASSUMES DEGRADATION BY AEROBIC

METABOLISM FOR TWO DAYS AFTER THE FINAL APPLICATION

(IF STABLE TO AEROBIC METABOLISM OR IF DATA IS

UNAVAILABLE, PLEASE ENTER ZERO (0))

ENTER SOIL AEROBIC METABOLIC HALF-LIFE (IN DAYS) \-\--\>

**There are often multiple half-life values from tests performed on a
variety of soil types. In order not to underestimate the actual value,
EFED policy is to use an upper 90% confidence limit on the mean value.
The aerobic metabolic half-life value used in FIRST is calculated by the
following formula:**

**if n = 1: single value × 3**

**n = number of half-life values**

**if n ≥2: µ + t~90~ × σ / √n, where**

**µ = mean of the half-life values**

**t~90~ single tail student\'s t, α= 0.1 (Table 1 below, n-1 d.o.f.)**

**σ = standard deviation of the n half-life values, and**

+-----------------------------------+-----------------------------------+
| **Number of Half-life Values      | **t90 Single Tail Student\'s      |
| (n)**                             | "t"**                             |
|                                   |                                   |
|                                   | **(n-1 degrees of freedom)**      |
+-----------------------------------+-----------------------------------+
| **2**                             | **3.078**                         |
+-----------------------------------+-----------------------------------+
| **3**                             | **1.886**                         |
+-----------------------------------+-----------------------------------+
| **4**                             | **1.638**                         |
+-----------------------------------+-----------------------------------+
| **5**                             | **1.533**                         |
+-----------------------------------+-----------------------------------+
| **6**                             | **1.476**                         |
+-----------------------------------+-----------------------------------+
| **7**                             | **1.440**                         |
+-----------------------------------+-----------------------------------+

SOME PESTICIDE LABELS REQUIRE THAT THE PESTICIDE BE

WETTED-IN EITHER THROUGH RAINFALL OR IRRIGATION:

IN THIS CASE, RUNOFF TO THE RESERVOIR IS ASSUMED TO

OCCUR IMMEDIATELY RATHER THAN AFTER TWO DAYS

IS THIS PESTICIDE TO BE WETTED-IN ? (Y or N) \-\--\>

**Choose the appropriate response based on the label. Some pesticides
must be activated by water. If so, this will be specified on the label.
In this case, the pesticide enters the pond on the day of the final
application rather than two days after the final application.**

**In the next section of the model, spray drift is added to the stream
and reservoir.**

THE DISSOLVED PESTICIDE CONCENTRATION MAY BE INCREASED BY

DEPOSITION OF SPRAY DRIFT EITHER DIRECTLY INTO THE RESERVOIR

OR INTO THE STREAMS THAT FLOW INTO THE RESERVOIR

PLEASE ENTER A, B, C, or D TO SELECT METHOD OF APPLICATION:

A: AERIAL SPRAY (DRIFT=16.0%; APPLICATION EFFICIENCY=95%)

B: GROUND SPRAY (DRIFT=6.4%; APPLICATION EFFICIENCY=99%)

C: ORCHARD‑VINYARD AIRBLAST SPRAY (DRIFT=6.3%; APP EFF=99%)

D: GRANULAR (DRIFT=0.0%; APPL. EFFICIENCY=100%) ‑‑‑\>

**Pesticide applied as a granular product or as a ground spray may be
incorporated into the soil by various types of equipment driven or
pulled through the field. The following section allows the model user to
simulate the impact of physical incorporation on the amount of pesticide
that runs off the field and is dissolved in the water-body: If the
Method = B (Ground spray) or D (Granular (Non-spray)), then the
following will be asked:**

THE DISSOLVED PESTICIDE CONCENTRATION MAY BE REDUCED BY

INCORPORATION OF THE PESTICIDE AT THE TIME OF APPLICATION

IN THIS CASE, THE FOLLOWING DEPTHS ARE SUGGESTED:

[METHOD OF APPLICATION]{.underline} [INCORPORATION DEPTH
(IN)]{.underline}

BROADCAST 0.0

DISKED IN AFTER BROADCAST 4.0

CHISEL PLOWED AFTER BROADCAST 6.0

SURFACE BANDED 0.0

BANDED - INCORPORATED 1.2

T - BANDED 1.5

IN FURROW 2.0

AERIAL or AIRBLAST SPRAY 0.0

GROUND SPRAY DEPENDS ON METHOD

PLEASE ENTER DEPTH OF INCORPORATION (IN INCHES) \-\--\>

**The method of application will be specified on the label. Enter one of
the suggested depths based on label instructions. The program limits the
depth of incorporation to six inches. If more than one application
method is possible, use the one which calls for the most shallow depth
of incorporation.**

THE SOLUBILITY OF A PESTICIDE IN WATER IS A MEASURE OF THE

MAXIMUM AMOUNT OF THE CHEMICAL THAT CAN BE DISSOLVED

THUS, THE AQUEOUS CONCENTRATION IN A WATER BODY

CANNOT EXCEED THE SOLUBILITY OF THE CHEMICAL.

PLEASE ENTER THE SOLUBILITY (IN PPM) ‑‑‑\>

**This number does not actually affect the exposure estimate *unless*
for some reason the estimated exposure concentration is greater than
this value. If so, the EEC will be automatically reduced to the maximum
solubility**.

THE CHRONIC DRINKING WATER PESTICIDE CONCENTRATION VALUE

IS ESTIMATED USING A DEGRADATION RATE THAT IS CALCULATED

BY SUMMING THE INDIVIDUAL AQUATIC DEGRADATION RATES (THE AEROBIC

AQUATIC METABOLIC RATE IS ASSUMED TO INCLUDE HYDROLYSIS)

ENTER ANY OR ALL OF THE FOLLOWING THAT ARE AVAILABLE:

(PLEASE ENTER ZERO (0) FOR ANY THAT ARE STABLE OR

FOR WHICH VALUES ARE UNAVAILABLE)

ENTER AEROBIC AQUATIC METABOLIC HALF-LIFE IN DAYS (IF

UNAVAILABLE, THE RECOMMENDED EFED DEFAULT IS 2 TIMES

THE AEROBIC SOIL INPUT VALUE) ‑‑‑\>

**If there is a range of half-lives, the half-life entered here is
usually the longest one that would result in the highest exposure. If
this value is not available or if the test was performed in a
water/sediment system rather than a water-only system, the appropriate
value is twice the aerobic soil half-life.** **If the choice is unclear,
the actual value used should be decided in discussion with OPP/EFED
environmental fate scientists.**

PLEASE ENTER pH 7 HYDROLYSIS HALF-LIFE (DAYS) \-\--\>

**The program requests the hydrolysis half-life value only if the
aerobic aquatic half-life value entered is zero. Otherwise the program
assumes the aerobic aquatic value includes the hydrolysis value. If
there is a range, the half-life entered here is usually the longest one,
that would result in the highest exposure. However, the actual number
used should be decided in discussion with EFED environmental fate
scientists.**

ENTER PHOTOLYSIS HALF-LIFE (DAYS) \-\--\>

**The half-life entered here is usually the longest one, which would
result in the highest exposure. However, the actual number used should
be decided in discussion with EFED environmental fate scientists. The
effective photolysis half-life will be 124 times longer than the one
entered in the program due to light attenuation in the reservoir.**

**Check over the output on the screen to ensure that all the values are
those that you wished to enter. The \"output\" will be saved to the
designated output file name *as it appears on the screen*.**

**At the bottom of the output screen is the following question:**

DO YOU WANT TO DO ANOTHER RUN (Y OR N) ‑‑‑\>

**If you wish to perform another simulation before leaving the program,
answer 'Y' to this question. If you continue to perform additional
simulations, results will be added to the end of the output file named
in the first run. You will be prompted to enter a new run for each
additional simulation:**

PLEASE ENTER A NEW RUN NUMBER ‑‑‑\>

**As above, the run number is a bookkeeping aid to allow the user to
keep track of multiple consecutive runs; any whole number may be
entered. This number will appear on the output screen and in the output
file to identify each run of the program. The run number is not used for
any calculation.**

**If you do not wish to perform another simulation before leaving the
program, answer 'N' to the previous question.**

**After entering a new run number, the program will start over and will
ask for the chemical name, etc. These results will be added to the
bottom of the existing output file. None of the inputs from the previous
run are saved and therefore must be entered again for subsequent runs.**

**RETRIEVING OUTPUT FILES**

Once you have finished running FIRST and have exited the program, the
output is automatically saved under the file name you specified in your
FIRST subdirectory.

This file may be retrieved and printed with any text editor or word
processing program. To insert the FIRST output file into a MSWord® or
WordPerfect® report, set the font to *Courier* to maintain the needed
spacing between alphabetic and numeric characters. Once retrieved , it
may be inserted directly into reviews and science chapters or printed
and included as an attachment.

**USING 'FIRST' RESULTS**

The program yields two values as output: The peak day concentration
value is an upper-end, conservative estimate for use in an acute
exposure assessment. The annual average concentration value is used as
an upper-end, conservative estimate for use in a chronic (including
cancer) exposure assessment.

**BIBLIOGRAPHY**

1 Burns, L.A. 2000. Exposure Analysis Modeling System (EXAMS),
Environmental Research Laboratory, Office of Research and Development,
U.S. Environmental Protection Agency, Athens, GA.

2.  R.F. Carsel, J.C. Imhoff, P.R. Hummel, J.M. Cheplick and J.S.
    Donigian, Jr. 1997. PRZM-3, A Model for Predicting Pesticide and
    Nitrogen Fate in Crop Root and Unsaturated Soil Zones: Users Manual
    for Release 3.0; Environmental Research Laboratory, Office of
    Research and Development, U.S. Environmental Protection Agency,
    Athens, GA.

3.  J. Hetrick, 1998. [Scientific Advisory Panel (SAP): Final Report for
    the July 1998 Meeting: Part
    1](http://www.epa.gov/scipoly/sap/meetings/1998/july/final1.pdf);
    <http://www.epa.gov/scipoly/sap/meetings/1998/july/final1.pdf>