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1. Maximum X value cm Maximum Time Value day2. cc g 0 73000E 01 Saturated water content oooooccnncccnonccconnncnonccnnnacinnncnns 0 39500E 00 Solid phase decay hr sess 0 22200E 03 Liquid phase decay hr sss 0 22200E 03 Curve coefficient anita 0 40500E 01 Bulk density g cc eee 0 15000E 01 Dispersion coefficient cm hr sssss 0 60000E 01 Saturated hydraulic conductivity 0 10000E 01 Minimum depth cm eene 0 00000E 00 Maximum depth CM eee 0 20000E 03 Minimum time day 0 00000E 00 Maximum time day sse 0 50000E 03 For application 1 the active ingredient ai applied is 0 112E 02 kg ai ha and has been applied 0 000E 00 days prior to recharge Results Projected water content 0 237E 00 Pore water velocity cm hr 0 147E 01 Pollutant velocity cm hr ene 0 101E 01 Length of pollutant slug cm 0 414E 01 Mass decayed prior to recharge kg 0 000E 00 Time 0 50E 02 days Depth cm Cw mg l Cs mg kg Ctot mg l 2 000 0 65E 01 0 47E 00 0 22E 01 20 000 0 79E 01 0 57E 00 0 27E 01 40 000 0 21E 00 0 15E 01 0 72E 01 60 000 0 19E 03 0 14E 04 0 67E 04 80 000 0 00E 00 0 00E 00 0 00E 00 100 000 0 00E 00 0 00E 00 0 00E 00 120 000 0 00E 00 0 00E 00 0 00E 00 140
3. 000 0 00E 00 0 00E 00 0 00E 00 21 Mass balance results for the total pollutant within the soil is given for each defined time value The mass balance output describes the mass of pollutant in the liquid phase the solid phase the total mass of pollutant remaining and the loss of pollutant due to decay An example of the mass balance output is shown below Mass Balance Results 0 590E 01 0 272E 01 0 862E 01 0 172E 01 Pollutant remaining in liquid phase kg Pollutant remaining in solid phase kg Total mass of pollutant remaining kg Liquid phase decay of pollutant kg The total mass of pollutant remaining is the sum of the mass of pollutant in the liquid phase and solid phase It should be noted that the loss of pollutant due to decay can occur prior to the pollutant leaching into the soil Therefore if the rate of decay is rapid and the time prior to recharge is sufficiently long it is possible for significant losses of mass to result prior to leaching Likewise since leaching is a function of the water velocity a quantity of mass may remain outside the soil system especially at times in the beginning of the simulation Thus the sum of the total mass of pollutant remaining and the loss of pollutant due to decay may not equal the total applied In addi tion losses due to leaching the pollutant from the defined depth interval will result in differences between the sum of the total mass of pollutant
4. 000 0 00E 00 0 00E 00 0 00E 00 160 000 0 00E 00 0 00E 00 0 00E 00 180 000 0 00E 00 0 00E 00 0 00E 00 200 000 0 00E 00 0 00E 00 0 00E 00 Mass Balance Results Pollutant remaining in liquid phase kg 0 590E 01 Pollutant remaining in solid phase kg E 0 272E 01 Total mass of pollutant remaining kg 0 862E 01 Liquid phase decay of pollutant kg 0 172E 01 31 Time 0 15E 03 days Mass Balance Results Time 0 30E 03 days Mass Balance Results Depth cm 2 000 20 000 40 000 60 000 80 000 100 000 120 000 140 000 160 000 180 000 200 000 Cw mg l 0 59E 00 0 28E 01 0 42E 01 0 17E 01 0 17E 00 0 46E 02 0 00E 00 0 00E 00 0 00E 00 0 00E 00 0 00E 00 Cs mg kg 0 43E 01 0 20E 00 0 31E 00 0 12E 00 0 13E 01 0 33E 03 0 00E 00 0 00E 00 0 00E 00 0 00E 00 0 00E 00 Pollutant remaining in liquid phase kg Pollutant remaining in solid phase kg Total mass of pollutant remaining kg Liquid phase decay of pollutant kg Depth cm 2 000 20 000 40 000 60 000 80 000 100 000 120 000 140 000 160 000 180 000 200 000 Cw mg l 0 26E 01 0 17E 00 0 72E 00 0 16E 01 0 17E 01 0 94E 00 0 27E 00 0 38E 01 0 27E 02 0 78E 04 0 00E 00 Cs mg kg 0 19E 01 0 12E 01 0 53E 01 0 11E 00 0 12E 00 0 69E 01 0 19E 01 0 28E 02 0 20E 03 0 57E 05 0 00E 00 Pollutant remaining in liquid phase kg Pollutant remaining in solid phase kg Total mass of pollutant remaining kg
5. 1982 Jones and Back 1984 Melancon et al 1986 Although the model is based on a simple analytical solution it may be useful in making preliminary assessments as long as the user is fully aware of its assumptions and limitations Therefore it is the principal objective of this User s Guide to provide essential information on the aspects such as model conceptualization model theory assumptions and limitations determination of input parameters analysis of results and sensitivity analysis parameter studies With the information presented it is hoped that this manual will help the user in making the best possible use of the model 2 MODEL CONCEPTUALIZATION ASSUMPTIONS AND LIMITATIONS The vertical transport of dissolved pollutants through the vadose zone is simulated in PESTAN as a slug of contaminated water that migrates into a homogeneous soil see Figure 2 1 The concentration of the chemical slug equals the solubility of the pollutant in water and the thick ness of the slug is conceptualized principally as the volume of pore water required to dissolve the total available pollutant mass at the solubility of the pollutant The total available mass is defined as that mass existing at the time of recharge When no lapse of time occurs between the application and recharge the total mass available will equal the applied mass see Figure 2 2a However when a significant time lapse occurs between the application and recharge events there
6. 25 25 mg l 20 15 10 Concentration ppb Time day Figure 8 1 The effect of solubility on the leachate breakthrough 23 80 7 Sorption Constant ES 252 10 ml g J 25 ml g 60 40ml g D e J a l 4 fe E E 404 5 S J o0 B O S o a O 207 a 0 100 200 300 400 500 600 Time day Figure 8 2 The effect of sorption constant on the leachate breakthrough 40 7 J Recharge Rate MEN gt gt gt gt 2 cm hr 3 cm hr 30 4cm hr j D a 4 a q S 4 g 4 S 20 7 4 S 2 O D e o 4 O 105 N 0 AO 0 100 200 300 400 500 600 Time day Figure 8 3 The effect of recharge rate on the leachate breakthrough 24 30 Saturated Hyd Cond Naren cae 1 cm hr 5 cm hr 25 cm hr a 20 a J S J Es J 5 J e amp El D J 2 o 104 OQ j A E 100 200 300 400 500 600 Time day Figure 8 4 The effect of saturated hydraulic conductivity on the leachate breakthrough 304 J Liquid phase Decay 254 sip Eta 2x 10 4 hr J 1x 103 hr zm J 5x 103 hr OB 5 amp 207 a j gt J e J 3 S 154 B B g j o j 2 J 104 u s Q0 Ir 5 100 200 300 400 500 600 Time day Figure 8 5 The effect of liquid phase decay constant on the leachate breakthrough 25 40 J Dispersion Coefficient d 2 E 2
7. remaining and the loss of pollutant due to decay and the total mass applied 7 3 Graphical output displays Using commercial graphics packages three graphs can be plotted using the output from the model simulation PESTAN automatically writes output data to three files named LEACHBTC DAT LEACHFLX DAT and SOILCON DAT The file LEACHBTC DAT contains the pollutant concentration versus time array for the specified depth LEACHFLX DAT consists of the pollutant flux versus time array for the specified depth The file SOILCON DAT contains the values for pollutant concentration versus depth array for the specified time 22 8 SENSITIVITY ANALYSIS A sensitivity analysis was performed to evaluate the effects of various model inputs on the model response concentration profiles This was accomplished by plotting the model simulations for three different values for each parameter These correspond to low typical and high values for each parameter The results are shown in Figures 8 1 through 8 9 It is seen that the model is most sensitive to changes in recharge values It is also quite sensitive to the changes in sorption coeffi cient dispersion coefficient and decay values The model is relatively insensitive to solubility saturated hydraulic conductivity and characteristic curve coefficient Figures 8 1 8 4 and 8 7 as evidenced by the overlapping of the curves corresponding to three different parameter values 30 Solubility
8. 0000E 03 Saturated hydrualic conductivity 0 10000E 01 Minimum depth cm esee 0 00000E 00 Maximum depth CM eese 0 20000E 03 Minimum time day eee 0 00000E 00 Maximum time day eese 0 50000E 03 For application 1 the active ingredient ai applied is 0 112E 02 kg ai ha and has been applied 0 000E 00 days prior to recharge After the summary of the model scenario the output lists the calculated values that define the water and pollutant conditions within the soil These parameters are 1 the projected water content 2 the pore water velocity 3 the pollutant velocity and 4 the length of pollutant slug An example of the output defining the water and pollutant conditions within the soil is shown below Project water content esse 0 237E 00 Pore water velocity cem hr ooococcccoccnoccconononancnnncnnno 0 147E 01 Pollutant velocity CM HL ocooccnococincncnonononnnooncnnnnnono 1 0 101E 01 Length of pollutant slug CM k 0 414E 01 Mass decayed prior to recharge kg 0 000E 00 20 1 The projected water content q is calculated from the following relationship 0 9 jE abe r lt Ks 13 0 20 r gt K where r is the rate of infiltration 2 The pore water velocity v describes the rate of movement of the interstitia
9. 5 cm hr 50 cm hr a 307 75 cm2 hr m a 4 a 4 c 4 2 Ss 207 B E 4 oO 4 o 4 ra o 4 O B 104 Oe ee ee 0 100 200 300 400 500 600 Time day Figure 8 6 The effect of dispersion coefficient on the leachate breakthrough 304 J x Curve Coefficient J ee 254 PA 5 0 a 6 0 d m on 70 2 202 a J 5 l J od 154 l B d g 4 o0 eal 104 O J J 54 J 4 N J 3 a 0 HA 5 5 gt 2 m E an mn m m m 100 200 300 400 500 Time day Figure 8 7 The effect of characteristic curve coefficient on the leachate breakthrough 26 30 Porosity PR EE 0 30 0 35 recep amp 207 a 4 4 e 4 2 S J E 5J oO 4 9 S 10 O jn 100 200 300 400 500 600 Time day Figure 8 8 The effect of porosity on the leachate breakthrough 404 Bulk Density Be ee d 1 50 g cc gt 1 65 g cc 304 1 75 glec f e J a De 4 a all a a E 204 B g J D J 9 d J O a O 10 Ee e 0 100 200 300 400 500 600 Time day Figure 8 9 The effect of soil bulk density on the leachate breakthrough 27 28 9 SAMPLE PROBLEM The following application of PESTAN is based on the study of Jones and Back 1984 Soil and water monitoring studies were conducted to characterize the movement
10. 7 no 6 pp 331 314 Clapp R B and G M Hornberger 1978 Empirical Equations for Some Soil Hydraulic Properties Water Resources Research vol 14 no 14 pp 601 604 Donigian A S Jr and P S C Rao 1986 in Vadose Zone Modeling of Organic Pollutants Chapter 1 eds S C Hern and S M Melancon Lewis Publishers Chelsea MI Enfield C G R F Carsel S E Cohen T Phan and D M Walters 1982 Approximating Pollutant Transport to Ground Water Ground Water vol 20 no 6 pp 711 722 Jones R L and R C Back 1984 Monitoring Aldicarb Residues in Florida Soil and Water Environmental Toxicology and Chemistry vol 3 pp 9 20 Jury W A 1986 in Vadose Zone Modeling of Organic Pollutants Chapter 11 eds S C Hern and S M Melancon Lewis Publishers Chelsea MI Li E A V O Shanholtz and E W Carson 1976 Estimating Saturated Hydraulic Conductiv ity and Capillary Potential at the Wetting Front Department of Agricultural Engineers Virginia Polytechnic Institute and State University Blacksburg VA McCuen R H W J Rawls and D L Brakensiek 1981 Statistical Analysis of the Brooks Corey and the Green Ampt Parameter Across Soil Textures Water Resources Research vol 17 no 4 pp 1005 1013 Melancon S M J E Pollard and S C Hern 1986 Evaluation of SESOIL PRZM and PESTAN in a Laboratory Column Leaching Experiment Environmental Toxico
11. 7 8e03 0 0035 7 3e 02 2 22e 04 2 22e 04 1 50 0 395 4 05 1 0 0 06 0 0 200 0 0 0 500 0 Water solubility mg l Recharge cm hr Sorption constant cc g Solid phase decay rate constant hr Liquid phase decay rate constant hr Bulk density g cc Porosity cc cc Characteristic curve coefficient Saturated hydraulic conductivity cm hr Dispersion coefficient cm 2 hr Minimum X value cm Maximum X value cm Minimum time value day Maximum time value day Number of time intervals for printing out the results Time values at which output is desired Number of applications of waste Application rate kg ha Starting time of appl day Option for creating a breakthrough curve data Yes No Location at which breakthrough curve is desired cm Option for creating a soil depth profile data Yes No Time at which soil depth profile is desired day 30 TABLE 9 2 RESULTS OF PESTAN SIMULATION FOR THE SAMPLE PROBLEM PESTAN Version 4 0 1992 Developed by Varadhan Ravi and Jeffrey A Johnson Dynamac Center for Subsurface Modeling Support Robert S Kerr Environmental Research Laboratory U S Environmental Protection Agency P O Box 1198 Ada OK 74820 TITLE STUDY OF ALDICARB RESIDUES IN FLORIDA SOIL AND WATER JONES AND Back 1984 Solubility mg l eere 0 78000E 04 Recharge rate cm hr eee 0 35000E 02 Sorption constant
12. Liquid phase decay of pollutant kg 32 Ctot mg l 0 21E 00 0 96E 00 0 15E 01 0 58E 00 0 60E 01 0 16E 02 0 00E 00 0 00E 00 0 00E 00 0 00E 00 0 00E 00 0 438E 01 0 202E 01 0 640E 01 0 466E 01 Ctot mg l 0 90E 01 0 59E 01 0 25E 00 0 54E 00 0 59E 00 0 33E 00 0 92E 01 0 13E 01 0 95E 03 0 27E 04 0 00E 00 0 256E 01 0 118E 01 0 375E 01 0 744E 01 Figure 9 1 Figure 9 2 Leachate breakthrough curves at 3 different depths Depth cm Leachate concentration profiles across depth at 3 different times Concentration ppb en 2 5 150 200 250 4000 3000 2000 1000 0 50 days 150 days 300days 0 2000 4000 6000 8000 10000 12000 Concentration ppb 50 cm 100cm 150cm N 0 FLTTPETTF T TTTTTTT 400 LLLI 600 FLEET 800 PETA 1000 TTT 1200 Time day 29 34 10 11 12 13 10 REFERENCES Biggar J W and D R Nielsen 1976 Spatial Variability of the Leaching Characteristics of a Field Soil Water Resources Research vol 12 no 1 pp 78 84 Brakensiek D L R L Engleman and W J Rawls 1981 Variation Within Texture Classes of Soil Water Parameters Transactions of the American Society of Agricultural Engineers pp 335 339 Campbell G S 1974 A Simple Method for Determining Unsaturated Conductivity from Moisture Retention Data Soil Science vol 11
13. PESTAN Pesticide Analytical Model Version 4 0 Developed for The United States Environmental Protection Agency Office of Research and Development Robert S Kerr Environmental Research Laboratory Center for Subsurface Modeling Support P O Box 1198 Ada Oklahoma 74820 By Varadhan Ravi and Jeffrey A Johnson Dynamac Corporation Readme The following will be consistent throughout the documents distributed by the Center for Subsurface Modeling Support via Acrobat Reader Red text signifies a link Bookmarks have been developed and will vary from document to document and will usually include table of contents figures and or tables Most figures graphics will be included at the end of the document DISCLAIMER The information in this document has been funded wholly or in part by the United States Environmental Protection Agency However it has not yet been subjected to Agency review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred ii ACKNOWLEDGEMENTS We would like to acknowledge the following people for their valuable assistance with this project Dr Carl Enfield Robert S Kerr Environmental Research Laboratory U S Environmental Protection Agency for his valuable support in this revision of PESTAN Patricia Powell Dynamac Corporation for helping with the preparation of the manual Kevin Rumery Dynamac Corporation for his assista
14. R PESTAN INP PESTAN EXE ALDCB1 INP SHOW EXE PESTAN OUT WHAT EXE ALDCBI OUT PMENU BAT LEACHBTC DAT FORMENUI TXT LEACHFLX DAT FORMENU2 TXT SOILCON DAT CHGNAME TXT Prior to installing or implementing the program make a back up copy of PESTAN using the DISKCOPY command of MS DOS or PC DOS Once completed copy the PESTAN files to the hard disk in a selected directory Because the program requires ample storage for the output files approximately 700KB the program should be run from the hard disk In addition a text editor will have to be defined in the AUTOEXEC BAT file The text editor could be DOS edlin DOS edit Norton Classic editor WordPerfect or any other commercial editor Define the text editor in AUTOEXEC BAT including its path For example SET EDITOR C WP5 1 WP Finally the ANSLSYS driver see your MS DOS manual must be installed in the CONFIG SYS file This is done by adding a statement such as DEVICE C DOS ANSLSYS It is important that the correct path for ANSI SYS is given 13 5 1 Program execution PESTAN is executed by typing lt PMENU gt at the appropriate directory prompt C PMENU This will initiate the model execution and a menu of options will be displayed on the screen PESTAN PREPROCESSOR lt lt lt lt Welcome to PESTAN Version 4 0 gt gt gt gt Current Working File NONE INP List of input files Select an input file View the input file Edit Create input file Run
15. ant cannot be determined it can be obtained from the table presented by Clapp and Hornberger 1978 for different soil textures These values are presented in Appendix B Saturated Hydraulic Conductivity K This parameter is a coefficient of proportion ality that describes the rate at which water can move through a soil at saturation The units of conductivity are centimeters per hour cm hr It should be noted that the density and kinematic viscosity of the water are considered in the measurement The standard value of hydraulic conductivity is defined for pure water at a temperature of 15 6 C 16 10 11 12 13 14 15 16 17 Appendix B provides average values for saturated hydraulic conductivity for different soil textures Dispersion Coefficient D Dispersion is a difficult parameter to define as it is not fully understood despite considerable efforts by the researchers in the field This parameter may be best evaluated through calibration of the model However it should be noted that empirical relationships have been developed based on numerous experiments Biggar and Nielsen 1976 proposed the relationship D D 2 93 y 12 P where D diffusion coefficient of the chemical in soil cm day and v the interstitial pore velocity cm day The parameter D can be estimated at 0 72 cm day Biggar and Nielsen 1976 Minimum x value The minimum x value refers to the upper depth of the model d
16. cular infiltration can significantly exceed K when the rainfall event is relatively short When simulating large time periods the recharge parameter can be viewed in terms of net groundwater recharge which incorporates losses due to evapotranspiration Sorption Constant K The sorption constant is the linear partition coefficient K which describes the relative distribution of the pollutant between that which is sorbed to the solid phase and that which is dissolved in water The higher the value of the partition coefficient the greater the tendency for sorption to the solid phase in contrast low partition values indicate most of pollutant distribution is retained in the water The partition coefficient is a constant for a given set of conditions As a result it is a site specific value In particular it is a function of the fraction organic content of the soil f and can be estimated as the product of the fraction organic content and the organic carbon partition coefficient K of the pollutant K K f 11 15 Appendix A lists the organic carbon partition coefficient for numerous pollutants The fraction organic content of the soil f_ can be determined from laboratory analyses or is commonly documented in soil descriptions by the U S Soil Conservation Service Generic values for organic content for soils of different texture are listed in Appendix B Solid phase degradation rate constant k This parameter describes th
17. e decay of the pollutant at the surface prior to infiltration into the soil The decay is defined as rate of loss per hour It should be noted that in PESTAN degradation begins at the time of application Values for solid phase decay could involve processes such as photodecomposition and volatilization Rates for solid phase decay may be obtained from pollutant reference texts see Appendix C Liquid phase degradation rate constant k Liquid phase decay describes those processes where mass is lost within the soil system In general degradation occurs primarily by soil microorganisms and may vary depending upon soil temperature and moisture Appendix C lists pollutant reference texts that document values for the liquid phase degradation rate constant Bulk Density p This parameter defines the mass of dry soil relative to the bulk volume of soil It is described in units of grams per square centimeters Ranges for bulk density with respect to different soil types are given in Appendix B Saturated Water Content 9 The saturated water content of the soil is the volume of water at saturation relative to the bulk volume density Typical values for saturated water content for different soil textures are given in Appendix B Characteristic Curve Coefficient b This parameter is defined by equation 1 which relates the relative saturation of the soil to the relative conductivity of the soil under steady state conditions If this const
18. eady state flow conditions are assumed in the code The time required for flow to establish steady conditions during a rainfall event is determined as being approximately equal to 5S 2K based on Philip s 1969 work where S is sorptivity LT and K is saturated hydraulic conductivity Steady state conditions in clay rich soils develop in about 48 hours and in sandy soils develop in less than 1 hour see Table 2 1 Therefore results for simulations made prior to reaching steady state conditions could be in error Homogeneous soil conditions are assumed in the model This assumption will rarely occur in the field The user can estimate the impact of non uniform soils by comparing results from several simulations covering the range of soil properties present at the site Linear isotherms describe the partitioning of the pollutant between the liquid and soil phases Local or instantaneous equilibrium between these phases is assumed First order degradation of the pollutant is assumed Solid phase degradation occurs at the surface between the time of application and time of recharge Liquid phase degradation occurs within the soil system The rate of liquid phase degradation does not change with soil depth or time This assumption ignores potential changes in biological activity with soil depth The water content of the soil is related to the hydraulic conductivity as described by Campbell 1974 1 KL 0 2b43 Ksat Osat where K i
19. echarge rate experienced during an actual rainfall event Hence the calculated pore water velocity will be considerably less than that under true conditions and will result in the simulated slug migrating at a slower rate than under true conditions PESTAN Conceptualization Dissolved Mass of Pollutant Mass of Granular Solid Pollutant an Dissolves F Slug Concentration Pollutant Solubility Pollutant slug enters soil at a rate equal to the pore velocity 0 Idg O A 4 905465 99 etes AL ASI PA 6 9 9 tt eg 0 so 9 6 9 sc 06 00 2900 e Do oo es 0 00700 e 99 S P gt af cee e o ELLI Figure 2 1 PESTAN conceptualization of pollutant migration with the soil system Application of Slug a Time of Recharge Time of Application Dissolved f Dissolved Mass of Mass E ing Soil Pollutant ass Entering gt 01 b Time of Recharge gt Time of Application Dissolved Mass of Pollutant Dissolved Mass Entering Soil Figure 2 2 PESTAN Conceptualization of pollutant application Granular pollutant is dissolved in slug at concentration equal to the pollutant solubility When time of recharge is the same as the time of application all the pollutant mass enters the soil When time of recharge occurs after the time of application pollutant mass will be lost due to decay hence the dissolved mass entering the soil will be less than original mass of pollutant St
20. in days at which the dataset will be defined If this graph is not desired delete this line 19 7 2 Output results PESTAN output file with the extension OUT provides information regarding the input parameters the physical nature of the water pollutant conditions within the soil the concentration profile within the soil and the pollutant mass balance The code allows the user to view the output as well as to print the output These options can be selected from the main menu screen The initial section of the output is a summary of the model scenario The information presented includes the title of the scenario and the input parameter values In particular the input summary should be closely reviewed to ensure that the appropriate values were utilized An example of the input summary is given below TITLE STUDY OF ALDICARB RESIDUES IN FLORIDA SOIL AND WATER JONES AND Back 1984 Solubility mg l eene 0 78000E 04 Recharge rate cm hr eene 0 35000E 02 Sorption constant cc g oconccnoccnccconnnoncnanncnnnnnnancnnnons 0 73000E 01 Saturated water content sese 0 39500E 00 Solid phase decay hr sss 0 22200E 03 Liquid phase decay hr sss 0 22200E 03 Curve coefficient uan Eee 0 40500E 01 Bulk density gfec ie Hessen 0 15000E 01 Dispersion coefficient cm hr ssssssss 0 6
21. l water in the soil It is calculated as v r q 14 3 The pollutant velocity describes the rate of pollutant movement within the soil Under most conditions due to sorption of the pollutant from the liquid to the solid phase the pollutant velocity will be less than the pore water velocity This is determined from the relation v Vv R 15 4 As was described in section 3 the length of the pollutant slug is determined by equation 10 The output describing the pollutant concentration profile is presented as a series of tables for each time value defined in the model input The defined time value is shown above each tabulation The output tabulation lists four columns 1 Depth cm 2 Pollutant Concentration in Water C mg l 3 Pollutant Concentration in Soil C mg kg and 4 Total Pollutant Concentration C mg l The concentration is given at eleven equally spaced depths between the previously defined tot minimum and maximum depths An example of the concentration profile tabulation is shown below Time 0 50E 02 days Depth cm Cw mg l Cs mg kg Ctot mg l 2 000 0 65E 01 0 47E 00 0 22E 01 20 000 0 79E 01 0 57E 00 0 27E 01 40 000 0 21E 00 0 15E 01 0 72E 01 60 000 0 19E 03 0 14E 04 0 67E 04 80 000 0 00E 00 0 00E 00 0 00E 00 100 000 0 00E 00 0 00E 00 0 00E 00 120 000 0 00E 00 0 00E 00 0 00E 00 140 000 0 00E 00 0 00E 00 0 00E 00 160 000 0 00E 00 0 00E 00 0 00E 00 180 000 0 00E 00 0 00E 00 0 00E 00 200
22. logy and Chemistry vol 5 pp 865 878 Philip J R 1969 Theory of Infiltration in Advances in Hydro Sciences vol 5 pp 215 290 Rawls W J 1983 Estimating Bulk Density from Particle Size Analysis and Organic Matter Content Soil Science vol 135 no 2 pp 123 125 35 36 Appendices Until further notice all Appendices to the PESTAN user s manual have been removed Tables in cluded in the Appendices contain suggested parameter values for chemical constituents and physical and hydraulic parameters for various soil media It was brought to the attention of CSMOS that certain parameters were in error Due to this the tables are being corrected The corrected tables will be included with the manual as soon as possible CSMoS apologizes for any inconvenience this might cause PESTAN MODEL DATA SHEET Simulation Title Date Chemical Name Soil Texture Required Data Chemical Parameters Water Solubility Sorption Constant Solid Phase Decay Rate Liquid Phase Decay Rate Soil Properties Bulk Density Saturated Water Content Curve Coefficient Saturated Hydraulic Conductivity Dispersion Coefficient Environmental Characteristics Recharge Number of Applications Application Rate Model Descritization Minimum X value cm Minimum Time Value day Input Value Source mg l cc g hr g cc cm hr cm hr cm r kg ha kg ha kg ha kg ha
23. nce in obtaining and tabulating pesticide and soil data Bob Wallin University of Arizona for his investigation of the model which initiated this project iii 1v TABLE OF CONTENTS iO IEE Do sie ae 1 2 0 Model Conceptualization Assumptions and l m tations ecce eee 3 EOS S igesusihrod cisci 9 40 Hardere end Sorbtware REQUITEMENES urinario reee 11 DO ESTE s eciau o PR drid 13 EV DIE PS ds 15 O o sooo MN 19 80 PSB AVES T P 23 20 aplasta 29 IOO TERIS asien 35 Appendix A Chemical Parameter Information Appendix B Soil Parameter Information Appendix C Reference Information Appendix D Model Data Sheet vi 1 INTRODUCTION The PESTAN Pesticide Analytical model is a computer code for estimating the transport of organic solutes through soil to groundwater The model is based on a closed form analytical solution of the advective dispersive reactive transport equation The model was developed by Enfield et al in 1982 and has since been used by the EPA Office of Pesticides Program OPP for initial screening assessments to evaluate the potential for groundwater contamination of currently registered pesticides and those submitted for registration Donigian and Rao 1986 The model has also been tested under field and laboratory conditions Enfield et al
24. of aldicarb trade mark TEMIK residues in Florida citrus groves TEMIK is primarily used for the control of nematodes aphids and mites in citrus groves Jones and Back 1984 compared the monitoring results with the simulations of PESTAN They used PESTAN to demonstrate that the use of TEMIK in Florida citrus groves would not result in the persistence of aldicarb residues in groundwater The input parameters as used by Jones and Back 1984 are summarized in Table 9 1 It should be noted that the first order degradation rates of the pollutant in both the liquid and the solid phases are provided The liquid phase decay was calculated based on a half life of 30 days k 0 693 30 x 24 9 63 x 10 per hour The solid phase decay was assumed to be equal to the liquid phase decay although in general these two values could be significantly different The value of recharge used 0 0035 cm hr corresponds to that of 30 cm year The value 4 05 for the characteristic curve coefficient corresponds to that of a sandy soil The model input and output are presented in Tables 9 1 and 9 2 Figures 9 1 and 9 2 illustrate respectively graphs of pollutant concentration in water as a function of time at three different depths and pollutant concentrations in water as a function of depth at three different times 29 TABLE 9 1 INPUT FILE FOR THE SAMPLE PROBLEM STUDY OF ALDICARB RESIDUES IN FLORIDA SOIL AND WATER JONES AND BACK 1984
25. omain In most cases this location will be the surface which defines the minimum x value at 0 The unit is centimeters Maximum x value The maximum x value defines the lower depth of the model domain This depth in many cases will be water table The maximum x value is defined in centimeters Minimum time value The minimum time value defines the initial time boundary in days Maximum time value This is the time in days when simulation ends It is the final time of interest Number of time intervals for printing out results Enter the number of time intervals at which the output will be documented Time values This parameter defines the time values in days at which the output will be documented Number of applications of waste Number of applications prior to recharge in the simulation I7 18 Waste application rate and starting time This is the mass of pollutant applied per hectare of land area One hectare equals 10 000 square meters The starting time is the time interval between the application and the initiation of recharge The code will simulate degradation during the time interval between the application and recharge event Conservative conditions would define the starting time as zero In creating or editing the input file separate the waste application rate value and the starting time value by a comma 18 7 OUTPUT 7 1 Options Several output options can be defined by the user to convert the o
26. ondition 1 is obtained based on the reasoning that the dissolved pollutant which is applied at the soil surface can be represented as a slug of thickness x that enters the soil at time zero x is calculated using water solubility when the chemical is applied in a granular form by determining the equivalent depth of water from the soil water content required to dissolve all of the available mass of pollutant The slug thickness is calculated as Ma exp kst Xo 10 S 0 Kap where x slug thickness in L M total pollutant mass applied per unit area M L k solid phase decay coefficient T t time lapse between application and recharge T S solubility of pollutant in water M L 10 4 HARDWARE AND SOFTWARE REQUIREMENTS The minimum hardware and software requirements for PESTAN are IBM PC or compatible computer with INTEL 8086 80286 80386 or 80486 CPU based system 256K RAM Color Graphic Adapter CGA board One floppy disk drive MS PC DOS 2 0 or higher Additional recommended hardware and software include A math coprocessor A hard disk A FORTRAN Compiler for modifications of the source code A commercial graphics software such as Grapher by Golden Software Inc 11 12 5 0 GETTING STARTED PESTAN is distributed by the EPA s Center for Subsurface Modeling Support CSMoS on a single IBM formatted 5 25 or 3 5 inch diskette PESTAN version 4 0 includes the following files PESTAN FO
27. s the hydraulic conductivity at a volumetric water content of 0 K is the hydraulic conductivity of the soil at the saturated water content 0 and b 1s the characteristic curve coefficient for the soil This relationship assumes steady state conditions for the flow TABLE 2 1 ESTIMATED TIME TO ESTABLISH STEADY FLOW CONDITIONS Soil Texture Time minutes Sm ss Se NN an 0 ie c S Table is based on the work of Philip 1969 It is obtained by multiplying 4K by a factor of 10 where S sorptivity and Ks saturated hydraulic conductivity 8 The model does not account for non aqueous phase liquids or any flow conditions derived from variable density The model presents results for the specific input values without accounting for any parameter uncertainty The user is encouraged to compare results for a series of simulations using a range of values to obtain an estimate of potential uncertainty For example if three different recharge values are likely three simulations should be run rather than averaging the three values to obtain only one value 3 MATHEMATICAL MODEL A brief discussion of the mathematical development and important aspects of the model theory with a few modifications from the formulation of Enfield et al 1982 is presented below A detailed description of the model theory is presented in the original paper by Enfield et al 1982 The vertical transport of a pollutant dissolved in wa
28. ter through the soil can be described by the following equation 2 cc p9 _ 2C Pb oS f ot ox Ox 0 ot k C 2 where C liquid phase pollutant concentration mass of pollutant in water volume of water M L t time T x distance along the flow path L D dispersion coefficient L T v interstitial or pore water velocity L T p bulk density M L 9 volumetric water content volume of pore water total volume L L S solid phase concentration mass of pollutant in soil mass of soil M M k first order decay coefficient in liquid phase T The term 0S dt is the rate of loss of solute from liquid phase to solid phase due to sorption Under the assumption of linear instantaneous sorption dS ot can be evaluated as os oC gt Ky 3 ot ot where K linear Freundlich sorption coefficient Substituting for dS dt from 2 into 1 one obtains 3 Le k C 4 ot Ox ox where Ka Pb R 1 unitless 5 The partial differential equation 4 can be solved for C x t along with the following initial and boundary conditions 0 lt X lt Xo C x t 0 Co x lt x lt 0 6 0 0 x oo m ge 0 7 Ix gt Ox The solution is given as follows vt vt E ext x C x exp kjt erf B erf 8 A OER NDUR i where erf z is the error function which is defined as erf z exp y2 d 9 z amp p y dy 9 Boundary c
29. the PESTAN program View the output file Print input data INP file Print output OUT file Quit and return to DOS 1 2 3 4 5 6 7 8 0 Please enter your selection Select an option by typing the appropriate number of the selection Do not hit ENTER the code will automatically continue 14 6 INPUT PARAMETERS The following describes the input parameters for PESTAN It is important that this informa tion be fully understood for proper application of the code 1 Water Solubility S Values defining the water solubility of the pollutant must have units of milligrams per liter mg l Appendix A provides water solubility information on over 50 different chemicals If data regarding the pollutant being modeled is not presented refer to the standard reference manuals that are documented in Appendix C or consult the chemical manufacturer Recharge This parameter describes the infiltration rate of water entering the soil This rate is dependent upon the nature of the precipitation or irrigation the character of the soil and the duration of the precipitation event The rate of infiltration will be equal to the rain or irrigation intensity when this precipitation rate is less than the saturated hydraulic conductivity K of the soil For the special case when the rainfall intensity is greater than the saturated hydraulic conductivity the recharge value may be greater than K In parti
30. utput from PESTAN into files which can be plotted using GRAPHER Golden Software 1987 or other compatible commercial graphics packages Three graphs can be constructed a breakthrough curve a pollutant flux curve and a soil depth pollutant concentration profile These can be selected by defining the following options J Option for creating a breakthrough curve dataset This output constructs two datasets one for the breakthrough curve and one for the pollutant flux graph The breakthrough curve dataset consists of values of pollutant concentration versus time and the pollutant flux dataset consists of values of pollutant flux versus time To construct the breakthrough dataset and the pollutant flux dataset type either Y or y If this is LAA OF not desired type N or n Location at which breakthrough curve is desired If a breakthrough curve and pollutant flux graphs are desired then input the depth in centimeters at which the dataset will define If these curves are not desired delete this line Option for creating a soil depth profile graph This output option constructs a dataset with values of depth and concentration that can be used with a commercial graphics package to depict the concentration soil depth profile To construct a soil depth dataset Mom an type Y or y if this is not desired type N or n Time at which soil depth profile is desired If a soil depth profile is desired input the time
31. will be a loss of mass due to solid phase decay which begins at the time of application and the total available mass will be less than the applied mass see Figure 2 2b The slug begins to enter the soil at the first precipitation irrigation event at a rate equal to the pore water velocity PESTAN assumes steady flow conditions through the soil domain Once the slug enters the soil the pollutant transport is influenced by sorption and dispersion Mass of the pollutant can be lost via liquid phase decay or via migration out of the soil domain When developing a model simulation it is important to fully understand the implications of the PESTAN conceptualization The following assumptions are made in the development of PESTAN and are based primarily on those made by Enfield et al 1982 1 The PESTAN conceptualization assumes the leachate concentration equals the maximum possible concentration i e solubility This assumption results in maximum conservative concentration values and a minimum slug thickness Therefore the pollutant concentration profile in the soil will be thinner and at concentrations greater than those actually occurring in the soil 2 The slug enters the soil at the velocity of the pore water which is the ratio of the recharge rate to the pore water content If the recharge rate incorporates losses due to evapotranspiration or is averaged over long time periods then this value will be significantly less than the r
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