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BIOCHLOR - About GSI Environmental Inc.

1. 21 Installation and Startstlp adios occiso no cr eoe I ppc 21 BIOCHLOR TROUBLESHOOTING TIPS iim Re tg eure HH eru RR RR C eet kien 21 spreadsheet Related Problems Nomen 21 Common Error Messages nein eer e toes ento ect dues endet 21 EIGIGIBHDBS E nA uu A MR D MA 23 Appendix Domenico Single Species Analytical Model 25 27 Kinetics of Sequential First Order Decay 27 Chlorinated Ethenes 27 Chlorinated Ethanes ue ete a esta bo S Un E 28 Other Chlorinated CompoundS eo SO escolar eS pd vod va Dung 28 1 Zone vs 2 Zone Biotransformation 28 How BIOCHLOR Models 2 Zone Biotransformation 30 Appendix JS aite Heic tete teas 31 DUI e 31 Governing 31 Analytical Solution Strategy 31 Computational Procedure e ERE tex 33 Appendix A 4 Dispersivity Estimates e pene ternera ucc po eee
2. 37 Ratio of transverse dispersivity and vertical dispersivity to longitudinal dispersivity data vs scale reported by Gelhar et al 1992 38 BIOCHLOR source zone assumption TCE as 41 BIOCHLOR input screen Cape Canaveral Air Force Base Florida 43 Centerline output Cape Canaveral Air Force Base Florida 44 Individual centerline output for TCE Cape Canaveral Air Station Florida 44 Array concentration output for Cape Canaveral Air Station Florida 45 Tables 2 Zone Biotransformation Scenarios 28 Modeling Scenario for Chlorinated 29 Modeling Scenario for Chlorinated 5 29 Sensitivity Analysis Results Rate Coefficients 46 Sensitivity Analysis Results Retardation Factor 46 vii Introduction BIOCHLOR is an easy to use screening model that simulates remediation by natural attenuation RNA of dissolved solvents at chlorinated solvent release sites The software programmed in the Microsoft Excel spreadsheet environment and based on the Domenico analytical solute transport model has th
3. Natural Attenuation Lines of Evidence and the Role of BIOCHLOR To support remediation by natural attenuation it must be scientifically demonstrated that attenuation of the site contaminants is occurring at rates sufficient to be protective of human health and the environment According to the Technical Protocol For Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water U S EPA 1998 three lines of evidence can be used to support natural attenuation of chlorinated solvents including 1 Observed reductions in contaminant concentrations along the flow path downgradient from the source of contamination 2 Documented loss of contaminant mass at the field scale using a Chemical and geochemical analytical data including decreasing parent compound concentration increasing daughter compound concentrations depletion of electron acceptors and donors and increasing metabolic byproduct concentrations and or b A rigorous estimate of residence time along the flow path to document contaminant mass reduction and to calculate biological decay rates at the field scale 3 Laboratory microcosm or field data that support the occurrence of biotransformation and give rates of biotransformation At a minimum the investigator must obtain the first two lines of evidence or the first and third lines of evidence The second or third line of evidence is crucial because it provides biotransformation rate constants These rate constants
4. Vertical Dispersivity The user may choose a ratio of alpha z alpha x One commonly used ratio is Alpha z alpha x 2 0 05 ASTM 1995 Alternatively alpha z alpha x can be set to a very low number e g E 99 to yield a conservative estimate of vertical dispersion This is the default value used in BIOCHLOR Other commonly used relations include Alphax 0 1 Lp Pickens and Grisak 1981 36 Alpha 0 33 alpha ASTM 1995 EPA 1986 Alpha z 0 05 alpha x ASTM 1995 Alpha z 0 025 alpha x to 0 1 alphax U S EPA 1986 The BIOCHLOR input screen includes Excel formulas to estimate dispersivities from scale BIOCHLOR uses the modified Xu and Eckstein 1995 algorithm for estimating longitudinal dispersivities because 1 it provides lower range estimates of dispersivity especially for large values of x and 2 it was developed after weighing the reliability of the various field data compiled by Gelhar et al 1992 see Figure BIOCHLOR also employs low end estimates for transverse and vertical dispersivity estimates 0 10 alpha x and 0 respectively because these relations better fit high reliability field data reported by Gelhar et al see Figure A 4 and Gelhar et al recommend use of values in the lower range of the observed data The user can also enter a fixed longitudinal dispersivity value in the Change Alpha x Calc dialog box on the input screen Note that the Domenico model and BIOCHLOR are not form
5. D v he Ec 2 ac 9 c 9 c R D 2 D FD bec E 3 d a e ac R D 5 0 5 0 ye ke 4 ut T 7 Op Dos OC 5 y ox y D a My Deed 6 5 where C C and c are concentrations of TCE DCE VC and ETH respectively mg L D D and D are the hydrodynamic dispersion coefficients f yr v is the seepage velocity k is the first order degradation coefficient 1 yr y is the yield coefficient a dimensionless value for example y would represent the mg of TCE produced per unit mg of PCE destroyed and R R R R and are respective retardation factors In BIOCHLOR the retardation factor values of different species are averaged to compute an effective retardation factor which is in turn used to compute the effective transport velocity and dispersion coefficients Also biotransformation is assumed to occur only in the aqueous phase which is a conservative assumption and hence Fis used to divide all the degradation reaction terms Analytical Solution Strategy The Domenico 1987 solution with some minor improvements suggested by Martin Hayden and Robbins 1997 was used as the base solution to solve the three dimensional problem The solution was directly used to solve the independent equation 1 However since equations 2 to 5 are coupled equations the Domenico
6. ic DO i 1 ny WRITE 10 12 c j i ic j 1 nx ENDDO ENDDO FORMAT 10e15 6 A x A N 2 ao ao 0 34 c Ouput centerline concentrations OPEN 12 FILE center out FORM FORMATTED STATUS UNKNOWN i ny 1 2 1 center line location DO j 1 nx WRITE 12 14 j dx c j i ic ic 1 5 END DO 14 FORMAT F10 2 5e15 5 STOP END SUBROUTINE Domenico nx ny dx dy t xsloc ysloc xsdim ysdim zsdim v ax ay az c0 k c USE MSIMSL lusing IMSL subroutine REAL 4 k DIMENSION c nx ny DO j 1 ny DO i 1 nx c i j 0 0 ENDDO ENDDO c Domenico Anlytical Solution is used as in Martin Hayden and Robbins paper c See equations 5 amp 1 in GW vol 35 2 1997 pages p 345 and 340 cc SQRT 1 4 k ax v DO j 1 ny DO i 1 nx x i dx xsloc y j dy ysloc z 0 0 at the water table hx2 ERFC x v t cc 2 SQRT ax v t IF hx2 LE 1 0e 30 THEN h1 0 0 ELSE hx1 EXP x 1 cc 2 ax h1 hx1 hx2 END IF hx4 ERFC x v t cc 2 SQRT ax v t IF hx4 LE 1 0e 30 THEN h2 0 0 ELSE hx3 EXP x 1 c 2 ax h2 hx3 hx4 END IF hx hi h2 fy ERF y ysdim 2 0 2 0 SQRT ay x ERF y ysdim 2 0 2 0 SQRT ay x IF az LE 1 0e 30 THEN fz 2 0 ELSE fz ERF z zsdim 2 0 SQRT az x ERF z zsdim 2 0 SQRT az x ENDIF C i j CO 8 0 hx fy fz D DO END DO RETURN END 35 Appendix 4 Dispersivity Estimates Dispersion refers to the process whereby a dissolved solv
7. 1995 Alternatively alpha z alpha x can be set to a very low number e g E 99 to yield a conservative estimate of vertical dispersion This is the default value used in BIOCHLOR Other commonly used relations include Alphax 0 1 Lp Pickens and Grisak 1981 Alphay 0 33 alpha x ASTM 1995 EPA 1986 Alphaz 0 025 alpha x to 0 1 alpha x EPA 1986 Source of Data Typically estimated using the relations provided above see Appendix A 4 How to Enter Data Click on Change Alpha x Calc Method button Select an option for alpha x If you select Option 1 enter a fixed value in the box Enter ratios for alpha y and alpha z Note If the Reset button is depressed then the following are the default options and values used by BIOCHLOR Option 1 fixed value is used to calculate alpha x The user must input a value The alpha y alpha x ratio is set to 0 1 and the alpha z alpha x ratio is set to 1x 10 m 3 Adsorption Data Retardation Factor R Description Adsorption to the soil matrix can reduce the concentration of dissolved contaminants moving through the ground water The retardation factor is the ratio of the ground water seepage velocity to the rate that organic chemicals migrate in the ground water A retardation value of 2 indicates that if the ground water seepage velocity is 100 ft yr then the organic chemicals migrate at approximately 50 ft yr The degree of retardation depends on both aquifer
8. Determine the concentration of TCE discharging into the canal in 1998 given data collected in 1997 Given Input Data e Fig A 5 Source Map BIOCHLOR Modeling Summary e Fig A 6 BIOCHLOR Input Data Results e Fig A 7 BIOCHLOR Centerline Output Fig A 8 BIOCHLOR TCE Centerline Output Fig A 9 BIOCHLOR TCE Array Output 39 BIOCHLOR Example Cape Canaveral Air Station Florida Hydrogeology Hydraulic Conductivity 1 8x 10 cm sec Slug tests results Hydraulic Gradient 0 0012 ft ft Static water level measurements Effective porosity 0 2 Estimated Dispersion Longitudinal Dispersivity Intermediate value for 800 1200 ft plume from Gelhar et al 1992 Transverse Dispersivity 0 1 x long dispersivity Vertical Dispersivity Assume vertical dispersivity is zero since depth of source is approx depth of aquifer Adsorption Individual Retardation 7 1 x Calculated from Factors c DCE 2 8 14 5 3 29 Median value Common Retardation Factor 5 Esti d P 1 6 kg L stimate Aquifer Matrix Bulk Density 2 0 18496 ab analysis M 426 L kg 130 Literature correlation Koc 8 Pee o L kg using solubilities at 20 c DCE 125 L kg VC 29 6 L kg ETH 302 L kg Biotransformation Biotransformation Rate Based on calibration to Coefficients 1 yr field data using a simulation time of 32 PCE gt TCE years field data collected
9. Sun and Clement 1999 The model will predict the maximum extent of dissolved phase plume migration which may then be compared to the distance to potential points of exposure e g drinking water wells ground water discharge areas or property boundaries Analytical ground water transport models have seen wide application for this purpose e g ASTM 1995 and experience has shown such models can produce reliable results when site conditions in the plume area are relatively uniform BIOCHLOR is intended to be used in two ways 1 Asa screening level model to determine if is feasible at a chlorinated solvent site BIOCHLOR is intended to be used as screening level model to determine if natural attenuation is occurring at sufficient rates at a site to warrant a full natural attenuation study Ideally site specific biotransformation rate constants should be employed but literature values can be used if measured rate constants are unavailable Other useful attributes of BIOCHLOR include the facilitation of site characteriza tion data organization and the ability to carry out many simulations in short periods of time For fuel hydrocarbon release sites the BIOSCREEN model Newell et al 1996 is more appropriate 2 As an RNA ground water model to address selected chlorinated solvent problems The Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water U S EPA 1998 describes how ground water
10. gt 1 cm s Source of Data Pump tests or slug tests at the site It is strongly recommended that actual site data be used for all RNA studies How to Enter Data Enter directly If seepage velocity is entered directly this parameter is not needed in BIOCHLOR Hydraulic Gradient i Description The slope of the potentiometric surface In unconfined aquifers this is equivalent to the slope of the water table Typical Values 0 0001 0 05 ft ft Source of Data Calculated by constructing potentiometric surface maps using static water level data from monitoring wells and estimating the slope of the potentiometric surface How to Enter Data Enter directly If seepage velocity is entered directly this parameter is not needed in BIOCHLOR 1 Hydrogeologic Data cont Effective Porosity n Typical Values Source of Data How to Enter Data Dimensionless ratio of the volume of interconnected voids to the bulk volume of the aquifer matrix Note that total porosity is the ratio of all voids included non connected voids to the bulk volume of the aquifer matrix Differences between total and effective porosity reflect lithologic controls on pore structure In unconsolidated sediments coarser than silt size effective porosity can be less than total porosity by 2 5 Smith and Wheatcraft 1993 Values for Effective Porosity Clay 0 01 0 20 Sandstone 0 005 0 10 Silt 0 01 0 30 Unfract Limestone 0 001 0 05 Fine
11. in the development of the BIOCHLOR mathematical model To illustrate the appropriate application of BIOCHLOR EPA contributed field data generated by EPA staff supported by ManTech Environmental Research Services Corp the in house analytical support contractor at the RSKERC The computer code for BIOCHLOR was developed by Groundwater Services Inc through a contract with the U S Air Force Groundwater Services Inc also provided field data to illustrate the application of the model All data generated by EPA staff or by ManTech Environmental Research Services Corp were collected following procedures described in the field sampling Quality Assurance Plan for an in house research project on natural attenuation and the analytical Quality Assurance Plan for ManTech Environmental Research Services Corp The development of BIOCHLOR and its User s Manual were not funded by the U S EPA and as such are not subject to the Agency s QA requirements An extensive investment in site characterization and mathematical modeling is often necessary to establish the contribution of natural attenuation at a particular site BIOCHLOR is offered as a screening tool to determine whether it is appropriate to invest in a full scale evaluation of natural attenuation at a particular site Because BIOCHLOR incorporates a number of simplifying assumptions it is not a substitute for the detailed mathematical models that are necessary for making final regulatory decisions at compl
12. 10 10 10 10 10 105 Scale 5 Figure 4 Ratio of transverse dispersivity and vertical dispersivity to longitudinal dispersivity data vs scale reported by Gelhar et al 1992 Data includes Gelhar s reanalysis of several dispersivity studies Size of symbol represents general reliability of dispersivity esti mates Location of transverse dispersivity relation used in BIOCHLOR is plotted as dashed line Appendix A 5 Pump and Treat Comparison A useful way to estimate the clean up time for a contaminated aquifer is to consider the number of pore volumes that must be pumped from the contaminated zone to achieve clean up goals A pump and treat module was added to the BIOCHLOR array output page to permit users to test the feasibility of pump and treat systems and to compare pump and treat clean up times with natural attenuation predictions The user is provided with the volume of ground water in the plume i e a pore volume One pore volume is only a small fraction of the volume of ground water requiring treatment because dense non aqueous phase liquids DNAPLs such as solvents and sorbed constituents act as continuing sources of ground water contamination The number of pore volumes required for clean up i e the number of times the contaminated region must be flushed is a function of many different factors including the clean up standard the initial chemical concentration the degree of mixing of clean and contamin
13. 3 k 4 p52 y 2 y 3 y 4 k 2 k 3 k 4 pe SEE k 2 k 5 K S k S 3 4 1 5 2 5 3 5 4 5 Initial concentration is assumed to be zero for all species Transform all boundary conditions into a domain 0 1 0 1 2 0 2 p21 cO 1 3 0 3 p32 c0 2 p31 cO 1 4 0 4 43 0 3 42 0 2 41 0 1 0 5 0 5 54 0 4 53 0 3 52 0 2 51 0 1 Solve the problem using Domenico solution the domain DO ic 1 nc CALL Domenico nx ny dx dy t xloc ysloc xsdim ysdim zsdim v ax ay az a0 ic k ic a 1 1 ic END DO Transforming back into the c domain Transform Species 1 DO iy 1 ny DO 1 c ix iy 1 a ix iy 1 END DO END DO Transform Species 2 DO iy 1 ny DO 1 2 a ix iy 2 p21 c ix iy 1 END DO END DO Transform Species 3 DO iy 1 ny DO 1 C ix ly 3 a ix ly 3 p32 c ix iy 2 p31 c ix iy 1 END DO END DO Transform Species 44 DO iy 1 ny DO 1 1 4 a ix iy 4 p43 c ix iy 3 p42 c ix iy 2 p41 c ix iy 1 END DO END DO Transform Species 5 DO iy 1 ny DO 1 c ix iy 5 a ix iy 5 54 4 p58 c ix iy 3 p52 c ix iy 2 51 1 END DO END DO Output concentration array OPEN 10 FILE conc out FORM FORMATTED STATUS UNKNOWN DO ic 1 nc Write 10 Species
14. 36 Appendix A 5 Pump and Treat Comparison 38 AB p nte ete dst ed AL 39 BIOGHLEOR Example bh etate ter tne tee et AR uec IRR 40 BIOCHLOR Modeling Summary uctor detenti tonem box b duc eife 42 Cape Canaveral Air Station Florida 21d riae rrr ma apr den rir prae ei a pe Tr veda 42 Entering ice 42 Viewing Output Sensitivity Analysis Examples oet et vi Figure 1 Figure 2 Figure 3 Figure A 1 Figure A 2 Figure A 3 Figure 4 Figure A 5 Figure A 6 Figure A 7 Figure A 8 Figure A 9 Table A 1 Table A 2 Table A 3 Table A 4 Table A 5 Figures Reductive dechlorination pathways for common chlorinated aliphatic hydrocarbons from Vogel and McCarty 1987 3 Reductive transformation of chlorinated ethene 3 Initial screening process flow Chart 5 Mixed type plume conditions ceres 29 Comparison of solution techniques for BIOCHLOR 1 zone and 2 zone biotransformation models 30 Longitudinal dispersivity vs scale data reported by Gelhar et al 1992
15. The focus of the Laboratory s research program is on methods for the prevention and control of pollution to air land water and subsurface resources protection of water quality in public water systems remediation of contaminated sites and ground water and prevention and control of indoor air pollution The goal of this research effort is to catalyze development and implementation of innovative cost effective environmental technologies develop scientific and engineering information needed by EPA to support regulatory and policy decisions and provide technical support and information transfer to ensure effective implementation of environmental regulations and strategies This screening tool will allow ground water remediation managers to identify sites where natural attenuation is most likely to be protective of human health and the environment It will also allow regulators to carry out an independent assessment of treatability studies and remedial investigations that propose the use of natural attenuation Clinton W Hall Director Subsurface Protection and Remediation Division National Risk Management Research Laboratory iii Acknowledgments BIOCHLOR was developed by Drs Carol Aziz and Charles Newell Groundwater Services Inc Houston TX Customization and testing of the BIOCHLOR solution engine was performed by Drs Prabhakar Clement and Yunwei Sun Battelle Pacific Northwest National Laboratory Richland WA The authors woul
16. both production and degradation One zone means that one set of rate constants is used within the model area The model assumes that biotransformation starts immediately downgradient of the source and that no biotransformation of dissolved constituents in the source area occurs The sequential first order decay model does not directly account for site specific information such as the concentration of the electron donor i e hydrogen or the number of dechlorinating bacteria this is implicitly accounted for in the first order decay rate coefficient supplied by the user Ideally rate coefficients measured in the field or derived from model calibration to site data should be used Literature values may also be employed but the user must be aware that the literature value may have been measured under different environmental conditions than those present for the plume being modeled 3 Solute transport with sequential first order decay in two zones This model employs the same sequential first order decay kinetics as the preceding model but allows the user to use two different sets of rate constants within the model area This may be appropriate for plumes that undergo rapid biotransformation close to the source where there is an excess of fermentable substrates but negligible biotransformation further downgradient where fermentable substrates have been depleted or for plumes that go from anaerobic conditions to aerobic conditions Aerobic conditions can
17. cO nc aO nc Input data for Martin Hayden and Robbins test problem c Reference Vol 35 2 p 339 Groundwater 1997 dx 20 0 delta x dy 20 0 delta t 33 0 total simulation time years reta 5 3 leffective retardation factor v 111 7 reta velocity ft yr ax 16 4 lalpha x ft ay 1 64 lalpha y ft az 0 0 lalpha z xsdim 0 0 dimensions ysdim 100 0 zsdim 10 0 C Automatically set source locations xsloc 0 0 source x location is fixed at the left boundary ysloc ny 1 2 1 dy fix source y location at the grid center Input reaction parameters 2 0 reta leffective pce decay rate 1 k 2 2 1 5 reta tce decay rate k 3 0 8 reta dce decay rate k 4 0 65 reta vc decay rate k 5 0 000000001 ethene decay rate y 1 0 79492 ytce pce y 2 0 73744 ydce tce y 3 0 64499 yvc dce y 4 2 0 4496 lyeth vc Input source concentrations 0 1 0 1 mg l source concentration for pce 0 2 15 8 for tce c0 3 98 5 for dce 0 4 3 1 vc c0 5 0 03 for eth c Computing transformation coefficients p21 y 1 k 1 k 1 k 2 p32 y 2 k 2 k 2 k 3 33 Oo 12 p31 y 1 y 2 k 1 k 2 k 1 k 3 K 2 k 3 p43 3 3 3 4 p42 y 2 y 3 k 2 k 3 k 2 k 4 K 3 k 4 p41 y 1 y 2 y 3 k 1 k 2 k 3 K 1 k 4 k 2 k 4 K 3 k 4 p54 y 4 k 4 k 4 k 5 y 3 y 4 k
18. can be used in conjunction with other fate and transport parameters to predict contaminant concentration and to assess risk at a downgradient point of exposure U S EPA 1998 Compared to fuel hydrocarbon plumes use of natural attenuation as a stand alone remedy for chlorinated solvent plumes is appropriate for a much lower percentage of plumes because of their longer plume lengths Therefore it is particularly important to make an accurate assessment of the potential for natural attenuation prior to investing in a detailed natural attenuation study To assist in this endeavor the natural attenuation screening process is outlined in Figure 3 The shaded steps indicate the stages where BIOCHLOR plays a role in the screening process The first shaded stage i e Is Biodegradation Occurring is the stage where the natural attenuation scoring system comes into play The scoring system requires the concentrations of electron acceptors parent and daughter chlorinated solvents methane TOC and chloride and ORP temperature and pH measurements U S EPA 1998 These field data are evaluated and scored for evidence of biotransformation BIOCHLOR incorporates this scoring system which can be accessed from the input page If there is evidence of biotransformation BIOCHLOR may be used subsequently to compare the rate of chlorinated solvent transport without biotransformation to the rate of attenuation with biotransformation Being a transient mod
19. convert a 0 in the data entry cell to a very low number to avoid DIV 0 errors There once were formulas in some of the boxes on the input screen but they were accidentally overwritten Press the closest C button or click on the Restore Formulas button on the bottom right hand side of the input screen The graphs seem to move around and change size This is a feature of Excel When graph scales are altered to accommodate different plotted data the physical size of the graphs will change slightly sometimes resulting in a graph that spreads out over the fixed axis legends You can manually resize the graph to make it look nice again by double clicking on the graph and resizing it refer to the Excel User s Manual The source dialog boxes keep closing If you press Enter when inputting data in a dialog box pop up window then the dialog box will close Do not press Enter and move to the next cell by using the mouse and clicking If you do press Enter by accident simply select your source option again The scale on the 3 D graphic on the array page is not even This is a feature of Excel There is no way to create an even scale when using unevenly spaced data in a 3 D graphic Common Error Messages Unable to Load Help File The most common error message encountered with BIOCHLOR is the message Unable to Open Help File after clicking on a Help button Depending on the version of Windows you are using you may get an Excel
20. daughter product generation Under aerobic conditions the solvent is assumed to degrade directly to carbon dioxide via first order kinetics and degradation is not linked to daughter product generation Input parameters can be manipulated to avoid accounting for daughter product generation The user should be aware that BIOCHLOR is primarily designed to display the original anaerobic pathways The input output will not 28 Anaerobic Aerobic High Carbon Low Carbon HE Figure A 1 Mixed type l Type III plume conditions indicate that an aerobic path was used or what the degradation products are The user should extract only the pertinent output information using the guidance below Table A 2 outlines how to input rate constants for both zones anaerobic zone 1 and aerobic zone 2 for each simulation Rate constants denoted as indicate a rate constant for an aerobic process Note that the rate of ethene degradation under anaerobic conditions in zone 1 is assumed to be zero If only c DCE degrades under aerobic conditions then scenario 3 can be completed in one run If c DCE VC and ETH degrade aerobically three runs will be required Run 1 will yield the concentration profiles for PCE TCE and c DCE Concentration profiles for VC and ETH must be ignored Run 2 will yield the concentration profiles for VC Concentration profiles for all other compounds must be ignored Run 3 will yield the concentration profile for ethene aga
21. is uncertainty in the value chosen sensitivity analyses should be conducted to determine the effects of the uncertainty on model predictions Examples of a sensitivity analysis can be found in Appendix A 7 1 Hydrogeologic Data Seepage Velocity Vs Description Actual interstitial ground water velocity equaling Darcy velocity divided by effective porosity Note that the Domenico model and BIOCHLOR are not formulated to simulate the effects of chemical diffusion Therefore contaminant transport through very slow hydrogeologic regimes e g clays and slurry walls should probably not be modeled using BIOCHLOR unless the effects of chemical diffusion are proven to be insignificant Typical Values 0 5 to 200 ft yr Source of Data Calculated by multiplying hydraulic conductivity by hydraulic gradient and dividing by effective porosity It is strongly recommended that actual site data be used for hydraulic conductivity and hydraulic gradient data parameters effective porosity can be estimated How to Enter Data 1 Enter directly or 2 Fill in values for hydraulic conductivity hydraulic gradient and effective porosity as described below and have BIOCHLOR calculate seepage velocity by pressing the button Hydraulic Conductivity K Horizontal hydraulic conductivity of the saturated porous medium Typical Values Clays lt 1 10 cm s Silts 1x10 1x10 cm s Silty sands 1x10 1x10 cm s Clean sands 1x10 1 cm s Gravels
22. methods for selection of appropriate half lives are the same as for the rate coefficients How to Enter Data Enter directly in gray cells and press the C button If the first order decay coefficient is entered directly this parameter is not needed in BIOCHLOR Abiotic First Order Rate Coefficient 1lyr Description Typical Values Source of Data How to Enter Data Rate coefficient describing first order abiotic decay process for chloroethane Chloroethane degrades to ethanol under abiotic conditions Note Although 1 1 1 TCA can abiotically decay to 1 1 DCE via elimination and to acetic acid as a result of hydrolysis BIOCHLOR cannot simulate abiotic decay and chlorinated ethane daughter product generation simultaneously BIOCHLOR can be used to simulate the degradation of 1 1 1 TCA alone by setting the initial daughter product concentrations to zero the biological rate constants for DCA and CA to zero and entering a TCA degradation rate coefficient on the input page This rate coefficient represents the sum total of all abiotic and biotic coefficients for processes observed in the field at your site BIOCHLOR will generate TCA predictions but daughter product predictions should be ignored Note that the abiotic rate coefficients for the chlorinated ethenes are very slow greater than 10 years half life Jeffers et al 1989 and therefore abiotic degradation can be ignored for PCE TCE DCE and VC chloroethane to et
23. on Sun et al 1999a work a transformation for the second equation can be written as e 12 a c Differentiating equation 12 partially with respect to time we get Od c y k c 13 ot ot k k Substituting 10 and 11 into 13 we get 2 2 yk c k c D 14 Equation 14 be rearranged 2 2 k i C v C 15 k k k k k Using 12 equation 15 can be written as k 22 p 22 ke he LAE 16 Combining the last three terms equation 16 can be simplified to 2 _ oe 17 ot Ox ox 32 To solve 11 first standard one dimensional solution should be used to solve 17 for computing a values and to solve 10 for computing values note that is always same as a Then c values can be computed using equation 12 in an inverse mode This procedure can be repeated for solving any number of coupled reactive species A more general analysis of this solution strategy and a detailed comparison of the analytical results against the numerical results of the RT3D code are discussed in Sun and Clement 19998 If retarding species are assumed then an effective retardation factor is used to divide the transport velocity dispersion coeffic
24. order decay coefficients using 0 693 see dissolved solvent half life Note Because the use of literature values may overestimate the amount of biotransformation occurring the user should conduct sensitivity analyses to determine the impact of the chosen rate coefficients on plume lengths see Appendix 7 Other Methods The Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water USEPA 1998 describes other methods for obtaining rate coefficients including the use of microcosm data and use of field scale tracer data How to Enter Data 1 Enter directly or 2 Fill in the estimated half life values as described below and have BIOCHLOR calculate the first order decay coefficients by pressing the button 12 4 Biotransformation Data cont Dissolved Solvent Half Life t 2 Typical Values Time in years for dissolved plume concentrations to decay by one half as contaminants migrate through the aquifer The amount of degradation that occurs is related to the time the contaminants spend in the aquifer Considerable care must be exercised in the selection of a half life for each contaminant in order to avoid significantly over predicting or under predicting actual decay rates Perchloroethylene 0 58 to 9 9 yr Trichloroethylene 0 77 to 13 9 yr cis 1 2 Dichloroethylene 0 21 to 3 9 yr Vinyl Chloride 0 27 to 5 8 yr from Wiedemeier et al 1999 Source of Data Optional
25. solution cannot be used to solve them Therefore in BIOCHLOR a new transformation procedure is used to first uncouple equations 2 to 5 and recast them in the form of equation 1 Sun and Clement 1999 Sun et al 1999a Sun et al 1999b The transformation equations used are dico p 6 y E y y k 7 ky k E Rs a C 31 a c yk V2V3k k cy k 8 k k K k k k k ky y k 12321217 4 kk k 4 k k k k k k k Yiy iy y k kk k ks ky 6 ky It can be shown that using transformation equations 6 to 10 the reactive transport equations 2 to 5 can be written in a transformed a domain where the coupled transport equations reduce to a form similar to equation 1 For illustration purposes the steps involved in proving the strategy for a one dimensional 2 species transport problem are given below d C Consider the following set of one dimensional fate and transport equations that describe two reacting species that are coupled by first order decay reactions 96 10 Of c 2 c 22 oC E AR 1 Since equation 10 is already in the standard form it can be solved using standard analytical solution Based
26. 1996 BIOSCREEN Natural Attenuation Decision Support System S Environmental Protection Agency Center for Subsurface Modeling Support Ada OK EPA 600 R 96 087 23 Newell C J L Bowers and S Rifai 1994 Impact of Non Aqueous Phase Liquids NAPLs on Groundwater Remediation Proceedings of American Chemical Society Symposium on Multimedia Pollutant Transport Models Denver CO August 1994 Pankow J F and J A Cherry Eds 1996 Dense Chlorinated Solvents and Other DNAPLs in Groundwater Waterloo Press Portland OR Pickens J F and G E Grisak 1981 Scale Dependent Dispersion in a Stratified Granular Aquifer Water Resour Res 17 4 1191 1211 Powers 5 L M Abriola and W J Weber Jr 1994 An Experimental Investigation of Nonaqueous Phase Liquid Dissolution in Saturated Subsurface Systems Transient Mass Transfer Rates Water Resour Res 30 2 321 332 Smith L and S W Wheatcraft 1993 Groundwater Flow in Handbook of Hydrology David Maidment Editor McGraw Hill New York Sun Y and T P Clement 1999 A Decomposition Method for Solving Coupled Multi species Reactive Transport Problems Transp in Porous Media 37 327 346 Y J N Petersen and Clement 1999a A New Analytical Solution for Multiple Species Reactive Transport in Multiple Dimensions J Contam Hydrol 35 4 429 440 Sun Y J N Petersen T P Clement and R S Skeen 1999b Development of Analytical Solution
27. 994 43 55 Domenico 1987 An Analytical Model for Multidimensional Transport of a Decaying Contaminant Species J Hyarol 91 49 58 Domenico P A and F W Schwartz 1990 Physical and Chemical Hydrogeology Wiley New York NY Gelhar L W C Welty and K R Rehfeldt 1992 A Critical Review of Data on Field Scale Dispersion in Aquifers Water Resour Res 28 7 1955 1974 Gossett and S H Zinder 1996 Microbiological Aspects Relevant To Natural Attenuation of Chlorinated Solvents Proceedings of the Symposium on Natural Attenuation of Chlorinated Organics in Ground Water September 11 13 1996 Dallas TX EPA 540 R 96 509 Hartmans S J A M de Bont J Tamper and K Ch A M Luyben 1985 Bacterial Degradation of Vinyl Chloride Biotechnol Lett 7 6 383 388 Hartmans 5 and J A M de Bont 1992 Aerobic Vinyl Chloride Metabolism in Mycobacterium aurum Li Appl Environ Microbiol 58 4 1220 1226 Holliger C G Schraa A J M Stams and A J B Zehnder 1993 A Highly Purified Enrichment Culture Couples the Reductive Dechlorination of Tetrachloroethene to Growth Appl and Environ Microbiol 59 2991 2997 Howard P H R S Boethling W F Jarvis W M Meylan and E M Michalenko 1991 Handbook of Environmental Degradation Rates Lewis Publishers Inc Chelsea MI Hughes J B C J Newell and R T Fisher 1997 Process for In Situ Biodegradation of Chlorinated Aliphatic Hydrocarbons by Su
28. A alone Chlorinated Ethenes The reaction rate equations describing the sequential first order decay of the chlorinated ethenes are shown below AC PCE 1 PCE r AC TCE 1 1 2 DCE 2 2 3 C 3 3 DCE 4 AC ETH 44 VC 5 ETH where A A 2 and A are the first order biotransformation rate coefficients y y y are the daughter parent compound molecular weight ratios and Coce Cy and are the aqueous concentration of PCE TCE DCE vinyl chloride and ethene respectively Note BIOCHLOR assumes no degradation of ethene A 0 in zone 1 From these expressions it is clear that TCE DCE and VC are simultaneously being produced and degraded which often results in net accumulation before observed degradation Furthermore these reaction expressions cause the reactive transport equations to be coupled to each other as discussed in more detail in Appendix A 3 Chlorinated Ethanes The following are the rate expressions for the degradation of the chlorinated ethanes AC TCA 5 TCA yAC_ DCA 5 5 TCA 6 DCA r CA 6 6 DCA 7 A CA where A A and are the biotransformation rate coefficients is the abiotic rate coefficients for chloroethane y and y are the daughter parent compound molecular weight ratios and Cy and are the concentration of 1 1 1 trich
29. CHLOR assumes uniform hydrogeologic and environmental conditions over the entire model area Being an analytical model BIOCHLOR assumes constant source hydrogeological and biological property values for the entire model area and therefore simplifies actual site conditions For this reason the model should not be applied where extremely detailed accurate results that closely match site conditions are required More comprehensive numerical models should be applied in such cases 3 BIOCHLOR is primarily designed for simulating the sequential reductive dechlorination of chlorinated ethanes and ethenes The sequential biotransformation feature in BIOCHLOR should not be used for compounds that do not degrade via sequential first order kinetics While the interface is designed for simulating the biotransforma tion of chlorinated ethenes i e PCE TCE DCE and vinyl chloride VC and chlorinated ethanes i e TCA DCA and chloroethane CA the model can be adapted for other sequential decay reactions by experienced users see Appendix A 2 Fundamentals of Natural Attenuation Overview of Natural Attenuation Natural Attenuation refers to naturally occurring processes in soil and ground water environments that act without human intervention to reduce the mass toxicity mobility volume or concentration of contaminants in those media These in situ processes include biotransformation dispersion dilution adsorption volatilization and c
30. Data 200 128 wie Das Distance From Source ft ETHFiekd Data HET Te individual Time Input sms Figure A 7 Centerline output Cape Canaveral Air Force Base Florida DiESOLVED CHL RINATED SOLVENT CONCENTRATIONS ALONG PLUME CENTERLINE Distance from Source fi Dep Risener Sequential It Onder ec Fd Dl from Sie 106 000 Ta non 1 nou 2100 apin anal Conceniration mg L Uu A anu 00 on Don 200 Distance From Source ft Figure A 8 Individual centerline output for TCE Cape Canaveral Air Station Florida 44 004 0034 0019 0110 0005 n4a3 0208 0090 0055 0034 0019 0010 0000 0000 0000 0000 0000 ami Current pf Ground Wier in Fire Rte vi ater Through Source rea Distance fram Seuraa Plot Data gt Targat Figure 9 Array concentration output for TCE Cape Canaveral Air Station Florida 45 Sensitivity Analysis Examples Sensitivity analyses are recommended when literature values are used or if there is uncertainty in an input parameter To illustrate the response of the BIOCHLOR model to changes in the input parameters a sensitivity analysis was conducted for the first order decay coefficients and also for the common retardation factor In the first sensitivity analysis example the case study baseline problem was run with the
31. Dialog Box a Windows Dialog Box or you may see Windows Help load and display the error This problem is related to the ease with which the Windows Help Engine can find the data file BIOCHLR HLP are some suggestions in decreasing order of preference for helping WinHelp find it e Ifyou are asked to find the requested file do so The file is called BIOCHLR HLP and it was installed in the same directory folder as the BIOCHLOR model file BIOCHL7 xls or BIOCH97 xls Usethe File Open menus from within Excel instead of double clicking on the filename or Program Manager icon to open the BIOCHLOR model file This sets the current directory to the directory containing the Excel file you just opened 21 Change the WinHelp in the VB Module to hard code the directory information That way the file name and its full path will be explicitly passed to WinHelp If you have Excel 7 0 go to Tools and select Options From Options select the View tab and check sheet tabs You will then see the worksheet tabs Select the Macro Module tab and search for the text Enter the new path If you have Excel 97 go to the Tools menu and select Macro Enter btnBasic Help click for the macro you are searching for This will take you to all the help files Enter the new path As a last resort you can add the BIOCHLOR directory to your path located in your AUTOEXEC BAT file and this problem will be cured You will ha
32. Estimate Extent of NAPL Residual and Free Phases Determine Groundwater Flow and Solute Transport Parameters Along Core of Plume Using Site Specific Data Porosity and Dispersivity may be Estimated Estimate Biodegradation Rate Constant Compare the Rate of Transport to the Rate of Attenuation using Analytical Solute Transport Model BIOCHLOR Screening Criteri PROCEED TO FULL Appear that Natural Evaluate use of Selected NATURAL ATTENUATION STUDY Attenuation Alone will Additional Remedial Options Meet Regulatory along with Natural Attenuation Perform Site Characterization to Evaluate Natural Attenuation PROCEED TO FULL NATURAL ATTENUATION STUDY Figure 3 Initial screening process flow chart BIOCHLOR Concepts The BIOCHLOR Natural Attenuation software is based on a sequential first order coupled reactive transport model The transport problem is analytically solved using the Domenico model 1987 by uncoupling the transport equations using a novel analytical strategy Sun et al 1999 1999b Sun and Clement 1999 as discussed in Appendix The original Domenico model assumes a fully penetrating vertical plane source oriented perpendicular to ground water flow to simulate the release of organics to moving ground water and accounts for the effects of one dimensional advective transport three dimensional dispersion linear adsorption and first order decay In BIOCHLOR the Domenico sol
33. REEN 0 150 300 LEGEND Monitoring point BIOCHLOR SOURCE ZONE Monitoring well location ASSUMPTIONS TCE AS EXAMPLE TCE detected in groundwater sample mg L TCE concentration isopleth mg L CCFTA 2 Cape Canaveral Air Station Florida No TCE detected Figure 5 BIOCHLOR source zone assumptions TCE as example 41 BIOCHLOR Modeling Summary Cape Canaveral Air Station Florida Entering Input BIOCHLOR was used to reproduce the movement of the plume from 1965 the best guess for when the release occurred to 1998 The hydraulic conductivity hydraulic gradient and the effective porosity were entered and the C button was pressed to generate the seepage velocity For longitudinal dispersivity a fixed dispersivity of 40 ft Option 1 was chosen The ratio of lateral dispersivity to longitudinal dispersivity was set to 0 1 and the vertical dispersivity was set to 0 This last value was chosen because the depth of the source area is similar to the depth of the saturated zone To determine the retardation factors the aquifer matrix bulk density the partition coefficients at 20 C and the fraction of organic carbon were input into the gray cells and the button was pushed to yield the retardation factors BIOCHLOR uses one retardation factor not individual retardation factors for each constituent The default value for the common retardation factor is the median retardation factor but the user can ove
34. Sand 0 10 0 30 Fract Granite 0 00005 0 01 Medium Sand 0 15 0 30 Coarse Sand 0 20 0 35 Gravel 0 10 0 35 From Wiedemeier et al 1995 originally from Domenico and Schwartz 1990 and Walton 1988 Typically estimated One commonly used value for silts and sands is an effective porosity of 0 25 The ASTM RBCA Standard ASTM 1995 includes a default value of 0 38 to be used primarily for unconsolidated deposits Enter directly Note that if seepage velocity is entered directly this parameter is still needed to calculate the retardation factor and plume mass flux 2 Dispersivity Longitudinal Dispersivity alpha Transverse Dispersivity alpha y Vertical Dispersivity alpha z Description Dispersion refers to the process whereby a dissolved solvent will be spatially distributed longitudinally along the direction of ground water flow transversely perpendicular to ground water flow and vertically downward because of mechanical mixing and chemical diffusion in the aquifer These processes develop the plume shape that is the spatial distribution of the dissolved solvent mass in the aquifer Selection of dispersivity values is a difficult process given the impracticability of measuring dispersion in the field However simple estimation techniques based on the length of the plume or distance to the measurement point scale are available from a compilation of field test data Resear
35. TCE gt c DCE in 1997 Started with c DCE gt VC i literature values and then adjusted model to fit field data General Modeled Area Length 1085 ft Based on area of affected Modeled Area Width 700 ft ground water plume From 1965 first release Simulation Time 33 yrs to 1998 Source Data Source Thickness 56 ft Based on geologic logs and monitoring data see Area figure A 5 for TCE Source Widths ft 105 Example Modeled source area as Source Concentrations mg L Area 1 variable source PCE 0 056 Source concentrations are 15 8 aqueous concentrations TCE 98 5 c DCE 3 080 VC 0 030 ETH Actual Data Distance From Source ft 650 930 1085 Based on 1997 observed ND lt 0 001 lt 0 001 concentrations at site near centerline of plume 0 0165 0 0243 0 019 0 776 1 200 0 556 c DCE mg L VC mg L per 5 024 ETH mg L 0 150 Array Concentration See Figure A 9 Po PCE Conc mg L TCE Conc mg L 40 2 11 ND CCFTA2 1 4 2 18 0 001 0 001 CCFTA2 6 0 001 CCFTA2 4 0 001 Banana River FS CCFTA2 208 0 008 Source Zone Assumption Source 7 Actual Source Conc Width ft in 1997 mg L How Derived 105 15 8 Maximum concentration 175 0 316 Geometric mean between edge of zone 1 and 2 298 0 01 Geometric mean between edge of zone 2 and 3 This method of determining widths is different from the method SCALE ft used in BIOSC
36. W United States Office of Research and EPA 600 R 00 008 Environmental Protection Development January 2000 Agency Washington DC 20460 BIOCHLOR Natural Attenuation Decision Support System User s Manual Version 1 0 SURFACE TOP OF WATER BEARING UNIT BOTTOM OF WATER BEARING UNIT EPA 600 R 00 008 January 2000 BIOCHLOR Natural Attenuation Decision Support System User s Manual Version 1 0 by Carol E Aziz and Charles J Newell Groundwater Services Inc Houston Texas James R Gonzales and Patrick Haas Technology Transfer Division Air Force Center for Environmental Excellence Brooks AFB San Antonio Texas T Prabhakar Clement and Yunwei Sun Battelle Pacific Northwest National Laboratory Richland Washington Project Officer David Jewett Subsurface Protection and Remediation Division National Risk Management Research Laboratory Ada Oklahoma 74820 NATIONAL RISK MANAGEMENT RESEARCH LABORATORY OFFICE OF RESEARCH AND DEVELOPMENT U S ENVIRONMENTAL PROTECTION AGENCY CINCINNATI OHIO 45268 NOTICE The information in this document was developed through a collaboration between the U S EPA Subsurface Protection and Remediation Division National Risk Management Research Laboratory Robert S Kerr Environmental Research Center Ada Oklahoma RSKERC and the U S Air Force U S Air Force Center for Environmental Excellence Brooks Air Force Base Texas EPA staff contributed conceptual guidance
37. and constituent properties Typical Values 1 to 6 for solvents in typical shallow aquifers Source of Data Usually estimated from soil and chemical data using variables described below p bulk density effective porosity organic carbon water partition coefficient K distribution coefficient and fraction organic carbon on uncontaminated soil with the following expression K R 1 gt e where Koc foc When biotransformation rates are insignificant the retardation factor can be estimated by comparing the plume length of an adsorbed compound to the plume length of a conservative non adsorbing compound How to Enter Data 1 Enter the retardation factor for each constituent directly Do NOT press the C button The worksheet will be updated automatically OR 2 Fill in the estimated values for bulk density partition coefficient effective porosity and fraction organic carbon and calculate the retardation factor by pressing the C button Common R BIOCHLOR uses one retardation factor for all the constituents not individual retardation factors Currently BIOCHLOR calculates the median retardation factor and uses that value in all calculations Alternatively the user can enter another retardation value in the cell beside Common R The Common R value that is chosen should be representative of the retardation factors of the constituents modeled In addition sensitivity analyses should be conducted to evalua
38. arty 1985 Vogel and McCarty 1987 Therefore it is possible for daughter products to increase in concentration before they decrease as shown in Figure 2 BIOCHLOR accounts for sequential first order decay of this nature and this sets it apart from BIOSCREEN Newell et al 1996 which models the biodegradation of fuel hydrocarbons via first order decay or electron acceptor limited instantaneous reaction processes 1 1 DCA Chloroethane Ethane CH3CH3 Cis 1 2 DCE Trichloroethane TCE Trichloroethene DCA Dichlorethane Minor pathway DCE Dichloroethene PCE Perchloroethene TCA Major pathway Figure 1 Reductive dechlorination pathways for common chlorinated aliphatic hydrocarbons after Vogel and McCarty 1985 Vogel and McCarty 1987 A 00 80 70 20 0 0 Distance From Source ft Figure 2 Reductive transformation of chlorinated ethenes For biological reductive dechlorination to occur the following conditions must exist 1 The subsurface environment must be anaerobic and have a low oxidation reduction potential ORP 2 Chlorinated solvents that are amenable to reductive dechlorination must be present 3 A population of dechlorinating bacteria must be present 4 An adequate supply of fermentation substrates to produce dissolved hydrogen must be present The environmental chemistry and the ORP of a site play an important role in determini
39. ated ground water geologic heterogeneities the presence and quantity of DNAPL and sorbed constituents NRC 1994 In the pump and treat module the user enters the system pumping rate and the number of pore volumes treated removed in one year is calculated by the program This value provides the user with an indication of the feasibility of the pump and treat system If the extraction rate is less than one pore volume per year the attainment of clean up criteria will likely take decades even under the most favorable conditions NRC 1994 Another cell asks the user to input the number of pore volumes that must be removed in order to clean up the aquifer Using this value and the pumping rate the time to clean up the contaminated aquifer can be estimated The number of pore volumes required to remediate the aquifer is a site specific and technology specific value document Guidance Remedial Actions for Contaminated Ground Water at Superfund Sites U S EPA 1988 describes two methods for estimating ground water clean up times based on the number of pore volumes the batch flushing model and the continuous flushing model Neither of these methods account for DNAPL and therefore underestimate clean up times third method accounting for DNAPL is reported in Newell et al 1994 and Wiedemeier et al 1999 38 Appendix 6 BIOCHLOR Example Example Cape Canaveral Air Station Fire Training Area Florida Problem
40. ays Can t Calc for Volume If the contaminant concentration in the plume at the end of the model length is greater than 0 005 mg L then the model concludes that the model area see Input Screen Section 5 General Data is not sized to capture the entire plume volume in the 5x10 array and writes Can t Calc in the box The user is encouraged to adjust the modeled length and width to capture the plume in the 5x10 array Flow Rate of Water Through Source Area ac ftlyr Using the Darcy velocity the source thickness and the source width BIOCHLOR calculates the rate that clean ground water moves through the source area where it will pick up dissolved solvents Note that the ground water Darcy velocity is equal to the ground water seepage velocity multiplied by effective porosity 20 Quick Start Minimum System Requirements The BIOCHLOR model requires a computer system capable of running Microsoft Excel 7 0 or 97 for Windows If you have Excel 97 you are advised to use the Excel 97 version of BIOCHLOR Operation requires an IBM compatible PC equipped with a Pentium or later processor running at a minimum of 150 MHz A minimum of 32 MB of system memory RAM is strongly recommended Installation and Start Up The software is installed by copying the BIOCHLOR model file BIOCHL7 xls BIOCH97 xls and the BIOCHLOR help file BIOCHLR hlp to the same folder on your computer hard drive To use the software start Exce
41. be considered only in the second zone and should be modeled only by experienced users as discussed in Appendix A 2 Note This two zone model should be employed only when the plume is at steady state throughout the first zone The plume is at steady state if plume concentrations field measurements or model predictions are not changing with time This condition is required to ensure the constant concentration boundary condition at the boundary between zone 1 and zone 2 Refer to Appendix A 2 for a more detailed discussion BIOCHLOR Data Entry Three important considerations regarding data input are 1 To see the example data set in the input screen of the software click on the Paste Example Data Set button on the lower right portion of the input screen 2 Because BIOCHLOR is based on the Excel spreadsheet you must click outside of the cell where you just entered data or hit return before any of the buttons will work 3 Parameters used in the model can be entered directly into the white cells or they can be calculated by the model using data entered in the gray cells e g seepage velocity can be entered directly or calculated using hydraulic conductivity gradient and effective porosity followed by pressing the button NOTE Although literature values are provided it is strongly recommended that the user employ measured hydrogeological and biotransformation values whenever possible If literature values are used and there
42. bsurface Hydrogen Injection U S Patent No 5 602 296 Issued March 11 1997 Jeffers P M L M Ward L M Woytowitch and N L Wolfe 1989 Homogeneous Hydrolysis Rate Constants for Selected Chlorinated Methanes Ethanes Ethenes and Propanes Environ Sci Technol 23 965 969 LaGrega M D P L Buckingham J C Evans 1994 Hazardous Waste Management McGraw Hill New York Mackay D W Y Shiu and K C Ma 1993 llustrated Handbook of Physical Chemical Properties and Environmental Fate for Organic Chemicals Vol Ill Volatile Organic Chemicals Lewis Publishers Boca Raton FL Martin Hayden J M and G A Robbins 1997 Plume Distortion and Apparent Attenuation Due to Concentration Averaging in Monitoring Wells Ground Water 35 2 339 346 Maymo Gatell X Y Chien Y J M Gossett and S H Zinder 1997 Isolation of a Bacterium That Reductively Dechlorinates Tetrachloroethene to Ethene Science 276 1568 1571 McCarty P L 1996 Biotic and Abiotic Transformations of Chlorinated Solvents in Groundwater in Symposium on Natural Attenuation of Chlorinated Organics in Ground Water Dallas TX Sept 11 13 1996 McCarty P L and L Semprini 1994 Groundwater Treatment for Chlorinated Solvents In Handbook of Bioremediation Lewis Publishers Boca Raton FL National Research Council 1994 Alternatives for Ground Water Cleanup National Academy Press Washington D C Newell C J J Gonzales and McLeod
43. chers indicate that dispersivity values can range over 2 3 orders of magnitude for a given value of plume length or distance to measurement point Gelhar et al 1992 For more information on dispersivity see Appendix A 4 Typical Values The user also has the option to enter a fixed diffusivity value or dispersivity relation as a function of x distance from the source in ft BIOCHLOR is programmed with some commonly used relations based on scale that are representative of typical and low end dispersivities A fixed dispersivity value should be used for 2 zone simulations Longitudinal Dispersivity The user is given three options Option 1 the default option allows the user to specify a fixed value for alpha x One commonly used relation is to assume that alpha x is 1096 of the estimated plume length This option is required for conducting 2 zone biotransformation simulations Option 2 assumes that alpha x 0 1 x Pickens Grisak 1981 Option 3 calculates the longitudinal dispersivity using the following correlation Alpha x x 3 28 0 28 lo CEDE and Eckstein 1995 Al Suwaiyan 1996 Transverse Dispersivity The user may choose a ratio of alpha y alpha x One commonly used ratio is Alpha y alpha x 0 10 Based on high reliability points from Gelhar et al 1992 Vertical Dispersivity The user may choose a ratio of alpha z alpha x One commonly used ratio is Alpha z alpha x 0 05 ASTM
44. d like to acknowledge the U S Air Force Center for Environmental Excellence AFCEE for supporting the development of BIOCHLOR We would like to specifically acknowledge Marty Faile and Jim Gonzales We also wish to acknowledge Ann Smith Radian International Austin TX for contributing to the development of BIOCHLOR Special thanks also to Phil deBlanc Leigh Ita Ric Bowers Julia Aziz Tariq Khan and Martha Williams The BIOCHLOR software and manual was reviewed by a distinguished review team We wish to acknowledge members of the team for their comments and suggestions Dr Harry Beller Lawrence Livermore National Laboratory Livermore CA Ned Black U S EPA Region 9 San Francisco CA Joan Elliott U S EPA National Risk Management Research Laboratory Ada OK Dr Rolf Halden Lawrence Livermore National Laboratory Livermore CA Enamul Hoque ManTech Environmental Research Services Corp Ada OK Dr David Jewett U S EPA National Risk Management Research Laboratory Ada OK Dr Ann Azadpour Keeley U S EPA National Risk Management Research Laboratory Ada OK Dr Roger Lee U S Geological Survey Dallas TX Herb Levine U S EPA Region 9 San Francisco CA Dr Elise Striz ManTech Environmental Research Services Corp Ada OK Luanne Vanderpool U S EPA Region 5 Chicago IL iv Contents 1 Intended Uses for BIOCHLOR 1 Fu
45. del and estimate rate coefficients be aware that the Domenico model assumes constant dispersivity values The user must choose between using a variable dispersivity that is likely to be more physically accurate at each point or a fixed dispersivity value that makes each point mathematically consistent with each other In general if the user would like the best estimate of concentration at each point in a BIOCHLOR simulation use a variable dispersivity If the user would like accurate mass balances between each point use a fixed dispersivity Fixed dispersivity values should be used for two zone simulations BIOCHLOR is programmed with some commonly used relations based on x distance from the source in ft that are representative of typical and low end dispersivities The user also has the option to enter fixed diffusivity values Longitudinal Dispersivity The user is given three options Option 1 the default option allows the user to specify a fixed value for alpha x One commonly used relation is to assume that alpha x is 1096 of the estimated plume length Option 2 assumes that alpha x 0 1 x Option 3 calculates the longitudinal dispersivity using the following correlation 2 446 Alpha x 3 28 082 log 4 Xu and Eckstein 1995 Al Suwaiyan 1996 Transverse Dispersivity The user may choose a ratio of alpha y alpha x One commonly used ratio is Alpha y alohax 2 0 10 Based on high reliability points from Gelhar et al 1992
46. e ability to simulate 1 D advection 3 D dispersion linear adsorption and biotransformation via reductive dechlorination the dominant biotransformation process at most chlorinated solvent sites Reductive dechlorination is assumed to occur under anaerobic conditions and dissolved solvent degradation is assumed to follow a sequential first order decay process BIOCHLOR includes three different model types 1 Solute transport without decay 2 Solute transport with biotransformation modeled as a sequential first order decay process 3 Solute transport with biotransformation modeled as a sequential first order decay process with two different reaction zones i e each zone has a different set of rate coefficient values BIOCHLOR was developed for the Air Force Center for Environmental Excellence AFCEE Technology Transfer Division at Brooks Air Force Base by Groundwater Services Inc Houston Texas The mathematical technique to solve the coupled reactive transport equations was developed by researchers at the Battelle Pacific Northwest National Laboratory Intended Uses for BIOCHLOR BIOCHLOR attempts to answer the following fundamental question regarding RNA How far will a dissolved chlorinated solvent plume extend if no engineered controls or source area reduction measures are implemented BIOCHLOR uses an analytical solute transport model with sequential first order decay for simulating in situ biotransformation Sun et al 1999a
47. e residual DNAPL behind that act as a source of ground water contamination that extends vertically from the water table to the bottom of the saturated zone SURFACE TOP OF WATER BEARING UNIT Source Thickness BOTTOM OF WATER BEARING UNIT Typical Values 20 50 ft Source of Data This value is usually determined by evaluating ground water data from wells near the source area screened at different depths If this type of information is not available then the depth of the aquifer can be used as a conservative estimate How to Enter Data Enter directly 7 Field Data for Comparison Field Concentrations and Distances from Source Units mg L Description These parameters are concentrations of dissolved organics in wells near the centerline of the plume These data are used to help calibrate the model and are displayed with model results in the Run Centerline option Typical Values 0 001 to 50 mg L Source of Data Monitoring wells located near the centerline of the plume How to Enter Data Enter as many or as few of these points as needed The data are used only to help calibrate the model when comparing the results from the centerline option Enter the distance from the source that corresponds to the field concentration Warning Do NOT cut and paste field data from one column to another This can cause spreadsheet errors Copy data and then erase unwanted data 18 Analyzing BIOCHLOR Output The
48. el the simulation time can be varied to determine the future extent of contamination Field derived biological rate coefficients should be used if possible but literature values may be used in the absence of site specific rate constants or the model may be calibrated to field data The primary purpose of comparing the transport rate to the attenuation rate is to determine if the residence time along the flow path is adequate to protect human health and the environment i e to estimate if the contaminant degrades to an acceptable concentration before receptors are exposed In the case of rate coefficients or any other parameter that is not known accurately or that varies over the extent of the plume sensitivity analyses should be conducted If modeling shows that the receptors will not be impacted by contaminants at concentrations above regulatory criteria then the screening criteria are met and the investigator can proceed with a full natural attenuation evaluation Details of a full natural attenuation evaluation can be found in Technical Protocol For Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water U S EPA 1998 Analyze Available Site Data Along Core of Plume to Determine if Biodegradation is Occurring Collect More Screening Data Sufficient Data Engineered Remediation Available Required Implement Other Protocols INSUFFICIENT DATA Locate Source s and Potentia Points of Exposure
49. elineate the two zones by looking at field data D O fermentable carbon hydrogen concentrations etc and determine an appropriate distance from the source How to Enter Data Enter the value for zone 1 directly The value for zone 2 will be automatically calculated by deducting the zone 1 length from the model area length when the button is pressed If only one biotransformation zone is being modeled be sure that the zone length is the same as the model area length 15 6 Source Data Source Area Concentrations Description Aqueous phase concentration of chlorinated solvents in the source area The source term corresponds to a vertical source plane normal to the direction of ground water flow located at the downgradient limit of the area serving as the principal source of solvent release to the ground water e g affected unsaturated zone soils NAPL plume land disposal unit spill area etc In the absence of such data the source term should be located at the point of the maximum measured plume concentration s One rule of thumb for inferring the location of DNAPL is to look for aqueous phase concentrations in excess of 1 of solubility Pankow and Cherry 1995 Cohen and Mercer 1993 Distance to downgradient points of exposure should then be measured from this location along the principal direction of ground water flow Affected Soil Zone Affected Ground Water Flow Ground Water P
50. ent will be spatially distributed longitudinally along the direction of ground water flow transversely perpendicular to ground water flow and vertically downward because of mechanical mixing and chemical diffusion in the aquifer These processes develop the plume shape that is the spatial distribution of the dissolved solvent mass in the aquifer Selection of dispersivity values is a difficult process given the impracticability of measuring dispersion in the field However dispersivity data from over 50 sites has been compiled by Gelhar et al 1992 see Figures and A 4 The empirical data indicates that longitudinal dispersivity in units of length is related to scale distance between source and measurement point Gelhar et al 1992 indicate 1 there is a considerable range of dispersivity values at any given scale on the order of 2 3 orders of magnitude 2 suggest using values at the low end of the range of possible dispersivity values and 3 caution against using a single relation between scale and dispersivity to estimate dispersivity However most modeling studies do start with such simple relations and BIOCHLOR is programmed with some commonly used relations representative of typical and low end dispersivities Note Based on Gelhar s work use of variable dispersivity values should yield a better estimate of concentration at each distance downgradient of the source However when using field data to calibrate the mo
51. ested in centerline predictions and the mass flux into the canal the source area will be modeled as a Spatially variable source By pressing the Source Options button and selecting Spatially Variable Source a dialog box pops up that allows for the input of source area concentration and width data To obtain the most conservative centerline predictions the maximum concentration in the source area were used for zone 1 The other two concentrations were obtained by taking the geometric means between adjacent isopleths see Figure 5 Once these data are entered and OK is pressed the data are transferred to the input page and you will see the layout shown in Figure A 6 Note that any subsequent changes to the source area concentrations can be done directly on the input page without going through the dialog box Lastly the thickness of the source area was determined by entering the deepest depth where chlorinated solvents were detected in the aqueous phase Finally there is an input area for field data In this example the 1997 field data were used previously to determine the rate constants provided If one does not have field scale rate constants or rate data from microcosm studies these values become important for calibrating the model Viewing Output There are two choices for viewing the output Centerline predictions are shown for all five species in Figure A 6 and for TCE in Figure A 8 Figure A 7 shows the centerline predict
52. ex sites BIOCHLOR and its User s Manual have undergone external and internal peer review conducted by the U S EPA and the U S Air Force However BIOCHLOR is made available on an as is basis without guarantee or warranty of any kind express or implied Neither the United States Government U S EPA or U S Air Force Ground Water Services Inc any of the authors nor reviewers accept any liability resulting from the use of BIOCHLOR or its documentation Implementation of BIOCHLOR and interpretation of the predictions of the model are the sole responsibility of the user ii FOREWORD The U S Environmental Protection Agency is charged by Congress with protecting the Nation s land air and water resources Under a mandate of national environmental laws the Agency strives to formulate and implement actions leading to a compatible balance between human activities and the ability of natural systems to support and nurture life To meet these mandates EPA s research program is providing data and technical support for solving environmental problems today and building a science knowledge base necessary to manage our ecological resources wisely understand how pollutants affect our health and prevent or reduce environmental risks in the future The National Risk Management Research Laboratory is the Agency s center for investigation of technologi cal and management approaches for reducing risks from threats to human health and the environment
53. hanol 0 37 20 C 1 1 1 trichloroethane to 1 1 DCE 0 058 0 32 10 20 C 1 1 1 trichloroethane to acetic acid 0 25 to 0 41 from Vogel McCarty 1987 McCarty 1996 Optional methods for selection of appropriate rate coefficients are as follows Literature Values Various published references are available that list rate coefficients for hydrolysis and other abiotic processes e g Howard et al 1991 Press A button Enter values in the dialog box and press 13 4 Biotransformation Data cont Description Because biotransformation rate expressions are calculated on a molar basis and BIOCHLOR accepts concentration data on a mass basis i e mg L a conversion factor must be incorporated to account for the amount of mass of daughter product produced from the degradation of the parent compound The yield is the ratio of the daughter product molecular weight to the parent compound molecular weight Note This is NOT the biomass yield Typical Values TCE PCE 0 795 DCA TCA 0 742 DCE TCE 0 737 CA DCA 0 652 VC DCE 0 645 ETHA CA 0 465 ETH VC 0 450 Sources of Data Values for the chlorinated ethenes and ethanes have been provided The user only needs to input yields if working with other substances that decay by sequential first order decay How to Enter Data Enter directly 5 General Data Model Area Length and Width L and W Description Physical dimensions in feet of the
54. hemical or biological stabilization or destruction of contaminants U S EPA 1998 Biotransformation can often be a dominant process in the natural attenuation of chlorinated solvents At chlorinated solvent contaminated sites most of the solvent degradation occurs by reductive dechlorination U S EPA 1998 Reductive dechlorination is a microbially mediated reaction whereby a chlorine atom on the chlorinated solvent is replaced by a hydrogen atom Vogel and McCarty 1987 In many bioremediation processes an organic contaminant such as benzene acts as an electron donor and another substance such as oxygen nitrate etc acts as the electron acceptor However during reductive dechlorination hydrogen acts as the electron donor and halogenated compounds such as chlorinated solvents act as electron acceptors and thus become reduced as shown in the following half reaction R Cl H 2e gt Figure 1 shows the reductive transformation pathways for the common chlorinated aliphatics details on the biotransformation of chlorinated solvents can be found in Appendix A 2 Reductive dechlorination can be modeled as a sequential first order decay process This means that a parent compound undergoes first order decay to produce a daughter product and that product undergoes first order decay and so on Generally the more highly chlorinated the compound the more rapidly it is reduced by reductive dechlorination Vogel and McC
55. ial concentration 0 for x y z gt 0 2 c 0 Y Z 0 C Source concentration for each vertical plane source C at time 0 The key assumptions in the model are 1 The aquifer and flow field are homogenenous and isotropic 2 The ground water velocity is fast enough that molecular diffusion in the dispersion terms can be ignored may not be appropriate for simulation of transport through clays 3 Adsorption is a reversible process represented by a linear isotherm The key limitations to the model are 1 The model should not be applied where pumping systems create a complicated flow field 2 The model should not be applied where vertical flow gradients affect contaminant transport 3 The model should not be applied where hydrogeologic conditions change dramatically over the simulation domain The most important modifications to the original Domenico model are 1 Biotransformation is assumed to occur only in the aqueous phase The original Domenico model was derived assuming that biotransformation occurred equally rapidly in the soil and aqueous phases To make this adjustment the rate constants were divided by the retardation factor 2 To simulate a spatially varying source BIOCHLOR superimposes three Domenico models each with a different concentration and source width Connor et al 1994 The original Domenico model was derived for a single planar source of constant concentration 26 Appendix A 2 Kinetics of Sequen
56. idth Typical Values Source of Data How to Enter Data The Domenico 1987 model assumes a vertical plane source of constant concentration The source width is the extent of the source area perpendicular to the ground water flow 120 700 ft To determine a source width across the site draw a line perpendicular to the direction of ground water flow direction in the source area The source area is typically defined as being the area with contaminated soils having high concentrations of sorbed organics free phase NAPLs or residual NAPLs If the source area covers a large area it is best to choose the most downgradient or widest point in the source area for determining the source width Single Planar For a single planar source choose one width Spatially Varying For a spatially variable source BIOCHLOR allows the user to enter up to three widths and concentrations to define the source area using isopleth data See the diagram below Enter directly on input page or press Source Options button and follow instructions 17 6 Source Data cont Source Thickness In Saturated Zone Z Description Thickness of dissolved solvent in the source area The Domenico 1987 model assumes a vertical plane source of constant concentration For many solvent spill sites the thickness of this source area will be the saturated thickness of the aquifer As these solvents sink to the bottom of the aquifer they leav
57. ients and degradation rates since degradation is assumed to occur only in the aqueous phase It should be noted that the proposed analytical solution strategy would work only when the constant effective retardation factor is used to represent the retardation characteristics of all the transported species Computational Procedure In BIOCHLOR the initial concentration of all the species is assumed to be zero The boundary conditions at the source location can be non zero for one or more of the species The first step involved in applying the solution strategy is to convert all initial and boundary conditions of all daughter species into the transformed a domain using the transformation equations 6 to 9 After transforming all initial and boundary conditions the Domenico solution is used five times to prepare the solution array a a values at all nodes for all five species in the transformed domain Finally the solution arrays are transformed back into the concentration domain domain using an inverse form transformation equations 6 to 9 The FORTRAN code given below shows the implementation procedure Modeling Coupled PCE TCE DCE VC and ETH Transport and Degradation in 3 Dimensional Ground water Aquifers This Fortran code was developed by T P Clement amp Y Sun Battelle Pacific Northwest National Laboratory PARAMETER nx 60 ny 31 nc 5 ny should always be an odd number REAL 4 k DIMENSION c nx ny nc a nx ny nc k nc y nc
58. in concentration profiles for all other compounds must be ignored The clearest way to present this data is to transfer data from each run to a new Excel spreadsheet and re plot Table A 2 Modeling scenario 3 for chlorinated ethenes Compound Run 1 Run 2 Run 3 Shaded boxes indicate compounds whose output data should be recorded during each run For the chlorinated ethanes chloroethane is the only solvent that is degraded aerobically so that scenario 3 can be accomplished with one run as outlined in Table A 3 Table A 3 Modeling Scenario 3 for Chlorinated Ethanes 1 1 DCA 0 29 How BIOCHLOR Models 2 Zone Biotransformation The Domenico solution was developed assuming a constant source concentration and a constant biotransformation rate coefficient Simply changing the value of the rate constant at the boundary between zones 1 and 2 yields a large discontinuity in the concentration profile Therefore a new source area was defined at the boundary of zones 1 and 2 The new source was defined using the concentrations in the last cells of the zone 1 array and modeled as a spatially variable source To test the validity of this approach two simulations were carried out In the first the model length was modeled as one zone of 1200 ft In the second simulation the model length was divided into two zones 200 ft for zone 1 and 1000 ft for zone 2 and the biological rate constants that were used in the 1 zone si
59. ions for each chlorinated solvent and a no degradation curve for all of the chlorinated solvents added together as well as field data From this screen the user can view the centerline predictions of each constituent individually or go to the array screen Figure A 8 shows the centerline prediction for TCE with and without biotransformation However any of the constituents can be viewed by pressing the buttons to the right of the graph Here we can see that the TCE concentration discharging into the canal at 1085 ft is 0 003 mg L 42 th BIOCHLOR Natural Attenuation Decision Support System Version 1 0 Fire Trainin 115 et Emer wus directly or 2 filling in ars TYPE OF CHLORINATED SOLVENT 8 5 GEHERAL Emer then ij From this screen from the input screen the array page can be selected The array output for this problem is displayed in Figure A 9 This three dimensional figure shows the longitudinal and lateral extent of contamination Again the user can select the constituent to be viewed and the no degradation or biotransformation prediction Note that the scale on the array automatically changes depending on the magnitude of the concentrations These array values are maximum values because the array is evaluated at z 0 Other information that is presented on the output screen includes the mass removed the percent biotransformed and e mass f
60. l and load the BIOCHLOR model file from the File Open menu If you are using Excel 97 you may see a message box that asks you whether you wantto disable or enable the macros For BIOCHLOR to operate effectively you must enablethe macros BIOCHLOR Troubleshooting Tips Spreadsheet Related Problems The buttons won t work BIOCHLOR is built in the Excel spreadsheet environment and to enter data one must click anywhere outside the cell where data was just entered If you can see the numbers you just entered in the data entry part of Excel above the spreadsheet the data have not yet been entered Click on another cell to enter the data is displayed in a number box The cell format is not compatible with the value e g the number is too big to fit into the window To fix this press the Unprotect Sheet button Then select the cell pull down the format menu select Cells and click on the Number tab Change the format of the cell until the value is visible If the values still cannot be read select the format menu select Cells and click on the Font tab Reduce the font size until the value can be read DIV 0 is displayed in a number box The most common cause of this problem is that some input data are missing In some cases entering a zero in a box will cause this problem Double check to make certain that data required for your run have been entered in all of the input cells Note that for vertical dispersivity BIOCHLOR will
61. length is the same as the model length if the user is modeling the plume as one zone Modeling a site using two zones allows the user to specify different first order decay coefficients for each zone of the aquifer One biotransformation zone is appropriate for sites where the environmental conditions D O ORP hydrogen concentrations etc do not change appreciably over the extent of the plume For sites where environmental conditions change significantly over the extent of the plume a 2 zone model may be more appropriate For example sites with high levels of fermentable organics high H5 near the source but not near the plume front may be best modeled in two zones because the concentration of hydrogen affects the the rate of reductive dechlorination The hydrogen concentration in turn affects the first order decay coefficient Although BIOCHLOR is primarily designed to model the anaerobic sequential decay of chlorinated solvents and no degradation zones aerobic zones can also be modeled by experienced users see Appendix A 2 for instructions Note that two zone biotransformation estimates should only be used when the plumes in zone 1 are at steady state i e concentrations not changing with time Refer to Appendix A 2 for a more detailed discussion Typical Values 500 3000 ft Source of Data If only one biotransformation zone is being modeled then use the same value as the model length If the plume will be modeled in two zones d
62. loroethane 1 1 dichloroethane and chloroethane respectively Because BIOCHLOR is programed in mass units yield constants i e Y to account for molecular weight differences between parent and daughter compounds were incorporated The constants are necessary because kinetic expressions are valid on a molar basis only Other Chlorinated Compounds Although BIOCHLOR is programmed to model the reductive dechlorination of chlorinated ethenes and ethanes primarily it can also be used to model any chlorinated compound that degrades via sequential first order decay kinetics To use BIOCHLOR for compounds other than chlorinated ethenes and ethanes the user must input the yield constants the ratio of daughter product to parent compound molecular weights on the input page Be aware that output graphs will still show the chlorinated ethene or ethane labels 1 Zone vs 2 Zone Biotransformation If the contaminant plumes are at steady state BIOCHLOR can be used to model the plume in two zones with a different set of biotransformation rate coefficients in each zone BIOCHLOR is primarily designed to handle zones with anaerobic degradation and no degradation but it can be manipulated by experienced users to accommodate an aerobic zone in zone 2 in some cases BIOCHLOR cannot model aerobic conditions in zone 1 Table A 1 presents the scenarios that BIOCHLOR can execute A Type environment occurs when the primary substrate is anthrop
63. lume Ground Water Ground Water Source Area Transport Area Constituent influent to Lateral transport attenuation of ground water system constituents in ground water system For the single planar option the maximum source area concentration should be entered on the input page or in the dialog box that transfers the data to the input page For the spatially varying option the user may enter three concentrations The maximum concentration in the source area can be used in area 1 and geometric mean concentrations can be used in areas 2 and 3 Using a single planar source yields accurate centerline concentration profiles but concentrations off the centerline will be overestimated The use of a spatially variable source will yield better off centerline concentration estimates but requires considerably more computation time For centerline simulations the single planar option is recommended Typical Values 0 010 to 120 mg L Note Source area dissolved solvent concentrations should not exceed the aqueous solubility at a given temperature The following are the aqueous phase solubilities at 20 C Mackay et al 1993 PCE 150 mg L 1 1 1 TCA 4400 mg L TCE 1100 mg L 1 1 DCA 5500 mg L cDCE 800 mg L CA 5710 mg L 6800 mg L Source of Data Source area monitoring well data How to Enter Data Enter directly on input page or press Source Options button and follow instructions 16 6 Source Data cont Source Area W
64. lux The TCE mass flux discharging to the canal is approximately 83 mg day Data Input Instruetiam Canaveral 3 D rdias 1 ADVECTIOR Aroa Disha dus dal Seapaga mz hee Madalad Aroa Zona 1 Hydraulic E Hydraulic Gradient i ETecike Porosity LR 7 IMSPEHSHIM Alpha x Calc Method a m Blaha 417 n1 Alpha si 11 99101 3 ADSORPTION Retardation Facia Soil Bulk Density 15 Tac Eat E r g TCE Li DCE 31 ETH xu L amp d Cummun in i i E TCE DCE 1m 070 nan 4 Zone ap POE amp amp 22 DCE DCE YE ETH non 4 Ethene igure A 6 BIOCHLOR input screen Cape Canaveral Air Force Base Florida 43 DISSOLVED CHLORINATED SOLVENT CONCENTRATIONS ALONG PLUME CENTERLINE Degradation Total Ethenes 1000 008 Prediction 100000 Prediction E Prediction 5 Prediction E Prediction E ras PE Pied Gate a TCE Fimi Oats 0001 a DCE Field
65. models in conjunction with other types of analysis can be used to evaluate the effectiveness of natural attenuation BIOCHLOR is an appropriate model at sites where simplifying assumptions e g uniform ground water flow a vertical plane source first order decay can be made so that the resulting simulations provide useful information for the problem being addressed At other sites where these assumptions do not hold a more sophisticated numerical model such as RT3D Clement 1997 would be appropriate As with any modeling study the authors recommend that proper care be used to select the model that is best suited to 1 the source hydrogeology and biotransformation processes present at the site and 2 the type of problem being addressed e g screening of alternatives providing supporting evidence of natural attenuation developing detailed design information BIOCHLOR has the following limitations 1 Asan analytical model BIOCHLOR assumes simple ground water flow conditions The model should not be applied where pumping systems create a complicated flow field In addition the model should not be applied where vertical flow gradients affect contaminant transport Note that a vertical distribution of chlorinated solvents throughout the saturated zone does not preclude the use of BIOCHLOR as this phenomenon is related to the initial vertical migration of dense non aqueous phase liquids in source areas 2 Asa screening tool BIO
66. mulation were used in each zone of the 2 zone simulation These simulations were carried out at steady state These simulations show that this solution technique yields good concentration estimates when the plume is at steady state Figure A 2 The steady state condition is required to ensure that the concentrations are constant at the boundary between the two zones The use of the 2 zone biotransformation model should NOT be used when the plume is not at steady state throughout zone 1 l Zone 2 Zone 5 3 8 8 S 5 5 40 60 800 Distance from Source ft Figure A 2 Comparison of solution techniques for BIOCHLOR 1 zone and 2 zone biotransformation models 30 Appendix BIOCHLOR Solution By T Prabhakar Clement and Yunwei Sun Battelle Pacific Northwest National Laboratory Richland WA 99345 Governing Equations The BIOCHLOR software solves a set of coupled partial differential equations to describe the reactive transport of chlorinated solvent species such as PCE TCE DCE VC and ETH in saturated ground water systems The equations describe one dimensional advection three dimensional dispersion linear sorption and sequential first order biotrans formation All equations except the first are coupled to a parent species equation through the reaction term as shown below ac 9 c 9 6 06 a Bag ae D p D x 1 amp de S D ac D
67. nce from top of saturated zone to measurement point assumed to be 0 concentration is always given at top of saturated zone Longitudinal ground water dispersivity ft Transverse ground water dispersivity ft Vertical ground water dispersivity ft Effective Soil Porosity First Order Degradation Rate Coefficient day Seepage Velocity fuyr Ki 99 Chemical Velocity ft yr v R Hydraulic Conductivity ft yr Constituent retardation factor Hydraulic Gradient cm cm Source Width ft Source Depth ft 25 Note that because biotransformation is assumed to occur only in the aqueous phase the first order rate constant A has been divided by R However can be canceled out by replacing v the compound velocity i e v the original Domenico solution with v the seepage velocity The Domenico solution was modified for chloroethane CA reactive transport to take into consideration both biotic and abiotic reactions The first order rate constant for abiotic decay A is added to the biological rate constant for reductive dechlorination as shown below All other terms in the Domenico equation remain the same 1 4 p 0 5 1 4 A XA Jax Vs x vtl 40 20x 2 axvt xf 1 4 A otx Vs 4 A aax Vs exp erf 20 2 a vt The initial conditions of the Domenico model are 1 c x 2 0 20 Init
68. ndamentals of Natural Attenuation ricercare eter ideae 2 Overview of Natural 2 Natural Attenuation Lines of Evidence and the Role 4 BOCH 91 50 61 M A 6 BIOCHEOR Model Types ti Beet e ERR 6 Data TM TT 6 T Hydrogeolodic Data oxi ette bul 7 ZA 1 181 1 INT PL E 9 3 Adsorption ela eade 10 4 Biotrarstormatorn tt po imde o UU nd EI 12 By 4 Mc 14 D DOHICO Dal Loon oet testo aus sel PLE es Et EL es 16 7 Field Data Tor Comparison eine ted e d RR M ree ERR 18 Analyzing BIOGBEOR OUIEDULDS bn ea aste n 19 Centerline 01 1 19 22 19 Calculating the Mass Balance Order of Magnitude Accuracy 19 21 Minimum System Requirements
69. ng whether reductive dechlorination will occur Based on thermodynamic considerations reductive dechlorination will occur only after both oxygen and nitrate have been depleted from the aquifer because oxygen and nitrate are more energetically favorable electron acceptors than chlorinated solvents when hydrogen is the electron donor U S EPA 1998 The role of hydrogen as an electron donor during reductive dechlorination is now widely recognized as a key factor governing the dechlorination of chlorinated compounds Gossett and Zinder 1996 Holliger et al 1993 Maymo Gatell et al 1997 Hughes et al 1997 Carr and Hughes 1998 The hydrogen is produced in the terrestrial subsurface by the fermentation of a wide variety of organic compounds including anthropogenic compounds such as petroleum hydrocar bons and natural organic matter Hydrogen is then used by the dechlorinating bacteria as an electron donor Although BIOCHLOR primarily models the degradation of chlorinated solvents via reductive dechlorination which occurs under highly reduced anaerobic conditions some of the chlorinated solvents may degrade under aerobic conditions TCE c DCE and VC degrade cometabolically McCarty and Semprini 1994 and VC Hartmans et al 1985 Hartmans and de Bont 1992 and possibly c DCE Bradley and Chapelle 1998 can be directly oxidized to carbon dioxide under aerobic conditions PCE has not been found to degrade aerobically McCarty and Semprini 1994
70. ogenic carbon e g BTEX or landfill leachate and microbial fermentation of this anthropogenic carbon produces dissolved hydrogen that drives reductive dechlorination A Type Il environment occurs in areas with high concentrations of biologically available native organic carbon The microbial utilization of the native organic carbon produces dissolved hydrogen which drives reductive dechlorination A Type environment occurs in areas characterized by low concentrations of both anthropogenic and natural organic carbon and an oxygen concentration greater than 1 0 mg L USEPA 1998 For all two zone simulations a single fixed longitudinal dispersivity value must be used for both zones Table A 1 2 Zone Biotransformation Scenarios 1 Type I or II anaerobic high Type I or II anaerobic lower rates or no rates degradation No Degradation Type I or Type I or II Type III Scenario 3 is illustrated in Figure A 1 Here all the solvents degrade anaerobically in zone 1 but only VC c DCE and ETH degrade to carbon dioxide under aerobic conditions in zone 2 In modeling scenario 3 for the chlorinated ethenes it may be necessary to carry out three separate simulations to generate concentration profiles for all of the chlorinated solvents and ethene Multiple simulations are necessary because the equations programmed in BIOCHLOR incorporate sequential first order kinetics expressions and therefore link dissolved solvent degradation with
71. orce Center for Environmental Excellence April 1995 Wiedemeier T H H S Rifai C J Newell and J W Wilson 1999 Natural Attenuation of Fuels and Chlorinated Solvents John Wiley amp Sons New York Xu M and Y Eckstein 1995 Use of Weighted Least Squares Method in Evaluation of the Relationship Between Dispersivity and Scale J Ground Water 33 6 905 908 24 Appendix 1 Domenico Single Species Analytical Model Domenico 1987 developed a semi analytical solution for reactive transport with first order decay and a two dimensional i e planar source geometry BIOCHLOR uses the Domenico solution with Martin Hayden and Robbins 1997 improvements and assumes that degradation reactions occur only in the aqueous phase BIOCHLOR evaluates centerline concentrations at y 0 2 0 and the 2 D array at 2 0 The model equation boundary conditions assumptions and limitations are discussed below Domenico Model with First Order Decay C x y z t fff x 1 1 420 x vt 1 4A0 v erfc 0 5 20 2 a Vt f exp x l 1 4A0 x vt 1 4X0 v exp 2 erfc 05 0 2 a Vt v Yi2 a 2 Definitions C x y z t Concentration at distance x downstream of source and distance y off centerline of plume at time t mg L Concentration in Source Area at t 0 mg L Distance downgradient of source ft Distance from plume centerline of source ft Dista
72. output shows concentrations along the centerline for two kinetic models at the same time or as an array one kinetic model at a time Note that all results are for the time entered in the Simulation Time box Centerline Output Centerline output is displayed when the Run Centerline button is pressed on the input screen The centerline output screen shows the concentration at the top of the saturated zone z 0 along the centerline of the plume y 0 The first screen shows the concentration profiles and field data for all the constituents on one plot as well as a no degradation curve for the total chlorinated solvents This information is plotted on a linear plot The user may view the output on a semi log plot by pressing the Log lt gt Linear button On the second output screen the user can view the no degradation curves and the biotransformation curves for each constituent one at a time by pressing the buttons to the right The model predictions are also presented in tabular form and may be printed out After a simulation has been run and the user has returned to the input page the user may opt to use the See Output button This button allows the user to go directly to the output without running the model If the See Output button is pressed prior to running a simulation output errors may result Array Output The array output is displayed when the Run Array button is pressed on the Input screen Choose the constituent
73. porosity the mass balance calculation assumes 2 D transport The mass of organics in each cell is then determined by multiplying the volume of ground water by the concentration and then by the retardation factor to account for sorbed constituents Mass Removed kg Biotransformed and 96 Change in Mass Flux The mass removed is the difference between the mass of contaminant if no biotransformation occurs and the mass of contaminant if biotransformation productions occurs For some daughter products the mass removed may be negative as more mass is created than would be present if no biotransformation occurred The percent biodegraded 18 the mass of solvent removed divided by the mass of solvent if no biotransformation occurs The percent change in mass flux is the difference in mass flux at the source compared to the mass flux at the boundary of the model area 19 Current Volume of Ground Water in Plume ac ft BIOCHLOR counts the number of cells in the 5 x 10 array with concentration values greater than 0 and multiplies this by the volume of ground water in each cell length width source thickness effective porosity If the user wishes to estimate the volume of the plume above a certain target level enter the target level in the appropriate box and press the appropriate model No Degradation or Biotransformation to display the result Note that the model does not account for any effects of vertical dispersion If BIOCHLOR S
74. r is not needed in BIOCHLOR Fraction Organic Carbon foc Units unitless Description Fraction of the aquifer soil matrix comprised of natural organic carbon in uncontaminated areas More natural organic carbon means more adsorption of organic constituents on the aquifer matrix Typical Values 0 0002 0 02 Source of Data The fraction organic carbon value should be measured if possible by collecting a sample of aquifer material from an uncontaminated area and performing a laboratory analysis ASTM Method 2974 87 or equivalent If unknown a default value of 0 001 is often used LaGrega et al 1994 How to Enter Data Enter directly If the retardation factor is entered directly this parameter is not needed in BIOCHLOR 11 4 Biotransformation Data First Order Decay Coefficients lambda for Zones 1 and 2 Description Rate coefficient describing first order decay process for dissolved constituents The first order decay coefficient equals 0 693 divided by the half life of the contaminant in ground water If a dissolved solvent is undergoing first order decay only the rate of biotransformation depends on the concentration of the contaminant and the rate coefficient In the case of sequential first order decay the solvent is assumed to degrade by first order kinetics but it is also simultaneously being produced by the first order decay of the preceding compound see Appendix A 2 Considerable care must be e
75. r ride this value In cases where the retardation factor varies significantly among the constituents it is advisable to do a sensitivity analysis to determine how the choice of the common R affects the model predictions For this simulation the median value of 2 85 was chosen For modeling biotransformation the user has the choice of modeling the plume in one or two zones Modeling in two zones permits the use of a different set of rate coefficients in each zone but requires that the plumes be at steady state as established from field data In this example we will model the plume as one anaerobic zone using one set of rate coefficients Field dissolved oxygen ORP and geochemical data were used to establish anaerobic conditions Because field scale rate coefficients and rate data from microcosms were unavailable rate coefficients previously obtained by calibrating the model to 1997 field data were used Here the rate coefficients were entered into the white cells In the General Section the model area length width and simulation time must be entered The model area length is the distance from the source to the receptor the canal in this case study A width of 700 ft is chosen to be significantly larger than the plume width to capture all of the mass discharging into the canal A simulation time of 33 years was chosen because the simulation is being conducted for 1998 and the solvents were released starting in 1965 Because we are inter
76. rectangular area to be modeled To determine contaminant concentrations at a particular point along the centerline of the plume a common approach for most risk assessments enter this distance in the Modeled Area Length box and see the results by clicking on the Run Centerline button If one is interested in more accurate mass calculations make sure most of the plume is within the zone delineated by the Modeled Area Length and Width Find the mass flux results using the Run Array button Typical Values 500 3000 ft length 250 1000 ft width Source of Data Values should be slightly larger than the final plume dimensions or should extend to the downgradient point of concern e g point of exposure If only the centerline output is used the plume width parameter has no effect on the results How to Enter Data Enter directly Time in years for which concentrations are to be calculated For steady state simulations enter a large value i e 1000 years would be sufficient for most sites Source of Data To match an existing plume estimate the time between the original release and the date the field data were collected To predict the maximum extent of plume migration increase the simulation time until the plume no longer increases in length How to Enter Data Enter directly 14 5 General Data cont Zone 1 Length and Zone 2 Length Description Lengths of first and second biotransformation zones in feet The zone 1
77. s for Multi Species Transport Equations with Serial and Parallel Reactions Water Resour Res 35 1 185 190 U S Environmental Protection Agency 1986 Background Document for the Ground Water Screening Procedure to Support 40 CFR Part 269 Land Disposal EPA 530 SW 86 047 January 1986 U S Environmental Protection Agency 1988 Guidance on Hemedial Actions for Contaminated Ground Water at Superfund Sites EPA 540 G 88 003 Directive 9283 1 2 Washington D C EPA Office of Solid Waste and Emergency Response U S Environmental Protection Agency 1998 Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water EPA 600 R 98 128 September 1998 Vogel T M and P L McCarty 1985 Biotransformation of Tetrachloroethylene to Trichloroethylene Dichloroethylene Vinyl Chloride and Carbon Dioxide under Methanogenic Conditions Appl Environ Microbiol 49 5 1080 1083 Vogel T M and P L McCarty 1987 Abiotic and Biotic Transformations of 1 1 1 Trichloroethane under Methanogenic Conditions Environ Sci Technol 21 12 1208 1213 Walton W C 1988 Practical Aspects of Groundwater Modeling National Water Well Assoc Worthington Ohio Wiedemeier T H Wilson J T Kampbell D H Miller R N and Hansen J E 1995 Technical Protocol for Implementing Intrinsic Remediation With Long Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater Revision 0 Air F
78. s in the concentrations due to the changes in the retardation factor can probably be attributed to the plume being near steady state in this example Table A 5 Sensitivity Analysis Results Retardation Factor Constituent Concentrations mg L In this example the BIOCHLOR model is more sensitive to changes in the first order decay coefficient and less sensitive to changes in the retardation factor However the results of these sensitivity analyses are site specific and do not apply to all sites 46
79. same input parameters except that the first order decay coefficients were multiplied by 2 Similarily another simulation was conducted whereby the rate coefficients were 0 1 times those used in the baseline example The centerline concentrations of PCE TCE and the daughter products 1085 ft downgradient from the source are shown in Table A 4 for each simulation In this instance the simulated concentrations of PCE and its daughter products increase substantially when the rate coefficient is decreased by a factor of ten and doubling the rate coefficient decreases the chlorinated solvent concentrations at the canal location In this example the chlorinated ethene concentrations are very sensitive to the magnitude of the rate coefficient TableA 4 Sensitivity Analysis Results Rate Coefficients Constituent Concentrations 2 2 0 003 0 202 19 443 baseline 5 72 00 1 00 0 70 0 40 In contrast changes in the retardation factor have nominal effects on the dissolved chlorinated solvent concentrations as shown in Table A 5 In this sample case when the retardation factor is decreased from the baseline value of 2 9 chlorinated solvent concentrations increase slightly Also with an increase in the retardation factor chlorinated solvent concentrations at the canal location decrease by a small amount These small variation
80. te the effect of the choice of the common retardation factor on the results see Appendix A 7 for an example Aquifer Matrix Bulk Density kg L or g cm Description Bulk density in kg L of the aquifer matrix related to porosity and pure solids density Typical Values Although this value can be measured in the lab in most cases estimated values are used A value of 1 7 kg L is used frequently Source of Data Either from an analysis of soil samples at a geotechnical lab or more commonly application of estimated values such as 1 7 kg L How to Enter Data Enter directly If the retardation factor is entered directly this parameter is not needed in BIOCHLOR 10 3 Adsorption Data cont Organic Carbon Partition Coefficient mg kg or Like oF mL Ig Description Chemical specific partition coefficient between soil organic carbon and the aqueous phase Larger values indicate greater affinity of contaminants for the organic carbon fraction of soil Typical Values Perchloroethylene 426 L kg Trichloroethylene 130 L kg Dichloroethylene 125 L kg Vinyl Chloride 29 6 L kg at 20 Note that there is a wide range of reported values and these values are temperature dependent Source of Data Chemical reference literature or relations between K and solubility or K and the octanol water partition coefficient How to Enter Data Enter directly If the retardation factor is entered directly this paramete
81. that you would like to view by selecting it in the upper right hand corner Then select one of the two model types No Degradation or Biotransformation A 3 D graphic presents the concentration profile on an 11 point long by 5 point wide grid To alter the modeled area adjust the Model Area Length and Width parameters on the input screen To see the plume array that exceeds a certain target level such as an MCL or risk based cleanup level enter the target level in the box and push Plot Data Target Only sections of the plume exceeding the target level will be displayed To see all the data again push Plot All Data Note that BIOCHLOR automatically resets this button to Plot All Data when the Run Array button is pressed on the input screen Approximate mass flux data are presented on the array output screen Calculating the Mass Balance Order of Magnitude Accuracy Plume Mass kg BIOCHLOR calculates the mass of organics in the plume array for two models 1 No Degradation and 2 Sequential First Order Decay Biotransformation Production The mass is calculated by assuming that each point represents a cell equal to the incremental width and length except for the first column which is assumed to be half as long as the other columns because the source is assumed to be in the middle of the cell The volume of the affected ground water in each cell is calculated by multiplying the area of each cell by the source depth and by effective
82. tial First Order Decay BIOCHLOR primarily models reductive dechlorination which is assumed to follow sequential first order kinetics The user may model the sequential decay of chlorinated ethenes such as PCE and TCE or the decay of chlorinated ethanes such as 1 1 1 TCA as shown below Vogel and McCarty 1987 Acetic Acid CH3COOH 4 L s L 11 DCE Aa i 5 Maior biotic pathwa PCE Perchloroethene TCA Trichloroethane 3 TCE Trichloroethene DCA Dichlorethane Abiotic pathway DCE Dichloroethene Although the chlorinated ethenes primarily degrade biologically chlorinated ethanes can degrade both biologically and abiotically BIOCHLOR allows the user to input both biological and abiotic rate constants for chloroethane For chloroethane CA abiotic decay to ethanol occurs much more rapidly than biotransformation to ethane The abiotic decay of 1 1 DCA is slow relative to biotransformation so its abiotic degradation is ignored in BIOCHLOR 1 1 1 TCA can degrade abiotically to both acetic acid by hydrolysis and to 1 1 DCE by elimination Vogel and McCarty 1987 Abiotic decay of 1 1 1 TCA cannot be modeled using BIOCHLOR if accurate chlorinated ethane daughter product predictions are required However if only TCA predictions are needed a lumped rate coefficient sum of abiotic and biotic first order rate coefficients can be input to model the degradation of TC
83. ulated to simulate the effects of chemical diffusion Therefore contaminant transport through very slow hydrogeologic regimes e g clays and slurry walls should probably not be modeled using BIOCHLOR unless the effects of chemical diffusion are proven to be insignificant Longitudinal Dispersivity 1096 of scale Pickens and Grisak 198 Longitudinal Dispersivity 0 83 Log scale 2 414 Xu and Eckstein 1995 RELIABILITY o Low O Intermediate High Data Source Gelhar et al 1992 Longitudinal dispersivity m 107 100 101 102 103 104 105 105 Scale Figure Longitudinal dispersivity vs scale data reported by Gelhar et al 1992 Data includes Gelhar s reanalysis of several dispersivity studies Size of circle represents general reliability of dispersivity estimates Location of 10 of scale linear relation plotted as dashed line Pickens and Grisak 1981 Xu and Eckstein s regression shown as solid line Shaded area defines 1 order of magnitude from the Xu and Eckstein regression line and represents general range of acceptable values for dispersivity estimates 37 Data Source Gelhar et al 1992 Data Source Gelhar et al 1992 Low A O Intermediate B 8 102 Transverse a Dispersivity 0 10 i 0 0 o 3 107 o o 9 5 X 10 4 Low B A Intermediate 10 107 10 10 10 10 10 10 107
84. ution has been adapted to provide three different model types representing i transport with no decay ii transport with sequential first order decay in one zone and iii transport with sequential first order decay in two zones see Model Types Guidelines for selecting key input parameters for the model are outlined in BIOCHLOR Input Parameters For help on Output see BIOCHLOR Output BIOCHLOR Model Types The software allows the user to view results from three different types of ground water transport models 1 Solute transport with no decay This model is appropriate for predicting the movement of conservative non degrading solutes The only attenuation mechanisms are dispersion in the longitudinal transverse and vertical directions if present and adsorption of contaminants to the soil matrix if present 2 Solute transport with sequential first order decay in one zone With this model the reactive transport of both parent and daughter chlorinated solvents can be modeled This model accounts for dispersion adsorption advection and sequential biotransformation The reductive dechlorination of the parent solvent to daughter product is assumed to be a first order process That is the solute degradation rate is assumed to be proportional to the solute concentration However the daughter products are also produced by the first order degradation of the preceding parent compound Therefore the daughter product can simultaneously undergo
85. ve to reboot your machine however to make this work 22 References American Society for Testing and Materials ASTM 1995 Standard Guide for Risk Based Corrective Action Applied at Petroleum Release Sites ASTM E 1739 95 Philadelphia PA Al Suwaiyan M 1996 Discussion of Use of Weighted Least Squares Method in Evaluation of the Relationship Between Dispersivity and Field Scale by M Xu and Y Eckstein Ground Water 34 4 578 Bradley P M and F H Chapelle 1998 Effect of Contaminant Concentration on Aerobic Microbial Mineralization of DCE and VC in Stream Bed Sediments Environ Sci Technol 32 5 553 557 Carr C S and J B Hughes 1998 Enrichment of High Rate PCE Dechlorination and Comparative Study of Lactate Methanol and Hydrogen as Electron Donors to Sustain Activity Environ Sci Technol 32 12 1817 1824 Clement T P 1997 RT3D A Modular Computer Code for Simulating Reactive Multi Species Transport in 3 Dimensional Groundwater Aquifers Battelle Pacific Northwest National Laboratory Research Report PNNL SA 28967 Cohen M and J W Mercer 1993 DNAPL Site Evaluation CRC Press Boca Raton FL Connor J A C J Newell J P Nevin and H S Rifai 1994 Guidelines for Use of Groundwater Spreadsheet Models in Risk Based Corrective Action Design National Ground Water Association Proceedings of the Petroleum Hydrocarbons and Organic Chemicals in Ground Water Conference Houston TX November 1
86. xercised in the selection of a first order decay coefficient for each constituent to avoid significantly over predicting or under predicting actual decay rates For guidance on how to model your site assuming one or two biotransformation zones see General Data Section 5 Typical Values Perchloroethylene 0 07 to 1 20 Trichloroethylene 0 05 to 0 9 yr cis 1 2 Dichloroethylene 0 18 to 3 3 Vinyl Chloride 0 12 to 2 6 from Wiedemeier et al 1999 Note The equations in BIOCHLOR cannot accept a zero value for any of the rate coefficients BIOCHLOR checks entered values and assigns a low value if zero is entered Also no two rate constants in the same zone can be identical BIOCHLOR will issue an error message and ask the user to re enter the rate coefficients Source of Data Optional methods for selection of appropriate decay coefficients are as follows Calibrate to Existing Plume Data BIOCHLOR can be used to determine first order decay coefficients that best match the observed site concentrations One may adopt a trial and error procedure to derive a best fit decay coefficient for each contaminant by varying the decay coefficient until predicted concentrations match measured concentrations Literature Values Various published references are available listing biotransformation rate coefficients e g USEPA 1998 Howard et al 1991 Many references report the half lives these values can be converted to the first

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