User s Guide 14-Compartment Model

Transcription

1 User s Guide 14-Compartment Model SERDP Project # ER-1740 Issued: July 2014 Prepared for: Strategic Environmental Research and Development (SERDP) Gary Wealthall Michaye McMaster Matt Vanderkooy Tom C. Sale Ahmad Seyedabbasi Greggory Marquardt Charles J. Newell

2 User s Guide 14-Compartment Model SERDP Project # ER-1740 Cite the 14-compartment model toolkit using Marquardt, G.P., M.A. Seyedabbasi, M. Vanderkooy, M. McMaster, G. Wealthall, T.C. Sale, C.J. Newell (2014) 14-Compartment Model Toolkit, prepared for the Strategic Environmental Research and Development (SERDP) Program, July CITE the User s Guide using Vanderkooy M., M. McMaster, G. Wealthall, M.A. Seyedabbasi, Sale, T.C., C.J. Newell (2014) User s Guide for 14-Compartment Model, prepared for the Strategic Environmental Research and Development (SERDP) Program, July CONTACTS Mr. Matt Vanderkooy, Geosyntec Consultants, Inc., (519) , MVanderkooy@Geosyntec.com Mr. Greggory Marquardt, GSI Environmental Inc., (713) , Dr. Ahmad Seyedabbasi, GSI Environmental Inc., (713) , masabbasi@gsi-net.com Ms. Michaye McMaster, Geosyntec Consultants, Inc., (519) , MMcMaster@Geosyntec.com Dr. Gary Wealthall, Geosyntec Consultants, Inc., (519) , GWealthall@Geosyntec.com Dr. Tom Sale, Colorado State University, (970) , tsale@engr.colostate.edu Dr. Charles Newell, GSI Environmental Inc., (713) , cjnewell@gsi-net.com

3 Quick Start 1- Go to the webpage! Note: Please read the section on the type and versions of the web browsers to use. 2- Create a site name and password! Note: Be sure to remember your password! There is no password retrieval system. 3- At each step be sure to save your work before moving to the main menu or next step! 4- Enter input information for current condition and remediation technology performance and your objectives in Steps 2 and 3! 5- At each step you may visualize the output! 6- You may create a report at the end. Note: Make sure the Print Background (colors & images) box is checked in the page setup section of your web browser. 7- Please contact us if you have any questions/comments Web developer/administrator (admin@serdp14cmodel.com) Greggory Marquardt (GSI Environmental Inc.) Technical team (technical@serdp14cmodel.com) Ahmad Seyedabbasi, Charles J. Newell (GSI Environmental Inc.) Tom Sale (Colorado State University) Gary Wealthall, Michaye McMaster and Matt Vanderkooy (Geosyntec Consultants, Inc.) i

4 Contents INTRODUCTION AND OVERVIEW... 1 Need for 14C Model... 1 Need for Web Based 14C Model Tool C MODEL DESCRIPTION... 3 Model Basis C Model Zones C Model Phases... 6 DNAPL... 7 Vapor... 7 Aqueous... 7 Sorbed... 8 Orders of Magnitude (OoMs) C Model Concentration Color Coding... 9 Equivalent Aqueous Phase Concentrations C Model Applications Mapping Fluxes Between Compartments Mapping Evolution of Site Identifying Data Gaps Anticipating and Mapping Remedy Outcomes C Model Limitations WEB-BASED TOOL DESCRIPTION Tool Components Setup Model Set Current Conditions Remediation Alternatives-Performance View Output Reports Session Options and Information Using the Tool HELP Help Boxes in 14C Model Main Page Help Boxes in 1. Setup Model Sub-Page Help Boxes in 2. Set Current Conditions Sub-Page ii

5 REFERENCES ATTACHEMENT Acronym List DNAPLs ESTCP mg/l OoM SERDP TCE PCE URL 14C Model µg/l Dense Non-Aqueous Phase Liquids Environmental Security Technology Certification Program Milligrams per liter Order of Magnitude Strategic Environmental Research and Development Program Trichloroethylene Perchloroethylene / Tetrachloroethylene Uniform Resource Locator 14-Compartment Model Micrograms per liter iii

6 INTRODUCTION AND OVERVIEW This document is a User s Guide for a web-based tool of 14-Compartment Model (14C Model) by Sale and Newell (Environmental Security Technology Certification Program (ESTCP) Project ER ) found at serdp14cmodel.com. The tool lets users analyze sites contaminated with chlorinated solvents and compare the likelihood of success for potential remedies. Users can then generate printable reports of their analyses. This User s Guide first gives a background of why the 14C Model and the web based tool were created. Then the 14C Model is described. Next the web-based tool is described, including step by step directions of how to use the tool. Last, the text of help boxes built into the web-based tool are provided. Prior knowledge of "A Guide for Selecting Remedies for Subsurface Releases of Chlorinated Solvents (ESTCP Project ER )" is required before continuing with this User s Guide. Need for 14C Model Managing chlorinated solvents contamination involves more than managing Dense Non-Aqueous Phase Liquids (DNAPLs). Vapor, dissolved, and sorbed phase chlorinated solvents (particularly those that occur in low permeability zones) often govern what can be achieved with current remediation technologies. There are important differences how various hydrogeologic settings store and release contaminants, and these settings control how sites evolve with time and respond to remediation efforts. The 14C Model provides a holistic foundation for tracking four phases (DNAPL, vapor, aqueous and sorbed) of chlorinated solvents that can occur in transmissive and low permeability zones, in source zones and plumes. Specific applications include mapping fluxes between compartments, analyzing of the distribution and concentrations of contaminants over time, identifying data gaps, and anticipating and mapping the outcomes of remedies at sites. In all of this the 14C Model provides a relatively simple tool to manage complex issues and interactions. At the same time the 14C Model is a highly idealized simplification of real systems and is only one part of a quantitative Conceptual Site Model. 1

7 Need for Web Based 14C Model Tool To increase the use the 14C Model in site characterization, management and remedy selection Strategic Environmental Research and Development Program (SERDP) funded the creation of a web-based the tool. The web based tool is free, simple and intuitive to use. 2

8 14C MODEL DESCRIPTION The 14C Model is a useful tool in building a conceptual site model. It provides a holistic view of the problem of chlorinated solvents in subsurface environments by blending hydrogeology, contaminant phases, and location data together. The 14C Model helps ensure that all of the different phases and zones are considered when making management decisions, but should not be used alone, rather as a part of a quantitative conceptual site model. This section provides an overview of the 14C Model. First the basis of the model is described including the phases and zones in the model. Then the color coding of the model to represent concentrations ranges is detailed. Next applications of the 14C Model are given. Last limitations of the model are listed. More detail than given here is available in the Sale and Newell (ESTCP Project ER ). Model Basis The 14C Model recognizes contamination can exist in four phases DNAPL, Vapor, Aqueous, & Sorbed and in either transmissive or low permeability geologic media present in source zones and plumes. These delineations give rise to an initial set of 14 possible compartments (e.g. Aqueous-Transmissive-Source). Table 1 delineates the initial 14 compartments in which chlorinated solvents occur and the possible directions of mass flux between the compartments. The web based tool lets users subdivide the plume into 3 segments and include a surface water discharge zone. This adds 16 optional compartments, bringing the total possible number of compartments to 30. Further, the model lets users add a second transmissive unit (layer) underneath the original unit that has the same compartments as the original unit bringing the total possible number of simultaneously displayed compartments to 60. For simplicity and model name recognition the model will be referred to as the 14C Model in this User s Guide. 3

9 Table 1 14 subsurface compartments potentially containing chlorinated solvents. Arrows show mass potential transfer links between compartments. Dashed arrows indicate irreversible fluxes. 14C Model Zones In the 14C Model described in Sale and Newell (ESTCP Project ER ) there are four zones. There is a source zone and a plume. Each zone has two sub-zones, a low permeability zone and a transmissive zone. The zones can be visualized in Figure 1 where a site cross-section and a plan view diagram are displayed. The diagrams show both a source area and plume sections with progressively lower concentrations away from the source area. Each area contains low permeability zones within the transmissive layer. The diagrams are taken from Section 5, Example 1 of Sand and Newell (ESTCP Project ER ). At the site depicted 10,000 gallons of perchloroethene (PCE) were rapidly released into a thick, highly heterogeneous alluvial fan deposit containing interbeds of moderately to poorly sorted silt, fine sand, and coarse sand. Over a period of twenty years, a plume extended from the release area, or source zone, downgradient across the industrial property and ultimately into an adjacent residential neighborhood. In general when filling out 14 compartment models, the source zone is where DNAPL was released, and is the source of downgradient vapor or aqueous plumes. The source zone may not contain DNAPL depending on release history and site evolution. Source 4

10 zone compartments will generally have higher concentrations than plume compartments. The plume is where contaminants in the vapor or aqueous phase from the source zone migrate. In the plume the phase DNAPL is never present by definition. The low permeability zones consist of finer grained media. With the exception of secondary permeability features (e.g., fractures, root holes, animal burrows), high displacement pressures typically preclude DNAPL from low permeability layers. Rather contaminant mass enters the low permeability zones through primarily diffusion and some slow advection. The transmissive zones consist of coarser grained media and are the transport conduit for DNAPL, vapor, and aqueous phase contamination. Figure 1 Plan-view and cross-sectional representation of a DNAPL contaminated site. Diagram taken from Section 5, Example 1 of Sale and Newell (ESTCP Project ER ). The web-based tool let users include in addition to the original 14 compartments two additional plume segments (6 compartments each) and a surface water discharge zone (4 compartments) bringing the total possible number of compartments to 30 for a single layer. The option to add additional plume segments recognizes that there are often significant concentration gradients in a plume. Figure 2 shows a screenshot from the 5

11 web-based tool where concentrations in all possible 30 compartments in a single layer have been specified to match concentrations in the site conceptual model diagrams in Figure 1. Figure 2 also includes discharge to surface water, which is not shown in Figure 1. Despite the model being extended to 30 compartments, for simplicity and model name recognition the model will be referred to as the 14C Model in this User s Guide. The web-based 14C Model tool also allows users to model contamination into two separate layers. Conceptually layer 1 is a transmissive layer lying above a semiconfining to confining layer with layer 2, another transmissive layer, below. Each transmissive layer contains dual porosity, regions of lower permeability within the transmissive layer. Adding the second layer brings the total possible number of compartments to 60. Figure 2 Screenshot from web based tool showing original 14 compartments at left along with additional 16 compartments to represent sections of plume with lower concentrations and discharge of contamination to surface waters. Cross section and plan view diagram in Figure 1 do not depict a surface water component. 14C Model Phases Chlorinated solvents in subsurface environments can occur in four different phases as described in the following sections: (1) Dense Nonaqueous Phase Liquid (DNAPL), (2) gas phase in soil vapor, (3) dissolved phase in water, a (4) sorbed phase on aquifer solids. 6

12 DNAPL DNAPLs are the original source of the contamination. Depending on the age and history of the release the DNAPL compartments may contain the majority of contaminant mass. This DNAPL can then sustain contamination in groundwater and vapor plumes. When released at surface, DNAPL migrates downward through the subsurface, driven by gravity and capillary forces. Above the capillary fringe, DNAPL displaces air and typically occurs as an intermediate wetting phase between water and air. Over time, volatile DNAPL components partition into soil gas. This produces vapor plumes near releases. Given a sufficiently large release, DNAPL will migrate into and below the water table. In the groundwater zone, DNAPL displaces water and occurs (typically) as a nonwetting phase. With time, soluble constituents in DNAPL partition into groundwater, forming aqueous plumes in transmissive zones downgradient of the DNAPL zone. The formation of plumes depletes of DNAPL. Ultimately, all of the DNAPL will be depleted. Vapor Vapor plumes present two primary challenges. First, they can contaminate underlying groundwater via diffusion and/or percolation of soil water through the unsaturated zone. Second, vapor plumes can adversely impact indoor air quality. Both of these conditions are common drivers for remedial actions. Vapor phase chlorinated solvents originate from direct volatilization of DNAPL in the unsaturated zone or from volatilization of aqueous phase chlorinated solvents in pore water to air in the subsurface. Vapors are transported primarily via gas phase diffusion in natural settings. Transport of vapors can also be driven by changes in atmospheric pressure, engineered systems (e.g., soil vapor extraction) and negative pressure in buildings. As chlorinated solvent vapor plumes expand, contaminants partition into pore water and adsorb onto the matrix solids. Initially, this process retards the expansion of vapor plumes. At later times, chlorinated solvents stored in pore water and sorbed to solids can sustain vapor plumes. Aqueous Aqueous plumes may contaminate drinking water supplies, give rise to vapor plumes, and contaminate surface water bodies through groundwater discharge. Aqueous plumes are formed as soon as DNAPL encounters water in the subsurface. Constituents in the DNAPL begin to partition into water they share pore space with and are transported 7

13 away from the source by a combination of advection, dispersion, and diffusion. The transport away of aqueous contamination depletes concentrations at the water-dnapl interfaces allowing further dissolution of DNAPL thus continually producing a contaminant plume. Within transmissive portions of the saturated zone, advective transport produces groundwater plumes that can extend over large distances, for as much as several miles in some cases. As plumes advance, dissolved phase solvents are lost through degradation, sorption and diffusion into low permeability layers. At some sites, natural rates of attenuation are rapid enough to create stable or even shrinking plumes (Wiedemeier et al., 1999). Dissolved phase constituents also migrate into low permeability zones such as clay lenses and aquitards through a combination of diffusion and slow advection. Once in low permeability zones, chlorinated solvents will also partition into the sorbed compartment/phase. As long as the concentration of aqueous phase solvents is greater in the transmissive zones than in the low permeability zone, solvents will be driven into the low permeability zones. This matrix storage can be an important mechanism for attenuation of solvents in plumes. However, once the aqueous concentration of the solvents declines in the transmissive layer(s), solvents will begin diffusing back out of the low permeability layers. This process, back diffusion, can sustain plumes for long periods of time (e.g., Liu and Ball, 2002; Chapman and Parker, 2005; AFCEE, 2007; and Sale et al. 2008). Because back diffusion is far slower than the initial inward diffusion process (Parker et al. 1996), it can sustain plumes for extended periods even after all DNAPL is depleted (Figure 3). Sorbed Sorbed contaminant mass presents a long term source of aqueous phase contamination. The sorbed phase is contaminant mass residing in or on the matrix solids. As the aqueous phase concentrations increase, there is a net transfer of contaminants to the sorbed phase. This equilibrium partitioning attenuates and slows, i.e. retards, the migration of dissolved phase contaminant concentration as the plumes advance by removing dissolved contaminants from the transmissive zone. This retardation creates an in situ reservoir of immobile sorbed contaminants. As aqueous phase concentrations decrease as the site ages (due to natural weakening of the source or active source remediation), sorbed contaminants are released back into the 8

14 aqueous phase. This desorption has the net effect of sustaining the aqueous phase concentrations. Like matrix diffusion, desorption can sustain low-concentration groundwater plumes for long periods of time. Orders of Magnitude (OoMs) An Order of Magnitude (OoM) is a factor of 10 changes in a variable. For example, if a remediation technology reduces the dissolved phase concentration of trichloroethylene (TCE) by one OoM, then the concentration is 10 times lower, equivalent to a 90% reduction. Two OoMs thus represents a reduction in concentration of 99%. The concept of OoMs is an important short hand for evaluating remediation performance in the 14C Model. The concept of OoMs is used because chlorinated solvent concentrations in groundwater typically span several orders of magnitude, and are generally represented best by a log-normal statistical distribution. 14C Model Concentration Color Coding Each compartment of the 14C Model is color coded to denote the concentration of contaminants. The color coding follows an order of magnitude (OoM) approach where the each color level indicates a 10 fold increase in the concentrations range. More detail on the OoMs is given below and in the Help section. Each compartment is given a color and corresponding OoM number based on its concentration. The OoMs levels go from 0 to 4; an example set of concentration ranges and corresponding colors are as follows: OoM 0 Not impacted; white OoM 1 0 to 9.9 micrograms per liter (µg/l) in water; green OoM 2 10 to 99.9 µg/l in water; yellow OoM to µg/l in water; orange OoM 4 1,000 or greater µg/l in water; red NA Not applicable, compartment does not exist; black Users can use different units as appropriate. For example the OoM levels can use units of milligrams per liter (mg/l) instead of µg/l. Users should explicitly note the OoM units and concentration ranges used in their analyses for each of the four phases. The units in the OoM levels must be the same for all compartments used in a 14C Model. 9

15 Equivalent Aqueous Phase Concentrations In compartments other than aqueous phase transmissive compartments, the concentrations must be expressed as equivalent aqueous phase concentrations (also referred to as equilibrium aqueous phase concentrations). In other words concentrations for each compartment are given as the concentration of an aqueous phase in equilibrium with the compartment. Therefore vapor, DNAPL, and sorbed phase contaminant concentrations must be expressed as equivalent aqueous phase concentrations. This driven by two factors: Using equivalent aqueous concentrations allows tracking and predicting of fluxes between phases and compartment; and Water quality data is often the only data available at field sites, hence it is the basis for comparing mass and mass partitioning between compartments. Ideally concentrations for all compartments would be informed by field data. Typically, rigorous field data are not available. In these instances additional field data can be collected or concentrations in compartments can be estimated based on an understanding of the hydrogeologic setting, age of the releases, and an understanding of contaminant transport processes. A basis for estimating concentrations is presented in Chapter 2 of the Decision Guide. Concentrations in Aqueous Phase Equivalents 0 Not impacted s of ug/l in water 10s of ug/l in water 100s of ug/l in water > 1000s of ug/l in water Simple partitioning models are available for relating vapor, DNAPL, and sorbed phase concentrations to aqueous phase concentrations (see Chapter 2 of the Decision Guide). General principles covered in the guide include: At early time most of the contaminant mass is likely to be DNAPL in transmissive zones Equivalent concentrations in aqueous and sorbed compartment in transmissive and low permeability zones are likely to be equal. Given DNAPL, equivalent aqueous phase concentrations for DNAPL can be estimated as the effective solubility of the primary DNAPL constituent of concern. 10

16 Equivalent aqueous phase concentration for vapor can be estimated using Henry s law and or Raoult s law. When selecting the aqueous transmissive compartment s concentration use the median current concentration. When selecting aqueous concentrations for aqueous low permeability compartments use highest historical median concentration from any groundwater wells in that region of the site for a coarse approximation. For a more accurate estimate the ESTCP Matrix Diffusion Toolkit can be applied (ER ). When calculating/selecting the equivalent aqueous phase concentration for sorbed compartments if concentrations in the aqueous phase compartments are greater than 100 µg/l use the same concentration as aqueous phase compartments. If concentrations in the aqueous phase compartments are less than 100 µg/l either double the aqueous phase compartment concentration for a coarse estimate or apply the Dual Equilibrium Desorption Model described in Chen et al., (2002). When calculating/selecting the equivalent aqueous phase concentration for vapor compartments unless significant biodegradation is suspected, concentrations for aqueous phase compartments near the water-soil gas interface can be used. The partitioning between the vapor and aqueous phase is rapid process. 14C Model Applications The 14C Model provides the ability to analyze contaminant concentrations at a Site for many purposes. Below four useful applications of the 14C Model are described, (1) mapping fluxes between compartments, (2) mapping evolution of site, (3) identifying data gaps, and (4) anticipating and mapping the outcomes of remedies at sites. Mapping Fluxes Between Compartments The 14C Model identifies the direction of fluxes that can occur (see arrows in Table 1) between compartments. Using a filled in 14C Model, the direction of flux between compartments can be identified and the magnitude of mass flux estimated. Mapping Evolution of Site The 14C Model can track the evolution of the site over time; the location of mass changes as the site ages. This occurs both to the spatial location of the vapor and dissolved phase plumes, but more importantly, to the distribution of the contaminant 11

17 mass between the four phases. Separate 14C Models can be constructed for different time points to chart the evolution of the contamination distribution over time. Specific detailed scenarios of site aging are presented in Sale and Newell (ESTCP Project ER ). Figure 3 illustrates typical contaminant distribution for Five Geologic Type Setting (introduced in the Decision Guide) as a function of the site stage. Methods to resolve the stage of a site, if unknown or uncertain, are presented in Attachment 1. Generally the age progression at a site is as follows: Early Stage Site: Equivalent aqueous phase concentrations will likely be highest in DNAPL compartments. Middle Stage Site: Equivalent aqueous phase concentrations will likely be the same in the aqueous phase source zone compartments and the DNAPL compartments. These compartments will likely have higher equivalent concentrations than all other compartments. Late Stage Site: Equivalent aqueous phase concentrations will likely be highest in low permeability compartments compared other compartments. 12

18 Figure 3 - Illustration of plausible distributions of chlorinated solvent as a function of type setting and the stage of release. Gray boxes are considered to be absent in the type setting. Note that conditions presented are plausible in the noted situations, but not necessarily the only possible scenario. Image from decision guide (Sale and Newell ER ). Identifying Data Gaps The 14C Model can help point out the limitations of a site characterization. In many cases sites have been characterized solely on water quality data from monitoring wells. Groundwater sampling, while useful for resolving potential exposures via groundwater, unfortunately provides little if any information about vapor, DNAPL, or sorbed phases in transmissive zones and no information regarding contaminants in low permeability zones. The 14C Model often emphasizes that water quality in wells provides direct insight into only two of the fourteen compartments. 13

19 Anticipating and Mapping Remedy Outcomes The 14C Model can be used to analyze the anticipated outcome of remedies. The anticipated degree of OoM reduction in each compartment for each remedy is applied to the Site s base case 14C Model. This generates before and after 14C Model realizations for each remedy. Interpreting these data can help select the most appropriate remedy for the site objectives. 14C Model Limitations The 14C Model provides a relatively simple tool for managing complex issues and interactions. At the same time, it is important to note that the 14C Model is a highly idealized simplification of real systems. Key limitations include: Contaminant Concentration vs Contaminant Mass - The model relies on concentrations to evaluate alternatives and impacts on various compartments. A sound conceptual site model should also consider the mass of contamination in all relevant compartments. The 14C Model's concentration-based interpretations can potentially be misleading if not used in conjunction with a mass-based site model. Only an Element of a Site Conceptual Model - The model is a tool for aiding decision-making, and should be based on a comprehensive conceptual site model that includes mass balances, the spatial distribution of mass, the site hydrogeology, and the mass discharge and mass flux distribution. The 14C Model is simply a potential part of a site conceptual model. Uncertainty - Care is needed in recognizing uncertainties in 14C Model entries. This particularly true for compartments where little or no hard field data is available. For example, in many cases the little to no data may be available from low permeability zones. Oversimplification - Regardless of the scale of analysis the 14C Model simplifies systems. Care is needed in not ignore details that may be consequential to the outcomes of proposed remedies. We encourage readers to think carefully about the unique aspects of their sites, their site-specific goals, and their own knowledge of how specific technologies work. 14

20 WEB-BASED TOOL DESCRIPTION This section first describes the main components of the web-based tool and then gives a step by step example of how to use the too. Tool Components The tool can be accessed at The tool has five main components that let users build, compare and print 14C Models. The components are described below in the order they appear on the web-based tool. Setup Model Users access this section to setup site models. The site model controls the layers and phases available when entering current concentrations and comparing anticipated remedy performance using 14C Models. Set Current Conditions Users access this section to define the current concentrations in each compartment. This creates a status quo 14C Model that remediation technologies can be compared against. Users can also enter in how the site is expected to perform compared to objectives in the short and long term. Expected performance is denoted using green, beige, grey or black fill. The colors denote success, moderate success, no clear benefit, and potentially adverse outcomes respectively. The objectives include specific items under headings of: risk, extent of contamination, longevity of contamination, regulatory concerns, community, land use, economic, sustainability, resource conservation, and implementability. Users can add specific objectives as desired. Remediation Alternatives-Performance Users access this section to compare remedies. Remedies are modeled by applying the anticipated OoM decrease achieved by the remedy for each compartment. Users can also enter in how remedies are expected to perform compared to objectives in the short and long term. Expected performance is denoted using green, beige, grey or black fill. The colors denote success, moderate success, no clear benefit, and potentially adverse outcomes respectively. 15

21 View Output Reports Users access this section to create and print reports of the current site conditions, expected remedy performance, and how various management options/remedies are meeting objectives. The report section is flexible. It allows users to create reports by selecting or omitting components as desired and placing them in the report in any order desired. Session Options and Information Whenever the user modifies, adds or uploads content to the tool within one of the components the user must click the Save Site Model button to save the changes. Changes must be made before navigating away from a sub-page otherwise changes will be lost. The Save Site Model button is present on all pages except the Main Menu and View Output Reports pages where no changes can be made. Users can access saved sessions by returning to the Uniform Resource Locator (URL) provided next to the label, Session URL just below the Update Session heading. Users should bookmark, or otherwise save this session URL for future retrieval. Users will be required to enter the session password when they return, before they can continue working on their site model. Using the Tool The following steps illustrate most features of web-based 14C Model tool and also provide users with an example of how to use the tool. 1. Open up a web browser (e.g. Google Chrome) and go to serdp14cmodel.com. 2. Scroll down towards the bottom of the page and enter in a Site Name and Project Password and then press the Start New Session button. 16

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23 3. The next page will display your session s unique URL next to the text Session URL. Save this URL. It will let you access any data you input and save in this session. Press Click Here to Continue. IMPORTANT: Save this URL. It is the only future way to access the model you are creating. You can also access this URL once inside the session. See step Click on the hyperlink Setup Model. 18

24 5. If desired a cross section of the site can be uploaded. Later when generating reports users have the option of including the site cross section. Here we have uploaded the site cross section and plan view from Section 5, Example 1 of the Decision Guide (Sale and Newell, ER ). 6. Select segments to be modeled. Use default selection of the Source and Plume 1. Two additional plume segments and a surface water discharge zone may be included. An additional layer may also be included, e.g. a deeper transmissive unit. Next phases possible in principle for each layer must be selected. Select all four phases for Layer 1. Press the Save Site Model button. Before navigating away from any sub-page press the Save Site Model otherwise changes will be lost. Press the Return to Main Menu hyperlink. 19

25 7. As an alternative to pressing Return to Main Menu or going to the next step hyperlinks at the bottom, users can also press the Main Menu hyperlink at the top left of the page or press the browser back button. This approach can be used in all other sub-pages. 8. Click on the Current Site Conditions hyperlink. 20

26 9. Enter in the equivalent aqueous phase concentration OoM level for each compartment using site data and the drop down lists. OoM scale units different from default can be used, for example mg/l can be used instead of µg/l if contamination concentrations at site warrant using a higher concentration scale level. If a different OoM scale is used, this should be noted, and must be used in all compartments. This can be done by clicking on the yellow note button that is beside each drop down list. Again, remember concentrations in all compartment must be expressed as equivalent aqueous phase concentrations. 21

27 If desired, the model can be visualized by pressing the Visualize Current Site Model button. To further edit the model, press the Return to Enter Current Conditions button. 22

28 10. Optional Step - entering predicted outcome of objectives. Scroll to the top of the Current Site Conditions page. Click on the Objectives tab below the Step 2 heading. 23

29 Scroll down the page and select the appropriate color for the anticipated objective outcome in the short and long term for the status quo. You have the option to delete any of the objective items if not applicable to your site. Additional user specified objectives can be added by clicking the Add buttons. Objectives can be visualized by scrolling to the bottom of the page and clicking on the Visualize Objectives button. Be sure to click on the Save Current Site Model to save any changes. 11. Save any changes made to the model then return to the main menu. Click on the Remediation Alternatives hyperlink below the heading 3. Remediation Alternatives-Performance. 24

30 Next click on the Create New Alternative button. Name the Remedy! Each compartment has 3 components, B before, T treatment, and A after. Enter in anticipated OoM reductions in concentrations for each compartment using the dropdown menu under T. The results will be displayed to the right under A-after. Some anticipated reductions for different geological environments and remedies are given in Sale and Newell (ESTCP Project ER ). Save the reductions achieved by the remedy by pressing the Save Remediation Alternative Button. This examples uses the expected reductions for In Situ Biological Treatment from Sale and Newell (ESTCP Project ER ) page 86 as shown below. 25

31 12. Optional Step - entering predicted outcome of objectives at site based on remedy implementation. Scroll to the top of the Remediation Alternatives page and click on the Objectives tab. 26

32 Scroll down the page and select the appropriate color for the anticipated objective outcomes in the short and long term for the remedy. Additional user specified objectives can be added by clicking on the Add button. Objectives can be visualized by scrolling to the bottom of the page and clicking on the Visualize Objectives button. Be sure to click on the Save Remediation Alternative to save any changes. 13. To add additional remedies scroll to the top of the page and click on the Remediation Alternatives hyperlink. Press the Create New Alternatives button and repeat previous steps. 27

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34 14. To modify existing remedies, press the magnifying glass icon at the right side of the page on the same line as the remedy. To delete the remedy, press the X icon on the right side page on the same line as the remedy. Save any changes made to the model or remedies then return to the main menu. 15. Click on the Create / View Reports hyperlink below the heading 3. View Output Reports. 16. Grab and drag desired components from the Components List and place in the Report Components list. Components can be placed in any order. Press the View Report button to view and print the report. 29

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36 Print the report using the browser s print feature. Ensure background colors and images are being printed. Reports can be printed to hard copy or PDF. Exit from the report view by pressing the browser back button, then return to the main menu. 31

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38 17. Press the browser back button to leave the output report. Then navigate back to the main menu and scroll down to the Session Options & Information section. Here the session data can be updated, i.e. stored, by re-entering the site name and password and the pressing the Update button. Save the session URL to access your data in the future. The session can also be ended or deleted by pressing the End Session or Delete Session buttons respectively. IMPORTANT: Save this URL. It is the only future way to access the model you are creating. 33

39 HELP This section contains the text from help boxes in the web-based tool. If you have questions that are not covered in this Guide, the help texts below or by the Guide for Selecting Remedies for Subsurface Releases of Chlorinated Solvents (ESTCP Project ER ) please contact support at Help Boxes in 14C Model Main Page 1. Setup Model After a New Session was created, the first step is to setup a model. Your site model controls the layers, segments and phases available in the steps for current conditions and remediation alternatives. A cross-sectional map of the site can be added in this section that visually provides an additional mechanism to verify whether the data depicted in the tool are consistent with the site conditions. 2. Set Current Conditions After the Model Setup step was completed, the current conditions of the site should be defined. In this step the Order of Magnitude (OoM) current concentrations as well as Objectives should be entered. 3. Remediation Alternatives-Performance This step is similar to Step 2 and the Remediation Performance (i.e., OoMs reduction in concentrations) as well as Objectives should be entered. Click the Create New Alternative button to start creating a new remediation alternative. Multiple alternative remediation models can be created. In the Performance tab assign a name to the remediation alternative created. Enter the technology performance in OoMs reduction in concentrations, this variable is assigned the letter T (i.e., Technology). The before treatment (i.e. status quo) OoMs value is named variable B (i.e., Before) and has already been entered during Step 2 (Current Conditions). The after treatment OoMs variable is named A (i.e., After) and is calculated using the before OoM value and OoM reducing via the technology: A=B-T. Note that if A<0 then A=0. Enter the remediation alternative objectives by clicking on the Objective tab. A summary table comparing the Performance of all remediation alternatives and the status quo is shown on the Performance tab of the in Step 3 main page. The same summary table comparing the Objectives of all remediation alternatives and the status quo is shown on the Objective tab of the in Step 3 main page. Click the button to the 34

40 right of each alternative to edit, delete, or view the current conditions (status quo) or created remediation alternatives. 4. View Output Reports After Steps 2 and 3 are completed, use the report builder below to design your report. Click the Create / View Reports button to view, create and print reports on session output. Drag and drop the item(s) you want to show up in the report from the Component List on the right column to the Report Components on the left column. The order in which the components are sorted on the Report Components will be the order that the components show in the printed report. Once adding items to your report are completed; click the view button to show the final report. Help Boxes in 1. Setup Model Sub-Page Step 1.1: Enter a cross section of your site (optional) Adding a cross-section of the site, which is scaled and oriented to the source and plume configuration shown in the 14C Model tool, provides an additional mechanism to verify whether the data depicted in the tool are consistent with the site conditions. Step 1.2: Configure your compartment model The tool should be configured to provide a simplified, but accurate, representation of the site conditions. The complexity of the geologic sequence may demand sub-dividing the model to represent the mass distribution in multiple phases across several transmissive and low permeability units. Step 1.3: Determine which contaminant phases are in your model The availability of site data for each of the four phases should be evaluated to determine mass distribution in the model. Where a data gap analysis indicates that information for a specific phase is not available, the user should evaluate whether the data gap can be addressed with further site investigation, or consider appropriate phase partitioning calculations to populate the compartment model. Help Boxes in 2. Set Current Conditions Sub-Page What is OoM? An Order of Magnitude (OoM) is a factor of 10 change in a variable. For example, if a remediation technology reduces the dissolved phase concentration of TCE by one OoM, then the concentration is 10 times lower, equivalent to a 90% reduction. Two OoMs thus represents a reduction in concentration of 99%. The concept of OoMs is an important short hand for evaluating remediation performance in the 14C Model. We use 35

41 the concept of OoMs because chlorinated solvent concentrations in groundwater typically span several orders of magnitude, and are generally represented best by a lognormal statistical distribution. OoMs are used to describe the change in concentrations, contaminant mass, and mass discharge. The method relies on effective concentrations in each phase, e.g. sorbed and dissolved concentrations and does not account for de-sorption, back-diffusion etc. 36

42 How to convert to OoM? To calculate the percentage reduction caused by a remediation action with the initial amount (A) and end-point (B): % 100 The percentage reduction is then compared to the list below, to obtain the reduction in OoM. 0 OoM: 9% or less reduction in concentration, mass, or mass discharge 1 OoM: 90% reduction in concentration 2 OoM: 99% reduction in concentration 3 OoM: 99.9% reduction in concentration If one action is continued by another, which leads to a further reduction to (C), then the overall reduction expressed in terms of Oom, can be calculated directly from the expression by use of (A) and (C). Otherwise, a stepwise calculation can be performed from (A) to (B) and then (B) to (C), where the overall reduction in OoM is the sum of the step-wise found OoMs. An example is provided below on the two methods. Overall OoM reduction C [mg/l] Reduction [%] Method OoM Before remediation 99 0 After remediation (99-11)/99*100 1 After remediation ( )/99*100 2 Step-wise reduction to overall OoM C [mg/l] Reduction [%] Method OoM Before remediation 99 0 After remediation (99-11)/99*100 1 After remediation ( )/11*100 1 Overall OoM 2 37

43 REFERENCES AFCEE (Air Force Center for Environmental Excellence) AFCEE Source Zone Initiative. Prepared by Sale TC, Illangasekare TH, Zimbron J, Rodriguez D, Wilking B, and Marinelli F for the AFCEE, Brooks City-Base, San Antonio, TX, USA. Accessed June 23, Chapman SW, Parker BL Plume Persistence due to aquitard back diffusion following dense nonaqueous phase liquid removal or isolation. Water Resource Res 41:W Chen, W., Kan, A.T., Newell, C.J., Moore, E. and Tomson MB More realistic soil cleanup standards with dual-equilibrium desorption. Ground Water 40: Decision Support System for Matrix Diffusion Modeling: Matrix Diffusion Toolkit, developed for the Environmental Security Technology Certification Program (ESTCP) by GSI Environmental Inc., Houston, Texas. (ER ). Groundwater/Persistent-Contamination/ER , Accessed May 15, Farhat, S.K., C.J. Newell, T.C. Sale, D.S. Dandy, J.J. Wahlberg, M.A. Seyedabbasi, J.M. McDade, and N.T. Mahler, Liu C, Ball WP Back diffusion of chlorinated solvent contamination from a natural aquitard to a remediated aquifer under well-controlled field conditions: Predictions and measurements. Ground Water 40: Marquardt, G.P., M.A. Seyedabbasi, M. Vanderkooy, M. McMaster, G. Wealthall, T.C. Sale, C.J. Newell (2014) 14-Compartment Model Toolkit, prepared for the Strategic Environmental Research and Development (SERDP) Program, July Accessed July 1, Parker BL, Cherry JA, Gillham RW The Effect of Molecular Diffusion on DNAPL Behavior in Fractured Porous Media. In Pankow JF, Cherry JA, eds, Dense Chlorinated Solvents and Other DNAPLs in Groundwater, Waterloo Press, pp

44 Sale, T. and Newell, C A Guide for Selecting Remedies for Subsurface Releases of Chlorinated Solvents. Developed for the Environmental Security Technology Certification Program (ER ). Sale T, Zimbron J, Dandy D Effects of reduced contaminant loading on downgradient water quality in an idealized two layer system. J Contam Hydrol 102: Wiedemeier TH, Rifai HS, Newell CJ, Wilson JT Natural attenuation of fuels and chlorinated solvents in the subsurface. John Wiley & Sons, New York, NY, USA. 39

45 ATTACHEMENT 1 Screening Method to Estimate if a Chlorinated Solvent Site is in its Early, Middle or Late Stage (C. Newell, T. Sale, D. Adamson) 40

46 Screening Method To Estimate if a Chlorinated Solvent Site is in its Early, Middle or Late Stage (C. Newell, T. Sale, D. Adamson) In the Chlorinated Solvent FAQ, the idea that chlorinated solvent sites went through various stages during the site s life cycle was presented (Sale et al., 2008): With time, subsurface chlorinated solvent releases age. Early in their lives, they are dominated by DNAPL, but slowly DNAPLs dissolve, plumes develop, and contaminants accumulate in permeable zones. Eventually, little to no DNAPL remains, and plumes are sustained by the release of contaminants from low permeability zones via diffusion (Chapman and Parker, 2005). Although recoverable DNAPL can still be found within some source zones, it is notoriously difficult to find DNAPLs at the heads of many persistent plumes. At some sites (see late stage below), it simply may not be there any longer, even though the source zone (see FAQ 4) is still active. Key factors controlling the rate at which chlorinated solvent releases age include the amount of DNAPL released, the solubility of the constituent in the DNAPL, the rate of groundwater flow, and the architecture of transmissive and low permeability zones. The following is a methodology we developed to help site managers, consultants, remediation specialists, and regulators try to understand if they are working on an early, middle, or late stage site. The method is based on experience working in chlorinated solvent source zones with some assistance from recently developed matrix diffusion models developed by the authors that form the basis of the ESTCP Matrix Diffusion Toolkit (Farhat et al., 2013). The method is our first attempt at this classification system, and the approach may change as we all learn more about how chlorinated solvent sites age. Some key considerations about the Screening Method are: It is designed for chlorinated solvent sites, although it may be possible to adapt it for other contaminants. It is mainly derived from our experience at trichoroethene (TCE) sites. Although it has provisions for applying it for other DNAPL constituents, the body of site experience is fro DNAPL sites. It is relatively general and relies on several interpretations when compiling the data required to apply the Screening Method. Therefore it is possible two different users may generate two different answers. It may take some time to go through this; it requires some careful thinking about your site and the data required to use the method.

47 Early, Middle or Late Stage? Screening Method To Estimate if a Chlorinated Solvent Site is in its Early, Middle or Late Stage (C. Newell, T. Sale, D. Adamson) Is it important to distinguish between early, middle, late stage chlorinated solvent sites? No Examples: I m going to use containment. I m going to use a DNAPL-insensitive technology (like thermal remediation). YOU DON T NEED TO KNOW WHICH STAGE Yes Examples: My regulatory guidance says I need to remove the DNAPL if it is there (for example, DNAPL is considered a Primary Threat Waste). I want to consider using a DNAPL-specific technology (like an injection based technology). Has DNAPL ever been observed directly (such as in wells or soil cores) Yes Is most of the original DNAPL still there?(see page EML-3) Yes THIS SITE MOST LIKELY EARLY STAGE No No THIS SITE MOST LIKELY MIDDLE STAGE Evaluate Lines of Evidence #1 and #2 (page EML-4), # 3 (page EML-5), and #4 (page EML-6) and determine how many YES s you have If only one or two Lines of Evidence are YES: POSSIBLE Evidence for Late Stage Site, But Unclear If three of four Lines of Evidence are YES: MODERATE Evidence for Late Stage Site If four of four Lines of Evidence are YES: STRONG Evidence for Late Stage Site EML- 2

48 Early, Middle or Late Stage? Has Most of the Original DNAPL Still There? This can be a difficult and controversial question to answer. The following are some thoughts, observations, speculations from the authors. These may change over time as better methods to understand DNAPL source zones are developed. In this application, when we refer to DNAPL we mean DNAPL chemicals rather than an insoluble oils or other chemicals in the original release. The answer depends on several variables that can be very difficult to determine, such as the amount of the release, the composition of the DNAPL, the source architecture; as well as more commonly measured geochemical and hydrogeologic variables. There are simple dissolution models that can be used to provide some guidance. But generally if on assumes the DNAPL is mostly in the ganglia or blob form, the resulting dissolution times are often just a few years. DNAPL pools, particularly long ones (10s of meters), can last many many decades. In general, the answer is more likely to be a No if the site has more of these characteristics than not: There are only a few indicators of DNAPL presence (e.g., a couple of stains on just a few cores); No significant DNAPL accumulation in groundwater monitoring wells has been observed; The source release is small (a few hundred or few thousand kilograms or less); The source release mechanism and the geology will spread the DNAPL into a large volume in the subsurface; Groundwater seepage velocities are moderate to high (tens of meters per year or more); There has been successful removal of much of the DNAPL mass from the transmissive zone with an in-situ remediation technology; The key constituents are more soluble (several hundred or thousand mg/l or more); It has been several decades since most of the DNAPL was released. In general, the answer is more likely to be a Yes if the site has more of these characteristics than not: There are only a multiple indicators of DNAPL presence (e.g., many cores with positive dye test tests; several monitoring wells with DNAPL accumulations); No significant DNAPL accumulation in monitoring wells has been observed; The release was very large (hundreds of thousands or millions of kilograms); The release point and subsurface geology result in the formation of large DNAPL pools; Groundwater seepage velocities are low (meters per year or less); No remediation or DNAPL removal has occurred; The key constituents have relatively low solubility (tens or a few hundreds of mg/l); It has been just a few years since most of the DNAPL was released. At most sites, DNAPL is never observed so this is not needed to go through this flowchart. EML- 3

49 Early, Middle or Late Stage? LINE OF EVIDENCE 1: Adequate DNAPL Search? Was a thorough direct DNAPL investigation was conducted, where one or more of the following were performed: Interfaces above low perm zones were sampled. OR A vertical transect was used to identify high flux zones that were then sampled for DNAPL. OR Soil samples were investigated using enhanced techniques like hydrophobic dye. OR Other DNAPL-specific characterization technologies were used. If ANY of these were done, Line of Evidence 1 is YES If NONE were done, Line of Evidence 1 is NO (VERY IMPORTANT: the 1% rule should not used to indicate the presence of DNAPL) LINE OF EVIDENCE 2: Old Plume + Heterogeneity? Does your site meet both of these qualitative conditions? Site has identified low k zones (such as silts, clays, sandstone, limestone) with hydraulic conductivity of at least 100 times lower than fastest transmissive zones that is or was in contact with the plume. AND The original release likely occurred more than 30 years ago. If BOTH of these are TRUE, Line of Evidence 2 is YES If EITHER IS FALSE, Line of Evidence 2 is NO EML- 4

50 Early, Middle or Late Stage? LINE OF EVIDENCE 3: Can the Low-k Zone Hold Enough Mass? (see EML-7 for basis) 1. Calculate TCE Mass per cubic meter of low-k material with Graph A. 2. Estimate the volume of low-k material at your site using Graph B. 3. Multiple the two values together to get an estimated mass in low k unit in kilograms. 4. This particular chart is designed for TCE and for a source zone. You can apply this to other chlorinated solvents by multiplying by the pure-phase solubility of your DNAPL chemical in mg/l and dividing by 1000 mg/l (value we used for TCE). 5. You can do this for different parts of the site, such as the original source zone, a high concentration part of the plume, and a low concentration area, each with a different concentration, year since low-k diffusion started, and areas, and add the numbers. Multiply these two values to get mass of TCE in low-k zone >100 kg: YES <100 kg: NO If the Mass is > 100 kilograms, Line of Evidence 3 is YES If the Mass is < 100 kilograms, Line of Evidence 3 is NO Contaminant Mass in Low- k Material (kilograms per cubic meter) Poten&al Volume of Low- k Material for Matrix Diffusion (cubic meters) ,000,000, ,000,000 10,000,000 1,000,000 Graph A - Mass TCE Per Cubic Meter of Low- k Material Years Since Low- k Diffusion Started Graph B - Poten&al Volume of Low- k Material for Matrix Diffusion 100,000 10,000 1, ,000 10, ,000 1,000,000 Area of Poten&al Matrix Diffusion Zone (square meters) EML- 5 Estimated Average Loading Concentration to Low-k Zone Since Diffusion started in mg/l*: * If unknown, just use maximum historcal concentration for this area. Total Thickness of Clay + Silt in Contact with Plume in Meters (maximum of 1 meter per layer): 1 acre 10 acres