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Natural Attenuation of Groundwater Contaminants: New Paradigms,…

- - - - Abandons dispersion as basis for accounting for local heterogeneities in aquifers and as an explanation for dilute concentration in wells
      - Embraces diffusion and slow advection as fundamental governing processes at contaminated sites
      - Diffusion vs Dispersion is important for understanding how natural attenuation works
    - - Then do high resolution sampling of low -k zones to determine presence and concentration of contaminants in low-k zones
  - - - Variations in flow velocity
      - Different solute flow paths
      - Cause the plume to spread
    - - The spread of particles through random motion from regions of higher concentration to regions of lower concentration
  - - - Groundwater samples
        
        Plume delineation
      - Soil Samples
        
        Focus on unsaturated zone
    - - Soil subsampling
  - - - Parallel Fractures type site
      - Fracture Network
      - Two layer Sand/Clay
      - Multi-layer San/Clay Type site
      - Random Clay Layer Type Site
    - - Dandy-Sale Analytical matrix Diffusion model
  - - - Sometimes
      - Some evidence based on lab/field studies
      - Not investigated much yet
      - Slow attenuation could be significant for chlorinateds
    - - Long retention times
      - Reducing conditions are common, favorable for biological and biogeochemical reductive dechlorination
      - Potentially large reservoir of organic carbon
      - Potentially large reservoir of reactive mineral species
    - - Smaller pore throat size restricts migration of microbes, influx of nutrients/ carbon sources, and growth density
      - Salinity can be high and may limit microbial activity
      - Limited bioavailability of organic carbon
      - Reactivity of mineral species may be limited due to dependen on microbial activity
    - - Molecular biological data confirming presence and/or activity of degraders within low k zone
      - Daugther product distribution suggests greater extent of degradation in low k zone relative to adjacent transmissive zone
      - Favorable geochemical conditions within low k zones
      - CSIA data showing higher fractionation within low k zone
      - Mineralogical analysis of low k zone soil samples that show minerals capble of abiotic degradation of contaminants
- - - - i: dH/dL
    - - K
  - - - Biodegradation no so strong
    - - Infiltration
      - Groundwater mixing zone thickness
      - Dispersions
    - - Low flow surface water techniques come into play such as 7-day, 10 year low flow and base flow stimation
  - - - Soil to GW pathway
        
        GW soil: Leachate dilution factor (LDF)
        
        GW darcy velocity
        
        GW mixing zone thickness
        
        Net infiltration
        
        Width of affected soil in direction of GW flow
      - Key factors
        
        Area of source
        
        Aquifer thickness
        
        Distance to receptor
        
        Screened interval
        
        Infiltration rate
        
        Ground water velocity
        
        First order decay
      - Human Health PCLs: Groundwater
        
        Groundwater to surface water pathway
        
        Risk-Based Exposure Level
        
        Dilultion factor for affected GW entering SW
        
        Three SURFACE water specific rules RCRA
        
        Plume must already have reached the stream
        
        No statistically significant increase over background in the surface water
        
        No receptors at unsafe level before discharging
  - - - CSw : Md/ Qsw
      - Csw is the maximum concentration of contaminant in water extracted from the supply well
      - Md is the mass discharge
      - Q sw is the pumping rate from a supply well
  - - - Use mass discharge of plume to predict constituent of concern concentration in downgradient water supply well
    - - Mass per area per time
    - - Mass per time
    - - Transect method
        
        Step-by-step approach assuming uniform groundwater velocity
        
        Draw transect: with polygons for each well
        
        Determine area
        
        Multiply and sum together
        
        Md: Sum( CnAnVd)
        
        Md: Mass discharge
        
        Cn: Concentration in polygon n
        
        An: Area de segment n
        
        Vd: Darcy velocity
      - Well capture/ Pumping methods
        
        Measure Q, Cwell from well
        
        Md: Q*Cwell
        
        Md: Mass discharge (grams per day)
        
        Cwell: Concentration in recovery well (grams per liter)
        
        Q: Well pumping rate (liters per day)
      - Passive flux meters
        
        Permeable sorbent
        
        Accumulates contaminant based on flow and concentration
        
        Contaminant adsorbed onto passive flux meter over time to get concentration
        
        Soluble tracers
        
        Loses tracer based on groundwater velocity and flux convergence calculations
        
        Tracer desorb from passive flux meter over time to get flow
      - Using existing data (Isocontours)
        
        Uses plume map
        
        Combine with flow data
        
        Two dimensional transect based on isocontour data
      - Solute transport models
        
        Enter flow, concentration data and calibrate model
  - - - Combine flow/size, concentration
    - - Concentration, hydraulic conductivity have a log normal distribution
    - - 9 OoM
    - - Mag 2 plume
        
        Domestic well
      - Mag 5 plume
        
        Municipal well
      - Mag 8 Plume
        
        Stream
      - Managing surface water Quality with mass Discharge: Total Daily Loads (TMDL)
- - - - Radioactive
    - - Fractionation
        
        Ligther isotopes are degraded preferentially
        
        More rapidly
        
        Degradation causes remaining TCE to become enriched in heavier isotopes
        
        The isotopic ratio is changing due to degradation
    - - Unit are "per mil" or%o
    - - Rt/Ro: f(alfa-1)
        
        Rt: R of compound at time t
        
        R0: R of compound at time 0
        
        f: Fraction of compound remaining
        
        alfa: Fractionation factor
    - - dt:E Ln f + d0
      - d of compound at time t
        
        From analysis of site samples by lab
        
        Provides LOE for degradation
      - Enrichment factor (E): 1000*(alfa-1)
        
        Literature or lab value
        
        Compound and pathway specific
      - Ln f : Fraction of compound remaining
      - d0: d of compound at time 0
    - - Groundwater is typical matrix
      - 40-ml VOAs w/ preservative (Chech with lab)
      - Soil samples also an option
    - - More specialized analysus (GC/IRMS)
      - Fairly limited number of commercial labs (relative to standar analytes)
      - 100s of $ per isotope per analysis (Plus need concentration too)
      - May require lots of sample to get detectable signal
  - - - Increased fractionation *("Heavier") over time
      - Need > 2 %o for to confirm C fractionation
      - The hight in y reflects extent of paren degradation
      - Pattern can be used to estimate fraction degrades and rate degraded
      - Maybe better than estimates based on standard C vs t data?
    - - No degradation of daugther product
        
        Daugther approaches d parent s as C parent approaches 0
      - Degradation of daughter product
        
        d daughter exceeds d0 parent as C parent approaches 0
    - - Derivation assumes first-order degradation (pretty standard)
      - Can be calculated with time or distance
      - kt: (d0-dt)/(E*t)
        
        kt: 1st-order rate coefficient
        
        d of compound at time 0 and at time t
        
        Enrichment factor (Look up value)
  - - - Data can be difficult to interpret
        
        Might get different interpretations
      - Recognition that fractionation occurs even with non destructive processes
      - MNA processes showing evidence of isotope effects:
        
        Biotic degradation
        
        Abiotic degradation
        
        Dispersion
        
        Diffusion
        
        Sorption
        
        Volatilization
    - - C12-C13
      - O16-O18
      - N14-N15
      - H1-H2
      - Cl35-Cl37
    - - Increased Centainty that fractionation is ocurring
        
        Isotope ratios in benzene in groundwater samples from multiple wells
        
        Shifts in one isotope may be more apparent than other isotope
    - - Isotope ratios in benzene in groundwater samples from multiple wells
      - Provides better basis for degradation extent and rate
    - - Identify relevant reaction pathways
        
        Lab test suggest pathways have characteristic and distiguishable fractiation paaterns
      - Identify Relevant reaction Pathways
        
        Lots of uncertainty about whether this is really possible
        
        Complicated by contribution of other non-destructive processes
        
        Conceptual diagram of isotope ration in 1.1.1 TCA samples along plume transect
        
        Identify Relevant reaction Pathways
        
        Very powerful for source apportionment
        
        Less of a priority for MNA applications
        
        Distinguishing two sources of perchlorate
    - - CSIA data combined with reactive transport modeling
      - ESTCP-funded project (ER-201029) rovides model and extensive guidance
      - PHAST 2 D Model cross-section assuming complete reductive dechlorination to ethene
  - - - Document loss of contaminants at the field scale
        
        Graphical ans statistical analyses of contaminant concentration trends
        
        Plume contour vs time
        
        Concentration vs distance
        
        Well transects
        
        Can be used to determine contaminant flux at transects
        
        Fi: Suma( ViCiAi)
        
        Vi: Contaminant velocity perpendicular to the line of wells
        
        Ci: Contaminant concentration at the well screen
        
        Ai: Tributary area for a given well screen
        
        A decrease in flux over travel distance indicates natural attenuation
        
        The first-order decay coefficient (Lambda) can be obtained as the slope of Ln (Flux) versus travel time (x/v)
        
        The mass balance approach
        
        Needs a dense monitoring well cluster (good for non-steady plumes)
        
        Useful to assess whether a plume is shrinking, stable, or expanding
        
        Total mass of dissolved contaminant monitored over time by interpolation and integration of monitoring well data
        
        Lambda is determined as the percent of contaminant deplected per time, usually normalized to a unit of per day
        
        Lambda: (-dM/dt)/M:[(Mo-M)/Mo]/dt
      - Geochemical indicators
        
        To demonstrate indirectly the type of degradation processes active at the site
        
        For spills of oxidizable pollutants (e.g hydrocarbons) look for O2, NO3 and SO4 levels below background in the core of the plume, and Fe2 and Ch4 levels above background.
        
        Also, Higher CO2 and alkalinity
        
        For chlorinated solvents, look for higher Cl- levels than backgorund as well as for appearance of dechlorinated byproducts
      - Laboratory or in situ microcosm showing biodegradtion in biologically active incubation but not in sterile controls
        
        Stainless steel cylinders that isolate about 2 L of the acuifer.
        
        Valves allow for adding test contaminants and for sampling
        
        ISM is open to the ambient aquifer at the bottom
        
        Thus, one needs to correct for dilution effects using tracers
        
        Single well push-pull test
        
        During the injection phase, a prepared test solution containig a tracer and a subtrate is injected into the saturated zone using an existing monitoring well
        
        During the extraction phase, flow is reversed and samples are collected and anlyzed to determine mass recovered for tracer, substrate, and byproducts
      - Molecular Evidence
      - Stable Isotope Enrichment
  - - - Target
        
        Ribosomal (r) RNA
        
        Genes for r RNA on DNA
        
        Catabolic genes on DNA
        
        Messenger (m) RNA
        
        Protein
      - Information gained
        
        Phylogenetic identity
        
        DGGE band preferentially enriched after anaerobic benzene degradation
        
        Corresponds to desulfobacterium sp
        
        Highest biomarker concentration coincided with point of highest anaerobic benzene degradation activity
        
        Phenotypic potential
      - Question answered
        
        Who is there?
        
        What can they degrade?
        
        What genes are being expressed?
        
        Who is active and what are they doing?
      - Benzylsuccinate Synthase (Coded by bssAgene)
        
        Initiates anaerobic Toluene or Xylenes biodegredation
        
        bssA biomarker concentration predicted anaerobic toluene degradation rates in microcosms
      - 1, 4 Dioxane biodegradation by dioxane mooxygenase
        
        20 microcosm sets mimicking dioxane natural attenuation
        
        Degradation activity predicted by dxmA Probe but not by a generic total bacteria (16S)Probe
  - - - Add radiolabeled contaminant and see if it accumulates in biomarkers over time
        
        If it accumulates, then it means that organisms are growing on the contaminant
        
        If it's growing, then that means degradation is ocurring
    - - Measure naturally occurring isotopic ratio in contaminant and track over time and/ or distance to show degradation
    - - PFLA (Phospholipid fatty acid)
      - DNA/ RNA
      - Proteins
    - - C 13
      - N 15
      - O 18
      - Very high isotopic enrichment is needed to see signal
        
        10-100% heavy isotope
        
        Beacuse microbes would prefer to use ligther isotope
    - - Benzene
      - Toluene
      - Phenol
      - PAHs
      - RDX
      - TNT
      - MTBE
      - 1,4 Dioxane
      - VC
        
        Aerobic pathway
      - All are carbon/energy sources for microbes
    - - PCE
      - TCE
      - cDCE
      - VC
        
        Anaerobic pathway
      - 1,1,1, TCA
      - Other chlorinated ethanes
      - Chlorinated methanes
      - Perchlorate
      - Compounds that serve as electron acceptors- SIP won't work for processes that aren't assimilatory
    - - Passive microbial sampling devices
        
        Bio traps are installed in monitoring well for 30 days or more
      - Strengths of SIP for MNA
        
        Strong line of evidence that attenuation can occur/is occuring
        
        Establishes how attenuation is ocurring and who is responsable
        
        Mimics in situ conditions
        
        Can be used to support rate calculations
        
        Culture independent
        
        Complmentary and adaptable
        
        Can use existing monitoring wells
      - Limitation of SIP for MNA
        
        Not all compounds can be tested
        
        False positives
        
        Cross feeding
        
        In situ test are conducted in preferential conditions
        
        Cost
        
        Availability
        
        Few labs
        
        Requires expertise
        
        Protocols not always standarized
        
        Stakeholder unfamiliarity with results
- - - - Groundwater samples
        
        Collected as primary characterization data
        
        Plume delineation and to monitor trends
        
        Long/screened well provides florw/weigthed average concentration
        
        Domitade by high K zones with little info on low K zones
      - Soil samples
        
        Collected for sources delination
        
        Soil coring often focuses on unusaturated zone * not extended to saturated low Kzones( with limited vertical sampling density
    - - Simultaneous measurements of groundwater flow and concentration are made at representative grid points.
      - Mass flux is calculated using those estimates in eq. 2-1
      - Summing the segments of all mass flux values across the entire plume cross section yields the contaminant mass discharge
    - - A series of transects is ahown, with the leading edge of contaminant arrival on the right
        
        Note the changes in the mass storage in less transmissive zones with distance from the source
    - - The mass flux at any location along a plume represents the combined effects of contaminant transport.
        
        destructive attenuation (if any), and storage processes (sorption and difussion into low-K zones)
        
        Losses of contaminat mass temporarily lower mass flux relative to the flux that is later observed at plume maturity.
  - - - The scale must be appopriate for the site conditions
  - - - Must use high resolution sampling for this
    - - But Ok to use monitoring wells for this?
  - - - Line of evidence
        
        Decreasing historical trends in concentration/mass
        
        Favorable geochemical and daughter product data
        
        Microcosm or field data showing degradation is ocurring (and rate)
      - Long-term performance monitoring
    - - Demonstrate that natural attenuation is ocurring
      - Detect changes in conditions that reduce attenuation efficiency
      - Identigy toxic/mobile by-products
      - Verify that plume is not expanding
      - Verify no impact to downgradient receptor
      - Detect new releases
      - Confirm institucional controls are working
      - Verify attainment of medical objectives
      - For site specific
        
        Remedial action objectives (RAOs)
        
        Preliminary Remediation Goals (PRGs)
    - - Source zone attenuation, identify new seleases, monitor institucional controls, assess performance
      - High concentration plume core
        
        Monitor conditions in highly transmissive zones, transects for mass discharge measurements
        
        Low concentration plume fringe
        
        Potential for earlier attainmen of remediation goals due to more rapid concentration reductions
        
        Plume boundaries
        
        Monitor plume expansion or shrinkage at sidegradient or downgradient locations or transects, confimr no risk receptor
        
        Recalcitrant zones
        
        Areas where progress towards remedial goals is slow due to matrix diffusion or poor characterization, may require higher resolution monitoring
        
        Upgradient areas
        
        Establish backgorund conditions, identify changes in conditions
    - - Constituents of concern
      - Transformation products
        
        Daughters products, metals
      - Geochemical indicators
        
        Oxidation- reduction potential, pH, temperature, methane, sulfate, iron, nitrate
      - Others
        
        Water level, isotopes, biomarkers, minerals
    - - MNA monitoring program can involve characterization to support the selection of MNA as a remedy, or long-term performance monitoring to document that MNA is working
      - MNA monitoring programs are designed to address specific remedial action objectives
      - MNA monitoring locations and analytes are selected to ensure that objectives like performance and plume stability can be assesed
      - Short term variability makes it harder to determine trend and increases the amount of monitoring needed to evaluate progress in remediation
      - It comonly takes seven years or more of quarterly monitoring data to characterize the attenuation rate with even a medium level of accuracy
      - Less frequent monitoring over longer periods of time may be more cost appopriate for detemining trands during MNA
  - - - Short-term variability makes it harder to determine trend and increases the amount of monitoring needed to evaluate progress in remediation
      - Long term trend apparent over longer monitoring period
      - Increasing the time between monitoring events will increase the confidence and accurancy of your long-term attenuation rate...
    - - Medium Confidence
        
        Statistically- significant
        
        Decreasing concentration trend (p<1) for 80% of monitoring wells
      - Medium Accuracy
        
        Determine the long term attenuation rate with an accuracy of +- 50 % or 0.1 yr-1 for 80% of monitoring wells
      - It commonly takes seven years or more of quarterly monitoring data to characterize the attenuation rate with even a medium level accuracy
      - Making decisions based on insufficient data can result in incorrect decisions
  - - - Short term variability can make this challenging
      - Need statistical methods
      - Avoid " Recency bias"
      - Are contaminant concentrations decreasing over time?
      - When will concentration fall below the clean up goal?
    - - Linear regression
        
        Parametric test
        
        Isn't always applicable
      - Non parametric test
        
        Requires no assumptions about distribution
      - Only cares about relative magnitudes of concentrations
      - Easier to establish trend
      - Non-detects more easily handled
      - Simple method
      - How to perform Mann-Kendall?
        
        Calculate three Different Metrics
        
        S statistic (S)
        
        Indicates if trendis increasing or decreasing
        
        Confidence Factor (CF)
        
        Reflects degree of confidence in results
        
        Confidence of variation (COV)
        
        Variability in concentration vs. t data
        
        Used to distinguish between stable and no trend
  - - - Variability is inherent to monitoring data
      - Implications for manitoring frequency and data requiriments
      - Sources of variability not well understood
    - - source attenuation
        
        Not really short-term variability
      - Laboratory analysis
        
        Minor source
      - Well and sampling dynamics
        
        Minor source
      - Signal variability
    - - Ambient flow
        
        Groundwater flows through screened interval
        
        Less resistance to hydrostatic pressure
      - Continuous flushing of well with water from aquifer
      - Greater contribution from zones of higher permeability
      - Ambient mixing
        
        Groundwater mixesvertically within the well
        
        Temperature, pressure, salinity
        
        Seasonal when driven by temperutre
        
        Mostly affects shallow wells
        
        < 10 m deep
      - Redistribution of contaminants
        
        Closer to flow weighted average
    - - Well Purging
        
        Sampled water representative of formation water
      - Flow weighted average concentration
        
        Obtained if well has been "Sufficiently" purged
      - Concentration result would be similar to no- purge sample
        
        If ambient flow and in-well mixing occur
    - - Sample method has little or no effect on concentration or variamility
      - No apparent benefit to monitoring purge parameter comáred to fixed volume purge
      - Select sample method based on cost, ease of implementation, and sample colume requirements
  - - - LOE Historical contaminant mass reduction monitoring data vs time
        
        I shrink therefore I am
        
        Direct method to demonstrate decreasing trend
        
        Always
      - Mass Loss and plume stability
        
        Define groundwater plume status as stable, shrinking, or expanding
        
        Evaluate historical concentration measurements in gorundwater
        
        Always apply based on sufficient historical data
      - Demonstrate mass loss, plume stability
        
        Two common graphical methods
        
        Plume outer contour vs time
        
        Concentration vs distance at different times
        
        Rate calculations
- - - - Gorundwater transport Modeling
        
        Advective -dispersive -degradation equation
        
        Concentration at Downgradient LocationX
        
        Source concentration
        
        Longitudinal dispersivity
        
        Groundwater seepage velocity
        
        First order Decay Constant
        
        Retardation Coefficient
        
        Error Function (erf)
        
        Transverse dispersivity
        
        Gorundwater source width and depth
        
        Vertical Dispersivity
    - - Source term mass balance
        
        Assume source zone is a Box
        
        Flow rate through source zone
        
        Concentration in source zone at time
        
        Total mass of contaminant in source zone
        
        Concentration declines with tail
    - - Calibrate model to existing monitoring data
        
        Increase time to some time in the future
        
        See if plume gets larger or smaller or becomes stable
    - - Systems to organize site data
      - Tool to help understand site processes
      - Additional line of evidence
      - Screen for applicability of MNA
    - - Computer models can help answer two types of questions:
        
        How far will the plume travel?
        
        How long will the source and plume persist?
      - Models are good for organizing site data, help understand key processes
      - But models don't provide detailed, precise answers
  - - - Source zone
      - Groundwater flow direction
      - Advection alone
      - Dispersion/Difussion
      - Sorption/ retardation
      - Degradation
    - - Analytical models are useful tool to assess if natural attenuation is occurring
        
        Compare plume with "No MNA" simulation, using Lamda =0)
      - Limited predictive capability (Order of magnitud capacity) because groundwater flow and microbial behavior rarely follow the simplyfying model assumptions
  - - - Bioscreen
      - Biochlor
      - RemChlor
        
        Source
        
        Zone 1
        
        High anaerobic decay rates
        
        Zone 2
        
        Possible enhanced aerobic decay
        
        Zone 3
        
        Low or Background decay rates
      - REMFuel
      - Matrix Diffusion Toolkit
      - REMChlor-MD
        
        Semi-analytical method adapted to the perform of chemical diffusion with first order decay
        
        4 types
        
        Aquifer/ Aquitard system
        
        Transmissive zone
        
        Low permeability confining
        
        Layered system
        
        Low permeability layers
        
        Transmissive zones
        
        Low permeability confinig layer
        
        Heterogeneous system
        
        Transmissive zone
        
        Low permeability confinig layer
        
        3D Fractured Media
    - - Analytical model for source behavior
        
        Mass balance model on source zone predicts discharge including effects of remediation
    - - Couple models at the edge of the source zone to provide contaminant discharge to plume model
    - - Plume model simulates mass balance based on advection, dispersion, retardation, and degradation reactions
      - plus plume remediation
    - - Source Mass
        
        Source depletion % Mass Removed
        
        Source Decay Rate Constant
        
        Mass discharge
      - Plume mass
        
        Mass Discharge
        
        Plume remediation Lamda
        
        MNA
    - - Menor 1
        
        NAPL is mostly in high conductiviy zones, or as pools in homogenous media
      - Mayor 1
        
        NAPL is mostly in low permeability zones in heterogeneus system
    - - Divide space and time into "Reaction zones"
      - Solve the coupled parent daugther reaction for chlorinated solvent degradation in each zone
      - Each of these space time zones can have a different decay rate for each chemical species
    - - Quick overview of a powerful but relatively simple gorundwater model that can be used to evaluate MNA
        
        REMChlor
      - It has an innovative source term so you control when and how contaminants leave the source (Gamma)
      - The plume has Space- Time zones to model different times and places that biodegradation occurs
      - REMChlor- MD will be important new tool- includes matrix diffusion in plume
  - - - Logarithmic extrapolation
        
        SourceDK-Tier 1
        
        Enter concentration vs time data
        
        Enter clean up level
      - Box Model (First order decay)
        
        SourceDK Tier 2
        
        BIOSCREEN
        
        BIOCHLOR
        
        Assuming constant concentration leaving source (Step function)
        
        Flow Rate Through source
        
        Total Mass in source
        
        Concentration in source zone at time
        
        Deacay function
      - Power Model (Any Type of decay)
        
        REMChlor
        
        REMFuel
      - Diffusion Models
        
        Matrix diffusion toolkit
      - Mass Balance
        
        NAs Toolkit
    - - Remaining fraction of source mass source deleption
        
        RTF sd: Remediation timeframe with source depletion
        
        RTF mna: Remediation timeframe MNA (untreatd source zone)
    - - Gamma: 0
        
        Step function
      - Gamma: 0.5
        
        Linear
      - Gamma: 1.0
        
        First order
      - Gamma> 1
        
        Matrix difussion
    - - Several timeframe models available
      - Time reduction is not linearly related to mass removal
      - Consideable uncertainty in remediation timeframe estimates
  - - - Experimental Science
      - Theoretical Science
      - Computational modeling
      - Application of massive databases
    - - Data mangment system for sites in california with affected gorundwater
    - - Big data studies give insightsa on how big plumes are and how fast they change
      - Numerous studies for variety of contaminant classes
      - Geotracker important resource
  - - - Limited
        
        Hand calculations
        
        Basic
      - Site data
        
        TAxonomic Screening
        
        Binning/ Screening
      - Site data: Simplifying assumptions
        
        Simple analytical models
        
        Exploratory or desision level
      - Complex incorporates more site data
        
        Numerical models
        
        Detailed site-specific simulations
    - - See how macro scale heteogeneities affect you
      - Simulates recharge, discharge to streams
      - More complex reactions for sorption, biodegradation
      - More realistic
    - - More time and expenses
      - Have to be careful with matrix diffusion
      - Typically you have to enter your source concentrationvs time
    - - Can be used to model the complexities of flow, geology, and reaction for natural attenuation or accelerated in situ bioremediation scenarios.
    - - Modular 3D multispecies transport model for sminulation of advection, dispersion and chemical reactions of contaminants in groundwater systems
    - - Parallel fractures type site
      - Fracture Network
      - Two layer sand/Clay
      - Multi layer sand/CAly type site
      - Random Clay layer type site
    - - Numerical models can model thing analytical models cannot
      - Some limitations: Can be very powerful but with some limitations
        
        Don't often have " Modeled Source term"
        
        May need very fine grid to model matrix diffusion
      - Type site can be middle ground
- - - - A systematic approach to evaluate wheter MNA is an appropiate remedy based on site specific conditions
    - - Use BioPIc to confirm if that rate is consistent with rates that have been observed in other studies for any potentially-applicable pathways
    - - Attenuation pathways that are included
        
        Complete anaerobic reductive dechlorination
        
        Partial anaerobic reductive dechlorination
        
        Aerobic biological oxidation
        
        Abiotic degradation
      - Parameters found to have direct correlation on attenuation rate
        
        Dehalococcoides density (for TCE, cDCE, and VC)
        
        Magnetic susceptibility
        
        Iron sulfide
        
        Methane
        
        Ferrous iron
    - - Free on lin e that helps decide if MNA is right for your site
      - If MNA is not appropiate, it helps decide between biostimulation and bioaugmentation
      - Uses correlations between paramete concentrations and known attenuation rates to determine wich processes can explain field rates
  - - - Plume is not expanding and sorption is occurring
      - ID the attenuation mechanism and stimate rate
      - Determine capacity and sustainability
      - Develop monitoring and contingency measures
      - Key points
        
        Primary attenuation pathway for many inorganic is transformation to less mobile forms through co precipitation or sorption
        
        REactions ares generally more complex and highly influenced by geochemical conditions
    - - Not promising in early protocols
      - Lots of research and field work in the following 5-10 years and we ended up with a completely different story
    - - MTBE exhibits similar characteristics to BTEX in terms of median plume size and attenuation rate
      - TBA also similar to BTEX but fewer are stable/shrinking
    - - Dioxiane
      - TCP
      - NDMA
      - Phthalates
      - Other problems
        
        Prevalence at individual sites is largely unkown
        
        Absence of well established tratment technologies
        
        Absence of tools for establishing MNA
    - - USEPA has detailed guidance for MNA of inorganics metals and rads
      - Example of how scientific knowledge advances: MNA of oxygenates
      - Lots of research on MNA for emerging contaminants: some contaminants look promising, others not so much
  - - - Need vadose zone gas monitoring points
      - Plot oxygen concentration vs depth
      - Get oxygen gradient
      - Multioly of effective diffusion coeficient
      - Gives NSZD rate
    - - In LNAPL world, some amazing research regarding LNAPL source zone attenuation
      - Methanogenesis, followed by ebullition and off-gassing followed by methane oxidation in unsaturated zone is very importantn, under appreciated processes
      - Three conventional methods to measure: gradietn, traps, dynamic closed chamber
      - Typical rates: 100 to 1000s gallons per acre per year
  - - - Key concept
        
        Measure heat generation to get NSZD rate
      - O2 Diffusion Down, CO2 Diffusion Up
      - Methane Oxidation
      - CH4, CO2 Outgassing
      - CH4 and Co2 ebullition. Anaerobic biodegradation of LNAPL
    - - Thermocouples on temperature monitoring "stick"
      - Installation of sick using direct push rig
      - Solar power supply and weatherproof box with data logger and wireless comunications sytem
    - - Biodegradtion of LNAPL generates heat
      - If we measure subsurface temperatures, we can get the rate of heat generation, and ultimately, the rate of biodegradation
      - Field deployment: Several thermocouples on NSZD " Stick" with datalogger and wireless comunication system
      - Thermal NSZD DAshboard: Web-based subscription that provides remote daily data downloads and continuous monitoring of NSZD rates
  - - - Are the risk acceptable?
      - Is the plume stable or shrinking?
      - Are conditions sustainable?
      - Is the remediation timeframe acceptable?
      - Are the cost benefits acceptable?
    - - Site must be in service area of public water system
      - Release must consist of "petroleum"
      - Release has been stopped
      - Free product removed to the extent practicable
      - Conceptual site model prepared and validated
      - Secondary source removaal has been addressed
      - MTBE testing requirement
    - - If site is Late Stage
        
        Different source process
        
        Mass discharge % from NAPL is low
        
        Matrix diffusion % is high
        
        Not "Princiapl threat waste"
      - Conceptual model
        
        No potential source migration
        
        Further source remediation difficult
        
        Not practicable to remove mass in low-perm zones
    - - Low risk means MNA the rest of the way
      - Recogniton that complete closure is difficult/ unattainable
      - Concentrations low
      - MAtrix diffusion
    - - MNA is likely to be a component of almost all remedies at some time during the site life cycle
      - Not a matter of if, but when MNA is applied