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Remediation

Remediation. Topics Covered. Clean up standards Source Control Risk Assessment Natural Attenuation Pump and Treat Limitations to Pump and Treat Alternatives. Introduction. Contaminated soil and GW most prevalent problems at HW sites VOCs/metals most prevalent problem at NPL sites

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Remediation

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  1. Remediation

  2. Topics Covered • Clean up standards • Source Control • Risk Assessment • Natural Attenuation • Pump and Treat • Limitations to Pump and Treat • Alternatives

  3. Introduction • Contaminated soil and GW most prevalent problems at HW sites • VOCs/metals most prevalent problem at NPL sites • SVE most widely used innovative tech • NPL Status ~ 1100 on NPL • RCRA - 3000 sites $7.4-41.8 billion. primarily corrosive/ignitable wastes, HM, org solvents, oil

  4. General - Cont’d • UST - 161,000, 91% pet, 2% hazardous materials • DOD - 9300 potential petroleum, solvents, metals, pesticides, paints • DOE - 10,500 areas, VOCs and mixed wastes • 700 Other federal sites • 30,000 state sites

  5. Site Cleanup • Source Control • Source removal and disposal • Source containment • Institutional control • Groundwater/soils cleanup

  6. Groundwater Contaminant Cleanup • Physical containment • Hydraulic containment/treatment (pump and treat) pump to isolate contaminant zone • Required as long as source exists to meet cleanup standards

  7. Typical Standards - Numerical Cleanup Criteria • Meet requirements of existing laws, or • Protective of human health or ecological receptors, or • Background concentration, or • Analytical limits

  8. Fallacy of Numerical Clean up Criteria • Not the only way to protect (paving, capping, fencing) • treatment may reduce some contaminants but not all • May be over protective and too costly • May not be feasible

  9. Technical Impracticability • Study recognized that pump and treat cannot restore all sites • Recommendations • Categorize sites • increase incentive to use innovative technology • use experts to determine technical feasibility • charge fee at these sites to fund research

  10. Hydrogeology Contaminant Chemistry Mobile, Dissolved Strongly sorbed, dissolved LNAPL DNAPL Homogeneous, single layer 1 2 2-3 3 Homogeneous, multiple layers 1 2 2-3 3 Heterogeneous, single layer 2 3 3 4 Heterogeneous, multiple layers 2 3 3 4 Fractured Bedrock 3 3 4 4 Relative of Remediation

  11. Risk Based Corrective Action • ASTM standards for conducting risk based assessment for corrective action • Risk Assessment Primer

  12. Risk Assessment

  13. Topics Covered • Definitions • Risk Assessment Process • Uncertainty

  14. Definitions • Risk is the probability that a specific negative outcome will occur • Safety is the complement of risk, or the probability that an adverse effect will not occur

  15. Risk Values ActivityAnnual Risk Smoking 10 cigarettes/day 1 x 10-3 Motor vehicle accidents 2 x 10-4 Manufacturing work accident 8 x 10-5 Pedestrian hit by automobiles 4 x 10-5 Drinking two beers/day 4 x 10-5 Person in a room with a smoker 1 x 10-5 Peanut butter (4 teaspoons/d) 8 x 10-6 Drinking water with EPA limit of Trichloroethene 2 x 10-9

  16. Factors in Risk Acceptability • Voluntary vs. Nonvoluntary • Degree of control • Magnitude of the outcome • Awareness • Catastrophic Potential • Group involvement • Cost of alternatives

  17. Process

  18. Hazard Identification • Toxicity assessment determines whether exposure to a chemical, physical, or biological agent can cause an increase in the incidence of an adverse effect. • Necessary condition for a health or safety risk • Physical, metabolic, and chemical properties of the agent; • Potential routes of exposure; toxicological effects; results of animal studies; and site characteristics

  19. Dose-Response Assessment • Relationship between the level of exposure and the extent of injury • Carcinogenic and non-carcinogenic effects • Responses vary from death to tumors, skin irritation, respiratory effects, genetic mutation, and fetal development problems

  20. Dose-Response Curve

  21. Dose-Response Curve

  22. Noncarcinogenic Reference Dose Rfd: mg/kg-d

  23. Safety Factor • Intrahuman variations • Extrapolation from animals • subchronic to chronic • LOAEL to NOEL • Incomplete database

  24. Exposure Assessment • Calculates the dose which an exposed individual receives • Delineates the affected population by identifying possible exposure paths • Exposure routes • ingestion • inhalation • dermal absorption

  25. Dose Daily Dose (mg/kg-day) = (C)(I)(EF)(ED)(AF) (AT)(BW) C = Concentration, mass/volume I = Intake Rate, volume/time EF = Exposure Frequency, time/time ED = Exposure Duration, time A = Absorption Factor, unitless AT = Averaging Time, time BW = Body weight, mass

  26. Typical Exposure and Intake Rates for Risk Assessment

  27. Risk Characterization Risk = Toxicity x Exposure

  28. Risk Characterization • Probability of adverse incidence occurring under the conditions identified during the exposure assessment. • Carcinogens, • the daily dose is multiplied by the CSF • Risks are additive for multiple carcinogenic contaminants.

  29. Risk Characterization • Non-carcinogens, • Hazard index (HI) is calculated by dividing the daily dose by the RfD • Where more than one contaminant is present a hazard quotient (HQ) is determined by summing all of the HIs • A HI over one indicated an unacceptable risk

  30. Risk Management • Regulatory action • Decision to mitigate risk • Action level

  31. Uncertainty • The risk assessment process is extremely conservative in nature and utilizes measurements which are uncertain. • insufficient data or information gaps often exist in characterizing the potential risk of an agent, necessitating the need for assumptions or educated guesses.

  32. Uncertainty • Use computational tools from the field of decision analysis to account for the uncertainties in the process • These tools allow risk to be expressed as a probability distribution rather than a single number which can then be used to make a more informed decision during risk management

  33. Natural Attenuation • Process whereby concentration and areal extent of contaminant plume is maintained or reduced over time by natural processes • Monitoring only • No physical encouragement of process • Usually petroleum hydrocarbons (Oregon permitted PCP to be naturally attenuated)

  34. NA Considerations • Is the plume increasing, decreasing, or stable? • Has the source been removed? • Is there free product? • Will the plume affect off site properties? • How long will the plume persist? • Receptors? • What mechanism(s) are controlling plume?

  35. Mechanisms • Biological processes • Dispersion/dilution • Sorption • Volatilization • Chemical transformation

  36. NA Verification • Plume characterization (delineation) • Mass declines over time • decreasing concentration over time • Plume stable or decreasing with time • Plume movement slower than predicted

  37. NA Verification • Geochemical changes • Laboratory microcosms • GW modeling • Breakdown products • Loss of electron donors/receptors

  38. NA of Chlorinated Solvent Plumes - Anaerobic systems • Due to biodegradation of anthropogenic organic carbon • drives reductive dechlorination • strongly reducing conditions • H2 > 5 nanomolar • Rapid and extensive dechlorination of PCE, TCE, TCA, and CT

  39. NA of Chlorinated Solvent Plumes - Anaerobic Systems • Anaerobic conditions result from naturally occurring organic carbon • Coastal or stream/river deposits, shallow aquifers (swamps), natural oil seeps

  40. NA of Chlorinated Solvent Plumes - Aerobic Systems • Well oxygenated, little organic carbon • no degradation of PCE, TCE; only VC and DCE • advection, dispersion , and sorption

  41. NA of Chlorinated Solvent Plumes - Mixed Environments • Favors NA • Sequential anoxic-oxic conditions beneficial for complete degradation of chlorinated solvents

  42. Pump and Treat System • Location of plume and/or NAPL • Design of capture system

  43. Design of P/T System • mass reduction occurs when extraction and injection wells positioned in most concentrated portion • minimize distance that contaminant plume pulled to extraction well • design to produce convergent flow toward central extraction location • minimize divergent flow along periphery

  44. Pump and Treat Systems • Installation of wells/monitoring points • Pumping to contain/remove contaminant • Treatment of extracted water • Recharge to subsurface, treatment facility, or surface water

  45. Appropriate Site Characteristics • high hydraulic conductivity • adequate possible flow rates to create sufficient capture zone • mobile contaminant

  46. Inappropriate Sites • heterogeneous aquifer • low hydraulic conductivity • sorbed or precipitated contaminant, slowly desorbing, dissolving • immobile NAPLs contributing to miscible plume (residual saturation in aquifer)

  47. Limitations • The need to reach drinking water standards (ppb at times) exacerbates physical problems • Asymptotic behavior Flushing from large pores Interrupted pumping, additional desorption Concentration Flushing from smaller pores Drinking Water Standard Time

  48. Limitation - Cont’d • Sorbed compounds • Kinetic limits to desorption • Effects of geologic complexity • immobile water zones • Effects of fugitive NAPL • Design failure to contain plume • Operational failures

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