Realistic Goals for Thermal: Regulatory Limits and Achievable Concentrations. Eva Davis, Ph.D. Hydrologist, Kerr Lab

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1 Realistic Goals for Thermal: Regulatory Limits and Achievable Concentrations Eva Davis, Ph.D. Hydrologist, Kerr Lab Office of Research and Development National Risk Management Research Laboratory January 8, 2013

2 Superfund Program Goal The Superfund program remains committed to restoring groundwater to beneficial reuse consistent with CERCLA and the NCP... In light of the continuing scientific advances in groundwater remediation technologies which continue to evolve, regions should not be limited by previouslyapproved TI waivers... as justification for what may be appropriate when evaluating and documenting current or future TI waivers. 2 EPA, Summary of Technical Impracticability Waivers at National Priorities List Sites, August 2012

3 TI Waiver Statistics As of Dec 2012, NPL consists of 1313 sites, 54 proposed 91 sites with TI waivers listed in the 2012 summary 47 of those have NAPL ~ 2 sites/year obtain TI waivers 2 sites with TI waivers are proceeding towards the implementation of thermal remediation 3

4 Why Emphasize Realistic Goals? 4 Theoretically and thermodynamically speaking, with a robust system and enough energy input, can meet as stringent a goal as desired However, Cost/lb of contaminant recovered in terms of $$ and Life Cycle Costs likely to increase substantially as the amount of contaminants remaining in the ground decreases

5 Distinction between Remedial Goals and Final or Ultimate Goal for Some Sites Assumption that further remediation of some type will occur after the thermal remediation Appropriate for VOCs, below the water table or for those that are subject to natural attenuation Not as appropriate for recalcitrant contaminants 5

6 Recalcitrant Contaminants Creosote Ahlambra Coal Tar North Adams PCBs Missouri Electric Works Mare Island When above the water table, and high temperatures are reached, low residual concentrations (ppb range) are achievable, even in tight formations 6

7 Why are Realistic Remedial Goals Important? Influences choice of technologies at Feasibility Study stage Influences plume lifespan after remediation Influences answer to, When are we done? Goals that are too stringent increase energy consumption, costs Goals that are too lenient fail to get the full benefit of what thermal remediation can achieve 7

8 What Factors Determine what is Realistic for a given Site? Contaminant composition 8 Boiling point, coboiling point Stratigraphy Affects thermal technology choice Hydrogeology Water influx determines whether treatment temperature can be met

9 Co boiling lowers the boiling temperature When NAPL and water are present PCE Water Combined 1000 Vapor Pressure, mm Hg Temperature, C Co-boiling temperature 83 C

10 Co boiling temperatures for VOCs Chemical Boiling Pt. (ºC) CoBoiling Point (ºC) 1,2-Dichloropropane Tetrachloroethene Benzene Trichloroethylene Toluene Naththalene o-xylene m-xylene p-xylene VOC contaminants with boiling points less then 150 C, when present with water, will boil at temperatures less than 100 C Chlorobenzene Carbon Tetrachloride ,1,2-Trichloroethane ,1,2,2- Tetrachloroethane

11 Visalia Pole Yard Steam Remediation Injection well Extraction well Injection well Steam zone Shallow aquifer Water table Steam zone Intermediate aquifer Intermediate aquitard Deep aquifer 11a

12 Visalia Pole Yard Steam Remediation Injection well Extraction well Injection well Steam zone Shallow aquifer Water table Steam zone Intermediate aquifer Intermediate aquitard Deep aquifer 11b

13 Visalia Pole Yard Steam Remediation Injection well Extraction well Injection well Steam zone Shallow aquifer Water table Steam zone Intermediate aquifer Intermediate aquitard Deep aquifer 11c

14 Visalia Pole Yard Steam Remediation Injection well Extraction well Injection well Steam zone Shallow aquifer Water table Steam zone Intermediate aquifer Intermediate aquitard Deep aquifer 11d

15 12 Free product recovered at Visalia was an oil in water emulsion; this was a key aspect of DNAPL recovery.

16 13 Affects of Water Influx Arnold AFB Western Zone

17 Significant amount of Data available from Field Implementation of Thermal Remediation When determining what was achieved, must evaluate overall system to determine if that site represents what can be accomplished Was all of the NAPL contaminated area treated? What were the objectives? 14

18 Approaches to setting Remedial Goals NAPL removal: Based on soil concentrations or absence of NAPL in wells Percent reduction: Soil and/or ground water concentrations Mass removal: to the extent practicable Diminishing returns Regulatory driven: MCLs, soil concentrations protective of ground water, residential land use 15

19 Remedial Goal: NAPL removal For many VOC sites, very achievable Achieved by reaching the coboiling temperature everywhere in the vadose zone Exceed coboiling temperature everywhere below the water table 16

20 Thermodynamics of Coboiling Degrees, C Heating Time When 2 immiscible liquids are at their co-boiling temperature, the input of additional energy will cause boiling (ie, vaporization) When NAPL gone, temperature increases 17

21 NAPL Removal Goal Remaining adsorbed and dissolved phase exceeds MCLs by orders of magnitude Ground water concentrations higher than baseline concentrations Sets bar too low should expect to accomplish more 18

22 Remedial Goal: % Reduction in Concentration How stringent depends on what % Reduction is specified Complicated by heterogeneity of contaminant distribution in soils Complicated by variability in ground water concentrations over time 19

23 PCE in Ground Water during ERH Arkla Terra Site PCE, ug/l X01 X02 X03 X04 X05 X06 X07 X08 11/7/ /12/ /17/ /22/ /27/ /2/ /7/ /12/ /17/ /22/ /27/2012 1/1/

24 Remedial Goal: Diminishing Returns May also be considered removing mass to the extent practicable Based on premise that $/lb contaminant removed increases as the amount remaining in the subsurface decreases Often relies on follow on technology (P&T, MNA) to reach ultimate goal When are we done? is subjective 21

25 Contaminant Recovery vs Time Arkla Terra kg PCE Days of Heating 22

26 Remedial Goal: MCLs Ground water based ground water concentrations can vary widely during thermal remediation For common VOCs, very small numbers Recovery rate may decrease significantly before these numbers are reached due to slow desorption from solids May be hampered by higher concentrations outside of the treatment area 23

27 My normal recommendation for a Remedial Goal: Diminishing Returns Monitor ground water to document increase and then decrease in concentrations Monitor removal rate, look for low removal rates Followed by P&T or MNA Can lead to rapid approach to regulatory standards 24

28 CVOC Recovery vs Time Ft Lewis Area 1

29 Ground Water Concentration vs Time Ft Lewis Area 1 Interior Shallow Wells Total CVOC Concentration (ug/l) MWE07A1 MWF03A1 MWF14A1 MWH06A1 MWI08A1 MWJ04A1 MWJ10A1 MWL07A1 MWL10A1 Begin Thermal End Thermal 26

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34 Sites where MCLs (or close to that) have been achieved Visalia Pole Yard Young Rainy STAR Area A Ft Lewis NAPL Areas 1 & 2 Pemaco Groveland Wells ICN Pharmaceuticals Alameda 31

35 Sites where stringent soil concentrations have been achieved Camelot Cleaners Dunn Field Arnold AFB East Treatment Area Urbana Site 32

36 What about a Mass Flux Goal? May be attractive when overall goal is to attenuate the plume within a given time frame If mass flux can be accurately measured If plume lifespan can be accurately predicted based on mass flux Not practical as a remedial goal for thermal remediation 33

37 Can Realistic Expectations be Determined from a Pilot Scale? Hasn t happened at many pilot scale systems Conducted in the middle of a contaminated area thus recontamination happens Conducted for too short of a time frame $$ limitations Time limitations 34