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Steam-Air-Injection: In-Situ-Remediation of a CHC Contamination below a historical Building Oliver Trötschler, Hans-Peter Koschitzky Universität Stuttgart, VEGAS Pfaffenwaldring 61 D-70550 Stuttgart (Germany) http://www.vegasinfo.de A contaminant source of chlorinated hydrocarbons (CHC, mainly PCE) under an old historical building caused by a former dry-cleaner in the unsaturated and saturated zone leads to a long persistant contaminant plume. The groundwater level is in the range of 3 - 3.5 m b.g.s.. Situation 1.5 m: replenishments 2.5 m: sandy soil with fine silt layers (k f < 1 x 10 -5 m/s) 4 m: fine silty sand (k f ~ 5 x 10 -5 m/s) 7 m: fine and medium sand (k f ~ 0.8 - 3 x 10 -4 m/s) 8 m: medium sand with gravel (k f ~ 0.5 - 2 x 10 -3 m/s) 10 m: gravel (k f ~ 3 - 8 x 10 -3 m/s) Numerical Simulation Steps of the pilot injection: (1) One week groundwater and soil-vapour extraction to achieve constant conditions; PCE extraction: 70 kg (2) One week Air-Sparging: injection of approx. 20 m³/h air through the injection well; PCE extraction: 33 kg (3) Four weeks injection of a steam-air mixture (105 - 110°C), decreasing rates from 200 to 120 kg/h; PCE extraction: 200 kg (4) Six weeks cooling phase: starting with one week of air sparging accompanied by soil-vapour and groundwater extraction; PCE extraction: 135 kg. Total extraction of more than 440 kg PCE confirmed the efficiency of the steam air injection at the location Contact: Hans-Peter Koschitzky, Oliver Trötschler [email protected] [email protected] Principle of Remediation Technology and local situation Full Scale Remediation Design vertical expansion of the contamination approx. 6 - 7 m b.g.s. unsaturatted zone: concentrations of PCE in the soil samples up to 3800 mg/kg soil (1 - 2.5 m b.g.s) saturated zone (3-4 m b.g.s.), concen- trations up to 850 mg/kg, as well as 70 mg/kg (4-5 m), and 6 mg/kg (5-6 m) CHC concentration up to 40 - 60 mg/l of CHC in the groundwater indicate residual NAPL in the near field of the sampling location (source zone). Results -800 -700 -600 -500 -400 -300 -200 -100 -400 -300 -200 -100 0 100 -300 -200 -100 0 I6 BR38 E8 EK2 24 h -800 -700 -600 -500 -400 -300 -200 -100 -400 -300 -200 -100 0 100 -300 -200 -100 0 I6 BR38 E8 EK2 168 h -800 -700 -600 -500 -400 -300 -200 -100 -400 -300 -200 -100 0 100 -300 -200 -100 0 I6 BR38 E8 EK2 552 h -800 -700 -600 -500 -400 -300 -200 -100 -400 -300 -200 -100 0 100 -300 -200 -100 0 I6 BR38 E8 EK2 48 h 2 d 21 d 7 d 1 d Partners and Acknowledgement Pilot - Test t = 6 h t = 12 h t = 24 h t = 36 h 36 h) -10 -9 -8 -7 -6 -5 -4 -3 273 283 293 303 313 323 333 343 353 363 373 383 T [K] z [m] uGOK TC 7 (0,1 m) TC 1 (0,5 m) TC 3 (2,05 m) TC 5 (2,9 m) TC 7 mess TC 1 mess TC 3 mess TC 5 mess 36 h) -10 -9 -8 -7 -6 -5 -4 -3 273 283 293 303 313 323 333 343 353 363 373 383 T [K] z [m] uGOK TC 7 (0,1 m) TC 2 (0,9 m) TC 4 (1,55 m) TC 6 (4,25 m) TC 7 mess TC 2 mess TC 4 mess TC 6 mess 0,9 1,55 4,33 0 ,5 2, 05 3, 01 0 1 m 2 m 3 m 4 m 5 m 1,27 2 , 9 1 4,24 0,11 7 ,0 8 Source zone A mixture of steam-air is injected into the contaminated zones to evaporate organic contaminants by active convective heating of the soil to steam-air temp- erature. The contaminants are carried by the amount of hot air towards the soil- vapour extraction wells. The extracted soil-vapour is treated conventionally on- site. TSVE can be applied for organic contaminants with boiling points lower than 180°C and aquifers of medium permeability, e.g. sands and silty sands. In case of a DNAPL contamination the risk of a downward migration due to the accumulation of the organic phase in front of the steam front has to be prevented. Therefore, steam-air injection is advised. The injected air functions as an inert gas to transport the evaporated organic phase to prevent accumulation, the steam serves as the energy-transfer medium. On behalf of the environmental agency of the city of Karlsruhe, a pilot remediation test was carried out using one injection well for the steam-air mixture with parallel soil- vapour and groundwater extraction. The pilot was accompanied by the numerical simulation of the steam propagation. The goal was to determine the range of the steam propagation in the saturated zone, as well as to verify the site-specific applicability and efficiency of the remediation technology in order to design the full scale application. steam extension radius > 3 m within some days (200 kg/h steam-air) steam zone extension maintained with an injection of 120 kg/h - 140 kg/h to heat up highly contaminated silt layer by conduction (steam override), fast heat propagation during the first two days in the medium permeable sand layers below 5 m (temperatures between 80 and 100°C), after approximately 20 days, the subsurface between 2 - 7 m bgs. was effectively heated (> 90°C) with 3 m radius, most of the pollutants were evaporized and extracted (> 99,5 % mass removal due to soil sampling) The accompanying numerical simulation for the determination „of the thermal radius“ as a basis for the design of the full scale remediation (distance of injection wells, determination of the mass flows) requires a detailed investigation of the subsurface (vertical distribution of k f -values). The anisotropy of the layered aquifer plays a significant role in steam propagation. The pilot application was funded by the environmental agency of Karlsruhe. The consultant dplan, Karlsruhe was responsible project director and controller. Based on the results of the pilot the full scale remediation was designed, the time frame (less than 1 year) and the costs (515 k€, ~ 300 € p. m³ soil) were estimated. Declined and horizontal drilling is required to install injection and extraction wells due to local situation (historical building). On-Site Treatment Installation Historical building “source zone” Scheme of TSVE (Thermally Enhanced Soil Vapour Extraction) in Karlsruhe Top view of test field Sketch of test field I6: steam injection well E8: SVE wells EK2, Br38: SVE and GW wells T1 – T8: in-situ temperature measurement Numerical simulation of steam propagation (S. Ochs, IWS, Universität Stuttgart) Comparison of temperature distribution: simulation and field measurements (S. Ochs, IWS, Universität Stuttgart) The numerical simulation almost matches perfectly the field data for an anisotropy (k h /k v ) of 3. For distances larger than 3 m the simulation underestimates the steam propagation. This may be addressed to inhomogeneities of the subsurface or a lower permeable soil compared to the simulation. Steam propagation in the target zone 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 concentration PCE (g/m³) SVE 0 50 100 150 200 250 300 350 400 450 500 sum PCE [kg] PCE (g/m³) Summe LCKW (g/m³), dplan Summenkurve PCE (kg) Summenkurve LCKW (kg), dplan Air Sparging steam-air injection (17 kg/h air) 180 kg/h cooling phase 120 kg/h steam 100 kg/h steam air (25 kg/h) Air Sparging SVE Mass balance based on SVE 1 2 3 4 (GW-Infiltration) wells: SI: Injection well: declined drilling, 2", 8 m bgs. E: Extraction well: vertical drilling, 4", 5 m bgs. EK: combined well (SVE + GW) vertical drilling, 4", 10 m bgs. horizontal well SVE-Hor, 2.8 - 3 m bgs. temperature measurement lances: Pt100 by vertical and declined drilling: appr. 72 pcs. PT-SVE in wells annulus: appr. 50 pcs. 0 1 m 2 m 3 m 4 m 5 m The site is to be divided into 4 areas to be remediated stepwise by the injection of 350 kg/h steam-air. Groundwater is extracted with 2 m³/h and after treat- ment infiltrated upstream the source zone. In total 300 m³/h of soil vapour are to be extracted. designed full scale remediation
