Session J. Investigation and monitoring of Soil and Groundwater

Transcription

1 Session J Investigation and monitoring of Soil and Groundwater Part II Chair: Patrick van Hees Associate Professor, Eurofins, Sweden High Resolution Site Characterization and 3D Geological Modelling Tools for Interpretation of Plume Migration in a Complex Geology Bo Tegner Bay M.Sc., COWI, Denmark Development of an innovative methodology for monitoring of in situ remediation of chlorinated solvents the MIRACHL-project Haakan Rosqvist Ph.D., Lund University and Tyréns, Sweden Use of geostatistical modelling in investigation of soil contamination working toward a better definition of remedial mass and volume Per Loll R&D Manager, Ph.D., DMR, Denmark Do we as practitioners have a general challenge with leaking wells causing crosscontamination to deeper aquifers? Swedish and Danish results and paths forward Maria Heisterberg Hansen, Project Manager NIRAS, Denmark Filip Nilsson, Environmental Consultant, NIRAS, Sweden

2 Do we as practitioners have a general challenge with leaking wells causing cross-contamination to deeper aquifers? Swedish and Danish results and paths forward NORDROCS Filip Nilsson Maria Heisterberg Hansen

3 Background What is a leaking well Leaks are caused by: Missing or improper sealing Joint of well casings that are not tight Leaking wells causes: Wrong conclusions and risk assessments Challenges with installation and behavior of sealing Some contaminants dissolve the sealing Example of channels within bentonite sealing 2

4 Why is this important There is a risk of making wrong conclusions and the risk of spreading contamination We risk a false positive result Contamination of samples caused by well construction We introduce a contamination to uncontaminated aquifers Consequences Waste of money for further investigations and / or unnecessary remediation Possible risk for nature end people 3

5 Why is this important There is a risk of making wrong conclusions and the risk of ignoring contamination We risk a false negative result Contamination diluted by clean water leaking in through the well construction Contamination ignored Consequence Risk for nature end people 4

6 Leaking wells do exist When we look for leaks we find leaks Joint 14 meters below surface Precipitation drips from water seeping in through joint Broken casing 6 meters below surface Contaminated groundwater dripping into casing and continues to screen in primary aquifer 5

7 Leaking wells do exist.and it is not only a problem from the past! When we look for leaks we find leaks Leakage out of joints in liter per day at 1 meter water column JC Video from well in Sweden Droplets of DNAPL leaking through untight joint at top of screen 8,7 meters below surface 6 L Experiment with joints from deep well in Denmark. Between 100 and liter water per day leaking out of joints per day Use O-rings with your PEHD joints

8 Recognizing a leaking well Be sceptic to your results - water samples taken over time or during pumping Remarkable increase in concentrations after 3 years in deepest screen This well was later proven leaking Tracer added to screen 2 was found in screen 1 PCE TOC 2012: 3,5 9,9 2015/16: Remarkable drop in concentrations when pumping in deepest screen This well was later proven leaking Tracer added to screen 3 was found in screen 1 7

9 Video-inspection Pumping test Geophysical borehole logs Video-inspection Easy and available tools Packer test Methods used to recognize a leaking well Packer test 8 Pumping test Tracer test Tracer tests

10 Tracer test used to prove a leak in well construction Contamination in deep screen was a false positive caused by well construction What we did to test 2 different tracers were added to shallow screens (2&3) Passive samplers installed in water column of deep screen (1) Monitoring Background & 3 x in the following 9

11 Tracer test used to prove a leak in well construction Contamination in deep screen was a false positive caused by well construction Questions we wanted to answer Was there a leak from shallow aquifer to deep aquifer? A AB B How would results look if the leak was caused by: (A) untight joint (B) improper sealing B 10

12 Tracer test used to prove a leak in well construction We avoided to drill deep wells and thereby avoided to spend > DKK or more Results of chlorinated compounds in screen 1 Results of tracer in screen 1 Results showed clearly Untight joint causing shallow groundwater to enter deep aquifer Tracer entering through untight joint Tracer & PCE diluted in deep screen uncontaminated groundwater passes horizontally through the screen 11

13 What can consultants do now? Consider the need for drilling and analyze the situation Use the precautionary principles - Make a risk analysis regarding the need to drill in heavily contaminated areas Always use sealing materials in full depth when installing wells Consider to abandon and seal the well compliantly if it was unintended located in a hot-spot Choose sealing material according the location - Avoid bentonite pellets in unsaturated zone - We will gain more knowledge in the near future about this 12 Danish study is carried out (Initiated by COWI, GEO, NIRAS, ORBICON Sponsored by Regions, Miljøstyrelsen, ATV, AVJ, TUP)

14 What can consultants do now? Avoid making new leaking wells Avoid more than one screen per well Right method of applying the sealing materials Be aware of pipe materials and if joints with O-rings can be used Don t leave wells at location for longer time than needed Make right demands on the drilling-entrepreneur methods and materials to use and how to document the installation procedure Monitor amount of sealing material used 13

15 An available method to seal a drilling You don t have to wait 14 A liquid sealant product based on mixture of cement and bentonite is pumped in a hose from the plastic tank to the bottom of the drilling through the casing This is an alternative to bentonite pellets it can be used already today The method has a much better chance to fill out all available spaces and make a proof sealing

16 Wish list forward We as practitioners wish to have guidelines Improvements of well-installation material and methods Guidelines (e.g. from Swedish Geotechnical Society) Authorities who requires that best available materials and practice is used We don t wish to risk introducing more contamination when we work to investigate and reduce contamination 15

17 Thanks for listening! Please find us to discuss it further in the future! Thanks to: Peter Tyge (Geologist, NIRAS DK) Anders G. Christensen (Ekspertice Director, NIRAS DK) Susanne Rinette Pedersen, (Project manager, Region Zealand) Helle Overgaard (Civ. Ing., Capital Region of Denmark) Ulf Winnberg, (Project manager, Geological Survey of Sweden) 16

18 Møllevej 9, NivåModelling A Tool for 3D Geological Interpretation of Plume Migration in a Complex Geology Bo Tegner Bay, Kirsten Rügge, COWI Peder Johansen and Helle Overgaard, Capital Region of Denmark 1 MØLLEVEJ

19 Take home message

20 Background Location (Møllevej) in northern part of Sealand, Denmark

21 Background Drinking water abstraction wells Øresund 400 m 4

22 Background Large factory producing metal devices for gas containers Intensive usage of TCE in the period 1957 to 2000 Two main hot spot areas: Northern: Discharge of condensate from TCE facility Southern: Storage and handling of TCE Northern hot spot Southern hot spot

23 Geological model Secondary groundwater Primary groundwater

24 Simulated plume migration model Drinking water abstraction wells Upper groundwater Deeper groundwater

25 Distribution of groundwater contamination (unit: µg/l) Spreading of contamination in upper groundwater Unexplained flow direction Challenges in locating the plume Potentiel new undiscovered hot spots? High levels of TCE in the plume (> µg/l) 18 m BGS?

26 Possible pathway of plume migration Extensive data Comprehensive 3D model Helped understanding changing flow direction Helped plan further investigations Importance of high quality fieldobservations

27 Mapping of the plume by multilevel filters Complex flow of the plume Small permeable layers Large amount of deep boreholes Multilevel filters (7 filters) 10

28 Mapping of the plume by multilevel filters µg/l µg/l µg/l 50 µg/l

29 2D model (Section following the flow path of the plume) Southern hot spot Clay Sand S1 L1 Clay Sand S2 L2 Clay Sand L3 Clay Sand S3 S4 L4 L5 Limestone Kalk

30 2D model (Section following the flow path of the plume) Southern hot spot Clay Sand S1 L1 Clay Sand S2 L2 Clay Sand L3 Clay Sand S3 S4 L4 L5 Limestone Kalk

31 3D model 14

32 Distribution of chlorinated solvents in groundwater Southern hot spot Limestone

33 Distribution of chlorinated solvents in groundwater (possible situation without 3D modelling) "What if" situation Clear hot spot Plume is contained and welldefined 16

34 Distribution of chlorinated solvents in groundwater (situation with 3D modelling) The actual situation (as we see it) 3D model made it possible to get an essentiel geological understanding of the area. Answers some very important challenges regarding possible pathways of the plume. Helped planning future investigations. Without the model there was a risk that the plume was never found. A plume that may represent a risk towards the drinking water. 17

35 Situation now

36 Conclusion In sites with a high degree of complexity in geology 2D Geological Modelling not suffient to understand complex site-geology 3D Geological Modelling essentiel for the comprehension of the extent and flow pattern of the contamination visualized the answers to our frustrations Challenges with plume migration in complex geology enough data to stop the investigations or to continue to be honest it sometimes feels like finding Wally