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Multi-Level Ground-Water Monitoring

Multi-Level Ground-Water Monitoring. Travis von Dessonneck. Multilevel Ground-Water Monitoring. Most important discovery in the past 40 years “…is that the distribution of dissolved contaminants in the subsurface is spatially complex, especially in the vertical dimension (Nielsen 808).”.

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Multi-Level Ground-Water Monitoring

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  1. Multi-Level Ground-Water Monitoring Travis von Dessonneck

  2. Multilevel Ground-Water Monitoring • Most important discovery in the past 40 years “…is that the distribution of dissolved contaminants in the subsurface is spatially complex, especially in the vertical dimension (Nielsen 808).”

  3. Multilevel Ground-Water Monitoring • This is due to several factors • Labyrinthine distribution of residual contamination in most NAPL source zones • Geologic heterogeneity • Weak mixing mechanisms in ground-water flow systems

  4. Multilevel Ground-Water Monitoring • Weaknesses of single-interval monitoring wells • Plume distortion • Composite samples mask true vertical distribution • Samples strongly biased by the position and length of the well screens

  5. Why Three-Dimensional Plume Delineation is Necessary • Site assessment • Predicting plume migration • Long screened wells tend to over estimate risk • Effective remediation • Especially with Permeable Reactive Barriers (PRB)

  6. One Time Sampling vs. Permanent Multilevel Monitoring Devices • One Time Sampling advantages • Generally faster • No installation, development • No permanent structures • No long term monitoring requirement

  7. One Time Sampling vs. Permanent Multilevel Monitoring Devices • One Time Sampling disadvantages • Whole story not told • No information on hydraulic head • Numerous one time samples to get contaminant vs. time • Becomes costly • Holes usually grouted • Not long term cost effective

  8. One Time Sampling vs. Permanent Multilevel Monitoring Devices • When to install? • Determining hydraulic head distribution is necessary • Changes in head over time • Monitor remediation practices • Time series samples

  9. Where You Monitor is as Important as How You Monitor

  10. Options for Ground-Water Monitoring • Multiple Diffusion Samplers installed inside single-interval monitoring wells • Installation of diffusion samplers over the screened interval of a well • Samplers consist of dialysis cells or polyethylene bags with DI water • the DI water is isolated from water in the wells • Contaminants diffuse through the bag or cell into the water within

  11. Options for Ground-Water Monitoring • The samplers must stay in the well long enough for the contaminant to reach equilibrium with the aquifer • Assume no vertical flow in the well • Assume that water flows unobstructed through the well

  12. Options for Ground-Water Monitoring • Diffusion Multilevel System • Same idea as above, but individual dialysis chambers are isolated to reduce vertical flow • Can detect: • Chloride • Nitrate • Sulfate • DO • Tetrachloroethylene • 1,1,1-trichloroethane • Organic and inorganic compounds

  13. Options for Ground-Water Monitoring • Active Collection of Samples from Multiple Depths within a Single-Interval well using grab samplers or depth-discrete pumping • Grab or Thief Samplers • Samplers lowered to desired depth and activated • May yield ambiguous results • Vertical flow in the well • Sampler may cause mixing • Increase turbidity • Time demanding

  14. Options for Ground-Water Monitoring • Collecting depth-discrete samples by pumping from different depth in well screens • Pumping creates vertical flow within the well • Only the first sample is good

  15. Options for Ground-Water Monitoring • Nested Wells (multiple tubes or casing in a single borehole) • Bundle Wells installed in collapsing sand formations • Allow formation to collapse around the wells • Usually sampled using peristaltic pumps • Tube diameters as small as 0.5 inches • Up to 20 different wells

  16. Bundle Wells installed in collapsing sand formations

  17. Bundle Wells installed in collapsing sand formations

  18. Options for Ground-Water Monitoring • Well Clusters • Can act as vertical conduit for contaminants

  19. Options for Ground-Water Monitoring • Dedicated Multilevel Ground-Water Monitoring Systems • Advantages • Facilitate the collection of samples and measurement of head from many more discrete depths • Only one pipe/tube per borehole • Total project costs significantly lowered • Less drilling • Less waste

  20. Options for Ground-Water Monitoring • Less time spent monitoring and sampling • Fewer wells for decommissioning • Little or no purging required • Less cost • Little water stored in the well, quicker reaction time to head changes • Smaller “footprint” on the ground

  21. Options for Ground-Water Monitoring • Disadvantages • Fewer options for sampling • Due to size of tubes • Some training required • May be more difficult to decommission the wells

  22. Options for Ground-Water Monitoring • Currently there are four commercially available systems • Westbay MP® System • Solinst Waterloo™ System • Solinst CMT™ System • Water FLUTe™ System

  23. Options for Ground-Water Monitoring

  24. Westbay MP® System • Two parts • Casing system • Portable probes and tools • Each monitoring zone is valved • Probes are lowered inside the casing to each monitoring zone • The probes locate and open the valve ports • Multiple probes can be used at the same time on different ports

  25. Westbay MP® System • Notebook accessible • No limitation on number of ports except space • Samples taken at formation pressure, no purge

  26. Westbay MP® System

  27. Westbay MP® System

  28. Solinst Waterloo™ System • Modular system • 2 in schedule 80 PVC • Each port has a 1 or 2 valved stem connected to: • An open tube that runs up to the surface • A double valve pump • A bladder pump • Pressure tansducer

  29. Solinst Waterloo™ System • Can be connected to data logger for continuous logging • Typically 3-8 monitors per well

  30. Solinst Waterloo™ System

  31. Solinst CMT™ System • Continuous Multichannel Tubing • 1.6 in OD flexible HDPE tubing • Up to 7 discrete zones • Ports are staggered around the tube • Channels are plugged a few inches below each port • Samples taken with peristaltic pumps, small diameter bailers, inertial lift pumps, or small diameter double-valve pumps

  32. Solinst CMT™ System

  33. Water FLUTe™ System • Flexible Liner Underground Technology • Flexible impermeable liner of polyurethane-coated nylon • More than 20 zones • Can monitor boreholes 2-20 inches in diameter • Intervals inserted at factory • 0.17 and 0.5 in OD tubing

  34. Water FLUTe™ System • Tubes have two valves on them to prevent flow back into the aquifer • Can be installed into nearly horizontal wells

  35. Water FLUTe™ System

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