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Multi-Level Ground-Water Monitoring Travis von Dessonneck.

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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 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 Multilevel Ground-Water Monitoring

4 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


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



25 Options for Ground-Water Monitoring

26 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

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

28 Westbay MP ® System


30 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

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

32 Solinst Waterloo™ System

33 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

34 Solinst CMT™ System

35 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

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

37 Water FLUTe™ System

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