Can CMT wells be used for soil gas sampling?
Yes. Special fittings are available to collect soil gas samples from all channels of the CMT tubing. Contact us for details.
What kind of hydraulic tests can I perform in CMT wells?
CMT wells make ideal multilevel observation wells during groundwater pumping tests. Hydraulic tests have also been performed in the wells themselves. Most tests performed in CMT wells performed to date have been slug tests where compressed air is used to depress the water level in the test zone. The compressed air is suddenly released, and the recovery of the interval is monitored by measuring the rising water level over time. Small diameter transducers greatly simplify monitoring of the water level recovery, especially in coarse-grained formations that recover quickly. A good source of information pertaining to hydraulic testing in small-diameter wells can be found at the University of Kansas website: http://www.geo.ku.edu
Why is the System not available in Teflon®?
We explored the idea of making CMT tubing out of Teflon but rejected it for a couple of reasons. First, Teflon is a difficult polymer to work with and it is not possible to extrude Teflon in the shape of the current CMT system. Second, Teflon is very expensive, which would drive the cost of the CMT system up by as much as ten-fold. Finally, Teflon isn't immune to sampling biases; hydrophobic VOCs can diffuse through the walls of Teflon tubing just as they can through the walls of polyethylene tubing.
Are groundwater samples collected from CMT wells as good as samples collected from 2-inch or 4-inch conventional monitoring wells?
Groundwater samples from CMT wells are not only as good as samples collected from traditional monitoring wells, they are usually better! Most importantly, samples from CMT wells are discrete samples from the aquifer, not composite samples typical of long-screened conventional monitoring wells. Consequently, if the concentration of a contaminant in a sample collected from a particular CMT channel is low, you can be confident that the concentration in the aquifer at that depth is indeed low, rather than being low because of dilution as may be the case with a conventional monitoring well. Additional discussion of the sampling biases associated with conventional monitoring wells and the technical advantages of multilevel groundwater monitoring is presented in our Papers Section. In addition, water samples collected from CMT wells are often less turbid than samples collected from conventional monitoring wells. The screen slot size and sand pack of a conventional monitoring well is often a compromise owing to the wide range of grain sizes present within the screened interval of most wells. The well screens and sand pack may be too small for the coarser fraction, but too large for the fine-grained layers within the screened zone. This leads to high levels of turbidity in the water samples since the fine-grained sediments are not effectively filtered by the well screens and sand pack. CMT wells, on the other hand, typically monitor short, discrete intervals in an aquifer. The well screen and sand pack in each monitored zone can be optimized for the grain size of the sediments within each interval. Each intake port in a CMT well can have a different well screen and sand pack size depending on the lithology of the aquifer materials in each monitored zone. This flexibility in well construction optimizes the filtration characteristics of the CMT well, resulting in clear, turbidity-free water samples. CMT wells have other advantages over conventional monitoring wells. First, the purge volume of CMT wells is very small. That means that there is less contaminated water requiring treatment or disposal during routine sampling. Take the case of a 4-zone CMT well that has ports at depths of 20, 40, 60, and 80 feet. Assuming that the static water level is 10 feet below the ground surface, the volume of water required to purge two times the "casing volume" of the four channels would be about 7 liters or less than 2 gallons! Second, CMT wells detect changes in piezometric pressure more accurately than traditional monitoring wells. Two- or 4-inch-diameter monitoring wells store a lot of water compared to the individual channels in a CMT well. The large amount of water stored in a conventional monitoring well means that the well will be slow to respond to changes in piezometric pressure in the aquifer. This is especially true in low-yield formations, where weeks and even months may be required to fill the well casings to the static water level. CMT wells, on the other hand, respond and equilibrate quickly because of the low volume of the various channels.
How are CMT wells different than "nested wells"?
CMT wells are indeed very different than "nested wells". In fact, the CMT System was designed in part because of the problems inherent with nested wells. Nested wells are multilevel wells that have multiple casings in a single borehole. That type of well construction was popular in the 1970s and early 1980s. However, the use of nested wells is strongly discouraged by US EPA and other regulatory agencies because of the many documented cases where poor seals between the casings led to cross-connection of the various monitored zones.
Most boreholes are not perfectly straight or plumb, and the casings inevitably end up lying against each other in some portions of the borehole. Bentonite pellets and/or cement grouts may not completely fill in the spaces between the casings, resulting in void spaces that allow cross-communication between the different monitoring zones. In areas where nested wells are still allowed, there are usually requirements that spacers be used to keep the various casings apart in the borehole. There is usually also a requirement that 2-inch annular seals be installed between each of the individual well casings. This requirement results in boreholes that must be 12 inches in diameter or larger. The increased cost of the larger boreholes quickly makes nested wells less attractive than clusters of individual wells, especially when the uncertainty of the annular seals is factored in. With the CMT System, the various monitoring channels are inside the CMT tubing. Thus, there is only one, smooth-walled tube within the borehole. The tubing is centered inside the borehole using Solinst's low-profile centralizers, and 2-inch-thick annular seals can be installed easily and reliably in a single borehole as small as 5.6 inches in diameter.
Do CMT wells comply with state and county well construction standards?
Well construction standards vary from region to region, but CMT wells should be in full compliance with well construction standards in most areas. Many states and counties require a 2 inch annular seal between the well casing and borehole wall. That is easily achieved with CMT wells. Given the relatively small diameter of the system (1.6 inches), the requirement for a 2 inch seal is met by installing the system in a borehole that is 5.6 inches in diameter or larger. Low-profile centralizers ensure that CMT wells are centered in the borehole and that the sealing material fills the space surrounding the CMT tubing evenly.
Are CMT wells accepted by regulators? How do I convince my regulator that the System yields reliable data?
Based on what we hear, an emphatic YES! However, the system is still new to many people, including many State and local regulators. Once they are introduced to the system, though, most regulators whole-heartedly support the use of CMT wells. They look forward to the better plume definition afforded with multi-level monitoring, especially compared to the composite samples from long-screened monitoring wells that they have had to settle for in the past. A common concern expressed by the regulatory community is the integrity of the borehole annular seals that prevent vertical movement of groundwater between different zones. This is one of the key advantages of the CMT System. Unlike nested wells where several casings are placed in a single borehole, there is only one casing - or more accurately, one tube - in the borehole with the CMT System. This simplifies the installation and improves the reliability of annular seals installed between the various monitored zones. Another concern expressed by some regulators is the quality of the groundwater samples collected from CMT wells. Until recently, the only way to sample CMT wells was with a Peristaltic Pump or Mini Inertial Pump. Now Solinst has a Micro Double Valve Pump and sample integrity is no longer an issue. Several government and university studies show that pneumatic pumps like the Micro Double Valve pump yield very high quality groundwater samples. The best way to inform your regulator of the advantages of multilevel monitoring using the CMT System is to direct them to the recently published paper on the CMT System authored by its inventors, Murray Einarson and John Cherry. That paper (Einarson and Cherry, GWMR Fall 2002) can be downloaded from our website.
What papers or guidance documents have been published that describe the CMT System?
Several papers describing the CMT multilevel monitoring system have been published and more are being published all the time. The most complete description of the CMT system is contained in a technical paper published in the fall 2002 issue of Ground Water Monitoring and Remediation (Einarson and Cherry, 2002). Note, however, that several improvements to the system have been made since that paper was written. The CMT system is also described in the American Petroleum Institute's 2000 guidance document titled "Strategies for Characterizing Sites with Releases of MTBE and other Fuel Oxygenates." These documents and others can be downloaded from the Papers section of our website.
Why is the CMT System less expensive than other multilevel systems?
There are a couple of reasons for this. First, the tubing is made of high-density polyethylene (HDPE), which is an inexpensive material that is commonly used for environmental sampling. Second, there are no joints in the tubing; the tubing is continuous from the ground surface to the bottom of the borehole. Joints increase the cost of monitoring wells because they require sophisticated design and careful machining to maintain tensile strength and prevent leakage.
Does the Waterloo Multilevel System have any advantages over the CMT System?
Yes, the Waterloo System is more suitable for deeper applications, applications that require special materials, such as stainless steel or Teflon and for applications which require dedicated pumps and pressure transducers in up to 8 zones.
Why is the CMT tubing not available in larger diameters?
We explored making the CMT tubing in larger diameters, but found that doing so had undesirable results. First, increasing the diameter of the tubing resulted in a decrease in the collapse strength of the tubing. Second, the larger-diameter tubing was more difficult to coil, and could not be coiled in diameters small enough to ship with common carriers. Rather than make the tubing larger, we developed water level measuring tapes and sampling pumps that would easily fit down all of the channels of the existing CMT tubing. See Model 101M and Model 102 Water Level Meters.
What is the history of the CMT System?
The CMT system was originally developed by Murray Einarson while he was a graduate student at the University of Waterloo in Ontario, Canada. At the time Murray was a partner in the California-based company, Precision Sampling, which retained ownership of the CMT patent rights until Precision was sold to Conor Pacific Environmental in 1998. In 1999, Murray obtained sole ownership of the patent rights from Conor Pacific and signed an agreement with Solinst, giving them exclusive world-wide rights to manufacture and sell the system. Since that time, Solinst has further developed the CMT System, designing reliable mechanical seals for each channel, a guide point port to allow easy access to the central channel, and a set of specialized tools to simplify system assembly.
How many CMT wells have been installed?
Thousands of CMT wells have been installed on four continents around the world. CMT wells have been installed in most states in the US and in Canada, the UK, Italy, Singapore, and South Africa.
® Solinst and CMT are registered trademarks of Solinst Canada Ltd.
*Patents #6,865,933 B1, #6,758,274 B2, #2,260,587, #6,581,682, #2,347,702, and #2,381,807
