CMT monitasoinen järjestelmä FAQ: Usein kysytyt kysymykset: Usein kysytyt kysymykset: Usein kysytyt kysymykset

{ "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [{ "@type": "Question", "name": "Can segments of the CMT tubing be coupled together?", "acceptedAnswer": { "@type": "Answer", "text": "No. The system is designed to be installed in one continuous length, thus eliminating the possibility of leakage at joints." } },{ "@type": "Question", "name": "Are CMT wells accepted by regulators? How do I convince my regulator that the system yields reliable data?", "acceptedAnswer": { "@type": "Answer", "text": "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. 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." } },{ "@type": "Question", "name": "Are there any chemical affects or biases associated with the polyethylene tubing or other parts of the CMT system?", "acceptedAnswer": { "@type": "Answer", "text": "Here are chemical biases associated with all types of groundwater monitoring wells and sampling pumps. Potential chemical biases associated with the CMT system relate to (1) the use of polyethylene tubing and (2) the sampling devices used to collect water samples. Hydrophobic organic contaminants can sorb to the polyethylene tubing, potentially causing a negative sampling bias. In some situations, those same compounds can diffuse through the polyethylene, either from outside of the well or from adjacent channels, potentially causing a positive sampling bias in some channels. Potential biases with hydrophyllic contaminants, e.g. MTBE or most inorganic compounds is minimal. A thorough discussion of these potential sampling biases is presented in the Einarson and Cherry Paper describing the CMT system that was published in the Fall 2002 issue of Groundwater Monitoring and Remediation. (See the Papers Section of this web site.)" } },{ "@type": "Question", "name": "Why is the system not available in Teflon®?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "How are CMT wells diffferent than \"nested wells\"?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "Do CMT wells comply with state and county well construction standards?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "What is the purge volume of the various CMT channels per foot of tubing?", "acceptedAnswer": { "@type": "Answer", "text": "The outer 6 pie-shaped channels of the CMT tubing each hold 40 ml of fluid per linear foot of tubing. The central channel holds approximately 30 ml per linear foot." } },{ "@type": "Question", "name": "Why is the CMT System less expensive than other multilevel systems?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "What papers or guidance documents have been published that describe the CMT System?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "Does the Waterloo Multilevel System have any advantages over the CMT System?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "I don't have room at my job site to lay out the tubing in order to mark and install the intake ports and well screens. What other options do I have?", "acceptedAnswer": { "@type": "Answer", "text": "For long lengths of tubing, e.g. greater than 100 feet, it is often impractical to lay the tubing on the ground at the job site in order to mark and install the various intake ports and well screens. We recommend that you mark the locations of the ports on the tubing ahead of time and bring the coiled CMT tubing to the jobsite. You can then install the ports and well screens at the proper locations as you are lowering the CMT tubing into the borehole. Alternatively, the CMT System can be built anywhere that room is available, then coiled and transported to the site." } },{ "@type": "Question", "name": "Why is the CMT tubing not available in larger diameters?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "What is the history of the CMT System?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "How many CMT wells have been installed to date?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "Can CMT wells be used for soil gas sampling?", "acceptedAnswer": { "@type": "Answer", "text": "Yes. Special fittings are available to collect soil gas samples from all channels of the CMT tubing. Contact us for details." } },{ "@type": "Question", "name": "What kind of hydraulic tests can I perform in CMT wells?", "acceptedAnswer": { "@type": "Answer", "text": "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" } },{ "@type": "Question", "name": "Are groundwater samples collected from CMT wells as good as samples collected from 2-inch or 4-inch conventional monitoring wells?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "How are CMT wells different than \"nested wells\"?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "Do CMT wells comply with state and county well construction standards?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "Are CMT wells accepted by regulators? How do I convince my regulator that the System yields reliable data?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "What papers or guidance documents have been published that describe the CMT System?", "acceptedAnswer": { "@type": "Answer", "text": "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." } },{ "@type": "Question", "name": "What is the maximum depth that CMT wells can be installed?", "acceptedAnswer": { "@type": "Answer", "text": "CMT wells have been installed to a maximum depth of 260 feet. Stock coil lengths are 100 ft, 200 ft & 300 ft. On special order 400 ft coils are available." } },{ "@type": "Question", "name": "Can segments of the CMT tubing be coupled together?", "acceptedAnswer": { "@type": "Answer", "text": "No. The system is designed to be installed in one continuous length, thus eliminating the possibility of leakage at joints." } },{ "@type": "Question", "name": "What if I don't want to monitor seven zones? Do I have to use all the channels?", "acceptedAnswer": { "@type": "Answer", "text": "No. You can use as many or as few as you like. Unused channels do not affect the rest of the CMT System. Some people use two channels to monitor a single zone. They dedicate one of the channels to a Micro Double Valve Pump and use the other channel for measuring water levels. If you use two channels to monitor a single zone, however, you will reduce the number of discrete zones that you can monitor by 50%." } },{ "@type": "Question", "name": "What papers or guidance documents have been published that describe the CMT System?", "acceptedAnswer": { "@type": "Answer", "text": "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.'" } },{ "@type": "Question", "name": "Is there a minimum borehole diameter that should be used for CMT wells?", "acceptedAnswer": { "@type": "Answer", "text": "For installations where sand and bentonite pellets are poured into the borehole annulus from the ground surface, we recommend using CMT centralizers and a borehole diameter of at least 5 inches. That gives the well installer ample space to avoid bridging the sand and bentonite and allows easy access for the Solinst Tag Line. Solinst Double Acting Inflatable Packers are available, by special order, to seal 3\", 3.7\" and 4\" boreholes. Seven-channel CMT wells can be installed through direct-push casing having an inside diameter (ID) of 2 inches or larger. These installations rely on the formation collapsing around the CMT tubing." } },{ "@type": "Question", "name": "What kinds of drilling methods can be usd to install CMT wells?", "acceptedAnswer": { "@type": "Answer", "text": "CMT wells have been installed in boreholes created with nearly all types of drilling equipment. A summary of Drilling Methods & Techniques for installing CMT wells in Unconsolidated Aquifers can be found in the Papers & Information section of the Solinst website." } },{ "@type": "Question", "name": "How do I find a drilling contractor who has experience installing CMT wells?", "acceptedAnswer": { "@type": "Answer", "text": "A listing of drilling contractors who have experience installing CMT wells is included on our website. If you have a contractor that you would like to work with but who has not yet installed a CMT well, please have the contractor contact Solinst to explain the various options for installing CMT wells with different types of drilling equipment. We are happy to assist you and/or your contractor to make sure that your CMT wells are installed successfully. Telephone support is available at no cost. On-site training for you and/or your contractor is available for a small additional fee necessary to cover our time and travel costs." } },{ "@type": "Question", "name": "I've seen pictures of the CMT System installed with bentonite packers. Are they available from Solinst?", "acceptedAnswer": { "@type": "Answer", "text": "Prototype bentonite packers were used during the initial development and testing of the CMT system. Those bentonite seals, which are described in the 2002 Einarson and Cherry paper, proved to be too difficult and time-consuming to construct in the field. Therefore, we recommend that all annular materials, including sand pack and bentonite seals, be poured from the surface in conjunction with CMT System Centralizers." } },{ "@type": "Question", "name": "I've heard that inflatable packers exist that allow for temporary or permanent installations in bedrock aquifers. How do they work?", "acceptedAnswer": { "@type": "Answer", "text": "We have developed Double-Acting Inflatable Packers that are used to seal the annular space between the CMT tubing and the borehole wall in bedrock installations. They are \"double acting\" in that the inside of the packers expand along with the outside of the packers. By applying a small vacuum to the packers, the inner gland expands slightly. The packers then slide easily over the CMT tubing and can be positioned where needed. When the vacuum is released, the inner gland retracts, securing the packers to the CMT tubing. Clamps are attached to the packers to ensure that they don't move when the well is inserted into the borehole. An inflation tube connects to each of the packers and extends to the ground surface. When the CMT well is fully inserted, the packers are inflated with air, nitrogen, or water. Inflating the packers seals both the borehole annulus and the space between the CMT tubing and the packers. An advantage of this system is that the packers can be deflated and the system removed when monitoring is no longer needed." } },{ "@type": "Question", "name": "Can I install CMT wells with direct-push equipment?", "acceptedAnswer": { "@type": "Answer", "text": "Yes. Many DP contractors are installing 7-Channel CMT wells. The wells are typically installed inside of probe rods equipped with disposable drive points. Once the probe rods have been advanced to the desired depth, the CMT tubing is inserted. Then, the probe rods are retracted, leaving the CMT well in the ground. Most of these installations have been in sandy formations where the soil collapses around the CMT tubing when the probe rods are retracted. Installations in formations that do not collapse are more difficult, especially with small-diameter probe rods. The small inside diameter of the probe rods leaves little space to pour annular materials (i.e. sand and bentonite pellets) from the ground surface." } },{ "@type": "Question", "name": "What is the best way to install sand packs and annular seals between the various monitored zones?", "acceptedAnswer": { "@type": "Answer", "text": "The best way to install sand pack and annular seals is by pouring them into the borehole annulus from the surface or using a tremie pipe. When installing 7-Channel CMT wells this way, we suggest that you have a borehole no smaller than 5 inches in diameter. A borehole 5 inches in diameter or larger allows plenty of room for sand and bentonite pellets to fall to the bottom of the borehole without bridging. Also, be sure to use Solinst's low-profile centralizers to keep the CMT tubing centered in the borehole. These centralizers have been designed to minimize the likelihood of bridging the annular materials when building the well. Also, you may want to use an Anchor Plate to keep the CMT from rising up in the borehole, especially when drive casing (if used) is incrementally withdrawn from the borehole. The Anchor Plate is bolted directly to the Guide Point Port. After you have inserted the CMT well to the bottom of the hole, place a sandpack across the deepest monitoring zone by pouring sand into the annulus until it comes up to the level specified in your well construction design diagram. Be sure to measure the depth of the sand pack frequently with Solinst's Model 103 Tag Line while you are pouring the sand. This ensures that you don't bring the sand pack too high up in the borehole. Once the sand pack is above the bottom monitoring port, pour bentonite pellets to make a seal between the bottom monitoring zone and the overlying one. Contractors have reported good success using coated bentonite pellets for the annular seals. Pour the pellets slowly, and measure the depth of the seal frequently with the tag line to avoid adding too much bentonite. Continue adding alternating layers of sand pack and bentonite seals as described above, up to the levels specified in your well construction design diagram. Additional information about constructing CMT wells is presented in our Model 403 CMT Installation Manual (available on our site)." } },{ "@type": "Question", "name": "I don't have room at my job site to lay out the tubing in order to mark and install the intake ports and well screens. What other options do I have?", "acceptedAnswer": { "@type": "Answer", "text": "For long lengths of tubing, e.g. greater than 100 feet, it is often impractical to lay the tubing on the ground at the job site in order to mark and install the various intake ports and well screens. We recommend that you mark the locations of the ports on the tubing ahead of time and bring the coiled CMT tubing to the jobsite. You can then install the ports and well screens at the proper locations as you are lowering the CMT tubing into the borehole. Alternatively, the CMT System can be built anywhere that room is available, then coiled and transported to the site." } },{ "@type": "Question", "name": "How do I decommission CMT wells?", "acceptedAnswer": { "@type": "Answer", "text": "CMT wells can be pressure grouted using a bentonite or cement slurry. The injected fluid will fill each CMT channel and the sand pack adjacent to each intake port. CMT wells can also be over drilled if necessary." } },{ "@type": "Question", "name": "What is the purge volume of the various CMT channels per foot of tubing?", "acceptedAnswer": { "@type": "Answer", "text": "The outer 6 pie-shaped channels of the CMT tubing each hold about 40 ml of fluid per linear foot of tubing. The central channel holds approximately 30 ml per linear foot." } },{ "@type": "Question", "name": "What if I don't want to monitor seven zones? Do I have to use all the channels?", "acceptedAnswer": { "@type": "Answer", "text": "No. You can use as many or as few as you like. Unused channels do not affect the rest of the CMT System. Some people use two channels to monitor a single zone. They dedicate one of the channels to a Micro Double Valve Pump and use the other channel for measuring water levels. If you use two channels to monitor a single zone, however, you will reduce the number of discrete zones that you can monitor by 50%." } },{ "@type": "Question", "name": "How do I measure water levels inside CMT wells?", "acceptedAnswer": { "@type": "Answer", "text": "Water levels can be measured with Solinst's Model 101 or Model 102 small-diameter water level tapes. If continuous recording of water levels is desired, you can install Solinst's Model PDCR 35/D Druck transducers. The transducers can be connected to a wellhead datalogger or a telemetry unit for remote reading from a central data collection center. These transducers will only fit inside the outer channels and not the narrower center channel." } },{ "@type": "Question", "name": "What are the best ways to purge and sample CMT wells?", "acceptedAnswer": { "@type": "Answer", "text": "You basically have 3 choices for purging and sampling in narrow diameter applications. The Model 410 Peristaltic Pump can be used where the suction lift is less than 25 ft (7.5 m). Solinst's Mini Inertial Pump (MIP) can also be used. The MIP uses 1/4\" (6mm) dia. riser tubing fitted with a \"push-in\" foot valve. Repeated up and down strokes brings the sample to surface from depths up to 150 ft. (46m). Purge & sampling can also be done with the Model 408M Micro Double Valve pump which is ideal for low flow sampling. The 408M is made of 3/8\" (10mm) dia. flexible coaxial tubing available in LDPE for use to 50 ft. (15m) or Teflon for use down to 150 ft. (46m) The 408M uses a drive gas which is delivered through a controller." } },{ "@type": "Question", "name": "Are there any chemical affects of biases associated with the polyethylene tubing or other parts of the CMT system?", "acceptedAnswer": { "@type": "Answer", "text": "There are chemical biases associated with all types of groundwater monitoring wells and sampling pumps. Potential chemical biases associated with the CMT system relate to (1) the use of polyethylene tubing and (2) the sampling devices used to collect water samples. Hydrophobic organic contaminants can sorb to the polyethylene tubing, potentially causing a negative sampling bias. In some situations, those same compounds can diffuse through the polyethylene, either from outside of the well or from adjacent channels, potentially causing a positive sampling bias in some channels. Potential biases with hydrophyllic contaminants, e.g. MTBE or most inorganic compounds is minimal. A thorough discussion of these potential sampling biases is presented in the Einarson and Cherry Paper describing the CMT system that was published in the Fall 2002 issue of Groundwater Monitoring and Remediation." } },{ "@type": "Question", "name": "Are groundwater samples collected from CMT wells as good as samples collected from 2-inch or 4-inch conventional monitoring wells?", "acceptedAnswer": { "@type": "Answer", "text": "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 13 liters or less than 3.5 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 recharge 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." } },{ "@type": "Question", "name": "I have flowing artesian conditions at my site. Do you have a way to plug and sample the ports at the wellhead?", "acceptedAnswer": { "@type": "Answer", "text": "Yes. Special expansion plugs are available to seal the various channels at the wellhead. The plugs have optional valves which allow you to collect groundwater samples simply by opening the valves. Pressure gauges can also be attached to the plugs at the wellhead in order to measure the piezometric pressures in each monitored zone." } },{ "@type": "Question", "name": "How do I develop CMT wells?", "acceptedAnswer": { "@type": "Answer", "text": "We have had good success purging the wells with Peristaltic Pumps and Mini Inertial Pumps. You cannot, of course, develop CMT wells the way you would a water supply well, but that type of rigorous development isn't required with small-diameter monitoring wells. The goal of developing CMT wells, which is usually easily achieved, is to establish hydraulic connection with the formation. The well won't be 100% efficient, but the hydraulic head values measured in the well will be accurate, and the well will yield more than enough water to sample (assuming that the formation is reasonably permeable). If you added water when drilling the borehole or constructing the well, the best way of dealing with this is to simply wait several days for the water you've added to \"drift\" down gradient. For sites with typical groundwater velocities (0.5 to 2 feet per day), the water added during drilling and/or well construction will have drifted away from the CMT intake ports in several days. If the water added during drilling has a different electrical conductivity (EC) than the formation water, you can monitor the EC in water pumped from the well to confirm that the drill water is gone. Some consultants have added potassium bromide (an inert tracer commonly used in groundwater research) as a tracer to the drill/construction water and then monitored the purge water in the CMT well with a bromide-specific electrode to verify that the drill water is no longer in the vicinity of the CMT well prior to collecting samples. Contact us for details." } }] }