Barrier integrity, monitoring and verification systems can be designed to include constant assessment of temperature, pressure, and soil moisture characteristics by installing the necessary components along with underground freezing assemblies, providing real-time monitoring, modeling and control of the overall operation of the barrier (remotely if required). In addition, ground penetrating radar and electropotential devices can provide assurance that a barrier has formed a hermetic seal, offers a visual representation of the forming ice barrier, and locates any unfrozen "windows" in the barrier. These systems combined with the temperature monitoring systems provide continuous real-time surveillance of the ice barrier, which can be remotely monitored. Three-dimensional imaging through computer animation techniques enhance the monitoring process throughout the barrier's life-cycle.
Barrier Control with on-line, real-time monitoring with supportive modeling is an integral part of our CRYOCELL technology. The component parts of this combined control/monitoring system are described in the following paragraphs. This description is not meant to imply that all methods would be implemented at all sites and is not intended to be all-encompassing in scope. It is important to note that since the CRYOCELL frozen soil barrier establishes a temperature gradient in the soil it is very easy to detect and verify by a number of different monitoring techniques. Other monitoring methods may be identified which also provide cost effective verification capabilities and will be incorporated into the overall system as they are proven effective and become available.
Instrumentation is required to monitor:
Frequency of all measurements of the recorded data will be established by site requirements and submitted with the Final Design.
To monitor the performance of the barrier the following instrumentation is installed as standard:
Note: Systems D through I are optional and are not included as Standard.
Temperature readings of coolant supply and return provides a direct measure of heat transfer (in BTU's) during barrier formation. The comparison of BTU's removed can be compared to BTU projections made during the conceptual design (Finite Element Analysis as it relates to heat transfer and fluid flow applications using compressor exchanger pump and valve selection) to develop accurate estimating standards relating to this single data dimension of optimal system performance. RKK's proprietary modeling program and/or other modeling software can be used to model a site before freezedown and a number of performance milestones established. During the design phase, the model provides data on BTU's required to form a CRYOCELL® barrier which in turn relates to the energy costs of barrier formation and operation. This allows us to compare the model site performance of freezedown with actual site freezedown facilitating for adjustments to be made thereby optimizing the freezing process.
Each condensing (freeze) unit*-this applies to the temporary as well as the permanent outdoor air cooled condensing units-is equipped with instrumentation to monitor and control:
Performance parameters are monitored by an electronic control panel that is programmable to operate within limits prescribed by the engineering superintendent. In case of the permanent freeze units, the electronic control panel can be accessed by a remote computer (not provided in our basic scope).
Instrumentation within the freeze units is important to ensure that the units operate without mechanical problems. Data will be automatically recorded for the freezing operation. As mentioned earlier, the plants will run fully automatic, and after testing, start-up and system stabilization, continuous unmanned operation will be provided.
In addition, the refrigeration capacity from the plant is monitored with a coolant flowmeter and temperature instrumentation at the evaporator. Data will be collected from these instruments utilizing the Data Acquisition System, designed and supplied by a subcontracted refrigeration company as part of their subcontract.
A data acquisition system will be used consisting of a data acquisition station (DAS), a personal computer (PC), a printer, and a modem for remote access. All temperature and flow data will be collected by the DAS and stored on the PC's hard disk for further processing. Windows 95-based software will be used to graphically display all data for easy viewing. Type T copper-constant thermocouples (TC) or 1,000-W resistance temperature detectors (RTD) are used for the temperature sensors. Temperature sensors will be installed in the coolant supply lines and in the return of each freeze.
*Hussman Corporation, Seattle, WA., contact Greg Dimmitt at
(206)763-9050. Secondly, Kimmel-Motz Refrigeration Company, Los
Angeles, CA, contact Vern Vetter, Phoenix, AZ, at (602)274-5431.
Were appropriate, water level readings in the piezometer inside the impoundment will be used as another indicator for closure of the frozen barrier. Once the barrier is closed, the water level inside the frozen barrier should behave independent from the water levels outside the barrier. Vibrating wire piezometers will be installed for easy data retrieval at the surface without concern for the subsurface contaminants.
If required, up to eight heave markers will be installed on the existing cap and four heave markers outside the cap to monitor long-term heave during operation of the frozen barrier. Location of these heave markers will be determined in the field after the installation of the barrier system but prior to placement of the final cover over the existing cap. Special surveying equipment will be used so that readings can be done by one person.
The same Windows 95-based software will be used for the graphical display of all water level and heave data.
Six underground temperature monitoring pipes, with temperature sensors typically on 5ft. centers, will be placed at locations where the underground freezing assemblies are furthest apart; two of them to monitor the core temperature of the frozen barrier, and two each inside and outside of the frozen barrier to monitor long-term growth of the barrier. The exact location of these monitoring pipes will be determined in the field after the alignment checks of the pipes.
Our active gas pressure monitoring system would be used to verify barrier integrity and performance once barrier formation is complete. Any cracking due to earth movement or other environmental stimuli (example: concentrated liquid waste streams) will be detected and located via this system before any breach of barrier integrity occurs. Barrier violations are detectable before reaching one quarter through the barrier wall. This system can be expanded to other data gathering capabilities also.
The active gas pressure monitoring system (perforated well casing)
within the frozen barrier area uses N2 under pressure to mechanically
verify that barrier is not only water-tight but also gas-tight.
*This proprietary monitoring and verification system is developed by RKK, Ltd., contact Ron Krieg at (425)861-6010, email to rkk@cryocell.com. Secondly, Gaseous Tracer System To Evaluate The Integrity Of In-Situ Barriers, Science & Engineering Associates, Inc., Santa Fe, NM, contact William Lowry.
An additional on-line monitoring system can be provided via high
frequency acoustic and radar imaging techniques*. This technique is
able to differentiate the density of ice versus soil and provides
additional supportive data to verify barrier integrity. This system
is under development by MIT and was successfully used during the Oak
Ridge demonstration. The successful demonstration of this technology
verified that the system was able to scan the barrier before, during
and after formation and develop a computer image of barrier
status.
* Ground Penetrating Radar Investigation of a Frozen Earth Barrier, by Professor Dale Morgan and Dr. David Lesmes of Earth Resources Laboratory at the Massachusetts Institute of Technology. Secondly, Subsurface Interface Radar by Geophysical Survey Systems, Inc., North Salem, NH, contact Daniel J. Delea at (603)893-1109, email to gssisales@aol.com.
Another continuous data gathering and modeling technology
available is the elektrokinetic energy system* which uses electrical
flow tests. Cathodes and electrodes embedded inside and outside the
barrier provide on-line data with the ability to model before and
after formation, and during operation. Any pathway of unfrozen water
through the barrier is detectable with this system.
* Isotron Corporation, New Orleans, LA, contact Henry L. Lomasney at (504)254-4624. Secondly, Hyrostratigraphy and Recharge Distributions From Direct Measurements of Hydraulic Conductivity Using the UFA Method, by Judith Wright, James L. Conca and Xiaobing Chen of Pacific Northwest Laboratory, Richland, WA.
In addition to the direct monitoring methods described above, remote geophysical methods* may be applied if appropriate. The application of geophysical methods will be dependent on the proposed scope of the EPA-SITE characterization and assessment planned for this project. The firm of Golder and Associates, Inc. could conduct geophysical surveys to complement the direct tracer methods that may be used to assess the barrier integrity.
Golder's geophysics group supports a wide variety of projects throughout the DOE sites and the private sector. The equipment and procedures meet ISO-9000 standards for quality assurance. Golder has recently completed barrier integrity studies at the Hanford and Sandia sites. The geophysical component of the projects included ground penetrating radar, neutron moisture and electromagnetic induction and they produced excellent results. The geophysical program, complimenting the tracer program, may assess the integrity of the barrier more rapidly than tracers, and interpretations may be less sensitive to background conditions. The geophysics program may include:
* Soil Properties Monitoring, The University of Washington, Seattle, WA, contact R. French Ledger at (206)616-1505.
Outside and around the barrier, there will be a series of wells with monitoring equipment. This equipment will have automatic operations and reporting capabilities and will posses the capability of tying into the barrier operational system to alert observational or operational personnel if targeted contaminants, or a change in the level of identified contaminants, are detected.
This equipment, combined with the integrated system, would benefit sites where CRYOCELL is installed to completely isolate/contain the identified waste source.
Additional monitoring systems being developed by others can be incorporated into the overall verification system as they are proven and made available.
By overlaying data gathered by some or all of the systems mentioned, the RKK copyright modeling program is able to compare its pro forma predictions of barrier formation time and performance against known real-time data and develop a real-time computer generated picture (geophysical or digital imaging) of the barrier's status. Optionally if required, the program can be custom tailored and will provide a computer animation of the barrier status throughout its life-cycle. This picture verifies barrier closure and operational status at all times.
The barrier's control is regulated via this same system to maintain upper and lower performance limits. Should any irregularities be detected with equipment operation, temperature design limits, or other design levels, the operation of the freeze units can be modified based on model observation and return the system within acceptable performance limits before barrier integrity is effected.
Data and the barrier's operational performance can be supplied at multiple observation points via modem hook-up. Performance scans can be performed automatically or on demand from any of the observation points. (This would allow the EPA the option to have an observation point on-line at any site or a central reporting point covering any number of sites that they wished to observe.) This can be done via remote microwave satellite transmission, cellular telephone, radio remote, telephone line, fiber optic link, or other as required to meet the communication needs of a specific site. This series of active systems will provide any client or regulator a real-time guarantee of barrier integrity and an accurate model of barrier performance. The system is self-auditing by use of many independent data types, data scans, with many thresholds of performance to measure to.