Description
The borescope is used as in situ instrumentation to directly observe colloidal size particles and subsequent groundwater flow direction and rate. Current applications include:
The borescope is inserted into a monitoring well and fixed at the surface with a clamp. The instrument consists of a charge coupled device (CCD) camera, an optical magnification lens, an illumination source, a downhole compass to assess direction of natural flow, and a watertight stainless steel housing. The instrument is approximately 60 cm long, with a diameter of 44 mm. The electronic image is transmitted to the surface by a 33-m fiber optic cable. The image is viewed on a high-resolution 25-cm monitor and recorded on VHS tape for further analysis. The magnified image corresponds to a 1.0 × 0.4 × 0.1 mm field of view.
Technical Performance
Operation of the borescope is not complicated. The instrument is inserted into a well, and the flow is observed on a surface video monitor. The instrument can be used in a well as small as 5 cm in diameter. A measurement is obtained in about 30 min. The stainless steel construction allows for easy decontamination and little maintenance is required. The integrity of water-proof seals is checked periodically.
The colloidal borescope is capable of determining the vertical and spatial distribution of local groundwater velocity, both in magnitude and direction. It is capable of these measurements in low- and high-permeable material. The instrument also permits observation of flow processes at the pore scale. The instrument can assess local flow velocities ranging from 0 to 15 mm/s. Colloidal density is greatly affected by perturbations caused by instrument insertion. A period of 30 min. is generally required for transient turbulence to decline.
Cost. The borescope is more cost effective than conventional methodologies. Since flow velocities are measured directly under ambient flow conditions, unlike measuring in conventional methods, no water disposal is required, thus minimizing water disposal costs. The instrument presently costs approximately $20K. Costs should significantly decrease when production begins.
Projected Performance
Continued software development is necessary to address the variability of water flow, and additional work is currently under way to address the variability observed in well bores. The effects of subsurface magnetism on the compass is yet to be determined.
Waste Applicability
Since this technology is specifically used for characterization and monitoring of the ground media at problem sites, the technology is waste independent.
Status
Prototypes are presently available. An advanced version with associated software are expected to be available in 1994.
Regulatory Considerations
Compliance with the Occupational Safety and Health Administration regulations is required for hazardous waste operations and protection of occupational workers from electrical power. Also, permits may be required for drilling at hazardous waste sites.
Potential Commercial Applications
The Colloidal Borescope can be used at any site where information on colloidal size particles and subsequent groundwater flow velocity is necessary. The Colloidal Borescope can be used for site characterization by determining preferential flow paths and fractures. It can also be used for assessing heterogeneities associated with porous media, establishing the existence of immiscible contaminated layers and their associated flow properties, assessing the efficiency of groundwater remediation programs by determining the effective radius of influence of groundwater extraction systems, determining the amount of biological activity present in a bioremediation system, and evaluating the effects of sampling on colloidal concentrations.
Baseline Technology
The baseline technology is a standard technique used to measure hydraulic head gradients and hydraulic conductivities in boreholes to determine flow velocity. Four holes are required for a measurement using this standard technique as compared to using one hole with the Colloidal Borescope. With the standard technique, information about the hydraulic conductivity of the medium is required and is generally determined using a pump test in which large quantities of water are pumped from the well. Disposal of this purge water can be difficult and expensive.
Intellectual Property Rights
The property rights are unknown or do not exist. Contact the principal investigator for further information.
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References
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