Subsurface Leak Detection and Monitoring (LDM) using resistivity is used in the management of waste storage and the detection of leaks in containment structures such as subsurface liquid waste tanks. Time-based monitoring for changes in the electrical resistivity of the subsurface lithology surrounding these structures can yield significant information relating to remediation, environmental regulation, and economic impact.
When deployed as a subsurface monitoring system, LDM provides stakeholders, managers, and operators with information on subsurface hydrogeological conditions in near real-time, 24 hours a day, 365 days a year. This information is readily integrated with the data acquired using a network of electrodes and or monitoring wells. The net result is an enhanced real-time knowledge base to help make better decisions concerning waste management.
hydroGEOPHYSICS, Inc. (HGI) is currently operating monitoring systems on underground storage tanks at the Hanford facility in Richland, Washington, USA. Our system offers improved lateral and vertical resolution and enhanced sensitivity compared to conventional galvanic resistivity methods.
In a blind test conducted on a mock tank, our system successfully detected every release from the tank. In contrast, the previously considered best available technology, nuclear borehole logging, failed to detect any releases. Additionally, our team at HGI estimated the volume of the material released with a 14% margin of error.
We take pride in our advanced technology and the accuracy it brings to underground storage tank monitoring. If you want to learn more about HGI and how our systems can enhance your monitoring capabilities, please contact us. Below is more information on HGI’s Hanford LDM project.
Hanford Case study Doc
hydroGEOPHYSICS, Inc. (HGI) currently operates leak detection and monitoring (LDM) systems on underground storage tanks at the Hanford facility in Richland, Washington USA. Electrical resistivity is the geophysical method used for monitoring. The method is similar to conventional galvanic resistivity methods but has improved lateral and vertical resolution and sensitivity.
The figure below shows a schematic diagram of HGI’s monitoring system currently deployed at the Hanford facility. In a blind test on a mock tank, the system detected every release from the tank. In contrast, nuclear borehole logging –considered the best available technology at the time – detected zero releases. In addition, the scientists at HGI could estimate the volume of the material released to within 14% of the actual volume released.
Hanford Nuclear Site in Washington State manages liquid high-level radioactive waste stored in single-shelled tanks (SSTs) constructed between 1943 and 1964. To ensure proper containment and identify leaks, the Department of Energy has implemented an electrically-based geophysics monitoring program for leak detection and monitoring (LDM) since 2004. This program utilizes changes in contact resistance caused by conductive tank liquid seeping into the soil. By transmitting electrical current through various electrode types and measuring voltages, the monitoring system can continuously assess the tanks and analyze data in real-time to detect leaks.
Working in an industrial environment like the Hanford site poses several challenges for electrical monitoring, including cathodic protection, grounded electrical infrastructure, lightning strikes, diurnal and seasonal temperature trends, and precipitation. Overcoming these challenges is essential for effective leak detection in the tank farms.
The Hanford site currently stores approximately 30 million gallons of high-level radioactive waste in 149 SSTs and 28 double-shelled tanks (DSTs). The waste is a complex mixture of various chemical separation processes containing high concentrations of ionic constituents, heavy metals, and radioactive isotopes. Out of the SSTs, 67 are known or suspected to have leaked up to 1 million gallons of waste into the vadose zone, posing environmental and management challenges. To mitigate the risk of further leaks, the waste is being retrieved from the SSTs and transferred to more secure DSTs for temporary storage before final treatment.
Retrieving tank waste is a challenging process, with the method depending on the integrity of the tank. If the tank is structurally sound, high-pressure jets and pumps can be used for retrieval. However, if the tank’s integrity is questionable or leaks occur during retrieval, a more expensive vacuum retrieval system may be necessary. Therefore, monitoring the subsurface and detecting leaks during retrieval is crucial for verifying tank integrity.
Traditional leak detection methods involve spectral gamma and neutron logging in monitoring wells drilled near the tanks. However, these methods have limitations in terms of sample volume and time required for measurements. In order to minimize the time before potential leaks are detected and monitor tank integrity more effectively, an electrical geophysics monitoring program has been implemented on some of the Hanford tanks. This program relies on changes in resistivity caused by conductive liquid leakage into the soil. By transmitting current and measuring voltages on steel-cased wells the system continuously monitors and analyzes voltage data in real-time, providing a highly sensitive method for leak detection.
The Hanford site houses 177 underground storage tanks, including the SSTs and DSTs. The SSTs range in size from 208 m3 to 4400 m3, and 67 of them have leaked around 3800 m3 of liquid waste into the soil. The DSTs have an annulus around the inner tank to contain any potential leakage from the primary tank wall. Both types of tanks store waste generated during the reprocessing of irradiated uranium.
The Department of Energy is actively managing the waste by transferring it from SSTs to more secure DSTs and eventually turning it into a solid waste form. However, the retrieval process is challenging due to the diverse forms of tank waste and associated health and safety risks for workers. To support waste retrieval operations, the DOE conducts leak detection, monitoring, and mitigation to minimize additional leaks to the vadose zone.
The implementation of HRR-LDM technology was part of the Groundwater/Vadose Zone Integration Project Science and Technology program, established in 1999 to address uncertainties related to contaminant migration and tank waste leakage in the vadose zone at Hanford. The program aimed to develop efficient and cost-effective monitoring techniques, utilizing existing infrastructure within the tank farms.
The HRR-LDM technology was initially deployed at the Hanford site in 2004, specifically on the S-102 tank in the S tank farm. Monitoring took place for approximately 20 months before conducting a leak demonstration test within the tank farm to assess the effectiveness of the technology. The presence of complex electrical fields related to cathodic protection and grounded electrical infrastructure, as well as external factors like lightning strikes, temperature fluctuations, and precipitation, presented challenges in accurately detecting leaks.
The S-102 tank underwent a leak injection test, where a full HRR-LDM data acquisition system was deployed. One of the monitoring wells was converted into an injection well, and simulated waste was injected to simulate a tank bottom leak. The test involved multiple leak events over four months, with real-time data analysis to identify leak indications. The results showed that the HGI’s LDM system successfully detected eight out of ten leaks, with statistical analysis indicating its effectiveness in detecting leaks of a certain volume.
Overall, the implementation and testing of HRR-LDM technology at Hanford’s tank farms have provided valuable insights into leak detection and monitoring capabilities, despite the challenges posed by the complex industrial environment.
The current HRR-LDM technology used for long-term monitoring at the Hanford site consists of a data acquisition system (DAS) housed in a trailer near the tank farm. Cables connect the DAS to wells, surface electrodes, and a tank riser. Each electrode acts as both a transmitter and a receiver during data acquisition, except for the tank itself due to safety concerns. The acquisition time for a single data set depends on the number of electrodes and tank combinations, ranging from 12 minutes for a single tank to over 20 minutes for multiple tanks.
Different data types provide critical information about resistivity changes around the tank, and trends are evaluated to identify potential leaks. However, changes in trends do not automatically indicate a leak and require further analysis. Communication with tank farm operators is crucial for distinguishing between industrial-related changes and potential leaks. System malfunctions are addressed through a multilevel alarm system integrated into the DAS, which alerts operators of cable breaks, power disruptions, extreme thermal changes, and physical entry into the trailer. Automation has been implemented to streamline data processing and analysis, reducing operator errors and review time. Automation also enables instant access to data and system information, enhancing overall system performance. While anomalies may still occur, the operator’s knowledge and experience play a vital role in determining the presence of potential leaks.