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Liquid Management System
It is the process of disposing of water that has a high mineral content by injecting it below ground. This process does not impact underground drinking water sources. This process also meets the Environmental Protection Agency standards.
Prior to the wells being constructed and operated, the EPA will require Roseville Electric to have Plugging and Abandonment Plans in place to safely decommission the wells. The required plans will outline all aspects of the decommissioning from the financial requirements, engineering, ongoing monitoring as determined and making the site look as it did prior to the installation of the wells.
The only time that a fracture might be created is during step testing (required by the EPA to permit the well). The Step Rate Test (SRT) involves a series of constant rate injection tests, all with the same duration, with each successive step at a higher injection rate and injection pressure. The injection rate can be increased until the formation parting pressure is exceeded, at which point the injection pressure suddenly drops (showing up as in inflection point on the rate vs. pressure curve). However, the EPA does not always require that the parting pressure be reached, as long as the maximum injection rate and pressure attained in the SRT is greater than the desired operational injection rate (with a safety factor included). Having said this, any fracture produced in a SRT will be limited in size and should heal after injection ceases. The fracture shouldn't open again unless the formation parting pressure is exceeded again, which is not allowed under permit.
All "equipment" will be removed from both wells, and then the wells will be sealed underground and capped according to EPA direction and the Plugging and Abandonment Plans. This will be done in order to protect surface water and underground drinking water supplies.
The EPA will require monitoring during the operation of the wells. They will also determine what type of monitoring will be required after well closure. The monitoring duration and frequency will be based on items such as:
- Historical well operation data
- Details of well construction such as depth and condition of well at the time of decommissioning
- Any reported safety concerns or operational failures during the life of the well or at the time of decommissioning.
The equipment will be engineered to withstand the corrosive operating environment. Additionally, there will be routine inspections, safety devices and maintenance performed to ensure any issues that arise are resolved in a timely manner.
The injected water contains base constituents already found in the salt water aquifer we will be injecting into, but at a much lower percentage, and will remain in that salt water aquifer. This salt water is considered untreatable for drinking water by California and EPA standards, and as such the injected water will be diluted to such a degree within the salt water aquifer it would not be detected in a discrete sample.
The presentation to the RCONA group highlighted the selection criteria used to determine the LMS as the best option. Cost was one of the factors, but not the most important as the list below indicates. The selection criteria included the following:
- The new process will improve our system reliability
- The new process will be financially prudent
- The new process must be environmentally safe and compliant
- The new process must be a proven technology, acceptable to permitting agencies.
With proper engineering controls, direction from the EPA, and diligence in operating the process to the same high standard our customers already appreciate and enjoy with Roseville Electric, we do not expect to experience any of the adverse impacts mentioned in the question.
Due to the length of the answer, it will be posted on the FAQ page by Monday, July 6, 2013.
The cooling water is used to draw heat away from the equipment. The warmed cooling water then needs to be cooled and this is done through the process of evaporation. A side effect of evaporation is a high mineral content build up in the cooling water which can drastically reduce plant equipment efficiency. The management process removes the high mineral content water from the cooling water.
The current process to dispose of the water used to cool the plant is very expensive to operate and maintain. At the time the plant was permitted, it was the best available option approved by the California Energy Commission. Now six years later, it’s appropriate to seek viable alternatives. If the proposed liquid management system is appropriate for the REP, it could save Roseville Electric up to $1.8 million in operation and maintenance costs annually.
Roseville Electric would inject water that has developed a high mineral content more than 1,500 feet below the underground drinking water aquifer. The 1,500 foot layer separates and will protect the drinking water from injection water.
The proposed site located on 5,000 square feet of City owned property adjacent to the Roseville Energy Park (REP). As part of the project the REP fencing will be extended to enclose the injection process equipment.
Roseville Electric staff expects to have a schedule outlining the remainder of this project in early 2012. Roseville Electric staff will also provide the City Council with an update on the completed liquid management system feasibility study along with staff’s recommendations for the next phase.
The liquid management system process replaces the zero liquid discharge system in place at the Roseville Energy Park. Our analysis shows that a liquid management system is not as costly to operate or maintain when compared to the zero liquid discharge system.
The zero liquid discharge system, known as the ZLD, is the process of removing the high mineral content from cooling water used during the plant cooling process. The removed minerals form into a non-hazardous salt cake. The salt cake is then taken to the Placer County Materials Recovery Facility for disposal.
The process of removing and discharging cooling water from the plant must be approved by the California Energy Commission. During the plant permitting process, the ZLD was approved by the California Energy Commission because it was considered to be the best technology at that time.
Roseville Electric’s Energy Park’s ZLD is costly to operate and maintain. When Roseville Electric became aware that the California Energy Commission was permitting another plant using liquid management system technology, we initiated a study to determine if it would be cost effective to use at the REP.
In May 2010, a consultant study considered many alternatives and found the only option worthy of further consideration is a liquid management system. In 2011 a detailed feasibility study was completed.
While we do not have firm numbers, our consultant estimates the cost of a liquid management system at the Roseville Energy Park is $4.7 million. The study also estimates the annual operating and maintenance cost savings of the liquid management system project to be $1.8 million.
There are currently more than 100 liquid management systems utilizing injection wells permitted in California. Of those, four were permitted for power plants.
The liquid management process is considered to be an acceptable process to use in industrial process by the California Energy Commission and the U.S. Environmental Protection Agency.
Our study shows:
- The liquid management site’s separation from drinking water is more than required by federal standards.
- The injection zone exceeds the U.S. Environmental Protection Agency’s minimum criteria.
- The water from the power plant is cleaner than the water found (naturally) in the injection zone.
The liquid management process will be designed to have no impact on its neighbors.
We will continue to use the ZLD system. We are using that system now; By permit Roseville Electric cannot operate the Energy Park and not use the ZLD system.
The use of a liquid management system at the Energy Park will not increase operation and maintenance costs.
Assuming the City Council approves this project; Roseville Electric will prepare and submit permit applications to the U.S. Environmental Protection Agency and California Energy Commission to use the liquid management process.