CHAPTER 149
GEOTHERMAL WELL STANDARDS
GEOTHERMAL WELL STANDARDS
149.01 Purpose | 149.10 Vertical Closed Loop Systems |
149.02 Definitions | 149.11 Ground Water Protection for Vertical Closed Loop Systems |
149.03 Permit Required | 149.12 Vertical Loop Systems Within 1,000 Foot Radius of a City Water Well |
149.04 Application Procedure | 149.13 Closed Loop Vertical Systems Between 1,000 and 2,000 Feet Radius of a City Water Well |
149.05 Permit Suspension and Revocation | 149.14 Closed Loop Vertical Systems Outside of 2,000 Foot Radius of a City Water Well |
149.06 Well Permits | 149.15 Testing of System |
149.07 Permit Fee | 149.16 Abandonment of Geothermal Systems |
149.08 Open Loop Systems Prohibited | 149.17 Regulation Conflict |
149.09 Horizontal Closed Loop Systems Permitted | |
It is the purpose of this chapter to protect the health, safety and general welfare of the people of the City of Mount Vernon by ensuring that the ground waters will not be polluted or contaminated. Minimum requirements are contained in this chapter for the construction, reconstruction, repair, and destruction of geothermal wells.
For use in this chapter, the following terms are defined:
1. "Annular Space" - The space between the casing or well screen and the wall of the borehole, or between drilling pipe and casing, or between two separate strings of casing.
2. "Aquifer" - A subsurface water-bearing layer of soil, sand, gravel, or rock that will yield usable quantities of water to a well.
3. "Borehole" - A hole drilled or bored into the earth, usually for exploratory or economic purposes; a hole into which casing, screen, and other materials may be installed to construct a well.
4. "Casing" - An impervious, durable pipe placed in a borehole to prevent the walls of the borehole from caving, and to seal off surface drainage or undesirable water, gas or other fluids and prevent entrance into a well.
5. "Drinking Water" - Water which is intended for human consumption and other domestic uses, and is considered to be free of harmful chemicals and disease-causing microorganisms.
6. "Geothermal Borehole" - A hole drilled or bored into the earth into which piping is inserted for use in a geothermal system.
7. "Geothermal System" - A geothermal system uses the earth's thermal properties in conjunction with electricity to provide greater efficiency in the heating and cooling of buildings.
8. "Geothermal System (Closed Horizontal Loop)" - A mechanism for heat exchange which consists of the following basic elements: underground loops of piping; heat transfer fluid; a heat pump; an air distribution system. An opening is made in the earth. A series of pipes are installed into the opening and connected to a heat exchange system in the building. The pipes form a "closed loop" and are filled with a heat transfer fluid. The fluid is circulated through the piping from the opening into the heat exchanger and back. The system functions in the same manner as the open loop system except there is no pumping of ground water. A horizontal closed loop system shall be no more than twenty (20) feet deep.
9. "Geothermal System (Closed Vertical Loop)" - A borehole extends beneath the surface. Pipes are installed with U-bends at the bottom of the borehole. The pipes are connected to the heat exchanger and heat transfer fluid is circulated through the pipes.
10. "Geothermal System (Open Loop)" - Ground water is pumped from a water well into a heat exchanger located in a surface building. The water drawn from the earth is then pumped back into the aquifer through a different well or in some cases the same well. Alternatively, the ground water could be discharged to a surface water body. In the heating mode, cooler water is returned to the earth, while in the cooling mode warmer water is returned to the surface water body.
11. "Ground Water" - Water beneath the earth's surface, that occurs between saturated soil and rock that supplies wells and springs.
12. "Grout" - A low permeability material that is emplaced in the space between the wall of the borehole and the casing of a well and/or emplaced on the wall of the borehole. The emplacement of grout is to prevent the migration of water or fluid contaminants into and through the borehole. Grout shall consist of neat cement, high solids bentonite slurry, or hydrated bentonite chips.
13. "Heat Exchanger" - A device, usually made of coils of pipe, that transfers heat from one medium to another; for example, from water to air or water to water.
14. "Heat Transfer Fluid" - Any liquid used specifically for the purpose of transferring thermal energy from the heat source to another location.
15. "Low Permeability Material" - A geological unit of unconsolidated material (usually clay or till) or bedrock (usually shale) that is all or partially saturated, and having permeability low enough (10-7 cm/sec) to give water in the aquifer artesian head.
16. "Permeability" - The propensity of a material to allow fluid to move through its pores or interstices. Permeability is an important soil parameter when flow of water through soil or rock is a matter of concern.
17. "Separation/Isolation Distances" - The distance of a source of contamination from a surface drinking water source, a ground water source supply well, or any type of borehole.
18. "Surface Water" - Water located on the surface of the earth in water bodies such as lakes, rivers, streams, ponds, and reservoirs.
19. "Tremie" - A tubing string (typically about 2 to 3 inches in diameter) that is temporarily installed into the borehole during well construction. The tremie pipe is used for installing annular material such as filter pack sand and grout.
20. "Water Supply Well" - A well used by public water systems, or non-public use, for extracting ground water for human consumption.
21. "Well" - Any excavation that is drilled, cored, driven, dug, bored, augured, jetted, washed or is otherwise constructed for the purpose of exploring for ground water, monitoring ground water, utilizing the geothermal properties of the ground, or extracting water from or injecting water into the aquifer. "Well" does not include an open ditch, drain tiles, an excavation made for obtaining or prospecting for oil, natural gas, minerals, or products mined or quarried, lateral geothermal heat exchange systems less than twenty (20) feet deep, nor temporary dewatering wells such as those used during the construction of subsurface facilities only for the duration of the construction.
No person shall dig, bore, drill, replace, modify, repair, or destroy a geothermal well or any other excavation that may intersect ground water without first applying for and receiving a permit from the City. A permit is required for all closed loop horizontal and closed loop vertical systems.
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