Geothermal wells have been used for several decades as an adjunct to existing heating and cooling systems. The systems are designed to use the Earth’s relatively constant subsurface temperature along with a heat exchanger to either add to or remove heat from a dwelling.
With the recent increase in energy costs, the use of geothermal exchange systems is gaining in popularity and becoming more economical. The US Environmental Protection Agency and the Department of Energy both recommend geoexchange systems as a “green” technology for lowering energy costs and dependency on fossil fuels. Nonetheless, the Agencies have concerns that the potential for significant harm to Connecticut’s groundwater resources requires regulation of this largely unregulated industry.
In the spring of 2006 the Connecticut Water Well Association (CWWA) approached the Connecticut Department of Public Health (DPH) concerning regulation of the geothermal well industry. The CWWA was concerned about the need for standards in the industry in order to protect the environment and prevent substandard work practices. Following meetings with the DPH, the CWWA submitted proposed changes to the Well Drilling Code. While the Agencies involved are not in full agreement with all the proposed changes, the Agencies applaud the CWWA for its efforts and proactive stance on this issue. The Agencies do not intend to restrict the use of geothermal systems, but rather desire to promote a safe handling of our natural resources for the benefit of all. This can be accomplished by avoiding unnecessary risks of potential contamination and by paying close attention to possible groundwater overuse situations.
Geothermal wells (also known as geoexchange systems) have two basic designs; open looped and closed looped systems.
In an open looped system groundwater is pumped from a water well into a heat exchanger located in a surface dwelling. 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 groundwater 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.
The general consensus on open looped wells is that they raise serious concerns regarding potential adverse environmental impacts. The installation of geothermal open loop wells (not the geoexchange system, but the actual well) is currently regulated as a water supply well as defined in CGS Section 25-126. The construction and abandonment procedures are delineated in the Well Drilling Code, while separation distances are listed in the Public health Code. Open loop geothermal well discharges have been regulated through the DEP’s General Permit for the Discharge of Non-Contact Cooling and Heat Pump Water. The permit states “discharge of minor non-contact cooling water to groundwater shall be derived solely from once-through heat exchange systems or condensate which does not receive chemical additions of any kind and which uses on-site groundwater, public water, or surface water as source water.” Heat pumps used for residential buildings with flows under 50,000 gallons per day of groundwater are exempt from registration. Sites with existing groundwater contamination require a case by case site review and must receive written approval from DEP prior to construction.
Large open loop systems (those drawing greater than 50,000 gallons per day of groundwater) require a diversion permit and an individual wastewater discharge permit from the DEP. Authorization under a diversion permit is available for those wells withdrawing between 50,000 and 250,000 gallons per day of groundwater as long as they meet certain strict provisions regarding potential effects on water resources within the well’s area of influence.
The Agencies’ major concern is protecting the groundwater resource as the potential for open loop systems causing contamination of the aquifer is great. Open loop systems could have many potential problems:
In a closed looped system, an opening (either a borehole or trench) is made in the Earth. A series of pipes are installed into the opening and connected to a heat exchange system in the dwelling. The pipes form a “closed loop” (hence the name) 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 looped system, except there is no pumping of groundwater.
The major types of closed looped systems are horizontal loop, vertical loop, and pond loop.
In a horizontal loop (see figure on left) a trench is dug (3-6 foot depth). A series of parallel pipes is laid in the trench, which is then backfilled so as not to damage the pipes. The pipes are connected to the heat exchanger and heat transfer fluid is circulated through the pipes. Variations of this system include using a “slinky” (coils) of pipes (as seen on the left) instead of straight pipe.
If the area of disturbance is large enough, construction of horizontal closed loop systems may need to be registered with the DEP’s Permitting and Enforcement Division under the General permit for Storm water and Dewatering Wastewaters from Construction Activities. This general permit applies to construction activities that result in the disturbance of one or more total acres of land area on a site. For construction projects with a total disturbed area between one and five acres, the permittee is required to adhere to the erosion and sediment control land use regulations of the town in which the construction is located.
No DEP registration of this permit shall be required for such construction activity as long as it receives review and written approval by the town. In those instances where there is no town review or the total disturbed area is greater than five acres, registration with the DEP is required.
Vertical loop systems (see figure on right) require a borehole that typically extends several hundred feet beneath the surface. Pipes are installed with U-bends at the bottom of the borehole. Again the pipes are connected to the heat exchanger and heat transfer fluid is circulated through the pipes.
In a pond loop system (see figure on left) a body of surface water such as a pond or lake is used as the heat source or sink. A trench is dug from the dwelling to the pond and piping is run form the heat exchanger into the pond and back. Typically a coil of piping is placed in the pond to increase the efficiency of the system.
Construction and operation of a closed-loop pond system is subject to the jurisdiction of the Inland Wetlands and Watercourse Act (Sections 22a-36 through 22a-45a of the CGS). The local inland wetlands and watercourses agency would regulate privately-owned closed loop pond systems while such systems proposed by State agencies would be regulated by DEP’s Inland Water Resources Division. Regulated activities include, but are not limited to, filling or excavation within the pond, or any harmful thermal effect resulting from the ongoing operation of the system. In addition, certain activities taking place within an “Upland Review Area” adjacent to the pond could be regulated by a local wetland and watercourse agency.
If construction of the system involves placement of more than 5,000 square feet of fill into the waters of the United States, the activity may fall under the jurisdiction of Section 404 of the Federal Clean Water act administered by the United States Army Corps of Engineers (the Corps). If such jurisdiction is assumed by the Corps, a Section 404 permit can’t be issued by the Corps until DEP’s Inland Water Resources Division issues a Section 401 Water Quality Certificate certifying that the “discharge” of the fill is consistent with Connecticut’s water quality standards.
Special Act 06-6 requires recommendations regarding boreholes used for the development of closed loop geothermal heat pumps or similar systems. Although boreholes are only used with closed loop vertical systems, commentary and recommendations are also given for all geothermal systems concerning construction materials, heat transfer fluids, and separation distances.
As stated previously, protection of groundwater resources and Connecticut’s drinking water are the primary concern. Anytime a borehole is drilled into the Earth, the potential for contamination of the groundwater is increased exponentially. Surface contaminants can be channeled directly into the groundwater through leaks and cracks in the grout used to seal the geothermal well. Wells can be damaged through movement of heavy equipment on the surface during and after well construction. Leaks in the piping could allow the heat transfer fluid to enter the groundwater. Wells installed near sources of pollution, such as septic tanks, leaching fields, sewer laterals and associated pumps, and underground fuel tanks may allow pollutants to contaminate the groundwater and endanger the public health. Additionally studies have shown that larger closed loop systems affect the temperature of the aquifer resulting in an increase in the overall bacteria counts in the groundwater (1). Therefore there is a potential for the promotion of pathogenic microorganisms. A borehole can also act as a connection between different aquifers or a zone of contamination and an aquifer. This would allow contaminants to flow into an uncontaminated aquifer, resulting in contamination of both aquifers.
Heat transfer fluids are an important concern with geothermal wells. The concerns are not only limited to vertical systems, but horizontal and pond loop systems as well. If a system should leak or fail, allowing the heat transfer fluid to leak into the environment, not only might the aquifer become contaminated, but also significant costs could be incurred to the property owner for cleaning up any contaminated soil and remediating any damage to the aquifer. The types of heat transfer utilized should be non-toxic materials such as potable water, and Aqueous Solutions of Potassium Acetate or Propylene Glycol not to exceed 20% by weight. Also, owners of geothermal systems should obtain insurance in case of systems causing contamination. Routine pressure testing of the systems should be done to ensure no leaks have developed.
The Public Health Code specifies separation distances for drinking water wells, sub-surface sewage (septic) systems, drains, etc. The separation distances were developed to provide adequate protection of drinking water supplies from sources of contamination. The distances are based upon the time it would take probable contaminants to migrate from the source of pollution to the well taking into account the natural attenuation factors. Section 19-13-B51(d) of the Public Health Code states that drinking water wells shall “be as far removed from any known or probable source of pollution as the general layout of the premises permit; and so far as possible, be in a direction away from groundwater flow from any existing or probable source of pollution.” Separation distances vary based on the type of structure, groundwater withdrawal rates, and manner of construction.
The following separation distances are required for geothermal closed loop boreholes and trenches associated with horizontal closed loop systems, per Section 19-13-B103 of the Public Health Code as listed in the Technical Standards for Subsurface Sewage Disposal Systems Section II(A) Table 1.
Geothermal Closed Loop Borehole and Horizontal Loop Separation Distances. (All Distances Measured Horizontally):
Geothermal Separation Distance
|Private Water Supply well, withdrawal rate < 10 gal/min||25 Feet|
|Private Water Supply well, withdrawal rate > 10 gal/min||50 Feet|
|Public Water supply well, withdrawal rate <10 gal/min||25 Feet|
|Public Water Supply well, withdrawal rate >10 and <50 gal/min||50 feet|
|Public Water Supply well, withdrawal rate > 50 gal/min||200 Feet|
|Source of Pollution (subsurface sewage, leaching field, grinder pump on sewer lateral, known releases of hazardous materials, structures or containers (tanks) of hazardous substances located above or below ground or other known source of contamination)||50 Feet. A separation distance of 25 feet may be used for septic tanks that meet the performance testing criteria specified in Section V(A)(6) of the Technical Standards for Subsurface Sewage Disposal Systems|
|Separation Distance from high water mark of any surface water body or drain carrying surface water or of a foundation drain||10 Feet|
Separation distances for open loop systems shall follow the current distances set forth in Section 19-13-B51(d) of the Public Health Code. Distances from open looped geothermal wells to water supply wells should be the same as specified in Table 1 of Section 19-13-B51(d) of the Public Health Code.
It can be expected that at some point in time any geothermal system will be put out of service. When this occurs the well must be properly abandoned in order to protect groundwater. The procedure used for abandonment should be the same as is currently in the Well Drilling Code with a few modifications. Initially the heat transfer fluid must be removed via displacement with grout. The fluid should be collected and disposed of according to current State and Federal regulations. Closed loop geothermal wells do not have a cap over the vertical section of the well that prevents water from defusing into the well. On abandonment the top of the borehole should be uncovered and capped with grout.
As of October 1, 2002, pursuant to Section 3 of Public Act 02-102, the district has been authorized to issue permits for the installation of a water supply well on residential premises for irrigation or other outside purposes. However, where a residence is connected to a community water supply system and a new well is installed for irrigation or other outside uses, the well may not be used for human consumption and the domestic supply must be provided with a reduced pressure device to protect the public supply from contamination. In addition, a residential property owner receivihg a well drilling permit for irrigation purposes, or other outside uses, pursuant to Public Act 02-102, must notify the community water supply system prior to the installation of the reduced pressure device in accordance with RCSA Sec. 19-13-38a(f)(6). In order for our department to review and approve such a well, the following information must be submitted:
The following requirement must be met before approval of the permit can be granted:
The follwing requirements must be adhered to at all times in order to protect the public water supply:
In cases where Ethylene Dibromide (EDB) is present in the area, EPA test method 504.1 is required including testing the water for EDB, 1, 2, 3-trichloropropane (TCP) and 1, 2-dibromo-3-chloropropane (DBCP). Where nitrates are present equal to or above 10 mg/l, EPA test method 505 (organochlorine pesticides) and method 555 (chlorinated herbicides) water tests are recommended by the State Department of Environmental Protection. The following minimum tests are required: alachlor, atrazine, dicamba, ethylene dibromide, metolachor, simazine and 2, 4-D.