Ground-source Heat Exchange (GHEX) Borehole Drilling
Geothermal heat pumps systems (sometimes referred to as GHEX, GeoExchange, earth-coupled, ground-source, or water-source heat pumps) have been used for several decades in Iowa to help Iowans’ utilize the natural thermal properties that exist under their property.
Ground-source Heat Exchange Systems (GHEX systems) use the constant temperature of the earth as the exchange medium instead of the outside air or well water source to maintain a constant temperature. The GHEX system takes advantage of this by exchanging heat between the home or business and the ground through the use of a series of ground heat exchanger loops. This allows the system to operate at a very high efficiency using only a minor amount of electricity.
There are four basic types of geothermal heat exchange systems found in Iowa.
Three of these - horizontal loop, vertical loop, and pond/lake loop are closed-loop systems where the heat exchange fluid is circulated in a loop of piping placed in either a borehole in the earth or in a large body of water. The fourth type of system is actually a water-source heat exchange system and is called an open-loop system. This option uses one or more water supply wells to pump groundwater out of the earth and run the water through a heat exchanger in the building. The water that has been heat altered in the process is then placed onto the land surface or back into the aquifer through one or more additional water wells. Which type of system you install will depend on the contractor, the size of the application, the soil and geological conditions of the site, available land to place a system, and local site specific conditions that may limit the site for drilling operations like areas of contamination, local ordinances, or easement boundaries.
All closed loop systems placed 20 feet or greater in the ground and all open loop systems require the issuance of a private well construction permit before any loop drilling, trenching, or boring takes place. These systems also require the use of a certified well contractor and the use of defined construction standards. Depending on the actual drilling location, there may be additional requirements put in place to help manage fragile geological conditions, localized contamination and protect the state's drinking water aquifers.
In Iowa, GHEX closed loop systems currently make up 33% of the private well construction permits issued.
Closed loop boreholes require minimum setbacks from sources of contamination. The current setbacks can be found at the following web link: GHEX borehole setbacks.
Before You Plan Your GHEX Project and Start to Drill GHEX Boreholes
It is important for you, the department and the driller to know if the proposed GHEX borehole site can actually be drilled for the installation of GHEX loops. Even though all sites in our state have the potential for GHEX loop borehole systems to function properly, there are many sites in our state that should not be drilled because of pre-existing conditions and hazards.
One example is when your property is near one or more public water supply wells. If you have a public water supply well within 400 feet of your property, it will be difficult for you to install a GHEX systems due to the federally required setbacks between public water wells and private drilling activities. In addition, some communities may not allow the installation of GHEX boreholes due to local ordinances or other restrictions.
Additional examples are sites that are currently used for or were historically used for various industries. Iowa has a long history of industrial growth, technological advancements and progress. Progress of this type does not come without the use of raw materials, chemicals and fuels required by industry. One of the common issues that we encounter when looking at individual sites is that the site contains some form of contamination that may be limited to the footprint of the site or possibly even extend beyond property lines and onto nearby properties. When this happens it is difficult to find a location where the contamination does not pose a threat to the groundwater and/or the piping used in GHEX systems.
Here are some of the issues that we have experienced that may limit drilling on your site:
- Liquid hydrocarbon storage tanks - leaking tank sites or areas of spills. Gas stations, fuel depots, rail yards, etcetera.
- Landfills and dump sites both privately owned and community owned.
- Industrial and machine districts - even if the work no longer takes place. Factories, power generation, rail yards, etcetera.
- Ferrous and non-ferrous metal works including foundries, manufacturing/fabrication, and metal plating.
- Wastewater treatment infrastructure. Lagoons, sludge storage and application areas, etcetera.
- Ag and industrial chemical manufacturing, mixing, storage and loading areas.
- Consumer service areas like dry cleaning sites, automotive service, repair and body shops, pesticide services, etcetera.
- Many other contamination scenarios based upon manufacturing, storage and transport of goods.
- Local ordinances that limit drilling within a community.
All proposed GHEX sites that may contain contaminants require a more thorough review and construction plan. There are even cases when vertical boreholes may not be an option due to the type and extent of contamination on the actual property proposed for drilling or adjoining properties. If a detailed review is not performed in these scenarios, installation cost, inconvenience and liabilities increase for both the property owner and the drilling contractor and can ultimately result in increased monitoring requirements and wasted money and time. It is important to remember that a GHEX system may not be the most economical long-term solution on a site that requires extensive review, greatly increased construction standards, ongoing monitoring requirements and questionable long-term durability of the system piping when exposed to contaminants.
It is the responsibility of the property owner to initiate the site review process and to work with a groundwater professional and the department to determine the actual risks of drilling at the proposed location. There may be properties that will not be able to utilize GHEX systems due to pre-existing site contamination issues.
The Karst Geology Variable
One additional consideration for the construction permitting and placement of GHEX loop borehole fields is Karst geology
. Karst areas may be subject to additional requirements before the site can obtain construction permitting. In general, Karst sites require the use of more stringent construction standards to ensure that poor quality surface water and shallow groundwater do not reach the deeper protected drinking water supplies.
The additional standards can include a more detailed site survey and site analysis, geological investigation and profiling, the installation of test boreholes to collect and interpret geological and aquifer data, hydrogeological modeling, increasing setbacks from sources of contamination, setting specific minimum construction and grouting standards tailored to the geology and hydrology present under the construction site, and the use of long term monitoring to watch for ground settling and groundwater contamination.
When looking at the overall protections that GHEX boreholes require, full depth grouting for all boreholes is one of the most important steps you can take to protect the groundwater resource. It also helps your geothermal system perform with high efficiency which reduces your total operational lifecycle costs. You should hire only contractors who agree to utilize full depth grouting for your proposed borehole installation as they are vested in providing a quality service that helps your system work as designed and helps protect the groundwater used by your family and others.
Additional information regarding Karst geology in Iowa can be obtained from the Iowa Geological and Water Survey
For more information about how to determine if your property is suitable for GHEX or water supply well drilling please contact the Iowa DNR Private Well Program at 515-725-0462.
For additional information on GHEX systems please consider viewing the following pages:
IGSHPA - The International Groundsource Heat Pump Association - A national trade organization to develop, refine, and promote heat pump installations worldwide.
ASHRAE - The American Society of Heating, Refrigerating, and Air-Conditioning Engineers. A national trade organization to promote all heating and cooling systems including geothermal and ground source heating and cooling systems.
GeoExchange - A national organization to promote the manufacture, design and installation of GeoExchange® systems
- For more information contact -
Russell Tell, Environmental Specialist Senior
Wallace State Office Building
502 E. 9th Street
Des Moines, IA 50319-0034
(515) 725-0462 or by Fax: (515) 725-0348