Aquifer Storage and Recovery

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Aquifer Storage and Recovery (ASR) is the process of injecting water into the ground for storage and later recovering that water for use. One common use of ASR is for management of peak demand and raw water supply in public drinking water systems. In this scenario, excess treated drinking water can be injected in periods when supply exceeds demand and can be recovered when demand exceeds the treatment plant's capacity. If a clean aquifer is used as the injection zone and the aquifer matrix and native groundwater are chemically compatible with the injected water, the recovered water should be roughly the same quality as when it was injected and thus should require only additional disinfection treatment prior to distribution to the public.

An injection permit is required for construction and operation of a well for ASR. In addition to this permit, a water supply well permit is required and the Public Water Supply Section of the Division of Environmental Health must approve of the use of the ASR well in a public water system, although issuance of the injection well permit is independent of these approvals.

Major issues that must be addressed in an ASR permit application include:

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Geothermal Heating and Cooling Injection Wells

new - Map of Known High Chloride Groundwater - bentonite grouts cannot be used in groundwater with chloride concentration >1,500 mg/L. To contribute to an updated map send well location, chloride concentration, and sample depth to Thomas Slusser.

BMP Guide for Managing Water Produced During Well Drilling

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What is Geothermal Heating and Cooling?

Conventional heating and cooling systems use air to transfer heat into and out of buildings.  Geothermal systems use the nearly constant temperature of the ground as a heat source in the winter and as a heat sink in the summer. Properly designed and installed, these systems can heat and cool efficiently.  Because these systems are often intimately connected with underground sources of drinking water, the North Carolina Underground Injection Control (UIC) Program of the Division of Water Quality regulates the construction and operation of  these systems in order to keep the ground water suitable for drinking.

What Regulations and Permits Do You Need to Know About?

Proper well construction and maintenance can protect human health and ground water quality, plus help avoid problems with heat pump system operation.  As with other well types, only certified well drillers are permitted to construct wells for geothermal heating and cooling systems; please refer to the Well Contractors Certification Commission for more information.  Additionally, only HVAC contractors licensed by the State Board of Examiners of Plumbing, Heating and Fire Sprinkler Contractors can install heat exchange tubing into a well or borehole.  Permits are required for some types of systems in order to make sure they are operating safely. The specific type of geothermal heat pump system determines what permits or notification are required.

Four Main Types of Systems:

• Open loop heat pump systems
• Vertical closed loop heat pump systems
• "Pump and dump" heat pump systems
• Horizontal closed loop heat pump systems

Open Loop Heat Pump Systems

Open loop heat pump systems operate by withdrawing water from a well, circulating it through the heating/cooling system, and returning the water to the source well or another well.  This system is often used with an existing water supply well and may use separate wells for water supply and water return or may use a single well for both supply and return.  The wells used for these systems have the same grouting and casing requirements as water supply wells. A permit application is required to be submitted and a permit issued in order to construct and operate this type of injection well.

Following receipt of an application for a permit for this type of well, an inspector will visit your site to determine its suitability for construction of the proposed injection well. If the application is approved, a permit for construction and operation of the injection well will be issued to you. After construction of the well and heat pump system is complete, the inspector will return to your site to inspect the well and collect samples of the system’s influent and effluent. If the effluent does not meet the State’s groundwater quality standards, you will be required to take action to identify and correct the problem; otherwise, you will be allowed to continue operation of the system as long as you keep the permit valid. Permits are usually issued for five year intervals.

Vertical Closed Loop Heat Pump Systems

Vertical closed loop heat pump systems operate by recirculating a liquid within continuous piping that is enclosed in a well.  The continuous piping exchanges heat with the subsurface without direct contact between the recirculating liquid and the subsurface. There are two distinct types of closed loop systems:

• “Direct Expansion” or “Direct Exchange” systems circulate refrigerant gas via copper tubing and typically have cathodic protection to prevent corrosion of the copper tubing.
• Aqueous systems circulate potable water only or water with performance-enhancing additives such as antifreeze, biocide, or corrosion inhibitor via HDPE or types of materials specified in the NC Mechanical Code. 

 A State permit is not required, but a well construction notification form must be submitted prior to construction.  Closed-loop geothermal heat pump injection wells of either type must be grouted the entire length of the borehole. Bentonite grout or “thermally enhanced” bentonite-sand grout mixtures may be used as long as the groundwater does not contain chloride concentrations of 1500 mg/L or greater. In addition to these State requirements, your county or municipality may have additional requirements for construction and operation of geothermal heat pump systems.

"Pump and Dump" Heat Pump Systems

So-called “pump and dump” systems are heat pump wells that withdraw groundwater but do not re-inject the heat pump effluent. They are regulated only as water supply wells under 15A NCAC 2C .0100, “Well Construction Standards – Criteria and Standards Applicable to Water Supply Wells and Certain Other Wells”. No State permit is required for these systems unless the total design flow rate is greater than or equal to 100,000 gallons per day. You should check with your county and municipal authorities for any other applicable rules and regulations. 

Horizontal Closed Loop Heat Pump Systems

Horizontal closed loop heat pump systems operate just like vertical closed loop systems except that the continuous piping is placed in trenches in the ground.  A variation of this type has the piping located in a pond or lake, exchanging heat with the water body instead of the ground.  A permit is not required for this type of system, but you should check with your county and municipal authorities for any other applicable rules and regulations.

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In Situ Groundwater Remediation

 Injection wells are typically used for groundwater remediation in the following ways: 

• Injection of remediation compounds
• Air sparging
• Tracer injection
• Aquifer hydraulic testing

Injection of remediation compounds

Substances are injected to chemically or biologically degrade contaminants, or to assist in their physical removal by recovery wells.  Many smaller projects are permitted by rule and only require submittal of a notification form.  Other larger projects require submittal of a permit application and issuance of an individual permit before injection or well construction can begin.  Click here for a list of approved injectants.  If you do not see the substance you are considering for injection on this list, you must fill out the appropriate risk assessment evaluation form when submitting an injection well permit application or notification form.  Any new substance to be injected must be reviewed by the Occupational and Environmental Epidemiology Section (OEES) of the Division of Public Health, Department of Health and Human Services.  

Air sparging

Ambient air is injected under pressure into a well in order to volatilize contaminants and to stimulate aerobic bioremediation. No injection well permit is required; however, notification is required 2 weeks prior to injection.  Additionally, well construction and abandonment reporting forms are to be submitted within 30 days.

Tracer injection

An aqueous solution containing a dye or chemical tracer is injected into a well and its presence is monitored at monitoring or recovery wells in order to determine groundwater flow paths. Many smaller projects are permitted by rule and only require submittal of a notification form.  Other larger projects require submittal of a permit application and issuance of an individual permit before injection or well construction can begin.  Click here for a list of approved injectants.  If you do not see the substance you are considering for injection on this list, you must fill out the appropriate risk assessment evaluation form when submitting an injection well permit application or notification form.  Any new substance to be injected must be reviewed by the Occupational and Environmental Epidemiology Section (OEES) of the Division of Public Health, Department of Health and Human Services.

Aquifer hydraulic testing

These wells are used to estimate aquifer parameters by hydraulic slug testing or in situ constant head permeability testing. No injection well permit is required for construction or operation of an aquifer test well, but the injected fluid must be uncontaminated and the operation of the well must not cause contaminated groundwater to migrate into previously uncontaminated areas or cause an exceedance of groundwater quality standards.

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