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:
- A complete water quality analysis of the water to be injected (all National Primary and Secondary Drinking Water Standards) as well as a basic water quality analysis of native water in the aquifer.
- Modeling of potential reactions between the injected water and native waters and between the injected water and aquifer matrix. Modeling should evaluate the potential for oxide formation, swelling of clays, and other adverse water quality and aquifer reactions.
- Monitoring at points other than the ASR well itself.
- Disinfection by-products and disinfectants are the only compounds currently allowed to exceed 2L standards in the injected water, but this is only justified on the basis that the injected water is treated drinking water to be recovered and used as treated drinking water.