Edited by the IMDEA Water Institute

Deep disposal of wastes from water treatment (brines or other concentrated solutions) consists in the injection and isolation of the waste in porous and permeable geological formations within which the fluid remains safely. Hence, the main objective of deep-well injection, as treated in this document, is the storage of a highly concentrated saline fluid in a deep geological formation that grants it stays in a stable and sealed condition.

This technology has its limitations and problems, as the injection of the waste in underground formations, can have negative effects.

The main intrinsic risk of this practice is regarding underground water resources if the waste becomes in contact with underground water reservoirs, however this practice can also decrease the availability of strategic or prospective resources, as raw energetic and mineral resources.

In addition to these intrinsic risks, other technical issues related to perforation and fluid injection have to be taken into account, i.e. when the concentrate is injected in the storage formation, it does not only becomes in contact with the storage rock, and mixes with the formations water, but also undergoes an increase of temperature and pressure.

It is necessary to stablish some basic criteria and requisites to be fulfilled when selecting the storage formation as well as during the remaining phases of the injection process. The complexity of any underground storage project makes it necessary to evaluate each individual case, making it possible to set up security and environmental protection criteria to be applied for all cases. In this manual we stablish guidelines criteria and recommendations for each phase of the injection project, spanning from the selection of geological formations adequate for subterranean placement of the waste, to the closing of an injection well.

This manual, edited by the IMDEA Water Institute, aims to put together all security recommendations based on previous studies and injection experiences. These represent minimum criteria, and the specificity of the injected fluid and geological conditions of each particular case could determine the adoption of additional criteria for each case.

The goal of this manual and the guidelines presented in it is the assurement of a safe deep injection well that allows the preservation of underground resources (i.e. underground water), and assure the efficiency of the injection avoiding damaging the storage formation.

Although there are several documents that analyse the security recommendations made for deep well injection of different wastes derived from water treatment processes such as recycling or desalination, this document intends to be a good practice manual that compiles all requisites and recommendations and basic guidelines necessary for making a deep well injection of different residues. For this we took into account the different phases of the process: Location selection, preliminary studies, design, authorization, well construction, operation and closure.