Clogging of artificial recharge systems is a ubiquitous problem. It consists of porosity or infiltration area diminution induced by inter-related physical, biological and chemical processes, resulting in a decrease of recharge effectiveness. Clogging is a highly site-dependent phenomenon. As a consequence, clogging prevention and redevelopment are commonly addressed by resorting to previously reported practices. However, serious reductions can occur if there is a lack of experience or if special problems exist. Based both on a thorough literature review and on field investigations from certain European countries, several recommendations and operating guidelines are presented. These include identification of basic parameters, preventive and re-development techniques, specifically defined clogging-tools and limitations on a few magnitudes. Such recommendations should represent a good starting point in order to prevent clogging, although it is evident that pilot field tests are always unavoidable when accurate clogging estimates are needed.

Several tests are currently under execution at the Cornelia site within the framework of an European Project. One of the existing Aquifer-Storage-and-Recovery (ASR) wells was previously selected to perform specific experiments. The main objective is to study clogging around the ASR well itself, although redox reactions and water-aquifer material interactions are also being examined. Three different tasks were scheduled: analysis of recharge water and groundwater, analysis of soil cores, and completion of field tests. Both water and soil investigations served to obtain the basic parameters, to identify the aquifer characteristics and to assess some clogging-related properties. Still, natural heterogeneity and main hydraulic connectivity can not be derived through laboratory analysis. Therefore, various field tests are being carried out. The approach presented here is innovative as regards two aspects: first, a-priori relevant clogging parameters have already been measured, and, second, specifically derived numerical codes will be applied to obtained data.

Clogging is one of the most troublesome phenomena concerning Artificial Recharge. Different approaches exist in dealing with clogging, such as the measurement of specific parameters and determination of correlations, as well as empirical models. More sophisticated models have also been suggested in order to overcome the limitations of more simplistic methods. However, because clogging is affected by several mechanisms, a comprehensive model was not previously available. A new generic model is presented in this paper, which includes five fundamental processes: accumulation of suspended sediments, bacterial growth, chemical reactions (precipitation/dissolution), generation of gas, and compaction. As well as the mathematical framework, a brief description on the numerical implementation is given. An application of the model to a synthetic example, where a limestone confined aquifer is recharged by more acidic water that contains suspended sediments, is presented. This example shows how two processes, both of a very different nature, can modify the aquifer's effective porosity and, hence its permeability. Other issues, such as the validity of the conceptual model, its limitations and future work, are briefly discussed.

Evidence of the importance of clogging at many artificial recharge sites has led to the numerical implementation of an integrated mathematical model. The code, termed CLOG, pays attention to the most relevant clogging processes by considering three dimensional multiphase flow and reactive transport of suspended particles and solutes, and the associated porosity variations. A number of synthetic and real examples are currently being studied in order to determine the performance of CLOG. This paper presents the results obtained after validation of the model against laboratory and field data. The sensitivity of the simulations to the model parameters was also investigated in order to identify the more influential factors. This analysis confirmed that the kinetic rates and the apparent density of the clogging layer are critical. Furthermore, the issue of prediction is succinctly discussed, given the interest for design purposes. It is expected that existing generic tight guidelines could be relaxed and adapted to the prevailing site conditions.

Clogging of groundwater Artificial Recharge systems is a very ubiquitous problem that affects numerous recharge facilities and can have dramatic technological and economic impacts. A quantitative approach to clogging is presented in this paper by describing a new comprehensive numerical model.The current version of this code, termed CLOG, has been obtained by using two existing codes, one for multiphase flow and the other for reactive transport, and by adding specific clogging subroutines. As a result the model is capable of treating the basic clogging processes: transport of particles, bacterial growth (attached to the medium), chemical reactions (homogeneous and heterogeneous kinetics, with biocatalysed paths), gas flow, and compaction. Therefore, the code is integrating the elementary processes, as determined by numerous experiences.This paper summarises the numerical structure of CLOG, focusing on the implementation of the clogging-related issues. A real example is enclosed with the aim of remarking its capabilities and, also, discussing which are the main limitations. Finally, a rapid discussion of future trends and modifications is done.