This project proposes a strategic intervention in the Campo de Gibraltar aimed at restoring the functional capacity of coastal aquifers degraded by saline intrusion. The initiative responds to clear evidence that a large number of abandoned or illegal wells—resulting from decades of unregulated groundwater extraction—are acting as vertical corridors of contamination, connecting brackish layers with freshwater underground bodies. This situation not only compromises the quality of water available for industrial and agricultural use but also weakens the natural storage capacity of the subsurface and exacerbates the impacts of climate change on regional water availability.
The proposed solution is based on a multistage intervention that combines advanced remote sensing technologies, field validation using geochemical sampling equipment, hydraulic sealing techniques with sustainable materials, and applied bioengineering to establish new zones of controlled rainwater infiltration. Through this approach, the project aims to restore the natural hydrodynamic pressure of the aquifer, prevent the inland migration of saline fronts, and enable safe recharge zones, generating measurable benefits under the Volumetric Water Benefit Accounting (VWBA) and Water Quality Benefit Accounting (WQBA) methodologies, with full technical traceability and independent verification.
The Campo de Gibraltar is experiencing progressive degradation of its coastal aquifers due to three interrelated factors that compromise both hydrological function and water security:
Historical overexploitation of deep wells, most of which were drilled without technical records or administrative control. This excessive and uncoordinated extraction has led to a systematic drop in piezometric levels, reducing the aquifer’s ability to act as a natural barrier to seawater intrusion.
Saline intrusion caused by reversed pressure gradients, resulting from overextraction and a lack of effective recharge. The drop in the water table disrupts the balance between freshwater and saltwater in coastal systems, allowing the saline wedge to move inland, contaminating previously usable sectors for supply or agriculture.
Urban and peri-urban surface sealing, which prevents natural infiltration of rainwater. Urban development in industrial and residential areas has eliminated traditional diffuse recharge mechanisms, disrupting the connection between rainfall events and effective aquifer replenishment.
Many of the wells—both active and abandoned—currently function as critical entry points for saline or polluted water into shallow and deep aquifers. The absence of proper sealing and monitoring allows for unwanted vertical mixing between water layers, deteriorating the overall quality of the resource. This degradation not only limits the direct use of water for industrial, agricultural, or ecosystem purposes but also increases treatment costs and reduces the region’s hydrological resilience under conditions of climate-exacerbated stress.
The project operates on three coordinated fronts, articulating a technical-operational strategy to identify, intervene, and restore the affected aquifer:
Remote detection and technical validation: A systematic mapping effort is carried out using multispectral satellite imagery (Copernicus Sentinel-2), infrared thermal sensors, and LIDAR-equipped drones. These tools help identify thermal depressions, surface moisture variations, and linear features indicating the presence of active or abandoned wells. The resulting geospatial models are validated on-site through inspections, geolocation of water intakes, and initial physico-chemical sampling.
Physical intervention: Prioritized wells are sealed technically by injecting bentonite slurries or polymer resins into confined layers, depending on soil type and depth. This operation includes mechanical cleaning, borehole profiling, and staged sealing to ensure hydraulic separation between layers. All procedures follow environmental permitting and are carried out under the protocols of the Hydrographic Confederation or competent authority. Each intervention is documented for traceability and auditing purposes.
Managed recharge zones: In areas where natural infiltration historically occurred or in undeveloped lands, artificial recharge areas are designed using green infrastructure. These include biofilters composed of siliceous sand, gravel, and native coastal vegetation that act as living filters. Infiltration is regulated using surface distribution systems such as swales or infiltration trenches, designed to maximize slow recharge during rainfall events while offering temporary retention and runoff control.
The project is implemented in five successive technical stages, with continuous and integrated development of measurement, control, construction, and verification activities. These stages are designed to ensure both volumetric water benefits and water quality improvements in accordance with VWBA A-5 and WQBA standards.
During the remote diagnosis phase (0–2 months), the target area is characterized using multispectral satellite imagery (Sentinel-2) and high-resolution aerial thermography. This stage allows the detection of thermal anomalies, surface moisture changes, and linear features on the terrain that may indicate the presence of active, semi-abandoned, or illegal wells. The data are processed using geostatistical analysis tools and overlaid onto GIS layers covering land use, hydrogeology, and existing infrastructure. Variables such as NDVI, SWIR reflectance, and surface temperature are measured, enabling the generation of a georeferenced inventory of hydrological risk points and the establishment of a spatial baseline.
In the field campaign and sampling phase (2–4 months), the information generated in the remote diagnosis is validated on-site. Multiparametric probes are used to measure electrical conductivity (EC), temperature, salinity, and groundwater level in situ. A representative set of groundwater samples is collected for laboratory analysis focusing on chlorides, nitrates, sulfates, turbidity, and heavy metals. Active and abandoned wells are documented with precise coordinates, and a hydrogeological risk index is created based on depth, vertical connectivity, vulnerability to saline intrusion, and proximity to water bodies or urban areas.
The intervention design phase (3–5 months) includes a tailored technical formulation for each well to be sealed: depth, sealing method (bentonite, cement grout, or resins), access logistics, regulatory requirements, and work schedule. Simultaneously, managed recharge zones are designed using hydraulic modeling of the terrain, native vegetation selection, soil conductivity analysis, and rainfall event simulations to estimate potential infiltration rates. Key performance indicators (KPIs) are established, and a governance model for the construction phase is formalized.
During the technical sealing and construction phase (6–10 months), the selected wells are hydraulically sealed to eliminate uncontrolled vertical flows between aquifer layers. Each intervention is documented with technical sheets, georeferenced photos, and traceability of materials used. At the same time, recharge zones are implemented using siliceous sand biofilters and native coastal vegetation, designed as artificial wetlands or infiltration trenches with runoff control. Infiltrated flows begin to be measured using pressure sensors in monitoring chambers, and piezometric dataloggers are installed.
The continuous monitoring phase (10–24 months) includes the operation of an IoT sensor network that records variables such as groundwater level, EC, aquifer temperature, rainfall, and infiltrated flow. This network connects to a digital platform for data visualization and analysis, enabling real-time validation of project objectives. Monthly sampling is conducted to assess the evolution of groundwater quality, compared against the established baseline.
In parallel, the WQBA approach quantifies water quality improvements as the percentage reduction of contaminants compared to their baseline concentrations. A valid improvement is one that is consistent, verified by external laboratory testing, and maintained over at least three consecutive quarters.
Both the VWBA and WQBA methodologies are verified through external audits by accredited entities. Results are reported on the Aqua Positive platform using unique Water Benefit IDs (VWB IDs), ensuring transparency, comparability, and reputational value for stakeholders.
This project was conceived as a technical, environmental, and strategic response to the increasing degradation of coastal aquifers in the Campo de Gibraltar. It addresses the legacy of historical overextraction, unsealed and uncontrolled wells, and the saline intrusion associated with declining water tables. Against the backdrop of industrial pressure, coastal urbanization, and climate vulnerability, this initiative seeks to restore the hydrogeological balance of the subsurface by detecting, intervening in, and repurposing critical points of water loss and contamination.
The central objective is to identify, characterize, and technically seal abandoned, illegal, or disused wells that serve as vertical conduits for saline water intrusion, while simultaneously establishing new managed recharge zones to enhance natural rainwater infiltration. These actions are developed through an integrated water benefit accounting approach, combining VWBA to quantify effective recharge and WQBA to assess groundwater quality improvements.
Implementation begins with remote diagnosis using multispectral imaging (Sentinel-2), thermal analysis, and GIS modeling to map surface anomalies and generate a georeferenced inventory of potential risk points. Field campaigns with multiparametric probes and water sampling are then conducted to validate and prioritize wells based on their impact on aquifer quality. A piezometric and physico-chemical baseline is also established.
Following this characterization, a technical intervention plan is developed, including individual hydraulic sealing of each well using materials such as bentonite grout or expandable resins, depending on depth and geology. Recharge zones are created using vegetated biofilters, infiltration trenches, and runoff management systems. These zones function as green infrastructure to restore the aquifer’s hydrological balance, with real-time monitoring of infiltration flows and groundwater levels.
The final phase includes continuous monitoring for at least 24 months, utilizing IoT sensors, external audits, and reporting on platforms like Aqua Positive. Each benefit is assigned a traceable VWB ID and independently validated for additionality and permanence. In doing so, the project not only restores an essential ecological function but also enables the generation of Positive Water Credits (CAPs), which can be integrated into corporate water offset schemes.
In essence, is a model for advanced hydrological restoration in coastal water-stressed areas, with potential for national and international replication, and strong added value in terms of water sustainability, climate resilience, and collaborative groundwater governance.
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