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Geological model
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To determine the probable location of the aquifer, the layers exposed during excavations are analyzed and correlated with available geological information. This process helps develop a model describing the soil structure and identifying the hydrogeological features associated with the aquifer.
ID:(163, 0)
Basis of a soil model
Description
With the general information about the geological structure of the area, it is possible to estimate the probable configuration of the soil in the construction area. For this, the topography must be surveyed, producing profiles such as:
Profiles near the fence and on both edges of the embankment
Geological Data
• Base of the area: Composed of PzTrbm(a), a soil with high compressive strength, low porosity, and low permeability, forming a stable foundation.
• Surrounding hills: Composed of sediments from Msd1 (compacted silts and clays) and Msd2 (sandstones, siltstones, and conglomerates), which are susceptible to erosion from rain and surface runoff, being transported to lower areas.
• Mixing zones: The interaction between Msd1 and Msd2 creates areas with higher porosity and permeability, potentially allowing the formation of an aquifer.
Structure Study
To model the soil structure, reference points such as a calicata (test pit) are required. In this case, soil removal has generated long and deep cuts that provide insight into the soil structure:
Positions of the cuts available for study
ID:(972, 0)
Analysis of the upper profile
Description
The upper profile is located on the upper embankment, near the container:
Location of the upper profile
The cross-section shows two clearly distinct layers with noticeable differences in morphology and a well-defined dividing line in several sections. The layers differ significantly in their moisture content:
| Layer | Estimated moisture |
| Upper | 60% |
| Lower | 30% |
Upper profile (distorted due to angle and position changes during photography)
Detailed Observation of the Section
Detail of the upper profile
Conclusions by Layer
Upper Layer
The high moisture content and moss growth indicate a strong water retention capacity. This may be due to:
| Observation | Comment |
| Soil texture | Likely clayey or silty, which enhances water retention. |
| Low permeability | Inefficient drainage to the lower layers allows water to accumulate. |
| Surface accumulation | Likely caused by recent rainfall or poor infiltration due to soil characteristics. |
| Organic matter | The dark brown color suggests high levels of organic matter, which also contributes to water retention. |
Lower Layer
The lower moisture content and less cohesive texture suggest contrasting characteristics:
| Observation | Comment |
| Sandy texture | A higher proportion of sand or gravel promotes drainage and reduces water retention. |
| Transition zone | This may be a horizon connecting to more permeable materials, facilitating water flow. |
| Hydraulic disconnection | A possible lack of continuity with the upper layer limits vertical water movement. |
| Lighter color | Indicates lower organic matter content and reduced retention capacity, typical of looser or granular soils. |
ID:(969, 0)
Analysis of the lower profile
Description
The lower profile is located on the upper embankment, near the container:
Location of the lower profile
The cross-section reveals two clearly distinct layers in terms of morphology and moisture content:
| Layer | Estimated moisture |
| Upper | 30% |
| Lower | 60% |
Lower profile (distortion due to angle and position changes during photography)
Detailed Observation of the Section
Detail of the lower profile
Conclusions by Layer
Upper Layer
The upper layer exhibits characteristics of well-drained soil that acts as a transit zone for water moving toward deeper layers:
| Observation | Comment |
| Moderate moisture | Retains some water but allows good drainage downward. |
| Light brown to ochre color | Indicates the presence of iron oxides, typical of well-oxygenated soils and consistent with the observed moisture levels. |
| Sandy or loamy-sandy texture | These textures have lower water retention capacity and promote vertical water flow. |
| Good aeration | Porous spaces facilitate water movement downward, suggesting this layer does not act as a significant barrier to drainage. |
Lower Layer
The lower layer has higher water retention, indicating significant accumulation capacity due to its composition and proximity to the water table:
| Observation | Comment |
| High moisture close to saturation | Suggests this layer serves as a water accumulation zone, retaining infiltration from above. |
| Presence of silt and clay | These materials contribute to lower permeability, slowing down drainage. |
| Rock fragments and denser materials | Observed in the image, these may act as a partial barrier to drainage, trapping water in this layer. |
| Capillary fringe or water table proximity | The high moisture levels and behavior suggest this layer could be part of the capillary fringe or close to the water table. |
ID:(970, 0)
Sample from the upper profile: top layer
Description
A soil sample extracted from the top layer of the upper profile displays the following color:
Additionally, its microscopic structure appears as follows:
The estimated density of the sample in its undried state is 5.2 g/cm3.
ID:(984, 0)
Sample from the upper profile: bottom layer
Description
A soil sample extracted from the bottom layer of the upper profile displays the following color:
Additionally, its microscopic structure appears as follows:
The estimated density of the sample in its undried state is 2.4 g/cm3.
ID:(985, 0)
Sample from the lower profile: top layer
Description
A soil sample extracted from the top layer of the lower profile displays the following color:
Additionally, its microscopic structure appears as follows:
The estimated density of the sample in its undried state is 2.8 g/cm3.
ID:(987, 0)
Sample from the lower profile: bottom layer
Description
A soil sample extracted from the bottom layer of the lower profile displays the following color:
Additionally, its microscopic structure appears as follows:
The estimated density of the sample in its undried state is 5.6 g/cm3.
ID:(986, 0)
Soil model
Description
To build the model, it is necessary to study the properties of the soils Msd1, Msd2, and their mixture. In general terms:
| Msd1 | Fine particles (clays and silts) have a high water retention capacity due to their micropores. |
| Msd2 | Coarse particles, such as sands and gravels, have a lower water retention capacity due to their higher permeability. |
| Msd1 + Msd2 | The incorporation of sands reduces water retention, but a moderate capacity remains due to the silty content. |
Typical Properties of the Soils
| Soil | Porosity (%) | Permeability (m/s) | Moisture (%) |
| Msd1 | 5 - 15 | 1E-7 - 1E-9 | 30 - 50 |
| Msd2 | 25 - 35 | 1E-4 - 1E-6 | 10 - 20 |
| Msd1 + Msd2 | 15 - 25 | 1E-5 - 1E-7 | 20 - 35 |
| Parameter | Msd1 | Msd2 | Msd1 + Msd2 |
| Porosity (%) | 5 - 15 | 25 - 35 | 15 - 25 |
| Permeability (m/s) | 1E-7 - 1E-9 | 1E-4 - 1E-6 | 1E-5 - 1E-7 |
| Moisture (%) | 30 - 50 | 10 - 20 | 20 - 35 |
Conclusions Based on the Cuts
1. Upper layer:
There is a high-humidity layer at the surface with a defined boundary toward the underlying layer. This may be due to modifications introduced by the construction of the road.
2. Intermediate layer:
If the upper layer is assumed to be a recent deposit, the actual upper layer would correspond to the second layer, which shows low moisture, similar to that observed in the cut near the house. This suggests it could be a mixture of Msd1 (silts and clays) and Msd2 (sands and gravels).
3. Underlying layer:
The next layer shows higher moisture, which would indicate it corresponds predominantly to Msd1 (silts and clays). This layer is observed in specific areas, such as beneath the house (2), near the beach (3) and near the wetland (4).
4. Formation of a natural dam:
The outcrops observed above and below the rocky lower zone suggest that it acts as a subterranean dam. This helps maintain the wetland moist throughout the year, even though point (1) dries up in the summer.
Layer model for the area around the house
Model Interpretation
Water infiltration:
• The mixture of Msd1 and Msd2 allows water infiltration into the Msd1 layer, where it continues its descent toward the ocean.
• The relatively low permeability of the mixture causes slow water movement, which explains its independence from seasonal changes. This is consistent with historical Google Earth images.
Predominant vegetation:
• The good filtration capacity at the surface creates ideal conditions for vegetation adapted to well-drained soils.
ID:(973, 0)