Andean Mountain Groundwater, Drinking Water Sources, and Vulnerability: A Case Study… DOI: http://dx.doi.org/10.5772/intechopen.85016

where the headwater of the Diguillín River is located (Figure 5b and c). This cluster is due to local tectonic features related to the formation of valley, like the fault line shown at Figure 5a. This geological trait enhances recharge from snowmelt, rainfall, and runoff from adjacent watersheds to the Alto Diguillín sub-basin, explaining why it has more water than surrounding rivers as can be deduced from Figure 3.

In relation to the lower specific flow in the Renegado Creek sub-watershed, particular importance is to be given to the formation of the lava units that filled the valley of the Renegado Creek (Figure 6). In effect, this valley was formed from a sequence of lava flows. An earlier lava flow called the Pincheira lavas, of the middle Pleistocene, cut along a large glacier forming walls that give the valley its characteristic U shape; at the end of the glacier, the lava flow opened in what is today the locality of Los Lleuques. Later lava flows (Diguillín of the middle Pleistocene) went down the valley until being blocked by the Pincheira lavas, which forced them to turn toward the south, closing the Renegado valley and forcing a connection with the Diguillín River (Figures 6 and 7).

Two additional lava flows that fill the valley covering the Pincheira lavas are the Atacalco lavas (of the Middle-Upper Pleistocene, which correspond to one or more andesitic lava flows, with a layer thickness of 125 m) and the Democrático Volcano

#### Figure 5.

(a) Scheme of the plausible groundwater system at one volcanic complex; (b) headwaters of the Diguillín River at a thermal spring; (c) Diguillín River; (d) hot water spring; (e) cold water spring.

#### Figure 6.

Geology of the upper section of the Diguillín River adapted from [15] and pasted on Google Earth. The red line at the right corner indicates a river section where fractured rock springs are located; the dashed blue line represents probable groundwater paths.

lavas (LTd) of the Holocene, which are a fundamentally effusive structure of silicious, andesitic to dacitic block lavas (Figure 7).

The existence of the Agua Bonita springs is related to the formation of Diguillín lava. It is possible to assume that these lavas entered a postglacial lake which, through the cooling process [15], produced the fracture system which can be observed along the Renegado sub-watershed (Figure 4d). The presence of this fractured system causes the groundwater watershed boundary to differ from the surface watershed. In fact, groundwater is moving along paths that were created when the Diguillín lavas filled the valley, and surface water is moving across the watershed created by recent lava flows.

Also, the predominant soils in the upper part of the Renegado valley are sandy soils with high infiltration rates (larger than 200 mm/hr). The existence of these soils on a basement formed by fractured rocks favors groundwater recharge and explains why the Renegado Creek does not have significant superficial runoff. A large amount of rainwater and snowmelt infiltrate into the sandy permeable soil and percolate to the fractured rock system where the water moves through the fractured rock system and discharges in the Diguillín River at the springs described in the previous paragraph.

#### 3.2 Discussion

This case study illustrated how groundwater storage and release can be significant hydrological processes in a mountain watershed where the presence of fractured volcanic rock geology produces the conditions for complex groundwater systems.

#### Andean Mountain Groundwater, Drinking Water Sources, and Vulnerability: A Case Study… DOI: http://dx.doi.org/10.5772/intechopen.85016

In recent years it has been understood that volcanic complexes—such as the Nevados del Chillán complex—produce the conditions necessary for significant mountain groundwater systems. At Mount Fuji in Japan, water can flow vertically through fractures, with water from different aquifer formations mixing, as established using isotopes, major ion chemistry, and multivariate statistical methods [7]. In Mexico, the hydrothermal system of El Chichón volcano was also studied using isotopes [6] and water chemistry, allowing the identification of two aquifers that make up the volcanic structure in a system that is controlled by infiltration from rainfall, water percolation, and heating and production of hydrothermal vapor. In Italy, environmental isotope techniques, hydrogeochemical analysis, and hydraulic data were used to identify recharge areas and trace groundwater flows at Mount Vulture [18].

In a tropical mountain cloud forest catchment located in a volcanic area in Mexico, it was found that rainfall-runoff responses are controlled by rapid vertical rainfall percolation through the high permeable volcanic soils, which recharges the groundwater system, while groundwater storage and discharge modulate the streamflow regime of the catchment [9].

In a mountain watershed without glaciers where volcanic processes are the dominant geological feature, spring discharge plays a major role in streamflow generation [19, 20]. Due to the expansion of second home construction in some mountain valleys, especially those associated with a tourist attraction like ski or hot spring resorts, spring water has become more common as a source of drinking water. However, as the recharge areas are also impacted by housing development, the risk of groundwater pollution increases [21], exacerbating the vulnerability of water quality in mountain groundwater systems [21].

As previously stated, land cover changes in Chile have been driven by an increase in income levels, which has led to significant growth in second home construction in the Renegado watershed area, as it is a major tourism center based on skiing and hot springs. There are now more than 1000 vacation houses and several resorts that have been constructed on more than 5000 small parcels that are available in the area. This explosive increase in construction has taken place without any planning or control, as the area is considered rural land.

The lack of a formal drinking water system has led to a trade in building clandestine catchments that are connected to the slopes by rough plastic pipes. Homeowners pay local people to build illegal water connections, which are unfit to provide drinking water. These connections are not only unhealthy; they also affect the few springs that are located around the valley (Figure 8a).

While the situation related to drinking water distribution was referred to in Figure 8a as "chaotic," the situation related to wastewater is unknown, but there are reasons to dubiosity. According to Chilean law, disposal of wastewater from small houses located in rural areas should be carried out through the use of septic tanks. With the extensive use of septic tanks, located above the highly permeable soils that overlie the fractured rock aquifer, there is a concern that water quality in the Diguillín River could be impacted by housing and tourism development. Pollutants from the wastewater disposal systems will move through the fractured rock network and discharge into the springs that are used as drinking water sources for the houses and communities that are located down gradient (Figure 8b).

In recent years it has been shown that pharmaceuticals and personal care products (PPCP) can be used as indicators of groundwater pollution [22, 23]. A review summarized the use of frequently detected PPCPs, including antibiotics, anti-inflammatories, lipid regulators, carbamazepine, caffeine, and N,N-diethylm-toluamide, in groundwater to identify groundwater pollution, analyzing how adsorption to soils and degradation may affect the use of these elements as

Figure 8.

(a) Chaotic drinking water distribution system at the Renegado Valley; (b) scheme of the plausible pollutants' recharge and discharge processes along the Renegado Valley.

groundwater tracers [24]. In groundwater systems such as the Renegado Valley where transit time is expected to be short, adsorption and degradation effects will be less relevant and therefore PPCP would be a good indicator for consideration.
