Actividades recomendadas en el procedimiento propuesto para obtener los productos descritos

The Yucatan Peninsula is underlain by a highly permeable unconfined karstic aquifer of 48 meter depth in average at the MAM area, increasing to 80m at south and decreasing up to 0.5m depth at the north coast (González-Herrera et al., 2002).

According to Morris et al., (1994), aquifers can be classified into two groups:

consolidated and unconsolidated (deposits). Consolidated includes limestone, sandstone and some volcanic terrains. When fractured it is highly permeable. Some of

Metropolitan Area of Mérida

Case study:

Metropolitan Area of Mérida (MAM) State: Yucatán Región: Yucatán

the world’s cities examples relying on this type of aquifer are Cebu City (Philippines), Jaffna (Sri Lanka), and Tai Yua (China). Examples of fractured volcanic aquifers are San Juan (Costa Rica), Guatemala City (Guatemala), and San Salvador (El Salvador).

Unconsolidated aquifers are characterised by high porosity and great thickness. Some of the world’s largest cities that rely on this type of aquifer are Mexico City, Beijing and Jakarta (See Appendix B of karstic aquifer worldwide). The MAM karstic aquifer is an unconsolidated aquifer of limestone and dolomites deposits (Teixeira, 2004; Sanchez y Pinto, 1999; RAMSAR, 2009; Yucatan Government, 2013).

The Ring of Sinkholes (RS) is a semi-circular, around 10 km broad and 240 km long band of natural waterholes (sinkholes) that spans from Celestun in the northwest cost to Dzilam at the northeast coast of the Yucatan Peninsula (Figure 10). Several researches describe the RS as a hydraulic barrier and highly conductive channel through which groundwater flows from the centre of Yucatan Peninsula to the sea (Perry et al., 1995; Holliday, 2007; CONABIO, 2010; SEDUMA, 2012). This might be questionable depending of local or regional levels of analysis. For instance González-Herrera et al., (2002) suggested that the RS has a hydraulic conductivity only slightly higher than the surrounding rock on the basis of groundwater flow modelling.

Geologically, the Yucatan aquifer was formed by a meteor collision ~65 Million years ago, which resulted on the development of the RS, where sinkholes are locally called

“cenotes” from the Maya language “dzonot”, meaning a cave with water (Lugo-Hubp et al., 1992; BGS et al., 1995; Urrutia-Fucugauchi et al., 2011; Marin et al., 2003;

Gonzalez et al., 2007). Since 2009 the RS was declared as a wetland site of international importance due to its geological nature (Anton, 1993; RAMSAR, 2010).

The Yucatan aquifer is a mature karstic formation and it constitutes the only source of water supply for the MAM. Due to the karstic complexity with dissolution conduits, fractures and underground channels, water quality is difficult to monitor, thus a relatively simple model for “effective” groundwater flow has been suggested (González-Herrera et al., 2002), in which the karst aquifer was treated as homogeneous, granular-porous medium of very high hydraulic conductivity. There is limited evidence for the high permeability assigned to the “Sierrita de Ticul” (Figure 11), the highest area of Yucatan, which also has been modelled as a flow barrier (Perry et al., 2002; González-Herrera et al., 2002; Marin, 1990). Others more refined modelling approaches have tried to address regional-scale complexity of groundwater flow patterns, as documented in Bauer-Gottwein et al., (2011), but there is still not a consensus for modelling this system.

The Yucatan water table is less than 2m ±0.5masl (metres above mean sea level), with a freshwater lens of 1m thick at the north coast increasing to the south up to 80m

(Marin, 1990). On the basis of regional hydrological and geological characteristics, the national water authority CONAGUA (for its Spanish acronyms) has divided the Yucatan Peninsula in three regions (Figure 11): the coastal zone, the belt of cenotes, which includes the RS and the Sierrita de Ticul, and the inner plateau where the MAM is located (Anton, 1993; Sanchez y Pinto, 1999).

Figure 11 Hydrogeological regions of Yucatan aquifer. Source: Sanchez y Pinto, (1999)

Karstic aquifers can be defined as highly soluble freshwater bodies that conduct water principally via porosity by the dissolution of the rock. In the MAM area this dissolution phenomenon together with the high water table results in a high vulnerable aquifer (Holliday, 2007; Schmitter-Soto et al., 2002).

Figure 12 Diameter of microorganisms related to aquifers pore size. Source: Morris et al., (1994)

Even though natural attenuation, an intrinsic characteristic of the aquifers that often control contaminant loads through adsorption, dilution and filtration, in the MAM it has been reported to be limited. For instance, Figure 12 shows the nature of the unconsolidated limestone strata with fissures and apertures of larger pore opening than the size of the microbial pollutants (Morris et al., 1994).

3.3. Water management

Despite of the fact that Merida is the largest city in the southeast of Mexico, its urban development plan created every four years by Merida City Council has failed in terms of water management. The unsuccessful management may be due to political changes

every three years at municipal level, every four years at Yucatan State level as well as every six years at National level, cutting off the creation of robust and uninterrupted action plans to protect and safeguard the natural water resources (Teixeira, 2004).

Febles and Hoogesteijin, (2008) analysed the water management regulations at the three government levels in Mexico: municipal, state and federal, in order to identify the cause of failure in terms of water management in Yucatan. After identifying many discrepancies in government jurisdiction and lack of congruence among the three authority levels, it was suggested the creation of a State law for drinking water and wastewater treatment, and the development of norms for a) pluvial water infiltration in green areas; b) design, construction and operation of drainage systems and treatment plants; c) infiltration of septic tanks discharges, and d) promotion of infiltration fields for septic tanks and treatment plants effluents.

Septic tanks (ST) are of particular concern in the MAM area. ST are designed with 2/3 of the tank volume set aside for sludge and scum accumulation and 24hr hydraulic detention time in the remaining 1/3 volume, which under effective operation leads to a total tank volume equal to 3 times the daily flow volume (Quintal, 1992; Gill et al., 2004). Nevertheless current status of ST in Yucatan do not comply with these specifications (Quintal, 1993).

One recent attempt to improve water management policies with a hydrological and political administrative approach has been the creation of a new decree by Yucatan Government in 2013. The aim of this new decree is to declare the Ring of Sinkholes as a protected reservoir area. This decree provided valuable data for this research in terms of water abstraction (Table 12) and wastewater discharge volumes (Table 13) within the study area (Yucatan Government, 2013).

According to the new 2013 decree, the area between the RS (as southern boundary) and the coastline area (as the northern boundary), is now a priority area to implement sustainable water management policies for the MAM (Figure 13). This priority area has been divided into four sub-zones A, B, C, D, and each subzone is again divided in:

recharge, transition, and discharge zones according to its geographical location (Table 9) (Yucatan Government, 2013). A total of 53 municipalities are distributed as follows:

- Sub-zone A: MAM and its periphery. It comprises 17 municipalities: 7 are recharge zone (A1), 8 are transition zone (A2) and 2 are discharge zone (A3).

- Sub-zone B: influence zone of the MAM. It comprises 16 municipalities: 6 are recharge zone, 7 are transition zone and 3 are discharge zone.

- Sub-zone C: eastern zone of the sinkholes ring influence. It comprises by 14 municipalities: 11 are transition zone, and 3 are discharge zone.

- Sub-zone D: western zone of the sinkholes ring influence. It comprises 6 municipalities: 5 are transition zone, and 1 is discharge zone.

Twenty seven municipalities are comprised as RS municipalities (Figure 13), which are major recharge zone on this new decree (13 recharge municipalities from sub-zones A and B shown on Table 9). As an ecosystem, sinkholes are particularly vulnerable to drastic environmental changes (i.e. wastewater discharge from the MAM), thus these RS municipalities are of priority importance for this thesis (RAMSAR, 2010).

Additionally, the technical committee for water management of the MAM has reported that sub-zone A is of major concern for both water supply and wastewater disposal, because it encompasses 57% of total Yucatan population and 41% of total water abstraction (CCPY, 2012).

Due to the above, this new priority area was the basis to establish the study area of this research. The Sustainable Integrated Water Management Model (SIWMM) uses the data of the new ordinance, to serve as a strategy tool for the current and future sustainable water management of the MAM. Summarising, the selected area for the implementation of the SIWMM includes a total of 31 municipalities, 25 of which are within the priority area (Figure 13). The selection was based on two criteria, the geographical location of the MAM (municipalities highlighted on Table 10), and the regional groundwater flow direction, in order to assume a continuous water flow from one aquifer section to another (see Chapter 4 for further information).

Figure 13 Priority area by Yucatan Government, (2013)

Table 10 Priority area from government for water management in Yucatan

A.3 Progreso B.3 Sinanche B.3 Telchac Pueblo

Note: Municipalities highlighted are included in the MAM study area of the present research