Abstract

BARRERA-DE-CALDERON, Marcia; GARFIAS, Jaime; MARTEL, Richard  and  SALAS-GARCIA, Javier. Geological controls upon groundwater flux and pumping rates distribution associated to a complex volcanic structure. Bol. Soc. Geol. Mex [online]. 2021, vol.73, n.1, 00011.  Epub Oct 11, 2021. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2021v73n1a170820.

Groundwater flux knowledge is of supreme importance for sustainable water resources planning, mainly in highly rising water demand regions. Distribution of geologic material and structural geology have been incorporated in a Tridimensional Hydrostratigraphic Model (THM) in order to assess groundwater flow occurrence in San Salvador aquifer, located in the east portion of San Salvador volcano. Geologic data have been analyzed, classified, reinterpreted and correlated from bore drilling reports and geology map of the zone to define layers with similar geologic characteristics. These layers were related with their hydraulic properties in order to define Hydrostratigraphic Units (HSU) in the aquifer. Faults distribution, hydraulic conductivity and water rate production in wells were spatially analyzed and correlatedfor assessing the groundwater occurrence. The model showed the existence of six interbedded HSUformed by pyroclastic and tuff material with the lowest hydraulic conductivity (K) from 10-2 - 1 m/d, fractured andesitic and basaltic lava with K values between 1 - 101 m/d, and volcanic scoria with the highest K from 101 to around 103 m/d. The model also showed the displacement of blocks associated to Central Graben in the Zone Fault of El Salvador (ESFZ), specially at south and east of the study area. Results showed that the low production Cuscatlán pyroclastic and tuffs material HSU extends throughout the study area and it is exploited by most of productive water wells in the Metropolitan Area of San Salvador (AALSS). While Cuscatlán and San Salvador lavas HSU are less extensive, locally exploited, even though they are more productive and are classified as good aquifers, mainly near geologicfaults. Meanwhile, Plan de La Laguna Escoria HSU is small, nevertheless, is the most productive of the area and densely fractured. Furthermore, there are four important faults in the zone that function as conduits and otherfault that function as a barrier. Faults exhibit influence on groundwater flux when they intersect lava flows, conversely, when porous materials are intersected by faults, groundwater flux remains the same. This model gives new insights about the spatial distribution and exploitation of the permeable materials in San Salvador aquifer area and could support some decisions for sustainable groundwater management, mainly those focus on new water development zones. This methodology could be applied in aquifers with similar conditions of poor and multisource data.

Keywords : San Salvador aquifer; tridimensional hydrostratigraphic model; aquifer in fractured volcanics; faulting on groundwater flux; El Salvador Fault Zone.

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