Recharge systems for protecting and enhancing groundwate

V
Geochemical evaluation of artificial recharge
to intermediate flow systems in a
carbonate aquifer from northeast Mexico
C. Gutiérrez-Ojeda, A. Cardona,
M. Martínez-Morales and F. Aparicio-Mijares
Abstract
Artificial recharge of groundwater has been implemented to replenish extracted groundwater in a coal mining
area of northeast Mexico, a semi-arid area where alternative water sources are scarce. In this region, the main
aquifer is overlying a coal seam and surface coal mining requires dewatering the aquifer around the open-pit
mining areas. Extracted groundwater (29 x 10 6 m 3 /year) is mainly injected into two sites, the geochemical evaluation
of the artificial recharge was made after the determination of a geochemical conceptual model, delineated
from the interpretation of the water chemistry analysed in 70 samples. Results indicate saturation of calcite,
dolomite, barite and chalcedony, no relation with salinity or groundwater flow was identified. Supersaturation of
carbonates and goethite was detected in some samples, especially in recharge water and lagoons. Subsaturation
of gypsum, strontianite, celestite, rhodochrosite and siderite is also a common characteristic. The chemical
changes derived from the mixing between original aquifer water and recharge water were simulated indicating
that some minerals can be precipitated from the mixture. The modeling exercise shows that calcite, goethite,
barite and chalcedony are precipitated from the mixture, however calcite shows the largest amount of precipitation
and represent the major cause of permeability reduction around the injection sites.
Keywords
Arid regions, groundwater recharge, hydrochemical modeling, hydrochemistry, injection wells.
INTRODUCTION
Successful groundwater management requires the understanding of the different properties within a groundwater
flow system. Artificial recharge is becoming an important component in groundwater management, especially in
semi-arid areas where alternative water sources are limited. Although almost 65% of Mexico has a semi-arid climate,
only few artificial recharge projects have been implemented within a sustainable groundwater management
scheme in the country.
Artificial recharge of groundwater has been implemented to replenish extracted groundwater in a coal mining area
of northeast Mexico. In this region within the Coahuila state, included in the Fuentes-Rio Escondido Carboniferous
Basin, coal mining is one of the main industrial activities. Surface coal mining requires overburden excavation using
walking dragline procedures, the main aquifer (Tertiary age) in the area is intercepted by the open cut because it is
located above the coal seam (Cretaceous age). Several wells have to be used to pump out groundwater
(29 x 10 6 m 3 /year) and dewater the aquifer around the open-pit mining areas, producing environmental impacts on
water quantity and modification of local and intermediate groundwater flow systems.
As a component of an integral environmental friendly strategy, Minera Carbonífera Rio Escondido (MICARE) has
designed, constructed and nowadays operates one of the most important and successful artificial recharge projects
in Mexico, injecting the total amount of extracted groundwater from the dewatering process into two recharge sites
ISMAR 2005 ■ AQUIFER RECHARGE ■ 5th International Symposium ■ 10 –16 June 2005, Berlin