Hydrogeochemical Approach Research Articles

Use of a hydrogeochemical approach in determining hydraulic connection between porous heat reservoirs in Kaifeng area, Henan, China

In this paper a case study of hydraulic connectivity in a 300–1600 m deep, low temperature, sedimentary geothermal system in Kaifeng area, Henan province, China is presented. Based on lithologic data from 52 geothermal wells and chemical data on geothermal water (GW) from six depth-specific and representative wells, the system was chemically grouped into two main hot reservoirs (300–1300 m and 1300–1600 m deep), which were in turn, divided into six sub-reservoirs (SRs). Data on stable isotope ( 2H and 18O) ratios, radioactive isotope ( 14C) radiation in conjunction with computation of mineral–fluid chemical equilibria were used to establish the recharge source (a mountainous region in the southwestern part of Zhengzhou, 60 km away); evaluate groundwater age which varied with well depth from 15630 ± 310 a to 24970 ± 330 a; and assess the chemical equilibrium state within the system. The results of different analysis did not suggest an obvious hydraulic connection between the two main hot reservoirs. The location of the recharge zone and the geohydrologic characteristics of the study area demonstrate that the GW utilized from the system is mainly derived from confined waters of meteoric origin.

Characterising the main karst aquifers of the Alvand basin, northwest of Zagros, Iran, by a hydrogeochemical approach

The Alvand River basin, situated in the northwest of the Zagros mountain range, Iran, drains carbonate aquifers through some important karst springs. The physical, chemical and isotopic characteristics of spring water were studied for two years in order to assess the origin of groundwater and determine the factors driving the geochemical composition. Principal components analysis was used to identify the main factors controlling the water chemistry. Two groups of springs were identified: (1) low mineralisation, ion concentration, especially sulphate, low temperature, light isotope composition and high elevation of the recharge area, and (2) moderate to high mineralisation, especially sulphate, higher temperature, heavy isotope composition and low altitude of the recharge area. The main factors controlling the groundwater composition and its seasonal variations are the geology, because of the presence of evaporite formations, the elevation and the rate of karst development. In both groups, the carbonate chemistry is diagnostic of the effect of karst development. The supersaturation with respect to calcite indicates CO2 degassing, occurring either inside the aquifer in open conduits, or at the outlet in reservoirs. The undersaturation with respect to calcite shows the existence of fast flow and short residence-time conditions inside the aquifer. A PCA analysis showed that, contrary to most developed karst systems, where dilution occurs during the wet season, leaching of the gypsum-bearing Gachsaran Formation by rainwater produced higher mineralisation.

Importance of the vertical component of groundwater flow: a hydrogeochemical approach in the valley of San Luis Potosi, Mexico

Fractured volcanics exert a control on groundwater flow in the San Luis Potosi (SLP) valley. The chemical composition and temperature of water pumped from boreholes partially penetrating the fractured volcanics indicate that the produced water originates from an upward vertical flow. Most of the thermal groundwater has been detected in areas related to regional faults and lineaments. Intensive and uncontrolled pumping from the upper 1 4 of the aquifer (total depth > 1500 m) causes the rise of water from a deep regional flow system that mixes with the shallower waters. The deep waters contain high fluoride concentrations that contaminate the mixture and cause substantial health related effects. The recharge controls on the regional flow system require further research; however, hydrogeochemical evidence supports the view that the origin of this recharge is limited to the western bounding Sierra Madre Occidental. Higher levels of dissolved Na +, Li +, F − (and SO 4 −2) derived from Tertiary volcanics have been introduced into the exploited region; the concentrations indicate lengthy and deep circulation flow. Li + concentration was used as an indicator of groundwater residence time, and therefore of the length of the groundwater flow path. Hydrogeochemical interpretation indicates the presence of three flow systems: a shallow local one controlled by a clay layer that subcrops most of the valley floor, an intermediate system in which water infiltrates just beyond the boundary of the clay layer, and a deep regional system which originates outside the surface catchment. The local and intermediate systems circulate through materials with comparatively low hydraulic conductivity. Low Cl − concentrations suggest rapid flow in the regional system. Concentrations of Li + and F − can be used to calculate percentages of waters in mixtures of regional and intermediate flows. Concentrations of Na +, Ca 2+ and SO 4 −2 appear to be controlled by water-rock reactions. Uncontrolled pumping increases will tend to enhance fluoride concentration and its undesirable effects. Lack of management of aquifers in basins similar to the SLP valley can result in groundwater contamination, not only from surface anthropogenic sources, but also from natural water-rock interactions.

Physico-chemical characteristics of the ground water in the fractured rocks in the ivory coast. Implications on their use

135 complete analyses and a few hundred of punctual measurements, carried out either in laboratory or on the fields, have permitted a first hydrogeochemical approach to the ground water of the fractures in the Ivory Coast. The main physico - chemical characteristics of these waters are briefly presented, regarding their quantity, as well as their variations within time and space. The implications with regard to their use are taken into consideration.