Concentrations In Groundwater Samples Research Articles

Comparative Analysis of Fluoride Concentrations in Groundwaters in Northern and Southern Ghana: Implications for the Contaminant Sources

Bongo and Sekyere South districts, both in the northern and southern parts of Ghana, respectively, have high populations living in rural areas and most of them use groundwater for drinking purposes. The groundwater in these areas is prone to contamination from natural and/or artificial sources. Therefore this study aims; (1) to present a comparative analysis of the fluoride concentration in groundwater samples from Bongo and Sekyere South districts and the associated groundwater–rock interaction that may be the cause for the varied fluoride concentrations, (2) to determine the leaching potential of fluoride from the host rocks as the possible mechanism for groundwater contamination. Sixty (60) groundwater samples from active pumping wells and twelve (12) rock samples from outcrops were collected from various communities in the two districts for fluoride concentration and mineralogical analysis. Based on the variations in fluoride concentration, fluoride spatial distribution maps were prepared using empirical Bayesian kriging interpolation method and analysed by means of hierarchical cluster analysis. The fluoride concentration in Bongo district varies between 1.71 and 4.0 mg/L, whereas that in Sekyere South district changes from 0.3 to 0.8 mg/L. From the mineralogical studies, biotite has the highest percentage in the Bongo district and has positive correlation with fluoride concentration in the analysed water samples than in the Sekyere South district. The elevated fluoride concentration in the Bongo district relative to the Sekyere South district is due to the dissolution of biotite in the groundwater and the sufficient groundwater–rock interaction since the water samples are mainly sourced from deeper boreholes. This high fluoride concentration has resulted in a plethora of reported cases of dental fluorosis and other health-related issues in Bongo.

Geographic Information System mapping of gross alpha/beta activity concentrations in ground water samples from Karnataka, India: A preliminary study

The activity concentrations of the gross α and β in ground water samples were determined for 178 bore wells of Karnataka state of India. The aim of this study was to develop a first insight regarding the radiological quality of ground water samples from Karnataka state. Sampling and measurements were carried out from 2013 to 2014. So far there has been no detailed study in the radioactivity measurements in drinking water of Karnataka state. TDS, pH and gross alpha and gross beta activity measurements have been performed according to standards. The gross alpha and gross beta activity concentrations in the bore water samples of Karnataka state have been found to lie between 0.69–15.26mBq/l with a mean of 5.66 ± 0.50mBq/l and 14.6–108.5mBq/l with a mean of 57.76mBq/l respectively. In general, the gross beta activity was higher than the alpha activity concentration. From the value of gross alpha and gross beta, it is clear that the water samples are investigated are acceptable for consumption, complying with the WHO recommendations for drinking water. The data obtained can provide information for to make decisions about potential future drinking water regulations.

CHANGES IN THE CHEMICAL PROPERTIES OF GROUNDWATER IN SOILS UNDER MEAT AND BONE MEAL, NATURAL AND MINERAL FERTILIZATION REGIMES

The objective of this study was to evaluate the effect of different doses of meat and bone meal (MBM) applied as organic fertilizer on the quality of groundwater in arable fields. The effect of meat and bone meal fertilizer applied at rates of 1.0, 1.5, 2.0 and 2.5 t ha-1 was compared with no fertilization, mineral fertilization, and manure fertilization (10 t ha-1). Groundwater samples for chemical analyses were collected every month during the growing season using piezometers installed in the experimental plots. Groundwater samples were analyzed to determine the concentrations of mineral nitrogen NO3-, NO2-and NH4+, total phosphorus, phosphate and potassium. The application of meat and bone meal at the rate of 1.0 to 2.0 t ha-1 with supplemental potassium fertilization does not lead to higher contamination of groundwater than mineral (NPK) fertilization. The use of meat and bone meal fertilizers at a rate of 2.5 t ha-1 significantly increased mineral nitrogen and phosphate concentrations in groundwater samples. The results of our analyses suggest that meat and bone meal can be successfully used at a rate of 2.0 t ha-1 to fertilize crops grown in a five-year crop rotation sequence on lessive soils. The application of higher doses of meat and bone meal intensifies the flow of biogenic elements into groundwater.

Perfluorinated compounds in surface waters of Shanghai, China: Source analysis and risk assessment

17 perfluorinated compounds (PFCs) were systematically investigated in the surface water from principal watersheds of Shanghai, China. 10 PFCs were above the detection limit (0.08–0.28ng/L) in 39 surface water samples. The perfluorooctanoic acid (PFOA) and perfluorobutanesulfonate (PFBS) were the two dominant compounds with a median concentration 50.67ng/L and 29.84ng/L, respectively. Concentrations of perfluorooctanesulfonate (PFOS) were generally less than PFBS, which might result from the global phase-out of PFOS production and the use of PFBS as a substitute for PFOS-based products. There were three major polluted areas of PFOA along the Huangpu River. The PFOA concentration in groundwater samples collected from one of the three areas indicated that chemical industry might be the possible source. The perfluoroalkane sulfonates (PFSAs) level had a spatial trend that indicated northwest had higher concentrations than the southeast. The distribution of PFCs was not much affected by atmospheric deposition. Mass loading analysis in the surface water revealed that the Huangpu River exhibited relatively large mass loading of total PFCs of 1742.43kg/year to Yangtze River Estuary. The predominant of the PFC species was PFOA with 652.65kg/year. The current concentrations of PFOA and PFOS were at middle level comparing to other studies in China and worldwide. Risk assessment of 6 PFCs showed that there is no risk to the aquatic organisms in Shanghai. PFOS and PFBS had low risk to the avian. Furthermore, the adults living in Shanghai were at low risk to exposure to PFCs through water consumption.

Effects of surface gold mining on surface and groundwater bodies in Bibiani, Ghana

A study of the water sources from Bibiani and its environs was conducted between November, 2009 and April, 2010 to determine whether contamination (of water sources) from (these parameters) physical, chemical and trace metal in Bibiani is as a result of mining or geochemicaland biochemical processes within the environment. This was done by collecting water samples from two streams, two rivers, three boreholes (BHs) and three hand dug wells (HDWs). These were analysed in the laboratory. Levels of Arsenic (As), Iron (Fe), Manganese (Mn), pH, TotalDissolved Solids (TDS), Electrical Conductivity (EC), Temperature, Alkalinity, Hardness, Phosphate (P) and Cyanide (CN) in water sources were determined. Mining related contaminants detected in water samples were As, CN, Mn and Fe. It was observed that surface water pH values were generally higher than that of groundwater samples. As concentrations in surface water samples were higher compared to that of groundwater samples. Also, CN concentration in ground water samples was higher than that of surface water. Ground water contained higher concentration of Mn than surface water; the opposite can be said of Fe concentration in surfacewater which was higher than that of ground water. The study also observed that pH, TDS, EC, total alkalinity, total hardness , Arsenic and total cyanide levels in the HDW and BH samples showed 100% compliance with the WHO and EPA limits while Mn and Fe levels indicated traces of non – compliance. Compared to WHO / EPA guidelines, few water sources had one or moretrace metal (Fe, As and Mn) levels outside acceptable limits for drinking. However, most of the levels were safe for human consumption.Keywords: Surface, gold mining, quality, degradation, Bibiani

Groundwater chemistry and radon-222 distribution in Jerba Island, Tunisia

The present study integrates hydrogeological, hydrochemical and radiogenic data of groundwater samples taken from the Plio-Quaternary unconfined aquifer of Jerba Island, southeastern Tunisia, in order to interpret the spatial variations of the groundwater quality and identify the main hydrogeochemical factors responsible for the high ion concentrations and radon-222 content in the groundwater analysed. Thirty-nine groundwater samples were collected from open wells widespread on the island. Physical parameters (EC, pH, TDS and T °) were measured, major ions (Ca2+, Mg2+, Na+, K+, Cl−, SO42−, NO3− and HCO3−) were analysed and 222Rn concentrations were determined using a RAD7-H2O. Hydrogeochemical characterisation revealed that groundwater from the Jerba aquifer has several origins. Basically, two water types exist in the island. The first one, characterized by a low to moderate salinity with a chemical facies CaMgClSO4, characterizes the central part of Jerba (a recharge area) due to carbonate and gypsum dissolution. The second water type with high salinities, dominated by NaKCl type, was observed in coastal areas and some parts having low topographic and piezometric levels. These areas seem to be affected by the seawater intrusion process. The 222Rn concentrations in groundwater samples in Jerba varied from 0 Bq.L−1 to 2860 Bq.L−1 with an average of 867 Bq.L−1.The highest values were registered in the western coastal wells and near the fault of Guellala. However, the central and eastern wells showed low radon levels. Compared to 222Rn activity in some countries with the same lithology, radon concentrations in the Jerba unconfined aquifer have higher values influenced by the structure of the aquifer and by seawater inflow enriched with 222Rn resulting from the decay of uranium derived from phosphogypsum deposits in the gulf of Gabes. The EC and 222Rn spatial variability in the study area were mapped using ARC Map 10.3 software. Hydrochemical results in addition to geological data and radon activities confirm the existence of vertical communication between the Miocene aquifer and the unconfined Plio-Quaternary aquifer through fault system and a lateral communication with the sea via seawater intrusion.

Tree Sampling as a Method to Assess Vapor Intrusion Potential at a Site Characterized by VOC-Contaminated Groundwater and Soil

Vapor intrusion (VI) by volatile organic compounds (VOCs) in the built environment presents a threat to human health. Traditional VI assessments are often time-, cost-, and labor-intensive; whereas traditional subsurface methods sample a relatively small volume in the subsurface and are difficult to collect within and near structures. Trees could provide a similar subsurface sample where roots act as the "sampler' and are already onsite. Regression models were developed to assess the relation between PCE concentrations in over 500 tree-core samples with PCE concentrations in over 50 groundwater and 1000 soil samples collected from a tetrachloroethylene- (PCE-) contaminated Superfund site and analyzed using gas chromatography. Results indicate that in planta concentrations are significantly and positively related to PCE concentrations in groundwater samples collected at depths less than 20 m (adjusted R2 values greater than 0.80) and in soil samples (adjusted R2 values greater than 0.90). Results indicate that a 30 cm diameter tree characterizes soil concentrations at depths less than 6 m over an area of 700-1600 m2, the volume of a typical basement. These findings indicate that tree sampling may be an appropriate method to detect contamination at shallow depths at sites with VI.

Ingestion doses and hazard quotients due to intake of Uranium in drinking water from Udhampur District of Jammu and Kashmir State, India

Ground water in environment is contaminated by atomic radiations of natural occurring radioactive elements like Uranium and Thorium. The Uranium (238 U) concentration has been measured in drinking water samples collected from different sources like the hand pumps and natural spring/bowli from wide range of locations in Udhampur District, Jammu and Kashmir (J&K), India by using LED flourimetry technique. The Uranium concentrations in four tehsils viz. Udhampur, Ramnagar, Chenani and Majalta are varied from (0.25–27.15) μg L−1 , (0.19–27.93) μg L−1 , (0.14–0.68) μg L−1 , and (1.63–28.06) μg L−1 with mean value 13.57 μg L−1 , 9.67 μg L−1 , 0.29 μg L−1 , and 17.61 μg L−1 , respectively. The values of ingestion dose for different age group and chemical risks have also been calculated. The purpose of this study is to investigate the Uranium concentration in ground water samples and to determine its health effects to the habitants of the study area. All the recorded values of Uranium are compared with the safe limits recommended for drinking water by various health and environmental protection agencies (WHO, USEPA, and AERB). Physico-chemical properties such as pH, conductance and total dissolved solids (TDS) have been determined in water samples.

Radioecological investigation of 3H, 14C, and 129I in natural waters from Fuhrberger Feld catchment, Northern Germany

Ongoing radionuclide releases from nuclear facilities, e.g. from reprocessing plants, but also from nuclear reactors require monitoring of the environment. Particularly drinking water reservoirs are prone to possible radionuclide accumulation fostering the need for routine surveillance. In this work, we investigated tritium (3H), radiocarbon (14C), and iodine-129 (129I) activity levels in natural aquatic samples at the water protection area of Fuhrberger Feld near Hannover city, Northern Germany. For that aim, a low-level liquid scintillation counting (LSC) technique was used to measure 3H in the water samples based on a distillation process after alkaline permanganate treatment. Isotopic ratios for both 14C and 129I were measured by accelerator mass spectrometry (AMS) after chemical separation and purification of the samples. Mean 3H levels in precipitation (8.8 ± 3.4 TU) were found to be comparable to its levels in precipitation data in Germany. Rivers and small streams revealed similar mean 3H value (11.0 ± 3.3 TU) as in lake water (10.6 ± 3.4 TU). Variations in 3H concentrations in groundwater samples were observed and discussed. 14C levels in all groundwater samples were below the atmospheric natural level of 100 pMC indicating no anthropogenic input of radiocarbon. The 129I/127I isotopic ratios in all investigated water samples were in the order of 10−8 to 10−7, which is significantly higher than the pre-nuclear natural equilibrium isotopic ratio (∼1.5 × 10−12). In strong contrast to all other regional groundwaters, the Fuhrberger Feld groundwater has much higher values of 129I concentration and 129I/127I isotopic ratio close to the ones of surface water. The overall annual effective dose via ingestion for all nuclides in the investigated groundwater remains substantially below the reference dose level of 0.1 mSv a−1.

Evaluation of Mercury Concentrations in Groundwater Samples of Coal Field Using a Matrix-less Cloud Point Extraction Procedure Prior to Analysis by Cold Vapor Atomic Absorption Spectrometry

Evaluation of Mercury Concentrations in Groundwater Samples of Coal Field Using a Matrix-less Cloud Point Extraction Procedure Prior to Analysis by Cold Vapor Atomic Absorption Spectrometry

Comparative statistical analysis of carcinogenic and non-carcinogenic effects of uranium in groundwater samples from different regions of Punjab, India

LED flourimeter has been used for microanalysis of uranium concentration in groundwater samples collected from six districts of South West (SW), West (W) and North East (NE) Punjab, India. Average value of uranium content in water samples of SW Punjab is observed to be higher than WHO, USEPA recommended safe limit of 30µgl−1 as well as AERB proposed limit of 60µgl−1. Whereas, for W and NE region of Punjab, average level of uranium concentration was within AERB recommended limit of 60µgl−1. Average value observed in SW Punjab is around 3–4 times the value observed in W Punjab, whereas its value is more than 17 times the average value observed in NE region of Punjab. Statistical analysis of carcinogenic as well as non carcinogenic risks due to uranium have been evaluated for each studied district.

Occurrence, fate and risk assessment of personal care products in river–groundwater interface

This work presents the occurrence and fate of selected personal care products (PCPs) in the urban river–groundwater interface. To this end, urban river and groundwater samples were collected in Sant Adrià del Besòs (NE of Spain) and a total of 16 PCPs were analyzed including benzophenone derivatives, camphor derivatives, p-aminobenzoic acid derivatives, triazoles and parabens in three different campaigns (from May 2010 to July 2014). These compounds reach the aquifer through the recharge of Besòs River that receives large amounts of effluents from waste water treatment plants. Results have shown that most of the compounds were not or barely detected (maximum concentrations around 200ng/L) in groundwater samples during the different sampling campaigns. Only two triazoles, namely benzotriazole (BZT) and methyl benzotriazol (MeBZT) were found at high concentrations in groundwater samples (maximum concentration around 2000ng/L). The fate of PCPs in the aquifer was assessed using mixing analysis considering the seasonal variability of the Besòs River. Overall, measured groundwater concentrations were significantly much lower than those estimated by the mixing of the river water. This observation suggested that most of the PCPs are naturally removed when river water infiltrates the aquifer. However, some compounds were more persistent in the aquifer. These compounds were in descending order: the triazoles BZT and MeBZT followed by the camphor derivative 4MBC and the paraben MePB. The measured concentrations allowed us to assess the environmental risk posed by the selected UV-filters and parabens in the river and groundwater samples. Hazard Quotients (HQs) for different aquatic species were calculated in order to characterize the ecotoxicity potential of the studied compounds in the river–groundwater interface. HQ values were always below 1 indicating that at the concentrations observed in the surface or aquifer water of Besòs River these compounds pose no risk to the selected aquatic organisms.

Significance of groundwater discharge along the coast of Poland as a source of dissolved metals to the southern Baltic Sea

Fluxes of dissolved trace metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) via groundwater discharge along the southern Baltic Sea have been assessed for the first time. Dissolved metal concentrations in groundwater samples were less variable than in seawater and were generally one or two orders of magnitude higher: Cd (2.1–2.8nmolL−1), Co (8.70–8.76nmolL−1), Cr (18.1–18.5nmolL−1), Mn (2.4–2.8μmolL−1), Pb (1.2–1.5nmolL−1), Zn (33.1–34.0nmolL−1). Concentrations of Cu (0.5–0.8nmolL−1) and Ni (4.9–5.8nmolL−1) were, respectively, 32 and 4 times lower, than in seawater. Groundwater-derived trace metal fluxes constitute 93% for Cd, 80% for Co, 91% for Cr, 6% for Cu, 66% for Mn, 4% for Ni, 70% for Pb and 93% for Zn of the total freshwater trace metal flux to the Bay of Puck. Groundwater-seawater mixing, redox conditions and Mn-cycling are the main processes responsible for trace metal distribution in groundwater discharge sites.

Geochemical Distribution of Trace Elements in Groundwater from the North Mara Large‐Scale Gold Mining Area of Tanzania

AbstractThe influence of large‐scale mining operations on groundwater quality was investigated in this study. Trace element concentrations in groundwater samples from the North Mara mining area of northern Tanzania were analyzed. Statistical analyses for relationships between elemental concentrations in the samples and distance of a sampling site from the mine tailings dam were also conducted. Eleven trace elements (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were determined, and averages of Fe and Al concentrations were higher than levels accepted by the Tanzanian drinking water guideline. Levels of Pb in three samples were higher than the World Health Organization (WHO) and United States Environmental Protection Agency (USEPA) drinking water guidelines of 10 and 15 µg/L, respectively. One sample contained a higher As level than the WHO and USEPA guideline of 10 µg/L. The correlation between element concentrations and distance from the mine tailings dam was examined using the hierarchical agglomeration cluster analysis method. A significant difference in the elemental concentration existed depending on the distance from the mine tailings dam. Mann–Whitney U‐test post hoc analysis confirmed a relationship between element concentration and distance of a sampling site from the mine tailings dam. This relationship raises concerns about the increased risks of trace elements to people and ecosystem health. A metal pollution index also suggested a relationship between elemental concentrations in the groundwater and the sampling sites’ proximity from the mine tailings dam.

Characterization and fingerprinting of soil and groundwater contamination sources around a fuel distribution station in Galicia (NW Spain).

Soil and groundwater contamination around a fuel distribution station in Tomiño (NW Spain) was evaluated. For this purpose, top and subsoil (up to 6.4 m) and groundwater were sampled around the station, approximately in a 60-m radius. Samples were analysed by HS-SPME-GC-MS to identify and quantify volatile fuel organic compounds (VFOC) (MTBE, ETBE and BTEX) and diesel range organics (DRO). Analysis and fingerprinting data suggested that the contamination of soil and groundwater was provoked by a fuel leak from underground storage tanks. This was reflected by hydrocarbon indices and principal component analysis, which discriminated a direct source of contamination of the subsoil samples around the station. The contaminants probably migrated from tank nearby soils to surrounding soils and leached to groundwater, following a SW direction. Irrigation with contaminated groundwater provoked a severe contamination of topsoils, which were enriched with the lightest components of gasoline and diesel. Fingerprinting also revealed the continuity of the leak, reflected by the presence of volatiles in some samples, which principally appeared in fresh leaks. MTBE was detected in a very high concentration in groundwater samples (up to 690 μg L(-1)), but it was not detected in fresh gasoline. This also evidenced an old source of contamination, probably starting in the mid-1990s, when the use of MTBE in gasoline was regulated.

Identification of salinization by bromide and fluoride concentration in coastal aquifers near Chennai, southern India

This study aims to use fluoride as an additional indicator for seawater intrusion apart from the known effective geochemical indicators such as EC, TDS, sodium, chloride and bromide. Groundwater in a coastal part of Arani-Koratalaiyar river basin located north of Chennai, Tamil Nadu, India was assessed to determine its suitability for domestic purpose and to delineate the region affected by seawater intrusion. Fluoride concentration in groundwater samples from forty nine locations varied from 0.02 mg/l to 2.9 mg/l with an average of 0.5 mg/l. As per the Bureau of Indian Standards, the permissible range of fluoride in drinking water is 0.6–1.5 mg/l. Fluoride concentration in groundwater of this area exceeds 1.5 mg/l in 6% of the groundwater samples and is below 0.6 mg/l in 74% of the groundwater samples. There is no known geological source for fluoride in this area. Spatial variation in fluoride concentration in groundwater indicates that the coastal areas have comparatively high fluoride due to seawater intrusion which was similar in comparison with EC and bromide concentration measured in groundwater. This study indicates that fluoride can be used as an indicator of seawater intrusion in coastal areas.

Effect of Different Sampling Methodologies on Measured Methane Concentrations in Groundwater Samples.

Analysis of dissolved light hydrocarbon gas concentrations (primarily methane and ethane) in water supply wells is commonly used to establish conditions before and after drilling in areas of shale gas and oil extraction. Several methods are currently used to collect samples for dissolved gas analysis from water supply wells; however, the reliability of results obtained from these methods has not been quantified. This study compares dissolved methane and ethane concentrations measured in groundwater samples collected using three sampling methods employed in pre- and post-drill sampling programs in the Appalachian Basin. These include an open-system collection method where 40 mL volatile organic analysis (VOA) vials are filled directly while in contact with the atmosphere (Direct-Fill VOA) and two alternative methods: (1) a semi-closed system method whereby 40 mL VOA vials are filled while inverted under a head of water (Inverted VOA) and (2) a relatively new (2013) closed system method in which the sample is collected without direct contact with purge water or the atmosphere (IsoFlask® ). This study reveals that, in the absence of effervescence, the difference in methane concentrations between the three sampling methods was relatively small. However, when methane concentrations equaled or exceeded 20 mg/L (the approximate concentration at which effervescence occurs in the study area), IsoFlask® (closed system) samples yielded significantly higher methane concentrations than Direct-Fill VOA (open system) samples, and Inverted VOA (semi-closed system) samples yielded lower concentrations. These results suggest that open and semi-closed system sample collection methods are adequate for non-effervescing samples. However, the use of a closed system collection method provides the most accurate means for the measurement of dissolved hydrocarbon gases under all conditions.

A study of natural uranium content in groundwater around Tummalapalle uranium mining and processing facility, India

Uranium (U) concentration and other associated risks have been studied in ground water around a newly established U mining and processing facility at Tummalapalle, India. The U concentration in groundwater samples was found to vary between 0.38 and 79.70 μg l−1. Data analysis revealed that more than 85 % of the samples had U concentration lower than the USEPA and current WHO recommended guideline value of 30 µg l−1. The annual effective dose, the lifetime excess cancer risk and chemical toxicity risk from drinking of this water have been found to be less and were within the prescribed limit.

Predicting Redox Conditions in Groundwater at a Regional Scale.

Defining the oxic-suboxic interface is often critical for determining pathways for nitrate transport in groundwater and to streams at the local scale. Defining this interface on a regional scale is complicated by the spatial variability of reaction rates. The probability of oxic groundwater in the Chesapeake Bay watershed was predicted by relating dissolved O2 concentrations in groundwater samples to indicators of residence time and/or electron donor availability using logistic regression. Variables that describe surficial geology, position in the flow system, and soil drainage were important predictors of oxic water. The probability of encountering oxic groundwater at a 30 m depth and the depth to the bottom of the oxic layer were predicted for the Chesapeake Bay watershed. The influence of depth to the bottom of the oxic layer on stream nitrate concentrations and time lags (i.e., time period between land application of nitrogen and its effect on streams) are illustrated using model simulations for hypothetical basins. Regional maps of the probability of oxic groundwater should prove useful as indicators of groundwater susceptibility and stream susceptibility to contaminant sources derived from groundwater.

Groundwater pollution by arsenic and other toxic elements in an abandoned silver mine, Mexico

This study evaluated the impact of an abandoned Ag mine on the quality of surface and groundwater. The mining site of Huautla is in south Morelos State, central Mexico. Ag–Pb–Zn and Au–Cu sulfide ores were mined in the district. The ores were characterized by the presence of Ag, galena (PbS), sphalerite (ZnS), and stromeyerite (CuAgS). Ag was the metal of greater interest. Other metals included Cu, Pb, Zn, and Au. Mining activities stopped in the early 1990s when the market price of Ag decreased; the abandoned mines then were flooded by rising groundwater levels. Because of the urgent demand for water by the inhabitants in the area, this water has been used as drinking water and as waterholes for livestock. Water sampling points included abandoned mines (America, Pajaro, Santiago, Tlachichilpa, and San Francisco), dams, and dug wells. The greatest concentrations of As and other toxic chemical elements (Fe, Mn, Pb, Cd, F) were detected in groundwater samples from flooded mines. The presence of these elements was related to the rock–water interaction process. The oxidation of sulfides appears to be the cause of increased metal concentrations in groundwater samples from flooded mine. Other possible water–rock interaction processes that can control the presence of arsenic in groundwater were the adsorption of arsenic in iron oxyhydroxides, the adsorption in carbonates, and/or coprecipitation with calcite. In the case of the San Francisco and America mines, the oxidation conditions, low correlation of As with SO4 2− and Fe2+, and concentrations of silica indicate that the presence of As in the groundwater could be due also to competition for adsorption sites.