Geochemical heterogeneity and isotope geochemistry of natural attenuation processes in a gasoline-contaminated aquifer at the Hnevice site,Czech Republic

The geochemical processes, water–rock interactions and stable isotopes distribution (δ¹³C of DIC and δ¹⁸O and δ³⁴S of \({\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}} \)) were investigated in the gasoline-contaminated aquifer at the Hnevice site, 50  km northwest of Prague, Czech Republic. Diesel, gasoline and oil leaks originate from a large fuel storage area causing heavy contamination of the saturated and unsaturated zones in an area of about 0.7  km². Groundwater investigations were conducted using five multilevel sampler wells with emphasis on redox parameters and degradation by-products and a solid-phase study focused on iron speciation and determination of principal and secondary minerals. Based on the study of groundwater and solid-phase geochemistry, four different geochemical zones were described. Zone I is thought to be background consisting of an aerobic aquifer and the absence of reduced species in significant concentrations. Zone II is situated in the plume core with methanogenic, sulphate and iron-reducing conditions accompanied by ankerite and kutnahorite precipitates and significant depletion of the oxidation capacity of the aquifer. Zone III is a mixing (corona) zone, situated at the fringe of the plume with high biodegradation rates and Fe(III)-precipitants. In zone IV, reoxidation of Fe(II) minerals (with e.g. the occurrence of psilomelane and cornelite) is typical.     

Integrated use of hydrochemistry and resistivity methods in groundwater contamination caused by a recently closed solid waste site

 In order to investigate the groundwater contamination by solid waste disposal using both hydrochemical and geophysical methods, the Halkalı (I˙stanbul) solid waste disposal site which was closed in 1994 was investigated. The disposal site lies on a ridge between two valleys filled with alluvium. A total of six boreholes were drilled on two lines across the Menekşe valley adjacent to the Halkalı site. Groundwater samples collected from these boreholes were analyzed for various contaminant parameters. The results indicate that TDS and chloride concentrations decrease horizontally away from the waste site whereas they increase with depth. Electrical soundings carried out at 12 locations yielded high resistivity values at the upstream part of Menekşe valley while lower values were obtained from the locations near the leachate seepage points. Received: 11 November 1997 · Accepted: 23 February 1998     

Field investigation of the natural attenuation and intrinsic biodegradation rates at an underground storage tank site

 Contamination of groundwater by petroleum-hydrocarbons is a widespread environmental problem. Natural attenuation is a passive remedial approach to degrade and dissipate contaminants in soil and groundwater. In this study, a mass flux approach was used to calculate the contaminant mass reduction and field-scale decay rate at a gasoline spill site. The mass flux technique is accomplished using the differences in total contaminant mass flux across two cross sections of the contaminant plume. The mass flux calculation shows that up to 88% of the dissolved BTEX (benzene, toluene, ethylbenzene, and xylene isomers) removal was observed by natural attenuation processes. The efficiency of intrinsic biodegradation was evaluated by the in situ tracer method. A first-order decay model was applied for the natural attenuation and intrinsic biodegradation rate calculation. Results reveal that intrinsic biodegradation process was the major cause of the BTEX reduction among the natural attenuation mechanisms, and iron reduction was the dominant biodegradation pattern within the plume. Approximately 87% of the BTEX removal was caused by intrinsic biodegradation processes. The calculated BTEX natural attenuation and intrinsic biodegradation rates were 0.24 and 0.16% l/day, respectively. Results suggest that natural attenuation mechanisms can effectively contain the plume, and the mass flux method is useful in assessing the efficiency of the natural attenuation. Received: 6 December 1999 · Accepted: 11 July 2000     

Application of a groundwater contamination index in Finland and Slovakia

A methodology is presented for evaluating and mapping the degree of groundwater contamination by applying the contamination index C _d . The applicability of the contamination index was tested in two distinctly different geological regions: the area between Uusikaupunki and Yläne in southwestern Finland and the Brezno area in central Slovakia. The index takes into account both the number of parameters that exceed the upper permissible concentrations of contaminants or potentially harmful elements and the part of the concentrations exceeding those values. The water-quality parameters reflect the effect of diverse natural (topographical, climatical, geological, biological) and anthropogenic (type of land use, local pollution) environmental factors on groundwater quality. In Finland, technical-aesthetic contamination was found over more than half the test area. These quality problems were most often related to acidity and high concentrations of organic carbon and Al and Fe in wells. Health-risk-based contamination, mainly caused by elevated concentrations of fluoride, radon, or nitrate, was found in only a few separate areas. In Slovakia, naturally contaminated and anthropogenically polluted groundwaters could be distinguished. The geogenic pollution is mainly derived from sulfide mineralizations. In both countries the strongest anthropogenic pollution was found in intensively cultivated areas.     

浅层地下水氯代烃污染天然衰减速率的估算

天然衰减恢复技术是恢复和控制浅层地下水氯代烃污染的技术之一,如何简便获取可靠的氯代烃衰减速率常数是该技术应用的一个关键。趋势线分析方法是一种简便有效的方法,在污染羽状体稳定的条件下,通过地下水流向上至少3口监测井的资料,能够比较准确地估算出污染物的天然衰减速率常数和生物降解速率常数。某氯代烃污染典型区的应用实例研究表明,该区四氯乙烯(PCE)的天然衰减速率常数和生物降解速率常数分别为0·000925d-1和0·000537d-1,证实该区浅层地下水中的PCE存在天然生物降解,但降解速率比较缓慢。忽略吸附作用的天然衰减容量计算所得出的天然衰减速率常数明显小于实际结果,说明尽管典型区包气带及含水层介质的有机碳含量很少,但它们对PCE的吸附作用不容忽视。     

Modelling natural attenuation of heavy-metal groundwater contamination in the Selebi-Phikwe mining area,Botswana

Seepage from a tailings dam is the major source of groundwater pollution in the Selebi-Phikwe area, where mining of sulphidic nickel–copper–cobalt ore started in 1973 and will continue until 2014. The seepage water has a pH in the range of 1.7–2.8 and is strongly enriched in SO₄ ²⁻ (5,680 g/L) and heavy metals (6,230 μg/L Ni, 1,860 μg/L Cu and 410 μg/L Co). The fracture aquifer affected by pollution from the dam exhibits a remarkable capacity of heavy-metal sorption. Most of the Ni, Cu and Co is scavenged at less than 500 m distance downgradient from the polluting source, whereas SO₄ ²⁻ is not immobilized significantly. The heavy-metal sorption process is assumed to be due to surface complexation, which is supported by a relatively high groundwater pH (in the range of 6.2–7.8 at >200 m distance from the tailings dam). The objective of this study is to demonstrate that the sorption process can be incorporated into a realistic three-dimensional reactive-transport groundwater model that is implicitly charge-balanced. The simulations are performed with the PHAST1.2 program, which is based on the HST3D flow and transport code and the hydrochemical PHREEQC2.12 code.     

Selenium attenuation via reductive precipitation in unsaturated waste rock as a control on groundwater impacts in the Idaho phosphate patch

Phosphate mining in southeastern Idaho has historically resulted in the release of dissolved metals and inorganics to groundwater and surface water, primarily due to leachate from waste rock in backfilled pits and overburden storage piles. Selenium (Se) is of particular concern due to its high concentration in leachate and its limited attenuation downgradient of source zones under oxic conditions. Assessments of potential groundwater/surface water impacts from waste rock typically involve laboratory characterization using saturated and unsaturated flow columns packed with waste rock. In this study, we compare the results of saturated and unsaturated column tests with groundwater quality data from the Mountain Fuel, Champ, South and Central Rasmussen Ridge Area (SCRRA), Smoky Canyon, Ballard, Henry, and Enoch Valley Mines, to understand the release and attenuation of Se in different geochemical environments. Column studies and field results demonstrate that the ratio of aqueous Se to aqueous sulfate (Se:SO₄ ratio) is a useful metric for understanding Se release and attenuation, where the extent of sulfate reduction is much less than Se reduction. Comparison of dissolved Se and sulfate results suggests that the net leachability of Se from unsaturated waste rock is variable. Overall, Se concentrations in groundwater directly beneath waste rock dumps is not as high as would be predicted from unsaturated columns. Lower Se:SO₄ ratios are observed immediately beneath waste rock dumps and backfilled pits relative to areas receiving shallow waste rock runoff. It is hypothesized that Se released in the oxic upper portions of the waste rock is subsequently attenuated via reductive precipitation at depth in unsaturated, low-oxygen portions of the waste rock. This highlights an important mechanism by which Se may be naturally attenuated within waste rock piles prior to discharge to groundwater and surface water. These results have important implications for mining practices in the region. A better understanding of Se dynamics can help drive waste rock management during active mining and capping/water management options during post-mining reclamation.     

Fluoride contamination in groundwater resources of Alleppey,southern India

Alleppey is one of the thickly populated coastal towns of the Kerala state in southern India.Groundwater is the main source of drinking water for the 240,991 people living in this region.The groundwater is being extracted from a multi-layer aquifer system of unconsolidated to semi-consolidated sedimentary formations,which range in age from Recent to Tertiary.The public water distribution system uses dug and tube wells.Though there were reports on fluoride contamination,this study reports for the first time excess fluoride and excess salinity in the drinking water of the region.The quality parameters,like Electrical Conductivity(EC) ranges from 266 to 3900 μs/cm,the fluoride content ranges from 0.68 to2.88 mg/L,and the chloride ranges between the 5.7 to 1253 mg/L.The main water types are Na-HC03,NaCO_3 and Na-Cl.The aqueous concentrations of F~- and CO_3~(2-) show positive correlation whereas F~- and Ca~(2+) show negative correlation.The source of fluoride in the groundwater could be from dissolution of fluorapatite,which is a common mineral in the Tertiary sediments of the area.Long residence time,sediment-groundwater interaction and facies changes(Ca-HCO_3 to Na-HCO_3) during groundwater flow regime are the major factors responsible for the high fluoride content in the groundwater of the area.High strontium content and high EC in some of the wells indicate saline water intrusion that could be due to the excess pumping from the deeper aquifers of the area.The water quality index computation has revealed that 62%of groundwater belongs to poor quality and is not suitable for domestic purposes as per BIS and WHO standards.Since the groundwater is the only source of drinking water in the area,proper treatment strategies and regulating the groundwater extraction are required as the quality deterioration poses serious threat to human health.     

Assessment of natural attenuation of aromatic hydrocarbons in groundwater near a former manufactured-gas plant, South Carolina, USA

 Shallow, anaerobic groundwater near a former manufactured-gas plant (MGP) in Charleston, South Carolina, USA, contains mono- and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively). Between 1994 and 1997, a combination of field, laboratory, and numerical-flow and transport-model investigations were made to assess natural attenuation processes affecting MAH and PAH distributions. This assessment included determination of adsorption coefficients (K _ad ) and first-order biodegradation rate constants (K _bio ) using aquifer material from the MGP site and adjacent properties. Naphthalene adsorption (K _ad =1.35×10^–7 m³/mg) to aquifer sediments was higher than toluene adsorption (K _ad =9.34×10^–10 m³/mg), suggesting preferential toluene transport relative to naphthalene. However, toluene and benzene distributions measured in January 1994 were smaller than the naphthalene distribution. This scenario can be explained, in part, by the differences between biodegradation rates of the compounds. Aerobic first-order rate constants of ¹⁴C-toluene, ¹⁴C-benzene, and ¹⁴C-naphthalene degradation were similar (–0.84, –0.03, and 0.88 day^–1, respectively), but anaerobic rate constants were higher for toluene and benzene (–0.002 and –0.00014 day^–1, respectively) than for naphthalene (–0.000046 day^–1). Both areal and cross-sectional numerical simulations were used to test the hypothesis suggested by these rate differences that MAH compounds will be contained relative to PAHs. Predictive simulations indicated that the distributions of toluene and benzene reach steady-state conditions before groundwater flow lines discharge to an adjacent surface-water body, but do discharge low concentrations of naphthalene. Numerical predictions were "audited" by measuring concentrations of naphthalene, toluene, and benzene at the site in early 1997. Measured naphthalene and toluene concentrations were substantially reduced and the areal extent of contamination smaller than was both observed in January 1994 and predicted for 1997. Measured 1997 benzene concentrations and distribution were shown to be relatively unchanged from those measured in 1994, and similar to predictions for 1997. Received: 26 June 1997 · Accepted: 25 August 1997     

Impact of past mining activity on the quality of groundwater in SW Sardinia (Italy)

Hydrogeochemical surveys were carried out in SW Sardinia (Italy) to investigate the impact of past mining activities on the quality of groundwater. The chemistry of waters from flooded galleries, adits and dumps has been compared with that of springs and wells in the same area at sites relatively far from any mine legacy. A feature, common to all waters, is the circumneutral pH, since the carbonate formations in the area neutralise the acidity produced by the oxidation of Fe-bearing sulphide minerals in the mine impacted water. However, groundwater interacting with mine workings is degraded in quality; it shows high dissolved SO₄, Zn, Cd and Pb contents. In some cases groundwater exceeds the limit established by the guidelines of the World Health Organization for Pb content in drinking water, so that groundwater is mixed before entering the local aqueducts. Results from this study suggest that more attention needs to be paid to the impact on the streams from contaminated water flowing out from some mine areas because during the dry season these streams are only fed by mine groundwater. We recommend focusing efforts to reduce the chemical contamination prior to discharge.     

Assessment of groundwater quality and contamination problems ascribed to an abandoned uranium mine (Cunha Baixa region,Central Portugal)

The assessment of groundwater quality and its environmental implications in the region of the abandoned Cunha Baixa uranium mine (Central Portugal) was carried out from 1995 to 2004. Shallow groundwater is the major water supply source for irrigation in the neighbourhood of Cunha Baixa village. Water samples from the mine site as well as from private wells were collected in order to identify the mining impact on water composition, the extent of contamination and the seasonal and temporal groundwater quality variations. Some of the sampled private wells contain waters having low pH (<4.5–5) and high values of EC, TDS, SO₄, F, Ca, Mg, Al, Mn, Ni, U, Zn and ²²⁶Ra. The wells located through the ESE–WSE groundwater flow path (1 km down gradient of the mining site) display the most contaminated water. In the summer season, the levels of SO₄, Al, Mn, and U were 50–120 times higher than those registered for uncontaminated waters and exceeded the quality limits for irrigation purposes, presenting soil degradation risks. Nevertheless, this study indicates that groundwater contamination suffered a small decrease from 1999 to 2004. The bioaccumulation of toxic metals such as Al, Mn, and U within the food chain may cause a serious health hazard to the Cunha Baixa village inhabitants.     

Fluoride contamination in groundwater: A global review of the status,processes, challenges,and remedial measures

Groundwater pollution by fluoride is one of the prime concerns of the world population due to its toxicity, which results in adverse health impacts. In this paper, we review the current scenario of the fluoride contamination of groundwater in various countries across the globe and its impact on human health. During the last decade, several newly affected regions have been reported all over the world, with more than 100 countries affected by fluoride contamination in groundwater (concentration exceeding the acceptable limit of 1.5 mg/L defined by the World Health Organization). Fluoride poisoning is mainly due to the unsupervised ingestion of products for dental and oral hygiene and over-fluoridated drinking water. It is estimated that more than 200 million people from different countries are affected by fluoride-related groundwater issues and health problems. The highest among these are from the countries in Africa (38), Asia (28), and Europe (24), followed by countries like South America (5), North America (3), and Australia (2). The source of fluoride in drinking water is primarily geogenic, together with forage, grasses and grains, tea, and anthropogenic sources. These countries affected were correlated with climatic zones and geological factors to gain insights into geospatial relations. Our analyses show that most of the fluoride pollution-prone zones are located in high-grade metamorphic terranes with granitoid or alkaline intrusions, geothermal hot springs, and volcanic regions with arid or semi-arid climatic conditions. This study also finds that children across the globe are more vulnerable than adults to fluoride contamination. The review finds that, although there are efficient fluoride removal techniques, including filters with next-generation nanomaterials, to date, there has not been a single technique developed that can claim to be a practically robust solution for fluoride removal from drinking water. Therefore, we suggest developing next-generation filters that can retain essential minerals in water and remove only harmful ones and selecting purification technologies according to need, climate, geology, and geographic location. The findings from our review would help policymakers take effective and sustainable measures for safe water supply in the affected areas. Within the framework of the Sustainable Development Goals (SDGs), particularly SDG 3 (Good Health and Well-being) and SDG 6 (Clean Water and Sanitation), this study emphasizes the critical role of fluoride as a key indicator. It underscores the imperative of addressing elevated fluoride levels in drinking water, particularly in African and Asian countries, to achieve the overarching objective of universal and equitable access to safe, affordable, and uncontaminated drinking water for global society by the targeted year of 2030.     

Migration and contamination of major and trace elements in groundwater of Madras city,India

Groundwater samples collected from both open and bore wells in an area of about 270 km² from Madras City, India, have been analyzed for major ions (HCO₃, Cl, Si, Na, Ca, and Mg) and trace elements (As, Se, B, V, Cr, Fe, Co, Pb, Cu, Zn, Cd, Mn, Ni, Mo, and Ba). The study reveals that the quality of potable water has deteriorated to a large extent. Seawater intrusion into the aquifer has been observed in nearly 50 percent of the study area. The toxic elements (As and Se) have already exceeded the maximum permissible limits of drinking water in almost the entire city. A positive correlation of As and Se with other toxic metals such as V, Cr, Fe, B, etc., indicates that all these elements are anthropogenic in origin. Applying multivariate analysis, the source for trace elements in groundwater has been grouped into two major factors: pollution and mobilization factors. The groundwater in the study area is largely contaminated by organic effluents and reflects the intensity of pollution caused by the overlying soil sediment and rapid infiltration of the pollutants.     

Arsenic contamination in surface drainage and groundwater in part of the southeast Asian tin belt,Nakhon Si Thammarat Province,southern Thailand

The occurrence of human health problems resulting from arsenic contamination of domestic water supplies in Ron Phibun District, Nakhon Si Thammarat Province, southern Thailand was first recognized in 1987. The area has an extensive history of bedrock and alluvial mining, the waste from which is typically rich in arsenopyrite and related alteration products. In 1994 a collaborative study was instigated involving Thai and British government authorities to establish the distribution and geochemical form of As in surface drainage and aquifer systems in the affected area, the probable sources of As contamination, and the potential for problem alleviation. Hydrochemical analyses of surface- and groundwaters have confirmed the presence of dissolved As at concentrations exceeding WHO potable water guidelines by up to a factor of 500. Contamination of the shallow alluvial aquifer system is systematically more severe than the underlying carbonate-hosted aquifer. Deep boreholes may therefore provide the best available potable water source for the local population. The presence of up to 39% of total As as arsenite (H₃AsO₃) within the carbonate aquifer may, however, constitute a hidden toxicological risk, not evident in the shallow groundwater (in which arsenate species account for > 95% of total As). Mineralogical investigations of As-rich tailings and flotation wastes were undertaken to evaluate their likely impact on water quality. The results indicate that although some flotation wastes contain up to 30% As, the rate of leaching is extremely low. Consequently the As loading of drainage emanating from such waste is below the subregional average. Analyses of the silty alluvium that covers much of the central sector of the study area have highlighted As concentrations of up to 5000 mg kg^–1, probably carried by disseminated arsenopyrite. Following sulfide dissolution, the mobility of As in this material may be high (with resultant contamination of shallow groundwater) due to the low Fe content of the soil. On the basis of the data acquired, a range of pollution mitigation schemes are currently under investigation including Fe supplementation of alluvium and microbial degradation of disseminated arsenopyrite.     

Amelioration of groundwater nitrate contamination following installation of a central sewage system in two Israeli villages

This study traces both the long-term deterioration of the ground water supply in two neighboring villages that had relied upon cesspits/cesspools for waste disposal, as well as the subsequent progressive improvement to original water quality levels. The rapid improvement is attributed to the replacement of the cesspits by a central sewage disposal network. In each of the villages of Kefar Bara and Kefar Kassem, a single, relatively deep, community well supplies drinking water. These wells were drilled into the underlying carbonate Judea Group aquifer that initially provided very high quality potable water. Over time, large increases in the nitrate contamination, reaching to as high as 67 mg/L nitrate, paralleled the population growth. The higher dissolved nitrate concentrations were also marked by enrichments in the δ¹⁵ N (approximately +8 ‰_(air)) values above those of the surrounding and regional uncontaminated background δ¹⁵ N values (in the range of +3 to +6 ‰ _(air)). Within several years after the cesspit disposal was terminated the nitrate values declined to concentrations that were reported (approximately 25 mg/L-NO₃) decades prior, when the water quality monitoring had just commenced. This study demonstrates not only how water quality can degrade but also how it can be restored once the problem is identified and countered. This simple method of ameliorating a water quality problem that was tending towards reaching serious proportions would seem to be quite efficacious for any area lacking economic alternative water resources.     

A study on the hydrogeology and hydrogeochemistry of groundwater from different depths in a coastal aquifer: Annamalai Nagar,Tamilnadu, India

Chemical characterization of groundwater is essential to bring out its nature and utility. Samples from shallow and deep ground water of the same location were collected and studied for their geochemical characteristics following standard procedures (APHA 1998). Sediment samples from different depths were collected and analysed for minerals using FTIR and SEM. Resisitivity logging was carried out in the bore well to understand the variations in depth to fresh water potential. The shallow ground water is dominated by Na–Cl–HCO₃–SO₄ and deeper groundwater by Na–HCO₃–SO₄–Cl types. It is observed that there is a significant ionic variation with depth. The ionic strength of the deeper samples is lesser than in the shallower samples. Wide pH variations in the shallow water samples are due to ion exchange process. Thermodynamic stability plot was used to identify the state of stability. It is inferred that there is no major significant difference in the thermodynamic state of stability in the shallow and the deeper aquifers as the aquifer matrix for the shallow and deeper aquifers are almost similar. Saturation index of Gibbsite, Kaolinite, Calcite, Dolomite and anhydrite, were studied for shallow and deep aquifers, to identify the difference in hydro chemical signatures. The Si/Al ratios of shallow samples are less when compared with the deeper samples. Leaching of secondary salts was the chief mechanism controlling the ground water chemistry of the region.     

Investigation of groundwater flow in karst areas using component separation of natural potential measurements

 The natural (electrical) potential (NP) method – also known as self-potential, spontaneous potential and streaming potential (SP) – has been used to locate areas of groundwater flow in karst terrane. NP is the naturally occurring voltage at the ground surface resulting from ambient electrical currents within the earth. The measurement of NP can be used to characterize groundwater flow in karst terrane because electrical potential gradients are generated by the horizontal flow of water along fractures or conduits and the vertical infiltration of water into fractures or shafts. NP data from a site on the Mitchell Plain of southern Indiana, USA, revealed that NP data can be decomposed into three components: topographic effect, residual NP and noise. At this site, NP was inversely proportional to elevation, but the correlation varied with time. The topographic correction factor varied from –2.5 to –1.2 mV/m (NP change per unit elevation increase), with an average linear correlation coefficient (R) of 0.95. Because the site slopes toward an adjacent creek that is the local groundwater discharge zone, one possible explanation for this effect is a streaming-potential mechanism generated by groundwater movement toward the creek. The residual NP data revealed three negative anomalies at the survey area. Two of them coincide with sinkholes. A part of the third anomaly is coincident with a small valley, and concentrated infiltration does occur at this elevation in other valleys at the site, as evidenced by the existence of sinkholes. However, the dispersed, low-magnitude nature of the third anomaly does not prove the existence of concentrated groundwater recharge activity. Received: 18 March 1998 · Accepted: 27 April 1998     

Field scale remediation of mine wastes at an abandoned gold mine,Australia II: Effects on plant growth and groundwater

This second paper reports the results of plant growth, plant mortality, plant leaf tissue metal and salt concentrations and leachate quality monitoring from lysimeters in four large field trial treatments established on sulfidic waste rock/soil that was used for haul road construction at a closed gold mine in Australia. The TerraB™, lime and clay treatments allowed good tree growth of four Eucalypt species, compared to the control. There was no statistical difference in tree growth between the TerraB™, lime or clay treatments over the 2 years of monitoring in this paper. However, the growth of one tree species was poor in the TerraB™ treatment. Leaf tissue metal and major ion data are also presented. Leachate pH in the control became increasingly acidic (pH 4.57–3.95). The addition of Ca(OH)₂ and biosolids led to an initial increase in leachate pH, compared to the control; however, this has decreased over the duration of the study (pH 5.37–4.89) and may affect the sustainable growth of plants in the future. In the TerraB™ and biosolids treatment leachate pH increased to 6.92 after the first rainfall event and continued to increase over the duration of the study to pH 7.4 after 24 months. After 24 months average heavy metal leachate concentrations (mg/L) in the lysimeters for Al, Cd, Cu, Mn and Zn were, control: 32.55, 5.67, 12.71, 39.29, 121.80, TerraB™: 0.07, 0.02, 0.07, 0.57, 0.23, and lime: 2.19, 1.19, 2.33, 3.6, 28.4. No leachate was available for collection from the clay treatment indicating that this technique was functioning in terms of minimizing the infiltration of water into the mine soil.     

Effects of water extraction in a vulnerable phreatic aquifer: Consequences for groundwater contamination by pesticides, Sint-Jansteen area, The Netherlands

Pesticides are a potential threat to the quality of extracted groundwater when the water-supply area is used for agricultural activities. This problem is discussed for the water-supply area of Sint-Jansteen, The Netherlands, where measured pesticide concentrations in the extracted water regularly exceed EU limits (0.1 μg/L). Groundwater samples taken from the aquifer within the water-supply area show low contamination, but samples taken from the extracted water occasionally contain pesticides, making the water inadequate for drinking-water purposes. The more intense contamination of the extracted water is caused by the change in the natural groundwater flow pattern near the extraction wells. In this area, pesticide use cannot be avoided easily, and an approach is given to differentiate pesticide use in the area according to expected travel time toward the wells and the chemical characteristics of the pesticides. A groundwater flow model for the area is developed and the effects of groundwater extraction on the natural flow pattern are evaluated. Using particle tracking, the travel-time zones are determined. Combining these results and the degradation behavior of certain pesticides led to an optimal scheme to integrate agricultural activities and groundwater extraction in the area. This is illustrated for five different types of pesticides (atrazine, simazine, bentazone, MCPA, and mecoprop). Received, October 1998/Revised, July 1999, September 1999/Accepted, November 1999     

Influence of topsoil of pyroclastic origin on microbial contamination of groundwater in fractured carbonate aquifers

The aim of the research was to analyse the influence of a topsoil of pyroclastic origin on microbial contamination of groundwater in a carbonate aquifer and verify the reliability of thermotolerant coliforms and fecal enterococci as bacterial indicators. The research was carried out through hydrogeological and microbiological monitoring at an experimental field site in Italy during two hydrologic years and through column tests in a laboratory. The taxonomic classification of fecal indicators detected in spring water samples was performed using API20 galleries. Fecal enterococci were also identified by means of 16S rRNA gene sequencing. The topsoil of pyroclastic origin significantly retains both thermotolerant coliforms and fecal enterococci. Results of column tests carried out in soil blocks collected randomly within the test site suggest that Escherichia coli was more retained than Enterococcus faecalis, even though this difference is statistically significant in only two out of six soil samples. Thus, a non-uniform difference in retention is expected at field scale. This suggestion is in agreement with the results of the microbiological monitoring. In fact, fecal enterococci were a more reliable indicator than thermotolerant coliforms for detecting contamination at both seasonal springs of the aquifer system, while no significant differences were observed at the perennial spring.