哈尔滨市地下水的易污性评价及计算机编图

介绍了目前在国际上采用的地下水的易污性评价方法－DRASTIC评价方法，用与地下水有关的多因子－地下水的埋深，含水层的净补给，岩性，土壤类型，地形，渗流区介质，水力传导系数等7个相关因子对地下水进行评价，并结合GIS地理信息系统对哈尔滨市地下水的易污性进行评价，编制了哈尔滨市地下水的易污图，为今后地下水资源管理，土地利用，城市环境管理者等进一步制定管理方针政策提供了重要的依据。     

Comparison of DRASTIC and DC resistivity modeling for assessing aquifer vulnerability in the central Nile Delta,Egypt

DRASTIC indexing and integrated electrical conductivity (IEC) modeling are approaches for assessing aquifer vulnerability to surface pollution. DRASTIC indexing is more common, but IEC modeling is faster and more cost-effective because it requires less data and fewer processing steps. This study aimed to compare DRASTIC indexing with IEC modeling to determine whether the latter is sufficient on its own. Both approaches are utilized to determine zones vulnerable to groundwater pollution in the Nile Delta. Hence, assessing the nature and degree of risk are important for realizing effective measures toward damage minimization. For DRASTIC indexing, hydrogeological factors such as depth to aquifer, recharge rate, aquifer media, soil permeability, topography, impact of the vadose zone, and hydraulic conductivity were combined in a geographical information system environment for assessing the aquifer vulnerability. For IEC modeling, DC resistivity data were collected from 36 surface sounding points to cover the entire area and used to estimate the IEC index. Additionally, the vulnerable zones identified by both approaches were tested using a local-scale resistivity survey in the form of 1D and 2D resistivity imaging to determine the permeable pathways in the vadose zone. A correlation of 0.82 was obtained between the DRASTIC indexing and IEC modeling results. For additional benefit, the obtained DRASTIC and IEC models were used together to develop a vulnerability map. This map showed a very high vulnerability zone, a high-vulnerability zone, and moderate- and low-vulnerability zones constituting 19.89, 41, 27, and 12%, respectively, of the study area. Identifying where groundwater is more vulnerable to pollution enables more effective protection and management of groundwater resources in vulnerable areas.     

Groundwater vulnerability map of the Chrzanów karst-fissured Triassic aquifer (Poland)

A map shows intrinsic vulnerability to pollution of the Chrzanów karst-fissured aquifer (273 km²) in the southern part of Poland. This aquifer is intensively drained by numerous intakes and Zn-Pb ore mines. A DRASTIC-type parametric system was applied for groundwater vulnerability evaluation. Vulnerability assessment is based on six factors (depth to groundwater table, lithology of the unsaturated zone, net recharge, hydraulic conductivity of the aquifer, groundwater flow velocity, aquifer thickness). For the final vulnerability map construction at the scale of 1:50,000, a combination of the aquifer simulation model (using MODFLOW) and a geographical information system was applied. Maps of the net recharge, hydraulic conductivity of the aquifer and groundwater flow velocity were derived by aquifer modelling. Based on the vulnerability index (21-182), six relative vulnerability classes were selected. Reliability of the map has been verified.     

Estimating aquifer thickness using multiple pumping tests

A method to estimate aquifer thickness and hydraulic conductivity has been developed, consisting of multiple pumping tests. The method requires short-duration pumping cycles on an unconfined aquifer with significant seasonal water-table fluctuations. The interpretation of several pumping tests at a site in India under various initial conditions provides information on the change in hydrodynamic parameters in relation to the initial water-table level. The transmissivity linearly decreases compared with the initial water level, suggesting a homogeneous distribution of hydraulic conductivity with depth. The hydraulic conductivity is estimated from the slope of this linear relationship. The extrapolation of the relationship between transmissivity and water level provides an estimate of the aquifer thickness that is in good agreement with geophysical investigations. The hydraulically active part of the aquifer is located in both the shallow weathered and the underlying densely fractured zones of the crystalline basement. However, no significant relationship is found between the aquifer storage coefficient and initial water level. This new method contributes to filling the methodological gap between single pumping tests and hydraulic tomography, in providing information on the variation of the global transmissivity according to depth. It can be applied to any unconfined aquifer experiencing large seasonal water-table fluctuations and short pumping cycles.     

Assessment of groundwater vulnerability based on a modified DRASTIC model, GIS and an analytic hierarchy process (AHP) method: the case of Egirdir Lake basin (Isparta, Turkey)

A DRASTIC-model method based on a geographic information system (GIS) was used to study groundwater vulnerability in Egirdir Lake basin (Isparta, Turkey), an alluvial area that has suffered agricultural pollution. ‘Lineament’ and ‘land use’ were added to the DRASTIC parameters, and an analytic hierarchy process (AHP) method determined the rating coefficients of each parameter. The effect of lineament and land-use parameters on the resulting vulnerability maps was determined with a single-parameter sensitivity analysis. Of the DRASTIC parameters, land use affects the aquifer vulnerability map most and lineament affects it least, after topography. A simple linear regression analysis assessed the statistical relation between groundwater nitrate concentration and the aquifer vulnerability areas; the highest R ² value was obtained with the modified-DRASTIC-AHP method. The DRASTIC vulnerability map shows that only the shoreline of Egirdir Lake and the alluvium units have high contamination potential. In this respect, the modified DRASTIC vulnerability map is quite similar. According to the modified-DRASTIC-AHP method, the lakeshore areas of Senirkent-Uluborlu and Hoyran plains, and all of the Yalvaç-Gelendost plain, have high contamination potential. Analyses confirm that groundwater nitrate content is high in these areas. By comparison, the modified-DRASTIC-AHP method has provided more valid results.     

Evaluation and zoning of groundwater hazards in Pingshuo No. 1 underground coal mine,Shanxi Province,China

Coal mining safety has been compromised with water inrushes from aquifers either overlying or underlying the coal seams. Detailed studies of the associated hydrogeological conditions in China have led to different approaches to mitigate the water inrush risks from these two types of aquifers—the ‘three diagram method’ for overlying-aquifer water inrushes and the ‘vulnerability index method’ for underlying-aquifer water inrushes. The ‘three diagram method’ consists of: (1) aquifer water-abundance distribution charts derived from a geographic information system and analytic hierarchy process based water-abundance index model; (2) a fracture height map showing mining-induced fractures above the coal seam, established with stratified numerical simulations; and (3) a comprehensive partition map identifying the overlying-aquifer water inrush risk. The ‘vulnerability index method’ uses site-specific data to establish thematic maps for major factors that affect the underlying-aquifer water inrushes, whereas the weight of each control factor is determined by the analytic hierarchy process. The calculated vulnerability index is indicative of water inrush risks. The effectiveness of these methods is illustrated with a case study at the Pingshuo No. 1 underground coal mine, Shanxi Province, China.     

Regional variations in water quality and relationships to soil and bedrock weathering in the southern Sacramento Valley, California, USA

Regional patterns in ground- and surface-water chemistry of the southern Sacramento Valley in California were evaluated using publicly available geochemical data from the US Geological Survey’s National Water Information System (NWIS). Within the boundaries of the study area, more than 2300 ground-water analyses and more than 20,000 surface-water analyses were available. Ground-waters from the west side of the Sacramento Valley contain greater concentrations of Na, Ca, Mg, B, Cl and SO₄, while the east-side ground-waters contain greater concentrations of silica and K. These differences result from variations in surface-water chemistry as well as from chemical reactions between water and aquifer materials. Sediments that fill the Sacramento Valley were derived from highlands to the west (the Coast Ranges) and east (the Sierra Nevada Mountains), the former having an oceanic provenance and the latter continental. These geologic differences are at least in part responsible for the observed patterns in ground-water chemistry. Thermal springs that are common along the west side of the Sacramento Valley appear to have an effect on surface-water chemistry, which in turn may affect the ground-water chemistry.     

Sensitivity analysis for the GALDIT method based on the assessment of vulnerability to pollution in the northern Sfax coastal aquifer,Tunisia

Coastal aquifer of northern Sfax (Tunisia) suffers from the high risk to seawater intrusion and the water quality degradation due to the overexploitation. Hence, assessing the study area vulnerability to pollution is highly crucial so as to protect the groundwater resources. The assessment has been performed by applying the GALDIT method using Geographic Information System (GIS) software and multi-criteria evaluation techniques, and the sensitivity analysis approach to evaluate the effect of each GALDIT parameter on the vulnerability assessment. The GALDIT vulnerability map classifies the study area into three vulnerability classes: low vulnerability (30–50), moderate vulnerability (50–70), and high vulnerability (70–90), which represent 5, 30, and 65 % of the study area, respectively. The map illustrates that the coastal zones of the aquifer are the most threatened areas. The sensitivity analysis results show that the aquifer hydraulic conductivity (A) and the thickness of the aquifer (T) represent the determining factors in the modified vulnerability model. The real weight was used to elaborate the modified GALDIT model which was correlated with resistivity values for validation. This study could serve as a scientific basis for sustainable land planning and groundwater management in the study area.     

Assessing groundwater vulnerability and its inconsistency with groundwater quality,based on a modified DRASTIC model: a case study in Chaoyang District of Beijing City

Depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone media, and hydraulic conductivity of the aquifer (DRASTIC) model based on a geographic information system (GIS) is the most widely adopted model for the evaluation of groundwater vulnerability. However, the model had its own disadvantages in various aspects. In this work, several methods and the technologies have been introduced to improve on the traditional model. The type of the aquifer was replaced by the thickness of the aquifer, and the index of topography was removed. The indexes of the exploitation of the groundwater and the type of land use that reflected the special vulnerability were added to the system. Furthermore, considering the wideness of the study area, the fixed weights in the DRASTIC model were not suitable. An analytic hierarchy process (AHP) method and an entropy weight (Ew) method were introduced to calculate the weights of parameters. Then, the Spearman Rho correlation coefficients between IVI and the Nemerow synthetical pollution index (NI) of the groundwater quality were significantly improved, after the four steps of modification. The level differences with little gaps between Nemerow comprehensive pollution indexes and groundwater vulnerability occupied the proportion of the area from 75.68 to 84.04%, and finally, a single-parameter sensitivity analysis for the two models was used to compute the effective weights of these parameters. By comparison, the DRMSICEL model seems to perform better than the DRASTIC model in the study area. And the results show discrepancies between the vulnerability indices and groundwater quality as indicated by existence of vulnerable areas with bad water quality and vice versa.     

Modeling approaches and strategies for data-scarce aquifers: example of the Dar es Salaam aquifer in Tanzania

Management of groundwater resources can be improved by using groundwater models to perform risk analyses and to improve development strategies, but a lack of extensive basic data often limits the implementation of sophisticated models. Dar es Salaam in Tanzania is an example of a city where increasing groundwater use in a Pleistocene aquifer is causing groundwater-related problems such as saline intrusion along the coastline, lowering of water-table levels, and contamination of pumping wells. The lack of a water-level monitoring network introduces a problem for basic data collection and model calibration and validation. As a replacement, local water-supply wells were used for measuring groundwater depth, and well-top heights were estimated from a regional digital elevation model to recalculate water depths to hydraulic heads. These were used to draw a regional piezometric map. Hydraulic parameters were estimated from short-time pumping tests in the local wells, but variation in hydraulic conductivity was attributed to uncertainty in well characteristics (information often unavailable) and not to aquifer heterogeneity. A MODFLOW model was calibrated with a homogeneous hydraulic conductivity field and a sensitivity analysis between the conductivity and aquifer recharge showed that average annual recharge will likely be in the range 80–100 mm/year.     

An aquifer vulnerability assessment of the Benin Formation aquifer,Calabar, southeastern Nigeria,using DRASTIC and GIS approach

An aquifer vulnerability of the Benin Formation aquifer (Calabar, southern Nigeria) has been assessed using a combination of DRASTIC index and GIS technology. The assessment was necessitated by the fact that uncontrolled disposal of domestic, industrial and agricultural wastes have caused groundwater contamination. Therefore, prevention of contamination, monitoring and management of the aquifer was urgently required to increase the efficient use of the current water supplies. The DRASTIC method uses seven parameters (depth to groundwater table, net recharge, aquifer media, soil media, topography, influence of vadose zone and hydraulic conductivity), which were used to produce vulnerability maps. The drastic vulnerability index ranged between 124 and 170. The vulnerability map shows that the aquifer is highly vulnerable in southeastern parts of the area covering about 22 %. The medium vulnerability area covers about 56.8 % of Calabar extending from the southwest to northern parts. 21.2 % of the area covering the central and northern parts the area lies within the low vulnerability zone. The present industrial and activities are located in the eastern and western parts, which falls within the low-medium vulnerability areas. Documented nitrate concentration in hand-dug wells and boreholes are in agreement with vulnerability zones. Sensitivity analysis was performed to evaluate the sensitivity of each parameter between map layers such that subjectivity can be reduced to an extent and new weights computed for each DRASTIC parameter. As management options sensitive areas, especially in the southern parts of Calabar area, should be protected from future development.     

Evaluation of groundwater vulnerability in El-Bahariya Oasis,Western Desert,Egypt, using modelling and GIS techniques: A case study

The Nubian Sandstone Aquifer (NSSA) is the main groundwater resource of the El-Bahariya Oasis, which is located in the middle of the Western Desert of Egypt. This aquifer is composed mainly of continental clastic sediments of sandstone with shale and clay intercalations of saturated thickness ranging between 100 and 1500 m. Vulnerability assessment to delineate areas that are more susceptible to contamination from anthropogenic sources has become an important element for sustainable resources management and land use planning. Accordingly, this research aims to estimate the vulnerability of NSSA by applying the DRASTIC model as well as utilising sensitivity analyses to evaluate the relative importance of the model parameters for aquifer vulnerability in the study area. The main objective is to demonstrate the combined use of the DRASTIC and the GIS techniques as an effective method for groundwater pollution risk assessment, and mapping the areas that are prone to deterioration of groundwater quality and quantity. Based on DRASTIC index (DI) values, a groundwater vulnerability map was produced using the GIS. The aquifer analysis in the study area highlighted the following key points: the northeastern and western parts of the NSSA were dominated by ‘High’ vulnerability classes while the northwestern and southeastern parts were characterised by ‘Medium’ vulnerability classes. The elevated central part of the study area displayed ‘Low’ aquifer vulnerability. The vulnerability map shows a relatively greater risk imposed on the northeastern part of the NSSA due to the larger pollution potential of intensive vegetable cultivation. Depth-to-water, topography and hydraulic conductivity parameters were found to be more effective in assessing aquifer vulnerability.     

Multiple-methods investigation of recharge at a humid-region fractured rock site,Pennsylvania, USA

Lysimeter-percolate and well-hydrograph analyses were combined to evaluate recharge for the Masser Recharge Site (central Pennsylvania, USA). In humid regions, aquifer recharge through an unconfined low-porosity fractured-rock aquifer can cause large magnitude water-table fluctuations over short time scales. The unsaturated hydraulic characteristics of the subsurface porous media control the magnitude and timing of these fluctuations. Data from multiple sets of lysimeters at the site show a highly seasonal pattern of percolate and exhibit variability due to both installation factors and hydraulic property heterogeneity. Individual event analysis of well hydrograph data reveals the primary influences on water-table response, namely rainfall depth, rainfall intensity, and initial water-table depth. Spatial and seasonal variability in well response is also evident. A new approach for calculating recharge from continuous water-table elevation records using a master recession curve (MRC) is demonstrated. The recharge estimated by the MRC approach when assuming a constant specific yield is seasonal to a lesser degree than the recharge estimate resulting from the lysimeter analysis. Partial reconciliation of the two recharge estimates is achieved by considering a conceptual model of flow processes in the highly-heterogeneous underlying fractured porous medium.     

Aquifer vulnerability using recharge,depth to groundwater,soil type and slope to classify the vadose zone (Molototsi and Middle Letaba quaternary catchments,Limpopo Province,South Africa)

The aquifer vulnerability of the Molototsi (B81G) and Middle Letaba (B82D) quaternary catchments was assessed to determine the influence of the vadose zone on the groundwater regime. The aquifer vulnerability was assessed by developing a new method, which evaluates the vadose zone as a pathway for pollutants using the following four parameters: recharge, depth to water table, soil type (saturated vertical hydraulic conductivity) and slope (RDSS). Recharge was estimated using the chloride mass balance method, and the depth to the water table was measured in the field using dipmeter. The seepage behaviour (soil type) was determined as hydraulic conductivity from in situ infiltration and percolation testing (SABS 0252-2:1993 and double ring infiltrometer). The slopes were determined with the digital elevation method using ArcGIS software. The four parameters were overlaid using weighted sum, weighted overlay and raster calculator to produce the vulnerability map. Different weightings were attributed in the methods and the best selected. The results obtained indicated high vulnerability on the lower and upper parts of both catchments. The benefits of the method described are (a) the easy quantification of the parameters through fairly simple methods and (b) the exclusion of arbitrary index values.     

Impacts Of Urbanisation And Protection Of Water Resources In The Vilnius District,Lithuania

Vilnius municipality, Lithuanian Republic, is revising the general plan of city development. Different environmental scenarios of the city's growth possibilities have been evaluated. One of the most serious problems limiting the city's growth is water-resources protection. Increasing eutrophication of rivers and lakes is the result of pollution. Untreated sewage, recreation and agriculture are the most important sources of contamination. Therefore, certain limitations on the expansion of the city in the zones of surface-water protection are planned. The necessity of groundwater protection is further limiting the city's growth. The shallow water-table aquifer is vulnerable pollution almost everywhere, so it needs be highly protected where it is utilised for water supply or where it is replenishing deeper exploited aquifers. Eighteen to nineteen groundwater intakes are operated within the limits of the city and its suburbs. The principal artesian aquifer in the central and southwestern parts of the town is fairly vulnerable to pollution. Two groups of territories for controlling city growth are identified, on the basis of surface-water importance for recreation and groundwater for water supply. A method similar to GIS technologies was applied for this purpose.     

Assessment of aquifer vulnerability based on GIS and DRASTIC methods: a case study of the Senirkent-Uluborlu Basin (Isparta, Turkey)

Aquifer vulnerability has been assessed in the Senirkent-Uluborlu Basin within the Egirdir Lake catchment (Turkey) using the DRASTIC method, based on a geographic information system (GIS). There is widespread agriculture in the basin, and fertilizer (nitrate) and pesticide applications have caused groundwater contamination as a result of leaching. According to hydrogeological data from the study area, surface water and groundwater flow are towards Egirdir Lake. Hence, aquifer vulnerability in the basin should be determined by water quality in Egirdir Lake. DRASTIC layers were prepared using data such as rainfall, groundwater level, aquifer type, and hydraulic conductivity. These data were obtained from hydrogeological investigations and literature. A regional-scale aquifer-vulnerability map of the basin was prepared using overlay analysis with the aid of GIS. A DRASTIC vulnerability map, verified by nitrate in groundwater data, shows that the defined areas are compatible with land-use data. It is concluded that 20.8% of the basin area is highly vulnerable and urgent pollution-preventions measures should be taken for every kind of relevant activity within the whole basin.     

Groundwater vulnerability assessment for the karst aquifer of Tanour and Rasoun springs catchment area (NW-Jordan) using COP and EPIK intrinsic methods

Groundwater vulnerability maps were constructed for the surface water catchment area of Tanour and Rasoun spring (north-west of Jordan) using the COP and EPIK intrinsic groundwater vulnerability assessment methods. Tanour and Rasoun springs are the main water resources for domestic purposes within the study area. A detailed geological survey was carried out, and data of lithology, karst features, precipitation, vegetation and soil cover, etc. were gathered from various sources for the catchment area in order to determine the required parameters for each method. ArcGIS software was used for map preparation. In the resulting COP vulnerability map, spatial distribution of groundwater vulnerability is as follows: (1) high (37%), (2) moderate (34.8%), (3) low (20.1%), and (4) very low (8.1%). In the EPIK vulnerability map, only two out of four vulnerability classes characterize the catchment area: very high vulnerable areas (38.4%) and moderately vulnerable areas (61.6%). Due to limited soil thickness, the low vulnerability class is absent within the catchment. The high percentage of very high to moderately vulnerable areas displayed by both the COP and EPIK vulnerability assessment methods are reflected by different pollution events in Tanour and Rasoun karst springs especially during the winter season. The high sensitivity of the aquifer to pollution can be explained by different factors such as: thin or absent soil cover, the high development of the epikarst and karst network, and the lithology and confining conditions of the aquifer.     

Modeling water-table fluctuations in a sloping aquifer with random hydraulic conductivity

To prevent environmental problems like water logging and increase in soil salinity which are responsible for the degradation of the top productive soils, an optimum ditch drainage design is required. For this purpose a knowledge of the spatio-temporal variation of the water table is essential. In this study the spatio-temporal variation of the water table in a sloping ditch drainage system has been modeled from a stochastic point of view, incorporating randomness in hydraulic conductivity to get the expression for the mean and the standard deviation of the water-table height. The hydraulic conductivity has been considered to be a realization of a log-normal distribution. Application of these expressions in the prediction of mean water-table variation with the associated error bounds has been demonstrated with the help of a ditch drainage problem of a sloping aquifer. The sensitivity analysis has also been carried out to see the effect of variability in the hydraulic conductivity on the water-table fluctuations. The error bounds quantified on the water-table height will thus help in the decision-making process for proper drainage design.     

Modified DRASTIC assessment for intrinsic vulnerability mapping of karst aquifers: a case study

Groundwater in karstic aquifers can be dangerously sensitive to contamination. In this paper, DRASTIC assessment was modified and applied, for the first time, to address the intrinsic vulnerability for karst aquifers. The theoretical weights of two of DRASTIC’s parameters (aquifer media and hydraulic conductivity) were modified through sensitivity analysis. Two tests of sensitivity analyses were carried out: the map removal and the single parameter sensitivity analyses. The modified assessment was applied for the karst aquifers underlying Ramallah District (Palestine) as a case study. The aquifer vulnerability map indicated that the case study area is under low, moderate and high vulnerability of groundwater to contamination. The vulnerability index can assist in the implementation of groundwater management strategies to prevent degradation of groundwater quality. The modified DRASTIC assessment has proven to be effective because it is relatively straightforward, use data that are commonly available or estimated and produces an end product that is easily interpreted.     

Intrinsic vulnerability assessment of Saturnia thermal aquifer by means of three parametric methods: SINTACS,GODS and COP

Three different parametric methods for the evaluation of intrinsic vulnerability to pollution have been applied in a hydrothermal carbonate aquifer located in central-northern Italy and the results obtained were compared with each other. The study area, large, approximately 152 km², lies in an area of the northern Apennines. The investigated aquifer feeds the hot thermal springs of Saturnia. The vulnerability assessment methods used are: SINTACS, GODS and COP. The vulnerability maps obtained were first individually examined, and then they were compared with each other by means of spatial analysis. These maps show similar results for the estimation of the vulnerability just in some areas. SINTACS yields areas potentially vulnerable to pollution along the Albegna River and its major tributaries in the northern part of the study area. The GODS index map reflects the great importance that this method gives to the lithological characteristics of the unsaturated zone in the subdivision of areas with different vulnerability. GODS and COP methods agree in classifying low vulnerability in the most part of central-southern study area, where the aquifer is confined by the Pliocene clay deposits. Based on the conceptual model of groundwater flow developed for the aquifer under investigation, COP seems the most appropriate method among those applied in this work, in particular with regard to the assessment of the vulnerability of the recharge area of thermal groundwater. Located in the northern part of the study area, where karst carbonate formations of the Tuscan Nappe outcrop, this recharge area is classified by the COP method as highly vulnerable to pollution.