A GIS-based DRASTIC model for assessing aquifer vulnerability in Kakamigahara Heights, Gifu Prefecture, central Japan

A GIS based DRASTIC model for assessing groundwater vulnerability in shallow aquifer in Aligarh, India

Assessing the quality of groundwater is important to ensure sustainable safe use of these resources. However, describing the overall water quality condition is difficult due to the spatial variability of multiple contaminants and the wide range of indicators (chemical, physical and biological) that could be measured. This contribution proposes a GIS-based groundwater quality index (GQI) which synthesizes different available water quality data (e.g., Cl−, Na+, Ca2+) by indexing them numerically relative to the World Health Organization (WHO) standards. Also, introduces an objective procedure to select the optimum parameters to compute the GQI, incorporates the aspect of temporal variation to address the degree of water use sustainability and tests the sensitivity of the proposed model. The GQI indicated that the groundwater quality in the Nasuno basin, Tochigi Prefecture, Japan, is generally high (GQI <90). It has also displayed the natural (depth to groundwater table, geomorphologic structures) and/or anthropogenic (land-use and population density) controls over the spatial variability of groundwater quality in the basin. Temporally, groundwater quality is more variable in the upper and lower parts of the basin (variation, V, 15–30%) compared to the middle part (V, <15%) probably attributed to the seasonality of precipitation and irrigation of rice. In the lower southeastern part of the Nasuno basin and the vicinity of the Naka and Houki rivers the sustainable use of groundwater is constrained by the relatively low and variable groundwater quality. The model sensitivity analysis indicated that parameters which reflect relatively lower water quality (high mean rank value) and those of significant spatial variability imply larger impacts on the GQI and must be carefully and accurately mapped. Optimum index factor technique allows the selection of the best combination of parameters dictating the variability of groundwater quality and enables an objective and fair representation of the overall groundwater quality.

Assessing groundwater quality using GIS

Groundwater contamination and vulnerability in urbanized areas are of major concern and need proper attention. Several models including the DRASTIC model are used to evaluate groundwater
 vulnerability. In the present study, a modified DRASTIC model named as DRASTICA was used, by including anthropogenic influence as a model parameter. The study included an innovative methodology to characterize the anthropogenic influence by using satellite observations of night-lights from human settlements as a proxy and land-use/land-cover surrounding the urbanized area in Lucknow, the capital city of the most populous State of Uttar Pradesh in India. Geographical information system was used for spatial integration of different parameter maps. The groundwater vulnerability to pollution indicated that about 0.7 % area is covered under very high vulnerable zone, 24.5 % area under high vulnerable zone, 66.6 % area under moderately vulnerable zone and 8.2 % area under low vulnerable zone. The results were validated using nitrate concentration in ground water. It was shown that the proposed DRASTICA model performed better than conventional DRASTIC model in an urbanized environment. Sensitivity analysis indicated that anthropogenic impact and depth to water table largely influenced the groundwater vulnerability to pollution, thereby signifying that anthropogenic influence has to be addressed precisely in such studies. The modified-DRASTIC/DRASTICA model proposed in this study will help in better categorization of groundwater vulnerable zones to pollution where anthropogenic contamination is high, particularly in and around urban centers.

A modified-DRASTIC model (DRASTICA) for assessment of groundwater vulnerability to pollution in an urbanized environment in Lucknow, India

The multivariate statistical structure of DRASTIC model

deterministic techniques are more appropriate for sub-regional predictive (quantitative) assessment and are tied to specific perceived processes. Probabilistic techniques are data intensive and involve groundwater numerical modelling as they are thus inappropriate for broad, regional vulnerability assessments based on readily available spatial variables. It is concluded that stochastic techniques offer more promise than other techniques involving weights-of-evidence modelling; new work in this area is described. We review here available approaches and discuss their merits and drawbacks in relation to attempts to validate the procedures. The overall aim is to produce, eventually, a method of vulnerability assessment applicable at regional (and in simplified form at State or National) scale, using information which is readily available from existing or planned databases. We regard data availability as essential in development of these models/assessment procedures, and below we evaluate the different methods against this constrain t. Assessment procedures

Assessment of the relative vulnerability of groundwater to pollution: a review and background paper for the conference workshop on vulnerability assessment

The DRASTIC vulnerability assessment procedure, a standardised system developed in the US, has been evaluated against a simpler, region-specific spatial modelling approach in an agricultural area of complex geology in northern New South Wales. There was a broad relationship between nitrate in groundwater and relative vulnerability determined by both DRASTIC and spatial modelling. Both assessments, however underestimated vulnerability to pollution by nitrate particularly for point sources such as poultry farms and piggeries. Vulnerability maps derived from spatial models are much easier to develop and apply than DRASTIC, and overcome the subjectivity of the standardised approach. They still underestimate vulnerability to pollutants like nitrate which behave semi-conservatively in soils and groundwaters which emphasises the need for caution in applying vulnerability maps. These are only meant to be regional scale guides which are inappropriate to infer pollutant behaviour at local scale.

Comparison of Standardised and Region-specific Methods for Assessment of the Vulnerability of Groundwater to Pollution: A Case Study in an Agricultural Catchment

R Barron

Papers

Assessment of the relative vulnerability of groundwater to pollution: a review and background paper for the conference workshop on vulnerability assessment

Comparison of Standardised and Region-specific Methods for Assessment of the Vulnerability of Groundwater to Pollution: A Case Study in an Agricultural Catchment