Aquifer Unit Management Plan (AUMP) For Groundwater Resources Management of Multi-layered Coastal Aquifer System

To address the vulnerability of coastal aquifer to over exploitation and sea water intrusion, a groundwater resources management plan titled as Aquifer Unit Management Plan (AUMP) is designed to provide valuable guidance for groundwater management of a multi-layered cuddalore coastal aquifer system located east coast of South India. The aquifer unit management plan is based on the summative examination of the aquifer unit disposition, response of hydraulic heads to recharge and discharge and effect of increased pumping on aquifer hydraulics. The safe hydraulic heads and annual exploitable potential were considered as the guiding factors to manage fresh groundwater resources of the coastal aquifer. The results show that the process of sea water intrusion has already started and with the present rate of pumping (1034.86 mcmy-1), the sea water intrusion risk has increased manifold all along the coast. The salient management strategies recommended are; restricting pumping to 695 mcmy-1, stepping up recharge activities in recharge zone, adopting water use efficiency methods and regulation in the coastal zone. AUMP is simple and can guide water managers to plan for sustainable groundwater withdrawal and safe guard the coastal aquifer from sea water intrusion and ensure sustainability of groundwater abstraction structures.

Groundwater vulnerability study using SINTACS method in Banguntapan district, Bantul Regency

As one of the districts in Bantul Regency which borders directly with the City of Yogyakarta, the District of Banguntapan has the potential to be an area affected by city development. This is what drives population growth in this district, so that the waste it generates also increases. The purpose of this study is to determine the level of groundwater vulnerability to pollution by using the SINTACS method and analyzing the dominant factors that influence it. Calculation and analysis results show that the variation of groundwater vulnerability index values in the study area ranged from 182.8 to 200.3, with 10 locations classified as high vulnerability and 2 locations classified as rather high vulnerability. Because it is located in a similar geological condition, namely the Aquifer Unit of Merapi Volcanic Fluvio Plain where most of the constituent material of this aquifer is sand and a little clay as inserts, the difference in groundwater vulnerability to pollution in the study area is only determined by the difference in groundwater depth.

Hydrogeophysical Survey of Groundwater Development at Okada Community Ovia North – East L.G.A. Edo State

Geophysical investigation was conducted at Okada community in ovia North Local Govertment area of Edo state to determine the prospect of aquifer zone. The Petrozenith PZ-02 Terrameter, one of the Electrical Resistivity Equipment was used to conduct a Vertical Electrical Sounding (VES) in the study area. The Garmin Etrex 10 Global Navigation satellite systems (GNSS) was used to acquire Geodetic coordinates of point where VES observations were made. This research was carried out as a pre-drilling Hydro-geophysical survey conducted for the purpose of surveying and studying the proposed water borehole site at Okada Community that has suffered acute water problems for a very long time. There have been series of boreholes drilled in the studied area but all are dry wells. This survey was conducted to investigate the subsurface complexity of the sites in respect of lithology and to recommend the total drill depth based on the prospective aquifer unit so identified. Result of interpretation suggests that the area is underlain with substantive aquiferous formation but at a depth not exceeding 121.60 m (398.95 ft), which is the lower aquifer unit. The value of elevation at point of observation referenced to mean sea level is 94 m.

MINIMAL GEOLOGICAL DATA FOR MODELLING COMPLEX HYDROGEOLOGICAL SYSTEM USING GIS

Geological model is part of groundwater modelling processes. 3D geological models such as GSI3D and GOCAD are used extensively for modelling subsurface geology. These models require multiple input datasets from boreholes, geology maps, and geophysical data. However, due to insufficient definitive data, widely spaced data points that are interpolated were usually used for representation of a geological unit. Since the requirement of extensive data is always the main issue, a geological model is only applied for an area with sufficient data. In this study, minimal and accessible spatial datasets were used in the model for representation of the geological unit. These datasets were chosen to allow the model to be applied in areas of limited datasets. Via the GIS platform, the methodology was developed for the representation of geology in particular the aquifer unit. The raster surface of the geological layer was created in GIS using the information of dip, strike and faults displacement taken from the geological map. The developed GIS based geological model is capable of viewing a geological cross section, modelling the thickness and outcrop boundary of an aquifer unit. The model was tested by reconstruction of the geology map for the Slea catchment, in the United Kingdom and prediction of the thickness of the Lincolnshire Limestone aquifer.

Research on the deformation of a confined aquifer based on Cosserat continuum mechanics

Recent monitoring of land subsidence and soil deformation indicates a new phenomenon where excessive and continuous deformation occurs in the sandy aquifers in Shanghai and the Su-Xi-Chang region of China. It is hard to explain factors contributing to this phenomenon with traditional Cauchy continuum mechanics in which low normal stress in the ground could not cause such large deformation. Steep hydraulic gradient would be formed in the aquifer if groundwater is pumped from densely distributed wells, and shear stresses would develop then. Accumulated shear stress could then lead to deformation of the aquifer or even land subsidence. Accumulated shear stress due to the drawdown of groundwater level is one of the main factors that contribute to deformation within an aquifer. Traditional Cauchy continuum mechanics cannot consider this shear stress because of the hypothesis of equal shear stress in the aquifer unit. Cosserat continuum mechanics can be applied to analyse the mechanism of aquifer deformation controlled by accumulated shear stress by considering the scale effect and the asymmetric distribution of shear stress in the aquifer unit.

Geoelectrical Assessment of the Impact of the Ilokun Dumpsite, Ado-Ekiti Southwestern Nigeria, on Surrounding Groundwater Aquifers

The area around the Ilokun dumpsite, Ado-Ekiti was investigated with the aim of establishing the possible impact the contaminant plumes emanating from the dumpsite have on the subsurface aquifers. The Vertical Electrical Sounding (VES) field technique of the electrical resistivity method was adopted for the study, and the half-electrode spacing AB/2 varied from 1 to 65 m. A total of eight VES stations were occupied and a control VES point was located on the refuse dump. The VES data were interpreted quantitatively by partial curve matching and computer iteration, after which the geoelectric parameters were used to evolve a 2-Dimensional geoelectric section beneath the study area.The weathered layer beneath the control VES point was identified to be the aquifer unit, but the anomalously low resistivity of 18 ohm-m within the unit was interpreted as an evidence of pollution from conductive contaminant plume. The geoelectric section beneath VES 1 to 7 delineated four layers, these include the topsoil; the weathered layer; the fractured basement and the fresh basement. The resistivity and thickness range of the layers are 177 – 399 ohm-m and 0.7 – 1.2 m; 29 – 842 ohm-m and 1.0 – 3.4 m; 16 – 446 ohm-m and 4.5 – 45.5 m; and 289 – 2144 ohm-m respectively. The fractured layer constitutes the main aquifer unit beneath the seven VES points, but the anomalously low resistivity of 16 – 47 ohm-m within the fractured layer beneath VES 4, 5, 6 and 7 is suspected to be as a result of pollution from conductive contaminant plume emanating from the dumpsite. The fractured layer beneath VES 2 and 3 which does not show any evidence of pollution yet is at a risk of being contaminated, due to its interconnection with the polluted zone.