Cooperation in hydrogeophysics: Enhancing practitioners and institutions′ groundwater assessment capacity, Vientiane Plain, Lao PDR

The lowland floodplains of the Lao PDR experience prolonged dry seasons characterized by pronounced and common water scarcity, with water supplies increasingly offset with groundwater. Groundwater assessment is still at a very rudimentary stage in Laos, making it difficult to ensure that new water supplies are developed successfully and managed sustainably. The goal of this study was to apply a variety of field hydrogeophysical techniques to this problem, and in the process, help build and strengthen human and institutional capacity with various stakeholder groups from government, university and the community. The study area focused on a cross-section of the Vientiane Plain in the Lower Mekong Basin in central Lao PDR to identify and characterize the hydrogeology and groundwater quality. The research collaboration built and strengthened stakeholder capacity by developing and progressing the hydrogeological field mapping of the Vientiane Plain. It provided local undergraduate and postgraduate training opportunities using several different near-surface geophysical and hydrogeological techniques; some previously untested in Lao PDR. At one of the survey sites, the geophysics showed the spatial extent of the shallow aquifer, and in the process identified an extensive conductive zone, interpreted as more saline groundwater. Any groundwater development within this or similar zones is likely to be unsuitable as sources for drinking and irrigation water. Engagement with the local village authorities supported local community members and government to expand groundwater development for rural water supplies. Access to groundwater as a reliable, safe and secure resource provides an opportunity to strengthen the resilience of farmers to changing climatic conditions. Participatory research collaboration of this kind can positively enhance data and build capacity, which is a required precursor for improving knowledge and management of poorly understood groundwater resources.

Changes in Pumping-Induced Groundwater Quality Used to Supply a Large-Capacity Brackish-Water Desalination Facility, Collier County, Florida: A New Aquifer Conceptual Model

Brackish-water reverse osmosis (BWRO) desalination facilities are designed to treat feedwater within a fixed range in salinity. If the salinity and ion concentrations of the feedwater rises above the maximum design concentrations, then the plant may ultimately fail. BWRO plants typically use groundwater as a feedwater source. Prior to the process design, a detailed groundwater assessment is made to characterize the source aquifer system and to develop a solute-transport model that is used to project the changes in water quality over the expected useful life of the facility. Solute transport-modeling performed for the Collier County (Florida) South BWRO facility, which was designed to produce 30,303 m3/d with an expansion to 75,758 m3/d, used an aquifer system conceptual model that assumed upwards migration over time of brackish waters with higher salinities into the production zones. This conceptual model is typical of how most BWRO systems developed in the United States operate. The original solute transport model predicted a range of increases in dissolved chloride concentrations over a 20-year period from a low of 5 mg/L/yr, a mid-range of 35 mg/L/yr, and a high range of 85 mg/L/yr. Actual data collected over a 11- to 13.5-year period showed that the dissolved chloride concentration average of the feed water decreased by 16 mg/L/yr. The original conceptual model was found to be inaccurate in that it suggested an upwards recharging system, whereas downward leakage (or perhaps lateral migration) of fresher water appears to be occurring in the system. This is an example of a long-term solute-transport model audit, which is rarely performed, in which a new conceptual model was found to be applicable to an aquifer system used to feed a BWRO facility.

Integration of geophysical, hydrogeological and geospatial analysis for groundwater assessment in Chotanagpur Granite-Gneiss Complex, Ranchi

Integrated study combining electrical resistivity tomography, geology, hydrogeomorphology, and weighted overlay analysis of various surface and subsurface thematic layers proved to be a very useful tool for evaluating the heterogeneous hard aquifer systems for groundwater assessment and development. A comprehensive study was carried out at representative and varied geological settings viz., Chotanagpur Granite-Gneiss Complex (CGGC), Ranchi has been accomplished from geology and geophysical datasets. The electrical resistivity tomography results revealed potential target zones at three sites in the study area up to a maximum of 170 m depth with a large variation in aquifer resistivity ranging from 80 to 800 Ω.m. These significant findings depicted a good correlation and are validated with the lithology in the surrounding of the resistivity tomography results. Nevertheless, the weighted overlay technique act as an essential tool for spatial analysis and interpretation of potential groundwater zones in the study area as well as validated the geophysical depth models whereas in-depth study on geology and hydrogeomorphology provides a detailed hydrogeological scenario throughout the study area for the long-term sustainability of the groundwater resources both at a local and in regional scale in the typical hard rock aquifer system.

Assessment of Underground Water Quality in Karimunjawa Island, Central Java – Indonesia

As a small island and tourist destination, Karimunjawa municipal is need fresh water to support the tourist activity, mainly to supply drinking water. Unfortunately, freshwater on a small island is obtained from groundwater which is very limited and vulnerable to climate change and anthropogenic activities. A groundwater assessment is necessary to receive up-to-date information on groundwater quality, to assess the groundwater feasibility for drinking water, and determine the pollutant source. The assessment was conducted by collected groundwater sampling from dug wells and swamp area in Karimunjawa municipal and then analyzed the samples in the laboratory to obtain the value of Nutrient (NO3-, NO2-, NH3-N); Heavy Metals (Cu, Fe, and Pb); and Salt (TDS, Cl-, Na+). These obtained parameters were compared with the quality standard of the minister of health regulation of the Republic of Indonesia about water quality standards for drinking water. In this study, 14 samples were collected and analyzed. The result shows that nutrient contaminant is low, but some groundwater sample was contaminated by ammonia. Heavy metal is undetectable, but almost all samples are contaminated by salt. Therefore, the groundwater in Karimunjawa municipal experienced seawater intrusion and not feasible to be consumed as drinking water.

Groundwater Assessment and its Implication for Irrigation in Selected Coastal Areas of South-Western Nigeria

Physicochemical and ionic characteristics of groundwater aquifers have been of tremendous importance in water applications. Groundwater in selected coastal communities (Badagry, Epe, Ikorodu, and Ilaje/ese-odo) of south-western Nigeria was assessed for domestic and irrigation suitability. One hundred and ninety-two (192) groundwater samples were obtained and analyzed for chemical composition and major ionic ratio over a period of four seasons using standard methods. Results indicated abundance of ions in the order HCO3– > Cl–> SO42– for anions, and K+ > Na+ > Ca2+> Mg2+ for cations. Piper's diagram revealed calcium (Ca2+) and magnesium (Mg2+) as the dominant cations, while sulphate and chloride were the dominant anions with a mixture of two major groundwater types: Ca–Cl water and mixed Ca–Mg–Cl. The presence of Ca–Cl facies water type suggests potential ion exchange (Na2+ with Ca2+) reaction in these coastal aquifers. Cation exchangeable values (CEV), and molar ratios of Mg/Ca, HCO3/Cl, and Na/Cl, showed high values (>1) across all locations indicating the occurrence of saline water ingression in groundwater samples, especially during the dry spell. The increasing K+, Na+, and Cl– characteristics of the groundwater and calculated ionic indices values indicated the influence of seawater intrusion. However, total hardness values showed that the samples were very soft in nature. Irrigation water quality suitability, as indicated by sodium adsorption ratio (SAR), permeability index (PI), and percentage sodium (PS) varied with seasons and location, showing that water will cause soil deterioration and poor crop performance if intensively used for irrigation without proper precautions.