Groundwater vulnerability assessment and mapping in shallow groundwater

The increasing population density can contaminate groundwater. So far, groundwater is still the primary source to fulfill clean water and drinking water in Muntilan, Salam, and Ngluwar Sub-District. Studies on groundwater vulnerability are essential to minimize the contamination risks as a piece of basic information for land use planning. This research aims to assess groundwater vulnerability in Muntilan, Salam, and Ngluwar Sub-District. The simple vertical vulnerability (SVV) method with GIS was selected to develop a groundwater vulnerability map. The parameters of this method consist of the type of soil/rock, the thickness of the water-unsaturated zone, and the recharge value. The results show that the research area can be divided into three vulnerability classes: very low, moderate, and high groundwater vulnerability. Very low groundwater vulnerability has a value of more than 70 with very high protection effectiveness. The class is distributed in Muntilan and Salam Sub-Districts. Moderate groundwater vulnerability has a value less than 35 to 65 with moderate protection effectiveness, and high groundwater vulnerability has a value ranging from 24 to 35 with low protection effectiveness. Both of the class is evenly distributed in Muntilan, Ngluwar and Salam Sub-Districts.

New species of Elaphoidella Chappuis, 1929 and Schizopera Sars, 1905 (Copepoda: Harpacticoida) from two caves in northeastern and southern Thailand

Two new copepod species from two caves in northeastern and southern Thailand are described. Elaphoidella isana sp. nov. and Schizopera paktaii sp. nov. were collected from the unsaturated zone of freshwater pools fed only by dripping water. They are closely related to E. intermedia Chappuis, 1931 and S. validior Sars, 1909, respectively. Elaphoidella isana sp. nov. can be distinguished from its closest relative by the armature of P4 and P5, and by the ornamentation of caudal rami. Schizopera paktaii sp. nov. differs from its relative S. validior in the armature of P1, P5 and caudal rami.

Depth to water table correction for initial carbon-14 activities in groundwater mean residence time estimation

Carbon-14 (14C) is routinely used to determine mean residence times (MRTs) of groundwater. 14C-based MRT calculations typically assume that the unsaturated zone is in equilibrium with the atmosphere, controlling the input 14C activity. However, multiple studies have shown that unsaturated zone 14C activities are lower than atmospheric values. Despite the availability of unsaturated zone 14C data, no attempt has been made to generalise initial 14C activities with depth to the water table. We utilise measurements of unsaturated zone 14C activities from 13 studies to produce a 14C–depth relationship to estimate initial 14C activities. The technique only requires the depth to the water table at the time of sampling or an estimate of depth to water in the recharge zone to determine the input 14C activity, making it straightforward to apply. Applying this new relationship to two Australian datasets (113 14C measurements in groundwater) shows that MRT estimates were up to 9250 years younger when the 14C–depth correction was applied relative to conventional MRTs. These findings may have important implications for groundwater samples that suggest the mixing of young and old waters and the determination of the relative proportions of young and waters, whereby the estimated fraction of older water may be much younger than previously assumed. Owing to the simplicity of the application of the technique, this approach can be easily incorporated into existing correction schemes to assess the sensitivity of unsaturated zone 14C to MRTs derived from 14C data.

Assessment of organic carbon contamination in the unsaturated zone: a case of Yogyakarta City, Indonesia

In 1997, groundwater pollution was caused by a diesel leak at the Yogyakarta City Railway Station. People in the south of the railway station discovered the presence of diesel in dug wells in 2001. The existing diesel is still found in dug wells even though the pollutant source had been removed. The current source of pollution comes from diesel residues trapped in the unsaturated zone. Understanding the distribution and concentration of diesel in the unsaturated zone is the goal of this study. In this study, diesel concentration was measured based on Total Organic Carbon (TOC) levels. The research was conducted through shallow core and deep core drillings. Shallow core drilling was done at 14 points with a depth of 50 cm, and deep core drilling was done at nine drilling points with a depth of 15-17 m. 14 shallow core drilling samples were taken from a depth of 30 and 50 cm and nine deep core drilling samples were taken from a depth of 4-5 m and 10-11 m. The lithology logs in both drills were tested for diesel odour and TOC levels using the Soli TOC tool. Based on the test results, the smell of diesel was found at a depth of 10 to 15 m. TOC levels in the unsaturated zone ranged from 340 to 90,870 mg/L. TOC levels >30,000 mg/L were dominant at shallow depths even though they did not smell like diesel. At a location close to the source of the diesel tank leak at a depth of 4-5 m, the measured TOC level was 30,100 mg/L. The results showed that there were zones of high TOC levels associated with diesel odour layers. The zones existed because of the infiltration and percolation processes that had carried surface water and diesel pollutants and eventually moved horizontally following groundwater flow.