Environmental geology problems in the Tyrrhenian coastal area of Santa Marinella, province of Rome, central Italy

 The Tyrrhenian resort of S. Marinella (central Italy) is subjected to significant anthropogenic pressures during the summer vacation period, a common situation all along the Italian coast. Located 65 km NW of Rome on the southern slopes of the Tolfa Mountains, S. Marinella is built on a gently sloping, E–W trending belt which is cut by 14 N–S oriented ephemeral streams that discharge into the Tyrrhenian Sea. The low to medium permeability turbiditic sandstones which outcrop along this belt belong to the Late Cretaceous Pietraforte unit. Three environmental problems are addressed in this study. The first problem is related to the high water supply demand during the summer months which has forced local residents to dig a large number of wells. Extensive pumping from these wells has caused salt-water intrusion into the Pietraforte, thus compromising the domestic use of the groundwater. The second problem consists of the illegal dumping of urban solid waste, material that represents a hazard during significant rain events as well as a possible cause of groundwater contamination. The final issue addressed concerns the flooding potential of the 14 ephemeral streams that cross the inhabited area of S. Marinella, a risk which is highlighted by the disastrous flood which occurred on 2 October 1981 and during the period of the Roman Emperor Settimio Severo (205 A.D.). Some suggestions are proposed to mitigate and contain the effects of these problems. Received: 7 November 1995 / Accepted: 5 December 1996     

漳州热田的对流热流和传导热流的研究

漳州地热系统属对流型地热系统.漳州热田是我国东南沿海地区目前所见热田中温度最高（121.5℃）的一个.地表热流值的研究表明,热田中心具有最大的实测热流值（359mw/m²）.本文根据热田内152个钻孔的测温资料和56块岩石样品的热导率数据,采用三种不同方法计算出漳州热田及其邻近地区的大地热流值,并讨论了热流值分布的特点.     

Hydrology and hydrogeology of Sakaryabaşı Karstic springs, Çifteler, Turkey

The Sakarya River is one of the largest rivers in Turkey and is fed mainly from Sakaryabaşı springs. The Sakaryabaşı springs are located in the Central Anatolia and issue from confined/semi-confined karst having a thermal component and therefore, having quite different hydrogeological characteristics as compared to the Taurus Karst region, a typical example of the Mediterranean type of karst. The karstic carbonate rocks that form the groundwater reservoir are overlain by a thick semi-pervious overburden of mainly clastics of Neogene age. Tectonics is the major factor controlling the occurrence of the karst springs in the area where topography is rather flat. This study aimed at explaining the occurrence and movement of the karst groundwater within the system by use of hydrogeological, chemical, and isotopic tools. Isotopic composition of the waters revealed that all waters in the region are of meteoric origin and the thermal component is due to deep circulation. The catchment area of the hydrogeological system extends to the south and groundwater movement is towards the outlets, which are in a depression along a major fault. The movement of the groundwater, based on analysis of remotely sensed images, is controlled mainly by structural elements.     

Is the spring water responsible for the fossilization of faunal remains at Florisbad, South Africa?

It is has been suggested that faunal remains at Florisbad were fossilized in a spring context due to the mineralized spring water. However, the environment conducive to the precipitation of CaCO₃ and other authigenic minerals was formed largely through the salinization of the organic layers and clay, and the mineralization of the groundwater. Factors contributing to this favorable environment include: CaCO₃ saturation, pH, the decomposition of halophytes, Eh, rainfall, biomineralization, and aeolian deposition. With the exception of pH, none of the above factors feature in a spring context, with evidence suggesting that the spring water may historically never have carried sufficient minerals for fossilization, and that contact with the spring water may actually have resulted in the demineralization of previously fossilized material. In light of this evidence, it is concluded that the fossilization of faunal remains at Florisbad took place in a sedimentary organic matter and clay environment and could not have taken place in the spring vents where there is an undersaturation of Ca.     

Radiomagnetotelluric mapping, groundwater numerical modelling and 18-Oxygen isotopic data as combined tools to determine the hydrogeological system of a landslide prone area

Three methods were combined to determine the groundwater recharge and transfer processes of a landslide prone area. First, the radiomagnetotelluric method was used to investigate the distribution of electrical resistivity (ρ) of the subsurface and build a three-dimensional model of permeability (k), through an experimental relation between ρ and k. Second, this structural model of permeability and additional climatologic data were used to fix boundary and recharge conditions to perform a three-dimensional and transient numerical simulation of the groundwater flow. Finally 18-Oxygen time series observed at the main springs were used to validate the model. This association of methods led to an improved characterization of the groundwater flow system at local scale and a better understanding of the role of this system on the landslide phenomenon. This structured approach is thought to be useful to design specific remediation strategies to drain the unstable mass.     

2D Self-Potential tomographies for studying groundwater flows in the Varco d''Izzo landslide (Basilicata, southern Italy)

A geoelectrical monitoring activity has been carried out to improve the geological and hydrogeological knowledge about the Varco d'Izzo landslide (Potenza, Basilicata, Southern Apennine, Italy), an active rotational–translational slide evolved in earth-flow. In this work we have focused on the Self-Potential (SP) method by applying three different SP measuring techniques and combining modern technologies for data acquisition and new methods for tomographic inversion. A SP map and three static SP tomographies have been carried out to better analyse the groundwater circulation system and to better reconstruct the geometry of the landslide body. In the accumulation zone, which is the area more exposed to the geomorphological activity, a new SP measuring strategy has been applied. This strategy, based on time-continuous 2D SP tomographies, helps identify water flow changes in subsurface by studying the time series of SP tomographic images. The analysis of time-dependent changes of water infiltration in near surface is the key to better understand the hydrogeological processes underlying the ground instability phenomena. The time-lapse analysis of tomographic images has allowed us not only to investigate the correlation between the temporal changes of SP signals and rainfall events, but also to quantify the range of these changes. The modification of the distribution of the SP source accumulation zones is associated with the dynamics of the groundwater flows. These preliminary results allow us to consider the SP tomographic method as a tool for geophysical monitoring of landslide areas and encourage to develop new measuring systems for near-real time applications.     

An approximate projection of availability of the fresh groundwater resources in the South West district of NCT Delhi, India: a case study

The future availability and sustainability of fresh groundwater resources in the South West district of the national capital territory (NCT) Delhi, India, have been projected. Due to a rapid decline in groundwater level and quality, the district has been required by the Government of India to regulate development of groundwater resources. Shallow groundwater is mostly saline and water resources in the area are limited. The methodology applied here involves microzonation of the district in terms of thickness of fresh groundwater and then quantification of present and future availability of freshwater in different freshwater zones, including tentative timescales. The calculation method has been aided by data on historic trends in water level at representative groundwater monitoring stations, located either in fresh groundwater zones or near to them. It is estimated that the presently available 481 million m³ of resources will be reduced to 374 million m³ by year 2007 and to 303 million m³ by the year 2012, and by the year 2022 the district will have only 176 million m³ of available fresh groundwater resources.     

Evidence for deep groundwater flow and convective heat transport in mountainous terrain, Delta County, Colorado, USA

The Tongue Creek watershed lies on the south flank of Grand Mesa in western Colorado, USA and is a site with 1.5 km of topographic relief, heat flow of 100 mW/m², thermal conductivity of 3.3 W m^–1 °C^–1, hydraulic conductivity of 10^-8 m/s, a water table that closely follows surface topography, and groundwater temperatures 3–15°C above mean surface temperatures. These data suggest that convective heat transport by groundwater flow has modified the thermal regime of the site. Steady state three-dimensional numerical simulations of heat flow, groundwater flow, and convective transport were used to model these thermal and hydrological data. The simulations provided estimates for the scale of hydraulic conductivity and bedrock base flow discharge within the watershed. The numerical models show that (1) complex three-dimensional flow systems develop with a range of scales from tens of meters to tens of kilometers; (2) mapped springs are frequently found at locations where contours of hydraulic head indicate strong vertical flow at the water table, and; (3) the distribution of groundwater temperatures in water wells as a function of surface elevation is predicted by the model.     

Study of geothermal water intrusion due to groundwater exploitation in the Puebla Valley aquifer system, Mexico

Significant intrusion of geothermal water into fresh groundwater takes place in the Puebla Valley aquifer system, Mexico. The decline in the potentiometric surface due to the overexploitation of the groundwater induces this intrusion. This hydrological system comprises three aquifers located in Plio-Quaternary volcanic sediments and Mesozoic calcareous rocks. The hydraulic balance of the aquifer shows that the annual output exceeds the natural inputs by 12 million m³. Between 1973 and 2002, a drop in the potentiometric surface, with an 80 m cone of depression, was identified in a 5-km-wide area located southwest of the city of Puebla. Chemical analyses performed on water samples since 1990 have shown an increase in total dissolved solids (TDS) of more than 500 mg/L, coinciding with the region showing a cone of depression in the potentiometric surface. A three-dimensional flow and transport model, based on the hydrogeological and geophysical studies, was computed by using the MODFLOW and MT3D software. This model reproduces the evolution of the aquifer system during the last 30 years and predicts for 2010 an additional drawdown in the potentiometric surface of 15 m, and an increase in the geothermal water intrusion.     

Fracture and bedding plane control on groundwater flow in a chalk aquitard

Shallow groundwater in the northern Negev desert of Israel flows preferentially through a complex system of discontinuities. These discontinuities intersect what would otherwise be a massive, low-conductivity, high-porosity Eocene chalk. Vertical fractures and horizontal bedding planes were observed and mapped along approximately 1,200 m of scanline, 600 m of core and 30 two-dimensional trace planes. A bimodal distribution of size exists for the vertical fractures which occur as both single-layer fractures and multi-layer fractures. A bimodal distribution of log transmissivity was observed from slug tests conducted in packed-off, vertical intervals within the saturated zone. The different flow characteristics between the horizontal bedding planes and vertical-type fractures appear to be the cause of the bimodality. Two distinct conceptual models (discrete fracture network) were developed based on the fracture orientation, size, intensity and transmissivity statistics derived from field data. A correlation between fracture size and hydraulic aperture was established as the basis for calibrating the simulated model transmissivity to the field observations. This method of defining transmissivity statistically based on prior information is shown to be a reasonable and workable alternative to the usual conjecture approach towards defining transmissivity in a fractured-rock environment.