Trevor M. Hunt, Chris J. Bromley, George Risk, Steve Sherburn and Suprijadi Soengkono.

Geothermics, Vol. 38, No. 1, Mar 2009, pp. 85-97.

Geophysical studies of the Wairakei sector of the Wairakei-Tauhara geothermal system started shortly after exploration drilling began in the early 1950s. These investigations have made a major contribution in defining the boundary of geothermal systems and understanding the changes that have occurred in the reservoir as a result of fluid production. The most successful tools have been electrical resistivity methods for delineating the field, while microgravity, heat loss and groundwater level monitoring surveys were useful to interpret production-induced changes. Seismic, gravity and magnetic surveys had only limited success.

G. R. Foulger, B. R. Julian, F. Monastero and Durham University (England), United States, performer (USA).

FINAL REPORT SUPPLEMENT 2, 2008

We studied high-resolution relative locations and full moment tensors of microearthquakes (MEQs) occurring before, during and following Enhanced Geothermal Systems (EGS) experiments in two wells at the Coso geothermal area, California. The objective was to map new fractures, determine the mode and sense of failure, and characterize the stress cycle associated with injection. New software developed for this work combines waveform cross correlation measurement of arrival times with relative relocation methods, and assesses confidence regions for moment tensors derived using linear programming methods. For moment tensor determination we also developed a convenient Graphical User Interface (GUI), to streamline the work. We used data from the U.S. Navy's permanent network of three-component digital borehole seismometers and from 14 portable three-component digital instruments. The latter supplemented the permanent network during injection experiments in well 34A-9 in 2004 and well 34-9RD2 in 2005. In the experiment in well 34A-9, the co-injection earthquakes were more numerous, smaller, more explosive and had more horizontal motion, compared with the pre-injection earthquakes.

T. E. Thorhallsdottir.

Environmental Impact Assessment Review, Vol. 27, No. 6, Aug 2007, pp. 545-568.

A method for evaluating and ranking energy alternatives based on impact upon the natural environment and cultural heritage was developed as part of the first phase of an Icelandic framework plan for the use of hydropower and geothermal energy. The three step procedure involved assessing i) site values and ii) development impacts within a multi-criteria analysis, and iii) ranking the alternatives from worst to best choice from an environmental-cultural heritage point of view. The natural environment was treated as four main classes (landscape+wilderness, geology+hydrology, species, and ecosystem/habitat types+soils), while cultural heritage constituted one class. Values and impacts were assessed within a common matrix with 6 agglomerated attributes: 1) diversity, richness, 2) rarity, 3) size (area), completeness, pristineness, 4) information (epistemological, typological, scientific and educational) and symbolic value, 5) international responsibility, and 6) scenic value. Standardized attribute scores were used to derive total class scores whose weighted sums yielded total site value and total impact. The final output was a one-dimensional ranking obtained by Analytical Hierarchical Process considering total predicted impacts, total site values, risks and uncertainties as well as special site values. The value/impact matrix is compact (31 cell scores) but was considered to be of sufficient resolution and has the advantage of facilitating overview and communication of the methods and results. The classes varied widely in the extent to which value assessments could be based on established scientific procedures and the project highlighted the immense advantage of an internationally accepted frame of reference, first for establishing the theoretical and scientific foundation, second as a tool for evaluation, and third for allowing a global perspective.

A. Baldacci.

Perfect compatibility of geothermal plants with the development of the other resources of the area (tourism, quality agriculture, etc.) is a key issue for the sustainability of the geothermal resource and its acceptance by the communities hosting the plants. In this framework, cleaning of power plant emission and, in particular, the elimination of the bad smell of hydrogen sulphide is crucial. Owing to the characteristics of the Italian geothermal fluids and of the power plant features, the technologies used elsewhere were not readily applicable without modification and anyway they entailed excessive costs. A new patented process (AMIS) overcoming these limitations has been developed by ENEL SpA. and successfully applied both to new and existing plants. A substantial retrofitting of the geothermal generation park with AMIS plants is in progress and will be completed by 2006. AMIS is an environmentally friendly process because it doesn't require the use of chemicals and doesn't produce sulphur based by-products, to be landfilled or recycled.

F. Bussotti, R. Tognelli, G. Montagni, F. Borghini, P. Bruschi and C. Tani.

Environmental Pollution, Vol. 121, No. 3, 2003, pp. 349.

In the geothermoelectric basin of Larderello, located in southern Tuscany, Italy, the environmental impact of geothermal plants was investigated in terms of the effects on leaves of Quercus pubescens. Leaves were collected at three different times from trees located at three sampling locations in the basin, and concentrations of boron and sulfur were measured and related to leaf morphology. Both S and B concentrations in leaves were found to be higher than reference values, and foliar injury became obvious when the B concentrations exceeded 300400 ppm. The accumulation of proteic substances in the vacuoles of the mesophyll was consistent with the metabolic pattern of hydrogen sulfide. As the levels of B and S in the leaves did not match the concentrations in the soils, foliar uptake appeared to be the prevalent role.