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Some of the techniques that the writer has found useful in the assessment of analytical data are described. These have been culled from statistical text books and scientific journals and it is hoped that the bringing together of this information will be helpful to other workers dealing with analytical data. The techniques include the ordering of data and elimination of outliers, the mean and median and their respective confidence intervals and a description of robust estimates of central tendency and non‐normal distributions. These are followed by methods that can be used in the comparison of data sets such as t‐tests and analysis of variance. There are three appendices, the first being a comprehensive list of statistical expressions and formulae; the second gives worked examples using the various techniques and tests described in the text; the third consists of statistical tables and notes on their use.

Magmatic volatiles can be considered as the surface fingerprint of active volcanic systems, both during periods of quiescent and eruptive volcanic activity. The spatial variability of gas emissions at Earth's surface is a proxy for structural discontinuities in the subsurface of volcanic systems. We conducted extensive and regular spaced soil gas surveys within the Los Humeros geothermal field to improve the understanding of the structural control on fluid flow. Surveys at different scales were performed with the aim to i) identify areas of increased gas emissions (reservoir scale), ii) their relation to (un)known volcano-tectonic structures (fault scale) favoring fluid flow, and iii) determine the origin of gas emissions. Herein, we show results from a CO2 efflux scouting survey, which was performed across the main geothermal production zone (6 km x 4 km) together with soil temperature measurements. We identified five areas with increased CO2 emissions, where further sampling was performed with denser sampling grids to understand the fault zone architecture and local variations in gas emissions. CO2 efflux values range from below detection limit of the device to 1,464 g m -2 d -1 with a total output of 87 t d -1 across an area of 13.7 km 2 . Furthermore, δ 13 CCO2 and 3 He/ 4 He analyses complemented the dataset in order to assess the origin of soil gases. Carbon isotopic data cover a broad spectrum from biogenous to endogenous sources. Determined 3 He/ 4 He ratios indicate a mantle component in the samples of up to 65 % being most evident in the northwestern and southwestern part of the study area. We show that a systematic sampling approach on reservoir scale is necessary for the identification and assessment of major permeable fault segments. The combined processing of CO2 efflux and δ 13 CCO2 facilitated the detection of permeable structural segments with a connection to the deep, high-temperature geothermal reservoir, also in areas with low to intermediate CO2 emissions. The results of this study complement existing geophysical datasets and define further promising areas for future exploration activities in the north-and southwestern sector of the production field.

Around 200 words, intelligible without reference to the text or references Geochemical and related studies have been made of near surface sediments from the Clyde estuary and adjoining areas, extending from Glasgow to the north and west as far as the Holy Loch. Multibeam echosounder, sidescan sonar and shallow seismic data, taken with core information indicate a shallow layer of modern sediment, often less than a metre thick, rests on earlier glacial and post-glacial sediments. The offshore Quaternary history can be aligned with onshore sequences with recognition of buried drumlins, settlement of muds from quieter water probably behind an icedam and later tidal delta deposits. The geochemistry of contaminants within the cores also indicates shallow contaminated sediments often resting on pristine pre-industrial deposits at depths less than 1 m. The distribution of different contaminants with depth in the sediment, such as Pb (and Pb isotopes), organics and radionuclides allow chronologies of contamination from different sources to be suggested. Dating was also attempted using microfossils, radiocarbon and 210 Pb but with limited success. Some of the spatial distribution of contaminants in the surface sediments can be related to grain size effects. Contaminants are highest, both in absolute terms and in enrichment relative to the natural background, in the urban and inner estuary and in the Holy Loch reflecting the concentration of industrial activity.