No abstract available

[en] Access to two boreholes at the Carwynnen test site in Cornwall enabled the trial of a number of innovative approaches to the hydrogeology of fractured crystalline rock. These methods ranged from the use of seisviewer data to measure the orientation of fractures to the use of the sinusoidal pressure technique to measure directional hydraulic diffusivity. The testing began with a short programme of site investigation consisting of borehole caliper and seisviewer logging followed by some single borehole hydraulic tests. The single borehole hydraulic testing was designed to assess whether the available boreholes and adjacent rock were suitable for testing using the sinusoidal method. The main testing methods were slug and pulse tests and were analysed using the fissured porous medium analysis proposed in Barker and Black (1983). Derived hydraulic conductivity (K) ranged from 2 x 10^-12 m/sec to 5 x 10^-7 m/sec with one near-surface zone of high K being perceived in both boreholes. The results were of the form which is typical of fractured rock and indicated a combination of high fracture frequency and permeable granite matrix. The results are described and discussed. (author)

[en] The project summarised in the paper aimed to assess the different existing methods of measuring vertical hydraulic conductivity in single boreholes by carrying out some actual field testing. The measurements are relevant to the disposal of radioactive waste into argillaceous rocks, where the primary geological barrier to potential leachate migration is the mudrock. Also the prime parameter of interest in the assessment of mudrocks is the vertical component of hydraulic conductivity. A description of the methods of test analysis and interpretation is given. The experimental programme for open borehole testing and cased borehole testing is described, along with the practical and theoretical considerations. (U.K.)

No abstract available

[en] As observational evidence of the existence of very large interstellar molecules grows, it is important to assess their consequences for interstellar chemistry. The very large molecules, exemplified by polycyclic aromatic hydrocarbons (PAHs) of approximately 50 atoms, can have large effects on the ionization balance in interstellar clouds. According to some estimates, such molecules might contain several per cent of the total interstellar carbon. The possible effects of PAHs on the production of smaller molecules, on interstellar heating, and on the ionization state of predominantly neutral gas will be reviewed. If PAHs are formed only in the envelopes of cool, evolved stars and not in the interstellar medium itself, their distribution in interstellar space may provide an important probe of the overall chemical evolution of the Galaxy

[en] A theory is developed to describe the excitation of the diatomic carbon moelcule in interstellar clouds. The probabilities of quadrupole transitions within the ground state and of intercombination transitions between levels of the lowest triplet and singlet states are computed. The populations of excited rotational levels can be used as a diagnostic probe of local temperature, density, and strength of the radiation field, although all three parameters cannot usually be determined from C² data alone. Calculated rotational populations are presented for a range of physical conditions and are used to interpret existing interstellar absorption line observations of C². Because of the competition between radiative and collisional excitation processes, the rotational excitation temperature tends not to be a good measure of kinetic temperature. An unusual radio frequency spectrum of C² is predicted

[en] The hydraulic sub-programme of the Crosshole Project is outlined together with its aims and its unusual features. These include the use of computer-controlled equipment to produce hydraulic signals of almost any type and the sinusoidal pressure technique. The advantages of the sinusoidal technique are seen to be its detection in a mine environment and the investigation of the interaction between fissures and rock matrix. The results of the single borehole tests are examined in a number of ways. It is shown that hydraulic conductivity derived from single-borehole tests varies unpredictably. The combined use of the hydraulic conductivity and the radar results show that fractures have highly variable properties as regards water conduction. The head data show a general flow of water towards the old mine working rather than towards the experimental drift. Early crosshole sinusoidal results are presented and agree broadly with the single borehole results. The frequency dependent response is difficult to interpret at present but should be explained by work within remaining year of the project

[en] Field investigations of hydrogeology are placed in the context of Performance Assessment (PA) modelling. Field programmes have to be strongly linked to the use of data in PA modelling in order to control costs and define required data quality. Risk based PA modelling is suggested for this purpose. The dangers of reducing testing in heterogeneous rocks is demonstrated for a clay/silt formation. Lastly the innovative technique, Focussed Packer Testing, is introduced as a method for reducing field programme costs by at least a half. (author)

[en] Few suitable stars behind molecular clouds have been identified. A limited survey was performed of interstellar lines toward highly reddened stars in the southern sky, using the ESO 1.4 m CAT telescope with a Reticon detector, and the Cerro Tololo 4 m telescope equipped with a GEC charge coupled device (CCD) detector. Because of the reduced extinction at longer wavelengths, molecules were searched for with transitions in the red part of the spectrum such as C₂ and CN. For some lines-of-sight for which C₂ was detected, the 4300 A line of CH was also observed. Absorption lines of interstellar C₂ around 8750 A were detected in the spectra of about 1/4 of the 36 observed stars. The inferred C₂ column densities range between 10 to the 13th power and 10 to the 14th power sq. cm., and are up to an order of magnitude larger than those found for diffuse clouds. The observed column densities of CH correlate very well with those of C₂ over this range. In contrast, the measured column densities of CN vary by orders of magnitude between the various regions, and they do not correlate with those of C₂ and CH. The observed rotational population distribution of C₂ also provides information about the physical conditions in the clouds. Models of translucent molecular clouds have been constructed along the lines described by van Dishoeck and Black (1986) for diffuse clouds. The models compute accurately the fractions of atomic and molecular hydrogen as functions of depth into the clouds, as well as the excitation of H2 by ultraviolet pumping. They also incorporate a detailed treatment of the photodissociation processes of the molecules (cf. van Dishoeck 1986), which play an important role in the chemistry up to depths of about 3 mag

[en] Molecules, like H₂, provide excellent probes of molecules in intergalactic clouds and interstellar clouds of distant disk-type galaxies. This chapter considers the early chemistry of the universe and the most distant and primitive material. Molecules formed in the early universe are likely to be destroyed by the ultraviolet photons and hot gas that accompany the first stars. However, studying these molecules may provide some understanding of how molecules form in dust-free material of primordial composition. The chapter concludes with information about stable abundant molecules like H₂ and CO which are observed, via absorption lines, in the spectra of high-redshift quasars. (UK)