Kinematics of Diffuse Interstellar Clouds :Recent GMRT Results

A high latitude HI 21 cm-line absorption survey toward extragalactic sources was recently completed using the Giant Meterwave Radio Telescope (GMRT). A total of 104 sources with mod(b) > 15 deg. and with a 21 cm flux density greater than 1 Jy were observed for about 120 hours. With an optical depth detection limit of about 0.01 this is the most sensitive high-latitude survey as yet. Most of the detected HI 21 cm-line absorption features belong to a population with a velocity dispersion of about 7.6 km/s. These are the 'standard' HI clouds and have been well-studied for decades. However, we also detect a second population of absorbing clouds with a velocity dispersion of about 21 km/s. About 20 percent of the total number of absorbing clouds belong to this population. This new population of 'fast' clouds can be identified with a similar velocity dispersion Ca II absorbing clouds and with the Halo clouds recently detected in HI emission from Green Bank.Comment: 5 pages, 6 figures, uses basi.cls, to be published in Bull. Astr. Soc. Indi

A High Galactic Latitude HI 21cm-line Absorption Survey using the GMRT: II. Results and Interpretation

We have carried out a sensitive high-latitude (|b| > 15deg.) HI 21cm-line absorption survey towards 102 sources using the GMRT. With a 3-sigma detection limit in optical depth of ~0.01, this is the most sensitive HI absorption survey. We detected 126 absorption features most of which also have corresponding HI emission features in the Leiden Dwingeloo Survey of Galactic neutral Hydrogen. The histogram of random velocities of the absorption features is well-fit by two Gaussians centered at V(lsr) ~ 0 km/s with velocity dispersions of 7.6 +/- 0.3 km/s and 21 +/- 4 km/s respectively. About 20% of the HI absorption features form the larger velocity dispersion component. The HI absorption features forming the narrow Gaussian have a mean optical depth of 0.20 +/- 0.19, a mean HI column density of (1.46 +/- 1.03) X 10^{20} cm^{-2}, and a mean spin temperature of 121 +/- 69 K. These HI concentrations can be identified with the standard HI clouds in the cold neutral medium of the Galaxy. The HI absorption features forming the wider Gaussian have a mean optical depth of 0.04 +/- 0.02, a mean HI column density of (4.3 +/- 3.4) X 10^{19} cm^{-2}, and a mean spin temperature of 125 +/- 82 K. The HI column densities of these fast clouds decrease with their increasing random velocities. These fast clouds can be identified with a population of clouds detected so far only in optical absorption and in HI emission lines with a similar velocity dispersion. This population of fast clouds is likely to be in the lower Galactic Halo.Comment: 19 pages, 19 figures. Accepted for publication in Journal of Astrophysics & Astronom

The interstellar clouds of Adams and Blaauw revisited: an HI absorption study - I

This investigation is aimed at clarifying the nature of the interstellar gas seen in absorption against bright O and B stars. Towards this end we have obtained for the first time HI absorption spectra towards radio sources very close to the lines of sight towards 25 bright stars previously studied. In this paper we describe the selection criteria, the details regarding our observations, and finally present the absorption spectra. In the accompanying paper we analyse the results and draw conclusions.Comment: 20 pages, 12 figures, accepted by Journal of Astrophysics and Astronom

Characterization and Remediation of Aquifers Contaminated by Nonaqueous Phase Liquids Using Partitioning Tracers and Surfactants

The main objectives of this work were the development of the partitioning interwell tracer test for estimation of nonaqueous phase liquid (NAPL) saturation in saturated porous media, performance assessment of surfactant enhanced aquifer remediation using partitioning tracers and screening and selection of environmentally acceptable surfactant solutions for surfactant enhanced aquifer remediation (SEAR) of soils contaminated by NAPLs. The contaminants studied in this work were tetrachloroethylene (PCE), trichloroethylene (TCE), jet fuel (JP4) and contaminant from Hill Air Force Base, site Operational Unit 2 (Hill OU2 DNAPL) and contaminant from Hill Air Force Base, site Operational Unit 1 (Hill OUl LNAPL). The first step in screening partitioning tracers involved performing several batch experiments to determine partition coefficients of about 28 alcohols and 10 NAPLs. Partitioning tracer tests were performed to estimate NAPL saturation in soil packs with known amounts of NAPL. A close match between NAPL saturation estimates based on mass balance and partitioning tracers was obtained in column experiments with several NAPLs thus validating the partitioning interwell tracer test as an effective tool for estimating residual NAPL saturation. The next step involved the development of laboratory procedures for designing field partitioning tracer tests. Two field partitioning tracer tests were designed using these procedures. The first field test was a partitioning interwell tracer test (PITT) performed by The University of Florida and EPA at the Operational Unit 1 site at Hill Air Force Base, Utah and the second test was the PITT performed by INTERA Inc. at the Operational Unit 2 site at Hill Air Force Base, Utah. Surfactants were selected by performing phase behavior experiments with surfactant, NAPL, alcohol, electrolyte and water mixtures. The surfactants used were the anionic surfactants, sodium diamyl sulfosuccinate, sodium dihexyl sulfosuccinate and sodium dioctyl sulfosuccinate. Surfactant solutions with low viscosities and quick equilibration times were selected for use in soil column experiments. Alcohols such as isopropyl alcohol and secondary butyl alcohol were used to minimize gel/liquid crystal formation and emulsions and to lower equilibration times. These favorable characteristics were confirmed by measurement of low pressure losses (hydraulic gradients) across the soil packs during surfactant flooding in several column experiments. The effect of the addition of polymer to the surfactant solution on surfactant remediation was investigated by performing several surfactant remediation experiments with surfactant, alcohol and polymer solutions. Based on all the column experiments, a laboratory procedure for designing field surfactant enhanced aquifer remediation tests was developed. This was used to design a surfactant flood at Hill AFB, site Operational Unit 2. Both the laboratory and field results showed that with the proper surfactant selection, laboratory procedures and process design, more than 99% of the DNAPL can be removed from sandy/gravely soil of the type found in Hill AFB, Utah. This is a much more favorable result than previously reported and a strong indication that surfactant remediation is a viable alternative, perhaps the best alternative for these very difficult DNAPL sites. Partitioning tracers and other site characterization played a key role in this success and were an integral part of all this research. The main contributions of this work were the validation the PITT for estimation of NAPL saturations and performance assessment of surfactant remediation and development of laboratory procedures for selection of both partitioning tracers and surfactants for application in field PITT and SEAR operations.Petroleum and Geosystems Engineerin