Arrays of Unpumped Wells for Plume Migration Control by Semi-Passive In Situ Remediation

Arrays of unpumped wells can be used as discontinuous permeable walls in which each well serves both as a means to focus ground water flow into the well for treatment and as a container either for permeable reactive media which directly destroy dissolved ground water contaminants or for devices or materials which release amendments that support in situ degradation of contaminants within the aquifer downgradient of the wells. This paper addresses the use of wells for amendment delivery, recognizing the potential utility of amendments such as electron acceptors (e.g., oxygen nitrate), electron donors (primary substrates), and microbial nutrients for stimulating bioremediation, and the potential utility of oxidizers, reducers, etc., for controlled abiotic degradation. Depending on its rate and constraints, the remedial reaction may occur within the well and/or downgradient. For complete remediation of ground water passing through the well array, the total flux of amendment released must meet or exceed the total flux demand imposed by the plume. When there are constraints on the released concentration of amendment (relative to the demand), close spacing of the wells may be required. If the flux balance allows wider spacing, it is likely that limited downgradient spreading of the released amendment will then be the primary constraint on interwell spacing. Divergent flow from the wells, roughly two times the well diameter, provides the bulk of downgradient spreading and constrains maximum well spacing in the absence of significant lateral dispersion. Stronger lateral dispersion enhances the spreading of amendment, thereby increasing the lateral impact of each well, which allows for wider well spacing.     

Tectonothermal events in the Olympic IOCG Province constrained by apatite and REE-phosphate geochronology

The Olympic iron oxide–copper–gold province in South Australia contains numerous deposits and prospects, including the Olympic Dam Cu–U–Au–Ag deposit and the Acropolis prospect. The Acropolis prospect comprises massive, coarse-grained magnetite–apatite veins partly replaced by a hematite-stable assemblage. The apatite grains in the veins contain zones with abundant inclusions of other minerals (including monazite and xenotime) and low trace-element concentrations relative to the inclusion-free zones. The inclusion-rich apatite zones are interpreted to be formed from the recrystallisation of the inclusion-free apatite and remobilisation of U, Th and rare earth element (REE) from apatite into monazite and xenotime. Apatite, monazite and xenotime are all established U–Th–Pb geochronometers and offer the potential to constrain the alteration history of the Acropolis prospect. The LA-ICPMS U–Pb age of inclusion-free apatite is within error of the age of the host volcanic units (ca 1.59 Ga). Inclusion-rich apatite yields both near-concordant analyses that are within error of the inclusion-free apatite as well as highly disturbed (discordant) analyses. The most concordant analyses of monazite (Th–Pb) inclusions and xenotime (U–Pb) inclusions and rim grains indicate an alteration event occurred at ca 1.37 Ga and possibly also at ca 500 Ma. The disparity in age of the inclusion-rich apatite and the REE-phosphate inclusions (and rim grains) is suggested to be owing to the apatite being initially recrystallised at ca 1.59 Ga and modified again by a later event that also formed (or coarsened) most of the inclusions. Partial resetting of the majority of the monazite inclusions as well as the presence of significant amounts of common Pb has complicated the interpretation of the monazite results. In contrast, xenotime is a more robust geochronometer in this setting. The ages of the two post-1.59 Ga events that appear to have affected the Acropolis prospect do not correspond to any events known to have occurred in the Gawler Craton. The earlier (ca 1.37 Ga) age instead corresponds best with metamorphic–magmatic–hydrothermal activity in Laurentia, consistent with the proximity of Laurentia and the Gawler Craton inferred from palaeogeographic reconstructions. The later (ca 500 Ma) event corresponds to the Delamerian Orogeny and has been shown by prior studies to have also affected the Olympic Dam deposit.     

Damping characteristics of friction damped braced frame and its effectiveness in the mega-sub controlled structure system

Based on energy dissipation and structural control principle, a new structural configuration, called the mega- sub controlled structure (MSCS) with friction damped braces (FDBs), is first presented. Meanwhile, to calculate the damping coefficient in the slipping state a new analytical method is proposed. The damping characteristics of one-storey friction damped braced frame (FDBF) are investigated, and the influence of the structural parameters on the energy dissipation and the practical engineering design are discussed. The nonlinear dynamic equations and the analytical model of the MSCS with FDBs are established. Three building structures with different structural configurations, which were designed with reference to the conventional mega-sub structures such as used in Tokyo City Hall, are comparatively investigated. The results illustrate that the structure presented in the paper has excellent dynamic properties and satisfactory control effectiveness.     

The use of optimization to construct critical accelerograms for given structures and sites

In this paper a methodology has been presented for constructing the most critical accelerogram from among a be class of candidate accelerograms for a given site and structure. This most critical accelerogram could be used to assess seismic resistance of a structure with a high level of confidence. Specifically, the method superimposes accelerograms recorded at similar sites to create the candidate accelerograms, then uses optimization and approximation techniques find the most critical accelerogram. The most critical accelerogram is defined as the one which maximizes damage is structure, as computed by non-linear dynamic structural analysis, as well as satisfies constraints on ground parameters to ensure credibility. The damage has been defined as cumulative inelastic energy dissipation or sure of interstorey drifts. The method is applied to ten examples in the paper.     

A Syringe and Cartridge Method for Down-Hole Sampling for Trace Organics in Ground Water

A newly developed technique which allows the down-hole sampling and subsequent analysis of ground water for trace organic contaminants was tested during an investigation of contaminant migration at an inactive landfill site in Burlington, Ontario, Canada. The sampling device, which is lowered down piezometers with a tube, consists of a small cylindrical cartridge of sorbent material attached to a syringe. Vacuum or pressure applied at the surface controls the movement of the plunger in the syringe. The volume of the syringe determines the volume of sample water that passes through the cartridge. The cartridge is removed from the syringe at the surface. One cartridge is used for each sampling; the syringe is reusable. The residual water in the cartridge is removed in the laboratory, and the cartridge is desorbed to a fused silica capillary column for analysis by gas chromatography (GC). The analyses discussed here were performed on a GC/mass spectrometer/data system (GC/MS/DS). Of the many organic compounds that were identified in the samples, three compounds were clearly landfill-related: 1,1,1-trichloroethane, chlorobenzene, and para-dichlorobenzene. The three compounds were found at levels substantially above blank levels in 9, 5, and 5 piezometers, respectively. The average concentrations were 14., 5.3, and 0.88μg/1 (ppb), respectively. The pooled coefficients of variation for the analyses for the three compounds were 27., 6.9, and 6.4%, respectively. The volatility of 1,1,1-trichloroethane was probably the cause of the greater variability in its analytical data. The main advantages of the technique over most conventional sampling methods include: (1) down-hole sampling in a manner which minimizes the potential for volatilization losses; (2) avoidance of passage of the sample through long sections of tubing that may contaminate the sample or cause adsorptive losses; (3) convenience of sample handling, storage, and shipping; and (4) high sensitivity.     

COOLING RATES, SKY VIEW FACTORS AND THE DEVELOPMENT OF INTRA-URBAN AIR TEMPERATURE DIFFERENCES

Intra‐urban cooling rates were monitored for a year in the centre of Göteborg on the Swedish west coast. Five sites with different building geometry ‐ from dense canyon to open space ‐ within a radius of 300 m were analysed. Results showed two modes of cooling during the night. In the first mode, the cooling was site‐dependent ‐the open space cooled the most and the dense canyon the least. In the second mode, which began about 3–4 hours after sunset, all sites cooled at the same rate. Our hypothesis is that in the early part of the evening both radiative divergence and sensible heat dominate the cooling. However, as the evening progresses, a spatially homogeneous inversion is established which controls the radiative cooling, making the cooling independent of both surface geometry and surface type. From April to November the sites cooled rapidly around sunset and the cooling slowly decreased during the rest of the night. However, between December and March, the cooling was less intense, with an almost constant rate during the entire night. It has been suggested that this might be the result of the draining of stored solar heat during the summer and a continuous flux of anthropogenic heating during the winter.     

Differences in trace metal concentrations among fluvial morphologic units and implications for sampling

 This study examines the segregation of trace metals within and between fluvial morphologic units in sand-sized and finer bed sediments in a cobble bed stream. The types of fluvial morphologic units sampled are low gradient riffles, high gradient riffles, glides, eddy drop zones, lateral scour pools, attached bars, and detached bars. Three to nine samples were collected from ten of each type of morphologic unit. All 12 metals show significantly different concentrations between some morphologic units in sediments smaller than 2 mm. Eddy drop zones and attached bars consistently have the highest metal concentrations, while low gradient riffles, high gradient riffles, and glides typically have the lowest concentrations. Metals showing the greatest between-unit variability are Al, Cr, Fe, Cu, and Ti, followed by Co, Mn, and Pb, while Mg, Mn, V, and Zn display relatively few differences between units. Lateral and longitudinal variations of metals within units are not significant, and there was no consistent, predictable variation in metal concentrations with distance downstream. Results indicate that metal studies in other gravel- and cobble-bed streams should include a reconnaissance survey to determine variations between morphologic units, stratify sampling by morphologic unit, and analyze spatial autocorrelation to determine sample spacing. Received: October 1997 · Accepted: 23 March 1998     

High-resolution stratigraphy of the northernmost concentric raised bog in Europe: Sellevollmyra, Andøya, northern Norway

From the Sellevollmyra bog at Andøya, northern Norway, a 440‐cm long peat core covering the last c. 7000 calendar years was examined for humification, loss‐on‐ignition, microfossils, macrofossils and tephra. The age model was based on a Bayesian wiggle‐match of 35 ¹⁴C dates and two historically anchored tephra layers. Based on changes in lithology and biostratigraphical climate proxies, several climatic changes were identified (periods of the most fundamental changes in italics): 6410–6380, 6230–6050, 5730–5640, 5470–5430, 5340–5310, 5270–5100, 4790–4710, 4890–4820, 4380–4320, 4220–4120, 4000–3810, 3610–3580, 3370–3340 (regionally 2850–2750; in Sellevollmyra a hiatus between 2960–2520), 2330–2220, 1950, 1530–1450, 1150–840, 730? and c. 600? cal. yr BP. Most of these climate changes are known from other investigations of different palaeoclimate proxies in northern and middle Europe. Some volcanic eruptions seemingly coincide with vegetation changes recorded in the peat, e.g. about 5760 cal. yr BP; however, the known climatic deterioration at the time of the Hekla‐4 tephra layer started some decades before the eruption event.