Conventional and combined pump-and-treat systems under nonuniform background flow

We investigate the performance of vertical hydraulic barriers in combination with extraction wells for the partial hydraulic isolation of contaminated aquifer areas. The potential advantage of such combinations compared to a conventional pump-and-treat system has already been demonstrated in a previous study. Here we extend the scope of the performance analysis to the impact of uncertainty in the regional flow direction as well as to highly heterogeneous aquifer transmissivity distributions. In addition, two new well-barrier scenarios are proposed and analyzed. The hydraulic efficiency of the scenarios is rated based on the expected (mean) reduction of the pumping rate that is required to achieve downgradient contaminant capture. The uncertain spatial distribution of aquifer transmissivity is considered by means of unconditioned Monte Carlo simulations. The significance of uncertain background flow conditions is incorporated by computing minimized pumping rates for deviations of the regional flow direction up to 30 degrees from a normative base case. The results give an answer on how pumping rates have to be changed for each barrier-well combination in order to achieve robust systems. It is exposed that in comparison to installing exclusively wells, the barrier-supported approach generally yields savings in the (average) pumping rate. The particular efficiency is shown to be highly dependent on the interaction of variance and integral scale of transmissivity distribution, well and barrier position, as well as direction of background flow.     

Boron isotopes as an artificial tracer

A field study was conducted using a combination of intrinsic and artificial tracers to estimate travel times and dilution during transport of infiltrate from a reclaimed water infiltration basin to nearby monitoring wells. A major study objective was to validate boric acid enriched in (10)B as an artificial tracer. Basin 10E at the Rio Hondo Spreading Grounds in Whittier, California, was the site of the test. The basin normally receives a mixture of treated municipal waste water, purchased State Project water, and local runoff from the San Gabriel River. Approximately 3.5 kg of (10)B-enriched boric acid was dispersed among 2.05 x 10(5) m(3) of basin water to initiate the experiment. The resultant median delta(11)B in the infiltration basin was -71 per thousand. Prior to tracer addition, the basin water had an intrinsic delta(11)B of +2 per thousand. Local monitoring wells that were used to assess travel times had delta(11)B values of +5 per thousand and +8 per thousand at the time of tracer addition. Analytic results supported an assumption that boron is conserved during ground water transport and that boron enriched in (10)B is a useful artificial tracer. Several intrinsic tracers were used to reinforce the boric acid tracer findings. These included stable isotopes of oxygen (delta(18)O) and hydrogen (deltaD), sulfate concentration, and the boron to chloride ratio. Xenon isotopes, (136)Xe and (124)Xe, also supported boron isotope results. Xenon isotopes were added to the recharge basin as dissolved gases by investigators from the Lawrence Livermore National Laboratory.     

A mechanism for anomalous decline in radon precursory to an earthquake

Mechanisms for interpreting anomalous decreases in radon in ground water prior to earthquakes are examined with the help of a case study to show that radon potentially is a sensitive tracer of strain changes in the crust preceding an earthquake. The 2003 Chengkung earthquake of magnitude (M) 6.8 on December 10, 2003, was the strongest earthquake near the Chengkung area in eastern Taiwan since 1951. The Antung radon-monitoring station was located 20 km from the epicenter. Approximately 65 d prior to the 2003 Chengkung earthquake, precursory changes in radon concentration in ground water were observed. Specifically, radon decreased from a background level of 780 pCi/L to a minimum of 330 pCi/L. The Antung hot spring is situated in a fractured block of tuffaceous sandstone surrounded by ductile mudstone. Given these geological conditions, we hypothesized that the dilation of brittle rock mass occurred at a rate faster than the recharge of pore water and gas saturation developed in newly created cracks preceding the earthquake. Radon partitioning into the gas phase may explain the anomalous decrease of radon precursory to the 2003 Chengkung earthquake. To support the hypothesis, vapor-liquid, two-phase radon-partitioning experiments were conducted at formation temperature (60 degrees C) using formation brine from the Antung hot spring. Experimental data indicated that the decrease in radon required a gas saturation of 10% developed in rock cracks. The observed decline in radon can be correlated with the increase in gas saturation and then with the volumetric strain change for a given fracture porosity.     

Organic carbon and nitrogen stable isotopes in the intertidal sediments from the Yangtze Estuary, China

The natural isotopic compositions and C/N elemental ratios of sedimentary organic matter were determined in the intertidal flat of the Yangtze Estuary. The results showed that the ratios of carbon and nitrogen stable isotopes were respectively −29.8‰ to − 26.0‰ and 1.6‰–5.5‰ in the flood season (July), while they were −27.3‰ to − 25.6‰ and 1.7‰–7.8‰ in the dry season (February), respectively. The δ¹³C signatures were remarkably higher in July than in February, and gradually increased from the freshwater areas to the brackish areas. In contrast, there were relatively complex seasonal and spatial changes in stable nitrogen isotopes. It was also reflected that δ¹⁵N and C/N compositions had been obviously modified by organic matter diagenesis and biological processing, and could not be used to trace the sources of organic matter at the study area. In addition, it was considered that the mixing inputs of terrigenous and marine materials generally dominated sedimentary organic matter in the intertidal flat. The contribution of terrigenous inputs to sedimentary organic matter was roughly estimated according to the mixing balance model of stable carbon isotopes.     

Macro- and meiofaunal recolonisation of dredged material used for habitat enhancement: temporal patterns in community development

In recent years, dredged material has become regarded as a potential resource and used to create and/or improve intertidal habitats (i.e., beneficial use). This paper presents the results of a sampling programme to investigate the long-term (42 months post-recharge) macro- and meiofaunal recolonisation processes of a beneficial use scheme in south-east England. While univariate indices of community structure indicated that the scheme’s meiofaunal community was never significantly different from that of a nearby reference area, such attributes for macrofauna were continually significantly below those of the reference area, although this was not the case for all reference stations. Multivariate analyses revealed that macro- and meiofaunal community structures were always significantly different from those of the reference communities. We discuss the factors responsible for these observations and propose that assessing recovery of a beneficial use scheme should be undertaken using pre-defined criteria in addition to comparisons with a reference site.     

Where do periodic variations in the discharge of a well become negligible?

A rule of thumb is presented to determine where variations in the discharge of a pumping well have a significant influence on the flow in an aquifer. The rule of thumb relates the period of the variation of the discharge to the distance from the well beyond which the transient effect on the flow in the aquifer is insignificant. For example, when an irrigation well pumps intermittently during the growing season, the rule may be applied to determine the distance from the well beyond which flow in the aquifer can be simulated with an average discharge during the growing season; the distance from the well beyond which flow can be simulated with a steady, yearly averaged discharge can also be computed.     

The use of the marine biotic index AMBI in the assessment of the ecological status of the Obidos lagoon (Portugal)

This study reports the longitudinal distribution of sediment properties, including inorganic and organic contaminants, and the structure of the benthic community in Obidos lagoon, a coastal system permanently connected to the sea and with negligible freshwater sources. Sediments from the upper to central lagoon consist of fine particles (91%) and from the lower lagoon of sands (94%). Chemical composition is strongly correlated to the percentage of fine particles. Contamination is relatively low in those sediments suggesting the effect of diffuse sources. The increase in organic matter content from down- to upstream areas was associated with the dominance of opportunistic species, while sensitive and indifferent species to organic enrichment were mainly associated to the clean sandy downstream area. The marine biotic index (AMBI) was suitable for the discrimination of the biological and environmental gradients in the Obidos lagoon and was highly related with the gradient of organic matter content in this system.     

Mediterranean fin whales at risk from fatal ship strikes

This paper reviews and analyzes ship collision records for the relatively isolated population of fin whales in the Mediterranean Sea from 1972 to 2001. Out of 287 carcasses, 46 individuals (16.0%) were certainly killed by boats. The minimum mean annual fatal collision rate increased from 1 to 1.7 whales/year from the 1970s to the 1990s. Fatal strike events (82.2%) were reported in or adjacent to the Pelagos Sanctuary, characterized by high levels of traffic and whale concentrations. Among 383 photo-identified whales, 9 (2.4%) had marks that were attributed to a ship impact. The reported rates are unusually high for baleen whales. The high likelihood of unreported fatal strikes combined with other anthropogenic threats suggests an urgent need for a comprehensive, basin-wide conservation strategy, including ship strike mitigation requirements, like real-time monitoring of whale presence and distribution to re-locate ferry routes to areas of lower cetacean density, and reducing ship speed in high cetacean density areas.     

Bioremediation and toxicity determination of natural seawater polluted with weathered crude oil by salt-tolerant consortia in a SBR

The aim of this research was to compare the bioremediation treatment of seawater polluted with two different concentrations of weathered crude oil (0.2 for experiment (a) and 1.14% for experiment (b), v/v) by salt-tolerant consortia enriched from the sludge of a refinery wastewater treatment facility, in a SBR. The use of a commercial bioremediation stimulant (S200) was also evaluated as an alternative to the traditional nitrogen and phosphorus supplement.