Sediment-filled fractures in Triassic sandstones : pathways or barriers to contaminant migration?

Observations of sediments infilling fractures in Triassic Sandstones, an important aquifer in the United Kingdom may explain sand production in some water supply boreholes in the UK and why the aquifer transmissivity increases with time, which would occur if sediments were being washed from the fractures. The fracture infills are variable from sands to complex interlaminated sand, silt and clay. It is clear that, depending on the fill material, fractures may form either pathways or barriers to contaminant migration, questioning current concepts for flow in fractured sandstones, and throwing doubt on our ability to predict or remediate contaminant migration in this nationally important aquifer. Mineralogical differences between the fracture fill material and the host sandstone may also affect sorption and precipitation reactions, which, if not considered, may significantly alter the prediction of contaminant migration through either the fracture fill or host sandstone matrix. At present, there is little knowledge of the extent of fracture fills, how they form, whether they occur above and below the water table and whether in vertical joints or bedding plane fractures. There are few measurements of their hydraulic properties to be able to assess their hydrogeological significance and how they should be represented in contaminant transport models. For instance, if the fill has a similar permeability to the rock matrix, a porous medium model may suffice. If the fractures are filled with clay with lower permeability, or if preferential flow along fractures exists, a different modelling approach involving a porous medium with planar barriers may be required. It is hoped the improved representation of fractures in solute or NAPL migration models will lead to better assessment of contaminant migration and risk, focused remediation techniques, and more precise evaluation and management of groundwater resources. This ongoing study aims to understand the nature and geological controls on how fracture fills develop and to improve the representation of fractures in solute or NAPL migration models. The first stage in this is to establish the distribution and occurrence of these features at outcrop, to establish formation mechanisms and provide data such as textural information and permeability measurements that will contribute to a better understanding of their influence on hydrogeology. This will lead to a better assessment of contaminant migration and risk, more focused remediation techniques, and more precise evaluation and management of groundwater resources. A key problem is that sediment infills may not be preserved at outcrop and may also be destroyed during standard borehole sampling procedures. This requires a careful approach to sampling, both at outcrop and in the borehole

Combining unsaturated and saturated hydraulic observations to understand and estimate groundwater recharge through glacial till

Although there has been much previous research into various aspects of the flow mechanisms through glacial till, an integrated analysis of the flow system from the ground surface to the aquifer is lacking. This paper describes such an approach with reference to a detailed field study of the hydraulic processes controlling groundwater recharge through lodgement till in Shropshire, UK. A fieldsite was instrumented with tensiometers and piezometers at a range of depths through the profile, and the geology investigated in detail through field and laboratory testing. The median matrix hydraulic conductivity of the 6 m thick till is found to be around 2 × 10−10 m/s on the basis of laboratory measurements. Using the barometric efficiency of the till derived from on-site pressure responses, the specific storage for the till is found to be in the range 2 × 10−6–6 × 10−6 m−1 and approximately 3 × 10−6 m−1 for the underlying Permo-Triassic sandstone, the regional aquifer. The hydraulic data indicate that till water table responses to rainfall occur during the summer period even when large tensions are present higher in the profile. This is thought to be due to preferential flow through hydraulically active fractures in the till, which were observed in a test pit dug on-site. The field evidence indicates that the fractures are usually infilled with a variety of materials derived and transported from clasts within the till. The bulk hydraulic conductivity of the till seems to be greatly enhanced by these features and it is shown on the basis of hydraulic testing and numerical modelling that the bulk hydraulic conductivity of the till is orders of magnitude greater than that of the till matrix and reduces with depth below ground surface. The paper furthers understanding of the hydraulic processes contributing to recharge through till and makes the link between the detail of these processes and simplified models of recharge estimation, which may be needed for larger scale water resource studies. The results are relevant also to contaminant migration studies and aquifer vulnerability assessments

The hydrodynamics of East Anglia fen systems

Report to the Nature Conservancy Counci1, National Rivers Authority and Broads AuthorityAvailable from British Library Document Supply Centre- DSC:3425.823(NCC-CS--88) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Importance of ticks and their chemical and immunological control in livestock

The medical and economic importance of ticks has long been recognized due to their ability to transmit diseases to humans and animals. Ticks cause great economic losses to livestock, and adversely affect livestock hosts in several ways. Loss of blood is a direct effect of ticks acting as potential vector for haemo-protozoa and helminth parasites. Blood sucking by large numbers of ticks causes reduction in live weight and anemia among domestic animals, while their bites also reduce the quality of hides. However, major losses caused by ticks are due to their ability to transmit protozoan, rickettsial and viral diseases of livestock, which are of great economic importance world-wide. There are quite a few methods for controlling ticks, but every method has certain shortcomings. The present review is focused on ticks importance and their control