Alcan Lynemouth smelter, geology and hydrogeology in the vicinity of the ash storage lagoons

The British Geological Survey (BGS) was commissioned by Mr John Clarkson, Alcan Smelting and Power UK, to carry out a desk study of the geology and hydrogeology information of the area around the waste landfill site and ash storage lagoons at Alcan, Lynemouth. The desk study was supplemented by a site visit. A main concern was the possibility that the ash in the lagoons might be contaminated by contact with leachate from the hazardous materials disposed in the landfill. The BGS was asked to provide an independent report on the contamination risk and of the suitability of the ash lagoon test bores plus any existing and proposed groundwater monitoring wells at the Alcan Lynemouth site to detect such contamination. An extensive search was made for previous site investigation reports. The information obtained, in particular the records of over 50 boreholes drilled in the study area since 1990, has been used to review the published geological interpretation and better understand the hydrogeological regime. In general the new information supports the existing solid geological interpretation, but enables improved understanding of the disposition of the superficial deposits including a glacial buried channel. The site is over a minor Coal Measure aquifer, the North Seaton Sandstone, which is underlain by a mudrock aquiclude sequence. Groundwater flow in the sandstone, is dominantly fracture controlled and is to the east. The groundwater system is isolated from the flooded, abandoned mine workings beneath the site where the water level is at about 90 m below Ordnance Datum and slowly rising. Saline intrusion is evident in the aquifer, and the saline interface appears to cut across the axis of the buried glacial channel. An unsaturated zone of sandstone hydraulically separates the landfill and the PFA lagoons from the water table in the North Seaton Sandstone aquifer. It is concluded that it is unlikely that the PFA will become contaminated from the landfill leachate via the groundwater pathway or through direct discharge of leachate through the retaining bunds. The Coal Measure sandstone is overlain, but hydrogeologically unconfined by a glacial till sequence where the flow is probably predominantly vertical through fractures. The landfill operates on the dilute and disperse principle and the limited hydrochemical data available indicates that the groundwater impact diminishes along a flow line from the landfill. The existing series of operational monitoring wells is useful in providing information on water levels to help determine direction of groundwater flow and hydraulic gradient, and chemical data to help determine the extent of saline intrusion from the sea and the extent of dispersion of contaminants from the landfill. However the limited area covered by the wells gives rise to uncertainty in the interpretation. These uncertainties are discussed and possible avenues of investigation and action recommended in order to reduce them. The recommendations include: • Increasing the range of parameters determined in the landfill monitoring wells to include major anions and cations as well as nitrate and ammonia. • Implementing the five additional monitoring wells proposed by URS with specific suggestions for screening of the two proposed on the eastern perimeter of the site • Including a new well, integrated into the monitoring network, at the south-west corner of lagoon 1 • Giving consideration to the complementary approach of building a numerical model for the sit

Ground-truthing airborne EM - Hydrochemical characterization of a coal mine plume

A trial airborne EM (AEM) survey was carried out across a 13 x 9 km area of the northern Nottinghamshire (UK) coalfield. One of the objectives was to examine the influence of collieries situated above the Triassic Sherwood Sandstone aquifer. The conductivity models obtained from the AEM survey revealed extensive zones of enhanced subsurface conductivity in the vicinity of all the collieries in the survey area. The purpose of the present study is to provide information regarding subsequent investigations (ground geophysics and borehole) to confirm the AEM results and to investigate the geochemical nature of the conductive zone identified in the vicinity of one of the collieries

The detection and tracking of mine-water pollution from abandoned mines using electrical tomography

Increasing emphasis is being placed on the environmental and societal impact of mining, particularly in the EU, where the environmental impacts of abandoned mine sites (spoil heaps and tailings) are now subject to the legally binding Water Framework and Mine Waste Directives. Traditional sampling to monitor the impact of mining on surface waters and groundwater is laborious, expensive and often unrepresentative. In particular, sparse and infrequent borehole sampling may fail to capture the dynamic behaviour associated with important events such as flash flooding, mine-water break-out, and subsurface acid mine drainage. Current monitoring practice is therefore failing to provide the information needed to assess the socio-economic and environmental impact of mining on vulnerable eco-systems, or to give adequate early warning to allow preventative maintenance or containment. BGS has developed a tomographic imaging system known as ALERT ( Automated time-Lapse Electrical Resistivity Tomography) which allows the near real-time measurement of geoelectric properties "on demand", thereby giving early warning of potential threats to vulnerable water systems. Permanent in-situ geoelectric measurements are used to provide surrogate indicators of hydrochemical and hydrogeological properties. The ALERT survey concept uses electrode arrays, permanently buried in shallow trenches at the surface but these arrays could equally be deployed in mine entries or shafts or underground workings. This sensor network is then interrogated from the office by wireless telemetry (e.g: GSM, low-power radio, internet, and satellite) to provide volumetric images of the subsurface at regular intervals. Once installed, no manual intervention is required; data is transmitted automatically according to a pre-programmed schedule and for specific survey parameters, both of which may be varied remotely as conditions change (i.e: an adaptive sampling approach). The entire process from data capture to visualisation on the web-portal is seamless, with no manual intervention. Examples are given where ALERT has been installed and used to remotely monitor (i) seawater intrusion in a coastal aquifer (ii) domestic landfills and contaminated land and (iii) vulnerable earth embankments. The full potential of the ALERT concept for monitoring mine-waste has yet to be demonstrated. However we have used manual electrical tomography surveys to characterise mine-waste pollution at an abandoned metalliferous mine in the Central Wales orefield in the UK. Hydrogeochemical sampling confirms that electrical tomography can provide a reliable surrogate for the mapping and long-term monitoring of mine-water pollution

Evidencias de un embalse volcánico en el valle del Colca

El valle del rio Colca esta ubicado aproximadamente 90 Km. Al norte de Arequipa en el sur del Perú; con una profundidad máxima de 3000 m. es considerado como el cañón mas profundo del mundo. Se sugiere aquí, que debido a in embalsamiento del rio Colca en el Pleistoceno, causado por flujos volcánicos del centro Ahuashune (inmediato al norte del Nevado Hualca Hualca) se formó un lago de unos 45 Km de extensión y 3.5 Kms de ancho detrás de la represa volcánica. El lago fue rellenado por depósitos lacustres y fluviales, alcanzando un espesor de aproximadamente 350 m

An evaluation of some mining related SSSIs within the context of Part IIA Environmental Protection Act

This report describes the results of jointly funded project by the British Geological Survey and English Nature to develop a GIS approach to prioritising mineralogical SSSIs. The object and rationale was to prioritise sites for follow on studies aimed at assessing pollution potential within the context of the Environmental Protection Act, Part IIA. The first part of the report introduces the main elements of the Part IIA legislation of relevance to abandoned mining. A brief account of the forthcoming EU Mine Waste Directive is also presented to set this study within a European context. The second part of the report deals with a description of the main environmental hazards linked to abandoned mining. The report goes on to briefly describe the English metallogenic setting relevant to the SSSIs and the minerals; both ore and gangue, of potential environmental concern are noted. An account of the GIS decision support application is then presented and the development of the scoring scheme based on the concept of ranked pollutant linkages. The final section of the report presents the GIS outputs in ranked tabular form and recommendations are made for prioritising follow up work based on this output. The site prioritisations for each site are presented on the CDs in the Appendix

Effects of old landfills on groundwater quality. Phase 2, investigation of the Thriplow landfill 1996–1997

Disused sand and gravel excavations overlying the major Chalk aquifer at Thriplow in Cambridgeshire have been filled with domestic waste in two phases. One area (Phase 1) was filled between 1957–77 with little compaction of the refuse and was left uncapped, while Phase 2 was deposited between 1981–87 and capped with clay. Aerial photography and surface resistivity surveys indicate that the site geometry is complex, with several phases of landfilling into excavations of differing depths. Drilling through the waste indicates that leachate production and waste stabilisation proceed at different rates in capped and uncapped landfills. Analysis of leachate obtained by centrifugation or squeezing appears to give more insight into the pollution potential than do leach tests with distilled water. The Biological Methane Potential (BMP) of the waste appears to be related to the quantity of decomposable material but the chemical oxygen demand (COD) values are distorted by the presence of reduced metals. Too few boreholes have been drilled to define the leachate source in terms of its spatial distribution and little is known of how its composition has changed with time. However, hydraulic conductivity measurements on the landfill caps suggest that it is sufficiently permeable for all rainfall to potentially infiltrate the waste. Boreholes outside the landfill penetrate the Upper and Lower Chalk, and identify the Melbourn Rock and underlying Plenus Marls at the junction of the two formations about 20 m below ground level (bgl). Surface resistivity surveys using the BGS RESCAN system, confirm aerial photographs of the extent of the landfill and also suggest that leachate has migrated beyond the base of the landfill. Evidence of leachate migration in pre-existing screened boreholes completed above and below the Plenus Marls suggests that leachate is flowing above the Plenus Marls. Hydraulic head measurements whilst drilling a borehole to the base of the lower Chalk approx. 70 m bgl revealed the potential for upward groundwater flow through the Plenus Marls. Thus, previously-drilled boreholes penetrating the Plenus Marls are expected to recharge upwards into the shallow aquifer above the Plenus Marls diluting any leachate in the upper aquifer and distorting the flow regime. Several of these boreholes have subsequently been modified to stem the flow across the Plenus Marls. One borehole down-gradient to the west of the site revealed a large thickness of drift composed of both sand and clay rich material. This suggests the existence of a buried channel, the hydrogeological significance of which has yet to be assessed. Groundwater chemistry appears to be influenced by three major factors. (a) the landfill leachate (b) the composition of shallow groundwater in the top 10 m of the Chalk, and (c) the composition of water from the Lower Chalk. Limited groundwater monitoring data appear to display a cyclic variation in chloride concentration. The origin for this is not clear but it may correlate with cyclic variations in groundwater levels when the water table rises into the waste. Cyclic flushing of the landfill may release leachate into the aquifer giving rise to pulses of chloride. Alternatively changes in chloride may arise by the changing direction of groundwater flow which as yet has not been assessed. A conceptual hydrogeological model in which flow is limited to above the Plenus Marls has been used to develop a more appropriate groundwater flow and solute transport model. However, the model lacks data on aquifer properties, on contaminant inputs concentrations, fluxes and spatial variations, and there is a paucity of monitoring data for calibration. Nonetheless preliminary transport modelling using an equivalent porous medium approach shows that an effective porosity of about 5% best fits the regional data. Since this is much less than the total porosity of about 40% for the Chalk, it would appear that only part of the Chalk is available for flow but that matrix diffusion could play an important role in leachate attenuation. Discrete fracture modelling using the FRACTRAN code has allowed some scoping to be made of the hydraulic properties of the aquifer by comparison with chloride hydrographs, but these again need to be better conditioned by in-situ measurement of fracture distributions and transmissivities. A number of additional activities are required to improve the understanding of flow and contaminant transport at the site. These include better spatial definition of the waste distribution, improved data on the hydraulic properties of the Chalk aquifer, and the use of automatic monitoring to record temporal changes in groundwater chemistry and groundwater levels

Human health risk assessment for exposure to soil in Kosovo and Bosnia

This report describes a human health risk assessment for British personnel serving in Bosnia and Kosovo. The mathematical description of the risk assessment model is developed based on algorithms used in the commercially available software Risk*Assistant. A simple conceptual exposure model of soil ingestion and soil dust inhalation is developed based on a six-month tour of duty. Two exposed groups have been identified, one with an exposure for 12 hours per day and an office based group with an outdoor exposure of 3 hours per day. It is assumed that there is no indoor exposure to soil and soil dust. The risk calculations indicate that there is no toxic risk at any of the sites and the increased risk of cancer due to soil ingestion and inhalation is below the currently accepted value of one in a million increased risk. Lifetime average daily doses are below the Index Dose thresholds for inhalation of chromium, cadmium and arsenic at all sites. Since the office based group have an exposure duration that is 75% less than the outdoor group the soil intakes are correspondingly linearly reduced by the same amount. Consequently the hazard quotients and carcinogenic risks are also reduced by 75%

Groundwater and its susceptibility to degradation : a global assessment of the problem and options for management

The Millennium Development Goals (MDGs) were adopted by member countries of the UN in 2000 as a global consensus on objectives for addressing poverty. Water has a key role in strategies for achieving all of the MDGs, which include a target to reduce by half the proportion of people without access to a safe water supply and a commitment to ensure environmental sustainability. The 2002 World Summit on Sustainable Development (WSSD) in Johannesburg made an important advance when it placed poverty eradication at the heart of efforts to achieve sustainable development. The Summit brought the development and environment movements together and committed the international community to a systematic effort both to reduce poverty and pursue sustainable development. A new target on sanitation and a commitment to have water resource plans for all countries in place by 2005 were made at WSSD. The importance of water and its fundamental contribution to sustainable development is now recognised, but the contribution of water to poverty reduction will only be realised if it is set in the broader context of social and economic development and environmental improvement

Hydrochemical characterisation of the Sherwood Sandstone Group in the vicinity of Thoresby Colliery, Nottinghamshire

This report describes the detailed ground investigations that were carried out in the vicinity of Thoresby Colliery as part of the BGS HiRES research programme and their results. The introduction to the report briefly describes the background airborne geophysics acquired as part of the joint Geological Survey of Finland (GTK) - British Geological Survey (BGS) trial airborne environmental and geological surveys flown in June 1999. The main objective of these surveys was to test the efficiency of the GTK airborne electromagnetic (AEM) system in the mapping of potential pollution problems in the UK environment. The survey in the vicinity of Thoresby Colliery identified a conductivity anomaly that was attributed to migration of colliery spoil leachate as a groundwater plume to the east of the site. Three boreholes were drilled into the geophysical anomaly. Section 2 of the report discusses the results of groundwater monitoring and pore water extraction from the drill core. The groundwater flow direction has been determined to be to the east of the colliery. Down hole geophysical logging is reported and it is demonstrated that there is a very strong correlation between the borehole induction logs, total dissolved solids and chloride in the pore waters. A comparison of background groundwater quality and pore water chemistry with published colliery spoil leachate data indicates that it is possible to explain the core, pore water chemistry as a result of mixing of groundwater with a colliery spoil leachate source term. The close similarity of the Cl/Br ratio of pore waters in the groundwater plume with Thoresby Colliery process waters provides supporting evidence for this model to explain the origin of the plume and hence of the AEM anomaly

Trihalomethane formation potential : a tool for detecting non-specific organic groundwater contamination

The trihalomethane formation potential (THMFP) was measured in groundwaters affected by infiltration of wastewater or landfill leachate from Mexico, Jordan and Thailand. THMFP was directly related to the concentration of dissolved organic carbon, except where leachate was produced from burnt waste or where bromide concentrations were unusually high indicating the proportion of brominated derivatives was dependent on the concentration of bromide. It is proposed that the THMFP provides a sensitive measure of low levels of organic contamination and can be used as a surrogate for dissolved organic carbon concentration where there are difficulties in measuring this parameter. A risk assessment model has been used and demonstrates indirect health effects due to the chlorination of leachate contaminated groundwater