Guidelines for assessing the risk to groundwater from on-site sanitation

There has been encouraging progress with access to safe drinking water and sanitation in both rural and urban areas since the United Nations Water Decade of the 1980s. However, more than 1 billion people around the world still lack access to safe water supplies and more than 2.4 billion are without adequate sanitation. A substantial majority of these people live in Asia where the lack of sanitation provision is particularly acute. In Africa, over one third of the population still remains without access to safe water and sanitation, and many of these can only be served by groundwater. The need for renewed efforts to improve the situation is recognised in DFID’s recently published water strategy paper – "Addressing the Water Crisis - Healthier and More Productive Lives for Poor People". The health benefits of safe water supply are only properly realised when programmes combine safe water supply with sanitation and the promotion of safe hygiene practice. With increasing population, the pressure on land in all cities is becoming intense. High levels of pollution are increasing the risk to groundwater from sanitation and drainage facilities. These guidelines are an important contribution to risk assessment and the avoidance of the contamination of groundwater supplies from on-site sanitation. They have been developed as part of a project funded by DFID through the water component of the Infrastructure and Urban Development Division’s Knowledge and Research Programme

Spheroidal dolomites in a Visean karst system - bacterial induced origin?

Spheroidal dolomite crystals occur in the karstified top of a Dinantian dolomite sequence in eastern Belgium. The spheroidal dolomite crystals are best developed at the base of the karst system. The dolomite crystals are characterized by a spherulitic or dumb-bell inclusion pattern, and are overgrown by dolomite cements with a rhombohedral outline. They are considered to be bacterially related precipitates based on, (1) textural similarities with documented bacteriogenic precipitates, (2) the presence of 'bacterial'microspheres and framboidal pyrite embedded within the dolomite, and (3) their general geological setting. The geochemical characteristics of the dolomites and associated minerals support a bacterial origin. The ubiquity of framboidal pyrite, depleted in 34S (δ34S=— 22.4 to — 25.5%oCDT), testifies to a period of bacterial sulphate reduction. The isotopic composition of the spheroidal dolomites (δ13C=— 2.4 to - 3.2%oPDB and δ18O=— 3.8 to - 3.4%oPDB) suggest a contribution from oxidized organic carbon produced during bacterial sulphate reduction. Sulphate reduction may also result in a concomitant 18O depletion if the system is nearly closed. It is however, evident from the sulphur isotopic composition of associated framboidal pyrite that the system was fairly open. The 18O depletion of the spheroidal dolomite crystals (δ18O=— 3.8 to — 3.4%oPDB) and their occurrence adjacent to, and within karst cavities suggests a mixing zone origin, with a significant proportion of freshwater in it. The rhombohedral cement-overgrowths have calculated δ18O values in the range of 0 to +5.3%oPDB, which reflect precipitation from normal to slightly evaporated contemporaneous seawater