A well surveillance study carried out in nine Divisional Secretariat Divisions on the west coast of Sri Lanka showed that 70.3% of 101 well sampling points were microbially contaminated with equal to, or greater than,...A well surveillance study carried out in nine Divisional Secretariat Divisions on the west coast of Sri Lanka showed that 70.3% of 101 well sampling points were microbially contaminated with equal to, or greater than, faecal coliform grade C (11 - 100 cfu/100 mL). Due to the very vulnerable hydro-geological setting of the coastal sand, laterite and alluvium aquifers occurring in the study areas, the recommended safe separation distance between an on-site sanitation system and a well could not be achieved. Hence, a cardinal rule of well protection was observed to be broken at almost every well study site. The existing excreta disposal systems need to be improved or replaced with more efficient ones before the impact of other sanitary hazards at the well, and wellhead area, on the microbial quality of well water, can be determined and addressed. The published (WHO, 1997) sanitary survey forms for open dug wells and tube wells need to be modified in the context of the study areas described. Based on a comparison of three different statistical methods used to assess the relative significance of each sanitary hazard modification to the methodology for determining the sanitary hazard index (SHI) was prescribed.展开更多
Concern for saline and microbial quality post-December 2004 tsunami, led to a field based surveillance study to systematically investigate the sanitary hazards which cause faecal contamination of groundwater. In seven...Concern for saline and microbial quality post-December 2004 tsunami, led to a field based surveillance study to systematically investigate the sanitary hazards which cause faecal contamination of groundwater. In seven islands, two duplicate sample sets, in two surveys, revealed that only 6.4% of the 173 well water samples (combining both surveys) satisfied the WHO Drinking Water Quality Guideline for 44°C thermo-tolerant (Faecal) Coliform (FC) indicator value (zero cfu/100 ml sample). Based on a combined risk analysis of Sanitary Hazard Score (SHS) and FC counts, more than 57.7% of the study wells were classified as at very high (FC: 100 to >1,000 cfu/100ml;and SHS: ≥ 9) microbial health risk. During this study, fundamental changes were made to the published generic sanitary inspection method (WHO, 1997) for identifying sanitary hazards, for its application in the extremely vulnerable hydro-geological setting of the Maldives. However, the most important hazard controlling the intensity of faecal contamination in the Maldives is the safe separation distance between a latrine seepage point and the well. It was demonstrated that, due to the prevailing hydro-geological conditions and the well and sanitation system densities, safe separation distance cannot be achieved. Consequently, septic tank effluent quality must be greatly improved.展开更多
文摘A well surveillance study carried out in nine Divisional Secretariat Divisions on the west coast of Sri Lanka showed that 70.3% of 101 well sampling points were microbially contaminated with equal to, or greater than, faecal coliform grade C (11 - 100 cfu/100 mL). Due to the very vulnerable hydro-geological setting of the coastal sand, laterite and alluvium aquifers occurring in the study areas, the recommended safe separation distance between an on-site sanitation system and a well could not be achieved. Hence, a cardinal rule of well protection was observed to be broken at almost every well study site. The existing excreta disposal systems need to be improved or replaced with more efficient ones before the impact of other sanitary hazards at the well, and wellhead area, on the microbial quality of well water, can be determined and addressed. The published (WHO, 1997) sanitary survey forms for open dug wells and tube wells need to be modified in the context of the study areas described. Based on a comparison of three different statistical methods used to assess the relative significance of each sanitary hazard modification to the methodology for determining the sanitary hazard index (SHI) was prescribed.
文摘Concern for saline and microbial quality post-December 2004 tsunami, led to a field based surveillance study to systematically investigate the sanitary hazards which cause faecal contamination of groundwater. In seven islands, two duplicate sample sets, in two surveys, revealed that only 6.4% of the 173 well water samples (combining both surveys) satisfied the WHO Drinking Water Quality Guideline for 44°C thermo-tolerant (Faecal) Coliform (FC) indicator value (zero cfu/100 ml sample). Based on a combined risk analysis of Sanitary Hazard Score (SHS) and FC counts, more than 57.7% of the study wells were classified as at very high (FC: 100 to >1,000 cfu/100ml;and SHS: ≥ 9) microbial health risk. During this study, fundamental changes were made to the published generic sanitary inspection method (WHO, 1997) for identifying sanitary hazards, for its application in the extremely vulnerable hydro-geological setting of the Maldives. However, the most important hazard controlling the intensity of faecal contamination in the Maldives is the safe separation distance between a latrine seepage point and the well. It was demonstrated that, due to the prevailing hydro-geological conditions and the well and sanitation system densities, safe separation distance cannot be achieved. Consequently, septic tank effluent quality must be greatly improved.
