Abstract
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.
Highlights
The risk of groundwater contamination is significant where water borne on-site sanitation system is used compared with dry on-site sanitation system, unless the dry on-site sanitation system is constructed directly into the aquifer
The published [7] sanitary survey forms for open dug wells and tube wells need to be modified according to the context of the Negombo study areas
Barthiban et al [10] showed that the published [7] surveillance form needed to be modified to be applied in the context of the Maldives islands which was characterized by: - Very vulnerable hydrogeological conditions aquifer with shallow groundwater table, - Limited land space and failure of maintaining safe separation distance between the on-site sanitation system and open dug wells, - Extensive usage of on-site sanitation system
Summary
The risk of groundwater contamination is significant where water borne on-site sanitation system is used compared with dry on-site sanitation system, unless the dry on-site sanitation system is constructed directly into the aquifer. The issue of microbial contamination of groundwater from on-site sanitation soakage pits becomes a more critical issue where shallow groundwater table presents. Groundwater exploitation using open dug wells together with on-site sanitation practices may cause them to become high risk drinking water sources in the study areas selected in Sri Lanka. The selected study areas have a need for well surveillance and sanitation improvement programme for the protection of the groundwater resource. According to the information available to the lead author, there has been no systematic well surveillance programme in the study areas with the aim of groundwater protection. A pilot scale well surveillance study was carried out in the west coastal region of Sri Lanka to identify and assess the sanitary hazards associated with groundwater wells. This paper presents the findings from the field work carried out in Sri Lanka
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