Abstract
Un-protected open dug wells of shallow groundwater environments are subjected to high risk of chemical and microbial pollution in many parts of the world. The present study was initiated in Pungudutivu, one of the surrounding islands of the Jaffna Peninsula, Sri Lanka, because the island totally relies on its limited groundwater resources extracted from open dug wells to meet all its needs. The study assessed the risk of pollution within the limited fresh groundwater found in unconfined aquifer systems of Pungudutivu, where high risk of pollution was expected mainly from organic sources, derived from human and animal wastes and easy infiltration and runoff returns. The fresh groundwater pockets of Pungudutivu were however found to be with less serious contamination risks other than high Fe2+ and high faecal coliform counts. Low nitrate and phosphate concentrations with high COD and low BOD demonstrated less pollution from biodegradable organic sources in the midst of high oxidising potentials in the shallow dug wells as implied by the stability field of Fe(OH)3 on the Eh-pH diagram; the argument of high Fe2+ in groundwater however, wasn't supported by the said oxidation potential. High faecal coliform counts with high DO in groundwater probably indicated conditions implied by on site waste disposal in groundwater of Pungudutivu.
Highlights
Un-protected open dug wells of shallow groundwater environments are subjected to high risk of chemical and microbial pollution in many parts of the world
A majority of groundwater source localities of Pungudutivu Island exemplify high salinity (95%) indicating that it cannot be used for drinking, domestic and livelihood purposes as seen in many parts of the Jaffna Peninsula (Saravanan et al, 2013; Pathmaja et al, 2016)
The remaining a few freshwater pockets do not indicate any serious contamination risks other than high levels of Fe2+ ranging from 0.44 to 11.79 mg/L where all groundwater localities exceed the permissible limit of 0.3 mg/L Fe of WHO and Sri Lanka standards (Table 1) (WHO 2008, 2017; SLS 2013)
Summary
Un-protected open dug wells of shallow groundwater environments are subjected to high risk of chemical and microbial pollution in many parts of the world. Adoption of effective management strategies incorporating public awareness and community participation were emphasised as prime requirements for managing shallow groundwaters and bringing them into optimum utilisation for feasible and economic management of the resource in Jaffna (Nesiah et al, 2005) In such context, monitoring and evaluation of the quality of shallow groundwaters and related risks of contamination was a prime requirement in Jaffna at the post war rehabilitation scenario because decisions are being taken on the development of infrastructures towards drinking water supplies and waste disposal in the Jaffna town and the surrounding islands involving high technologies and vast capital investments. The unconsolidated formation of lagoon and estuarine deposits of the study area were considered as a contributing factor to pollution by organic matter
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