2006; Montgomery and Elimelech 2007; Pedley and Howard 1997) are a source of groundwater contamination. Thus, the disposal of human waste using these facilities is a key issue for groundwater quality and public health protection. The Public Works Department of the Tuvalu government was surveyed about the design and integrity of
the septic tanks on the islet. Surprisingly, it was determined that the bottoms of the septic tanks were not sealed—so called ‘bottomless’. Construction specifications proposed by Australia require these tanks to be sealed; however, these tanks were constructed with a disregard for these specifications. Thus, considering also the fact that the Holocene sand aquifer with high permeability extends from the surface to the depth of ~ 20 m BGB324 concentration on Fongafale Islet (Ohde et al. 2002), the potential sources of pollution of the lagoon side coast are bottomless
septic tanks and pit toilets. Wastewater runoff mechanism Nakada et al. (2012) reported ground water dynamics in the lagoonal coast using electrical resistivity. Saline water extended landward from the coastal area during flood tides, and brackish water receded coastward from the inland PF-562271 chemical structure area during ebb tides. This indicates that if there are leaks from bottomless septic tanks and pit toilets, they subsequently flow into the coastal lagoon. The Eh value should then respond and fecal indicator bacteria, E. coli, would be detected, because the wastewater includes human Dichloromethane dehalogenase waste. As shown in Fig. 7, periodic variations were observed in Eh. The timing of these variations was similar to that of the sea level data obtained from the National Tidal Centre (2010). A periodic variation is observed during the whole tidal cycle. The Eh became more negative during ebb tides and then gradually became more positive with time. Salinity and EC also showed similar trends (data not shown). The observational period was during the transition from neap tide to spring tide; thus, the Eh increase is presumably due to the ongoing of water exchange between the lagoon and the ocean. Fig. 7 a Tide level and b redox potential (Eh) in the reef-flat seawater at site
2-2 At low tide, the number of E. coli was 1.1 × 10 MPN/100 mL at site 1; however, E. coli numbers ranged from 3.2 × 103 to 2.7 × 104 MPN/100 mL at sites 2-1, 2-2, 2-3 and 2-4, and reached 6.2 × 10 MPN/100 mL at site 3 (Fig. 8). At high tide, E. coli was not detected at site 1 and site 3. Sites 2-1, 2-2, 2-3 and 2-4 ranged from 5.5 × 102 to 1.2 × 103 MPN/100 mL. High numbers of E. coli were found at sites 2-1, 2-2, 2-3 and 2-4 compared to site 1 and site 3, and higher values were found at low tide than at high tide. Japanese water quality criteria stipulate that the number of colon bacilli should not exceed 1.0 × 103 MPN/100 mL for bathing beaches. Since E. coli forms part of colon bacillus species, such high numbers of E. coli in the coastal waters pose concerns as a human health risk.