Assessment of the sustainability and quality of groundwater in Malamawi Island, Isabela City, Basilan, Philippines

Assessment of the sustainability and quality of groundwater for agricultural and domestic purposes was conducted in Malamawi Island, Isabela City, Basilan [Philippines]. Sustainability was evaluated based on groundwater supply and demand analysis while the quality was evaluated based on suitability for irrigation and drinking. The shallow aquifer is confined with transmissivity of 1.70 m sup 2/d, storage coefficient of 0.001012, and specific discharge of 6.53 m sup 2/d.The estimated groundwater storage of 102,257.44m sup 3/d proved to be more than adequate to meet the estimated current water demand of 1,524.5m sup 3/d. The safe yield of 15,783.82 m sup 3/d based on the recharge of 1,013.92 mm/yr was also substantially more than the estimated demand. The groundwater quality for irrigation was assessed based on salinity, alkalinity, sodium, magnesium, and bicarbonate hazards. The study revealed that based on electrical conductivity and magnesium hazard, the use of groundwater from two separate sampling wells require 'slight to moderate restriction'. In one sampling well, the chloride concentration indicate that groundwater was slightly poor in quality but is still generally suitable for irrigation. But the calcium in one sampling well was considered unsuitable for irrigation.TDS concentration at one sampling well exceeded the PNSDW (2007) standard which means it is unsuitable for drinking. Alkalinity levels of the groundwater based on SAR, SSP, and RSC were suitable for irrigation but two sampling wells were unsuitable for irrigation based on magnesium hazard. Groundwater on the southern part of the study area was slightly acidic. Results of total solids analysis revealed that one sampling well in northern Lukbuton did not meet the Philippine standards for drinking water. Groundwater in barangays [villages] Santa Barbara and Diki is slightly acidic compared with standards. Bacteriological analysis revealed that 2 out of 6 sampling wells were contaminated with E. coli.