The aim of this study is to evaluate the quality of groundwater in terms of nitrogen nitrate and Salinity in a coastal area in South of Oman (Salalah Coastal Strip). This area was subjected to extensive pumping activities for different purposes such as supplying drinking water, agricultural activities, and industrial and commercial applications. Furthermore, the area was subjected to artificial recharge using treated wastewater in the last 10 years. Some water management strategies have been implemented to control the groundwater quantity and quality by the relevant authorities. Hence, this study tries to evaluate the groundwater quality by analyzing the collected data of groundwater levels, nitrogen nitrate, and salinity for the past 30 years. The obtained results showed that the groundwater in Salalah coastal area was suffering from declining water levels and increasing levels of nitrate and salinity due to the extensive pumping activities and contamination from sewer water leakages to the groundwater until 2002. However, the quality and level of groundwater started to improve since 2002 due to the artificial recharge of the groundwater with treated effluents. The results indicated gradual increase in the groundwater level in the aquifer system, especially at the down gradient side of approximately 1.0 to 2.0 km distant from the Arabian Sea shore along injection strip (where the saline water intrusion possibilities are more). Also, EC (Salinity) of the groundwater decreased in the injection area. The total dissolved solids (TDS) in and around the injection strip was found less than 2000 mg/L, whereas the outside of the injection strip the groundwater TDS value was found higher than 2000 mg/L. The results of Nitrogen Nitrate concentration values were found to be within Omani drinking water quality standard (except for one well). However, the results show higher values in the un-sewered zone (served by septic tanks and soak away pits) compared with the values noted in the areas downstream of the recharge line. The Nitrogen Nitrate concentrations on downstream of the treated water injection line ranged between 5 to 15 mg/L. The range was found from 10 to 20 mg/L in the un-sewered area upstream of the injection line and from 20 to 35 mg/L in the un-sewer area east of the injection line. Due to the importance of groundwater in Salalah plain from social, environmental and economic point of view, sustainable management and monitoring plans have to be developed to protect such valuable natural resource and to optimize its applications. It is believed that the artificial recharging project with treated effluents should continue but with better optimization and coordination with other water related authorities.
