English abstract
The Sultanate of Oman has seen a rapid development over the past three decades. As a result, water demand has risen in line with the development and improved standard of living. Many of the freshwater production wellfields are located in rapidly developing areas, where land values are high and frequent requests are received from landowners for various development activities. To protect the limited groundwater resources, Wellfield Protection Zones (WPZs) legislations were implemented in the Sultanate. The objective was to protect groundwater destined for the wellfields from contamination, over abstraction, saline water intrusion and adverse land development.
This study aims to determine whether groundwater in the Salalah wellfield protection zone is contaminated from existing development projects and whether the groundwater is of acceptable quality for drinking. Investigation of groundwater levels and salinity levels were part of the study. To achieve the aims of the study, a combination of collation, analysis of piezometric data and water quality data for Salalah wellfield protection zones were undertaken. A survey of existing development in red zone (the most critical zone) was done.
The study concludes that the net discharge from the production wells do not significantly caused changes in water levels in the aquifer. Water levels in the monitoring wells in the red and orange zones rose by 1.71m due to their location directly under the area of front of Jabel Al-Qara. Water levels declined by 0.13 m in the area where the large farms are located. Water quality parameters remained stable and comply with the Omani standards for drinking water. For example, Calcium level was 132 mg/1. Magnesium, Chloride, Sulfate, Nitrate and Fluoride some times approached the highest desirable levels but did not exceed them. They were at 27, 248, 42, 28 and 0.30 mg/l respectively. Trace metals, hydrocarbon concentration were within Omani drinking standards and no Coliform or E.Coli bacteria were detected in all of the groundwater samples. On the other hand, salinity in some monitoring wells increased marginally from 980 uS/cm in 1996 to 1100 uS/cm in 2004 in fresh groundwater zone. Whereas it increased from 4400 uS/cm in 1996 to 5000 uS/cm in 2004 in some wells in brackish groundwater zone. Increase in salinity was observed from 5000 uS/cm in 1996 to reach to 11000 uS/cm in 2004 in some wells in the closest part to the coastline. The increases in salinity may due to agricultural retum flow, mixing of saline water from the deeper part of the aquifer or direct saline water intrusion from the area especially in the wells closest to the coastline.
The study recommends adoption of best management practices for Salalah WPZ and other WPZs in the Sultanate.
