Civil and Architectural Engineering Department-College of Engineering-Sultan Qaboos University
Impact of Treated Wastewater Recharge in Salalah Costal Aquifer
on Groundwater Quality
Ahmed Qatan
Abstract
The city of Salalah is located on the southern coast of the Sultanate of Oman. The city is in the
center of a coastal plain, which extends from the foot of Jabal Al Qara to the Arab Sea and from
the coastal town of Taqah in the east to Raysut in the west. Groundwater is the only source of
water supply for the domestic and agricultural communities in the area. The abstraction rate from
the aquifer has gone beyond the annual recharge rate thus reducing freshwater storage and
allowing the saline water intrusion in the coastal area. Several studies targeted this problem in an
attempt to find feasible solutions. One of those proposed solutions was to inject treated
wastewater collected from the city of Salalah into the coastal aquifer to create an elevated head
to avoid further deterioration of water quality by salinity. The implementation of this solution is
currently in progress. A series of recharge wells were constructed in the agriculture strip near the
coast and Garziz farm to the upstream near the Salalah wellfield. These wells will receive treated
wastewater from the Salalah treatment plant through a pipeline. The present project aims at the
study of the impact of treated wastewater injection into the coastal aquifer of Salalah on the
upstream groundwater quality, and the effectiveness of the treated wastewater recharge in
controlling the advancement of saline water into the fresh water in the Salalah coastal.aquifer, In
the present study MODFLOW, a three-dimensional groundwater model-Tor flow through porous
medium, is used. The model is a well-known finite difference package developed by McDonald
and Harbaugh (1982). In -addition to that a Mass Transport Three-dimensional for Multi-Species
(MT3DMS), is a three-dimensional transport model for the simulation of advection and
dispersion of dissolved constituents in groundwater systems. Those models are utilized as part of
the Department of Defense Groundwater Modeling System (GMS), which provides a graphical
user interface' for performing groundwater simulations. Initially MODFLOW was calibrated in
steady state against observed water levels in 1990 then calibrated in transient state against the
observed water levels from 1990 to 2000. The results of the study showed that the proposed
project of injecting treated wastewater into the coastal aquifer will be effective in controlling
seawater intrusion. But the upstream groundwater quality will be adversely affected by the
Civil and Architectural Engineering Department-College of Engineering-Sultan Qaboos University
treated wastewater injection near the Garziz farm after 2020. The study recommends not to
operate the eight recharge wells near the Garziz farm for the injection of treated waste water into
the aquifer.