Abstract
Groundwater is regarded as a vital resource in the Erbil Basin. It represents one of the main sources of water supply for domestic, agricultural, and industrial purposes. The depletion of water supplies, increased by global climate change, and the over-exploitation of the aquifers, heighten the necessity of sustainable groundwater management. This study investigates the hydrogeological and hydrochemical characteristics and vulnerability assessment of the aquifers in the Qushtapa and Shamamik areas, within Erbil Basin. It covers an area of about 1,302 km2. The Quaternary deposit, Bai Hassan, and Mukdadiya Formations are the major geological outcrops in the study area.
The infiltration capacity rate was measured using the double-ring infiltrometer method. The average infiltration rate is 3.4 cm/h, ranging between 0.9 and 6 cm/h. The grain size analysis of the soil samples indicates that the average hydraulic conductivity of the top soil is 6.99*10-5 m/sec, ranging from 5.343*10-5 to 1.0422*10-4 m/sec. The average increase in the depth to the groundwater level, calculated for the period 2005–2024 from sixteen monitoring wells, is about 74.80 m, ranging from 30.2 to 102.5 m.
To estimate the hydraulic parameters of the aquifers, the Cooper-Jacob (1946) method and Theis (1935) method were used to analyze the pumping test and recovery data from 10 wells. The average transmissivity is about 20.09 m2/day, ranging from 8.613 to 47.725 m2/day. The average hydraulic conductivity is 0.069 m/day, ranging from 0.0245 to 0.191 m/day. The average storage coefficient was 0.204, ranging from 0.0707 to 0.323. The study area is classified as an area with a Low-Intermediate transmissivity class.
To investigate the hydrochemical characteristics, 72 groundwater samples were analyzed for two seasons, dry and wet. It involved physical, chemical (major ions and heavy metals), and biological analysis. During both analysis seasons, the groundwater samples are rated as good to excellent for drinking, with only two samples classified as poor quality during the wet season. The trace element analysis showed that most of the water samples are below the permissible limit as detected by WHO (2017), with a few exceptions in cadmium and lead. According to the irrigation water quality index, the majority of the water samples are classified as a moderate restriction class for irrigation. Microbiological indicators revealed bacterial contamination during both seasons, mostly resulting from sewage infiltration from municipal, household, agricultural, or industrial resources.
Evaluation of groundwater vulnerability of the aquifer in the study area was achieved by applying the DRASTIC and Pesticide DRASTIC models. Calculating the DRASTIC index divided the area into four zones varying from very low to high vulnerable classes. In the DRASTIC model, vadose zone tends to be the most effective parameter, while in Pesticide DRASTIC, soil media tend to be the most effective parameter. The vulnerability validation with nitrate concentration shows that the coefficient of determination R2 for a DRASTIC model is 0.58, and for Pesticide DRASTIC is 0.62.
In conclusion, this study on the Qushtapa and Shammaik areas succeeded in achieving its primary objectives. The results of this study provide valuable data and insights into the need for improved water management and enable decision-makers to develop optimal solutions for the sustainability of this resource.
