Delta Wadi El-Arish, Sinai Peninsula, Egypt, forms one of the most important parts of Egypt for industrial and agricultural expansion projects. This study focuses on the hydrogeology and the hydrochemistry of the Quaternary aquifer in the delta Wadi El-Arish area. Accurate information about the groundwater characteristics of the Quaternary aquifer will allow implementation of a sound water management policy for the Wadi El-Arish area. The objectives of this study include: 1) determining the relationships between groundwater extraction and water levels and water quality using water-level measurements, total extraction of the wells, and chemical analyses of water samples; 2) determining the direction of groundwater flow using water-level measurements; 3) calculating the hydraulic parameters of the Quaternary aquifer using pumping test data; and 4) determining the hydrochemical characteristics of groundwater in the Quaternary aquifer. The results of this study indicate that: 1. Potentiometric surface elevations have decreased by an average of about 0.5 m. 2. Potentiometric surface elevations have decreased in response to an increase in extraction rates. 3. The transmissivity of the lower Pleistocene calcareous sandstone (kurkar) unit is higher than the transmissivity of the upper Pleistocene sand and gravel alluvial deposits. 4. Groundwater in the upper Pleistocene sand and gravel aquifer is augmented with groundwater leaking from the overlying Holocene sand deposits through the intervening sandy clay aquitard. 5. Total dissolved solids (TDS) concentrations have been increased by an average of about 1,500 ppm. 6. An increase in sea water intrusion in the northern part of the study area has occurred. 7. Groundwater in the calcareous sandstone kurkar is of lower quality than groundwater in the alluvium sand and gravel. Management of the groundwater resources should include the following recommendations: 1. No new pumping wells should be drilled in the area. 2. Accurate estimates for the total recharge should be determined using a more detailed water budget for the delta Wadi El-Arish area. 4. The operation of wells should be managed by an automatic control system.