ABSTRACT: Hatay-Erzin plain is located in northeast of iskenderun gulf in the Mediterranean region. The area of plain isabout 300 km2 while its drainage area is 350 km2. Along the Yumurtalık thrust, units of Miocene M is is-And innbasin in north of study area, has a tectonic contact, with the units of Miocene*Iskendemn basin at south..In addition to general hydrogeologic characteristics of the study area, discharge-recharge relation of theBurnaz spring in the discharge area was also studied. Spring has a yield of 1.74 nrVsec. On the basis of regularmonthly discharge data of the spring in the years between 1976 and 1994, minimum, and. maximum, flows areÖ.947 nrVsec and. 4..997 m3/sec, respectively., October and April average discharge values for a 1.9-year period are 1,427 m3/sec and 2..206 mVsec, respectively,. Plain is governed by Mediterranean climate regime. The annualaverage precipitation value recorded at Yeşilkent Observatory for the years 1967-1995 is 930,.5 mm.There are a number of 200 wells (by 1995) in the area drilled, by DSI in order to supply irrigation water forErzin .and. Yeşilkent residential sites. .Discharge measurements show that withdraw from these: wells withincreasing number does not affect the Burnaz spring. Well depths are about 150-200 m in upper parts (between100-200 m) while 50s-150 m in discharge area (between 50-50 m) at west»Conglomerate levels of .upper Pliocene-Pleistocene Erzin formation of the iskenderun basin,, PlioQuaternary-Quaternary porous basalt and sandy and pebbly levels of Quaternary alluvium are. the main aquiferunits in. the study area. On the basis «of pumpage tests, transmissibility values are 105-6110 m2/day inconglomerate aquifer, 2708-14628 m.2/day in basalt aquifer and. 987-5576 m2/day in the whole aquifer. Flowdirection of groundwater is from northeast to southwest and east to west (to the Mediterranean Sea). Hydraulicslope, which is high in the east, decreases to the west due to high permeability of basalt. In Erzin-Yeşilkentplain,, groundwater recharge is 103.3 x 10e m3/y, groundwater discharge is 128.8 x 106 m.3/y and reserveexchange is A.V=-25.5 x 106 nrVy. On the basis of groundwater level changes in the years between 1977 and1996,», regional draw in the recharge area is 4-20 m which fluctuates 1-3 m in the discharge area by the rechargeof Burnaz spring. Recession coefficient (aAve ) for the conglomerate aquifer is 1.52 x 1Ö`3 day"`1 which representsa. tertiary type aquifer.,Burnaz spring issues from two points, through the Plio-Quaternary porous basalt, along the. impermeable partsof alluvium,, thus it can be thought as a contact spring. Discharge elevation of the spring Is about 5-6 m.. On thebasis of spring hydrographs obtained from monthly flow rates measured, in the years between 1976-1994,,, annualaverage discharge, annual recharge of the spring and recession coefficient were calculated as 53.3 x 10`` rn, ,/y,54.4 x 106 m3/y and 4.21 x 10"3 day"1, respectively. In this respect, spring issues through the basalt aquifer whichis greatly fed by annual precipitation,., The correlation coefficient between annual average flow and annual,rainfall Is r=Q.77..In order to examine hydrogeochemical relation between Burnaz spring and other water points in. the plain,samples collected in the area were analyzed for major1 ion and tritium contents. Chemical and tritium resultsindicate that Burnaz spring issues through the basalts in its own recharge area and. that it is a kind of contactspring., On the other hand, tritium contents of other water1 points located in the coastal areas changes, byproportionally of the replenishment from the evaporitic formations.