62

SubsurfaceHydrologyinConfinedCoastalAquifers(PhDThesis)

Acknowledgment: This research is supported by the Helmholtz Centre for Environmental Research - UFZ. The author also wants to thank the Impuls- und Vernetzungsfond of Helmholtz Association and the Scientific and Technological Research Council of Turkey (TÜBITAK) for supporting this project with a scholarship.

Characterizing the Spatial Distribution of Flow Parameters from Pumping Tests in a Confined Coastal Aquifer

- Site Description -W. Armin Pechstein1, Nadim K. Copty2, Gerhard Strauch1, Ronald Krieg3, Sabine Attinger4, Sascha Oswald5

1UFZ, Dept. of Hydrogeology, Leipzig, Germany; 2Bogazici University, Inst. of Environmental Sciences, Istanbul, Turkey; 3UFZ, Dept. of Catchment Hydrology, Halle, Germany;4UFZ, Dept. Computational Hydro Systems, Leipzig, Germany; 5University of Potsdam, Inst. of Earth and Environmental Sciences, Potsdam, Germany

HydrogeologyTwo aquifers are present at the site (Figure 1). The upper, shallow aquifer is about 25 m thick and consists of fluvial/deltaic to shallow marine sediments. A clay layer of 10 to 15 m thick separates the shallow and deeper aquifers.Object of investigation is the deeper aquifer of upper Cretaceous age (Maastrichtian). Volcanic rocks of the Kisirkaya formation, part of to the Kavaklar group, display a great resemblance to a sequence formed in a lava delta environment, in perspective of volcanic facies concept. Petrographically, Kisirkaya formation consists of olivine-basalts and their epi- and pyro-clastic equivalents (Keskin, 2003). The deeper aquifer can be divided into two parts (Figure. 2). The upper 40 m of olivin-basalts with intercaleted cinder show a low hydraulic conductivity. They are followed by altered basalt of intermediate hydraulic conductivity and different hydrochemistry (see below). Due to Cenozoic tectonics - collision between the Arabian and Eurasian plates and initiation of motion along the North Anatolian Fault Zone - the Cretaceous rocks are assumed to be fractured.

7,7< 0,50,8TUTritium

-24-68,8-58,5‰ SMOWDeuterium

-2,89-10,9-9,14‰ SMOWδ18O

8,258,29,3-pH

8.9301.570148mg/lChloride

29,26,91,17mS/cmElectrical Conductivity

Black Seasaline GW fresh GWUnitParameterConclusions

The deep aquifer is confined with artesian conditions at some location e.g. at well K2. The aquifer consists of fractured olivine basalts and can be divided into two parts with different water qualities. Groundwater from the deeper part shows relatively light δ18O-values and a higher salinity compared to water from the upper part of the aquifer. Due to very low Tritium-values aquifer groundwater is quite old and little direct infiltration from the shallow aquifer can be assumed. Further more Tritium and δ18O-values preclude sea water intrusion as source of saline groundwater. No evidence of seawater intrusion was observed at the pumped wells.Future hydrogeological work will include multiple pumping tests to assess spatial variability of the flow parameters of the aquifer to estimate possibilities of sustainable pumping for water supply at the site. In this regard novel pumping test interpretation techniques will be used to infer information about the spatial variability of flow parameter.

HydrochemistryHydrochemical investigations show the existence of two different, formation bounded groundwaters - fresh and saline - in the second aquifer. Values for significant parameters are given in Table 1. Fresh groundwater can be described as Na – HCO3 type and is present in the upper 40 to 50 meters of the aquifer, saline groundwater is of Na – Cl (SO4, HCO3) type and present in the lower parts of the aquifer (below 80m b.m.s.l.). Sea water from the Black Sea is of Na – Cl type.Figure 3 and 4 give the development of electrical conductivity, chloride content and δ18O-values during a step pumping tests. Pumped water of well K1, which is screened in the upper part of the aquifer, shows continuous increase in electrical conductivity/chloride and a decrease in δ18O with increasing pumping rate and time. K2 is screened in both parts of the aquifer and pumped water shows much higher, not continuously increasing values of electrical conductivity and even lighter δ18O-values than well K1. Hence, a mixing of both types of groundwater occurs during pumping. The mixing can also be verified by Cation/Anion-ratios and the distribution of strontium in the pumped water.

Figure 1: a) Geological map of Saritepe Campus, Bogazici University and surrounding area (Keskin, 2003), b) Location of pumping wells, A-B transect in Figure 2, Geological Units: Quartenary: Q, Tertiary: Tpl - Pliocene, Tmi - Miocene, Upper Cretaecous: uCki - Kisirkayaformation, uCga - Garipce formation

QQ

TplTpl

Black Sea

uCki

uCki

uCga

Fig.1a)

Fig.1b)

IntroductionThe purpose of this study is to characterize a coastal aquifer located at Saritepe Campus of Bogazici University, Istanbul. Groundwater is the primary source of water for the campus. The monitoring network at the site consists of 6 wells, ranging from 80 to 140 m in depth. Because of salinization of water, extraction from these wells was stopped some years ago. For a better understanding of the variability of the subsurface and of the origin of saline water an integrated approach for site characterization is adopted which includes: Seismic and geoelectric surveys, Well logs, Monitoring of water levels and water quality, Isotope analysis, Step pumping tests.

A

B

Figure 2: Geological cross-section A-B of the site - Saritepe Campus, Bogazici University, including depth of wells and screens (location of the profile is shown in Figure 1)

A B

Figure 3: Electrical conductivity and δ18O before, during and after step-pumping tests (PT) in wells K1 and K2

Figure 4: Chloride and δ18O before, during and after step-pumping tests (PT) in wells K1 and K2

Table 1: Parameters of fresh groundwater, saline groundwater and sea water

fresh groundwater

saline groundwater

mixed waterpumping K1

Trias

Paleozoic

References: Keskin, M., Ustaömer, T. and Yeniyol, M. (2003). İstanbul kuzeyinde yüzeylenen Üst Kretase yaşlı volkano-sedimenter birimlerinstratigrafisi, petrolojisi ve tektonik ortamı, İstanul'un Jeolojisi Sempozyumu bildiri kitabı, S. 23-35

1st aquifer

2nd aquiferupper part

2nd Aquiferdeep part

pumping K2

v  Groundwaterresearchforcampususe

v  Saltwaterintrusionincoastalaquifers