Assessment of Aquifer Mixing and Salinity Intrusion in the North-Western Sahara Aquifer System: a Hydrogeochemical Analysis- Algeria, Tunisia By David F. Meyer B.S., Kansas State University, 2011 Submitted to the graduate degree program in the Department of Geology and Graduate Faculty of the University of Kansas in partial fulfillment of the requirements for the Degree of Master of Science Advisory Committee ________________________________ Randy Stotler (Chair) ________________________________ G. L. Macpherson (Co-Chair) ________________________________ J.F. Devlin ________________________________ W.C. Johnson Date Defended: October 27, 2016 The Thesis committee for David Meyer certifies that this is the approved version of the following thesis: Assessment of Aquifer Mixing and Salinity Intrusion in the North-Western Sahara Aquifer System: a Hydrogeochemical Analysis- Algeria, Tunisia ________________________________ Randy Stotler (Chair) ________________________________ G. L. Macpherson (Co-Chair) Date Approved: December 7, 2016 ii Abstract The North-Western Sahara Aquifer System is a complex multilayer leaky aquifer system providing water to Algeria, Tunisia, and Libya. Changing the hydrologic equilibrium through pumping can cause previously isolated saline water to mix with the fresh water in the pumped aquifers, resulting in increased salinity over time and, creating the potential for water-related conflict. The objective of this study is to identify areas where salinity intrusion is occurring now and could worsen in the future. To accomplish this, fourteen existing datasets were analyzed, yielding new insights into regional and local occurrences of salinity intrusion. Major ion chemistry and ratios of Br/Cl indicate that the source of salinity in the saline aquifers of the system, which intrude into the freshwater, is the dissolution of evaporates in the aquifer matrix. A complex geochemical system where due to the common ion effect gypsum dissolution sustains calcite saturation producing a water rich in Ca and SO4. Stable isotopes of oxygen and total dissolved solids were the best geochemical indicators of areas of salinity intrusion. Contour mapping of the Total Dissolved Solids and δ18O has shown that considerable aquifer mixing and salinity intrusion affect the aquifer system. At this time, five areas in the North-Western Sahara Aquifer system are subject to salinity intrusion. iii Contents 1. Introduction ....................................................................................................................................... 1 2. Background ....................................................................................................................................... 3 2.1 Geology and Hydrogeology ...................................................................................................... 4 2.1.1 The Occidental Erg Desert Basin .................................................................................... 4 2.1.2 The Oriental Erg Desert Basin ......................................................................................... 5 2.1.3 The Tunisian Chotts Region and Dahar Uplands .......................................................... 6 3. Methods .............................................................................................................................................. 7 4. Results and Discussion.................................................................................................................. 8 4.1 Water-Rock Interaction .............................................................................................................. 9 4.1.1 Saturation indices and Major Ions ............................................................................................. 9 4.1.2 Br/Cl and SO4/Cl ..................................................................................................................... 10 4.2 Water Stable Isotopes ............................................................................................................. 12 4.3 Contour Maps ........................................................................................................................... 14 4.3.1 Tunisian Chotts Region ................................................................................................... 15 4.3.2 Regional-flow study area ................................................................................................. 17 5. Conclusions ..................................................................................................................................... 19 List of Figures Fig. 1 (a) Illustration of saltwater upconing in a pumped well (b) well development in an intermediate aquifer producing a new induced flow direction. .......................................................... 30 Fig. 2 The study area of the North-West Sahara Aquifer Syste. A) The regional flow area, including the regional flow paths of the CI and CT Aquifers. B) Inset of the Tunisian Chotts region, including the flow paths of the CT aquifer in 1980 and present day. .................................. 32 Fig. 3 Simplified East-West cross section of NWSAS, A-A’ (modified from Kamel, 2012). .......... 32 Fig. 4 a) Simplified N-S cross section (B-B’) of the CT aquifer in the Oriental Erg Desert Basin b)NW to SE cross section (C-C’) through the Tunisian Chotts Region to the Dahar Uplands (Modified from OSS, 2003). .................................................................................................................... 33 Fig. 5 Piper Diagram of CI, CT, and PQ groundwater showing 1) Ca-SO4-Cl water type and 2) Na-Cl water type. ...................................................................................................................................... 34 Fig. 6 Saturation indices of calcite, gypsum, and halite, and major ion relationships. .................. 35 4 Fig. 7 Graphs of (a) Br/Cl X 10 vs. Cl and (b) SO4/Cl vs. Cl. ........................................................... 36 iv Fig. 8 δ2H vs. δ18O (a) Local Tunisian Chotts Region, (b) The regional-flow area data. See text for explanations of numbered ellipses and lines. ................................................................................ 37 Fig. 9 δ18O and TDS contour maps of the Tunisian Chotts Region for the PQ, CT, and CI aquifers. ..................................................................................................................................................... 38 Fig. 10 δ18O and TDS contour maps of the Continental Intercalaire aquifer. ................................ 39 Fig. 11 δ18O and TDS contour maps of the Complex Terminal. ...................................................... 40 Fig. 12 Map showing the areas (1-5) affected specific processes of salinity intrusion, and with the greatest possibility of future degradation of water quality. .......................................................... 41 Supplementary Figures Appendix C 2+ - Fig. 13 Relationship between Ca and HCO3 .................................................................................. 120 2+ - Fig. 14 Relationship between Mg and HCO3 .................................................................................. 121 2+ Fig. 15 Relationship between saturation indices of anhydrite and Ca +SO4 ............................... 122 2+ Fig. 16 Relationship between Ca and SO4 ...................................................................................... 123 Fig. 17 Relationship between Na+ and Cl- .......................................................................................... 124 Fig. 18 Relationship between Br- and Cl- ............................................................................................ 125 Fig. 19 Relationship between Br-/Cl- X 104 and total dissolved solids ........................................... 126 Fig. 20 Relationship between Ca+/Na+ and Br-/Cl- X 104 .................................................................. 127 Fig. 21 Relationship between Na+/Cl- and Br-/Cl- X 104.................................................................... 128 - Fig. 22 Relationship between Br and SO4 ......................................................................................... 129 Fig. 23 δ2H vs δ18O plot (VSMOW) with trend lines for each aquifer ............................................. 130 Fig. 24 δ18O contour map of the Continental Intercalaire aquifer in Tunisia ................................. 131 Fig. 25 TDS contour map of the Continental Intercalaire aquifer in Tunisia ................................. 132 Fig. 26 δ18O contour map of the Complex Terminal Aquifer in Tunisia ......................................... 133 Fig. 27 TDS contour map of the Complex Terminal Aquifer in Tunisia ......................................... 134 List of Tables Table 1 Generalized stratigraphic and hydro-stratigraphic units of the NWSAS (sdy-sandy, cl- clay, cly-clayey, gyp-gypsum, anhy-anhydrite, hal-halite, ls-limestone, dol-dolomite, mrl-marl, and sst-sandstone) (Adapted from OSS, 2003 and Kamel et al., 2005) ......................................... 26 Table 2 Statistics of geochemical and isotopic data from each dataset and each aquifer ........... 27 Supplementary Tables Appendix B Table 3 Location, aquifer type, and field data of the NWSAS ........................................................... 50 Table 4 Major ion data and Charge Balance Error of the NWSAS ..................................................