Proceedings of the 13 th International Conference on Environmental Science and Technology Athens, Greece, 5-7 September 2013

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1 Proceedings of the 13 th International Conference on Environmental Science and Technology Athens, Greece, 5-7 September 2013 HYDROGEOLOGICAL INVESTIGATION FOR DELINEATING DRILLING SITES FOR ARTIFICIAL RECHARGE WELLS TO AQUIFER FOR GROUNDWATER SUSTAINAIBILITY ALONG WADI AL AIN IN THE UNITED ARAB EMIRATES A.A. MURAD1, S. MAHMOUD, H. ARMAN, H. BAKER, K. AL BLOUSHI & A. GABR United Arab Emirates University, Department of Geology P.O.Box: 17551, Al Ain, United Arab Emirates EXTENDED ABSTRACT The The study area lies at the downstream of Wadi Al Ain which crosses Al Ain city starting at the Oman borders, with an approximated total area of 300 km 2. The present study aimed at identifying some of the surface soil properties as well as the effective subsurface aquifer's parameters with the objective to recharge the aquifer through direct water seepage or by drilling recharge groundwater wells. The parameters, which have been considered in this study, include the measurement of infiltration rate, the hydraulic conductivity of the tested sites by using the double ring infiltrometer and sieve analysis, in addition to calculating the permeability and the transsmissivity from the pumping test data of one drilled well in the investigated area. The processing and the analysis of the data gave rise to infiltration rate that ranges from 1.8 to 23.5 cm/h, hydraulic conductivity that varies between 1.69 to 4 cm/s, but the acquired hydraulic parameters was 47.8 m 2 /day for transsmissivity and 2.39 m/day for the corresponding permeability. Comparing these results with standards for soil and groundwater aquifers revealed poor characters of both surface soil and subsurface water bearing formations. In sight of these results the recommendations were that there was no availability for harvesting any surface water bodies to recharge the present aquifers by a new water supply through any stream runoff along the wadi. Keywords: groundwater, infiltration rate, hydraulic conductivity, transmissivity, sieve analysis 1. INTRODUCTION The study area is situated in Al Ain City in the eastern part of Abu Dhabi Emirate, United Arab Emirates (UAE), near the border with Sultanate of Oman and at the western margin of the Northern Oman Mountains (Ellison et al., 2006) (Figure 1). Groundwater in Al Ain is mainly derived from the Oman Mountains to the East. The flow of water through soil layers (infiltration) comprises the important element of the hydrologic cycle. Infiltration tests are carried out in the study area to measure the infiltration rates of the soil layers.

2 Figure 1.Location Map of the study area. Inset map showing the location of Al Ain area relative to the Arabian The infiltration rate is the constant rate at which water can move into the soil and it starts high at the beginning of the infiltration process, and then decreases as infiltration continuous and the wetted zone in the soil extends downwards. The infiltration rate may eventually become constant. Incremental infiltration rates are calculated for each infiltration test from flow-rates needed to maintain a constant head in a double-ring infiltrometer (ASTM, 2003). This paper presents soil infiltration and laboratory test data measured at nine sites, three of them for measuring incremental infiltration rate and the others for hydraulic conductivity laboratory determination. All of these investigations were implemented in a pilot area along Wadi Al Ain, during the winter season mainly December 2011 and January The aim of this work was to investigate the ability of the surface sediments to permit or not the surface water seepage downward during any water storm. The later may participate in feeding the groundwater aquifers and in protecting the city from certain environmental hazards such as flash flooding, whenever an unexpected water storm may take place. The study of surface soil characters showed consistency with the subsurface soil conditions when implementing pumping test by using nearby groundwater well. Finally, the results of all combined investigations revealed the properties of the surface and the subsurface of the soil and the length of surface water flow to recharge the groundwater aquifer. 2. GEOLOGICAL AND HYDROGEOLOGICAL SETTINGS The surface geology of the study area reveals four deposition types: alluvial deposits, desert plain deposits, Sabkha deposits and Aeolian sands (Hunting, 1979). The alluvial deposits range from boulder gravel and conglomerate to fine sand and silt where the

3 main wadies become lost in the dunes further to the west. Towards the west, the area is partly covered by low sand dunes. Sabkha deposits occur where the main wadi channels enter the sand dunes, where the dunes are liable to flooding by the rising groundwater. Sabkhas are also developed on the lower parts of the gravel and sand plains west of the study area (NDC-USGS, 1993). Al Ain surficial aquifer is a relatively thin, unconfined of low to moderate permeability overlying a thick basal unit of very low permeability. The materials include Quaternary age sediments of mixed alluvial and aeolian origin. The thickness of the water table ranges from near zero where the Hafit anticline extends in subsurface into the city center to approximately 160 m in the southern and eastern areas of Al Ain. These areas coincide with the western terminus of two large wadies aligned with pre-quaternary valleys. The base of the water table aquifer roughly coincides with the top of the Miocene Age Post Fars formation. A productive aquifer is present within the limestone units of Asmari, Damam formations and is tapped by the majority of the irrigation wells within Al Ain. This aquifer likely ranges from confined to semi-unconfined in the study area. The Rus/Umm Er Radhuma is a marly limestone and conglomerate that provides some confinement from the Dammam and Simsima formations aquifers. Also, the aquifer within this limestone provides water to some of the deeper wells in Al Ain. These deeper aquifers are important to this study in that they add water to the surficial aquifer system through a few of the deeper irrigation wells (EAD, 2010). The aquifer in the area is recharged by the infiltration of the precipitation in the interdune areas and gravel plains and from the Jabal Hafit. Another source of recharge includes irrigation water, upward vertical recharge from deeper rocks and infiltration of water, lost from the leaky water transmission lines (NDC-USGS, 1993). All of these water sources may take its pathway to the aquifer through the gravely and sandy buried channels. The source of most present-day natural recharge to the groundwater is rainfall of the Oman Mountains in the east of Al Ain area. The majority of rainfall infiltration takes place in the surficial alluvial valleys with a lesser percentage infiltrating into the limestone, chert and fractured crystalline ophiolitic rock of the mountains. Surficial flows occur during periodic high rainfall events but are less significant given the time frames and water volumes addressed in this study. Approximately 64 km 2 of various land use types are irrigated with these sources of water (GTZ, 2009). 3. METHODOLOGY Infiltration data were collected from three sites in the study area. The site access was a primary consideration in the site selection. Each site location was determined using a global positioning satellite (GPS) unit (Figure 2). Cumulative infiltration and time were recorded, with each test generally lasting 300 minutes. The infiltration rate becomes constant when the saturated infiltration rate for the particular soil has been reached. Soils information for each site was obtained from field description as well as the sieve analysis of soil samples that were collected from each test location and the oppositional side along the study area. The results of sieve analysis for each sampling location are summarized in Table 1.

4 Figure 2. Location of double-ring infiltration tests, soil sampling and pumping test of groundwater well. Table 1. Compilation of relevant grain size parameter for 9 samples. ID E N Test D- 01 Test D- 02 Test D- 03 Test D Depth (from-to) cm d 10 (mm) d 30 (mm) The set-up of the double-ring infiltrometer with the Mariotte siphon is an efficient method of conducting a double-ring infiltrometer test. Three double ring infiltrometer tests in different locations of bare soil within the pilot area have been conducted using certain modifications that might be adopted with the procedure setup by the ASTM standard (ASTM, 2003). A pumping test was performed using one of the adjacent groundwater wells of Wadi Al Ain to determine hydrologic properties of the aquifer [Transmissivity (T) and Hydraulic Conductivity (K)] within the studied area. At the beginning of pumping test, the static water level relative to the ground surface was measured using the electric sounder. The field data were recorded as shown in Table 2. The liquid volume that used during each measured time interval of double ring infiltration test was converted into an incremental infiltration velocity for the inner ring measurements only (ASTM, 2003) as shown in Table 3. On the other hand, three basic soil parameters were determined from the grain size distribution curves, which are effective grain size d 50 (mm) d 60 (mm) Uniformity Coefficient Coefficient of gradation Hydraulic Conductivity (K) (Hazen (1911) cm/s o o o o o o

5 (D 10), uniformity coefficient (C u) and coefficient of gradation (C c). The hydraulic conductivity (K) was calculated using Hazen Method whereas d 10 is 0.1 to 3.0 mm. The calculations were done using the average of C values of medium sand, well sorted and coarse sand, poorly sorted sediments which are (Hazen, 1911). Table 2. Field pumping test field data. Static water level in the GWW=1.7m. Discharge rate= 10m 3 /h. Time since pumping start Depth to water level Drawdown (m) (min) (m) Table 3. Increment infiltration rate results. Incremental infiltration velocity Test-01 Test-02 Test-03 Mean Min Max To determine the hydraulic parameters of the groundwater aquifer (Transmissivity, T and Hydraulic Conductivity, K) in the study area, the pumping test data was treated using Jacob straight-line method (Jacob, 1946) as it shown in Figure 3.

6 Drawdown(m) Δs=0.92m s=0.92m T=48.8m2/day T=48.8m 2 /d K=2.39m/day Time(min) Figure 3. Time-drawdown plot for pumping test in the study area. 4. RESULTS AND DISCUSSIONS The results showed that the measured increment infiltration rates in the inner ring ranged from 9.1 to 23.5 cm/h, 7.7 to 18.1cm/h and 1.8 to cm/h over all tests consequently. These rates may be represented the moderately to highly compacted and cemented soil of fine, medium to little bit coarse sandy soils that also greatly affected by the occurrence of carbonate matrix. Also, the average of increment infiltration rate increases gradually from test-01 (8 cm/h), test-2 (11 cm/h) to test-03 (14 cm/h), which may refer to changes in the degree of lithological compaction and cementation of the tested soil in the downstream direction of the wadi. Plots of incremental infiltration rate versus elapsed time in hours (Figure 4) has obviously revealed that for all the studied soil, the slope of the obtained infiltration rate-time curves is high (high infiltration rate) at the beginning of the infiltration test. Then, it decreases gradually until it approximately approaches the steady state over the time. The grain-size distribution for nine soil samples was determined by sieve analysis for the collected samples after drying them at 110 C. Most of the soil samples revealed uniformly graded sands. The application of Hazen Method [9] was realistic for calculating the hydraulic conductivity due to consistency of the obtained results with those given by Hazen empirical method application whereas; d 10 is 0.1 to 3.0 mm (Vukovic and Soro, 1992; Kasenow, 2002). Accordingly, the calculated values ranged between 1.69 to 4 cm/s show poorly hydraulic conductivity of the studied soil section. Please do not use page numbers

7 Figure 4. Infiltration rate vs time graph for observed and simulated data of test-1, 2 & 3. The value of K at site 8 is the highest and the values of K varies from little at sites 1, 2, 3 and 4 to moderate values at sites 6, 7 and 5. The analysis of pumping test data using Jacob s straight-line method indicates that the value of (T) equals to 47.8 m 2 /day and the corresponding hydraulic conductivity was 2.39 m/day. This means that the water bearing formations in the study area have poor permeability and transmissivity.

8 5. CONCLUSIONS Three double ring infiltration tests and sieving analysis for nine soil samples as well as pumping test have been carried out in the study area. The incremental infiltration rate, the main lithological composition and the hydraulic properties of the surface and subsurface sedimentary sequence were determined. The results of the infiltration rate ranges from 1.8 to 23.5 cm/h suggested low to moderate infiltration process through the top soil section, which will not assist the surface water to seep downward. On the other hand, the sieving analysis of the collected soil samples indicated that soils are rarely exist separately as gravel, sand, silt, clay or organic matter, but are usually found as mixtures with varying proportions of these components. The physical properties of the top soil suggests uniformly graded type with hydraulic conductivity of 1.69 to 4 cm/s. The subsurface soil properties, which have been acquired from the pumping test results, gave rise to transmissivity of 47.8 m 2 /day and hydraulic conductivity of 2.39 m/day. The deduced properties of both surface and subsurface soil conditions reflect poor to moderate orders. In summary, the downward movement of the surface water during any seasonal or sudden water storms to the aquifer will be very low. Consequently, the expectation of flooding may happen, if the intensity of precipitation is high and the duration time is long which may cause environmental hazards on the adjacent residential areas. Therefore, it is not recommended to drill any artificial recharge wells within the study area, but it is suggested to apply the result of this study in a wide scale along wadi Al Ain and the other wadies crossing Al Ain City. This may lead to new surface water pathways to recharge the aquifer, which might mitigate the environmental hazards. REFERENCES 1. ASTM D3385, Date Test method for field measurement of infiltration rate using a double-ring infiltrometer with a sealed inner ring. 2. Ellison, R.A., Arkley, S.L.B., Warrak, M. and Farrant, A.R Geology of the Al Ain 1:50,000 map sheet, United Arab Emirates. (Keyworth, Nottingham: British Geological Survey). 3. Environment Agency- Abu Dhabi, 2010 Consultancy Services to Assess, Design and Supervise the Construction of Mitigation Measures for Al Ain Groundwater Rise. Report by Schlumerger and submitted to Environmental Agency Abu Dhabi (EAD) Abu Dhabi, United Arab Emirates, EAD/WR/0005/ GTZ, Al Ain Groundwater Study Report. 5. Hazen, A Discussion of dams on sand foundations by A. C. Koenig. Trans. Am. Soc. Civ. Eng., 73, Hunting Geology and Geophysics Report on Min-eral Survey of the U.A.E., Al- Ain Area, Vol. 9, p Jacob, C.D Drawdown test to determine effective radius of artesian well. Proc. Am. Soc. Civil Engineers, New York. 72 (5). 8. Kasenow, M., Determination of hydraulic conductivity from grain size analysis. Water Resources Publications, Littleton, Colorado. 9. National Drilling Company (NDC)- US Geological Survey (USGS), Groundwater Resources of Al Ain area, Abu Dhabi Emirate. Edited by D. V. Maddy, Ground- Water Research Project. 10. Vukovic, M., Soro, A., Determination of hydraulic conductivity of porous media from grain-size composition. Water Resources Publications, Littleton, Colorado. Weeks, E.P., 1969.