CE 199 – Undergraduate Research Project Final Presentation13 October 2010 Environment and Energy Engineering Group Groundwater Flow Modeling Using PMWIN near a Closed Dumpsite within the Vicinity of Laguna Lake MA. JENEREE C. KIMPO DANILO V. RODOLFA III Undergraduate Student, B.S. Civil Engineering Program Institute of Civil Engineering, University of the Philippines Diliman E-mail:
[email protected],
[email protected] Advisers: Dr. Augustus C. Resurreccion Associate Professor, Institute of Civil Engineering, University of the Philippines Diliman Dr. Maria Antonia N. Tanchuling Associate Professor, Institute of Civil Engineering, University of the Philippines Diliman Dr. Ariel C. Blanco Assistant Professor, Department of Geodetic Engineering, University of the Philippines Diliman Abstract: The groundwater flow is defined as the percolation of the water from precipitation that flows to the streams through the groundwater system. Water pumped from the ground-water system causes the water table to lower and alters the direction of ground-water movement, thus creating an imaginary surface called, the capture zone. The hypothetical groundwater flow movement of Tanay Dumpsite is investigated through a steady-state and transient flow model using the MODFLOW module of the PMWIN software. Different data such as the precipitation rates, hydrogeology, well and river, and topography are used in this simulation. The hypothetical Tanay PMWIN model is a one-layer covering an area of 40 square kilometers. The hydraulic head results for both types of simulation are attained. The capture zone is also described as well as the velocity vectors which correspond to the groundwater flow movement. From the analysis of the results, it is concluded that the well is properly located such that it can be used to advantage in treating the contaminated area. 1. INTRODUCTION 1.1 Background of the Study Groundwater flow is the movement of water that travels and seeps through underground porous media such as soil and rock. Bedient, et. al (1994) states that the groundwater flow follows the Darcy's Law, which states that the flow rate through porous media is proportional to the head loss and inversely proportional to the length of the flow path. Normally, the water that is flowing from a dumpsite contains contaminants like leachate that may affect the behavior and characteristics of the flow. Salem, et. al (2006) made an evaluation of the landfill leachate pollution and concluded that leachate formation occurs when soluble components are dissolved (leached) out of a solid material by percolating water. Leachate may also carry insoluble liquids (such as oils) and small particles in the form of suspended solids. Depending on the waste types, further contaminants may be introduced as a result of biodegradation of wastes. Simulating the groundwater-leachate flow is very useful in understanding the groundwater flow 1 principles contained in a given area. One of the most widely used programs for groundwater flow modeling is the MODFLOW. MODFLOW is a modular three-dimensional finitedifference groundwater model published by the U.S. Geological Survey. It is a computer code that solves the groundwater flow equation: Groundwater Flow Equation The governing partial differential equation used in the program is dependent on the hydraulic conductivity of the soil, initial head, volumetric flux, specific storage, and time period. In this study, the Processing Modflow for Windows (PMWIN) is used. PMWIN is one of the most complete groundwater simulation systems for modeling groundwater flow and transport processes. This software provides a three-dimensional visualization and animation of data from groundwater flow and transport models. Another software that used used in the study is the ArcGIS. ArcGIS is an integrated family of Geographic Information System (GIS) software products for building a complete GIS. In the study, a topographic map of the area is analyzed using ArcGIS and the necessary data are inputted to the PMWIN. Tanay Dumpsite The dumpsite is located in Sitio Tulay, Barangay Tandang Kutyo, Tanay, Rizal. Its geographical coordinates are North 14°32’28” latitude and East 121°17’58” longitude. It is 4.5 aerial kilometers north of the town proper of Tanay and has a land area of about 60,965 m2 or 6.0695 ha. There are several houses present within the dumpsite and in its immediate vicinity. The area has a type 1 climate with Dry Season from November to April and Wet Season from May to October. It started operating in 1989 and closed last September 30, 2008 due to the presence of cracks in the soil profile, as shown in Figure 1. On September 26, 2009, the Typhoon Ondoy caused the soil layers bearing the cracks to collapse. During the typhoon, some of the wastes were washed away by the flood going to Laguna Lake. resulting models from simulations would be used in the description of the flow. Also, the capture zone for a well present in the area will be determined. From this, it will be concluded if the location of the well is appropriate for washing the contaminants formed from the Tanay dumpsite. 1.4 Significance of the Study This study will aid in the establishment of information on the conditions of water bodies near dumpsites. Also, the modeling of the groundwater flow will help assess the impact of dumpsites on groundwater quality. Moreover, the dumpsites can be monitored and effective sustainable management of dumpsites as well as the groundwater resources can be addressed and put to practice. 1.5 Scope and Limitation Due to limitations on the gathered topographic map, the study cannot focus on the area of the Tanay dumpsite and Laguna Lake alone. Hence, the area of the groundwater flow model is along the Laguna Lake as well as the municipality of Tanay, Rizal. Also, due to difficulties in attaining the needed data in the simulation, the well and river parameters are assumed. 2. METHODOLOGY 2.1 Hydrogeology of the Site 2.1.1 Topography The topographic map of the study area as shown on Figure 2 is inputted in the ArcGIS and PMWIN. Figure 1. Cracks in the soil profile of the Tanay dumpsite 1.2 Statement of the Problem As in most developing countries in Asia, solid waste reaching open dumpsites in the Philippines is high in moisture and organic content, thus high in leachate and low in calorific value. Leachate from dumpsites represents a potential risk to both surrounding ecosystems and human population. Over time, leachate volumes generated would continue to increase steadily since leachate volumes are directly proportional to rainfall catchment's area and deposited waste mass. Currently, there are only few studies about the impact of Philippine dumpsites on the groundwater quality of its adjacent water bodies. 1.3 Objectives of the Study This study aims to apply existing software, PMWIN, to describe the groundwater flow near a closed dumpsite within the vicinity of Laguna Lake. The Figure 2. Topographic map of the study area The boundary conditions used are shown on Table 1. Table 1. Boundary Conditions of the Study Area Location 1 2 3 4 Boundary Condition Fixed Head No Flow Fixed Head No Flow 2 2.1.2 Geologic Information The site is underlain by vitric tuff belonging to the Guadaloupe Formation. The vitric tuffs that are directly in contact with the top soil are buff to dark gray in color due to considerable weathering. The vitric tuff is massive and highly fractured, and showed spheroidal weathering and conchoidal fracturing. Exposures of the bedrock were observed in the former quarry area about 200 to 300 meters east of the site. The soil type of the study area is sandy clay load with a horizontal hydraulic conductivity of 3.64x10-6 m/s and a vertical hydraulic conductivity of 3.64x10-7 m/s. 2.1.3 Precipitation The rainfall data are taken from an online free source of National Aeronautics and Space Administration (NASA). Table 2. Rainfall Data of the Study Area 3. RESULTS AND DISCUSSION 3.1 Steady State Simulation Figure 3. Steady State Simulation with and without fill. Climate Dry Season Wet Season Rainfall 0.35 mm/hr 0.475 mm/hr An instantaneous simulation of the groundwater flow was done using the semi-hypothetical PMWIN model of the Tanay dumpsite. The precipitation data used in this simulation is the annual average precipitation rate taken from the online free data source of NASA. The outputs of the simulation are the hydraulic heads (Figure 3), the velocity vectors (Figure 4), and the extent of the capture zone (Figure 5). The results of hydraulic heads for this simulation are used in the transient flow simulation. 2.2 Running the ArcGIS and PMWIN A. The topographic map is collected to provide an accurate representation of the elevation of the project site. B. Articles in relation with the groundwater modeling and landsite are reviewed as well. Data such as the precipitation is obtained in a free source site made by NASA. C. ARCGIS is used to interpolate the topographic into a data which would be compatible with the PMWIN. D. The different stress parameters such as the river and well data is assumed with consideration to the actual situation of the project area. E. Formulate the PMWIN groundwater flow model for the Tanay Dumpsite in a steady-state condition, that is, there’s only one stress period and the simulation is instantaneous. F. The hydraulic head results for the steady-state condition is obtained and used for the initial head of the transient flow. The transient flow is simulated during the wet and dry season. G. The model of the capture zone of the well is described using PMWIN. Figure 4. Velocity vectors are shown by the arrows Figure 5. Capture Zone 3.2 Transient Flow Simulation Two stress periods are used in this simulation which corresponds to the dry and wet season for the area. A one (1) year simulation was done to observe the change in water levels in the area. The states of the hydraulic heads for this simulation during wet and dry season are shown on Figures 6 for and 7, respectively. The wet season is simulated after 140 days while the dry season is simulated after 320 days. 3 A. That the research study should be continued for simulations using a more accurate data so that better representative results for the dumpsite would be attained. B. Given that the MODFLOW results are obtained from these simulations, there should be a separate study which would deal with MT3D (Model Transport in 3 Dimensional), a program in PMWIN which basically simulates the contaminant transport from the dumpsite going to the Laguna Lake so that numerical results of the leachate concentration would be attained. 6. REFERENCES 1. 2. 3. 4. Figure 7. Dry Season - Transient State Simulation After 320 Days 5. Bedient, P, et al (1994) GroundWater Contamination, Transport and Remediation, 18. Salem, Z, et. al (2006) Evaluation of landfill leachate pollution and treatment, December 2006. Processing Modflow for Windows (PMWIN) Information. www.pmwin.net. Rawat, M, et al (2007) Methane emission and heavy metals quantification from selected landfill areas in India, April 2007. Mendoca, et al (2005) Isotope measurements and groundwater flow modeling using MODFLOW for understanding environmental changes caused by a wellfield in semiarid Brazil, March 2005. Mines and Geosciences Bureau (2005) A report on the geohazard assessment of the proposed control dumpsite in Sitio Tulay, Barangay Tandang Kutyo, Tanay, Rizal, Department of Environmental and Natural Resources, Manila. Chiang, W.-H. (2005) 3D-Groundwater Modeling with PMWIN: A Simulation System for Modeling Groundwater Flow and Transport Processes. 2nd Ed. Amazon Introduction to Basic Groundwater Flow. [WWW] http://www.earthDrx.org (Accessed: December 12, 2010) National Aeronautics and Space Administration. [WWW] 3Hourly TRMM and Other Rainfall Estimate. Available at: http://disc2.nascom.nasa.gov/Giovanni/tovas/TRMM_V6. 3B43.shtml (Accessed: 2010) Rojas, David, (2004) A Study of the Potential Groundwater Contamination from the Leachate of the Payatas Dumpsite in Metro Manila, Philippines. University of the Philippines. Thorbjarnarson, K. Well Hydraulics and Capture Zone. [WWW] http://www.capital. edu/21424/ComputationalStudies/9756.pdf (Accessed: January 15, 2011) U.S. Geological Survey. [WWW] Groundwater flow and effects of pumping. Available at: http://ga.water.usgs.gov/edu/earthgwdecline.html (Accessed: 2011) Lee, Jared. [WWW] Definition and Causes of Groundwater Pollution. Available at: http://ezinearticles.com/?Definitionand-Causes-of-Groundwater-Pollution&id=3739 009 (Accessed: 2011) The World Bank Group. [WWW] Philippines Environment Monitor 2001 – Solid Waste. December, 2001. Available at: http://siteresources.worldbank.org/INTEASTA SIAPACIFIC/Resources/Philippines2001.pdf (Accessed: 2011) The World Bank Group. [WWW] Philippines Environment Monitor 2003 – Water Quality. December, 2003. Available at: http://www-wds.worldbank.org/external/defa ult/WDSContentServer/WDSP/IB/2004/05/24/000012009_20 040524135608/Rendered/PDF/282970PH0Environment0mon itor.pdf (Accessed: 2011) Figure 6. Wet Season - Transient State Simulation After 140 Days 4. CONCLUSION As shown on the figures, the hydraulic heads are depicted through equipotential lines, which are basically the groundwater contour lines. The groundwater flow paths, on the other hand, are described by the velocity vectors presented in Figure 4. Under normal conditions, the groundwater movement, which is perpendicular to the contour lines, follows the vertical change in gradient all the way through the Laguna Lake. Under pumping conditions, normal groundwater flow path directions change in response to changes in the water table gradient induced by the pumpage of ground water from the well, which is depicted by Figure 5. When groundwater is pumped out from a well, the water levels around it decline creating a bowl-like depression, which is attributed to the capture zone. The groundwater flow immediately outside the capture zone of the well, while not being captured by the well itself, can be used to exhaust contaminants by flushing the soil with clean water. In conclusion, the location of the well is appropriate to wash out the contaminants formed by the Tanay Dumpsite. 5. RECOMMENDATIONS 15. 6. 7. 8. 9. 10. 11. 12. 13. 14. Despite the difficulty of attaining various data to be used in the simulations, and the assumption of some data such as well and river parameters; the study graphically illustrates the groundwater flow movement in the area near the dumpsite as well as the capture zone of the well which could be used to treat the contaminated area. Hence, the following recommendations are made: 4