James W. Warner

The Effects of Urbanization on Groundwater Quantity and Quality in the Zahedan Aquifer, southeast Iran

Abstract This paper investigates the impacts of urban growth on groundwater quality and quantity in the Zahedan aquifer, which is the sole source of water supply for the city of Zahedan, Iran. The investigation is based on the collection of available historical data, supplemented by field and laboratory investigations. Groundwater levels in 40 wells were measured in December 2000. In addition, 102 water samples were taken in two periods during November and December 2000. Of these, 43 samples were analyzed for major ions, 32 samples were analyzed for nitrogen and phosphorus and the remainder for bacteriological contamination. The water level data show that there has been a general decline since 1977 due to over-abstraction. The magnitude of this decline has reached about 20 m in some places. However, in one area over the same period, a rise of about 3 m has been observed. This occurs as a result of the local hydrogeological conditions of shallow bedrock and relatively low permeability materials down stream of this area that limits the flow of groundwater towards the northeastern part of the aquifer. The general fall in groundwater levels has been accompanied by a change in the direction of the groundwater flow and an overall reduction of the areal extent of the saturated region of the aquifer. The city now has a serious problem such that even if the abstracted groundwater is rationed, water is not available for long periods because the demand far exceeds the supply. The heavy impact of urbanization on the groundwater quality is shown through the observed high nitrate (up to 295 mg/l as nitrate) and high phosphorus values (about 0.1 mg/l as P). Significant changes in the chloride concentration are also observed in two areas: increasing from 100 mg/l to 1,600 mg/l and from 2,000 mg/l to 4,000 mg/l, respectively. Furthermore, the bacteriological investigations show that 33 percent of the 27 collected groundwater samples are positive for total coliform and 11 percent of the samples contained fecal coliforms indicating that local sources are strongly influencing the observed chemical data. Greater depths to groundwater reduce the observation of coliform contamination. In general, the unplanned urban development in Zahedan has significantly degraded the regions water resources and significant actions such as upgrading the sewage waste disposal system, locating other sources of water supply, and strict groundwater management will all be needed to resolve the problems that have arisen.

Shortcomings of existing finite element formulations for subsurface water pollution modeling and its rectification: one-dimensional case

Contaminant transport in an underground system usually occurs in varied flow fields and in anisotropic and heterogenous media. Because the applicability of analytical solutions is extremely limited for such conditions, numerical techniques are essential for underground pollution modeling. Among the numerical techniques, the finite element method has become very popular and is recognized as a powerful numerical tool. The finite element method, particularly for pollution modeling, may be preferable to finite difference because it can link a node with the adjacent nodes in various directions. The main disadvantage with the finite element method is that its mathematical formulations are relatively complicated and follow set rules step by step. In a recent investigation, it was found that such prescribed rules are not applicable everywhere; they have many limitations and shortcomings. Shape functions that transform nodal values into element values are frequently used in an integration process to construct elem...

Sediment and microbial fouling of experimental groundwater recharge trenches

Abstract A common method of recharging groundwater is by the use of injection wells and/or recharge trenches. With time the recharge capacities of the wells/trenches progressively decline. Deposition of suspended fines in the recharge water and growth of microorganisms in the aquifer are common causes of this decline. This paper presents an investigation of the relative significance of these two factors under controlled laboratory conditions. Large-scale physical models of recharge trenches were conducted in the laboratory to monitor the decline with time of the recharge capacity under controlled conditions. The physical models consisted of four hydraulically separate cells in which six different experiments were conducted. In three of the experiments microorganism were added as an inoculant. A nutrient and carbon fine solution was constantly injected into the influent stream entering through the inflow pipe. Both carbon fines and microorganisms caused plugging of the model recharge trenches in the laboratory. However, initialy the microbes appeared to have a beneficial effect by hindering the transport of the carbon fines from the gravel pack in the trench. Later the microbes contributed to the plugging of the gravel pack. A significant correlation was determined between the extent of carbon fine deposition and microbial growth. In the experiment using a biodegradable slurry, microbial growth did not affect the recharge capacity of the trench. One laboratory experiment involved the introduction of silt as a source of sediment fines to the model recharge trench. This experiment simulated conditions often found in the field when no carbon fine adsoprtion system is used and natural surface water is recharged into aquifer. This research will be useful in understanding the relative importance of factors contributing to the decline of recharge capacity observed in the field.

A finite-element linked model for analysis of solute transport in 3-D space of multilayer subsurface systems

Abstract The computational burden and instability of the fully 3-D saturated-unsaturated unified approach can be lessened considerably by using the linked model of the quasi 3-D approach. This approach is applicable to a multi-layer subsurface system consisting of aquifers and aquitards. In this approach, 1-D vertical flow and solute transport is assumed in the vadose zone and aquitards, and 2-D horizontal flow and quasi 3-D solute transport are assumed in the aquifers to simulate flow and transport in 3-D space. In this paper, the aquifers are sliced into sublayers. In a aquifer with 2-D flow, transport in the horizontal direction is assumed to be caused by advection and dispersion while transport in the vertical direction is assumed to be caused solely by dispersion. As a mathematical simplicity, the equations for vertical flow and transport in the vadose zone and confining layers and the equations for flow and transport in the aquifer are solved separately in two different solution packages. During this time-marching analysis, the output in terms of source/sink obtained from one solution package is coupled with the equations in the other solution package. This linked model quasi 3-D approach was tested with other widely used numerical models and analytical solutions, and was found stable and technically robust.

Flow and transport modelling of a highly stressed aquifer to refine management strategies

Overexploitation of groundwater in the eastern part of San Jacinto Watershed Basin in conjunction with reservoir leakage in the western part has reversed the groundwater flow direction and has caused migration of groundwater with high total dissolved solids (TDS) into an area of better-quality groundwater. The regional groundwater flow and transport model presented here shows how decreased pumping and artificial recharge in the east and extraction of high-TDS groundwater in the west can impact the area.