Thesis (M.Sc.(Geology)) -- University of Limpopo, 2022 / The Limpopo Province is largely underlain by crystalline basement rocks, which are characterised by low porosity and permeability. The climate in this province is arid to semi-arid, with scarce surface water for domestic and industrial use. As a result, groundwater is the prime source of fresh water supply for various uses. The complex geology, the impacts of climate change and man-made interactions with groundwater and surface water are the main threat to the availability of a sustainable source of fresh water in the province. In addition, despite substantial research efforts conducted by academic institutions and government organisations, there is still a gap in understanding quantitatively the dynamics of the hydrological systems in large parts of the Limpopo Province. The present study is therefore focused on the investigation of hydrological stresses that are applied to groundwater and surface water in one of the catchments situated in the Limpopo Province. In this study, a three-dimensional steady-state numerical model of groundwater flow was carried out at Mogalakwena Subcatchment, which is situated in the western sector of the Limpopo Province. The area is situated approximately 40 km northwest of Mokopane and 50 km west of Polokwane town. The research aims to understand the dynamics of the exchange between surface water and groundwater, and to assess the influences of these processes on the sustainability of water supply in the area. Hydrologically, the area falls within the boundaries of the Mogalakwena River Catchment, which forms part of the Limpopo River Basin. Previous studies suggest that there is a continuous decline in groundwater levels in the study area due to extensive use of groundwater for mining, irrigation, and domestic purposes. Furthermore, continued climate changes have altered the rainfall events during the last couple of decades, which consequently had an impact on groundwater recharge, quality, and availability. In addition, the complex geology of the area has an impact on the aquifers’ productivity resulting in variability in borehole yields throughout the study area. To achieve the aims of the research project, a three-dimensional steady-state numerical model of groundwater flow was implemented using MODFLOW NWT and ModelMuse v graphical user interface. The model domain covers an area of 5896 sq. km and was discretised with a grid cell size of 200 m by 200 m. The MODFLOW Packages used include DIS, UPW, RCH, EVT, WEL, GHB, RIV and UZF as well as the ZONEBUDGET. The conceptual model of groundwater flow consists of two layers, and it was developed based on drillhole logs, hydrochemical data, environmental isotopes, geological, digital terrain models, and other spatial data relevant for the conceptualisation of boundary conditions and hydrological stresses. The results of the steady-state simulation of groundwater flow show that recharge contributes 99.6% of inflow, followed by river leakage (0.36%) and GHB (0.08%). Among the outflow components, surface runoff takes the lion’s share (83.3%), followed by evapotranspiration (16.6%) and river leakage 0.02%. The zone budget was implemented to evaluate the interaction between surface water and groundwater by quantifying the amount of water that flows from one zone to the other. This was achieved by assigning zone numbers to the objects that represent boundary conditions (e.g., aquifer, river and dam). Zone 1, 2 and 3 were assigned to the aquifer, river and dam, respectively. The results indicate that the rivers gain more water than they supply to the aquifer. Similarly, the Glen Alpine Dam gain more water from the aquifer than it supplies to the aquifer. This implies that the interaction between surface water bodies such as rivers and dams have a significant impact on the aquifer, which consequently partly contributed to the shortage of water in the area. A predictive analysis of the aquifer’s response to an increase in abstraction rate, evapotranspiration rate and a decrease in recharge was carried out to investigate the future fate of water availability in the study area. The results suggest that as recharge decreases, the river inflow slightly increases to compensate for the declining water level due to the river stage exceeding the piezometric surface. In addition, the decrease in recharge rate is accompanied by a slight decrease in both surface runoff and evapotranspiration rate. Thus, a decline in recharge causes a significant drop in piezometric surface relative to the evapotranspiration extinction depth, which ultimately decreases the rate of evapotranspiration. Similarly, a decrease in recharge rate lowers the depth of the water level below the river stage, which consequently triggers water vi exchange from Mogalakwena River to the aquifer. In general, the water balance shows that as recharge decreases by 20% or more, the outflows exceed the inflows resulting in a continuous drop in water level, which may ultimately risk the availability of groundwater in the area. / Council for Geoscience (CGs)

Water is an essential resource for basic human survival, but today several cities and people lack access to both reliable and clean water. Dar es Salaam in Tanzania is undergoing a rapid population growth and need to improve their current water delivery system in order to provide water to the city’s inhabitants. This report’s objective is to examine if Dar es Salaam Water and Sewerage Authority (DAWASA) manual water valve operation is improved with the usage of remote-controlled valves instead. The remote-controlled system will consequently be evaluated and compared against the manually controlled valves. In order to obtain necessary data for this study interviews and field trips were conducted at DAWASA as well as at the local market at Kariakoo. Additionally, information has also been gathered from the collaboration partners at College of Information and Communication Technologies (CoICT). The results provided information that a remote-controlled system could, in the measured reference area of 52 km of water pipes, save up to 900 U.S dollar monthly and 46 m3 of water daily for DAWASA. These savings would consequently contribute to an increase in resources which leads to further improvements to the current water distribution system. Because, today’s system is in need of a development in order to sufficiently provide potable water to the city. The remote-controlled system could also help to reduce the spread of waterborne diseases, destruction of roads and create a more reliable source of water since the water valves would be regulated more efficiently. A remote-controlled system would however need a sufficient amount of funding in order to be installed, but is both simpler to install and a more feasible solution compared to other alternatives. For these reasons, the designed system is concluded to be a more effective, sustainable and economical feasible solution for handling and managing the outdated valves.

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Orthophosphates and polyphosphates are rarely present at significant levels in raw water source but are purposefully added to the water in various forms to inhibit corrosion, iron oxidation (red water), or calcium carbonate precipitation (scale formation). Orthophosphates serve as building blocks for polyphosphates, which includes structures in linear chain, branched chains (metaphosphate) and "glassy" polyphosphate polymers. The advantage of polyphosphates over ortho phosphates lies in the fact that they slowly revert to orthophosphates and thus provide corrosion inhibition action over longer period of time in distribution systems. A study was completed for Tampa Bay Water on water distribution systems in a changing water quality environment. Blended orthophosphates was used as one of the corrosion inhibitors to study its effects on metal release and thus justify its application in comparison to other corrosion inhibitors like orthophosphates, zinc orthophosphates and silicates. This work focuses on the study of reversion of polyphosphates to ortho phosphates. A first-order model was developed that quantifies reversion as a function of the hydraulic residence time and initial poly phosphate concentration. The same model was used in two different forms - one for the hybrid lines and the other for single material lines. The results from single material lines (estimated by a non linear least square regression using ANOVA) showed that the reversion rate was highest for galvanized pipe followed by unlined cast iron, lined cast iron and the lowest rate in PVC. The first-order reversion rate constant in PVC was almost two log orders less than galvanized line. A high first-order rate constant for the galvanized pipe could be attributed to a rougher surface, large surface area, reaction with the wall surface, pipe material or a combination of these effects. The results from the hybrid PDSs (estimated by an algebraic manipulation of the first-order reaction) substantially agree with the results obtained from the single material lines, with the exception of the PVC material. The data from the hybrid lines confirms that the reversion rate constant is greatest for exposure to galvanized pipe materials, but the hybrid data indicate that the rate constant associated with PVC is somewhat larger than the constants determined for either LCI or UCI. Once an overall first-order rate expression was established, efforts were made to find a relation between polyphosphate reversions with bulk water quality. None of the major water quality parameters were found to significantly affect the reversion. This observation may be attributable to a similar water quality over the study duration. A positive correlation was found between first-order reversion rate constant and temperature. An empirical equation (modified Arrhenius equation) that relates the first-order reversion rate constant with temperature was developed that showed a strong sensitivity to temperature. The results from this study could be used to predict the stability of polyphosphates in distribution systems with varying pipe materials and temperature.

In this study, the bacterial growth dynamics of 14 pilot drinking water distribution systems were studied in order to observe water quality changes due to corrosion inhibitor addition. Empirical models were developed to quantity the effect of inhibitor type and dose on bacterial growth (biofilm and bulk water). Water and pipe coupon samples were taken and examined during the experiments. The coupons were exposed to drinking water at approximately 20°C for at least 5 weeks to allow the formation of a measurable quasi- steady-state biofilm. Bulk water samples were taken every week. In this study, two simple but practical empirical models were created. Sensitivity analysis for the bulk HPC model (for all 14 of the PDSs) showed that maintaining a chloramine residual at 2.6 mg/L instead of 1.1 mg/L would decrease bulk HPC by anywhere from 0.5 to 0.9 log, which was greater than the increase in bulk HPC from inhibitor addition at 0.31 to 0.42 log for Si and P based inhibitors respectively. This means that maintaining higher residual levels can counteract the relatively modest increases due to inhibitors. BF HPC was affected by pipe material, effluent residual and temperature in addition to a small increase due to inhibitor addition. Biofilm density was most affected by material type, with polyvinyl chloride (PVC) biofilm density consistently much lower than other materials (0.66, 0.92, and 1.22 log lower than lined cast iron (LCI), unlined cast iron (UCI), and galvanized steel (G), respectively). Temperature had a significant effect on both biofilm and bulk HPC levels but it is not practical to alter temperature for public drinking water distribution systems so temperature is not a management tool like residual. This study evaluated the effects of four different corrosion inhibitors (i.e. based on either phosphate or silica) on drinking water distribution system biofilms and bulk water HPC levels. Four different pipe materials were used in the pilot scale experiments, polyvinyl chloride (PVC), lined cast iron (LCI), unlined cast iron (UCI), and galvanized steel (G). Three kinds of phosphate based and one silica based corrosion inhibitors were added at concentrations typically applied in a drinking water distribution system for corrosion control. The data showed that there was a statistically significant increase of 0.34 log in biofilm bacterial densities (measured as HPC) with the addition of any of the phosphate based inhibitors (ortho-phosphorus, blended ortho-poly-phosphate, and zinc ortho-phosphate). A silica based inhibitor resulted in an increase of 0.36 log. The biological data also showed that there was a statistically significant increase in bulk water bacterial densities (measured as heterotrophic plates count, HPC) with the addition of any of the four inhibitors. For bulk HPC this increase was relatively small, being 15.4% (0.42 log) when using phosphate based inhibitors, and 11.0% (0.31 log) for the silica based inhibitor. Experiments with PDS influent spiked with phosphate salts, phosphate based inhibitors, and the silicate inhibitor showed that the growth response of P17 and NOx in the AOC test was increased by addition of these inorganic compounds. For this source water and the PDSs there was more than one limiting nutrient. In addition to organic compounds phosphorus was identified as a nutrient stimulating growth, and there was also an unidentified nutrient in the silica based inhibitor. However since the percentage increases due to inhibitors were no greater than 15% it is unlikely that this change would be significant for the bulk water microbial quality. In addition it was shown that increasing the chloramines residual could offset any additional growth and that the inhibitors could help compliance with the lead and copper rule. However corrosion inhibitors might result in an increase in monitoring and maintenance requirements, particularly in dead ends, reaches with long HRTs, and possibly storage facilities. In addition it is unknown what the effect of corrosion inhibitors are on the growth of coliform bacteria and opportunistic pathogens relative to ordinary heterotrophs. A method was developed to monitor precision for heterotrophic plate count (HPC) using both blind duplicates and lab replicates as part of a project looking at pilot drinking water distribution systems. Precision control charts were used to monitor for changes in assay variability with time just as they are used for chemical assays. In adapting these control charts for the HPC assay, it was determined that only plate counts ≥ 30 cfu per plate could be used for Quality Assurance (QA) purposes. In addition, four dilutions were used for all known Quality Control (QC) samples to insure counts usable for QC purposes would be obtained. As a result there was a 50% increase in the required labor for a given number of samples when blind duplicates and lab replicates were run in parallel with the samples. For bulk water HPCs the distributions of the duplicate and replicate data were found to be significantly different and separate control charts were used. A probability based analysis for setting up the warning limit (WL) and control limit (CL) was compared with the method following National Institute of Standard and Technology (NIST) guidelines.

ABSTRACT The network of pipes in potable water distribution systems (WDS) are comprised of thousands of pipes made of various materials including PVC, concrete, cast iron, and steel, among several others. The pipes are subjected to internal and external conditions that lead to their failure. Stress conditions include, but are not limited to internal pressures, traffic loading, and corrosion. The deterioration of a pipe decreases its mechanical strength which results in an increase of its probability of failure. Failures lead to loss of service which translates to loss of money due to the cost of repairs and buildup of traffic caused by street closures. The focus of this study is the pipe network underneath cities that make it possible for communities to have access to potable water. The objective of this analysis is to evaluate the physical conditions of each pipe in a water distribution system in order to assess its probability of failure and ultimately calculate the risk associated with each pipe in the case that it were to fail. This model focuses only on the pipes of the WDS and does not take into consideration fittings, pumps, and other network components. This model assesses pipe age, material, diameter, internal pressure, traffic loading (industrial or residential), and length to determine the probability of failure. It then utilizes several economic factors such as material cost, customer criticality, demand, traffic impact, and land use to calculate the risk associated with each pipe. The risk associated with each pipe can then be used as a ranking system to identify the most vulnerable pipes, those with the highest economic impact upon failure. Identifying the pipes with the highest risk allows municipalities to better allocate funds for maintenance or replacement of pipes. It highlights the most critical pipes within a network of thousands. In order to check its functionality, this model applied to the WDS of the City of Arroyo Grande, California. Information on the City’s distribution system was analyzed using Bentley’s WaterCAD, ESRI’s ArcGIS, MathWorks’ MATLAB and Microsoft’s Excel software to perform the analysis. The risk analysis model provided 3 pipes within the distribution system made of cast iron as having a high probability of failure and a critical level of risk. A critical level of risk is defined as falling within the highest range of risk within this study. Considering that only 3 pipe segments were highlighted as having a Critical Risk, 4 as High Risk, and 6 as Medium Risk, in a system of 3572 pipes indicates that the model functions properly. This model was compared to a method developed by Jan C. Devera in his thesis “Risk Assessment Model for Pipe Rehabilitation and Replacement in a Water Distribution System” (2013), which was also applied to the City of Arroyo Grande’s distribution system. Results provided by this analysis prove that both models are functional due to similar results. The current study utilizes the concepts of random variables and conditional assessment to run various Monte Carlo Simulations as the means of calculating the probability of failure of a pipe. Mr. Devera’s model utilizes simplistic approach that does not involve intensive calculations, but results for both models turned out to be similar when looking at the Arroyo Grande distribution system. This risk assessment model demonstrates that a risk assessment model can provide a framework to prioritize pipes based on risk. The approach can help create a schedule for a city’s pipe distribution network for maintenance and repair. It is important to note that it is not a predictive model. This study may be employed to better allocate funds for the rehabilitation and replacement of a city’s existing pipe network to promote optimal operating conditions and service to the public.

The standard design approach of water distribution systems requires that pressure at any point in the system is maintained within a range whereby the maximum pressure is not exceeded so that the likelihood of a pipe burst is reduced and the minimum pressure is always maintained or exceeded to ensure adequate flows for satisfying expected demands. High pressure systems tend to cause more frequent pipe breaks and an increase in energy use and leakage. Low pressure systems cause consumer complaints, make the system more susceptible to negative pressures, and possibly to the ingress of contaminants during transient events. The overall goal of establishing pressure standards is to balance these opposing tendencies to achieve a safe, reliable, and economic operation of the system. Yet, there are no universally acceptable or established rules or guidelines for establishing a pressure standard for water distribution system design, and few studies have considered whether the traditional standards are still applicable in modern systems. This study has made a critical appraisal on what pressure standards mean, where they are violated, and where they need revision to achieve a comprehensive picture about what the pressure standards really mean. The research also highlights the inter-related issues associated with pressure criteria. Assessment of the relationships governing water pressure, leakage, energy use and economics is realized via the analytical investigation of single pipes and the simulation of representative networks using the steady state analysis software EPANET 2. The role of minimum pressure standards, storage, pumping strategy, and resource prices on the energy and water loss of systems is analysed and assessed. In anticipation that pressure contributes to pipe break rates, a probabilistic approach considering uncertain water demand and pipe’s roughness modeled with a Monte Carlo simulation (MCS) algorithm is presented. This study also explores how the minimum pressure standards affect transient pressures and reviews how destructive transient pressures may be controlled to limit reduced pressure surges within acceptable limits even when the minimum steady state pressure is relatively low. In order to place the research in practical context, this study develops a surge limit control algorithm for the design of a portable device for limiting the down-surge pressures by creating a pressure control boundary in a pipe system during hydrant operations. This boundary is established using the portable control device to safely operate a hydrant in a water distribution system. This study also highlights the notion that high level of pressure standards may lead to a troublesome squandering of water and energy and may disrupt the performance of water distribution systems. Given the too often degraded nature of water supply infrastructures, the on-going challenges of urban growth, and the increased stress on natural resources, the significant benefits of better controlling water pressure are not only welcome but urgently needed. / Thesis / Doctor of Philosophy (PhD)

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