Nonlinear models of the dependence of nitrate concentrations on the pumping rate of a water supply system
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Geosciences Journal
GJ
Nonlinear models of the dependence of nitrate concentrations on the pumping rate of a water supply system Ivan Kovač1, Marko Šrajbek2, Lado Kranjčević2*, and Nikolina Novotni-Horčička3 1
Department of Hydrotechnics, Faculty of Geotechnical Engineering, University of Zagreb, Hallerova aleja 7, 42000 Varaždin, Croatia Department of Fluid Mechanics and Computational Engineering, Faculty of Engineering, University of Rijeka, Vukovarska 58, 51000 Rijeka, Croatia 3 Varkom d.d., Trg bana Josipa Jelačića 15, 42000 Varaždin, Croatia 2
ABSTRACT: The aim of this paper is to analyse the influence of a groundwater pumping rate on nitrate concentrations at the Bartolovec wellfield, which is part of a water supply system of the town of Varaždin, Croatia. Over the past 16 years both the pumping rate and nitrate concentrations have increased at the wellfield. The nonlinear models that describe the pumping rate to nitrate concentration levels were developed on the basis of Logistic, Gompertz, and Richards growth functions. For each function, three different types were established regarding the initial lower contamination limit parameter. The conditions that models have to meet were defined and their reliability was established. The models were implemented on the experimental data collected during the period under consideration. The models were validated and mutually compared using Akaike’s Information Criteria (AICc), while the data fitting was estimated by using a coefficient of determination. After the results were obtained by using different models, they were compared to the maximum allowable nitrate concentrations (MAC) in water for human consumption. The dependence of nitrate concentrations on a pumping rate was confirmed and the reliable model for nitrate concentration on pumping rate was created. The model was calibrated and tested on the experimental data. The model exhibits asymptotic behavior and result shows that with the further increase in the pumping rate of groundwater drainage at the Bartolovec wellfield, nitrate concentrations will not exceed the MAC value providing there are no new sources of contamination in the zone of a pollutant influence. Key words: groundwater, nitrate pollution, pumping rate, water supply system, nonlinear growth function Manuscript received November 30, 2018; Manuscript accepted December 9, 2019
1. INTRODUCTION Groundwater is the most important and the most abundant source of drinking water in the European Union (EU), covering more than 80% of the total water supply (Directive 2000/60/ EC). Croatia is a country relatively rich in water resources and as a full EU member it is obliged to carry out groundwater quality monitoring in accordance with local regulations (Official Gazette 73/13; 151/14; 78/15; 61/16) which are compliant with EU regulations (Commission Directive 2014/80/EU). In Croatia (Official Gazette 125/2017) and the EU the maximum allowable nitrate concentration *Corresponding author: Lado Kranjčević Department of Fluid Mechanics and Computational Eng
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