Multi-pollutant approach to model contaminants flow in surface and groundwater: a review

Pollution of surface and groundwater is largely caused by anthropogenic activities and the natural geogenic processes. Most of the contaminants in surface and groundwater have a common origin. The aim of this review is to highlight the importance of multi-approach modeling of pollutants which is required for various reasons, owing to the availability of different types and sources of water pollutants. We attempted a systematic review to assess the current progress in modeling water pollution using multi-approach methods. Results showed that (9) out of the eleven (11) chosen studies have applied some forms of multi-approach modeling methods to examine pollutants in surface and groundwater. Results also suggest that there is an increased concern on understanding how pollutants are transported from sources to surface water and how impurities are transported to groundwater aquifers by infiltering surface flows. A major limitation of water quality models is that models assumed a uniform environmental setting and can simulate contaminants only in the gas and aqueous states. The rationality of contaminant modeling using multi-pollutant approaches is mostly problematical to validate because suitable field data is wanting for comparison. Therefore, the model output must be scrutinized within the context of the uncertainty of the model inputs, data limitations and consistently essential application of established standards from the literature

First flush behaviour in urban residential catchments

The current state of knowledge in relation to first flush does not provide a clear understanding of the role of rainfall and catchment characteristics in influencing this phenomenon. This is attributed to the inconsistent findings from research studies due to the unsatisfactory selection of first flush indicators and how first flush is defined. The research study discussed in this thesis provides the outcomes of a comprehensive analysis on the influence of rainfall and catchment characteristics on first flush behaviour in residential catchments. Two sets of first flush indicators are introduced in this study. These indicators were selected such that they are representative in explaining in a systematic manner the characteristics associated with first flush. Stormwater samples and rainfall-runoff data were collected and recorded from stormwater monitoring stations established at three urban catchments at Coomera Waters, Gold Coast, Australia. In addition, historical data were also used to support the data analysis. Three water quality parameters were analysed, namely, total suspended solids (TSS), total phosphorus (TP) and total nitrogen (TN). The data analyses were primarily undertaken using multi criteria decision making methods, PROMETHEE and GAIA. Based on the data obtained, the pollutant load distribution curve (LV) was determined for the individual rainfall events and pollutant types. Accordingly, two sets of first flush indicators were derived from the curve, namely, cumulative load wash-off for every 10% of runoff volume interval (interval first flush indicators or LV) from the beginning of the event and the actual pollutant load wash-off during a 10% increment in runoff volume (section first flush indicators or P). First flush behaviour showed significant variation with pollutant types. TSS and TP showed consistent first flush behaviour. However, the dissolved fraction of TN showed significant differences to TSS and TP first flush while particulate TN showed similarities. Wash-off of TSS, TP and particulate TN during the first 10% of the runoff volume showed no influence from corresponding rainfall intensity. This was attributed to the wash-off of weakly adhered solids on the catchment surface referred to as "short term pollutants" or "weakly adhered solids" load. However, wash-off after 10% of the runoff volume showed dependency on the rainfall intensity. This is attributed to the wash-off of strongly adhered solids being exposed when the weakly adhered solids diminish. The wash-off process was also found to depend on rainfall depth at the end part of the event as the strongly adhered solids are loosened due to impact of rainfall in the earlier part of the event. Events with high intensity rainfall bursts after 70% of the runoff volume did not demonstrate first flush behaviour. This suggests that rainfall pattern plays a critical role in the occurrence of first flush. Rainfall intensity (with respect to the rest of the event) that produces 10% to 20% runoff volume play an important role in defining the magnitude of the first flush. Events can demonstrate high magnitude first flush when the rainfall intensity occurring between 10% and 20% of the runoff volume is comparatively high while low rainfall intensities during this period produces low magnitude first flush. For events with first flush, the phenomenon is clearly visible up to 40% of the runoff volume. This contradicts the common definition that first flush only exists, if for example, 80% of the pollutant mass is transported in the first 30% of runoff volume. First flush behaviour for TN is different compared to TSS and TP. Apart from rainfall characteristics, the composition and the availability of TN on the catchment also play an important role in first flush. The analysis confirmed that events with low rainfall intensity can produce high magnitude first flush for the dissolved fraction of TN, while high rainfall intensity produce low dissolved TN first flush. This is attributed to the source limiting behaviour of dissolved TN wash-off where there is high wash-off during the initial part of a rainfall event irrespective of the intensity. However, for particulate TN, the influence of rainfall intensity on first flush characteristics is similar to TSS and TP. The data analysis also confirmed that first flush can occur as high magnitude first flush, low magnitude first flush or non existence of first flush. Investigation of the influence of catchment characteristics on first flush found that the key factors that influence the phenomenon are the location of the pollutant source, spatial distribution of the pervious and impervious surfaces in the catchment, drainage network layout and slope of the catchment. This confirms that first flush phenomenon cannot be evaluated based on a single or a limited set of parameters as a number of catchment characteristics should be taken into account. Catchments where the pollutant source is located close to the outlet, a high fraction of road surfaces, short travel time to the outlet, with steep slopes can produce high wash-off load during the first 50% of the runoff volume. Rainfall characteristics have a comparatively dominant impact on the wash-off process compared to the catchment characteristics. In addition, the pollutant characteristics also should be taken into account in designing stormwater treatment systems due to different wash-off behaviour. Analysis outcomes confirmed that there is a high TSS load during the first 20% of the runoff volume followed by TN which can extend up to 30% of the runoff volume. In contrast, high TP load can exist during the initial and at the end part of a rainfall event. This is related to the composition of TP available for the wash-off

First flush analysis in urban catchments

The effectiveness of structural elements employed for stormwater mitigation such as bioretention basins and constructed wetlands depend on the compatibility between their design specifications and actual stormwater quality and quantity characteristics. These structural elements are commonly designed to accommodate the initial portion of runoff considering the occurrence of first flush. Therefore, the effectiveness of stormwater quality treatment primarily depends on the in-depth knowledge of the first flush phenomenon and the ability to provide appropriate treatment. The current scientific knowledge relating to first flush is limited primarily due to research investigations being undertaken based on lumped rainfall and runoff parameters. This paper presents the outcomes of an in-depth study undertaken of the first flush phenomenon using a set of indicators which are not only innovative, but is also able to accurately represent the characteristics of the different sectors in a runoff hydrograph. The analysis undertaken confirmed that pollutant wash-off during the initial 10% of runoff volume was critical for the occurrence of first flush. Typically first flush was found to last up to 40% of the runoff volume. The study outcomes provide new knowledge to enhance the effectiveness of structural stormwater treatment measures

Sectional analysis of the pollutant wash-off process based on runoff hydrograph

The validity of using rainfall characteristics as lumped parameters for investigating the pollutant wash-off process such as first flush occurrence is questionable. This research study introduces an innovative concept of using sector parameters to investigate the relationship between the pollutant wash-off process and different sectors of the runoff hydrograph and rainfall hyetograph. The research outcomes indicated that rainfall depth and rainfall intensity are two key rainfall characteristics which influence the wash-off process compared to the antecedent dry period. Additionally, the rainfall pattern also plays a critical role in the wash-off process and is independent of the catchment characteristics. The knowledge created through this research study provides the ability to select appropriate rainfall events for stormwater quality treatment design based on the required treatment outcomes such as the need to target different sectors of the runoff hydrograph or pollutant species. The study outcomes can also contribute to enhancing stormwater quality modelling and prediction in view of the fact that conventional approaches to stormwater quality estimation is primarily based on rainfall intensity rather than considering other rainfall parameters or solely based on stochastic approaches irrespective of the characteristics of the rainfall event

Influence of rainfall characteristics on first flush behaviour

Urban stormwater with impervious surface often produces runoff with a variety of contaminants. This paper discusses an investigation into the influence of rainfall characteristics toward the first flush behaviour. This study involved field investigations, sampling of urban stormwater runoff, laboratory testing and data analysis. 15 stormwater samples were collected and executed manually in a small catchment, which represents the higher institution area in Skudai, Johor. Data collections were carried out on 9 November 2017. Correlation of pollutants such as total suspended solids (TSS), total dissolved solids (TDS), biological oxygen demand (BOD), chemical oxygen demand (COD) and zinc with runoff were derived within the evaluation of hyetograph, hydrographs and pollutographs. The concentration varied at different stages of the same rainfall event. The higher strength of first flush was seen in case of TSS, BOD and zinc compared to TDS and COD. The finding shows that high rainfall intensity in the beginning of the event had contributed to the high wash off of some pollutants such as TSS, BOD and zinc. The concept of the first flush cannot be used alone to establish a reliable methodology to design treatment facilities. Additional knowledge and information are necessary

Reevaluating the hydrochemistry of groundwater in basement complex aquifers of Kaduna Basin, NW Nigeria using multivariate statistical analysis

Evaluation of groundwater using multivariate analysis is a valuable technique. It helps to detect the source of elements and the process(es) that controls the groundwater chemistry. This review intends to identify the hydrogeochemical process(es) that controls groundwater in Kaduna Basin. Water quality data were derived from the literature based on defined literature selection criteria. Subsequently, we applied multivariate analysis, notably, factor, cluster, and correlation analyses to classify and analyse the hydrochemical conditions. Results showed that groundwater is controlled by the rock weathering process based on correlation and factor analyses. Hierarchical cluster analysis categorised groundwater into three clusters. Cluster 1 contained locations that have an analogous concentration of pH and temperature. Cluster 1 relates to physical/external influence. Cluster 2 correlated with EC, Fe3+, HCO3−, and NO3−. Cluster 3 correlated with TDS, Na+, Mg2+, Ca2+, K+, SO42−, and Cl−. The two clusters are related to the rock weathering process, owing to low NO3− concentrations. Results of factor and correlation analyses concurred with Gibb's model. The study inferred that rock weathering is the primary mechanism controlling groundwater in Kaduna Basin. The multivariate analysis provides a simple tool for identifying the relationship between geology and hydrochemistry of aquifers

Hydrogeochemical evaluation and mechanisms controlling groundwater in different geologic environments, Western Sokoto Basin, Northwestern Nigeria

The hydrogeochemistry of aquifers in the western Sokoto basin was assessed. The objective of this study is to identify the impact of geological variability on groundwater hydrochemistry and the mechanisms controlling the hydrochemistry of aquifers. Univariate statistics (several samples ANOVA), Pearson’s (r), and multivariate statistics-hierarchical cluster analysis (HCA) and Factor analysis (FA) were used to interpret the hydrochemistry of aquifers. Subsequently, geochemical modeling was applied to assess the saturation index (SI) of rock minerals. Forty groundwater samples were collected from Gwandu (n = 20) and Illo (n = 20) formations. ANOVA results indicated that geological variability exerted a considerable impact on groundwater in Gwandu and Illo aquifers. It is characterized by a substantial amount of Ca2+, Mg2+, SO42−, HCO3−, Na+, and K+. The hydrogeochemical facies indicated mixing conditions. FA and correlations analysis further revealed that groundwater received the noticeable influence of silicate weathering and dissolution of carbonates. There were significant differences in SI values for chrysotile, goethite, gypsum, H2(g), H2O(g), H2S(g), illite, and sepiolite minerals between the two geologic environments. Positive SI values for gibbsite were noticed in eleven sampling locations, indicative of potential recharge zones. Likewise, all the sampling locations have positive values for K-feldspar and are supersaturated with mica, suggesting both discharge and transition zones. The HCA classified aquifers into three clusters based on their hydrogeochemical characteristics. Geochemical modeling, univariate, and multivariate analyses are user-friendly tools for hydrochemical analysis

Quality reassessment using water quality indices and hydrochemistry of groundwater from the Basement Complex section of Kaduna Basin, NW Nigeria

Water quality indices allow for defining the acceptable limits for water usage. This paper evaluates the suitability of water for industrial and domestic uses. Hydrogeochemical data were derived from previous studies and exposed to an internal consistency test. Groundwater was classified using physicochemical parameters and water quality indices. Multivariate analysis (factor and clustering analyses) was applied to identify the sources of ions and classify groundwater. Similarly, regression analysis was used to model the hydrochemistry of the study area. Results indicated groundwater of varying quality based on hardness, TDS, EC, chloride, and nitrate. Groundwater classification based on the Chadha diagram revealed a Na–HCO3 water type in the Kudenda–Nassarawa area. Kaduna South and Kakuri and its Environs have a Ca–Mg–Cl water type. Calcium, Mg, Na, and TDS constituted the major elements influencing the hydrochemistry of groundwater based on regression analysis. Factor analysis showed that aquifers are strongly influenced by rock weathering. Also, cluster analysis revealed different types of water sources based on their hydrogeochemical characteristics. The results of multivariate analysis concurred with Gibb’s model. However, groundwater is unsuitable for industrial use since it is undersaturated with calcium carbonate. Thus, water treatment is required to avoid serious corrosion