Intrinsic vulnerability assessment of Saturnia thermal aquifer by means of three parametric methods: SINTACS,GODS and COP

Three different parametric methods for the evaluation of intrinsic vulnerability to pollution have been applied in a hydrothermal carbonate aquifer located in central-northern Italy and the results obtained were compared with each other. The study area, large, approximately 152 km², lies in an area of the northern Apennines. The investigated aquifer feeds the hot thermal springs of Saturnia. The vulnerability assessment methods used are: SINTACS, GODS and COP. The vulnerability maps obtained were first individually examined, and then they were compared with each other by means of spatial analysis. These maps show similar results for the estimation of the vulnerability just in some areas. SINTACS yields areas potentially vulnerable to pollution along the Albegna River and its major tributaries in the northern part of the study area. The GODS index map reflects the great importance that this method gives to the lithological characteristics of the unsaturated zone in the subdivision of areas with different vulnerability. GODS and COP methods agree in classifying low vulnerability in the most part of central-southern study area, where the aquifer is confined by the Pliocene clay deposits. Based on the conceptual model of groundwater flow developed for the aquifer under investigation, COP seems the most appropriate method among those applied in this work, in particular with regard to the assessment of the vulnerability of the recharge area of thermal groundwater. Located in the northern part of the study area, where karst carbonate formations of the Tuscan Nappe outcrop, this recharge area is classified by the COP method as highly vulnerable to pollution.     

Vulnerability assessment for the Gaza Strip, Palestine using DRASTIC

The main usefulness of groundwater vulnerability assessment maps is their ability to be an effective preliminary tool for planning, policy, and operational levels of decision-making. DRASTIC is one such assessment method. The DRASTIC index is made up of a calculated sum of products rating and weights for seven hydrogeological parameters that contribute to aquifer vulnerability. With the help of GIS, and based on the available data, maps of DRASTIC parameters were prepared for the Gaza Strip area in a case study. Each map was given a proper rate and a special weight factor developed. The final vulnerability map was obtained as a summation of the seven maps after multiplying each one with the appropriate weight. The vulnerability map was checked against the actual pollution potential in the area and nitrate concentration. The obtained vulnerability map is strongly correlated to known pollution values in the area.     

Assessment of groundwater vulnerability based on a modified DRASTIC model, GIS and an analytic hierarchy process (AHP) method: the case of Egirdir Lake basin (Isparta, Turkey)

A DRASTIC-model method based on a geographic information system (GIS) was used to study groundwater vulnerability in Egirdir Lake basin (Isparta, Turkey), an alluvial area that has suffered agricultural pollution. ‘Lineament’ and ‘land use’ were added to the DRASTIC parameters, and an analytic hierarchy process (AHP) method determined the rating coefficients of each parameter. The effect of lineament and land-use parameters on the resulting vulnerability maps was determined with a single-parameter sensitivity analysis. Of the DRASTIC parameters, land use affects the aquifer vulnerability map most and lineament affects it least, after topography. A simple linear regression analysis assessed the statistical relation between groundwater nitrate concentration and the aquifer vulnerability areas; the highest R ² value was obtained with the modified-DRASTIC-AHP method. The DRASTIC vulnerability map shows that only the shoreline of Egirdir Lake and the alluvium units have high contamination potential. In this respect, the modified DRASTIC vulnerability map is quite similar. According to the modified-DRASTIC-AHP method, the lakeshore areas of Senirkent-Uluborlu and Hoyran plains, and all of the Yalvaç-Gelendost plain, have high contamination potential. Analyses confirm that groundwater nitrate content is high in these areas. By comparison, the modified-DRASTIC-AHP method has provided more valid results.     

Development of a GIS-based catastrophe theory model (modified DRASTIC model) for groundwater vulnerability assessment

This study developed a new paradigm for groundwater vulnerability assessment by modifying the standard DRASTIC index (DI) model based on catastrophe theory. The developed paradigm was called the catastrophe theory-based DI (CDI) model. The proposed model was applied to assess groundwater vulnerability to pollution index (GVPI) in Perak Province, Malaysia. The area vulnerability index was modeled by considering the DRASTIC multiple vulnerability causative factors (VCFs) obtained from different data sources. The weights and ranking of the VCFs were computed by using the inner fuzzy membership mechanism of the CDI model. The estimated vulnerability index values of the CDI model were processed in a geographic information system (GIS) environment to produce a catastrophe theory–DRASTIC groundwater vulnerability to pollution index (CDGVPI) map, which demarcated the area into five vulnerability zones. The produced CDGVPI map was validated by applying the water quality status–vulnerability zone relationship (WVR) approach and the relative operating characteristic (ROC) curve method. The performance of the developed CDI model was compared with that of the standard DI model. The validation results of the WVR approach exhibits 89.29% prediction accuracy for the CDI model compared with 75% for the DI model. Meanwhile, the ROC validation results for the CDI and DI models are 88.8% and 78%, respectively. The GIS-based CDI model demonstrated better performance than the DI model. The GVPI maps produced in this study can be used for precise decision making process in environmental planning and groundwater management.     

Mapping favorable groundwater potential recharge zones using a GIS-based analytical hierarchical process and probability frequency ratio model:A case study from an agro-urban region of Pakistan

In Punjab(Pakistan),the increasing population and expansion of land use for agriculture have severely exploited the regional groundwater resources.Intensive pumping has resulted in a rapid decline in the level of the water table as well as its quality.Better management practices and artificial recharge are needed for the development of sustainable groundwater resources.This study proposes a methodology to delineate favorable groundwater potential recharge zones(FPRI) by integrating maps of groundwater potential recharge index(PRI) with the DRASTIC-based groundwater vulnerability index(VI).In order to evaluate both indexes,different thematic layers corresponding to each index were overlaid in ArcGIS.In the overlay analysis,the weights(for various thematic layers) and rating values(for sub-classes) were allocated based on a review of published literature.Both were then normalized and modified using the analytical hierarchical process(AHP) and a frequency ratio model respectively.After evaluating PRI and FPRI,these maps were validated using the area under the curve(AUC) method.The PRI map indicates that 53% of the area assessed exists in very low to low recharge zones,22% in moderate,and 25% in high to excellent potential recharge zones.The VI map indicates that 38% of the area assessed exists in very low to low vulnerability,33% in moderate,and 29% in high to very high vulnerability zones.The FPRI map shows that the central region of Punjab is moderately-to-highly favorable for recharge due to its low vulnerability and high recharge potential.During the validation process,it was found that the AUC estimated with modified weights and rating values was 79% and 67%,for PRI and VI indexes,respectively.The AUC was less when evaluated using original weights and rating values taken from published literature.Maps of favorable groundwater potential recharge zones are helpful for planning and implementation of wells and hydraulic structures in this region.     

Groundwater vulnerability assessment in the Melaka State of Malaysia using DRASTIC and GIS techniques

The present work attempts to interpret the groundwater vulnerability of the Melaka State in peninsular Malaysia. The state of groundwater pollution in Melaka is a critical issue particularly in respect of the increasing population, and tourism industry as well as the agricultural, industrial and commercial development. Focusing on this issue, the study illustrates the groundwater vulnerability map for the Melaka State using the DRASTIC model together with remote sensing and geographic information system (GIS). The data which correspond to the seven parameters of the model were collected and converted into thematic maps by GIS. Seven thematic maps defining the depth to water level, net recharge, aquifer media, soil media, topography, impact of vadose zone and hydraulic conductivity were generated to develop the DRASTIC map. In addition, this map was integrated with a land use map for generating the risk map to assess the effect of land use activities on the groundwater vulnerability. Three types of vulnerability zones were assigned for both DRASTIC map and risk map, namely, high, moderate and low. The DRASTIC map illustrates that an area of 11.02 % is low vulnerability, 61.53 % moderate vulnerability and 23.45 % high vulnerability, whereas the risk map indicates that 14.40 % of the area is low vulnerability, 47.34 % moderate vulnerability and 38.26 % high vulnerability in the study area. The most vulnerability area exists around Melaka, Jasin and Alor Gajah cities of the Melaka State.     

Groundwater age,mixing and flow rates in the vicinity of large open pit mines,Pilbara region,northwestern Australia

Determining groundwater ages from environmental tracer concentrations measured on samples obtained from open bores or long-screened intervals is fraught with difficulty because the sampled water represents a variety of ages. A multi-tracer technique (Cl, ¹⁴C, ³H, CFC-11, CFC-12, CFC-113 and SF₆) was used to decipher the groundwater ages sampled from long-screened production bores in a regional aquifer around an open pit mine in the Pilbara region of northwest Australia. The changes in tracer concentrations due to continuous dewatering over 7 years (2008–2014) were examined, and the tracer methods were compared. Tracer concentrations suggest that groundwater samples are a mixture of young and old water; the former is inferred to represent localised recharge from an adjacent creek, and the latter to be diffuse recharge. An increase in ¹⁴C activity with time in wells closest to the creek suggests that dewatering of the open pit to achieve dry mining conditions has resulted in change in flow direction, so that localised recharge from the creek now forms a larger proportion of the pumped groundwater. The recharge rate prior to development, calculated from a steady-state Cl mass balance, is 6 mm/y, and is consistent with calculations based on the ¹⁴C activity. Changes in CFC-12 concentrations with time may be related to the change in water-table position relative to the depth of the well screen.     

Assessment of Groundwater Vulnerability in Upper Betwa River Watershed using GIS based DRASTIC Model

Groundwater, the most vital water resource being used for irrigation, domestic and industrial purposes is nowadays under severe threat of contamination. Groundwater contamination risk assessment is an effective tool for groundwater management. In the study, a DRASTIC model which is based on the seven hydrogeological parameters viz: depth of water, net-recharge, aquifer media, soil media, topography, impact of vadose zone and hydraulic conductivity was used to evaluate the groundwater pollution potentiality of upper Betwa watershed. ArcGIS was used to create the ground water vulnerability map by overlaying the seven layers. Based on groundwater vulnerability map, the watershed has been divided in three vulnerable zones viz; low vulnerability zone with 42.83 km² of area, moderate with 369.21 km² area and high having 270.96 km² of area. Furthermore, the DRASTIC model has been validated by nitrate concentration over the area. Results of validation have shown that in low vulnerable zone, no nitrate contamination has been recorded. While in the moderate zone nitrate has been found in the range of 1.6-10ppm. However, in high vulnerable zone 11-40ppm of nitrate concentration in groundwater has been recorded, which proves that the DRASTIC model is applicable for the prediction of groundwater vulnerability in the watershed and in similar areas too.     

Numerical Simulation of Groundwater Flow and Vulnerability in Wadi El-Natrun Depression and Vicinities,West Nile Delta,Egypt

During the last 25 years, rapid and unplanned land reclamation activity has been carried out in the areas located in both south and east of Wadi El - Natrun Depression of Egypt. Accordingly, negative effects on groundwater levels and vulnerability are frequently caused by localized high levels of abstraction and the return-flow of polluted irrigation water respectively. A groundwater model is a computational method that presents an approximation of an underground water system. In this study the groundwater system is simulated both in quantity and quality by using Mass Balance Transfer Model (NETPATH), Groundwater Modeling System (GMS) and DRASTIC Model to investigate the water - rock interactions, groundwater levels drawdown and vulnerability respectively. Three main geochemical processes namely dedolomitisation, dissolution of halite and silicate weathering were estimated during the flow path. The present over-abstraction of groundwater (105.84 million m³/year) has induced a general head drawdown from 3 to 40 m in years 2015 and 2050 respectively. Best estimate using a 3D GMS hydraulic model was (157000 m³/day) a strategy proposed for the management of groundwater without critical depletion (second scenario). The results document the extent to which a high drawdown can greatly reach 4 m by the end of simulation year 2050. The vulnerability maps of groundwater were constructed using the DRASTIC index method. The results indicated that, the southeastern and central portions of the study area are having high vulnerability rate (> 110). Modified DRASTIC map showed many more dominant high risk areas in the eastern parts of the study area that were low risk, which may be attributed to return flow of polluted irrigation water.     

Mapping groundwater vulnerable zones using modified DRASTIC approach of an alluvial aquifer in parts of central Ganga plain,Western Uttar Pradesh

A detailed hydrogeological and hydrochemical study was carried out in Yamuna-Krishni sub-basin which is a part of the vast central Ganga plain. Groundwater is the major source of water supply for agricultural, domestic and industrial uses. The excess use of groundwater has resulted in depletion of water levels. The groundwater quality, too, has deteriorated in areas dominated by industrial activity. This has led to the preparation of a groundwater vulnerability map in relation to contamination. Groundwater vulnerability maps are valuable derivative maps that show, quantitatively or qualitatively, certain characteristics of the sub-surface environment that determine vulnerability of groundwater to contamination. The modified DRASTIC method was used to prepare vulnerability map. The parameters like depth to water, net recharge, aquifer media, soil media, impact of vadose zone, hydraulic conductivity and land use pattern, owing to its bearing on groundwater regime, were considered to prepare vulnerability map. The vulnerability index is computed as the sum of the products of weight and rating assigned to each of the input considered as above. The vulnerability index ranges from 140 to 180, and is classified into four classes i.e. 140–150, 150–160, 160–170 and 170–180 corresponding to low, medium, high and very high vulnerability zones respectively. Using this index, a groundwater vulnerability potential map was generated which shows that 7%, 40% and 53% of the study area falls in low, medium and high to very high vulnerability zones respectively. The map, thus generated, can be used as a tool for protection and management of aquifers from contamination.     

Modelling the vulnerability of groundwater to contamination in an unconfined alluvial aquifer in Pakistan

The area of Thal Doab is located in the Indus Basin and is underlain by a thick alluvial aquifer called the Thal Doab aquifer (TDA). The TDA is undergone intense hydrological stress owing to rapid population growth and excessive groundwater use for livestock and irrigated agricultural land uses. The potential impact of these land uses on groundwater quality was assessed using a DRASTIC model in a Geographic Information System environment. Seven DRASTIC thematic maps were developed at fixed scale and then combined into a groundwater vulnerability map. The resultant vulnerability index values were grouped into four zones as low, moderate, high and very high. The study has established that 76% of the land area that is underlain by the TDA has a high to very high vulnerability to groundwater contamination mainly because of a thin soil profile, a shallow water table and the presence of soils and sediments with high hydraulic conductivity values. In addition, only 2 and 22% of the total area lie in low and moderate vulnerability zones, respectively. The outcomes of this study can be used to improve the sustainability of the groundwater resource through proper land-use management.     

Aquifer vulnerability and potential risk assessment: application to an intensely cultivated and densely populated area in Southern Italy

The use of indices, describing aquifer vulnerability and the risk of groundwater pollution, is a basic tool for the implementation of a sound water management plan, especially in densely populated and intensely cultivated areas. In this study, the groundwater contamination risk of the Caserta Plain (Southern Italy) was assessed through the integration of hazards defined on the basis of the different land uses, of the intrinsic vulnerability calculated by applying the SINTACS model and of the groundwater value evaluated by considering water wells density. In order to evaluate the evolution of the risk of groundwater pollution, the proposed methods were applied in the study area for both 2001 and 2009. The resulting specific vulnerability (SINTACS-L) and the risk (GRA) maps, created in a GIS environment, were validated by the comparison with the nitrate concentration distribution. The application of the proposed approach to the study area highlighted the strengths and weaknesses of each method and, at the same time, showed that their combination can provide an overall view of the threats posed to groundwater resources by the human activities affecting the territory. Considering both the benefits and the issues of the proposed approach, overall, the groundwater risk map is thought to be a robust tool to support water managers in defining future plans for water resources exploitation and land use.     

Evaluation of aquifers vulnerability to contamination in the Yarmouk River basin, Jordan, based on DRASTIC method

The existing different human activities and planned land uses put the groundwater resources in Jordan at considerable risk. There are evidences suggesting that the quality of groundwater supplies in north Jordan is under threat from a wide variety of point and non-point sources including agricultural, domestic, and industrial. Vulnerability maps are designed to show areas of greatest potential for groundwater contamination on the basis of hydrogeological conditions and human impacts. DRASTIC method incorporates the major geological and hydrogeological factors that affect and control groundwater movement: depth to groundwater (D), net recharge (R), lithology of the aquifer (A), soil texture (S), topography (T), lithology of vadose zone (I), and hydraulic conductivity (C). The main goal of this study is to produce vulnerability maps of groundwater resources in the Yarmouk River basin by applying the DRASTIC method to determine areas where groundwater protection or monitoring is critical. ArcGIS 9.2 was used to create the groundwater vulnerability maps by overlaying the available hydrogeological data. The resulting vulnerability maps were then integrated with lineament and land use maps as additional parameters in the DRASTIC model to assess more accurately the potential risk of groundwater to pollution. The general DRASTIC index indicates that the potential for polluting groundwater is low in the whole basin, whereas the resulting pesticide DRASTIC vulnerability map indicates that about 31% of the basin is classified as having moderate vulnerability, which may be attributed to agricultural activities in the area. Although high nitrate concentrations were found in areas of moderate vulnerability, DRASTIC method did not depict accurately the nitrate distribution in the area.     

Groundwater vulnerability map of the Chrzanów karst-fissured Triassic aquifer (Poland)

A map shows intrinsic vulnerability to pollution of the Chrzanów karst-fissured aquifer (273 km²) in the southern part of Poland. This aquifer is intensively drained by numerous intakes and Zn-Pb ore mines. A DRASTIC-type parametric system was applied for groundwater vulnerability evaluation. Vulnerability assessment is based on six factors (depth to groundwater table, lithology of the unsaturated zone, net recharge, hydraulic conductivity of the aquifer, groundwater flow velocity, aquifer thickness). For the final vulnerability map construction at the scale of 1:50,000, a combination of the aquifer simulation model (using MODFLOW) and a geographical information system was applied. Maps of the net recharge, hydraulic conductivity of the aquifer and groundwater flow velocity were derived by aquifer modelling. Based on the vulnerability index (21-182), six relative vulnerability classes were selected. Reliability of the map has been verified.     

Assessment of groundwater vulnerability to pollution: a combination of GIS, fuzzy logic and decision making techniques

The assessment of groundwater vulnerability to pollution aims at highlighting areas at a high risk of being polluted. This study presents a methodology, to estimate the risk of an aquifer to be polluted from concentrated and/or dispersed sources, which applies an overlay and index method involving several parameters. The parameters are categorized into three factor groups: factor group 1 includes parameters relevant to the internal aquifer system’s properties, thus determining the intrinsic aquifer vulnerability to pollution; factor group 2 comprises parameters relevant to the external stresses to the system, such as human activities and rainfall effects; factor group 3 incorporates specific geological settings, such as the presence of geothermal fields or salt intrusion zones, into the computation process. Geographical information systems have been used for data acquisition and processing, coupled with a multicriteria evaluation technique enhanced with fuzzy factor standardization. Moreover, besides assigning weights to factors, a second set of weights, i.e., order weights, has been applied to factors on a pixel by pixel basis, thus allowing control of the level of risk in the vulnerability determination and the enhancement of local site characteristics. Individual analysis of each factor group resulted in three intermediate groundwater vulnerability to pollution maps, which were combined in order to produce the final composite groundwater vulnerability map for the study area. The method has been applied in the region of Eastern Macedonia and Thrace (Northern Greece), an area of approximately 14,000 km². The methodology has been tested and calibrated against the measured nitrate concentration in wells, in the northwest part of the study area, providing results related to the aggregation and weighting procedure.     

Sensitivity analysis for the EPIK method of vulnerability assessment in a small karstic aquifer, southern Belgium

Applying the EPIK parametric method, a vulnerability assessment has been made for a small karstic groundwater system in southern Belgium. The aquifer is a karstified limestone of Devonian age. A map of intrinsic vulnerability of the aquifer and of the local water-supply system shows three vulnerability areas. A parameter-balance study and a sensitivity analysis were performed to evaluate the influence of single parameters on aquifer-vulnerability assessment using the EPIK method. This approach provides a methodology for the evaluation of vulnerability mapping and for more reliable interpretation of vulnerability indices for karst groundwater resources. Received, March 1999/Revised, December 1999, February 2000/Accepted, February 2000     

Geospatial and MCDM tool mix for identification of potential groundwater prospects in a tropical river basin,Kerala

The efficiency of GIS, RS and multi-criteria tools in isolating potential groundwater (GW) zones in the Kuttiyadi River basin (KRB), Kerala, has been robustly demonstrated by analysis of relevant data. To infer geohydrological makeup and consequent behavior of the KRB in respect of GW potential, firstly, various thematic layers viz. geomorphology, geology, slope, soil, lineament density and drainage density, were created. Secondly, thematic layers and their features were assigned suitable weights on the Saaty’s scale according to their relative significance for the presence and potential of GW. The assigned weights of the layers and their features were normalized using analytic network process method, and then the selected thematic maps were integrated in GIS using weighted overlay method to create the final groundwater prospect zone map. From the outcomes, the groundwater prospect zones of the KRB basin was found to be very good (166.21 km²), good (92.01 km²), moderate (180.33 km²), poor (237.25 km²), which constitute 24, 15, 26 and 35% of the study area, respectively. The GW prospect zone map was finally validated using geohydrology of area and GW level data from 43 phreatic wells in the study area. This study showed that groundwater prospect zone demarcation along with multi-criteria decision making is a powerful tool for proper utilization, planning and management of the precious groundwater resource.     

Vulnerability mapping of shallow groundwater aquifer using SINTACS model in the Jordan Valley area, Jordan

Jordan Valley is one of the important areas in Jordan that involves dense agricultural activities, which depend on groundwater resources. The groundwater is exploited from an unconfined shallow aquifer which is mainly composed of alluvial deposits. In the vicinity of the Kafrein and South Shunah, the shallow aquifer shows signs of contamination from a wide variety of non-point sources. In this study, a vulnerability map was created as a tool to determine areas where groundwater is most vulnerable to contamination. One of the most widely used groundwater vulnerability mapping methods is SINTACS, which is a point count system model for the assessment of groundwater pollution hazards. SINTACS model is an adaptation for Mediterranean conditions of the well-known DRASTIC model. The model takes into account several environmental factors: these include topography, hydrology, geology, hydrogeology, and pedology. Spatial knowledge of all these factors and their mutual relationships is needed in order to properly model aquifer vulnerability using this model. Geographic information system was used to express each of SINTACS parameters as a spatial thematic layer with a specific weight and score. The final SINTACS thematic layer (intrinsic vulnerability index) was produced by taking the summation of each score parameter multiplied by its specific weight. The resultant SINTACS vulnerability map of the study area indicates that the highest potential sites for contamination are along the area between Er Ramah and Kafrein area. To the north of the study area there is a small, circular area which shows fairly high potential. Elsewhere, very low to low SINTACS index values are observed, indicating areas of low vulnerability potential.     

Combining AHP and genetic algorithms approaches to modify DRASTIC model to assess groundwater vulnerability: a case study from Jianghan Plain,China

Accurate identification of vulnerability areas is critical for groundwater resources protection and management. The present study employed the modified DRASTIC model to assess the groundwater vulnerability of Jianghan Plain, a major farming area in central China. DRASTICL model was developed by incorporating the land use factor to the original model. The ratings and weightings of the selected parameters were optimized by analytic hierarchy process (AHP) method and genetic algorithms (GAs) method, respectively. A combined AHP–GAs method was proposed to further develop this methodology. The unity-based normalization process was employed to categorize the vulnerability maps into four types, such as very high (>0.75), high (0.5–0.75), low (0.25–0.5), and very low (<0.25). The accuracy of vulnerability mapping was validated by Pearson’s correlation coefficient between vulnerability index and the nitrate concentration in groundwater and analysis of variance F statistic. The results revealed that the modified DRASTIC model had a large improvement over the conventional model. The correlation coefficient increased significantly from 41.07 to 75.31% after modification. Sensitivity analysis indicated that the depth to groundwater with 39.28% of mean effective weight was the most critical factor affecting the groundwater vulnerability. The developed vulnerability model proposed in this study could provide important objective information for groundwater and environmental management at local level and innovation for international researchers.     

Assessment of the value of groundwater age time-series for characterizing complex steady-state flow systems using a Bayesian approach

In this work, the effectiveness of transient environmental tracer data in reducing the uncertainty associated with the inference of groundwater residence time distribution was evaluated. A Bayesian Markov Chain Monte Carlo method was used to infer the parameters of presumed residence time distribution forms—exponential and gamma—using concentrations of five tracers, including CFC-11, CFC-12, CFC-113, SF₆, and ⁸⁵Kr. The transient tracer concentrations were synthetically generated using the residence time distributions obtained from a model of the Plœmeur aquifer in southern Brittany, France. Several measures of model adequacy, including Deviance Information Criteria, Bayes factors, and measures based on the deviation of inferred and true cumulative residence time distribution, were used to evaluate the value of groundwater age time-series. Neither of the presumed forms of residence time distributions, exponential and gamma, perfectly represent the simulated true distribution; therefore, the method was not able to show a definitive preference to one over the other in all cases. The results show that using multiple years of tracer data not only reduces the bias of inference (as defined by the difference between the expected value of a metric of inferred residence time distribution and the true value of the same metric), but also helps quantify the uncertainty more realistically. It was found that when one year of data is used, both models could almost perfectly reproduce the observed tracer data, even when the inferred residence time distributions differed substantially from the true one. When the number of years of tracer data is increased to four years, the uncertainty associated with the distribution parameters and the model structural uncertainly increased, as the presumed forms were not able to reproduce all the data accurately. This resulted in a more realistic assessment of model uncertainty due to structural error. It was also found that regardless of the prescribed age distribution form, the Bayesian method does a better job of capturing the cumulative ages at older ages; however, it is not able to reproduce the early ages well. The ability of the model to capture older ages improves as a greater number of years of tracer data is used, in cases of both presumed exponential and gamma distributions.