Physicochemical Characterization and Evaluation of Seasonal Variations of Landfill Leachate and Groundwater Quality around Tanjaro Open Dump Area of Sulaymaniyah City, Kurdistan, Iraq

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Introduction
Open dump area (site) is thought to be active sources for the gradual release of harmful compounds mixed with nontoxic precursors into the environment. Leachate and gases are produced in the open dumpsite as a result of biological, chemical, and physical processes that promote waste disintegration [1]. Te most typical kind of landfll, which receives a combination of commercial, municipal, and mixed industrial waste, defnes landfll leachate as a water-based solution of four categories of contaminants (dissolved organic matter, inorganic macro components, heavy metals, and xenobiotic organic compounds) [2]. Leachate has a very high concentration of chemical oxygen demand (COD), biological oxygen demand (BOD), ammoniacal nitrogen, heavy metals, and other organic and inorganic contaminants. According to the ratio of BOD 5 /COD > 0.6, young leachate often contains organic fractions that are readily biodegradable and have signifcantly lower molecular weights. Older leachates with an organic proportion tend to have persistent features and contain humic and fulvic compounds with greater molecular weights, as seen by BOD 5 /COD ratios >0. 3. Tis is because landflls have a longer lifespan. In addition, fewer easily volatilized fatty acids are present in older leachates, which makes them largely comprise refractory materials and may lower the BOD 5 /COD ratio [3].
Leachate is dark brown or black in color, and if not collected and treated, it has a great potential to contaminate nearby soil and groundwater [4]. Depending on the type of waste and its age, leachate can have a wide range of compositions, and numerous elements are suspended and dissolved in it. Even at a single dump site, the quality of leachate is largely site-specifc and varies from place to place [5]. Municipal solid waste landflls will continue to create contaminated leachate after they are closed; this process can keep going for 30 to 50 years and can have a severe environmental impact if released into the environment untreated [6]. Leachate can have a direct or indirect impact on the properties of soil; however, as opposed to mechanical alteration, leachate contamination of soil typically concentrates on its chemical qualities [7]. When leachate is present, it may afect soil diferently than when normal water is present. Leachate contains a variety of chemical components that could regulate its electrical conductivity, which would then afect how it interacts with the soil [8].
In Tanjaro, groundwater is the main source of agriculture and drinkable water. In this study, the impact of open dump area leachate on groundwater quality determined through physical and chemical analysis of both open dump area leachate dumpsites and groundwater (tube wells) samples collected near the Tanjaro open dumpsite in Sulaymaniyah city.

Sample Collection.
In order to characterization of the leachate generated from open dumpsites and groundwater, three groundwater (tube well) samples surrounding the dumping area and three leachate samples were collected from the dumping during four seasons of the year 2021-2022. Site specifcations for sampling points are presented in Table 1 and Figure 1. Table 2 displays the Specifcations of  the sample analysis instrument, analytical methods, and  monitored parameters. Te groundwater samples (W1, W2, and W3) were collected close to the dumping sites; where it was found that the distance between W1 and (L1, L2, and L3) were 1,447, 955, and 925 meters, respectively, while W2 and (L1, L2, and L3) were 862, 448, and 382 meters, and W3 and (L1, L2, and L3) were 1,177, 780, and 714 meters, respectively. Te three samples for each were collected throughout four seasons, same like the leachate samples.

Material Preservation.
All samples were collected in 5.0 L precleaned polyethylene containers (MEDILAB-Company-India.), and returned to the laboratory at University of Sulaimani-College of Agricultural Engineering Science-Department of Natural Resources. Tey were kept at 4°C in the incubator (TC 135 S-Lovibond incubator) before being tested in accordance with standard procedures. To prevent the heavy metals from precipitating, samples for heavy metals were maintained separately by adding 1.0 ml concentrated nitric acid (from Merck).

Leachates.
Te mean values of physicochemical parameters of leachate samples as well as their seasonal variation are summarized in (Table 3 and S1).
Tere is signifcant efect of leachate temperature change on the organic decomposition, which afected on the gas production. Te biodegradation of the waste caused heat to be released, which raised the temperature and accelerated the composition of organic matter, which in turn to increase gas production. Tere is a clear correlation between temperature and each of the parameters of electrical conductivity, suspended particles, pH, and BOD 5 ; therefore, the warmer the season, the greater the values of the parameters [9]. Te seasonally average temperature distribution (Table 3) shows that the highest temperature in summer (28.5°C) were recorded, and the lowest temperature recorded in winter is (7°C). Tese values rise gradually from January and evolve into a summer character in July and August. Tere are a direct proportion between the temperature and each of electrical conductivity, suspended solids, pH, BOD 5 parameters, which means, the warmer is the season, the higher the values of the parameters. Based on the various landfll ages, three types of stabilized leachateyoung (less than a year), medium (1-5 years), and old (more than 5 years), can be distinguished in landflls [10]. Te pH is an important component in stabilizing the age of the leachate; it is typically found to range from 4.5 to 9, with young leachate having a pH of less than 5.5 and older landfll leachate having a pH of more than 7.5; while the pH in between is considered to be a medium leachate [11]. Te pH values of the dumpsites analyzed ( Table 3) were found that the pH mean value for L1 is around (6.0), L2 is around (8.0), and L3 is about (7.7). According to Christensen et al. and Salami et al. [11,12], the age of L1 can be referred to young, but the pH value of both L2 and L3 were referred to old leachate. Te leachate from L1 dumpsites is considered to be young because of its pH value, which is less than 6.5 due to the high concentration of volatile fatty acids; however, the leachate from L2 and L3 during the methanogenic stage has been converted into methane and carbon dioxide, causing the pH of the leachate to rise to alkaline levels [13]. Te Electro-Conductivity parameter (EC) is dependent on the presence of inorganic components, specifcally the levels of diferent anions, cations, and the soluble salts [14]. Te average EC mean values of the leachates for four seasons range from (498.56) to (144514.9) μS·cm −1 , which is considerably high amount. Te exceptionally high EC values are caused by the abundance of anions and cations. Leachate's weakly alkaline composition is a sign that the dumping site reached mature stage.
Total dissolved solids (TDS), another crucial parameter used to characterize leachate samples, can indicate the presence of some organic material as well as inorganic salts of major cations and anions, and it is used to show the degree of salinity and mineral contents of leachate. Total dissolved solids with high concentrations can reduce water's clarity, which makes it harder for plants for photosynthesis and raises the water's temperature. Te biotic components, such as photosynthetic bacteria and algae, are afected in terms of their growth and development. Many aquatic organisms might become weak and even die due to high TDS levels [15]. Te values of TDS as represented in Table 3, is (96825, 51602.5, and 779) for L1, L2, and L3, respectively, which have high TDS values make these leachates biologically polluted, which makes unfavorable tastes, odors, and colors as a result. A decrease in water clarity caused by high TDS levels might contribute to light limitation, which in turn reduces photosynthesis and raises water temperature. Tis has an impact on the genesis and proliferation of biotic elements like photosynthetic bacteria and algae. Many aquatic species may be killed by high TDS, which restricts their ability to grow [16]. Tis high concentration of TDS was a result of rainwater intrusion, which caused larger concentrations of contaminants to dissolve. Te highest EC and TDS values during dry seasons suggested that they might be the result of dry weather where the cations, anions, and total solids collected at these locations. In contrast, the winter and spring seasons revealed low EC and TDS levels as a result of the dilution of these ions following the season of signifcant rainfall [17].
Total Alkalinity (TA), caused by bicarbonate, carbonate, and hydroxyl ions, is one of the physicochemical parameters studied in leachate. Te high alkalinity in leachate gives a disagreeable favor that could have an impact on human health, and the higher levels in tube well samples indicate that the water is not used for drinking due to the taste. Te biological decomposition and dissolution process that takes place within disposal sites causes TA values for leachate to be much higher. Signifcant amounts of bicarbonate, which is dissolved carbon dioxide and one of the main components of alkalinity, are produced during the biodegradation of organic matter [16]. Alkalinity of leachate samples were mainly due to the presence of carbonate ions, in which high       Biological Oxygen Demand-5-day (BOD 5 ), an essential physicochemical parameter, was used to detect the presence of organic maters in the leachate and groundwater samples. Higher BOD 5 values signify a high concentration of organic matter that is either decomposing or being biodegraded [19]. Te BOD 5 and COD concentrations of leachate sample ranges from (184.8 to 11100) and (260.568 to 18204) mg·L −1 , respectively. High values of organic matter in the wastes are indicated by the high BOD 5 and COD concentrations. Te L2 was determined to have more organic matter than that of the other two leachates based on the BOD 5 and COD results [20]. Te results indicate that the BOD 5 /COD ratios exceeded 0.6 for all samples taken from the three dumpsites.      Te higher value shows that the young leachate has more organic fractions that can break down into biodegradable compounds (majority of organic compound is biodegradable). Old leachate is more resistant to degradation than young leachate primarily because it contains humic and fulvic acids [21]. ) and cations (Ca, Mg, Na, and K) are shown in Table 3. It is clear that the concentrations of cations and anions vary during the wet and dry seasons. Regarding the anions, the high amount of chloride contents of L1, L2, and L3 were (9292.5, 10912.5, and 1830.5) are due to mixing of domestic waste. Kitchen waste from homes, hotels, and restaurants are potential anthropogenic sources of chloride. Higher nitrate and sulfate concentrations in L1, L2, and L3 were (2321.75, 2272.75, and 1397.8) and (3569, 5040, and 1988.25), correspondingly, and these amounts are mostly attributable to domestic wastes [7,22]. A mature stage of the dumping site is also indicated by the increased phosphate values in L1, L2, and L3 (48.225, 59.25, and 28.1), respectively [23]. Domestic wastes are regarded as the most probable sources for leachate cations. Due to the increased evaporation impact in a semiarid climate, the concentrations of all cations-Ca, Mg, Na, and K-show greater values (8103, 3785, 1249.75, 438.75, 4543.75, and 1756, 2120.75, and 331.7, respectively [24].

Journal of Chemistry
Te mean concentrations of Cr, Mn, Ni, Cu, Fe, Co, Zn, As, Pb, and Se for L1, L2, and L3 were summarized in (Table 3 and Figure 2). Tere was a high concentration of Mn (74.0325 mg·L −1 ) and Fe (83.45 mg·L −1 ) detected in L1 samples of the study area. Te L3 exhibited that Cu, Co, As, Pb, and Se were not detectable, also represented relatively high concentrations of Cr (0.0125 mg·L −1 ), Mn (0.573 mg·L −1 ), Ni (0.0125 mg·L −1 ), Fe (0.1425 mg·L −1 ), and Zn (0.1625 mg·L −1 ). Relatively high concentrations of Cr, Mn, Ni, Cu, Fe, Co, Zn, As, Pb, and Se were detected in the L2. Similar outcomes were discovered by De et al. [25]. While the three leachates showed that Cd and Hg were not detectable.

Groundwater (Tube Wells).
Groundwater quality (tube well) seasonal variations have been well investigated, the mean values of physicochemical parameters of well samples as well as their seasonal variation are summarized in (Table 4). Table 4 displays the seasonal average temperature distribution, the highest temperature ever recorded was 23°C in the summer, and the lowest temperature ever registered was 16.9°C in the winter. Tese values gradually increase starting in January and take on a summer aspect by July and August. Te latitude and topographic heights, according to (Lee and Hahn) [26], play a signifcant efect in the temperature distribution, but there are also occasional values that cannot be described by the abovementioned simple criteria. In this instance, local man-made factors including groundwater pumping, surface vegetation, land use, and host rock geology could be potential drivers for the variations of temperature value. According to Table 4's analysis of the tube well pH values, W1, W2, and W3's respective mean pH values were (8.075, 7.435, and 7.3475). Tis table makes it clear that the pH fuctuated from 6.9 to 8.4, which is ideal for bacteria that produce methane. Similar outcomes were discovered by Visvanathan et al. [27], who discovered that ground water (tube well) samples had a slightly high pH and stayed in the range of 7.0-8.0 throughout the operations, indicating the brief acidic phase and early methanogenic phase. Te analysis revealed that the conductivity (EC) of the three monitored wells under investigation (W1, W2, and W3) recorded high values with means of (943.3594, 823.8281, and 674.2188) μS·cm −1 and a maximum value of 1078.125 μS·cm −1 detected in one of them.
Each of the three water samples (W1, W2, and W3) had a total dissolved solid (TDS) value of (603.75, 527.25, and 431.5) mg·L −1 , respectively. Total dissolved solids concentrations in groundwater may increase as a result of improperly lined landflls. Te mean BOD and COD values of the three monitoring wells (W1, W2, and W3), as shown in (Table 4), were determined to be (4.27, 6.95, and 5.97) mg·L −1 and (1.270325, 2.067625, and 1.776075) mg·L −1 , respectively, in groundwater, which contains little to no organic matter. Tis proves that the groundwater around the site is not contaminated with organic material due to leachate. Hassan and Ramadan [28], has also been found this after evaluating the efects of the same sanitary leachate on groundwater and found that there was no organic contamination of piezometer wells near the landfll's active cells. Heavy metal pollution of the groundwater was examined (Cr, Mn, Ni, Cu, Fe, Co, Zn, As, Pb, Se, Cd, and Hg). All the heavy metals were discovered to be absent during the summer for all three of the monitored tube wells, and most of them were absent during the other seasons of the year, with the exception of Fe and Zn. Te antiseepage system and the permeability of the soil are the causes of this phenomenon. Terefore, if the antiseepage system was compromised, the soil's permeability and unsaturated zone made it more likely for pollutants to infltrate the groundwater, the leachate might contaminate the groundwater [30], and the Journal of Chemistry chances of contaminant of the groundwater by heavy metals is by mixing with rain water in the rainy season [31]. Te mean concentrations of Fe and Zn W1, W2, and W3 were summarized in (Table 4 and Figure 3). Te concentration of Fe (0.028723, 0.0125, and 0.00) mg·L −1 and Zn (0.105, 0.13326, and 0.057373) mg·L −1 were detected in the three tube-well samples of the study area, while the other heavy metals were not detected. Tese values are acceptable for drinking-water compared with the standard of WHO, in which the upper limit of iron presence in drinking water is (0.3 mg·L −1 ) and zinc is (3 mg·L −1 ).

Statistical Correlations.
A preliminary descriptive method to determine the degree of relationship between the variables involved is correlation analysis. Te correlation matrixes of the physicochemical properties and heavy metals of the leachate and groundwater (tube well) samples are presented in (Tables 5 and 6). It was found that some parameters had statistically signifcant correlations with one another, indicating a close relationship between these parameters. Due to the combined efects of spatial and temporal fuctuations, the correlation coefcients (r) should be taken with care. However, it is simple to infer certain correlations. For the leachate's samples (Table 5), BOD 5 had a positive correlation with each of (COD, Cl − , NO 3 − , SO 4 2− , PO 4 3− , Na, K, Cr, Ni, Cu, Co, Zn, As, Pb, and Se) with positive correlations of (r > 0.9). Also, for groundwater (tube well) samples, since little to no organic matter was found in the groundwater, as revealed by the analysis, BOD 5 and COD had a positive connection, at the same time BOD 5 had a positive correlation with each of (NO 3 − , SO 4 2− , Ca, Mg, Na, K, and Fe) ( Table 6). Temperature and (TH, Ca, Mg, Mn, and Fe) also showed a good correlation (r) value of (0.83419, 0.88167, 0.98512, 0.95012, and 0.9208), respectively, and moderately correlations with (EC, TDS, and TA) with (r) value of (0.64902, 0.65092, and 0.69027), as shown in (Table 5). Te statistical correlation matrix for the three wells (Table 6) represented that the temperature and (SO 4 2− , Cl − , Na, Fe, and Zn) also showed a good correlations (r) value of (0.93752, 0.70613, 1.00, 0.9865, and 00.84892), respectively, also the temperature had a negative correlation with TH (r � −0.93906), NO 3 − (r � −0.94389), Ca (r � −0.9435), Mg (r � −0.98917), and K (r � −0.87728). Te high association between the pH of the leachate and the concentration of heavy metals is indicated by the negative correlation of pH with Mn, Fe, with r value (−0.98801 and −0.9717), respectively, and the slightly weaker negative correlation with Co (r � −0.52065). Reduced pH increases the solubility of several metals. Metals that form cations become more mobile as pH is lowered, in contrast to elements that produce anions and complexes, whose solubility decreases as pH is lowered [32]. Same thing repeated for the correlation matrix for the pH of the tube well and its association with and the concentration of (Fe and Zn), it is indicated by the good correlation of pH with Fe (r � 0.9999), and moderate correlated with Zn (r � 0.76038). Good correlations were found between Cr, Cu, Zn, As, and Pb (r > 0.9), whereas moderate correlations were found between Cr and Ni (r � 0.77137), Co (r � 0.62845), and Se (r � 0.86050). Te simultaneous accumulation of Cr, Cu, Zn, As, and Pb is a common occurrence at smelting sites and is caused by the elements' or compounds' shared chemical environment or absorptive pathways [33].
All the parameters in Table 5 exhibit high correlations, and some of the parameters in Table 6 also exhibit high correlations. Te three Tanjaro dumpsites' waste compositions appear to be comparable based on the signifcant connection between the leachate parameters in all three leachates. A preliminary indication that the particle size of waste, degree of compaction of waste, hydrology of the dumpsites, moisture content, and accessible oxygen in the Tanjaro dumpsite are also similar is provided by the signifcant connection between the leachate parameters in the Tanjaro dumpsites. Similar results indicating a substantial association was shown by leachate parameters from the dumpsites were shown by (Salami and Susu) [34]. Te leachate characteristics of the Tanjaro dumpsites show a strong association, which suggests that the existing approach of mixing garbage in the dumpsite is inefective. Wastes from the domestic, municipal, medical, hazardous, and industrial sectors should be separated into their own categories.

Conclusion
In this study, the main environmental issue is the physicochemical characterization and evaluation of seasonal variations of leachate of Tanjaro open dumpsite of Sulaymaniyah city, and its efect on the groundwater quality. High levels of organic and inorganic compounds, as well as their toxicity due to the presence of heavy metal concentrations, were the main characteristics of the leachates. Te leachate from the Tanjaro dumping area has extraordinarily high values for nearly all the physicochemical parameters. All heavy metals, with the exception of cadmium and mercury, were found in leachate at concentrations below their respective acceptable limits. Te characterization showed that the age of L1 can be referred to young, but the pH value of both L2 and L3 were referred to old leachate. According to the study's fndings, the Tanjaro dumpsites are currently functioning and in the initial stabilization process. Te leachate had a high degree of anaerobic phase biodegradability (BOD 5 /COD is about 0.63) and was highly biodegradable. Monitoring wells near the dumpsites showed that the groundwater was not severely contaminated, due to time required for migrations of H.M through soil profle till reaching groundwater which contains little to no organic matter. Whereas some parameters exceeded the WHO standards, in which the (conductivity, total dissolved solids, total hardness, Zn, and Fe) were some of these characteristics.

Recommendations.
Tanjaro dump area is an unengineered landfll. When considering remediation measures, the landfll site should be taken into account. Since it takes approximately 500 years for plastic bags and polythene to completely degrade, they should be strictly separated before MSW is dumped [35]. Composting and anaerobic digestion are the preferred methods for processing biodegradable trash, with landflling only being used for nonbiodegradable, inert, or garbage that cannot be recycled. Industrial and biomedical wastes must not be combined with MSW. Municipalities must upgrade their MSW storage facilities to protect residents who live close to open dump area, which lead to unclean and unhealthy conditions in the neighborhood. After closure, parks may be built on a landfll [31]. Te fndings of the current study therefore call for the Sulaymaniyah Municipality Directorate to implement adequate solid waste management in Tanjaro open dump area as a long-term policy, and the groundwater in and surrounding Tanjaro's open dumpsite has to be continuously monitored.

Data Availability
Te authors confrm that the data supporting the fndings of this study are available within the article.