Employing Geophysical Techniques to Detect and Assess Groundwater Pollution at El-Akader Landfill North Jordan

Abstract


Introduction
Groundwater is considered an essential water source in Jordan to fulfill domestic, agricultural, and industrial needs.It represents an important natural resource for people (Abed ,2022).Most Arab countries, with their vast dry areas, suffer a shortage of water resources.Jordan is among the ten least fortunate countries in terms of freshwater resources.Geophysical methods are considered essential for groundwater exploration because it enables studying physical properties of subsurface layers and their sequences and thickness.The interpretation of geophysical results yields valued information to assess groundwater situation including the depth of water table.Electrical resistivity and electromagnetic methods are globally recognized techniques usually used for water exploration (Wiederhold et al., 2021;Ghanem et al., 2021).
Water pollution has several forms: surface water, groundwater, purification, plants, air pollution, soil pollution, land cover or landfills.If a landfill is constructed on permeable layers that has shallow water table, there is a high risk of contaminating nearby aquifers unless certain engineering precautions such as work barriers and patting the ground to prevent Leachate.vertical and horizontal dispersion.For example, Rusaifeh landfill doesn't handle leachate properly, thus exposing the underneath Amman-Zerqa aquifer to potential contamination (Tadros, 2001).Similarly, El-Akader landfill, which is the focus of this paper, is situated above Yarmouk aquifer, was constricted back in the eighties of the previous century, and lacks proper leachate collection or handling.
The assessment and mitigation of water resources are the responsibility of Jordanian academic institutions, governmental authorities, as well as qualified NGOs.Therefore, This study is the first geophysical study at the vicinity of El-Akader landfill aiming to study groundwater quality in the impacted portion of Yarmouk aquifer to assess and quantify potential contamination Geophysical and geological studies are renowned techniques followed by several researchers to determine the groundwater pollution in Jordan (e.g., Al-Amoush, 1997;Abu Rajab, 2000;Al-Tarazi et al., 2006;Bardaweel, 2010).This study includes determining the depths to groundwater and water table, assessing the quality of water from the Yarmouk basin groundwater, contamination using geophysical techniques, namely electrical resistivity, and electromagnetic methods, and diagramming the flow direction and depth leachate in the study area.

The Study Area
The study area is located in the northern part of Jordan, at the boundary between Irbid and Mafraq Governorates (Fig. 1).The El-Akader dumpsite is located 27 km to the east of the city of Irbid, just at 1km of the Syrian border, Within the Yarmouk Watershed.It lies between 251° 22' E and 216° 33' N. The nearest village is about 1.58km to the southwest, called the El-Akader village.This site was chosen in 1980 because of the low population density, low land cost, and to minimize the leakage of contaminants into groundwater.Nowadays, the area near the landfill becomes populated, and the impact of the landfill on public health and the surrounding environment has been investigated (Khaldi, 2001;Abu-Rukah and Al-Kofahi, 2001).
El-Akader landfill is the second-largest dumping site in the country.It was commissioned in 1981; it has an area of 0.806km 2 .It is used to dispose of municipal solid waste and liquid industrial waste.The solid waste is landfilled in specially constructed cells, while the industrial liquid waste is discharged into unlined ponds where it is subjected to evaporation.The landfill receives the solid waste generated from 21 municipalities in northern Jordan, which comprise about 70 towns and villages.On the other hand, the primary source of industrial wastewater is from a garment olive mill, slaughterhouse, and dairy industries.In addition, the site receives dry sludge from the wastewater treatment plants in the northern region of Jordan (Qdais et al., 2010).

Geological Setting
In El-Akader landfill area, the rock units' range in age from late Cretaceous to Quaternary, the formations outcrop in the study area are Wadi Es-Sir formation (A7), Amman silicified limestone formation (B2), Muwaqqar chalk marl formation (B3), Umm Rijam chert limestone formation (B4), and Shallala (B5) formation.These units consist mainly of the carbonate rocks of the Upper Cretaceous and Tertiary and the soil and alluvial deposits of the Quaternary age.The lithological characteristics of the major rock units in the study area are listed in Table 1 and shown in Fig. 2. No clear structural features are outcropped in the study area (Abu-Rukah and Al-Kofahi, 2001).

Topography and Climate
El-Akader landfill is located above the Yarmouk Basin, forming a valuable water resource that cannot be neglected.The topography of the landfill area ranges from hilly to semi-flat, about 650 m above sea level.The site is located in a natural valley with a gradient of approximately 2% to 3 % fall from east to west, later turning towards the Northwest.The land on both sides of the river has a more than 12 % gradient.The lithological units include Quaternary alluvial deposits, Tertiary limestone, and chalky limestone (Abu-Rukah and Al-Kofahi, 2001) See (Fig. 2).
The area is characterized by semi-arid to arid areas Mediterranean climate, i.e., hot, dry summers and cool, rainy winters.The temperatures ranging from a maximum of around 40ºC in June to 4.9 º C in January of average annual precipitation are around (397.5) MCM, with a very high evaporation rate of around 85%.

Hydrogeology
Groundwater in the northeast of Jordan is divided into three aquifer complexes: shallow, middle, and deep aquifers.The upper aquifer has the Umm Rijam formation (B4).It consists mainly of limestone, chalk, chert, and marly limestone.The middle aquifer is the primary aquifer in the Yarmouk basin and in the study area, where it follows up to the Amman-Wadi Es -Sir (B2/A7) formation.It consists of limestone, chalk, chert, and dolomitic limestone and chert (Bardaweel, 2010) shown in Table 1.Eleven wells tapped this aquifer, as listed in Table 2.
The parameters of 11 wells found in the area distributed near and around the El-Akader landfill are listed in Table 2.The water table is not stable and fluctuates according to wet and dry seasons and according to the withdrawal of groundwater.Groundwater movement generally depends on the hydraulic conductivity and the hydraulic gradient, and groundwater moves from a high potential area to a lower potential.In the study area, there are many directions for groundwater movements, the main direction, namely the direction from southeast to west, and the second from east to west (after Bardaweel, 2010).

Materials and Methods
In this study, we used two geophysical methods to accomplish the purpose of the study, namely, the Transient Electromagnetic Method (TEM) and the Vertical Electrical Sounding (VES).Fig. 3 shows the flowchart of the methodology of the geophysical surveys followed in this study.
Forty-two TEM loops were performed in/and around the landfill, as shown in Fig. 4. Every loop is (50X50m), and further (6-VES) profiles were performed in this study.(VES6) is the shortest length as 2400m it was near the border, (VES3) is closest to the landfill, and (VES1) is the most extended length as 2500m.Schlumberger arrangement was followed in the implementation of the work (Fig. 4).TEM loops aimed to determine the depth to groundwater and determine the leachate distribution inside the subsurface and consider if the groundwater is polluted.Furthermore, detecting the structural fractures, mainly the faults and their effect on the leachate flow in the subsurface.Fig. 4 shows the location of these loops in and around El-Akader landfill.
The 42 TEM-loops were interpreted by using the TEM-fast48 software.To compare the results of the TEM survey, these loops were classified into six groups depending on their locations and orientation, as seen in Fig. 5 and Fig. 6a shows the geoelectrical cross-section resulting from TEM group no.1.This group is 2500 m long with East-West direction.In this section, at points 29, 30, 31, 32, 41, and 42, the resistivity values range between 1-60 ohm-m.These values are very low because these points are along the landfill.That may indicate the leachate effect that is found near the surface.On the other hand, resistivity increases as one move away from the landfill boundary.This cross-section is reached to 180-200m depth along the area (Fig. 6a).The geoelectrical cross-section resulting from TEM group no.2 (Fig. 6b) is 1500 m long that directed East-West.The values of the resistivity ranged between 1-60 ohm-m.At points 7, 8, 13, 14, and 15 (i.e., distances 600-1300m), the resistivity is very low between 1-15 ohm-m because these points pass over the landfill area.At depth 100m, there are low resistivity values at points 13, 14, and 15 that may indicate the leachate presence at this depth.The geoelectrical cross-section resulting from TEM group no.3 (Fig. 6c) is 1800 m long that directed East-Southwest.The resistivity values are ranged between 7-60 ohm-m.The resistivity values increased as a function of depth 90-100 m, and the values above 5 Ohm-m, may indicate no leachate in this section.The geoelectrical cross-section resulting from TEM group no.4 (Fig. 6d) is 1500 m long that directed North-South.The resistivity values are ranged between (1-60 ohm-m).At points 11, 12, and 13 ( the distance between 700-1350m), the values become very low because these points are passing through the landfill.That may be an indication of the leachate effect.This cross-section is reached 00-120 m depth along the area.
The geoelectrical cross-section resulting from TEM group no.5 (Fig. 6e) is 1500 m long that directed East-West.The resistivity values are ranged between 1-60 ohm-m.At points 13, 11, and 12 ( distance 600-1100m), the values become near 1 Ohm-m, because these points are passed along the landfill and may indicate the leachate effect.At other points.The resistivity is higher as one moves away from the landfill.Note that the presence of low resistivity values at depth (100m) under point 13 may indicate the presence of leachate.
Fig. 6f shows the geoelectrical cross-section resulting from TEM group no.6.This group is 2400 m long that directed East-West.The values of resistivity are range between 10-60 Ohm.m, no indication of leachate presence in this section (< 1 ohm.m).To have a clearer idea about the leachate distribution in the study area, nine geoelectrical layers were produced depending on the relationship between resistivity values and depth.These layers were selected at depths 5, 60, and 200 m (Figs 7-9), respectively.The geoelectrical layer of Fig. 7 at depth 5m shows that the leachate is concentrated at the middle of the landfill.This is the landfill's location as the value of the resistivity is less than 5 ohm-m and increases until it reaches 50 ohm-m in the westbound.In the geoelectrical layer (Fig. 8), at depth 60m the resistivity values are increased, and there are no values less than 5 ohm-m.At depth 200m there are values less than 5 ohm-m especially in the middle of the study area (Fig. 9).

Vertical Electrical Sounding (VES)
Depending on the results of the 42-TEM loops, further measurements are performed following Vertical Electric Sounding (VES).6-VES's are performed in the study area following the Schlumberger arrangement (Fig. 4).The purpose of VES is to check up the results of the TEM loop's especially concerning the depth to groundwater and detect the leachate availability as a function of depth.
The final interpretation of data from this survey revealed that, after analysis, the sounding consists of 9 electrical layers with a mean root square error (RMS) of (6.89%) (Fig. 10).From this sounding, we could determine the groundwater depth at a depth of about 300m.To cross-check the results of the VES's survey, the 6 VES's were classified into two cross-sections depending on their locations see (Fig. 11).The Geoelectrical section-1 is shown in Fig. 12a.It is composed of the sounding lines (VES-1), (VES-2), and (VES-3) and directed NW-S.From this section, lateral and vertical variations in resistivity values are apparent.The depth of groundwater is almost about 300m.There is an indication of possible inferred fault at the middle of the cross-section (Fig. 12a).(Fig. 12b) shows Geoelectrical section-2.The section is composed of the sounding points (VES-4), (VES-5), and (VES-6) and directed N-S.This section is located near the TEM geoelectrical section resulting from group no.1 (Fig. 6a).
The results of surveys of the electrical lines section-1, (VES-1), (VES-2), (VES-3) show the depth of groundwater around 300m that is confirmed from the adjacent wells (Table 2), no indication of leachate is formed in the section.The results of surveys of the electrical lines section-2, (VES-4), (VES-5), (VES-6) generally show anomaly values in comparison to section-1.Furthermore, possible inferred faults with displacement are detected (Fig. 12b).Fig. 12a.Geoelectrical section-1, directed S-NW, the above one is pseudo-section, while lower one is resistivity cross section.Fig. 12b.Geoelectrical section-2, directed N-S , the above one is pseudo-section, while lower one is resistivity cross section.

Discussions
Greater Irbid Municipality and other 70 towns and villages began using the landfill location El-Akader in 1981.This study aims to determine the impact of the landfill leachate on the groundwater in the area.The 42-TEM measured loops detect the presence of the leachate and the extent of pollution toward the groundwater as the cross-sections determine a gathering place of leachate at the center of the landfill.(Fig's 6a,6c,6f,and 7) show that the leachate is concentrated at the center of the landfill, and it flows towards the SE and SW of the landfill (Fig. 13).Similar results got from the GIS vulnerability study performed by Bardaweel (2010) and the hydrochemical investigation study performed by Majdalawi et al. (2013).The results of 42-TEM loops and their geoelectrical layer sections prove that the leachate is distributed mainly in the landfill area to 200m depth (Figs 7, 8, and 9).Majdalawi et al., (2013) confirm such results from their hydrochemical investigation of the wells around the landfill.The geoelectrical sections obtained from the analysis of the TEM's (Figs 6a -f) showed that the area from the analysis of the TEM's that the area around the landfill has higher resistivity values than the landfill area.Indication of the leachate presence is detected in the area SE of the landfill (Figs 12a and b).Furthermore, the possibility of geological structure (faults) is determined in this area.
The results of this study were compared with other studies related to the contamination of wells surrounding the landfill.According to Abu-Rukah and Al-Kofahi.2001, who estimated the various physical (pH, total hardness, electrical conductivity, and total dissolved solids) and chemical parameters (major cations (Ca +2 , Mg +2 , Na -, and K -), anions (HCO3 -1 , NO3 -2 , Cl -, and SO4 -2 ), minor ions (PO4 -3 ), and heavy metals (Pb, Fe, Mn, Cd, and Zn).They found that the water in this landfall is non-potable because most of the physical and chemical parameters examined exceed the permissible limits.Some sites are not suitable for irrigation because the conductivity is high.In addition to high concentrations of chloride, bicarbonate, and nitrate.Ultimately, all results presented show that the El-Akader dump site constitutes a severe threat to local aquifers.

Conclusions
The conclusions of this study are as follows: • The TEM and VES's geophysical methods are powerful approaches to determine groundwater pollution and detect the leachate and its flow.• The groundwater table is detected at a depth of 250-300m.
• The leachate is infiltrated to 200m deep under the landfill site.
• Some inferred faults detected at the southern part of the landfill boundary may accelerate the movement at the leachate and pollute the groundwater.• The El-Akader landfill site is the primary source of groundwater pollution in the study area.

Fig. 3 .
Fig. 3. Flow chart displays the adopted methodology used in this study

Fig. 4 .
Fig. 4. The TEM loops and VES's measured in the study area.

Fig. 5 .
Fig. 5.The cross sections for the 6 TEM groups of the study area.

Fig. 11 .
Fig. 11.The cross section of the VES's perfomed in the study area.