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The main tasks for this project are doing desk study and field study on groundwater level at two different locations in Belfast. The locations of the boreholes which have been chosen for this project are Lady Dixon and Orchardville which located at River Lagan. The data are collected and extracted from the well, and then it has to be analyzed and evaluated. This project has been supervised by Dr. Ulrich Ofterdinger.
Data has been gathered from different sources such as the previous researchers from Queen's University Belfast, Geological Survey of Northern Ireland (GSNI) and Northern Ireland Environmental Agency (NIEA). Based on the information gathered, the history of the area showed that there is fluctuation on the water level year by year. In the engineering field, the characteristics and behavior of the groundwater are important to know as it is needed in the planning of a construction project of a building or any structures. Groundwater is still a valuable source of water for drinking water and for everyday usage. The data are useful as it gives the properties and behavior of the aquifers of the two different locations.
Figure 1 shows where the location of the recorded data taken. The yellow mark represents the site location.
All the data have been collected and used for this report is from 7th October 2009 to 28th January 2010 which about 4 months of monitoring. The previous records are also using for comparisons. All the data on water level and barometric pressure are recorded every 30 minutes every day. From 12.00am to 11.30pm, the data are collected each day.
The groundwater of the two locations, Lady Dixon Park and Orchardville Park has been monitored for many years. For both these areas, the boreholes are installed at these locations where the water level and barometric pressure can be measured above ordinary datum.
By analyzing the given data, it can be seen that there are different types of aquifer and soil at each borehole. By identify the barometric efficiency at this borehole; it can determine whether the underground soil is permeable or impermeable.
The barometric efficiency is used to eliminate any barometric pressure present in the water levels in the well during the aquifer test. This can provide more assistance in finding out the water storage in the soil. Both wells at Lady Dixon Park and Orchardville Park were equipped with Solinst logger or barologger. Figure 2 represents how the device look likes.
Figure 2 shows the Solinst device which to measure the ground water-level and barometric-pressure.
There are several methods for calculating the barometric efficiency of groundwater. In this report, the Clark method has been used from other methods such as the graphical method, average of ratios, median ratios, and slope, to estimate the barometric efficiency. Although Clark method sometime gives overestimated values and does not give 100% accuracy but it gives consistency of value barometric efficiency, and has been used for recent day as it is simple to make use of it.
The main aims of this project is to determine the properties of the aquifer and the groundwater level at area of River Lagan in Belfast by using long-term monitoring records by the previous researchers.
There are much type of methods to determine the properties of the aquifer and the groundwater level. By analyzing the data given from the previous students, the barometric pressure and groundwater level is changing from time to time. With plotting graph with these two values against time, barometric efficiency can be made. Then the barometric efficiency will determine whether the aquifer is permeable or impermeable.
The objectives are:-
To analyze and understand the data of water level given in order to make sure that the ground is sufficiently adequate for any purposed of structures.
To determine the porosity of the aquifers by knowing the storage of water in the ground.
To describe the characteristic of the Sherwood Sandstone aquifers.
To be familiar with the soil around the location area.
To be independent and competent to handle the project well.
Manage to organize and complete the project within the time given.
Chapter 2 - Literature reviews
Background of Location
2.1.1 Lady Dixons Park Borehole
The coordinates of the borehole is 367490 Northing and 330374 Easting.
For Orchardville's well is located at 370512 Northing and 330179 Easting.
An aquifer is underground layer deposited by materials such as sand, silt, rocks, gravels and etc which saturated with water. Aquifer can also act as storage and transportation of water underground. It can be categorized into two types of aquifers which are unconfined and confined aquifer. In addition, the jointing of sandstone plays a significant role in the transport of groundwater within the aquifer (Bennett, 1976). Figure 3 shows how the layer of the aquifer look likes.
Figure 3 shows the formation of the aquifers.
2.2.1 Unconfined Aquifer
Unconfined aquifer is part of layer underground which allow water from land surface entered under the ground layer. This layer is where water table is free to change up and down, depending on the recharge or discharge rate of water.
The water recharges from downward seepage through the unsaturated zone, lateral ground water flow, or upward seepage from underlying strata.
This type of aquifer is situated between two layers of low permeability of aquifers which is known as aquitard. In confined aquifer, when the ground is under pressure, the water level in a well will rise above the upper boundary of the aquifer.
From the introduction earlier, the definition of barometric efficiency which is the ratio of changes in water level caused by a barometric-pressure to the barometric pressure changes (Clark, 1967).
α is the barometric efficiency,
ΔW is the water level change in a well
ΔB is the barometric pressure change.
An increase in water level during given time interval have a positive change and if the pressure is increase during a time interval will have negative change(less than zero) (Clark, 1967; Batu, 1998; USGS, 2007). Barometric efficiency is dimensionless and ranges from zero to one.
If the barometric pressure is increase, usually the water-level in an open well will decrease by an amount governed by the barometric efficiency (Todd, 1959; Ferris and others, 1962; Freeze and Cherry, 1979; Kruseman and de Ridder, 1991; Landmeyer, 1996; Rasmussen and Crawford; 1997; and Batu, 1998). It characterizes aquifer conï¬nement and elasticity, presence of borehole/skin eï¬€ects, and pneumatic diï¬€usivity in the unsaturated zone (Rasmussen, 1997). Therefore, barometric efficiency can estimate the storage of water and the properties of the aquifer.
Properties of Aquifer
Specific conductivity is a measurement of electric conduction in water which measure the water's ionic activity and content. It also can be used to measure water quality and indirectly test the pollutant of water in the ground. The more ions present in the water, the conductive it be. How the water underground contains conductive ions, it is because from the sea or river water flow, from rain water and sometimes rock or soil may release ions when water pass over them.
It is measured by using a sensor placed into the well, and measure the electric conductivity. But in this report, electric conductivity does not really related to barometric efficiency calculation. It is to check the quality of water in the ground whether the water is in good or bad condition. Still it is very important for the engineer to know about it.
2.4.2 Porosity of Aquifer
Porosity is the presence of voids or spaces between the soil materials underground which determines how easily water to flow through. The higher the porosity in the soil, the more permeable the aquifer and the lower the porosity, it can make the aquifer impermeable which will harden the soil on it. This porosity plays a major role on the stiffness of the soil whether a structure can build on it or not.
The changes in the volume of pore water in the soil will affect the water-level attitudes in a well that will have an opposite sense to changes in atmospheric pressure. The porosity usually depends on the grains size distribution, stuffing of grain and shape of the grains.
Unconfined aquifer and confined aquifer can be responded by the Earth tide and changes in atmospheric pressure which water will be released from or taken into storage in it by compression or expansion of aquifer skeleton and the volume of pore water (Ferris and other, 1962; Bredehoeft, 1967). This is because the aquifers are elastic (Lohman, 1979)
Equation for porosity of aquifer skeleton is related to specific storage and an elastic property of an aquifer is shown below (modified from Lohman, 1979):
Ss is the specific storage (in meter);
is the specific weight of water which equal to 9.087 KN/m;
β is compressibility of water =
θ is the porosity of aquifer skeleton (dimensionless); and
E is the elasticity of aquifer skeleton.
According to Jacob 1940, equation for specific storage is also related to barometric efficiency and porosity of aquifer skeleton:
α is the barometric efficiency (dimensionless);
γ is the specific weight of water;
β is the compressibility of water;
θ is the porosity of aquifer skeleton (dimensionless); and
Sg is the specific storage.
Factors Influencing Water-level Change
There are possible activities that can influenced the water-level change such as barometric-pressure change, recharge, seasonal or long-term trends, local or regional pumping, earth tides, ocean tides, evapotranspiration and surface-water fluctuation. These causes can be grouped into one term which is ΔWi at time intervals:
ΔWi = ΔWb+ ΔWr+ ΔWl+ ΔWp+ ΔWg+ ΔWm +ΔWe +ΔWs
ΔWb is the water-level change caused by barometric-pressure change;
ΔWr is the water-level-change caused by recharge;
ΔWl is the water-level-change caused by seasonal or long-term trends;
ΔWp is the water-level-change caused by local or regional pumping;
ΔWg is the water-level-change caused by earth tides;
ΔWm is the water-level-change caused by ocean tides;
ΔWe is the water-level-change caused by evapotranspiration and;
ΔWs is the water-level-change caused by surface-water fluctuations.
Barometric-pressure change usually effects on the water-level changed in the ground (ΔWb). Water-level changed which is caused by recharge because of rain events or snow melt (ΔWr). Seasonal or long-term trends (ΔWl) involve water-level changes for a long duration when it is greater than barometric variation. When aquifer tests and other local pumping or other regional pumping occur, it caused ground-water-level changes (ΔWp).
Due to gravitational influence from the sun and moon with the movement of sun and moon, it changes the gravitational forces on the earth which caused the water-level changes (ΔWg) (Rinehart, 1975). Water-level changes caused by ocean tides (ΔWm) can be from the compression of a confined aquifer due to the weight of ocean water during high tide (Robinson and Bell, 1971; Batu, 1998).
Effects of evatransporation causes water-level changes (ΔWe), is greatest during the warm season and normally will not have effects on the water-level changes during winter when the temperature is below freezing. Wells that have fractures directly connected to surface-bodies (include ponds and streams) may respond directly to surface-water fluctuation (ΔWs) which caused changes in ground-water-level.
There is a time lag between barometric pressure and water level which caused by skin effects (i.e. a reduction in hydraulic conductivity between borehole and undisturbed aquifers), storage of borehole, and time for the pressure wave to be transmitted through the vadose area (D.Rush, 2002). Vadose zone is the upper layer of the earth that contain a three-phase system of solid, liquid, and gaseous material which can also be called as unsaturated zone. When plotting the graph of water level against barometric pressure, a multiple linear regression should be used to estimate the barometric response function.
Table 1 represents the summary of factors that will effects the fluctuation of groundwater-level.
Table 1 shows the summary of mechanism leads to fluctuation of groundwater.
2.6 Alternative method to calculate Barometric Efficiency
2.6.1 Clark method
The outline rules to calculate barometric efficiency by using this method are:-
When ΔB is equal to zero, ignore ΔW to obtain ΣΔW,
When ΔB and ΔW have same signs, add ΔW to obtain ΣΔW,
And if ΔB and ΔW have unequal signs, then subtract ΔW to get ΣΔW.
By using Clark's method, the values of barometric efficiency can be overestimated or when the barometric pressure or water level change is instantaneous (David and Rasmussen, 1993).
The Clark method presents a sign test on ΔW compared to the sign of ΔB for each time interval;
is the continuing sum of ΔWj after the jth time interval;
is the continuing sum of ΔWj-1 after the (j-1)th interval;
is the absolute value of ΔWj;
is the continuing sum of ΔBj after the jth time interval;
is the continuing sum of ΔBj after the (j-1)th time interval; and
is the absolute value of .
Since the Clark method is depending on the sign of water-level change and barometric-pressure change, the absolute value of ΔWj and absolute value of ΔBj is introduced in this equation. At a specific time interval, ground-water-level rises whereas the barometric-pressure fall or vice versa. So if the sign of ΔWj agrees with the sign of ΔBj, then the absolute value for ΔWj will be positive. The absolute value of ΔWj will be negative if the sign of ΔWj disagrees with the sign of ΔBj (U.S. Geological Survey, 2007).
By plotting the value of on the y-axis and the values of on the x-axis, the slope of the best fit line drawn on the graph is the estimate of barometric efficiency.
2.6.2 Slope Method
This method has been introduced by Ferris and others (1962) on the slope of ΔW and ΔB with several time intervals. By plotting a graph of water-level changes at y-axis, ΔW against atmospheric pressure changes at x-axis, ΔB, and a best linear straight line is fitted to the plotted points. The slope of linear line estimates the value of barometric efficiency. According to USG-2007, the equation for estimating barometric efficiency had been modified from (Ott, 1988) is shown below.
j designates the jth time interval;
is the average water level for all time interval
is the average of barometric pressure change for all time intervals.
By plotting a graph of water level (W) on y-axis against barometric pressure (B), the barometric efficiency can be estimated using slope method (Hare and Morse, 1999; UGS, 2007). But it is recommended to use water-level change (ΔW) and barometric-pressure change (ΔB) plotting the graph rather than W and B because ΔW and ΔB is more mathematical accurate since the definition of barometric efficiency is the relationship between water-level change and barometric pressure change (ΔW/ΔB).
2.6.3 Graphical Method
Graphical method is used to estimate the barometric efficiency by using continuous water-level and barometric-pressure data from previous researcher. Continuous data present more information than discrete data to estimate barometric efficiency (USG, 2007). An Elliptical loop will be shown on the graph by using this graphical method.
At the horizontal x-axis double barometric-pressure changes ( is plotted and on the vertical y-axis is the double water-level changes. The equations below show the formula to find the and:
j is for the jth barometric-pressure or water-level loop or fluctuation
Bj1, Bj2, Bj3 and Bj4 are values of barometric-pressure at time t1, t2, t3, and t4, respectively,
Wj1, Wj2, Wj3 and Wj4 are values of water-level at time t1, t2, t3, and t4, respectively,
When all the data of water-level and barometric-pressure have convert to and, then graph of two water-level changes against two barometric-pressures can be plot. Slope of this graph represents the estimation of barometric efficiency using a graphical method.
2.6.4 Average-of-Ratios Method
By using this method, plotting the graph of water-level change against barometric efficiency is not necessary because it used the average ratios of water-level change to barometric-pressure (ΔW/ΔB) for many time intervals to estimate the value of barometric efficiency. This is the simplest mathematical method to find barometric efficiency. Equation below shows the average ratio of ΔW/ΔB:
Expressing equation above as the sum of mane (n) time intervals yields:
nα is , where each ΔWbj/ΔBj is a constant value for every time interval j.
Arrange the equation:
α is the barometric efficiency estimation.
The value of barometric efficiency is equals to the average of ΔW/ΔB minus the average values of ΔWi/ΔB. This concept is slightly similar to noise-reduction experiment which is used in reflection seismic (Yilmaz and Doherty, 1987).
The integrity of each ground-water-level records is evaluated for interference effects on water levels caused by nearby pumpage (water-level data caused by this pumpage is not used to determine the barometric efficiency) and Earth tidal influence, for wells near the coast (Landmeyer, 1996).
Pump test is also known as aquifer test and this test can determine the properties of unconfined or confined aquifer (i.e.transmissivity, conductivity, storativity and specific yield), as well as observing the aquifer response (drawdown) in observation of wells. Drawdown is the change of hydraulic head observed at a well in an aquifer. Pumping at a constant rate should be used during the test.
The result of specific yield for aquifer is not that satisfied to describe the drainage phenomena in the investigative solution used for pumping analyses (Nwankwor et al., 1984; 1992). It is a fact that the drainage process occurring during a pumping test in an unconfined aquifer is poorly understood. That is why understanding the processes at the field-scale, detailed observation of the relationship between hydraulic head and moisture content distribution during pumping tests are required (Anthony, 2004).
In pump test, there should be a recovery test which measuring the rebound of water levels towards preexisting conditions immediately after pump tests (US Army Corp, 1999). Recovery test also provide important aquifer information and usually when elastic storage effects have been dissipated, the time hydraulic head data are analyzed by this recovery test (Kruseman and de Ridder, 2000).
Chapter 3 - Methodology
From what has been given recourses from Geological Survey of Northern Ireland, they used a device called the 'Sloinst Logger' or the 'Levelogger' and barologger, so that the water level and the barometric pressure can be recorded. For water level measurement, the levelogger has been suspended by wire down the borehole beneath the water level. Manual dips have to be taken occasionally in order to calibrate the data and these water levels of course have to take into account barometric variations.
The barologgers tend to be highly similar to the logger down the well; except they are usually more sensitive devices so will pick up much smaller variations. It is suspended just at the top of the boreholes, above the water level. As a result, the barometric efficiency can be determined.
From the methods that have been mentioned in Chapter2, the Clark method is used to calculate the estimate barometric efficiency. The graph of water-level against time interval for both places, Lady Dixon and Orchardville has plotted and shown under the analysis sub-heading below.
By using the Clark Method formula given, the values of ΔW and ΔB can be calculated. Hence by plotting the ΔW on y-axis and ΔB on x-axis, the slope gradient of the graph can be calculated. Since all the points on the graph have scattered around, then the best linear line fitted through the points. This gradient of the graph is the estimate barometric efficiency; this is the main point for this project.
When the value of barometric efficiency has obtained, then the porosity of the aquifer can be calculated. By using the formula that has shown on chapter 2:
After calculating the porosity of the aquifer, then compared the values for both well. The higher the value of porosity, more permeable will be the aquifer.
As this project is a combining project with other researchers, comparing the barometric efficiency and the porosity of aquifer at each location should be done. The other researchers have monitored the water-level and barometric-pressure at Ashby and Glenburn. Barometric efficiency and porosity of the aquifer are also been calculated and then these values can be compared.
Chapter 4 - RESULT
From what info that had been given by the Geological Survey of Northern Ireland, the type of aquifer found on Ochardville Park and Lady Dixon Park is Sherwood sandstone. Below show the result of water-level and barometric-pressure of Lady Dixon Park and Ochardville that had been calculated.
Lady Dixon Park
(Water Level mH2O)
Table 2 shows the value of water-level and barometric-pressure for Lady Dixon Park from 07/10/2009 to 28/01/2010.
Figure 4 Graph of water level against barometric, in meter at borehole Lady Dixon.
From figure 4, by calculating the slope gradient of the graph, the barometric efficiency value can be obtained;
From calculation, the estimation barometric efficiency is negative 0.40 and with r2=0.0574 value from the graph.
γ = specific of water = 998.2 kg/m3
β = compressibility of water = 4.693707 x 10-9 m2/kg (Lohman, 1979)
Specific storage (Ss) values of aquifer calculated by GSNI is 1.5148 x 10-7m-1
θ = 0.0129
Porosity of aquifer at Lady Dixon is 0.0129.
Figure 5 shows a graph represents water-level against time from October-2009 to January-2010.
Full data of water-level and barometric-pressure for Lady Dixon Park which have been taken for this period of times are in Appendix A.
Figure 6 Graph of water level (red line) and barometric pressure (blue line) against times.
The great drop on the water-level is because of the pumping activity occurred during that time. Since location of Lady Dixon Park is somewhere near buildings, it is possible pump test happened. From figure 6, it shows that if an increase in water-level, the barometric-pressure decrease and vice versa.
All the recorded water-level and barometric pressure have been tabulated below and have been used for this project. These have been abstracted by Geological Survey Northern Ireland for past few months.
Baometric Pressure (mH2O))
water level (mAOD)
Table 3 shows the average of barometric-pressure and water-level for Orchardville Park from 07/10/2009 to 28/01/2010.
All the data of water-level and barometric-pressure for 2005-2007 and full data for oct2009-jan2010 have been attached at Appendix 1. At figure 6, the change of water-level against barometric-pressure change had been plotted by using the Clark method.
Figure 6 Graph of water level against barometric pressure, in meter at borehole of Orchardville.
From the graph: - (9.993, 16.553) and (10.44, 16.4) are obtained.
The value of estimation barometric efficiency is negative 0.34 and the r2 value is 0.2433.
γ = specific of water = 998.2 kg/m3
β = compressibility of water = 4.693707 x 10-9 m2/kg (Lohman, 1979)
Specific storage (Ss) values of aquifer calculated by GSNI is 1.5148 x 10-7m-1
θ = 0.0109
Porosity of aquifer at Lady Dixon is 0.0109.
Figure 7 shows a graph of water-level and barometric-pressure against times.
Chapter 5 - Conclusion
It is proved that an increase in water-level will decrease in barometric-pressure in the ground and vice versa as shown on the analysis part. From what had been given by Geological Survey of Northern Ireland, the type of aquifer at Ochardville and Lady Dixon is Sherwood Sandstone.
Properties of the aquifer and barometric efficiency of aquifer had been analyzed in chapter 4.it shows that the type of aquifer that had been found at Orchardville Park and Lady Dixon Park is Sherwood sanstone.
Chapter 6 - DISCUSSION
The Permian and Triassic sandstones offer the greatest groundwater abstraction potential throughout Northern Ireland. On figure 8 represent where the layer of Sherwood Sandstone at the River Lagan of Belfast from Geological Survey of Northern Ireland.
Figure 8 shows the diagrammatic geological cross-section of the Lagan Valley South-West of Belfast.
Analyses of the available data showed that barometric efficiency values of -0.40 at Lady Dixon and -0.34 at Orchardville and have an average of barometric efficiency of -0.37 for area around Lagan Valley aquifer.
From the figure 6, it shows that water-level changes when barometric-pressure changes at Lady Dixon Park. The water-level at this area keeps on increasing each year. The average for water-level on oct-2005 to jan-2006 is about 10.385m and for oct-2009 to jan-2010 is about 14.115m. This is because of the lake nearby and high level of ground. The water-level drops on 13th November 2009 at time 9.30a.m to 4.00p.m about 5.33mAOD but the average value for water-level for that day is at 11.68mAOD. Due to pumpage and recharge of water from lake nearby, it causes the fluctuation on the groundwater.
For Orchardville Park, the figure shows that there is no pump test occurred at that location. This was because of the residential area around it and it was difficult to pumpage the well when there are many buildings surround it. Water-level has been recorded and monitored for past few years. It shows that the water-level at Orhardville has not been many changes due to flat lands.
The groundwater level data from 2005-2007 and October 2009 to January 2001 has been gathered and have been given by Clair Burn, PhD students of Queens University of Belfast. Both the water level and barometric pressure are included in the data.
Partially analyzing the given data of Lady Dixon and Orchardville. It seems that the water level above sea level at Orchardville is slightly higher than water level at Lady Dixon.
It seems that both places have increase in water level for past few years, this is because water level of sea has increase every year.
The properties and behavior of the hydrogeology of Sherwood Sandstone aquifers are known from the information that been provided.
Finding the barometric efficiency from water level against time graph and barometric pressure against time graph.
Calculation of storage porosity of aquifer at the borehole.
The stability of the ground according on researching of barometric efficiency based on Clark Method.