Taking groundwater samples using monitoring well
We started the task by checking the
surroundings of the groundwater monitoring well. We noticed there was a big
hole next to the monitoring well (picture 1). It looked like rains and water
have washed off some land from there. That hole can effect to the quality of
the groundwater because water can be absorbed through the ground quicker and
that will reduce the purification result by filtering. Otherwise everything
else looked normal nearby the well. The structure of the typical groundwater
monitoring well in presented in the picture 2.
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| Picture 1 - Groundwater monitoring well. Pay attention to the big hole in the ground next to well. |
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Picture 2 - Structure of the typical
groundwater monitoring well.
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Secondly we checked the weather condition
of the moment. There was pretty, crispy and cool autumn weather in Päiväranta
23.10.2018. Weather parameters were taken from Finnish Meteorological Institute
and are shown in the table 1 below.
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| Table 1 - Morning’s weather condition from Finnish Meteorological Institute. |
We started the measuring part by measuring
the groundwater level. The initial data of the monitoring well were used in all
calculations and those specifications of the well are presented below.
- Well material: plastic
- Well diameter: 50/41 mm
- Location: 6980589.638 (xcoord)
27533434.308 (ycoord)
- Height - top of the well: 102.54 meters
(N2000)
- Height - surface of ground: 101.54 meters
(N2000)
- Height - bottom of the well: 91.45 meters
(N2000)
- Length of well screen: 5.00 meters
- Well screen slot opening size: 0.30 mm
The groundwater level was measured by using
measuring tape (picture 3). We set the measuring tape down in the well. The
apparatus in the end of the tape said “beep” when it touched the groundwater
level. Then we red the result from the tape. Height of the groundwater was
calculated by equation below.
Height
of the groundwater = Height of the monitoring well – measured height by
measuring tape
Height
of the groundwater: 102.54 – 2.46 = 100.08 meters (N2000)
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Picture 3 - Measuring
tape. In the end is the apparatus which will inform by
sound when it reaches the groundwater level.
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After
measuring the groundwater height, we took a groundwater sample by Bailer
(picture 4). Bailer is disposable water collector which is very simple and easy
to use. We had two risk factors when we took the sample. First of all we didn’t
use disposable gloves which makes a risk of contamination of the sample. And
secondly we didn’t pump the water out of the well before we took the sample.
The sample was collected into plastic bottle and we marked time, group name and
place in the bottle.
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Picture 4 - Sample was collected by Bailer,
which is disposable sample collector. The collected sample was released into
the plastic bottle at the moment.
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Then we calculated the water volume in
monitoring well. The used equation is shown below.
- A =
πr2 * V [m3] = 3.14159 [m] * (diameter/2)2 [m]* height of waterspout [m]
-
Height of waterspout = Top of the well – Measured groundwater level – Bottom of
the well
A =
3.14159 [m] * (00.41/2)2 [m]* (100.08 – 91.45) [m]
A =
0.0113937… m3
A= 11,4 l
Then we started pumping the water off the
well. We used specific inertia pump. We measured the pumping rate by volymetric
method. We used 1 000 ml container in that measurement and we repeated the
measurement five times and calculated the average time. The one litre container
took about 15.646 seconds to fill. The average pumping rate was calculated by
dividing the one litre by 15.646 seconds. The pumping rate was 0.064 l/s which
is 3.83 l/min.
We calculated how long it takes to pump out
whole volume of the water in the well. The time was calculated by using the
equation below.
Time
= Volume (litres) / pump production (litres/min)
Time
= 11.4 / 3.83 = 2.98 min
After calculations we stopped pumping and
measured the water level. The result was 4.88 meters in the measuring tape.
Then we set the goal to 3.5 meters and calculated how much time the water takes
to rise and achieve that height. The raise of 1.38 meters took time 3 minutes
and 30 seconds. That means the water is filling the well 0.39 litres in one
minute.
Then we took another sample with Bailer. The
depth we took the sample was about 8 meters from the top of the well. The color
of the water sample was gray and it wasn’t clear water anymore (picture 5).
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Picture 5 - The water sample which was taken
after pumping.
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Finally we detected groundwater quality by using
field measurements apparatus (picture 6). We measured temperature, pH,
conductivity and dissolved oxygen. The results of measurements are shown in the
table 2 below. All the results of this task are shown in the table 3.
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Table 2 - Results of field measurements
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Picture 6 - Field measurement apparatus in
use.
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Table 3 - All the results from groundwater
sampling task
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Measuring water level using leveling instrument
Our second task were to measure water level of pond Iso-Valkeinen. We measured it with leveling instrument.Level staff was placed above manhole’s cover and the levelling instrument about 30 meters towards pond Iso-Valkeinen. Leveling instrument was balanced with help of device's two bubble levels (picture 7). With levelling instrument, we estimated height of the horizontal level in relation to device. (Picture 8 and 9)
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| Picture 7 - Levelling instrument with bubble levels. |
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| Picture 8 - Levelling instrument in action. |
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| Picture 9 - View through the levelling device. Picture from wikipedia. |
After height value was wrote down, level staff was moved closer the pond and new height value was estimated. First value (measuring backward) was added to known elevation (manhole cover) and then second value was decreased (measuring forward). Now we had measured ground level for new point which is about 60 meter closer the pond than manhole. (Picture 10)
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| Picture 10 - Basics of levelling |
This step was repeated three times until the last measurement was for water level (picture 11). This time when we measured forward, graduated staff was placed in water. This means that we needed to add value of water level which can be read directly from level staff. (picture 12)
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| Picture 11 - Final station |
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| Picture 12 - Level staff placed in water. |
Result for water level of pound Iso-Valkeinen was +98.984 meters (table 4).
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| Table 4 - Results from first measurement |
After we had completed the first measurement, we reviewed the result by measuring it in the other direction (table 5). Now the starting elevation was measured water level. There was only 1.9 cm difference between these two measurement. This little error may be caused during reading height values from level staff.
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| Table 5 - Results from second measurement |
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