Achievements
SOIL SOLUTION SAMPLING TECHNIC AND THE APPLICATION OFSOIL SOLUTION SAMPLER AT GIVEN DEPTH IN WATER
Han Shuangping ，Jing Jihong
Institute of Hydrogeology and Environmental Geology, CAGS,
Abstract: Soil solution sampler is a kind of equipment for soil solution sampling in fieldwork, it can be used for water saturated zone sampling, also it can be used for solution sampling in unsaturated zone. The well developed equipment offered an important instrument for monitoring on soil solution componential variation and repeated soil solution sampling for laboratory and experimental ground in many research fields.
This paper described the ordinary methods of soil solution sampling namely direct soil sampling, flow automatically method and suction method, introduced the operation methods, suitable range and installation of figuline soil solution sampler. As an example of TQ-1 and TQ-2 type soil solution sampler developed by institute of hydrogeology and environmental geology CAGS, it special introduced the soil solution sampler used in fixed position sampling method with broad applicability. Besides, it introduced an extending application of figuline soil solution sampler. It is for procuring water sample at giving depth. It is suitable for componential analysis research in different layer in water.
Key worlds: water sampling, soil solution, sampler, layer sampling, fixed depth sampling
Soil solution is a kind of mixed liquid formed by the long term physics and chemic reaction of soil with moisture, atmosphere and others substance around in the environment. The analysis of soil solution is frequently needed in agrology hydrogeology botany and ecology research. The researching on soil solution often apply to thereinafter studies: The mechanism study and prevention methods on pickled soil, the research on element transference rule in unsaturated zone and underground water system, crop nutrient and assimilating in agriculture ecology, the pollution mechanism and prevention research for garbage stacking, liquid waste and pesticide effect on unsaturated zone and shallow underground water, the water quality background investigation and long term fixed position monitor work in unsaturated zone and shallow underground water. Soil solution sampling is a foundation work of soil solution research and application.
1 Methods of Soil Solution Sampling
The methods of soil solution sampling often as following：
(1)Directness soil sampling：sampling original soil sample into laboratory, separate solution from soil by the means of centrifugal method or compression method. This method disturbed hardly on sampling field, the component of soil solution and chemical balance changed easily. It is suitable for one-off sampling ,not for fixed field sampling in long term；
(2)Flow automatically method：mount solution collection devices separately by layer on fixed position ,let soil solution flow into them automatically by gravity .This method has less disturbing for sampling and you can made sampling time after time at fixed position, it is used for sampling collection on saturated and supersaturated soil solution ,but it is very difficult for sampling soil solution on unsaturated.(3)Suction method：mount porous liquid collect device in fixed position, suck soil solution by the means of pumping via pressure balance inside and outside of the collector, also This method has less disturbing for sampling and it can make sampling time after time at fixed position, it is suitable for unsaturated and saturated zone, but it is difficult to obtain soil solution sample in dry unsaturated zone.
This paper briefly introduced the soil solution sampler used in fixed position sampling which method with broad applicability, and the extending application of figuline soil solution sampler, the example is TQ-1 and TQ-2 type soil solution sampler developed by institute of hydrogeology and environmental geology CAGS.
2 Suction Method of Sampling Technology
2.1Application method
Soil solution sampler is composed of figuline head(porous cup) cavum water pipe and air suction pipe. Accessories include sample container, tri access, vacuum pump etc. The figuline head is an importance part of the sampler, the figuline is made of argil material with minuteness hole, the figuline distributed with invariableness quantitative micro holes which has less chemistry activity, when it mounted in soil, the figuline head correspond to the extending of soil medium with interspace containing structure. When the interspace of figuline head was filled with water, water and solution can flow through the figuline head wall. Commonly, As the soil has certain suction pressure(s>0), the soil solution is importable flow into sampler via figuline head wall. If we made negative pressure in the soil solution sampler and the absolute value of negative pressure is big than the soil suction pressure, the soil solution then flow into the sampler via figuline head wall tardily. The velocity of flow has relationship with the infiltration rate and the surface area of figuline head, furthermore it was restricted by water transmit rate of soil K(). The difference of water transmit rate in different soil is large, and K() is a function of soil moisture, so the amount of soil moisture has large effect to the rate of soil solution flow into the sampler. The water potential grads between inside and outside of the sampler determine the flow direction of water, it is the driving force of soil solution flow into the sampler. The soil solution stop flowing into the sampler when the inner pressure of the sampler is equal to the outer. When inner of the sampler is accumulated with some soil solution, you can pick-up the soil solution to the collector by means of under pressure or pressure or combination. See figure 1 to reference for application method.
Figure 1 Sketch map of figuline soil solution sampler
2.2 The main technical performance of TQ—1 and TQ—２types soil solution sampler
(1)Type TQ—1 soil solution sampler only can be used by negative pressure method, the ordinary operation depth between
(2)The soil solution sampler can be repeat used random or periodically, the soil solution sample can be obtained at fix position in difference time interval.
(3)The installation of soil solution sampler is quite convenient, it can be installed in straight inserting, tilted inserting or combine mode. Especially it can be installed into the soil, the sample pipe may apart from the installed sampler, so it can’t disturb soil and vegetation condition when sampling.
(4)Type TQ—1 and TQ—2 sampler has the same effect when soil moisture is high, but type TQ-2 excel TQ-1 when soil moisture is low or the sampling position is deep.
2.3 Installation mode
Different installation modes are adopted according to different sampling situation.
Straight inserting on the ground
The soil solution sampler is installed on the ground vertically, the figuline head centre located on designing sampling position, the back end of the sampler cavity come out on the ground. This mode can disturb the condition above the sample position on the ground easily, so it should be given special attention when sampling.
Hidden straight inserting
The soil solution sampler is also installed vertically, the figuline head centre located on designing sampling position, but the sampler is installed in the soil, only the water sample pipe and pump pipe lead out of the ground (or connect to observation room nearby). This mode can’t disturb the condition above the sample position on the ground.
The modes above are suitable to locale application on growth field or other experimentation.
On some occasion, such as for physics analog experimental device, underground infiltrometer barrel or other similar experimental device, mount soil solution sampler using straight installation mode can affected ground condition seriously, so tilted insert mode is suitable. Tiled inserting mode is also can be adopted when used in observation well (underground observation room) .
The soil solution sampler can be installed on underground tilted-straight inserting mode at farm experiment or other field experiment, namely tilted inserting mode is adopted on the upper part of soil section plane, straight inserting mode is adopted in the lower part of soil section plane. The sample pipe and pump pipe of the sampler can be centralized in a fix position, this is convenient for sampling operation, often used in observation well, see figure 2 for reference.
Figure2 Sketch map of underground tiled Installation and vertical installation
2.4 Installation technique
(1)Check-up
Look-over soil solution sampler carefully is necessary before installation, especially check if there is air leakage in connection parts of sampling device. Make sure airtight seal character of the system.
(2) drill
Make an installation hole before installing the soil solution sampler, the depth of the hole should suitable for figuline head centre is locating on designed sampling position. If the sampling depth is shallow or use tilted inserting mode, the diameter of the installation hole should be equal to the diameter of the figuline head.
(3) Installation
After drilling, mix the soil from the bottom of the installation hole with water compose to slurry, fill it to the bottom, then insert the soil solution sampler into designed position rapidly, make sure the figuline head contact with soil tightly, don’t pause in the inserting process, otherwise it can be fixed in intermedial position because the slurry contraction. In case of installation hole large than the figuline head, direct insert the soil solution sampler into the designed position, then fill in the gap with the soil took out before, make sure the figuline head contact with soil tightly.
2.5 Usage
(1) Vacuumize (negative pressure)
Close the release pipe of the sampler, connect pump pipe and vacuum pump (suction pump), pump the air until vacuum gage (at vacuum pump or suction pump) between -70KPa and -80KPa, then close in pump pipe, take off the vacuum pump. You can connect the sample container between the sampler and the pump when pumping.
(2)Take out the sample
The solution sample accumulated in soil solution sampler at certain time (such as 1 day) after pumping, then take out the sample into sample container use negative pressure method or positive method or the combination method according to the field condition, the sampling process is accomplished.
In ordinary the first obtained soil solution sample can’t be as formal sample, it is only for reference, because impurity was interfused in the installation process and sampling path, and the figuline has less chemical activity, a balance process is need.
The interval of sampling is subject to soil type, water content etc. Long time is needed in claypan and desiccation layer, even continuous pumping is need. Only a few minutes is needed when sampling in saturated zone.
3 The Application of Soil Solution Sampler in Fixed Depth in Water
Sometimes the study on variation of chemical components and distribution in various depth of water is need on the research of environmental science in lake, river and sea, fixed depth sampling is required. A kind of sampler which can sample difference layers water is needed for fixed depth sampling. Commonly the quantitative appropriative sampler with mechanical or electromagnetic valve control is used, the application principle is put the sampler into preconcerted depth with rope on the water, then open the valve let the water flow into the sampler, close the valve when estimated the sampler full filed of water, finally lift it up, the sample process is accomplished. Using negative pressure soil solution sampler can achieve fixed depth water sampling. The process is:
(1)Prepare a negative pressure soil solution sampler and measure its inner capacity.
(2)Prepare a rope with less pull extend distortion and its length long than sample depth such as steel wire rope, one end fixed with the sampler ,mark another position with length equal to sampling depth.
(3)Prepare a sample pipe which long than sample depth.
(4)In sample locale put the sampler to destine position slowly, first take out 3 times of sampler capacity water and discard it, the purpose is reducing the effect of infiltration of upper layer water in putting down the sampler.
(5)take out the water sample with need capacity.
Comparing with other valve controlled sampler, this method has 2 main advantages, first it need no power supply, especially suitable for the area discommodious using electricity, second the sample amount is not restricted with sampler capacity, extend sampling time or increase suction can increase sample quantity. But this method has its own restrict, according the theory, the max sample depth is about
Reference：
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