DE10353019A1 - Process and assembly to determine the characteristics of ground water in an elongated geological filtration strata - Google Patents

Abstract

In a process to measure the presence of ground water with respect to sub-surface depth in geological strata acting as an elongated filter, water is raised to the surface by pump and sampled at the surface. A sample is taken at the sub-surface abstraction point simultaneously with the surface sample, which is directly overhead the sub-surface sampling point. Further measurements are taken along the elongated sub-surface filter strata by the same method. The measurements are made at fixed distances. The samples are also subjected to physical and chemical assay. Also claimed is a suitable sensor array.

Description

The The invention relates to a method for depth-oriented measurement in groundwater measuring points with long filter sections, in which water from the filter section of the groundwater measuring station at one Withdrawal point is pumped off, wherein parallel to the pumping a Sampling takes place. Furthermore, the invention relates to a measuring arrangement with a main pump for pumping groundwater at a take-off point from the groundwater measuring point and a sampling device for Removal of a groundwater sample.

in the Over the past 30 years, a variety of proposals for depth-oriented sampling of groundwater samples. As the best technical solution is always to be considered the establishment of groups of measuring points in which several measuring points with filter positions of short length at different depths getting produced. In many exploration cases, however, arises Desire to come from existing conventional groundwater measuring points perfect expansion covering the whole aquifer or anyway longer (over 10 m) filter section to gain depth-oriented samples for hydrochemical differentiation, especially with regard to pollutant levels to recognize.

For this purpose, only two methods have currently gained practical significance. The first method is that of sectional flow-averaged sampling known from SUKOP, MC (20001: Estimation of vertical concentration profiles from existing wells-Ground water, 38: 836-841; Westerville, OH The sampling takes place parallel to the pumping out at different depths with a scooping device or a pump of very low power from the flowing wave, see 2 ,

mit
c_i: Stoffkonzentration in der Schicht i [mg/I]
c_iw: Stoffkonzentration in der Messstelle unmittelbar oberhalb Schicht i [mg/I]
k_fi: Durchlässigkeitsbeiwert der Schicht i [m/s]
M_i: Mächtigkeit der Schicht i [m]The sample thus represents the range from the filter end to the sampling depth or when operating the main pump at the bottom of the measuring point from the filter top edge or the free water level to the sampling depth. When the permeabilities of the individual layers are measured by flowmeters or other examinations, e.g. As sieve analyzes can be estimated, the substance concentrations in the aquifer in the individual layers m can be calculated by a simple mixing approach:

With
c _i : substance concentration in the layer i [mg / I]
c _iw : substance concentration in the measuring point immediately above layer i [mg / I]
k _fi : permeability coefficient of the layer i [m / s]
M _i : thickness of the layer i [m]

For the permeability coefficients k _fi , a weighted mean value may have to be used, depending on the distance of the sampling depths. The prerequisite is that a sufficient reduction is achieved in the measuring point so that the inflow from the individual layers is directly proportional to their contribution to the transmissivity and natural potential differences may be neglected.

With increasing length The built-in track will make the vertical resolution less favorable. Therefore, it is not reliable possible, next to each other the maximum concentration of a (harmful) substance and the limit of the unloaded depth range to determine. The choice of the arrangement of the pumps takes place on the Basis of preliminary information about the depth distribution of substances. Usually in one early Phase of the exploration (risk assessment) the maximum concentrations preferably be determined exactly. This assumes that the main pump on unloaded filter end is used. If due to insufficient Preliminary information a wrong expectation regarding the Depth distribution of substances, it may be a mistake with regard to the pump arrangement, so that the entire sampling process must be repeated. This will also be necessary if to one later Timing the limit of the unloaded area are determined as accurately as possible should, especially in the planning of remedial measures. The estimate from the calculated dilution is insufficient here as a planning basis. Also, in the interpretation of the data due to inaccurate permeability coefficients locally computationally negative concentrations are determined.

The second method is separation pumping in RAPP, MC; FULDA, C .; SCHÄFER, W. & KINZELBACH, W. (1998): The dual pumping technique (DPT) for level-determined sampling in fully screened groundwater wells. Journal of hydrology, 207: 220-235; Amsterdam. In this process, two or more pumps are operated simultaneously, see 3 , Sampling takes place either from all or individual selected pumps, with the remainder only serving to discharge the unwanted water (so-called protective sampling). The depth range of the samples is determined by means of flowmeters or estimated from a permeability profile. The quality of the possible demarcation of chemical fronts and the determination of maximum concentrations depend on the selected measuring arrangement.

If the permeabilities the individual layers by flowmeters or other examinations, z. As sieve analyzes estimated can be Here, too, the substance concentrations in the aquifer can be determined in the individual layers m by simple mixing approaches determine. In practice, the use of flowmeters is during the Sampling on the one hand by the design of most measuring points (Diameter) restricted, on the other hand problematic also metrologically and hydraulically. Furthermore it is relatively expensive, since flowmeter commercially only in conjunction be available with geophysical measuring equipment.

task The invention is a method and an associated measuring arrangement for depth-oriented Indicate measurements in groundwater measuring points where the vertical Delimitation of contaminated subsurface areas is improved. Further Under certain conditions, it is intended to record a permeability profile allows become.

Is solved This object with a measuring method according to claim 1 or with a Measuring arrangement according to claim 8th.

By the respective sampling both immediately above and immediately below the trigger point of the pumpdown process is a verification the (Schad) -stoffbelastung with regard to the delivering depth range allows. Devices are to in a simplest embodiment two sampling facilities, one above and one below the Provide extraction point of the main pump. The distance should be the sampling facilities to the point of withdrawal in relation to effective filter length small be.

In Further training of the method are preferred the deduction point together with the sampling points arranged above and below at least in sections over moved the filter section area of the groundwater measuring point and measurements performed at different depth positions. With this approach will for each Sampler determines a concentration profile. By sections Measurement of the flow-averaged concentrations at each measuring point above and below the withdrawal point of the main pump is a higher Accuracy in determining the actual concentrations in achieved the individual layers. Preference is given to deduction point and sampling points at fixed intervals over the Filter range moved and measurements on a variety of associated with the known stratification along the filter section Depth positions carried out.

Possibly. can additionally at the sampling points Measurements of the physical and / or chemical properties of the Groundwater executed to get more orientation for sampling and / or additional Measure the properties of the groundwater sample directly in situ can.

Of course it is It is also conceivable that the sampling facilities by the measuring equipment for determining the physical and / or chemical properties of groundwater, in particular conductivity probes, ion-selective Electrodes or optical fibers for the fluorescence spectrometry are replaced. With such Arrangement could in the absence of samples for chemical laboratory analysis only the hydraulic permeabilities be determined. In this case, a suitable measuring device is dependent from the hydrochemical conditions select.

Basically exists the measuring arrangement of a main pump, the groundwater at a Pumped off withdrawal point from the groundwater measuring station, and one each Sampling device above and below this trigger point.

When Sampling devices are particularly suitable for sampling pumps. Here is the delivery rate the main pump is much larger than the funding rates the sampling pumps. This is an influence of the by the Main pump generated flow regime avoided by sampling, bringing the state of the art known mixing approach can be used in good approximation.

Around on the one hand, the sampling devices as close as possible to the main pump to fix and on the other hand also a fixed distance between the sampling facilities on the one hand and the withdrawal site on the other ensure form the main pump and the at least two sampling devices an interconnected sampling unit. With such Sampling unit will also handle the drilling in the groundwater measuring point simplified. An undesirable Jamming several individually guided Measuring equipment and hoses is thus largely avoided.

following becomes an embodiment of the invention with reference to the accompanying drawings described in detail.

In this shows:

1 a schematically illustrated, inventive measuring arrangement in a groundwater measuring point in cross section,

2 a first known from the prior art measuring arrangement and

3 a second known from the prior art measuring arrangement.

In 1 is a groundwater measuring point 1 and a subsection U shown in cross section. The groundwater measuring station 1 consists of a hole 10 that with a filter section 11 is provided. In the area of the filter section 11 is a plurality of layers (i = 1, ..., n) with the following specific values
k _fi as the permeability coefficient of the layer i
M _i as thickness of the layer and
c _i as the substance concentration of the layer i.

The layers i are hydraulic with the groundwater measuring point 1 over the filter section 11 connected.

Furthermore, in 1 in the hole 10 a measuring arrangement 2 presented for sampling. In the illustrated embodiment, the measuring arrangement consists of a main pump 21 and two sampling pumps 22 and 23 , All three pumps 21 . 22 and 23 are designed as underwater motor pumps. The main pump 21 has a much larger delivery rate Q than the production rates Q _P1 and Q _{P2 of} the sampling pumps 22 . 23 ,

In a further embodiment of the invention form main pump 21 and sampling pumps 22 and 23 a firmly connected sampling unit 20 , This is in the schematic representation in 1 not shown.

At every pump 21 . 22 . 23 the groundwater is sucked in directly, leaving the location of the respective pump 21 . 22 . 23 with the deduction point 210 for the main pump 21 , with the sampling point 220 above the deduction point 210 and the sampling point 230 below the deduction point 210 to match. The distance between upper and lower sampling point 220 . 230 is when using submersible motor pumps 21 . 22 . 23 about 1.0 to 1.5 m.

Of course, even with the appropriate depth of the free groundwater level in the groundwater measuring point 1 also suction pumps are used. For suction pumps, the distance between the upper and lower sampling point can be reduced to approx. 0.5 to 1 m.

All in all, it should be noted that the sampling unit should be made as compact as possible in its vertical extent in order to ensure the applicability of the computational mixing approach (see below). It should be noted, however, that the sampling pumps are kept away from the immediate hydraulic failure area of the main pump. Accordingly arise depending on the type the suction the aforementioned distances between upper and lower sampling point.

To every pump 21 . 22 . 23 is a hose or a riser 211 . 221 . 231 associated with that of the pump 21 . 22 . 23 Promotes funded groundwater to the surface and further analysis.

Below is the measuring method with reference to 1 described.

The deduction point 210 for the main pump 21 will be together with the two sampling points 220 and 230 the assigned sampling pumps 22 and 23 moved across the depth. It is assigned in different depth positions in the groundwater measuring point 1 Known layering (n-layers) in each case carried out a measurement. In 1 is the measuring arrangement 2 set in a depth position, the layer m in the filter section 11 is assigned in the underground U.

• – Die Hauptpumpe 21 wird angesteuert, so dass von der Abzugsstelle, die einer Schicht m zugeordnet ist, Grundwasser über Schlauch 211 abgepumpt wird. Die Förderung erfolgt bis zur Einstellung konstanter hydraulischer und hydrochemischer Verhältnisse.
• – Dann wird parallel zum Abpumpvorgang der Hauptpumpe 21 oberhalb und unterhalb der Abzugsstelle 210 an den Probenahmestellen 220 und 230 mit geringer Förderrate jeweils eine Probe entnommen.
• – Die Pumpvorgänge werden beendet, sobald das geförderte Volumen eine ungestörte Probe geliefert hat.

Each measurement consists of the following sequence:

• - The main pump 21 is controlled, so that from the withdrawal point, which is assigned to a layer m, groundwater via hose 211 is pumped out. The promotion takes place until the setting of constant hydraulic and hydrochemical conditions.
• - Then it becomes parallel to the pumping process of the main pump 21 above and below the deduction point 210 at the sampling points 220 and 230 each sampled at a low rate.
• - The pumping operations are stopped as soon as the pumped volume has delivered an undisturbed sample.

Now the entire measuring arrangement 2 to the next measurement depth associated with the next layer (m + 1). The above-described measurement is again carried out at this new measuring point. Accordingly, a concentration profile for the sampling above the take-off point and a further concentration profile for the sampling below the take-off point can be created from the measured values for the respective layers.

bzw.

mit
c_i: Stoffkonzentration in der Schicht i [mg/I]
c_Pi: Stoffkonzentration in der Probenahmepumpe i [mg/I]
k_fi: Durchlässigkeitsbeiwert der Schicht i [m/s]
M_i: Mächtigkeit der Schicht i [m]The concentrations of the two sampling pumps are too

respectively.

With
c _i : substance concentration in the layer i [mg / I]
c _Pi : substance concentration in the sampling pump i [mg / I]
k _fi : permeability coefficient of the layer i [m / s]
M _i : thickness of the layer i [m]

From the two concentration profiles c _P1 and c _P2 , the actual concentrations in the individual layers according to the mixing batch in GI can be determined with known permeability profile k _fi . (1) calculate. Since twice the number of measured data is available in comparison to the method of section-by-phase flow-through sampling and the "true" concentration is measured directly for the uppermost and lowermost filter sections, significantly higher accuracy is achieved overall Sampling method can also be taken directly a permeability profile, so that the interpretation is also more reliable.

mit c -: durchflussgemittelte Konzentration des Grundwasserleiters [mg/I]The concentration of the main pump is the flow-averaged concentration of the aquifer, as far as potential differences are neglected:

with c -: flow-averaged concentration of aquifer [mg / I]

at usable hydraulic conditions inside the well pipe (see below) is this concentration independently from the hanger depth the sampling unit and therefore only needs to be determined once become. Since it is good practice, when taking depth-oriented To take samples in each case also a mixed sample, thereby falls no additional Analytics. Very cheap the situation presents itself when the physically-chemical Guiding parameters, in particular the electrical conductivity, a significant variance over show the depth. In this case, directly check whether the main pump mixed in all depths in the same composition Water supplies.

mitThe mean concentration can also be calculated from the concentrations of the two depth-oriented subsamples, if the length of the sampling unit is so small that there is no significant inflow between the pumps:

With

bzw.From the mixing ratio of the concentrations and the depth of immersion of the pump, the relative permeabilities can be determined:

respectively.

With these determination equations can be equivalent to GI. (1) establish a profile of relative permeabilities. A conversion into absolute values is possible by means of an estimation of the profile permeability from a pumping test or from the steady state reduction s [m]:

Regardless of the accuracy of the single measurement, this method provides a consistent estimate of permeabilities. The mean concentration c must always be between the individual values c _P1 and c _P2 , in other words:

The inventive method The two-part flow-averaged sampling allows in at the same time the determination of maximum concentrations and the reliable demarcation of the unloaded depth range without additional examinations or arithmetical assumptions. By the possibility of identifying a Permeability profile under suitable boundary conditions, in addition to concentrations also freights are determined. The compared to other methods increased Number of samples and thus chemical investigations is by the Gain of information justified.

There unlike the methods of "separation pumping" just a powerful one Pump (submersible motor pumps preferably with a maximum external dimension of 70 mm, eg Series SQ from the company Grundfos) is used, the process is off an extension diameter of DN 115 (clear internal dimension at least 110 mm) can be used. When using suction pumps is an insert also possible with smaller nominal widths.

1

Monitoring well

10

drilling

11

filter section

2

measuring arrangement

20

sampling unit

21

main pump

210

offtake

211

Tube, rising main

22

sampling equipment

220

sampling point

221

Tube, rising main

23

sampling equipment

230

sampling point

231

Tube, rising main

U

underground

Claims (13)

Method for depth-oriented measurement in groundwater measuring points with long filter sections, in which water is pumped out of the filter section region of the groundwater measuring point at a take-off point, whereby a sampling takes place parallel to the pumping process, characterized in that substantially simultaneously at the same time each sampling at a sampling point immediately above and a sampling be carried out at a sampling point immediately below the take-off point in the filter section area. Method according to claim 1, characterized in that that the withdrawal point is arranged along with the above and below Sampling points at least in sections over the filter section area the groundwater measuring station moves and measurements at different Depth positions are performed. Method according to claim 2, characterized in that that extraction point and sampling points with mutually defined Distances over the Filter range moved and measurements on a variety of associated with the known stratification along the filter section Depth positions carried out become. Method according to claim 1, 2 or 3, characterized that at the sampling points additional measurements of the physical and / or chemical properties of the groundwater. A method according to claim 1, 2 or 3, characterized in that the concentration at both sampling points result from:

with c _i : substance concentration in the layer i [mg / l] C _Pi : substance concentration in the sampling pump i [mg / l] k _fi : permeability coefficient of the layer i [m / s] M _i : thickness of the layer i [m] and From this, the actual concentrations according to the mixture formulation for the layers m with m = 1,..., n

result. Method according to one of the preceding claims, characterized in that a relative permeability profile from the measured data from the flow-averaged concentration of the aquifer (c, [mg / I])

With

from which the relative permeabilities determine

A method according to claim 6, characterized in that calculated from the relative permeabilities with the aid of the profile permeability calculated from the measured in the groundwater measuring point steady-state reduction s [m]

the absolute permeabilities of the individual layers are determined. Measuring arrangement, in particular for carrying out the method according to one of the preceding claims, with a main pump ( 21 ) for pumping off groundwater at a withdrawal point ( 210 ) from the groundwater measuring point ( 1 ) and a sampling device ( 22 ) for withdrawing a groundwater sample, characterized in that a second sampling device ( 23 ), wherein the one sampling device immediately above and the other sampling device immediately below the trigger point ( 210 ) of the main pump ( 21 ) is arranged. Measuring arrangement according to claim 8, characterized in that the sampling device ( 22 . 23 ) is a sampling pump. Arrangement according to claim 9, characterized in that the delivery rate of the main pump ( 21 ) much larger than the delivery rates of the sampling pumps ( 22 . 23 ). Measuring arrangement according to one of claims 8 to 10, characterized in that above and below the take-off point ( 210 ) of the main pump ( 21 ) are provided similar measuring devices for determining the physical and / or chemical properties of the groundwater. Measuring arrangement according to claim 11, characterized in that that the measuring device is a conductivity probe, an ion-selective Electrode or a light guide for is fluorescence spectrometry. Measuring arrangement according to claim 8 to 12, characterized in that the main pump ( 21 ) and the two sampling facilities ( 22 . 23 ) an interconnected sampling unit ( 20 ) form.