Investigation, technical methods and quality control
***47 research projects, including 16 key research projects: copper, palladium, zinc, cadmium, chromium, nickel, mercury, arsenic, total iron, iron, manganese, cobalt, vanadium, molybdenum, selenium and fluorine; General research project 3 1: temperature, pH, Eh, conductivity, DO, COD, total hardness, total salinity, K+, Na+, Ca2+, Mg2+, Cl-,,,,,, b, Br-, I-, H2SiO3, Li, Sr, etc.
I. Division of groundwater environmental units
The chemical composition of groundwater has its specific distribution and change law in a certain space and time, and the series of chemical composition of groundwater in hydrogeochemical units with the same environment should have the same overall distribution. The essence of classified random sampling is the combination of scientific grouping and sampling principle, that is, the background value is determined by dividing environmental units and randomly arranging points in the units according to a certain statistical model.
Figure 6-2 Survey Procedure and Quality Control System Diagram
The division of environmental units is based on the overall consistency of hydrogeochemistry, and the primary and secondary factors affecting the chemical composition of groundwater are comprehensively considered. Most of this area is located in the mainstream facies belt in the middle and upper reaches of the Yellow River alluvial plain, and there are ancient Yellow River alluvial plain and small area of Shuanghe alluvial plain in the west of Weishi County. The chemical composition of groundwater is mainly related to water-bearing medium, hydrodynamic conditions, redox environment and topography. Therefore, the shallow groundwater in this area is divided into four environmental units, the middle-deep groundwater into two environmental units, and the deep groundwater (300 ~ 600 meters) into 1 environmental unit. The specific division is as follows (Figure 6-3).
Figure 6-3 Division Diagram of Environmental Units
I 1: shallow freshwater environmental unit in alluvial plain of the Yellow River;
I2: shallow salt water environmental unit in alluvial plain of the Yellow River;
I3: environmental unit of shallow groundwater in alluvial plain of ancient Yellow River;
I4: environmental unit of shallow groundwater in Shuanghe alluvial plain;
Ⅱ1:the middle-deep groundwater environmental unit in the alluvial plain of the ancient Yellow River;
Ⅱ 2: Middle and deep groundwater environmental unit in alluvial plain of Yellow River;
Ⅲ: Environmental unit of deep groundwater in alluvial plain of Yellow River.
Among them, I 1 and I2 are the key units of this study, and II 1, II 2 and III are generally understood. See table 6- 1 for the geological environment characteristics of each environmental unit.
Table 6- 1 Summary of Geological Environment Characteristics of Water Environment Units
Second, the field investigation
(A) the preparations for the field investigation
On the basis of 65,438+200,000 hydrogeological investigation results, fully collect borehole geological and water quality data, conduct necessary site reconnaissance, fully understand the geological, geomorphological and environmental hydrogeological conditions of the work area, and understand and master the groundwater quality and environmental pollution, so as to prepare for field investigation.
First of all, the relevant drilling data are preliminarily screened indoors, and the main water outlet points are marked on the topographic map of1:50,000, and the relevant information is filled in the measuring card. The selection principle of investigation points is:
(1) The aquifer group to which the water outlet belongs is clear;
(2) The water quality conforms to the environmental geological conditions, and the content is less than 20 mg/L;
(3) The possibility of man-made pollution is small, and the distance from expressway is suitable;
(4) Considering the principle of random and uniform distribution.
Secondly, it is necessary to prepare instruments and reagents for rapid determination of total solution and site, as well as investigation supplies such as well depth and water level.
(2) survey methods and contents
Investigate through route crossing.
The investigation contents mainly include geological background, artificial environment and sampling feasibility.
1. Geological background investigation
Focus on understanding the basic situation of water points and the representativeness of water points in environmental units. To determine or verify:
(1) Basic information of water intake point: such as location, well depth, buried depth of water level, dynamic change, water output, well construction time, service life, etc.
(2) Drilling structure, mining horizon and water outlet point for exploitation and utilization.
(3) The physical properties and total dissolved solids of groundwater are measured on site to know its salinity.
(4) The topography, geomorphological features, surrounding soil and vegetation of the water intake point.
2. Man-made environmental investigation
The key point is to understand the natural degree and pollution status of water points as background points, and it is necessary to find out:
(1) Whether the surrounding environment, location and distance from residential areas are affected by factories, mines and sewage ditches.
(2) Hygienic protection status of water supply points.
(3) Determine the content on site to understand the water quality.
(4) Find out whether there is any abnormal situation or endemic disease in the history of development and utilization and in the process of use.
3. Sampling feasibility investigation
Mainly understand the traffic situation and sampling situation of the water intake point.
(3) Selection of sampling points
The selection of sampling points should be determined on the spot on the basis of the investigation of water intake points, and the number should be more than the actual sampling points. The selection principle is as follows:
(1) The staff should be familiar with the regional environmental geological conditions and implement them uniformly according to the overall design requirements.
(2) The sampling point should be selected as far as possible in the upper reaches of residential areas, and it is not allowed to be distributed in towns, factories, mines, polluted rivers and ditches.
(3) The aquifer (group) to which the water intake point belongs is clear and has a good representation in the environmental unit.
(4) Choose water intake points with good underground runoff conditions and frequently used, and don't choose wells that have been abandoned for a long time.
(5) the groundwater content is less than 20mg/L.
(6) Consider the convenience of transportation and sampling.
(7) Consider the principles of randomness and unity.
After the field investigation, the field investigation data are sorted, analyzed and calibrated to provide the basis for sampling design and sampling scheme.
Third, sampling design.
(A) the layout principle of sampling points
(1) The layout of sampling points must be representative in the environmental unit, avoiding pollution sources and polluted areas.
(2) Sampling points are randomly and uniformly arranged, and can be controlled for different environmental units at the same time.
(3) The number of sampling points should meet the requirements of mathematical statistics. For key research units with complex geological conditions and great changes in hydrochemistry, the number of sampling points should be appropriately increased.
(4) For non-key research units and target layers (middle and deep groundwater), only a certain number of control sampling points are set from the reality, and the number is determined according to the specific situation.
(5) Considering the principle of reasonable technology, economic feasibility and adapting measures to local conditions.
(2) Determination of sampling points and sampling quantity
1. Mathematical model for determining sampling number
According to the following nested analysis of variance system for sampling design:
yij = u+δyij，yij=Qi+βj+Cij
Where: yij—— the measured value of an element in the j-th unit and the i-th water point;
U-the average content of an element in groundwater;
δ yij-sampling error;
Qi- the deviation between the true value and the average value of an element;
βj- sampling system error;
Sampling accidental error.
Therefore, the total number of samples should meet the needs of controlling sampling error and analyzing systematic error and accidental error.
2. Determination of sampling points of each environmental unit
According to the sampling theory, the number of sampling units is related to the variation of the research population, the allowable limit sampling error and the reliability of sampling inference. Generally speaking, the variation degree of groundwater chemical composition is certain, and the basic sampling points required by environmental units are usually estimated by controlling sampling errors. That is, using the existing hydrochemical data, according to the allowable error statistics of some research projects with reliable analysis accuracy and great changes. The calculation formula is as follows:
When the population distribution is normal, the coefficient of variation is introduced.
therefore
Study on groundwater resources and environmental problems in Henan Province
3. Sample type and quantity
In this study, four kinds of groundwater samples were arranged: general survey samples, comparison samples, internal inspection samples and filtration test samples.
(1) Census samples: The samples collected at the same time at each sampling point are the main samples of the survey, which are representative, uniform, random and controllable. Its sample size meets the minimum number of sampling points required for environmental unit quantity statistics. According to the dynamic change law of groundwater and the experience of other regions, the general survey samples are arranged to be collected in normal water period.
(2) Control samples: duplicate samples collected in the census samples. It is collected 1 month after the general survey sample, which is used to evaluate the system error, and its number is determined according to the sampling points of environmental units.
(3) Internal inspection samples: quality control samples collected at the same time with all kinds of samples are used to check accidental errors in sampling and testing, and the number is 5% of the general survey samples.
(4) Filter test samples: test samples arranged to know the existing state of groundwater substances under different environmental conditions.
4. Other samples
In order to understand and study the relationship between the formation of groundwater environmental background value and other environmental factors, a certain number of surface water samples, soil samples and grain samples were arranged appropriately. See Table 6-2 for the sample types and quantities of each environmental unit.
Table 6-2 List of Sample Types and Quantity of Environmental Units
Fourth, sample collection.
Sample collection is one of the key links in environmental background value investigation. In addition to strictly implementing the relevant groundwater sampling regulations, practical quality control measures have been specially formulated to meet the requirements of environmental background value investigation and ensure the sampling quality.
(1) sampling preparation
The sample containers are (1) high-pressure low-density polyethylene plastic barrels with uniform materials and good chemical stability and hard frosted glass bottles.
(2) All sample containers are cleaned in the laboratory. After passing the inspection, put it in a clean plastic bag and seal it for later use.
(3) Prepare items needed for sampling, such as protective agent, sampling supplies, sealed paraffin gauze, plastic bags, packaging boxes, sampling record cards, etc.
(4) Specially equipped with a portable water pump and two trolleys to ensure continuous and smooth sampling.
(5) All sampling personnel have received necessary training and are familiar with sampling procedures and technical requirements.
(2) Collection of groundwater samples
1. Water source pretreatment
Its purpose is to pump out the accumulated water in the well and ensure the consistency of sampling conditions. Generally, pump wells pump water for 30 minutes, pump water by hand 10 minutes, and then take samples after fresh groundwater flows out. If the well is pumping water continuously, it can be sampled directly.
2. Sample collection and preservation
Before sampling, sample containers and sampling tools should be washed with raw water for 3 to 5 times. When sampling, it is usually taken directly from the water outlet with a container, and the protective agent is added on site, and the site number is given and the sample delivery form is filled in. See Table 6-3 for the collection quantity and preservation conditions of census samples.
Table 6-3 List of Collection Quantity and Preservation Conditions of Census Samples
3. Sample transportation and inspection
Samples of 1 batch shall be collected every two days, and sent to the laboratory by special car within 48 hours, with special circumstances not exceeding 72 hours. The laboratory shall designate a special person to receive the samples, go through the inspection procedures carefully, and notify the unqualified samples to be replenished in time.
4. Quality assurance measures in sampling process
(1) Sampling personnel are responsible for the division of labor and are familiar with the technical requirements of sampling. Designate professionals to add protective agents.
(2) In the process of sampling, if the water point shows signs of pollution or cannot be sampled for other reasons, the sampling point should be replaced according to relevant principles and the site should be located nearby.
(3) For individual wells that have not been used for a long time, the pumping time should be extended until the sampling requirements are met.
(4) Equipped with special water pump to unify sampling conditions. Do not extract directly from the well.
(5) When sampling, pay attention to the influence of weather change and surrounding environment, and take necessary protective measures.
(6) In the process of sampling, prevent the sampling supplies and sample containers from being polluted, and handle the problems in time when found.
(7) Smoking and make-up are prohibited during sampling.
(8) Fill in the sampling card carefully to prevent the samples from being confused.
(3) Collection of other samples
1. Surface water samples
The collection requirements and steps are similar to those of groundwater, and the sampling depth is controlled below 0.5m.
2. Soil samples
When collecting, peel off the topsoil first, and then collect according to the depth requirements. Two groups were collected for each sample, with depths of 0. 1 ~ 0.3m and 0.4~0.6m respectively. Bamboo utensils are used for collection, and ironware is prohibited. After collection, put it into a polyethylene plastic bag, seal it and put it into a cloth bag.
3. Food samples
At the soil sample collection place, 2.5 kilograms of dry samples of wheat particles were collected that year.
Verb (abbreviation of verb) data processing
Data processing is to test and calculate a large number of analytical data and correctly determine the background value of groundwater environment. Except for some data preprocessing, the whole data processing is completed on the computer, forming a processing system from original data input, editing and stereotypes, database establishment, statistical test calculation to result output.
(A) data preprocessing and quality inspection
1. Determination of pollution point
This area is an agricultural area, and the content is the main indicator of whether the groundwater is polluted. When the local groundwater content is more than 20mg/l, it is regarded as an obviously polluted water intake point. In statistical calculation, trace elements can participate in statistics, and constant components can be eliminated.
Table 6-4 lists the content distribution of shallow groundwater. As can be seen from the table, most sampling points are less than 5mg/l, that is to say, most shallow groundwater in this area is basically unpolluted, and this sampling survey point is representative.
Table 6-4 Distribution Statistics of Shallow Groundwater Content
2. Data selection
According to the following principles, the analysis data are processed and selected:
(1) Take the analysis data of census samples taken in the same period as one-time data to participate in background value statistics.
(2) Analyze the variance of analysis data for many times in the same period. If the error is not large, determine one as the use value or take its average value. If the error is large, the use value should be determined after analyzing the reasons.
3. Treatment of element content lower than the detection limit
(1) citation rate is less than 50%, and the minimum value of elements is taken as the background feature value;
(2) When the reporting rate is 50% ~ 80%, the median value of this book is sampled as the background characteristic value;
(3) When the quotation rate is 80% ~ 100%, take 0.7 times of the minimum value of elements to participate in background statistics;
(4) When the macro component is detected as 0, press "0".
4. Data availability testing
According to the results of comparative sample analysis, the data are analyzed by two-factor analysis of variance, and the test results are shown in Table 6-5. As can be seen from the table, the systematic error of the test data is even small, and the F test shows that most of the data are highly available, and the error change has little influence on the true value of the element, which can meet the statistical requirements of the background value. If there is a big error in individual elements, find out the reasons and use them after proper handling.
Table 6-5 Statistical Table of Difference Analysis Results
(B) the establishment of a database
According to the requirements of the project and the investigation results, the database of basic situation of sampling points, the database of original analysis data and the database of environmental background characteristic values are established, which are independent and interrelated, providing convenient conditions for data analysis, calculation and query.
1. Basic information database of sampling points
The database mainly includes basic information of sampling points, such as quantity, groundwater type of environmental unit, geographical location, well depth, water level buried depth, etc.
2. The original analysis data database
The database is an important achievement of this survey, which contains the measured contents of 46 chemical components of groundwater in various fields, units and water intake points, and more than 4,500 data. Each sample point is regarded as a record, and the corresponding classification code is determined to realize multi-directional sorting.
3. Groundwater environment background eigenvalue database
The database reflects the characteristic values of groundwater environment background in this area, including distribution types, concentration values, arithmetic mean, standard deviation, coefficient of variation, geometric mean, geometric standard deviation, geometric coefficient of variation, median, median, mode, background interval and content range of 46 elements in groundwater in 7 groundwater environment units, which is a comprehensive reflection of research results.
The database is programmed with DBASⅲ Ⅲ data management system and BASIC language, which has the characteristics of high speed and easy operation. Equipped with data retrieval, summary, printing, display and other functions, the corresponding text file has been established. The whole database information is stored on 360K B floppy disk, which provides a quick and convenient condition for the query, calculation and use of groundwater environmental background value.
(3) Inspection of outliers and distribution types
1. outlier test
Although various control measures have been taken in the process of distribution, sampling and testing, individual analysis data may still be abnormal due to human or natural factors. There are two kinds of data anomalies, one is hydrogeochemical anomalies, that is, objective existence; The other is caused by accidental factors such as human activities. The former is reserved and does not participate in statistics, showing high or low content. The latter was eliminated.
GUBBS method, T-M method and DIXON method are used to test outliers, and GUBBS method is the main method. Generally, α = 0.0 1 is taken to determine the abnormal value. The removal of abnormal values should fully consider the environmental geological conditions, and be cautious whether it is retained or removed, with the principle of less removal.
2. Distribution type test
The following methods are used in this distributed test:
(1)Visetivs confidence band method: It is suitable for samples with capacity of 10 ~ 30. This method has high accuracy and is the main testing method.
(2)W test method: the applicable sample size is 10 ~ 50, which is also the main test method.
(3) skewness and kurtosis method: it is suitable for samples with capacity greater than 10.
④ Kolmogorov. Smirnoff method: It is suitable for samples with capacity greater than 10. This method has a large tolerance.
(5)x2 test method: it is suitable for samples with capacity greater than 50.
The significance level of distribution test is α = 0.05. More than two methods are used when determining the distribution type. N< is at 10, and the distribution type is not tested.
3. Calculation of background eigenvalue
In order to fully reflect the characteristics of environmental background values, * * * calculated the statistical characteristic values such as arithmetic mean, arithmetic standard deviation, coefficient of variation, geometric standard deviation, geometric mean, geometric coefficient of variation, logarithmic mean, parameter standard deviation, logarithmic coefficient of variation, median, mode and percentile.
Six, the determination of groundwater environmental background value
(a) Division of statistical units
Taking the groundwater environmental unit as the basic statistical unit, the groundwater background values of each environmental unit are calculated and determined respectively. On this basis, each shallow groundwater environmental unit is regarded as an overall statistical unit, and the global environmental background value of shallow groundwater is determined. Taking the middle-deep groundwater as the overall statistical unit, the global environmental background value of the middle-deep groundwater is determined.
(B) the determination of environmental background characteristic values
Different statistical samples and distribution types are represented by different characteristic parameters.
(1) When the statistical items are normally distributed, the arithmetic mean (x) and standard deviation (s) are used to reflect the background characteristic parameters of the population, the arithmetic mean is used to represent the concentrated value of the statistical objects, and x α s is used to represent the background grading value.
(2) When the statistical object is lognormal distribution, the geometric mean (X N) and geometric standard deviation (Sn) are used to reflect the background characteristic parameters of the population, the geometric mean is used to represent the concentrated value of the statistical object, and X N× Sn α or X N÷Snα is used to represent the background grading value.
(3) When the statistical items are skewed, the median (Me) is used to represent the concentrated value of the statistical object, and the percentile (Pp) under a certain sample probability is used to represent the background grading value.
(4) When the sample number of the statistical object is less than 10, the median is used to represent its centralized value.
(c) Division of background intervals
In order to reflect the global distribution characteristics of each element, the background interval is divided into five levels: high background, high background, background, low background and low background. The background is a 95% confidence limit. The content outside the background interval is high or low. See Table 6-6 for background grading values, and Figure 6-4 for sample probability values of each background level.
Table 6-6 Table for Dividing Background Interval of Elements