The sampling section should have clear markers, and the sampling personnel must not change the sampling position without authorization. When sampling, Beidou or GPS positioning or fixed markers should be used to determine the sampling position to ensure the accuracy of the sampling point location.
It is recommended that items such as water temperature, pH value, dissolved oxygen, electrical conductivity, transparency and salinity be monitored on-site.
For river sections, distance meters and depth sounders can be used to measure the width and depth of the river. For lake and reservoir sites, a depth sounder can be used to measure the depth of the lake or reservoir. Then, in accordance with the requirements of HJ/T91, determine the number of vertical lines to be collected and the number of sampling points on the vertical lines, and collect water samples respectively.
When sampling, do not stir the sediment at the bottom of the water.
If the water sample contains settling solids (such as silt, etc.), they should be separated and removed.
The separation method is as follows: Shake the collected water sample well and pour it into a cylindrical glass container (such as a 1-2 L graduated cylinder). Let it stand for 30 minutes. Transfer the water sample that does not contain settling solids but contains suspended solids into the sample container and add a preservative. Except for water samples for the determination of water temperature, pH value, dissolved oxygen, electrical conductivity, total suspended solids and oil.
When determining the chemical oxygen demand, permanganate index, chlorophyll a, total nitrogen and total phosphorus of lake and reservoir water, the water sample should be left to stand for 30 minutes. Then, the water sample should be transferred by pipette or siphon. The tip of the pipette should be inserted to a position 50mm below the surface of the water sample, and then a preservative should be added for preservation.
Water samples for determining the five-day biochemical oxygen demand should be collected separately and in dry sample bottles. Before sampling, do not rinse the sample bottle with water sample. Collect the water sample in a brown glass bottle. The water sample must be filled to the brim, leaving no space at the top.
For the determination of sulfides, water samples should be collected separately. First, add an appropriate amount of zinc acetate - sodium acetate solution. Then, when the water is released to the bottleneck, add sodium hydroxide solution until a white precipitate just appears. Fill the container with the water sample, leaving no air under the bottle stopper.
When determining water samples of petroleum, they should be collected separately and dry sample bottles should be used. Before sampling, do not rinse the sample bottle with water sample. Before sampling, any possible oil film should be disrupted. Columnar water samples should be collected from the water surface to 300mm. All the collected water samples should be used for determination.
Water samples for the determination of chlorophyll a should be collected separately and in dry sample bottles. Before sampling, do not rinse the sample bottle with water sample. If the water sample contains settling solids (such as silt, etc.), let it settle in the dark with aluminum foil for 30 minutes. Take the upper layer of the water sample and transfer it to a brown hard glass bottle.
For the determination of heavy metals such as copper, lead, zinc and cadmium, as well as the monitoring items of iron and manganese at the control section for entering the sea, the collected water samples shall not undergo natural sedimentation. Instead, they shall be immediately filtered through a 0.45μm microporous filter membrane on site (except for sampling by ships where filtration conditions are not available) before collection.
Requirements for collecting bacteriological samples: When collecting samples, the sampling bottles must not be washed with the samples. The samples should be collected in sterilized sampling bottles. The sampling volume for clean water bodies shall not be less than 400mL, and for the rest of the water bodies, it shall not be less than 100mL.
When collecting surface water samples from rivers, lakes, reservoirs, etc., you can hold the lower part of the bottle and directly insert the sampling bottle with a stopper into the water, about 10 to 15cm above the water surface, with the bottle mouth facing the direction of water flow. Pull out the stopper to fill the sample into the bottle, then close the stopper and take the sampling bottle out of the water. If there is no water flow, you can hold the bottle and push it forward horizontally. The sampling volume is generally about 80% of the capacity of the sampling bottle. After the sample collection is completed, quickly wrap it with sterile wrapping paper.
When collecting surface water, wastewater samples and samples from a certain depth, sterilized dedicated sampling devices can also be used for sampling.
When collecting volatile organic compound samples, it is not advisable to use water samples for rinsing. The water samples should be allowed to overflow in the sample bottles without leaving any space. During sampling, efforts should be made to avoid or minimize the exposure of the samples to the air. All samples were collected as parallel double samples.
When sampling by vessel, the sampling vessel should be located downstream and sampling should be conducted against the current to avoid stirring the sediment at the bottom and causing water sample contamination. Sampling personnel should take samples at the front of the ship and keep the sampler as far away from the hull as possible.
When conducting stratified sampling at the same sampling point, it should be carried out from top to bottom to avoid interference between different levels of water bodies.
When measuring items such as dissolved oxygen, five-day biochemical oxygen demand and organic pollutants, the water sample must be filled to the full container to avoid aeration of the water sample or the presence of air bubbles in the bottle.
For the determination of oil content, five-day biochemical oxygen demand, dissolved oxygen, sulfide, residual chlorine, fecal coliform bacteria, suspended solids, radioactivity and other items, separate sampling should be conducted. At the same sampling point, water samples for bacterial monitoring items should be collected preferentially.
When on-site measuring the pH value and dissolved oxygen of lake or reservoir water, the depth of the measured water, the measurement time, water temperature and weather conditions, etc. should be recorded to explain possible abnormal situations of pH value and dissolved oxygen.
Water samples were collected from the monitoring sections affected by tides at both the ebb and ebb tide levels. To ensure the safety of sampling, it is generally advisable to complete the sampling at the time of high and low tide during the day based on the changes in the tide. Ebb tide water samples should be collected when the water level at the cross-section rises, and ebb tide water samples should be collected when the water level recedes.
For each batch of water samples, some items should be selected for on-site blank sampling and sent to the laboratory for analysis together with the samples.
When sampling, please fill in the "Water Quality Sampling Record Form" carefully and record it on the spot with a signature pen. The handwriting should be neat and clear. The project is complete.
Before the sampling is completed, the sampling plan, records and water samples should be checked. If there are any errors or omissions, supplementary sampling or re-sampling should be carried out immediately.
If the water body at the sampling site is very uneven and representative samples cannot be collected, the unevenness and the actual sampling situation should be recorded in detail for the reference of those using the data.