I would suggest to read this publication to get an idea

https://www.researchgate.net/publication/329283730_Development_of_a_UAV-mounted_system_for_remotely_collecting_mine_water_samples

If you meant the method, you should add enough HNO3 to get pH

Addition of nitric acid leads to distortion of results.

You will get not the real concentrations of Chemical elements in wastewater, but the concentration in acid solution!

The best way to take surface water samples of mine tailings to determine the concentration of heavy metals is to follow the following steps:

1. Identify representative sampling locations: Start by identifying the specific areas within the mine tailings where you would like to collect surface water samples. These locations should be representative of the overall area you are studying.

2. Use clean sampling equipment: Ensure that all sampling equipment is clean and free from any contaminants or residues that could affect the accuracy of the results. Use equipment made of non-reactive materials like stainless steel or high-density polyethylene.

3. Take multiple samples: Take multiple surface water samples from each identified location to account for natural variations in the water quality. This will help in obtaining a more accurate average concentration of heavy metals.

4. Collect composite samples: To get a comprehensive picture of heavy metal concentrations, collect composite samples by combining multiple individual samples from the same location. This helps to account for any spatial variability in heavy metal distribution.

5. Follow proper sampling techniques: Collect surface water samples using a grab sampling method, which involves filling a clean sample bottle directly from the water body. Alternatively, you can use a depth-integrated sampler or integrate samples over a specific volume of water to get an average value.

6. Take precautionary measures: Take appropriate safety precautions while handling mine tailings and heavy metals. Wear protective gear such as gloves and goggles to avoid direct contact with the tailings or any harmful substances.

7. Preserve samples: To ensure that the heavy metal concentrations remain stable during transportation, add a suitable preservative to the sample bottles immediately after collection. The preservative should be specific for heavy metals to prevent any changes in their concentration.

8. Analyze samples in a certified laboratory: Send the collected surface water samples to a certified laboratory for analysis. The laboratory should have appropriate equipment and expertise to accurately measure the concentration of heavy metals in the samples.

Remember to consult with environmental experts or professionals who have experience with mine tailings sampling to ensure compliance with specific regulations and guidelines for sampling mine tailings.