Sampling is a critical step in the analysis of water and wastewater. Proper sampling techniques ensure that the collected samples are representative of the water body or wastewater stream and that the results of subsequent analyses are accurate and reliable.

Objectives of Water and Wastewater Sampling

1. Monitoring Water Quality: To assess the quality of water bodies and ensure they meet regulatory standards.
2. Identifying Pollution Sources: To pinpoint sources of contamination and evaluate the effectiveness of pollution control measures.
3. Environmental Impact Assessment: To evaluate the impact of human activities on aquatic ecosystems.
4. Compliance and Regulatory: To comply with legal and regulatory requirements for water and wastewater discharge.

Types of Water and Wastewater Sampling

1. Grab Sampling:

   • Definition: A single sample collected at a specific time and place.
   • Uses: Suitable for parameters that do not vary significantly over short periods, such as pH and temperature.

2. Composite Sampling:

   • Definition: A combination of multiple samples collected at regular intervals over a specific period.
   • Uses: Ideal for pollutants that fluctuate over time, such as biochemical oxygen demand (BOD) and total suspended solids (TSS).

3. Continuous Sampling:

   • Definition: Samples are continuously collected using automatic samplers over a period.
   • Uses: Used in industrial monitoring and where precise, continuous data is needed.

Collection Techniques

1. Surface Water Sampling:

   • Lakes and Ponds: Use a boat to access different areas; collect samples from various depths using a depth sampler.
   • Rivers and Streams: Collect samples from the middle of the stream, away from the banks, and at different depths if required.

2. Groundwater Sampling:

   • Wells: Use a bailer or a submersible pump to collect water from specific depths within the well.
   • Monitoring Wells: Purge the well (remove stagnant water) before sampling to get fresh groundwater.

3. Wastewater Sampling:

   • Effluent Discharges: Collect samples at the discharge point of the wastewater treatment plant.
   • Sewer Systems: Use manholes or sampling ports to collect samples from within the sewer system.

Collection Containers and Preservation

1. Containers:

   • Material: Use containers made of glass, plastic, or Teflon, depending on the analysis. Glass is preferred for organic compounds, while plastic is often used for inorganic analysis.
   • Size: Choose appropriate sizes based on the volume required for analysis.

2. Preservation Methods:

   • Chemical Preservation: Add preservatives to stabilize certain parameters. For example, add sulfuric acid to samples for ammonia analysis to prevent biological activity.
   • Temperature: Store samples at 4°C to slow down biological and chemical reactions.
   • Holding Times: Follow standard holding times for different parameters to ensure the integrity of the sample. For example, microbiological samples should be analyzed within 6-24 hours of collection.

Field Measurements and Documentation

1. Field Measurements:

   • Parameters: Measure parameters like pH, temperature, dissolved oxygen, and turbidity on-site as they can change rapidly after sample collection.
   • Instruments: Use portable field instruments that are calibrated regularly.

2. Documentation:

   • Chain of Custody: Maintain a chain of custody form to document the handling of samples from collection to analysis.
   • Field Notes: Record details such as the date, time, location, weather conditions, and any observations that might influence the sample quality.

Sample Storage and Transport

1. Storage Conditions:

   • Refrigeration: Store samples in a refrigerator at 4°C to minimize changes before analysis.
   • Dark Conditions: Keep samples away from light to prevent photodegradation of light-sensitive compounds.

2. Transport:

   • Coolers: Use insulated coolers with ice packs to maintain low temperatures during transport.
   • Timing: Transport samples to the laboratory as quickly as possible to meet holding time requirements.

Sampling Equipment

1. Grab Samplers: Bottles, buckets, or specialized devices like Kemmerer bottles for discrete depths.
2. Composite Samplers: Automatic samplers that can collect samples at specified intervals.
3. Submersible Pumps: For collecting groundwater samples.
4. Bailers: Cylindrical devices for collecting groundwater from wells.

Quality Assurance and Quality Control (QA/QC)

1. Blanks: Use field blanks, equipment blanks, and trip blanks to check for contamination during sampling and transport.
2. Duplicates: Collect duplicate samples to assess the precision of the sampling process.
3. Spikes: Add known amounts of analytes to samples to evaluate the accuracy of analytical methods.

Proper sampling of water and wastewater is crucial for obtaining reliable data. It involves selecting appropriate sampling techniques, containers, preservation methods, and ensuring proper documentation and transport. Adhering to QA/QC protocols helps maintain sample integrity and ensures that the results are accurate and representative of the water body or wastewater stream being studied.