Samples are usually taken in pairs – influent and effluent. Paired samples must always be taken on the same day to calculate percentage reduction through the treatment process. You only have to collect an inlet sample if you need to calculate the percentage reduction compliance. Take the samples at the locations specified in your permit using automatic samplers. Inlet sample points must be representative of the sewage entering the WWTW by being upstream of any sludge returns or treatment processes. Discharge sample points must be representative of the treated sewage effluent discharge. If there are multiple outlets or other complex discharge arrangements, you may need to agree your sample point locations with the Environment Agency before they can be specified in your permit. There may be combined sample points before pipes split, or each outlet may be sampled separately with mass balance calculations used to determine overall compliance. Samples are taken as 24-hour composite samples so the sample point must allow a representative mixed sample to be taken at all times. The sampling equipment must be MCERTS certified, with temperature control. The automatic sampler should be certified for UWWTR purposes and to an appropriate lift height. As a minimum you must follow the manufacturer’s maintenance and cleaning procedures. Store samples Refrigerate samples in automatic sampling devices, including during retention time after sampling, intermediate depot fridges and during transportation. Maintain the storage environment between 1°C and 8°C, with the average temperature over the storage period not exceeding 5°C. An organisation carrying out sampling will have appropriate procedures for demonstrating this. It’s recognised that some time may be required to bring the sample temperature to within this range. No ice should form on the sample. The temperature range is to allow for the cycling of the refrigeration devices, their opening and closing during normal operation and effects of adding a number of warm samples. For most analytical purposes, you should keep the samples at a constant temperature of not more than 5°C.