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Clayton Group Services Page 3 Standard Operating Procedures SOP -7 - Groundwater Sampling is not possible. The final measurement of these parameters is taken as being characteristic of the groundwater. The general appearance of the water during purging (color, turbidity, and odor) should be recorded in the field logbook. Criteria based on purge volume - This is the most commonly used purging method. Although the suggested number of well volumes of groundwater to be removed varies, generally regulatory requirements specify 3 to 5 well volumes of water or until the well goes dry, whichever occurs first. The volume of water purged to dryness from low yielding wells should be reported in the field logbook. Water generally is removed using a bailer (generally stainless-steel, acrylic, or Teflon®) or pump (gas -activated positive displacement pump or submersible pump). • Criteria based on stability of physical properties - Using these criteria, water is removed until the physical properties, generally pH, temperature, Eh, specific conductance, and turbidity (less than 10 or 5 NTUs) stabilize. • Criteria based on hydraulic and chemical characteristics - This method uses aquifer transmissivity as determined by pumping or slug/bail test and field testing of the water characteristics. Although other purging protocols exist, they generally tend to be impractical. In general, purging is conducted near the upper surface of the groundwater, taking into account water drawdown during purging. Prior to sampling, the water level should be allowed to recover to at least 80% of the initial groundwater level. All purge water should be properly contained and containers labeled pending analytical results. If water can and is disposed to the storm drainage system, a NPDES permit is required form the California Regional Water Quality Control Board. 6. Groundwater Sampling Commonly the physical properties of the groundwater (pH, temperature, conductivity, turbidity) are measured prior to sample collection by obtaining a sample of groundwater in the same manner as the groundwater samples are collected. Sampling Device - The groundwater sampling device, generally either a pump or bailer, may be the same device as used for purging, with care taken to assure decontamination prior to use or using a device specific to the sampling. Although a wide variety of sampling devices are available, most fit into one of three categories: S:\Ennr`Proj\SOPS ,SOP -7. doe