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Clayton Group Services Standard Operating Procedures SOP -7 - Groundwater Sampling • Sample shipment to the laboratory; • Sample documentation and chain -of -custody requirements; • Sample analytical requirements; and, • Regulatory agency/reporting requirements. 2. Detection of Organic Vapors Page 2 Although commonly a neglected concern, the breathing zone in and around the groundwater monitoring well should be checked for organic vapors to protect the health and safety of field personnel. This commonly is done using an organic vapor analyzer such as a photoionization detector (PID) and/or a combustible gas meter. 3. Measurement of Static Water Level Prior to flushing the well, water level should be measured to determine horizontal and vertical flow gradients, the volume of water in the well and to provide a check of the integrity of the well. An electric depth -sounding device is recommended, and measurements should include depth to water and total well depth. Measurements should be taken prior to flushing and again prior to taking the water sample using a tape calibrated to 0.01 foot. Measurements are referenced to a fixed mark at the top of the well casing which has an elevation surveyed, commonly by a licensed surveyor. The tape should be decontaminated after use. 4. Detection of Non -Aqueous Phase Liquids If light organic liquids are floating or dense organic liquids are at the bottom of the aquifer as a distinct phase, samples collected from the well may contain a mixture of these layers and not be representative of the contaminant layer or the bulk of the water. Therefore, the presence and thickness of these layers, if present, should be determined using an organic liquid -water interface probe. If present, devices exist to sample each phase individually. 5. Well Flushing Although there is a debate as to the advisability of well flushing or purging and its effect, if any, on obtaining representative water samples, well flushing or purging prior to sampling currently is the standard procedure. Three approaches to purging and the amount of water to be purged are followed: the first advocates that a given number of well volumes should be removed; the second approach removes groundwater until certain field measurements have stabilized (pH, temperature, conductivity, turbidity); whereas, the third approach advocates that the amount of purged water is based on the hydraulic performance of the well. The easiest and most commonly used approach is to withdraw a certain number of well volumes, generally three (3) to five (5) and/or continue to remove water until pH, Conductivity, and temperature have stabilized. Commonly agencies require reaching a turbidity level of either 5 or 10 NTUs, although in many aquifers this S:Tnm'ProjAS0PS\S0P-7.doc