Protocol for the Collection, Transfer and ANSI/AARST MW-RN 2020 Measurement of Radon in Water 5 SECTION 4.0 FIELD OPERATIONS— LOCATIONS FOR COLLECTING WATER SAMPLES 4.1 Controlled flow and controlled prevention of aeration required Because radon will readily emanate from water that is exposed to air and thereby will diminish the reliability of the result, the location for sampling waterborne radon from water piping shall include: a) A faucet or spigot that can slow the flow rate until water flows out without turbulence. Water flow when collecting the sample shall be non-turbulent and shall be at a low flow rate; and b) Removal of all aeration devices at the spigot or faucet from which the water will be obtained. 4.2 Holding tanks and prior to water treatment equipment The sample shall be taken at a collection location that is prior to water treatment equipment. This includes collecting the sample prior to auxiliary water storage units, such as a spigot or faucet located prior to a holding tank, or directly associated with the initial (upstream) pressurized holding tank assuming the tank is flushed in accordance with Section 4.3 . Exception: An indoor faucet is a suitable collection location provided it is after only basic sediment filters (no treatment or holding) and the supply water line is flushed in accordance with Section 4.4 . If the sample is collected after any water treatment equipment or water storage unit, a full description of the treatment or holding tank configuration shall be documented. Note—Often an outside faucet or drainage spigot from the initial pressurized holding tank has no aerator and is untreated. Therefore, these locations may be ideal for collection of the raw water sample. Water collected after any storage unit or treatment device is expected to incur some degree of radon loss from the water and should be avoided. 4.3 Flush holding tanks and water Lines Prior to sample collection, a complete flushing of water from holding tanks and water piping is required to obtain a water sample that is representative of the water in the ground. The criteria for determining when a sufficient volume of water has been discarded is based on either: a) A noticeable decrease in water temperature that generally agrees with estimates of time it would take to discard a sufficient volume of water; or b) Calculations for the volume of water to be discarded and then measuring the volume of water that has been discarded while flushing. 4.3.1 Water volume calculations When estimating or calculating a sufficient volume of water to be discarded, the process shall include: a) Twice the volume capacity of the holding tank(s). b) Piping from the well or other source of water to the holding tank(s); and c) Water pipes that deliver water to the spigot, faucet or other sample collection location. Note—For flushing water pipes, Equation 1 can be used to determine the minimum volume of water (V; gallons) that should be flushed (discarded) prior to sample collection. V = 7.5 p r 2 L (1) where r = the radius of the piping (ft), L = total length of the piping (ft) from bottom of well to collection point, and 7.5 is the conversion from ft 3 to gallons.