Laserfiche WebLink
' Ground Water Sampling <br /> valves located above and below the bladder Water enters the membrane through <br />' the lower check valve, compressed gas is infected into the cavity between the <br /> housing and bladder The sample is transported through the upper check valve <br /> and into the discharge line The upper check valve prevents water from reentering <br /> the bladder The process is repeated to cycle the water to the surface Bladder <br /> volumes (e g , volume per cycle) and sampler geometry can be modified to <br /> increase the sampling abilities of the pump Automated control systems are <br /> available to control gas flow rates and pressurization cycles Bladder pumps <br /> prevent contact between the gas and water sample and can be fabricated entirely <br /> of fluorocarbon resin and stainless steel A nearly continuous flow can be attained <br /> with the proper cycles Pumps of this type can be used to sample wells greater <br /> than or equal to 5 cm (2 in) in diameter(Gillham et al , 1983) Pohlmann and <br /> Hess (1988)determined that bladder pumps can be suitable for collecting ground- <br /> water samples for almost any given organic or inorganic constituent <br /> Disadvantages of bladder pumps include the large gas volumes required to actuate <br /> the pump (especially for sampling deep ground water), and potential bladder <br /> rupture <br /> If a bladder pump has been chosen as the sampling device, it should be operated <br /> at a discharge rate of 100ml/min or less when collecting samples for volatiles <br /> analysis Higher flow rates can increase the loss of volatile constituents and can <br /> cause fluctuation in pH and pH-sensitive analytes Bladder pumps should be <br /> operated in a continuous, non-pulsating manner so that they do not produce <br /> samples that are aerated in the return tube or upon discharge Once the portions <br /> of the sample reserved for the analysis of volatile components have been collected, <br /> a higher pumping rate may be used, particularly if a large sample volume will be <br /> collected The pump lines should be cleared at a low rate before collecting <br /> samples for volatiles analysis,or else the sample collected will be from when the <br /> pump was rapidly operating Running the pump at a low flow rate will take time <br /> and may deter the use of a bladder pump when the wells are deep and the lines are <br /> long <br /> Helical Rotor Electric SubmersihlePumps <br />' The helical rotor electric submersible pump consists of a sealed electric motor that <br /> powers a helical rotor The water sample is forced up a discharge line by an <br /> electrically driven rotor-stator assembly by centrifugal action Submersible pumps <br /> provide relatively high discharge rates for water withdrawal at depths beyond <br /> suction lift capabilities Pumping rates vary depending upon the size of the motor <br /> and sampling depth A submersible pump provides higher extraction rates than <br />' the majority of other methods However, considerable sample agitation in the well <br /> results from operating at high rates, and this may cause alteration of the sample <br /> chemistry In addition, high pumping rates can introduce sediments from the <br /> formation into the well that are immobile under ambient ground-water flow <br /> conditions, resulting to the collection of unrepresentative samples Further, the <br /> potential exists for the introduction of trace metals into the sample from the pump <br /> materials Steam cleaning of the unit followed by rinsing with unchlormated, <br /> 1 deiomzed water in between sampling is recommended Where the submersible <br /> . pump is used for sampling,those parts of the pump in contact with water should <br /> be constructed of stainless steel <br />' 13 <br />