The reliability of ground water monitoring information can be assured by careful selection of sample handling and analytical procedures. Sampling mechanism selection has been studied far less than analytical methodologies (Scalf et al. 1981, Nacht 1983). This study has as its primary goal the identification of reliable sampling mechanisms for purgeable organic compounds and gas‐sensitive chemical parameters in ground water. Carefully controlled sampling experiments were run to investigate the error contributed to chemical results due to sampling mechanism alone. Fourteen commercial sampling devices in five mechanistic categories were evaluated for their performance in sample collection for solution parameters, dissolved gases and purgeable organic compounds. Systematic errors related to sampling mechanism can reduce the accuracy of monitoring data by factors of two to three times that involved in analytical procedures.
An inexpensive flow‐through cell was designed and constructed to enable the accurate measurement of redox potential (Eh), conductivity and pH from shallow monitoring wells. The cell accepts sample water from inert gas‐operated bladder pumps. The electrodes are monitored by meters mounted in a portable rugged waterproof carrying case. The cell is useful for monitoring the purging of stagnant water from the well prior to sample collection for chemical analysis, as well as to provide pH, Eh and conductivity data under conditions as close to in situ as presently practical. In conjunction with the development of the flow‐through cell and measuring system, a portable field kit was constructed and equipped to determine the alkalinity of the water via modified Gran plot titration, immediately upon sample collection.
In addition to the measurement cell system, an in‐line membrane filtration system was developed, that included valves to sequentially switch to different filter units, in case of membrane plugging.
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