Water Resources Professional Project Reports

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The purpose of this study is to determine how chemistry results vary from shallow alluvial wells during purging. We sampled seven shallow alluvial wells at four different purge volumes. Drawdown and the field parameters pH, DO, EC, ORP, and turbidity were collected to determine stabilization trends for each well. During each sampling event, water samples were collected after purging one-half, one, two, and three well bores, and later analyzed for metals (unfiltered), and major cations and anions (filtered). Drawdown and turbidity were the only field parameters measured that affected the results. LAO-0.7, MCO-5, MCO-7, and CDBO-6 each had drawdown in excess of 0.3 ft, which, in these cases, seemed either to increase turbidity readings or prevent stabilization. For five of the seven wells, chemistry analyses show the only consistent changes between samples were in Al and Fe, which followed changes in turbidity. The two exceptions were MCO-5 and CDBO-6, which had more drawdown. The major cations and anions showed little variation during purging. For the field parameters, pH and EC showed no change, while temperature, DO, and ORP were not representative of the formation water. In the end, this study suggests drawdown has the main effect on turbidity and turbidity has the main effect on sample quality. Therefore, when drawdown is minimal (around 0.3 ft), or in some cases a little more, and turbidity has stabilized, a representative sample may be collected after purging only one well bore. Otherwise, sample collection might require purging three well bores.

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Groundwater--Sampling., Water chemistry--Sampling., Groundwater--Quality--Measurement., Turbidity., Monitoring wells--New Mexico--Los Alamos National laboratory--Management.


A Professional Project Report Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Water Resources, Hydroscience Option, The University of New Mexico, Water Resources Program, Albuquerque, New Mexico, May 2003