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Effect of Screening and Pumping Rate on Measured Concentrations in a Heterogeneous Aquifer

1 Effect of Screening and Pumping Rate on Measured Concentrations in a Heterogeneous Aquifer [Pg.156]

The concentrations measured in the plume downstream of a contaminated site are an important parameter for evaluation of the site. The concentrations of the contaminants are traditionally used as indicators for commencement of remediation or protection measures. Together with the concentrations of electron acceptors they are also indicators for degradation processes in the subsurface. However, a virtual heterogeneous aquifer will be used to investigate the changes of measured concentrations due to variation of screen emplacement in an observation well and due to different pumping rates. [Pg.156]

A vertical slice of an aquifer with a heterogeneously distributed hydraulic conductivity is simulated in a two-dimensional model (Fig. 9.1). The hydraulic conductivity of the aquifer is assumed to follow a log normal distribution with an average hydraulic conductivity of 10 = 2.5 m/s, a standard deviation of log 0.8 and a correlation coefficient of 0.15 and 0.50 in thickness and length respectively. These statistical parameters are only more or less realistic assumptions since this example is not based on a real aquifer system. [Pg.156]

Flow occurs from the left to the right side due to a gradient of 2.5 %o, simulated by two constant head boundaries. The effective porosity of 20 % is assumed to be homogeneously distributed. The dispersivity for transport calculations is small, 0.5 m in longitudinal direction and 0.005 m in the vertical direction, since heterogeneities of hydraulic conductivity are already considered. [Pg.156]

The example therefore shows that heterogeneous hydraulic conductivity has significant consequences on concentration measurements in multilevel and full-screened sampling wells the measured concentrations depend on the position of the screen, the pumping rate and the duration of pumping. Consequently, due care must be exercised in the interpretation and evaluation of measured concentrations obtained in the traditional way. [Pg.159]




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A-SCREEN

Aquifer

Concentration measurements

Concentration, measures

Effect concentration and

Effect measure

Effect of Concentration on Rate

Effect of concentration

Effect on concentration

In aquifer

In pumps

In screening

Measure of effect

Measurement, of concentration

Measuring concentrations

Measuring rate

On pump

Pump rate

Pumping rate

Pumps and Pumping

Pumps effect)

Rate concentrations

Rate heterogeneous

Rate measurement

Rate of As

Screening effect

Screening effectiveness

Screens effectiveness

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