You\'ve been hired as a hydrogeologist to determine the transport of a contamina

Question

You've been hired as a hydrogeologist to determine the transport of a contamination plume at a local site. Three monitoring wells are installed at this site, which is underlain by a sandy unconfined aquifer. During the installation of the wells, soil samples were analyzed in permeameters for K and also for bulk density; these data are given in Table 2. Water levels at the monitoring wells were measured and given in Table 1. Your job is to estimate the porosity of the aquifer, estimate the hydraulic conductivity, find the hydraulic gradient, and then finally, estimate how far the advective front (v*t) has traveled and its coordinate location assuming the contaminant source is at the location of well A and that the contamination began 16 years ago Well field data. Geotechnical test results on an unsaturated sample: Dry bulk density: 1.70 g/cm^3 Density of solids: 2.65 g/cm^3 Constant head permeameter test: Core length: 15.24 cm Core diameter: 5 cm

Explanation / Answer

a)

Porosity = (1-(db/ds) x 100 = 1-(1.70/2.65)

           = 0.358

b) Hydraulic conductivity = (Q/A)*dl/dh

     K1 = (0.0258/(pi*5^2/4))*15.24/2

       =0.01001 cm/s

K2 = (0.064/(pi*5^2/4))*15.24/5

       = 0.00993 cm/s

K3 = (0.103/(pi*5^2/4))*15.24/8

       = 0.00999 cm/s

K = (K1+K2+K3)/3

= 0.01 cm/s

c) Hydraullic gradient = i1 = dh/dl = 2cm/15.24 cm= 0.131

    Hydraullic gradient = i2 = dh/dl = 5cm/15.24 cm= 0.328

    Hydraullic gradient = i3 = dh/dl = 8cm/15.24 cm= 0.525

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