Geofluids

Research Article

Palaeohydrogeology and Transport Parameters Derived from 4He and Cl Profiles in Aquitard Pore Waters in a Large Multilayer Aquifer System, Central Australia

Table 2

Solute transport model boundary conditions and scaled root mean squared error (SRMS). The model parameters determined from the aquitard core samples are bold, whereas the nonbold model parameters were allowed to vary from those calculated and estimated from the aquitard core measurements to improve model fit with measured pore water concentrations.
  (m/yr) (m/yr) (ccSTP//yrSolute (m2/yr Upper boundary Lower boundarySRMS
4He		SRMS
Cl
   
= 0 yrs > 417,000 yrs = 3000 yrs
Model 1 (diffusion only002.1 × 10−6Chloride1.9 × 10−30.1825200  21500 3738
4He1.1 × 10−20.2168.7 × 10−8  8.0 × 10−5 
Model 2 (calculated boundary conditions)4.6 × 10−52.3 × 10−52.1 × 10−6Chloride1.9 × 10−30.1825000  21500 3736
4He1.1 × 10−20.2168.7 × 10−8  8.0 × 10−5 
Model 3 (optimised boundary conditions)4.3 × 10−43.5 × 10−42.1 × 10−6Chloride7.8 × 10−40.1825000  21500 2012
4He1.2 × 10−30.2168.7 × 10−8  8.0 × 10−5 
Model 4 (model 3 - time to steady state)4.5 × 10−43.5 × 10−42.1 × 10−6Chloride7.8 × 10−40.182—21500—2012
4He1.2 × 10−30.216—8.0 × 10−5—
Model 5 (model 3 -chloride increase)4.5 × 10−43.5 × 10−42.1 × 10−6Chloride7.8 × 10−40.18221500—2010
4He1.2 × 10−30.216—8.0 × 10−5—
Model 6 (reduced concentrations)8.6 × 10−47.0 × 10−42.1 × 10−6Chloride1.9 × 10−30.1825000   1812
4He1.1 × 10−20.2168.7 × 10−8   
Model 7 (model 6 - groundwater extraction)8.6 × 10−47.0 × 10−42.1 × 10−6Chloride1.9 × 10−30.18250006390—16600610
4He1.1 × 10−20.2168.7 × 10−8——3.0 × 10−5
, so = 5.5 × 10−7 ccSTP//yr. inspection of the equations used in MT3DMS [24, 51], and the steady state solution [20, 52] reveals the effective diffusion coefficient input parameter is actually equivalent to , where . concentration units are mg/L and helium concentrations units are ccSTP/. 1 run in MT3DMS as cannot equal zero in the steady state solute transport analytical solution due to the development of the solution. initial concentration to represent possible initial conditions. reduction (freshwater flushing) to estimate minimum time required to reach steady state solute transport. chloride concentration increase (increased evapotranspiration) to give the minimum time required to match upper profile. chloride and helium concentrations in the lower boundary to give best steady state solute transport profile fit. increase in lower boundary concentrations as a result of groundwater extraction.