Poster Presentation NCGRT/IAH Australasian Groundwater Conference 2019

Simulation of contaminant capture by an hydraulic containment system (152)

Noel Merrick 1 , Tingting Liu 1
  1. SLR, Wollongong, NSW, Australia

Objectives

Using groundwater model to assess the efficiency of the hydraulic containment system (HCS). The HCS has been designed as a pump-and-treat mechanism to contain a nitrate/sulphate plume emanating from several identified contaminant source areas.

Design and Methodology 

A 6-month (182-days, 26 stress periods) transient MODFLOW-USG model was been built with time from 22nd April 2018 to 20th October 2018, during which forward tracking has been simulated from the southern boundary of Source Zone A towards six extraction bores (EBS1, EBS2, EBS4, EBS5, EBS6 and EBS7, Figure 1) assuming a uniform effective porosity of 0.03 (3%). The assumed extraction at EBS1 follows the same pattern as EBS4. The mod-PATH3DU Version 1.1 particle tracking post-processing package, developed by S. S. Papadopulos and Associates, Inc., has been used in this study to compute and display three-dimensional pathlines based on groundwater flow outputs from MODFLOW-USG.

Original data and results 

Four particle tracking model runs results show below:

Run 1 - Source Zone A was completely captured by three extraction bores (EBS1, EBS4, EBS6) after about 30 days, 85 days and a little more than 180 days, respectively.

Run 2 - With increased extraction rates on bores EBS1 and EBS4, all particles are captured after about 25 days and 80 days, respectively, and 180 days by extraction bore EBS6.

Run 3 - has a reduced porosity of 0.02, the same extraction rates as Run 1, and an extended simulation period (182-days plus 5 years). Except for one particle missing, Source Zone A was captured by four extraction bores EBS1, EBS4, EBS6 and EBS7 after about 30 days.

Run 4 - with reduced porosity, had the same extraction rate as Run 2. Source Zone A was also fully captured.

For 3% porosity, all Source Zone A was captured, which means both rates of extraction are optimal, the rates could be reduced if the bores are maintained in more continuous operation. For 2% porosity, the capture efficiency is similar. However, there is one new escape between EBS1 and EBS4 with lower extraction rate.

Conclusion

Despite periods of borefield shutdown, it is evident that the HCS bores are capturing all of the contaminants emanating from Source Zone A.  The current average rates of extraction are close to optimal and should not be reduced much. However, the rates could be reduced if the bores are maintained in more continuous operation.