How and when was the groundwater contaminated?
What contaminants are in the groundwater?
How are the contaminants being monitored?
How much contamination is present?
How far has the contamination spread?
Is the plume expanding or contracting?
How far could the contamination spread?
How deep are the contaminants?
Why do the contaminants move downward?
Are the contaminants becoming more or less concentrated?
Is the contamination dangerous to human health or the environment?
Can the contaminated groundwater be used?

• How and when was the groundwater contaminated?

PVC has been manufactured from VCM at the Altona Plant since the early 1960s. Prior to 1981, the VCM was also made on-site from EDC. Up to 1978, the EDC was supplied mainly from the adjacent Dow Chemicals plant. There has been no EDC used on site since 1980.

The plant which converted EDC to VCM was located near the south-east corner of the site.

The process used for making VCM from EDC generated tar residues which were kept in a pit, then drums and then a tank at a "tar storage area" in the south-west corner of the site.

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• What contaminants are in the groundwater?

Contaminants include:

• compounds containing chlorine, including VCM and EDC;
• compounds commonly associated with oil products; and
• low concentrations of other compounds including phenolics and metals.

Example concentrations are shown in the table below.

See the monitoring section for the most recently reported concentrations and discussion of observed concentrations trends (changes over time).

• How much contamination is present?

Most of the contamination is immediately under the site where the contaminant concentrations can be as high as 3000 mg/L. On the basis of contaminate concentrations, the total amount of contamination present in the groundwater is estimated to be in the order of 15 to 52 tonnes.

We have not found any "pure" contaminants either floating on top of the groundwater or settled out at the bottom of the aquifer. Most of the contamination in the aquifers is dissolved in the groundwater.

For details on current contamination please refer to the monitoring section of this web site.

• How far has the contamination spread?

A contaminated groundwater plume extends to the south under the Qenos Plastics site almost reaching as far as the Melbourne-Geelong railway line.

• Is the plume expanding or contracting?

Most recent site-wide monitoring data, compared with April 1997 data, shows that the plume may be contracting and contaminant concentrations are generally either consistent with historic data or showing decreasing trends.

• How far could the contamination spread?

The overall flow of the groundwater has been calculated to be relatively slow (in the order of metres per year). The contaminants may continue to move with the groundwater and for this reason regular monitoring of groundwater movement and quality will continue.

Some naturally occurring microbes are breaking down or "eating" the contaminants at the edges of the plume where contaminant concentrations are lower. This is limiting the spread of the plume.

• How deep are the contaminants?

Contaminants have been measured in both upper and lower aquifers. Monitoring results indicate most of the contamination is still in the upper aquifer. However, there is the possibility that contaminants will continue to move downwards, travelling deeper into and through the lower aquifer.

• Why do the contaminants move downward?

Many of the chemicals in the contamination are heavier than water. These chemicals have leached through the soil, into the upper aquifer and then into the lower aquifer.

Without intervention it is reasonable to expect that the contaminants will continue to move through the upper aquifer and into the lower aquifer until an impermeable surface is reached.

• Are the contaminants becoming more or less concentrated?

All above-ground sources of contamination have been removed. This means the total mass of contamination in the ground will not increase any further and is decreasing slowly because of natural degradation. However the distribution of contaminants in the ground may change over time.

Any contamination still present in the soil might slowly leach into the aquifers and move with the groundwater, becoming more dilute as it spreads. However, results from the regular monitoring since April 1997 suggests this process, if happening, is very slow as overall contaminant concentrations in the groundwater do not appear to have changed.

• Is the contamination dangerous to human health or the environment?

The risk to health or the environment is very low as there are no pathways, such as absorption through skin or ingestion, by which people or the environment might be routinely exposed to groundwater containing contamination.

The Environment Protection Authority and the Department of Community Services have reviewed the risk assessments undertaken and are satisfied that there is no immediate health or environmental risks on the basis that there is no known use of groundwater from the aquifers which have been contaminated. Should this situation change then it is likely that this position would be reassessed.

• Can the contaminated groundwater be used?

The uncontaminated groundwater is too salty for domestic (except possibly salt water swimming pools) and most industrial uses, but could be used for stock watering. The EPA has identified that this possible use for the groundwater needs to be protected, however no groundwater is currently used for this purpose and there appear no plans to commence use of groundwater for stock watering.

Altona Properties Pty Ltd.
Copyright © 2011 Altona Properties, except where indicated.
URL: www.altonagroundwater.info
last modified:07-05-2007 | next update due May 2011
Send comments or suggestions to Mark Wloch, mwloch@pb.com.au