Saturday, May 26, 2007

Canberra: Environmental issues of IPR

Two important reports were released regarding the preliminary assessment of the proposed indirect potable water recycling scheme for Canberra yesterday.

The Health and Public Safety report was the subject of yesterday’s blog post.

The second report is a “Preliminary Investigation of Environmental Issues” associated with the recycling scheme and the accompanying expansion of the Cotter Reservoir. This report was prepared by the eWater CRC.

The report is subtitled “Stage 1: Issues Discussion Paper”, which leads me to presume that there is a more detailed analysis to come. However, this general discussion provides a succinct summary of the environmental issues that are typically associated with IPR schemes.

In my opinion, the most significant environmental issues are consistently (in order of decreasing significance):

1. The impact on downstream river flow regimes
2. Sustainable management of concentrated waste streams
3. Energy intensiveness and associated greenhouse gas emissions.

I am pleased to see that the report has identified each of these as important issues requiring closer scrutiny. The executive summary is provided below. You can download the full report from here.



1 Executive Summary

This Discussion paper is the first of two reports from eWater CRC, assessing and reporting on potential issues that ACTEW's proposed Water2WATER project poses for the environment and ecology of the lower Cotter catchment and the Murrumbidgee River. Human health issues are being dealt with separately by an Expert Health Panel.

Conceptual information about two options for recycling Canberra water has been provided by ACTEW. With both options (A and B), treated wastewater derived from tertiary treatment of sewage will progress from the existing Lower Molonglo Water Quality Control Centre (LMWQCC) to a proposed new on-site facility, for further treatment. The ‘advanced’ treated water will then be recycled into the lower Cotter catchment where it will enter the Cotter Reservoir, via a constructed wetland and probably a local stream.

Two other outputs of the new plant will be liquid and solid wastes, depending on the treatment option the plant uses. These wastes will either re-enter the LMWQCC with the incoming raw sewage, or, in the case of the reverse osmosis plant wastewater (‘brine’) from Option A, be piped to evaporation ponds north of Uriarra, for ultimate disposal elsewhere.

ACTEW also proposes also to enlarge the capacity of Cotter Reservoir from 4 GL to 78 GL (GL stands for gigalitre, 1 thousand million litres) to hold the treated water along with other catchment in-flows. Recycling of 25 ML each day is expected initially, rising to 50 ML per day once the new dam wall has been constructed (ML stands for megalitre, 1 million litres).

eWater notes that the technical information so far available on the treatment options is insufficient to carry out a detailed evaluation or proper environmental risk assessment. Therefore, this report makes only preliminary comments on the plant performance and related environmental issues. More detailed analyses will be carried out for our second stage report.

1.1 Environmental issues identified

1.1.1 New treatment plant and water quality

Our preliminary evaluation of the international literature indicates that a well designed and well operating ‘Option A' type system (micro/ultrafiltration + reverse osmosis + UV/peroxide oxidation) has the potential to remove all viral and bacterial contaminants and organic pollutants, and to reduce salts, nutrients and heavy metals to concentrations similar to, or lower than, that found in natural catchment run-off — this being the appropriate environmental benchmark for our analysis. Notwithstanding, one potential environmental issue noted is the comparatively weaker removal of the nutrient nitrate by reverse osmosis. This could, subject to other environmental factors, increase the risk of algal blooms and uncontrolled aquatic plant growth in Cotter Reservoir.

No treatment system anywhere in the world can be guaranteed to be absolutely failsafe 100% of the time. Consequently, equally important to the treatment system chosen must be the provisions made for detecting failure and ensuring that there is no break-through or leakage of incompletely treated water or wastes. The environmental concerns relating to system failure include:

• infection of fish and other biota by viral and other pathogens — something that could occur during even a single, short failure event;
• accidental land and water contamination because of pipe rupture — especially the treated water pipe crossing over or under the Murrumbidgee River;
• contamination of local land, streams and groundwaters due to constructed wetland ‘overflow’ or leakage; and
• shut-down of flow at critical ecological times — especially for wetlands and stream ecosystems that become established under an artificial flow regime.

Advanced water treatment is an energy-intensive process, especially where significant water pumping is required (as here). Preliminary estimates of the power requirements for the new treatment process are about 6000 kW (kilowatts). Assuming operations 24 hours a day, 365 days per year, this translates to an estimated greenhouse gas emission rate of about 57,000 tonnes of carbon dioxide per year from plant operations.

The ‘Option B’ treatment train (using ozone–biologically activated carbon instead of reverse osmosis) would use a little less energy than Option A. However, there appear to be few other water treatment and environmental advantages of Option B over Option A.

To the extent of any new works required at the LMWQCC site, there are possible impacts on the threatened Pink-tailed Worm Lizard. Infrastructure associated with the proposal must ensure that connectivity is maintained between populations of this species in the immediate vicinity.

1.1.2 Waste management

In any treatment process, one of the biggest environmental risks lies with the handling and disposal of the concentrated waste stream. Issues that need to be further addressed are:
o contamination of birds and animals that will be attracted to the ‘brine’ ponds,
o groundwater contamination by the wastes,
o brine pond failure and run-off to adjacent streams,
o waste pipe eruption and discharge,
o waste management during prolonged wet periods,
o wind dispersal of dried waste accumulated on site,
o vehicular accident during transport of dried waste.

1.1.3 Water transfers to Cotter catchment

The proposed water-treatment wetlands will need to be sited where the soils, slope and drainage characteristics are capable of dealing with an inflow of 25–50 ML per day. Evaporation and loss through seepage need to be small to maximise the extra water the project aims to make available. The wetlands may be contaminated by pests carried on the wind or by birds, and bird excreta may also reduce water quality.

Water from the wetland is likely to be discharged into a nearby stream before reaching Cotter Reservoir. Subject to further analysis, it is reasonable to expect if water is discharged at rates approaching the proposed 25–50 ML/day that major ecological impacts on local streams will occur.

There may be ways to mitigate such impacts to some extent, for example through the use of more than one stream. However, consideration should be given to direct piping and discharge of treated water to the Cotter Reservoir as a less environmentally impacting option.

1.1.4 Enlargement of the Cotter Reservoir

Greatly enlarging the volume of the reservoir may stimulate:
• expansion of populations of alien fish species (Goldfish, trout, Gambusia, Oriental Weatherloach);
• predation on threatened fish species by trout and waterbirds such as cormorants;
• loss of fringing reed-beds which offer cover to Macquarie Perch in the present reservoir and upstream of it, at least until new reed-beds establish in some years time;
• potential loss of spawning habitat for Macquarie Perch upstream of the present reservoir, unless the new water level is kept downstream of natural rock barriers in the river;
• deposition of sediment at the narrow upstream end of the new reservoir, which may block the way for fish to swim out of the reservoir, and possibly smother at least some of the existing habitat on the riverbed for Two-spined Blackfish;
• a larger total habitat for deep-water birds, but temporary loss of habitat for reed-dwelling species such as warblers and grebes until the reeds re-establish; and probable change in amount of shallow-water foraging habitat and adjacent riparian and woodland habitat for other bird species;
• loss of some frog habitat, but for species that are common in this region;
• change in food availability for Platypus;
• low-temperature releases of water through the wall into the river below.

Most, if not all, of these issues are manageable through sound dam planning and design, and through appropriate adaptive management practices for dam operations.

1.1.5 Effects on flows in downstream rivers

A larger Cotter Reservoir will trap much greater volumes of the peak flood flows than the present Cotter dam wall can retain, which could have ecological consequences downstream in the Cotter River. Also, water that is now discharged into the Murrumbidgee River will be diverted to the new treatment plant and then into the Cotter catchment. In summer this may be a good thing, because the existing discharge from the LMWQCC causes the river to be unnaturally high at present. For the rest of the year, the reduced flow may hinder fish travel.

1.1.6 Construction of dam wall, pipelines and plants

Environmental issues that will need to be addressed during the treatment plant, pipeline and dam construction phase include:
• mobilising of sediment into the Cotter River and the Murrumbidgee River, damaging freshwater communities in the area by smothering habitats;
• spills of fuel and other materials that would contaminate land and water;
• drawdown of the Cotter Reservoir, affecting plants and animals in the existing reservoir;
• access through the existing or new dam wall, allowing pest fish to move into the Cotter River from the Murrumbidgee River;
• damage to populations of the Pink-tailed Worm Lizard that may exist near the proposed new treatment plant or pipelines; this species is listed in both Commonwealth and ACT environment protection legislation.

Also, it may take several years to fill the much-enlarged reservoir, causing the flow regime in the Cotter River to be additionally impacted for that time, to the likely detriment of aquatic biota that need seasonally variable flows.

1.1.7 Other issues

There is likely to be a requirement for development referral under the provisions of the Commonwealth Environment Protection and Biodiversity Conservation Act (1999). One lizard and two of the fish species present in the Cotter are listed as nationally threatened (Macquarie Perch and Trout Cod), and so the provisions of the EPBC Act are expected to apply.

All the issues listed above, as well as potentially beneficial opportunities presented by the Water2WATER proposal, will be considered in more detail in eWater CRC's stage 2 evaluation.

7 comments:

AJ said...

Hi again Stuart, I just want to know what would be in the brine waste stream from UF/RO other than salts?

Stuart Khan said...

G’day AJ,

As far as environmental concerns go, salts would certainly be the most significant issue. It may sound fairly benign, but if not properly managed, the environmental risks associated with large quantities of salt-concentrated water can indeed be significant. If evaporation ponds are poorly designed, concentrating brines can leak into groundwater tables, contaminating otherwise clean waters. Historically, this has been more of an issue with brackish water desalination brines than it has with water recycling brines, but it is fair to say that there is little international experience with managing brines from inland water recycling schemes. Most existing inland water recycling schemes (potable or non-potable) do not use reverse osmosis. Instead, they tend to rely on activated carbon treatment for organics removal. Appropriately managing RO brines from Canberra will certainly be a significant challenge.

Of course, RO brines from recycled water also contain numerous organic chemicals and pathogenic organisms. These also need to be safely dealt with. However, given that we are able to manage sewage sludges relatively effectively, I wouldn’t expect these contaminants to present insurmountable challenges.

amy said...

Stuart any problems with the Brisbane scheme pouring the ro into the Brisbane River?

Stuart Khan said...

Hi Amy,

Yes, it is certainly a significant enough issue that it will need to be planned and managed carefully to avoid significant environmental impact.

However, that situation is somewhat different to an evaporation pond since there is no opportunity for salts to concentrate and accumulate. In contrast, they will be dispersed and regularly flushed from the Brisbane River into Moreton Bay.

While an existing imperfect situation does not justify a future one, it is also worth remembering that all of the salts (and other contaminants) in the RO brine are already discharged to the Brisbane River, -its just that they are diluted in some rather valuable H2O.

As described previously, the RO concentrate from the Brisbane scheme will actually be further treated prior to discharge, so the final river-concentrations of the nutrients nitrogen and phosphorous are expected to be lower than they currently are.

amy said...

thxs!

Anonymous said...

This site suxs worse than the wiggles!! worst site everrrrrrrrrrrr

Stuart Khan said...

Thanks for the feedback Anonymous.

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