Banned evaporation ponds are the cheapest option of dealing with coal seam gas waste

The cheapest option for gas companies to get rid of their waste is to allow evaporation via their holding ponds or accumulation dams. The Santos ponds at Leewood Water Treatment Facility (pictured) recently received the residual waste from the ponds which were upgraded at Tintsfield (near the Wilga Park Power Station) and continue to receive produced water from operating Santos wells.

Whilst the Reverse Osmosis facility at Leewood is non-operational and irrigation is not occurring the sun is doing the job of evaporating the waste. Lawful or not this is definitely occurring as can be witnessed by images which show diminishing quantities of waste in the ponds over the last 12 months.

Flickr Album available here of the most recent images and here for an older album

What is an ‘evaporation pond’?

The NSW Government Resources and Geoscience Website states: Evaporation ponds ‘take up a large area of land’ and ‘must not store water with the intention of having it evaporate’. The Government agency states ‘temporary holding ponds or dams may be required for various treatment processes’. The key word here is ‘intention’. Do gas companies ‘intend’ for the waste to evaporate?

Across the English-speaking world, the words ‘pond’ and ‘dam’ are largely interchangeable words, with one exception, a naturally formed pond is not a dam. Some companies such as EHS Support call them ‘Accumulation Dams’. Clearly, Santos use the words interchangeably, while their REF is titled, Leewood – Produced Water and Brine Management Ponds Review of Environmental Factors.

Golder was engaged by Santos to design the Leewood ponds and they relied on the then QLD Department of Environment and Resource Management “Manual for Assessing Hazard Categories and Hydraulic Performance of Dams” (DERM 2012 manual) and the NSW Dam Safety Committee (DSC) requirements for water balance modelling and hydraulic design for the design of the Leewood ponds.

Leewood ponds were approved on the 19 March 2013.

Why are evaporation ponds banned?

Although evaporation ponds are banned in both NSW and Queensland there are loopholes and neither state has made any attempt to ban ‘holding ponds’ (another name for the same thing).

There are numerous risks associated with open ponds of this nature, including potential for overflow during rain, inadequate lining allowing seepage of waste water into soil and risks to wildlife and humans from off-gassing of the potentially hazardous waste that they contain.

Evaporation ponds take up a large area of land and discourage the treatment and re-use of water from the CSG exploration and production processes.

In NSW, CSG companies must treat or otherwise dispose of produced water. While they must not store water with the intention of having it evaporate, in some cases temporary holding ponds or dams may be required for various treatment processes.

FAQs on coal seam gas, NSW GOVERNMENT

How much evaporation occurs?

Leewood ponds location is 30°29′ 49” S 149°37′ 10.8” E. The calculated surface area of ponds is based on the concept design. Google Earth images show actual construction is very similar to concept design (which is detailed in the REF linked above). A co-efficient is applied for the location.

Google Earth image informed calculations of surface area etc
  • Produced water pond surface area at Maximum Operating Water Level (MOWL) 185.06m x 236.04m = 43,681.5m2 for each compartment. With two compartments total area = 87,362m2.
  • Produced water from MWL to MOWL varies due to ridge and valley and slope to leak detection sump from ~4.7m to ~4.0m, therefore average depth ~4.35m.
  • Brine water pond surface area at MOWL 189.18m x 218.54m = 41,343.4m2 for each compartment. With two compartments total area =  82,686m2.
  • Brine water from MWL to MOWL varies due to ridge and valley and slope to leak detection sump from ~5.9m to ~5.3m, therefore average depth ~5.65m.
  • Combined water surface of produced water and brine pond 170,048m2.
  • Catchment area of liner based on Google Earth image taken 28/11/2015 ~184,600m2.
Calculations developed with the use of the Ready Reckoner – a more detailed examination of these techniques is available here and an Engineering Toolbox Calculator here

Designed to evaporate because it’s cheaper

Evaporation from the Leewood ponds have been identified by EHS Support as being a more cost effective method of dealing with waste than reverse osmosis and brine crystallisation treatment. It makes sense that some companies would choose the cheaper option despite this option having environmental consequences.

Engineering Solutions to evaporation

There are many engineering solutions to reduce evaporation including floating covers, modular covers, shade structures, chemical covers, design features and biological technology. If government was serious about banning evaporation dams or ponds they would make it obligatory that the above engineering solutions be adopted.

In reality these engineering solutions are not suitable for the company because they do not facilitate the evaporation of waste. The sole purpose of the waste ponds structure is long-term evaporation and storage of waste.

As can be seen by the above data table the Leewood ponds have an annual evaporation rate of 177.9Ml. The holding ponds are working as intended.

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