As part of coal seam gas development, the management and treatment of produced water is a critical component requiring significant capital and operational expenses. To support agricultural activity and provide for environmental flows, produced water is treated and provided directly to landholders or placed within surface water bodies for use by downstream agricultural properties.
Boron is a naturally-occurring metal present in produced water and is also an additive used in hydraulic fracturing fluids. EHS Support completed a study to define the treatment requirements for boron in produced water, considering both the potential impact of boron on aquatic and benthic organisms within the river, as well as impacts on plant growth and livestock from use as irrigation water or uptake by vegetation and use as livestock feed.
Boron is a unique inorganic compound with respect to evaluating its toxicity to plants. It is an essential nutrient for plant growth; however, many crops have optimal ranges of soil-boron conditions that require boron amendments to ensure maximum productivity. Too much or too little boron can result in toxicity or deficiency, respectively.
EHS Support’s team leveraged literature and direct toxicity assessments to evaluate the surface water and benthic toxicity of boron, and in combination with a mixing model, to derive surface water criteria. In combination with these studies, plant toxicological data from the recent Albertan soil boron guidelines and other historical data sources were used to derive site-specific irrigation water criteria in accordance with the 2018 revised method for deriving Australian and New Zealand water quality guideline values for toxicants. The finalised derived irrigation water criteria were three times greater than the threshold limit recommended by the agency. The greater technical veracity of the derived boron irrigation criteria increased regulatory confidence in the selected limits and resulted in substantial operational cost savings to the client.
Following the derivation of irrigation guideline values, a boron uptake model was developed for livestock to assess daily dietary intakes of boron from stock watering and crops grown using this water source. The model assessed a range of livestock types, body weights and vegetation types (based on their differing ability to take-up boron) to determine if potential impacts would be observed on livestock. The assessment demonstrated that there were no unacceptable acute or chronic effects from application of a higher boron limit.
The net effect of this evaluation was to support the use of higher boron limits for the determination of treatment requirements and critically for the application of a monitoring plan and associated trigger response plan. The new discharge limits will aid in lower operational and monitoring costs but will also increase the potential volumes of water available to landholders for agricultural use and supporting environmental improvement and ecological function by maintaining higher baseflows within the river.