Innovative Stormwater Management at APLNG

Identifying and managing any associated environmental impacts related to our Australia Pacific LNG (APLNG) facility near Gladstone, is a cornerstone of our commitment to responsible operations. Managing the potential for large volumes of rainfall to fall on and near the facility was one of our early planning challenges. We explored different ways to manage storm and wastewater to minimize water releases as we worked to protect a range of critical environments within the Great Barrier Reef World Heritage Area. A review of system performance and receiving environment response was completed in 2019, with data indicating that stormwater releases have resulted in no noticeable adverse impacts on the mangrove communities in Gladstone Harbour near the facility.

An innovative stormwater management system was designed to segregate clean and potentially contaminated stormwater, minimize erosion and control the movement of suspended solids. The installation of a perimeter drain around the APLNG facility protects the environment during heavy rain, ensuring that runoff from external undisturbed areas does not mix with runoff from disturbed areas, while effectively minimizing the volume of water requiring management onsite. Improvements to manage stormwater in operational areas minimize erosion and capture suspended solids. This includes surface treatments such as:

• Concreting.
• Gravel sheeting and revegetation.
• Constructed slopes and internal drain protection using geocell and rock.

Five basins facilitate the settlement of sediments that may be contained in rainfall runoff from the site. These are designed to drain freely, discharging low flows through a geofabric-wrapped perforated pipe. Moderate flows are released through a discharge pipe operated by a manual valve, which can be closed to allow treatment if needed, and high flows are discharged via a rock armored spillway. Stormwater releases from perimeter diversion drains and sediment basins are channeled to concrete and rock armored outfalls that minimize erosion and support mixing in the receiving environment. Stormwater management within the plant is complimented by primary, secondary and tertiary containment areas that segregate potentially contaminated waters arising from production activities. These containment areas capture potentially contaminated stormwater during rainfall events so that water quality can be inspected prior to release as stormwater or diverted to on-site or off-site treatment or disposal facilities. Through an agreement with the Gladstone Regional Council (GRC), our sewage and wastewater are piped to existing facilities on the mainland, which reduces truck traffic on local roads. This agreement also meant that ConocoPhillips did not need to install treatment facilities on Curtis Island.

“The industry-leading stormwater management system installed at APLNG has proven effective even during periods of extremely heavy rainfall, with stormwater runoff from the site being cleaner than runoff from nearby undisturbed areas,” said Fiona McLeod, General Manager of Government and External Affairs for ConocoPhillips Australia.

Mangrove monitoring

Monitoring the health of mangrove communities in the receiving environment and at reference sites provides insight into whether there have been any impacts to biodiversity related to the construction and operation of the APLNG Facility. From the early construction phase in 2012 through to February 2019, we monitored:

• Height, diameter and leaf count of seedlings.
• Number of crab burrows.
• Water chemistry, including pH, turbidity and temperature.
• Leaf litter and herbivory damage.
• Diameter and height of mature trees.
• Canopy cover.

“The data shows that the health of mangrove communities adjacent to the facility has remained stable since operations commenced. Simply put, the ongoing operation of the facility is not expected to cause any negative impact to these significant ecosystems,” said McLeod.