The unit says it is now sharing key findings with stakeholders while it develops a final report.
“These results will provide valuable information that will help guide future decisions about assessment, monitoring, and management of water quality,” the update says.
The August update repeats earlier revelations that the unit is now certain that groundwater in the Muri catchment is directly connected to water in Muri Lagoon – something that will have come as no surprise to island residents concerned with environmental issues involving the lagoon.
“Past environmental studies of the Muri Lagoon did not confirm the factors contributing to the lagoon’s water quality, so we decided to undertake further studies to close the remaining information gaps,” the update says.
“The extent of connection between groundwater and the lagoon was one of these gaps.
“We installed monitoring wells in Muri, conducted ground surveys on Muri beach, and tested water in the lagoon.
“What this showed was that groundwater, even at very deep levels below the ground, responds to the lagoon tide. There were also chemical indicators of groundwater far out into the lagoon. This proves that groundwater and water in the lagoon are mixing.
“This means that toxic material dumped on the ground or in streams can make its way into groundwater and eventually into the lagoon. Examples of common products likely to cause issues are insecticides, weed killer, pharmaceuticals, paint and motor oil.
“Improving sanitation infrastructure can help protect groundwater and the lagoon, and we are working towards this, but we also need to take a more conscious approach to choosing products we use on the land. The newsletter says the full results of the project management unit’s environmental investigations will provide valuable information to help guide future decisions about assessment, monitoring, and management of water quality in the lagoon.
“As a part of the Mei Te Vai Ki Te Vai project, coastal engineers from the University of New South Wales have been working to gather data on nearshore ocean currents, and mixing processes in the ocean off Rarotonga.
“This work will help us to evaluate the feasibility of an ocean outfall for treated wastewater – one of the two options we’re considering for wastewater disposal.
As reported earlier in CINews, the update says work done so far has included dye tracing and current profiling at four locations along the coast.
“The team dropped dye at each location, and measured the movement of the dye for between 30 minutes and one hour. They also used acoustic measurements to help profile currents at each location, and to understand how the currents vary at different depths.
“The data on currents and mixing processes will help us to understand the potential mixing and movement of wastewater from an ocean outfall, and support the development of an outfall with the least possible environmental impact.
“Alongside ocean disposal, we are also evaluating and preparing information on land-based wastewater disposal, to enable government to consider both options before deciding on a preferred method.”