Monitoring and modeling groundwater and wastewater to inform land disposal limits

Rama Road Disposal Field

Everyday living creates wastewater that’s treated and often piped to wastewater disposal fields—where unsaturated soil receives pretreated wastewater via distribution piping onto soil infiltration surfaces. These surfaces are porous media, such as gravel or manufactured components placed in the field where the ground accepts, treats, and disperses wastewater as it percolates through the soil, ultimately discharging it to groundwater.

We were asked to help the Whangārei District Council determine the maximum allowable volume of wastewater that could be applied to the Ruakākā wastewater treatment plant disposal block at Rama Road. To do this, we monitored groundwater levels and modeled treated wastewater on the block to predict the levels of acceptable application rates without causing adverse effects. Using groundwater modeling software to model the hydrogeological system and produce projections helps the Council make informed planning decisions when designing any extensions to the wastewater requirements in Whangārei.

As a result of our work, the Council has the necessary information to make informed decisions about what their Rama Road disposal field can accommodate.