Up to 20% of households in parts of Aotearoa New Zealand are reliant on on-site wastewater management systems. ESR Senior Scientist Bronwyn Humphries and a team of microbiologists and environmental scientists work to understand how on-site wastewater systems impact groundwater.
Outside of reticulated wastewater areas, Aotearoa New Zealand relies on on-site wastewater management systems (OWMS), many of which were installed pre-2000, when resource consents were not required. While regional councils have information about consented OWMS since 2000, records for systems installed prior to this date often lack information about their location, type and/or condition. Anecdotal evidence suggests that systems are not adequately operated and maintained with wastewater removal companies reporting many failed systems around the country Management of these systems presents a challenge for both owners and regulatory bodies, and the risks from contamination can affect both environmental and human health.
In 2018, ESR led sampling from over 120 shallow wells around the country, and emerging organic contaminants (EOCs) where found in 70% of these sites. In fact, caffeine and sucralose EOCs were found upstream from centralised wastewater systems, suggesting on-site wastewater systems are ‘contributing’ these EOCs to groundwater.
Emerging Organic Contaminants
Emerging Organic Contaminants (EOCs) are like molecular ‘finger-prints’ of human activity. They are molecules that don’t occur in the environment naturally, so their presence can point to a source of contamination. Some of them are new contaminants recently introduced to products or medicines. Other EOCs may have been present as a contaminant for decades, but only recently detected or considered to be of a concern. Their impact on human, animal, and environmental health – as well as their presence in various environments – remains poorly understood. EOCs include preservatives, birth control hormones, caffeine, pharmaceuticals like paracetamol, plasticisers and many, many more.
Understanding how these on-site systems perform is important because of the downstream impacts on groundwater, which is where 40% of drinking water in Aotearoa New Zealand comes from. Bronwyn is leading a team to understand how these systems perform, with a specific focus on removal of microorganisms and viruses that cause human disease, and chemical contaminants such as nitrate.
The diagram below shows the opportunities for microbial and chemical removal in an on-site wastewater management system and the receiving environment: 1) the OWMS treatment plant, 2) land application system, 3) vadose zone (unsaturated zone) and 4) saturated zone.