On-Site Wastewater Management
Fraser Thomas have been at the forefront of on-site wastewater management projects for over 30 years in New Zealand.
We are very familiar with Auckland Council Technical Publication TP58 and AS/NZS 1546 and 1547 as well as the regulatory requirements of different regions of New Zealand and have extensive experience in providing on-site wastewater solutions ranging from individual households up to large community facilities on sites where soils range from poor to good drainage.
Such investigations involve desktop assessment of wastewater flows and composition; site investigations, including shallow boreholes to assess soil conditions; assessment and design of wastewater treatment and disposal options including upgrade or retro-fit to existing wastewater treatment and effluent disposal systems; preparation of technical reports in support of resource consent and/or building consent for a preferred option; liaison with treatment plant providers; and construction observation and certification.
Some of our recent, more challenging projects include:
Department of Conservation, Motutapu Island:
DOC were planning to relocate 4 existing buildings (a shearers quarters housing up to 20 people, a beach bach housing up to 4 people, and 2 houses) from different parts of Motutapu Island, clustering the buildings on the island closer together. Our role was to investigate, design and consent wastewater systems for the relocated buildings. This involved specific design for two buildings, due to variable wastewater flows and loads as a result of intermittent and variable occupation of these buildings, with conventional septic tank treatment and buried LPED (low pressure effluent disposal) systems being selected. For the 2 houses, intermittent sand filter treatment systems were selected, followed by buried pressure compensating driplines for disposal.
We have provided services to upgrade and consent a number of kennel facilities. A recent project involved checking the adequacy of the household wastewater treatment system and dealing with washdown water from the kennels which was discharged directly to land without treatment. We inspected the dwelling and kennels to confirm design wastewater flows, investigated how best to manage the wastewater generated from the kennels (as contaminated rainfall falling on open dog run areas requires treatment and disposal) and undertook a borehole investigation to determine the suitability of various locations on site for wastewater disposal. Wastewater irrigation areas were controlled by the location of the 100 year floodplain and the nitrogen loading in the treated effluent. Solutions for such sites have included retaining and upgrading the household wastewater treatment system, creating a new subsurface drip irrigation system for treated domestic effluent disposal, and managing the kennel wastewater by balancing the contaminated rainfall wastewater with the washdown wastewater with disposal via LPED or spray irrigation, depending on site constraints.
Cut and Carry 8 Hectare Effluent Disposal System:
Fraser Thomas investigated, consented, designed and observed construction of a large cut and carry effluent disposal system to serve a unique motorsports complex in the Waikato. Shallow groundwater and a sensitive receiving environment to nitrogen resulted in the most efficient means of effluent disposal to the low carbon, high nitrogen effluent being a cut and carry crop whereby the applied nitrogen was taken up by the crop and taken from the site as haylage.
- Resource management planning
- Preliminary design
- Resource and/or building consenting
- Detailed design and tendering (larger scale projects)
- Construction observation