Update re New South Wales On-site Wastewater Design and Installation Manual, November 2020

Following last week’s Blog Post mentioning the delay in release of the Auckland Council on-site wastewater management guideline document GD06, correspondent Joe Whitehead of Cardiff NSW has advised On-Site NewZ of the availability of the latest version (2019) of the Australian design manual entitled “WaterNSW Current Recommended Practice: Designing and Installing On-Site Wastewater Systems” (access via link below).

The original recommended practice manual issued in 2012 was based on a report to the Sydney Catchment Authority (now WaterNSW) by Joe’s consultancy (Whitehead & Associates Environmental Consultants Pty Ltd) together with Kerry Flanagan Wastewater of Grose Vale NSW. Joe was also closely involved in preparation of the November 2019 revision

Notable changes between 2012 and 2019 versions
(a) Linear Loading Rates: The concept of design sizing for land application systems based around linear loading rates (LLR) came out of work by Dr Jerry Tyler (et al) of the Small Scale Waste Management Project, University of Wisconsin-Madison, USA. Recommended LLR values are specified in litres per metre length of installed system along the contour. It relates to any type of land application system – in current NZ practice it is only applied as a toe loading limit in sizing Wisconsin Mound systems.

When effluent is applied to soil it will move vertically and horizontally away from the infiltration system until it meets a hydraulically limiting layer. The LLR is set at a limit to ensure that the effluent will not break out to the surface below the land application area as it moves downslope after reaching the limiting layer. It is used to size and configure the land application system in conjunction with effluent design loading rate (DLR or DIR) for the proposed system. LLR values are set according to soil depth and type along with ground slope. Highest LLR values are associated with deep and courser sandy soils on the steeper slopes, thus resulting in shorter system length along the contour. Lowest LLR values are associated with shallow clayey soils with flat to negligible slope, thus resulting in longer system length along the contour. The LLR is applicable for any land application system and any effluent quality (septic effluent or AWTS effluent).

The Pages Sidebar of this Blog under the title “Design Irrigation Rates – Origins and Development in On-site Wastewater Manuals and Standards” provides an example on application of LLR values in design on pages 14/15 of the downloadable report.

In respect of the 2019 WaterNSW manual there has been a relaxing of the limits imposed by LLR rates on system sizing with the rates being lifted between 25% to 30% (in some instances 50%). The original 2012 version of the manual used a table of LLR values from British Columbia (2006). The British Columbia Standard Practice manual design values were subsequently (2007) increased to those proposed by Tyler (2001) in order to provide more flexibility in design with a less conservative approach to establishing system length along the contour. The WaterNSW 2019 manual has also adopted the higher (therefore less conservative) Tyler values.

(b) Buffer distances: Some changes have been made to minimum buffer distances (clearances or setbacks) to site features, including a tightening up on separation distance from base of land application area to limiting layer. The 2012 version allowed a variation of 300mm to 600mm clearance to limiting layer – this has been amended to “should be a minimum of 600mm for all systems”.

(c) Emerging Technology: The 2012 manual provided information on dosing syphons, floating outlet (flood loading) units and solar power. Solar power was not accepted for treatment systems requiring continuous electricity supply, such as AWTS (aerated wastewater treatment systems). It could, in exceptional circumstances, be utilised for intermittent use such as sump pump-outs.

In the 2019 manual WaterNSW accepts solar power for systems “where continuous power is needed for normal operation, such as an AWTS, only when a detailed analysis is provided as part of the application” for approval.

(d) Supplementary Technology: The “emerging technology” section of 2012 has now been replaced by an expanded “supplementary technology” section. The covers an overview (without design details) of the following systems:
• constructed wetland treatment
• membrane treatment
• textile filter treatment
• sand filters
• subsurface media treatment (the AES system)
• buffering/balance tanks
• dosing mechanisms.

Link to the 2019 manual:

Click to access Designing-and-Installing-On-Site-Wastewater-Systems-WaterNSW-CRP-2019.pdf


News from On-Site NewZ

Update re On-Site NewZ Activity

Since the last Blog Post of 21 May 2019 On-Site NewZ has been somewhat in hibernation. However, it is noted that activity via reader access to the site has continued steadily with views over the past 9 months averaging eight daily involving three or four persons.

Progress on Auckland Council GD06 On-site Wastewater Management Guideline Document

Following the issue of the draft for consultation in September 2018 Auckland Council has been working through comments received from throughout the on-site wastewater management community and subjecting these to internal review. On-Site NewZ has no information as to when the final document will be published. When publication takes place the guideline will be accessible at http://www.aucklanddesignmanual.co.nz/regulations/technical-guidance with the September 2018 consultation version currently on this site being replaced by the final document.

Workshop on On-site Wastewater Management Systems (OWMS) postponed due to Covid-19

This event hosted jointly by SWANS-SIG (Small Wastewater and Natural Systems Special Interest Group of Water NZ) and NZLTC (NZ Land Treatment Collective) was originally scheduled for 30 March. A new date will be advised in due course.

Details of the proposed workshop as published on the Water NZ website on 12 March are as follows:

Purpose: For stakeholders to identify core OWMS issues in New Zealand (i.e what’s working and what isn’t)
1) Document outlining the OWMS issues as identified by each sector
2) Create a network of key stakeholders to be involved in future discussions
3) Set the agenda for a second workshop in the future to help address some of the issues
Format: Specialists from each industry sector have been invited to make 15 min presentations focused on core OWMS issues followed by 10 mins Q and A.
Sector presenters:

Designers: Andrew Dakers (Eco Eng) and John Cocks (John Cocks Ltd)
System suppliers: Brent Hawthorn (Innoflow), Mike Dawson (Hynds)
Installation and maintenance: Craig Rall (Envirolutions)
Irrigation suppliers: Bruce Richter (Netafim)
OSET NTP: Ray Hedgland (Technical Manager, National Testing Programme)
Regulators: Keith Peacock (Hawkes Bay Regional Council) Leif Pigott (Tasman     District Council)
Training: Brett Marias (WSP Training)
End user: Peter Carter (DoC)
Research: Malcolm McLeod (Landcare), Louise Weaver (ESR)
Public Health: John Whitmore (ADHB)
Regulatory reform: Noel Roberts (Water NZ)

On-Site NewZ will keep you posted as to the new date for this event once it is announced.

Origins of On-site Wastewater Design Irrigation Rates

Following the February 2019 post on the origins of on-site wastewater design loading rates a correspondent asked if On-Site NewZ would provide a similar paper setting out the origins of design irrigation rates. This task has now been completed and the resulting paper can be accessed from the Pages Sidebar of this Blog under the title “Design Irrigation Rates – Origins and Development in On-site Wastewater Manuals and Standards”.

The paper commences with information from the NZ TP58 design manual 1989, then covers TP58 2nd edition 1994, the Australian Standard AS 1547-1994, the Joint Australia-NZ Standard AS/NZS 1547:2000, TP58 3rd edition 2004, the revised and updated AS/NZS 1547:2012, and finally the draft GD006 2018 on-site wastewater management guideline from Auckland Council which when published will replace TP58. A plot of DIR values versus soil texture and structure categories is provided as a summary of the DIR values from the above sources.

The second part of the paper looks at the development of drip dispersal hydraulic loading rates in the US where the use of drip emitters was employed to distribute household wastewater effluent into the soil for subsurface infiltration rather than irrigation. The objective was to maximise inflitration into the soil throughout the year rather than meet the agronomic needs of crops/plants. Hence the hydraulic loading rate values for specific soils are very much higher than the DIR values for the same soils in Australia-NZ on-site wastewater practice.

Drip dispersal hydraulic loading rates are tablulated and plotted from some 10 sources in the US – research agencies, commercial suppliers of dripline and state administrations. Over time the high initial design values in the US have been scaled down closer to our local values.

A final summary plot of US values vs Australia-NZ values compares the high non-conservative values in the US with conservative US values and our local DIR values over all soil/structure categories.


Time to lift the game around On-site Wastewater Management

On-Site NewZ has received feedback regarding the 28 March post entitled “Time to lift the game around On-site Wastewater Treatment”.

There appears to have been some editorial confusion in reporting on the discussions at the Christchurch workshop in which the Water Journal article referred to “treatment units” being the subject of the proposed “best practice guide”.

A correspondent to On-Site NewZ noted that

“at Christchurch we were more concerned with on-site wastewater management and recognised that treatment was only one factor in this and somewhat minor compared with investigations and overall design, designers capability, Council process approvals, operation and maintenance, ongoing service contracts and reporting and so on”.

The writer indicated that

“the meeting clearly confirmed that treatment and OSET-NTP certification was only one aspect of the bigger picture of on-site wastewater management. For example Andrew Dakers was critical of Council approval of OSET certified plants in that he then found Council officers approving an overall design because it included an OSET certified plant, without considering the overall site investigation and design”.

Hence the commitment by Water New Zealand is for the development of a Best Practice Guide for On-site Wastewater Management which will focus on a “whole of system” approach.

The Pages Sidebar item of 26 March has now been replaced by an On-Site NewZ amended version of the Water Journal article which reflects the comments received above, the new title being “Time to lift the game around On-site Wastewater Management”.

Time to lift the game around On-site Wastewater Treatment

One of the outcomes of a recent one-day workshop in Christchurch to discuss on-site wastewater management practice in New Zealand was a commitment by Water New Zealand to develop a “Best Practice Guideline for On-site Wastewater Treatment Units”.

A report on the workshop by Noel Roberts, Water New Zealand Technical Manager, summarises key elements from the day’s discussions, citing concerns over high numbers of failing units and deficiencies in installation, maintenance and regulatory oversight.

Andrew Dakers of ecoEng in Christchurch presented a case for an approach that went beyond reliance on just the performance testing on treatment units as is carried out at Rotorua under the OSET-NTP (On-site Effluent Treatment National Testing Programme). Andrew advocates a whole of system approach involving evaluation and mitigation of individual site risks associated with the both the treatment unit and land application system, and including design, installation operation and maintenance.

Other issues raised at the workshop included a warrant of fitness for on-site wastewater systems, and national certification for installers and designers.

To read Noel’s report as published in the March/April 2019 issue of “WATER”, go to the Pages Sidebar of this Blog under the item “Time to lift the game around On-site Wastewater Treatment”.


Origins of On-site Wastewater Design Loading Rates

The “Nz-onsite-wastewater” forum (http://nz-onsite-wastewater.freeforums.net/) created in August 2018 includes a discussion thread relating to the variation in design loading rates (DLR) for land application of treated effluent where a new forum member raises questions re differences in DLR/DIR values in TP58, AS/NZS 1547 and those in the proposed new GD006. The Forum Administrator, Grant Hammond of Tauranga, makes the following comments on this matter:

It would be nice to think that our national design standards were all based on first principles of engineering design, but unfortunately all too often they include design parameters and fudge factors that have never been proved and are often derived from an assumption that was based on a prior assumption! TP58/GD06 and NZS 1547 are all primarily based on desktop compilations of other design standards and research.

I suspect TP58 had a stronger US influence, whereas NZS 1547 obviously had a strong influenced from Aussie. I can only assume these influences contributed to the different correlations between DIR and soil categories.

Perhaps someone who was involved in the NZS 1547 standard and knows a bit of the history behind the drafting of NZS 1547 could chip in on this question

As the author of TP58 Editions 1 and 2 (1989 and 1994) and as a participant in the Joint Standards committees that produced the 2000 and 2012 versions of AS/NZS 1547, On-Site NewZ has some insight into the process of drawing up design parameters. A discussion on this topic entitled “Design Loading Rates – Origins and Development in On-site Wastewater Manuals and Standards” can be accessed from the Pages Sidebar of this Blog.

Auckland Council Guideline Document: On-site Wastewater Management in the Auckland Region [GD06-2018] – Updated Draft, September 2018

Dr Gretel Silyn Roberts, Principal – Technical Guidance, Engineering and Technical Services, Infrastructure & Environmental Services at Auckland Council, has advised On-Site NewZ of the issue of an updated draft of GD06 as follows.

Thank you to all those who have provided initial feedback on GD06 – On-site Wastewater Management in the Auckland Region. We very much appreciate the effort put into the review of this draft. The deadline for feedback is October 12th, but we would much appreciate you sending through any major issues or questions prior to this date so we can address them fully.

Update of amended draft:
Based on feedback to-date, and some suggested changes, we have updated the document on the Auckland Design Manual website. Most changes are adjustments to cross references, corrections and clarifications.

The key changes we would like you to be aware of are:

1. Section D: Wastewater treatment units –

(a) Adjustment to the text around Section D1.4.3 Septic tank sizing

(b) Restructuring of Section D1.5.5 – Types of system

  • Removal of trickling filter
  • Removal of single pass packed bed filter
  • Removal of multi pass packed bed filter
  • Removal of diagrams for all “Alternative treatment systems”
  • Removal of diagrams for all “Alternative toilet systems”

2. Section G: Risk – Additional comment around the need to design for climate change

Please do not hesitate to contact our team if you have feedback.

Gretel Roberts Gretel.Roberts@aucklandcouncil.govt.nz

To access a PDF version of the September 2018 update go to the Pages sidebar and the topic heading for this Blog Item.