On-site wastewater management (GD06) Community of Practice: feedback and next steps Auckland Council Engineering & Technical Services and Heathy Waters
Agenda Morning tea available prior to meeting 9:00am – 9:30am Introduction and welcome 9:30am – 9:45am Details of on-site management in Auckland: • Development of document • Significant differences • Next steps/timeframes 9:45am – 10:45am • Unitary Plan Change • By-law update • Region-wide wastewater compliance monitoring programme Break out session: 10:45am – 11:30am Regroup and summary: 11:30am – 12:00pm
First things first… GD 06 Introduction Next steps Feedback Overview
Acknowledgements The team of authors & contributors Justine Bennet, Graham Boyle, Patricia Burford, Zhou Chen, Andrew Dakers, Simonne Elliot, Peter Gearing, Ian Gunn, Jack Feltam, Grant Fleming, Robyn Floyd, Kristina Healy, Anthony Kirk, Terry Long, Alan Moore, Sandy Ormiston, Noel Roberts, Ross Roberts, Gretel Silyn Roberts, Robyn Simcock, Karamjeet Singh Siani, Anna Tyrrell, Branko Veljanovski, Nick Walmsley, Dylan Walton, Robert Watson, John Whitmore, Sam Wiess, the Land Treatment Collective and WaterNZ Our mana whenua representatives Ngāti Manuhiri, Fiona McKenzie, Ngāti Maru, Geoff Cook, Ngāi Tai ki Tāmaki , Jeff Lee, Ngāti Tamaoho, Hero Potini & Lucille Rutherfurd, Ngāti te Ata Waiohua, Berenize Peita, Ngāti Wai, Dane Karapu, Ngāti Whātua Ōrākei , Moana Waa, Te Ahiwaru Waiohua, Kowhai Olsen, Te Ākitai Waiohua, Adrian Pettit, Te Kawerau a Maki, Scott Lomas, Te Rūnanga o Ngāti Whātua , Tame Te Rangi, Te Uri o Hau, Tina Latimer All our Community of Practice participants All those who will provide us valuable feedback in the coming months GD 06 Introduction Next steps Feedback Overview
Auckland Design Manual Send us your feedback Access the document GD 06 Introduction Next steps Feedback Overview
Document structure • Section A – Introduction • Section B – Site and subsurface evaluation • Section C – Design flow volume • Section D – Wastewater treatment units • Section E – Design of land application systems • Section F – Construction, commissioning and maintenance • Section G – Risk management GD 06 Introduction Next steps Feedback Overview
GD 06 Introduction Next steps Feedback Overview
Summary of key changes Item GD06 change Site and soil A revised chapter: both theory and technical guidance. Importance of evaluation functional soils, guidance on sample collection, testing, and analysis. Seven soil categories changed to six: to align with those of AS/NZS Soil classification 1547:2012 Methods for managing wastewater on slopes and limits for steep slopes. Slopes and Adjusted setback distances for different types of infrastructure and setbacks receiving environments. Design loading Revised design loading rates for different soil categories. rates Construction and Details of how on-site wastewater systems should be constructed and operation and how they should be operated and maintained. maintenance Risk management New chapter: hazard identification and risk management with examples GD 06 Introduction Next steps Feedback Overview
Site and subsurface evaluation • How do we assess soils? • How do we standardise our assessments? • Bore logs • Categorisation based on: • Texture • Structure • Clay content • Indicative permeability GD 06 Introduction Next steps Feedback Overview
GD06 soil categories Soil category Soil texture [Note 1] Soil structure [Note 2] Typical clay content Indicative permeability (K sat ) (m/d) [Note 3] 1 Granular, structureless or <5% >3.0 Gravel, coarse/medium weakly structured sand Weakly structured 5 – 10% >3.0 Loamy sand, sandy 2 loam Massive 10 – 20% 1.4 – 3.0 High/moderate structured 10 – 20% 1.5 – 3.0 Fine sandy loam, loam, 3 Weakly structured or 10 – 25% 0.5 – 1.5 silt loam massive High/moderate structure 20 – 30% 0.5 – 1.5 Sandy clay loam, fine Weakly structured 20 – 30% 0.12 – 0.5 4 sandy clay, clay loam, silty clay loam Massive 25 – 35% 0.06 – 0.12 Strongly structured 35 – 45% 0.12 – 0.5 Sandy clay, light clay, Moderately structured 35 – 40% 0.06 – 0.12 5 silty clay Weakly structured or 40 – 50% < 0.06 massive Strongly structured 40 – 55% 0.06 – 0.5 Clays (including Moderately structured >50% < 0.06 swelling and grey) and 6 Weakly structured or >50% < 0.06 hard pan massive
Soil classification – refer to page 3 • TP58 has seven categories • AS/NZS Standards has six categories • GD06 aims to realign with the six soil categories used nationally GD 06 Introduction Next steps Feedback Overview
Soil categories – refer to page 4 TP58 (Prepared by A Dakers)
Slopes – refer to page 5 Table 17 in GD06 Land application system Slope gradient Notes limitations* • Surface irrigation <5.7° (10%) Due to risks of effluent run-off during wet weather. (spray, drip and low-pressure • Assumes little disturbance occurs during construction. effluent distribution irrigation) • This is limited by natural infiltration rate and even distribution. • Subsurface drip irrigation <16.7° (30%) All irrigation lines should be installed along the land contours. (i.e. pressure compensating • If this is not possible, and if the lines have non-leak emitters, then drip irrigation) lines may run through contour lines in accordance with the manufacturer’s specifications. • A copy of the specifications should be included with the system design for approval. • Subsurface low-pressure <8.5° (15%) Shallow and narrow trenches for low pressure effluent distribution effluent distribution or low- or low-pressure pipe systems must be constructed along the pressure pipe contour. • Evapotranspiration beds <5.7° (10%) High soil disturbance and erosion issues may arise during construction on steeper slopes. • Trenches and beds, including <8.5° (15%) Construction becomes difficult and costly when slopes are high. discharge control trenches and • High soil disturbance and erosion issues may arise during beds construction on steeper slopes. • Mounds <8.5° (15%) High soil disturbance and erosion issues may arise during construction on steeper slopes. GD 06 Introduction Next steps Feedback Overview
Setbacks – refer to pages 6 - 9 Table 19 of GD06 • Adjustments for slopes to ensure steeper slopes have more conservative setbacks • Adjusted to six soil categories • Includes surface waters (with maximum slopes of 18 ° ) GD 06 Introduction Next steps Feedback Overview
Reserve areas – refer to page 10 Table 20: Reserve application area requirements Land application method Minimum reserve area allocation Subsurface drip irrigation (pressure compensating) 33% - 100% (Where non-conservative design flow based on less than (67% - 100%) 145 L/p/d) Surface drip irrigation (pressure compensating) 50% - 100% (Where non-conservative design flow based on less than (80% - 100%) 145 L/p/d) Shallow trenches (with primary treated effluent) 100% Standard/deep trenches (with primary treated effluent) 100% Evapotranspiration seepage beds 100% Shallow trenches (with secondary treated effluent) 50% - 100% Mound systems 100% GD 06 Introduction Next steps Feedback Overview
Design loading rates – refer pages 10-12 • Changes made to align with AS/NZS and Auckland soils • Ranges removed where possible (e.g. discrete values as minimums) • Very similar to TP58 for majority of soil types (3-5) • Reduced loading for soil category 1 (sands) GD 06 Introduction Next steps Feedback Overview
Construction, operation & maintenance • Installation • Protecting soils • Documentation (certification, management plans, product certification) • Commissioning • Operation: • Education for homeowners • “Do”s and “Don’t”s • Maintenance: • Sludge/scum removal at 50% • Need for a maintenance contract • Mechanisms for monitoring compliance GD 06 Introduction Next steps Feedback Overview
Risk management • System has to operate as designed • Protect public health • Protect receiving environment 5 Risk = Likelihood x consequence 4 Low risk Likelihood 3 Moderate risk 2 High risk 1 1 2 3 4 5 Consequence GD 06 Introduction Next steps Feedback Overview
Regulatory context • TP58 held much of the regulatory context for the Air, Land and Water Plan for Auckland Regional Council • GD06 has removed this regulatory context; this will need to be transposed into the Auckland Unitary Plan. GD 06 Introduction Next steps Feedback Overview
GD 06 Introduction Next steps Feedback Overview
Next steps • Deadline for feedback – October 12 th • Major feedback by mid-September please! • Document finalised and uploaded onto Auckland Design Manual • Adopted through a Plan Change within 18 months. Adopted into AUP GD06 Final through Plan Fully replaces TP58 draft released Change published Jun Jun Jan Dec Jan Dec 2018 2019 Deadline for feedback: Oct 13 GD 06 Introduction Next steps Feedback Overview
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