AS/NZS 1547:2012 EDITING & INTERPRETATION COMMENTARY [v1.0-june 2012]

Transcription

1 AS/NZS 1547:2012 EDITING & INTERPRETATION COMMENTARY [v1.0-june 2012] The publication of AS/NZS 1547:2012 in February this year followed extensive editorial and technical checks during the finalisation of content. However, it seems inevitable that given the complexity of the document some inaccuracies should slip through. None of the items identified to date by On-Site NewZ as in need of editing change are likely to have misled readers and users of the Standard. However, to make the document complete On-Site NewZ suggests a number of editing changes as set out in Table A below. In addition there are several locations in the Standard when the text can, in the view of On-Site NewZ, seem somewhat misleading an interpretation of and commentary on those matters is set out in Table B below. It should be emphasised that AS/NZS 1547:2012 is a standard and not a design manual. In on-site domestic wastewater management practice the difference between the two is: Standard Design Manual Sets out the performance requirements, criteria and design rules to be achieved/adhered to in delivering good practice outcomes ( what to do ). Sets out the implementation process for meeting the requirements and recommendations of the Standard in achieving a high quality treatment, land application and management system ( how to do ). This difference is illustrated in Table B below in reference to Item 3 on food waste disposal units (garbage grinder). The Standard (C [p.46]) states: The installation and use of a food waste disposal unit will result in an increased accumulation of solids, organic materials, oils, and grease in the septic tank and higher concentrations of some contaminants in the effluent discharged to the land application system. Consequently, additional allowances need to be made for the design of the on-site system. This implies that the designer should, in sizing the septic tank and selecting the DLR for the land application system, make allowance for the potentially higher levels of organic matter (BOD) and suspended solids (TSS) in the household wastewater flow. However, no guidance is given on how to do this this is where a design manual comes in. Design manual information has to be consulted regarding the likely increase in BOD and TSS in the septic tank effluent from food waste discharge to the tank, and what design measures are available to deal with these increases. [Note: Currently the NZ design manual TP58 (Auckland Regional Council, 3 rd Edition 2004) has no guidance on how to size and configure septic tanks and land application systems to handle the solids and organic loading from food waste disposal units.] There will no doubt be other editing and interpretation matters which come to attention from time to time, hence this set is labelled version 1.0. Additional items will be added on an as-required basis. Text suggested in need of changing is highlighted. Recommended replacement text is shown red underlined. AS/NZS 1547:2012 On-Site NewZ Editing and Interpretation Commentary [v1.0 3 July 2012] Page 1 of 7

2 TABLE A: EDITING MATTERS Item Clause Text as Published Edited Version Notes [p.9] Appendix K Land application methods Appendix K Land application systems See Title of Appendix K [p.128] Guidance on selection Guidance on selection [p.23] (c) Have a suitably qualified and experienced person make an assessment of the risks to public health and environment, and the costs and benefits of on-site versus reticulated wastewater; (c) Have a suitably qualified and experienced person make an assessment of the risks to public health and environment, and the costs and benefits of on-site versus reticulated sewerage; See Appendix C, clause C2 [p.90] [p.44] 4 C [p.52] 5 Figure A1 [p.73] 6 A3.2.7 [p.76] (b) Require sludge removal when sludge accumulation reduces settling volume below 24 hours retention, at no less than 3 5-year intervals; and (c) Maintain at least a 24-hour emergency storage volume above the high-water-level alarm sensor if the system has a pumped discharge to a land application area. Note during routine monitoring checks (see 6.3.2) any variations in use of the property which might compromise the performance of the land application system and remedy these afterwards. NOTES to Figure A1: 2 AS/NZS ISO uses the term treat risks where in the context of on-site wastewater management the term used is reduce risks. The oversight of on-site wastewater systems through a programmed management scheme or maintenance certification procedures (see and ) which provide operation, maintenance, and performance monitoring of systems on a regular basis is the best means of achieving this step in the risk management process. (c) Require sludge removal when sludge accumulation reduces settling volume below 24 hours retention, at no less than 3 5-year intervals; and (d) Maintain at least a 24-hour emergency storage volume above the high-water-level alarm sensor if the system has a pumped discharge to a land application area. Note during routine monitoring checks (see ) any variations in use of the property which might compromise the performance of the land application system and remedy these afterwards. NOTES to Figure A1: 2 AS/NZS ISO uses the term treat risks whereas in the context of on-site wastewater management the term used is reduce risks. The oversight of on-site wastewater systems through a programmed management scheme or maintenance certification procedures (see and ) which provide operation, maintenance, and performance monitoring of systems on a regular basis is the best means of achieving this step in the risk management process. AS/NZS 1547:2012 On-Site NewZ Editing and Interpretation Commentary [v1.0 3 July 2012] Page 2 of 7

3 Item Clause Text as Published Edited Version Notes 7 Table A1 [p.78] 8 Table A1 [p.78] 9 CB2.1 [p.84] 10 Table K2 [p.137] 11 Table K2 [p.138] 12 Table K2 [p.138] 13 Table K2 [p.138] Site constraints: For subdivisions, lots are to be sufficient size to ensure adequate capacity for the on-site wastewater system appropriate to site-and-soil conditions (reserve areas) along with suitable space for dwelling building platform and all onsite amenity areas) Highly permeable soils or soils with preferential pathways Shallow or spray irrigation to optimise exposure to evapotranspiration/natural UV The quantities indicated by the results of the desktop study are liable to be modified by the results of the SSE. Shallow soil ETA trenches and beds need at least 0.6 m of unsaturated soil below base for final polishing. See Appendix R for Category 1 soils and those with preferential pathway Groundwater quality at risk (especially for Category 1 and 2 soils) - Mounds, ETA beds or trenches, or irrigation systems - Mounds, ETA beds or trenches or irrigation systems, designed using water-balance analysis - Place soil of good permeability around absorption trenches, or around ETA beds and trenches Site constraints: For subdivisions, lots are to be sufficient size to ensure adequate capacity for the on-site wastewater system appropriate to site-and-soil conditions (including reserve areas) along with suitable space for dwelling building platform and all on-site amenity areas Highly permeable soils or soils with preferential pathways Shallow subsurface or spray irrigation to optimise exposure to evapotranspiration/natural UV The decisions based on the findings indicated by the results of the desktop study are liable to be modified by the results of the SSE. Shallow soil ETA/ETS trenches and beds need at least 0.6 m of unsaturated soil below base for final polishing. See Appendix R for Category 1 soils and those with preferential pathway Groundwater quality at risk (especially for Category 1 and 2 soils) - Mounds, ETA/ETS beds or trenches, or irrigation systems - Mounds, ETA/ETS beds or trenches or irrigation systems, designed using waterbalance analysis - Place soil of good permeability around absorption trenches, or around ETA/ETS beds and trenches AS/NZS 1547:2012 On-Site NewZ Editing and Interpretation Commentary [v1.0 3 July 2012] Page 3 of 7

4 Item Clause Text as Published Edited Version Notes 14 Table K2 [p.140] 15 L4.1 [p143] 16 Figure L5 [p.153] Very shallow soils over creviced bedrock - ETA trenches and beds normally need at least 0.6 m below base for final polishing. See Appendix R for Category 1 soils and those with preferential pathways Maximum design loading rates shall be used only where site-and-soil limitations are absent and where there is evidence that these rates can be effectively maintained without harm to the environment or without potential for failure of the system. Maximum design loading rates may also be used for primary treated greywater effluent and for improved primary effluent from septic tanks (see C5.4.1). Very shallow soils over creviced bedrock - ETA/ETS trenches and beds normally need at least 0.6 m below base for final polishing. See Appendix R for Category 1 soils and those with preferential pathways Maximum design loading rates shall be used only where site-and-soil limitations are absent and where there is evidence that these rates can be effectively maintained without harm to the environment or without potential for failure of the system. Maximum design loading rates may also be used for primary treated greywater effluent and for improved primary effluent from septic tanks (see C5.4.1). In this case italics are required to identify the referral as a commentary/explanation [see 1.6, page 9]. There is no clause C5.4.1 in Appendix C. The referral here is to C5.4.1 on page 42. FIGURE L5 CONVENTIONAL BED The topsoil depth over the distribution aggregate is incorrectly shown as 50 mm instead of 150 mm [see below]. FIGURE L5 CONVENTIONAL BED The 50mm should read 150 mm. AS/NZS 1547:2012 On-Site NewZ Editing and Interpretation Commentary [v1.0 3 July 2012] Page 4 of 7

5 Item Clause Text as Published Edited Version Notes 17 M1 [p. 155] 18 CM2.1 [p.155] 19 CM3.1 [p.157] 20 M4 [p.157] 21 CM9.1 [p.162] Irrigation systems increase evapotranspiration in the shallow topsoil layer of a land application area rather than replying fully on hydraulic seepage in the subsoil. Optimum performance from drip irrigation systems is obtained using effluent having a secondary effluent quality of BOD5:15 g/m3 and TSS 15 of g/m3 or better. Some regulatory authorities require that secondary effluent applied to covered surface drip systems to be disinfected prior to application. Primary effluent is not suitable for drip emitter irrigation systems but may be permitted under special circumstances by some regulatory authorities. Approval might include requirements for any one or more of the following: further solids, control measures, an increase in emitter density, an increase in the diameter of the irrigation lines, lower DIR values In spray irrigation; systems-disinfected, secondary-treated effluent shall be dispersed over the soil or vegetated area by sprinklers. In drip irrigation all effluent is discharged below the surface into the potential root zone of the vegetative cover. This helps the plants to reduce nutrient loads in the groundwater. Where, necessary good quality topsoil (see M5) should be sourced from a location acceptable to the regulatory authority. Irrigation systems increase evapotranspiration in the shallow topsoil layer of a land application area rather than relying fully on hydraulic seepage in the subsoil. Optimum performance from drip irrigation systems is obtained using effluent having a secondary effluent quality of BOD at 15 g/m3 and TSS at 15 g/m3 or better. Some regulatory authorities require that secondary effluent applied to covered surface drip systems to be disinfected prior to application. Primary effluent is not suitable for drip emitter irrigation systems but may be permitted under special circumstances by some regulatory authorities. Approval might include requirements for any one or more of the following: further solids control measures, an increase in emitter density, an increase in the diameter of the irrigation lines, lower DIR values In spray irrigation systems, disinfected secondary-treated effluent shall be dispersed over the soil or vegetated area by sprinklers. In drip irrigation all effluent is discharged below the surface into the potential root zone of the vegetative cover. This helps the plants to reduce nutrient loads in the groundwater. Where, necessary good quality topsoil (see CM1) should be sourced from a location acceptable to the regulatory authority. Good quality topsoil is referred to on some 11 occasions throughout the Standard. Although a definition is not given, topsoil --- of good quality is specifically referred to in CM1 [p. 155] as topsoil rich in humus and free of non-topsoil material. AS/NZS 1547:2012 On-Site NewZ Editing and Interpretation Commentary [v1.0 3 July 2012] Page 5 of 7

6 TABLE B: INTERPRETATION MATTERS Item Clause Text as Published Interpretation Commentary [p.13] [p.18] Definitions E. coli (Escherichia coli) A member of the faecal coliform group of bacteria, and indicative of faecal contamination Abbreviations BOD5 5-day biochemical oxygen demand In this 2012 version of the Standard, E-coli replaces thermotolerant coliforms throughout the document. The reason is that E-coli is the recognised term for thermotolerant coliforms. In clause M2.2 (c) [p.156] it will be noted that, in respect of effluent quality for spray irrigation, an average E-coli concentration of 10 cfu per 100mL is used instead of the median thermotolerant coliform count not exceeding 10 organisms per 100 ml (as per the 2000 version of the Standard). BOD 5 is used throughout the Standard without definition. However, general practice in the wastewater treatment industry has been for BOD 5 testing and reporting to be replaced by the cbod 5 testing and reporting. Carbonaceous biochemical oxygen demand testing uses an inhibitor to prevent nitrogenous oxygen consumption being exerted during the five day period. This removes any uncertainty regarding the results and ensures consistency in reporting by removing any uncertainty regarding the presence of nitrifying organisms in the test sample and the effects they may have on the result. 3 C [p.42] [p.57] The installation and use of a food waste disposal unit will result in an increased accumulation of solids, organic materials, oils, and grease in the septic tank and higher concentrations of some contaminants in the effluent discharged to the land application system. Consequently, additional allowances need to be made for the design of the on-site system. See AS/NZS for further guidance. An adequate depth of unsaturated soil below the base of the land application system shall be provided to help remove bacteria, protozoa, and viruses from the soil system. Hence, in respect of the interpretation used in this Standard, BOD 5 should be taken as cbod 5 The installation and use of a food waste A search of AS/NZS :2008 for further disposal unit will result in an increased guidance on additional design allowances can accumulation of solids, organic materials, find nothing that assists in addressing the issue oils, and grease in the septic tank and raised by this comment. There are some 10 higher concentrations of some provisions dealing with food waste disposal contaminants in the effluent discharged to units in AS/NZS 1547, and these provide all the the land application system. Consequently, necessary information for responding to the use additional allowances need to be made for of or potential use of such units in on-site the design of the on-site system. wastewater management practice.to find further guidance on additional design An adequate depth of unsaturated soil below the base of the land application system shall be provided to retain and inactivate bacteria, protozoa, and viruses within the soil system. allowances requires referral to a design manual. Such organisms are not removed from the soil system, but rather are adsorbed and inactivated via adequate retention time within the soil. AS/NZS 1547:2012 On-Site NewZ Editing and Interpretation Commentary [v1.0 3 July 2012] Page 6 of 7

7 Item Clause Text as Published Interpretation Commentary 5 G7 (h) (ii) [p.119] (h) State of soil: (i) Wet/moist/dry when hole excavated using auger (ii) Any presoaking details; (h) State of soil: (i) Wet/moist/dry when hole excavated using auger (ii) Any effects from prior rainfall events CG4.1 [p.117] indicates that no pre-soaking of test holes is necessary. Indeed, if soil in the test hole is saturated or near saturated, testing is not possible (see CG4.1 commentary below). Overnight presoaking of test holes is not necessary, as the test itself indicates when stable infiltration has occurred. In non-reactive soils, infiltration usually stabilises within an hour of the start of the test. In moist soils after rains, infiltration may stabilise almost immediately after the beginning of the test. 6 Table H3 [p.123] 7 CM9.3 [p.142] To ascertain the soil to be tested is not saturated, remove a portion of soil from the base of the test hole. If the soil glistens in the sunlight, it is saturated or nearly saturated. If any soil found within the depth of testing is glistening there is a perched water table and testing is not possible. Alternatively, auger a hole to a depth of 0.5 m below the selected depth of the test holes and cover the opening. Return 1 day later to determine if any water has entered the deep hole. If there is water, the test method described above cannot provide useful data. Source Households (greywater only) (see Notes 4 and 6) Typical wastewater design flows (L/person/day) On-site roof-water tank supply Reticulated community or a borewater supply NOTES 6. Flow allowances only apply where the greywater is to be treated and discharged to land disposal, where solids from kitchen and toilet waste flows are excluded from the wastewater stream (no food waste disposal unit). LPED systems are not appropriate on slopes greater than 27% due to uncertainty with even distribution being achieved on steep land. Greywater is defined [1.9, p.14] for the purposes of this Standard as the domestic wastes from a bath, shower, basin, laundry, and kitchen, but excluding toilet and urinal wastes. It may contain pathogens. Hence, Note 6 is incorrectly worded in that the solids to be excluded are to be those from toilet waste and food waste disposal units, and not those from kitchens. Hence the note should read as follows: 6. Flow allowances only apply where the greywater is to be treated and discharged to land disposal, and where solids from food waste disposal units and toilet waste flows are excluded from the wastewater stream. LPED systems are not appropriate on slopes greater than 25% due to uncertainty with even distribution being achieved on steep land. 27% is a most unusual figure. 25% represents a 1:4 slope (Table 1.1, p.19], and is easier to visualise. AS/NZS 1547:2012 On-Site NewZ Editing and Interpretation Commentary [v1.0 3 July 2012] Page 7 of 7