A Review of Onsite Wastewater Treatment System Installations and Failures in WA from 1997-2011 Water Unit Department of Health maria.gunady@health.wa.gov.au
Publications 2015 A review of Onsite Wastewater Treatment Systems in WA from 1997 to 2011 M Gunady, N Shishkina, H Tan, & C Rodriguez Journal of Environmental and Public Health http://www.hindawi.com/journals/jeph/2015/7169 57/ Water Journal http://digitaledition.awa.asn.au/default.aspx?iid= 122664&startpage=page0000096#folio=96
Aims To review the installations & failures of OWTS in WA from 1997 2011. Provide recommendations to DOHWA and Local Government re administration of OWTS.
Introduction Most common OWTS in Australia: septic tanks, ATUs, and composting toilets. In 1990s, around 20% Australian households rely on septic systems. >1million OWTS installed in Australia in 2001. Figures likely to increase. Cost effective & long-term option. Failure rate up to 40%, affecting public and environmental health. Figure 1. Distribution of OWTS in Australia in 2001. Source: Beal et al., 2003
Impacts of Poorly Performing OWTS Environmental & public health impacts Disruption of ecosystem balance. Eutrophication & algae blooms. Degradation of soil & water quality. Contamination of water bodies. Emission of offensive odours from untreated effluent. Transmission of diseases, e.g. gastroenteritis, hepatitis, skin infections.
Causes of Failures Inappropriate construction design. siting/ Poor public awareness. Poor maintenance. A change in occupancy. Poor knowledge of operation & maintenance procedures by occupiers/ homeowners.
Legislations and Guidelines Health Act 1911 (WA) Health (Treatment of Sewage and Disposal of Effluent and Liquid Waste) Regulations 1974. Code of Practice for the Reuse of Greywater in WA. Code of Practice for the Design, Manufacture, Installation, and Operation of ATUs. Code of Practice for Product Approval of On-site Wastewater systems in WA. Government Sewerage Policies. AS/NZS 1547: 2000 Onsite Domestic Wastewater Management http://www.public.health.wa.gov.au/3/672/2/wastewater_l egislation_and_guidelines_.pm
Conduct a lit review. Study Method Collect data re approval process: Centralised DOHWA Data Management System. Non-domestic/ commercial OWTS producing >540L/ day of wastewater. Data from LG. <540L/ day of wastewater. Obtained via emails sent out in August 2012 with a spreadsheet containing tables to record the number and type of OWTS approved each year. Survey on primary causes of OWTS failures. Type of OWTS and reasons for failures.
Results Table 1. OWTS approved by DOHWA (1997 2011). System Type 97 98 '99 00 01 02 03 04 05 06 07 08 09 10 11 Septic Tank 98 271 272 193 207 215 171 177 137 34 120 123 88 128 125 ATU 16 41 63 32 26 8 23 16 36 57 28 33 26 60 70 Treatment Plant 1 1 2 1 0 3 0 0 0 0 9 32 23 12 52 Composting Toilet 3 6 5 1 4 2 0 2 1 0 1 3 1 0 0 Other 10 23 19 29 24 26 38 31 60 118 48 36 56 73 59 Total 128 342 361 256 261 253 232 226 234 209 206 227 194 273 306
Results DOHWA >3700 approvals, on average 247 applications annually. Highest in 1999 (361 applications), lowest in 1997 (128 applications). Highest: Shire of East Pilbara and Shire of Derby- West Kimberley. Lowest: most of Perth urban. Perth urban recorded relatively low number of installations.
Results Table 2. OWTS approved by LG (1997 2011). System Type 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 Septic Tank 322 546 782 795 618 630 655 687 556 616 693 753 615 688 626 ATU 49 61 73 50 36 44 63 125 189 149 177 197 155 241 214 Treatment Plant 0 0 0 0 0 0 0 0 0 0 1 1 0 0 3 Composting Toilet 2 0 0 2 3 2 2 0 1 3 3 1 1 1 2 Other 0 7 7 11 9 16 24 17 35 58 56 61 48 46 41 System not specified 130 90 3 14 60 49 41 54 43 72 18 20 13 11 39 Total 503 704 865 872 726 741 785 883 824 898 948 1033 832 987 925
Results - LGs 28 LGs provided data on the number of OWTS installations (23%). 9 in Perth urban. 19 in the outer suburban & rural areas. >12,500 approvals. Highest in 2008 (>1000 applications), lowest in 1997 (<500 applications). Septic is most common. ATU becomes more prevalent.
OWTS Failures in WA Survey conducted in 2011. Total of 53 failures. From 21 LGs (6 metro, 15 country). Other factors: Increase in wastewater volume, Root invasion, Illegal installation, Cross connection to stormwater disposal.
Limitations Data collection on OWTS approvals relies on LG. Mere 23% responded (28 out of 120 LGs). Difficulties in retrieving information. Records were unavailable. Info not recorded in the early years. Not accessible as data stored in offsite storage. Inadequate manpower. OWTS described as other were not explained. Lack of a standardized, common system that allows LG to record the number of OWTS applications & to store information in a standard record system.
Recommendations to DOHWA To improve water quality from OWTS: Provide a standard management tool to all LGs to record OWTS applications (inc. GPS locations). Provide EHOs with onsite wastewater management training based on AS and other legislations. Produce educational materials to owners of OWTS.
Recommendations to LGs Implement OWTS risk management program based on AS to minimise failures. Distribute educational materials produced by DOHWA to owners. Update the register of installed OWTS & implement an inspection strategy to identify sites that require remediation works. Follow-up site inspections of approved OWTS, esp. high-risk areas.
Questions?