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A field study assessing the impact of on site valerie mc-carthy_slideshare

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A field study assessing the impact of on-site wastewater treatment systems on surface water quality in a Co. Monaghan catchment at the INTERNATIONAL SYMPOSIUM ON DOMESTIC WASTEWATER TREATMENT & DISPOSAL SYSTEMS TRINITY COLLEGE, DUBLIN, IRELAND Monday 10th & Tuesday 11th September, 2012

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A field study assessing the impact of on site valerie mc-carthy_slideshare

  1. 1. A field study assessing the impact of on-site wastewater treatment systems on surfacewater quality in a Co. Monaghan catchment Valerie McCarthy, DkITInternational Symposium On Domestic Wastewater Treatment & Disposal Systems Trinity College, Dublin, September 2012 www.valeriemccarthy.me
  2. 2. Background Collected Data Study Aims Site Summary Results Conclusions Study Site Location Milltown Lake is an abstraction point for the Churchill and Oram Group water Scheme Services 1,922 people Approximately 735 m3 of water being abstracted daily
  3. 3. Background Collected Data Study Aims Site Summary Results Conclusions Milltown Lake catchment Monitoring has taken place within Milltown Lake catchment for point & diffuse sources of contamination Identifying the various locations, land uses & activities, which are likely sources of contamination Actively engaging community support, commitment & participation through inclusion at all stages of the process
  4. 4. Background Collected Data Study Aims Site Summary Results Conclusions Milltown Lake catchment Pressures to water quality identified within the catchment include: Poor farmyard practices Direct access of cattle to water courses Run-off from slurry & fertiliser spreading Geological Survey of Ireland (GSI) subsoil permeability map records the subsoil in the general area as of ‘low’ permeability, suggesting that runoff usually dominates over infiltration.
  5. 5. Background Collected Data Study Aims Site Summary Results Conclusions Ability of OSWTS at effectivelytreating effluent is dependent on: Soil type: Grain size Chemical composition Depth to bedrock Proximity to surface water Potential presence of preferential flow path Capacity of the system in relation to the number of people using it Chemical composition of the effluent received by the system Frequency at which the tank is de-sludged Correct functioning of components of the system itself Depth of unsaturated subsoil layer
  6. 6. Background Collected Data Study Aims Site Summary Results Conclusions Collected data OSWTS were also identified as a potential source of contamination within the catchment Consequently they were characterised through a combination of: Household questionnaires Non-intrusive site inspections Intrusive monitoring programme
  7. 7. Background Collected Data Study Aims Site Summary Results Conclusions Household Questionnaire Total of 154 households surveyed Average number of occupants per house = 3.1 91 % of the systems were septic tanks 27 % of the respondents never de-sludged their tank Over half of the systems > 16 yrs old
  8. 8. Background Collected Data Study Aims Site Summary Results Conclusions Non-intrusive survey A subset of 42 systems were visually inspected 83 % of which were septic tanks 45 % had percolation areas 38 % of systems relied on soakways (pits filled with stones)
  9. 9. Background Collected Data Study Aims Site Summary Results Conclusions Non-intrusive survey 17 % of systems which direct discharges into drains (two of which had no settlement tanks at all)
  10. 10. Background Collected Data Study Aims Site Summary Results Conclusions Intrusive Study Five sites were selected for intrusive investigation Varying numbers of piezometers were installed down-gradient of each system depending on proximity to water courses & one control located outside predicted area of plume Samples collected once every two weeks between Aug 08 – Aug 09 from each piezometers and from nearest water course – up & down-stream from the OSWTS Analysed for a range of biological & chemical indicator parameters
  11. 11. Background Collected Data Study Aims Site Summary Results Conclusions Aims & Objectives This project focused on systems currently in use, regardless of age, type or level of maintenance & aimed to: Investigate the fate of contaminants arising from OSWTS To provide quantifiable data on the contribution of OSWTS to nutrient loading within the catchment Possible effects of factors such as poor maintenance, incorrect installation & operation & location in areas with unsuitable site characteristics were taken into account
  12. 12. Background Collected Data Study Aims Site Summary Results Conclusions Site summary System Dispersal Distance to No. of Age De-sludging method watercourse Residents (yrs) (m)Site D Secondary Percolation ~ 102 2-4 ~5 Every 2 yrsSite F Septic Tank Soakaway ~ 44 2-3 ~ 35 Every 1 yrSite K Septic Tank Soakaway ~ 12 1-3 ~ 30 intermittentlySite J Septic Tank Soakaway ~ 15 2 ~ 35 intermittentlySite S Septic Tank Percolation >200 2 ~ 30 intermittently
  13. 13. Background Collected Data Study Aims Site Summary Results Conclusions Site characterisation Site characterisation carried in Nov 2008 (EPA, 2000) Incorporated a percolation test to ascertain the assimilation capacity of the subsoil T value P value min/25 mm min/25 mm None of the sites were deemed Site D 38 23 suitable for a conventional septic Site F 98 25 tank system Site S > 100 63 Two were considered suitable for Site K the installation of an advanced > 82 60 wastewater sewage treatment Site J > 90 65 system by the assessor, both with Site S >100 63 recommendations for a soil polishing filterEPA (2000) Wastewater Treatment Manuals: Treatment Systems for Single Houses. Environmental Protection Agency
  14. 14. Background Collected Data Study Aims Site Summary Results Conclusions Water Table Levels Depth to Water Table The water table was relatively stable throughout the monitoring period Depth to Water Table The combined effects of a shallow (m.b.g.l.) water table and a thick capillary Site D fringe at these sites indicate a 0.15 - 2.65 reduced unsaturated zone Site F 0.18 – 2.9 Site K 0.37 – 2.77 Site J 0.77 – 1.37 Site F 0.12 – 0.93Number of issues relating to installationof systems were observed following siteassessment
  15. 15. Background Collected Data Study Aims Site Summary Results Conclusions Example of Site Layout (Site D)
  16. 16. Background Collected Data Study Aims Site Summary Results Conclusions Example of Site Layout (Site F)
  17. 17. Background Collected Data Study Aims Site Summary Results Conclusions Subsurface Water Quality Distribution of chloride (Cl-) concentrations, Site F, Aug 08 – Aug 09
  18. 18. Background Collected Data Study Aims Site Summary Results Conclusions Subsurface Water Quality Distribution of ammonia (NH3+-N) and nitrate (NO3--N) conc, Site F, Aug 08 – Aug 09
  19. 19. Background Collected Data Study Aims Site Summary Results Conclusions Subsurface Water Quality Mean values of indicator parameters up- and down-gradient along the effluent plume path, Site F and D, Aug 08 – Aug 09 Site F Site D Up- Up- Down-gradient Down-gradient gradient gradient BHF2 BHF8 BHD4 BHD9 Distance from Tank (6.4 m) (48 m) (22 m) (102 m) DIN (mg L-1-N) 46.7 9.57 128.2 8.11 DOC 16.5 2.4 29.1 2.6 (mg L-1) SRP (PO43--P mg L-1) 0.02 0.03 27.6 0.02 TC 96 - 397,260 0 - >2,420 18. - 241,960 0 - >2,420 (MPN/100 ml) E. coli 1 - 310,620 0 - >2,420 0 - 11,190 0 - 365 (MPN/100 ml)
  20. 20. Background Collected Data Study Aims Site Summary Results Conclusions Direct Discharges Site K Direct Discharges Accordingly, the principal pathway of potential contaminant delivery to nearby watercourses is unlikely to have been via subsurface flow Site J Direct Discharges
  21. 21. Background Collected Data Study Aims Site Summary Results Conclusions Direct Discharges Preliminary investigation of direct discharge points: Sampling carried out at 4 discharge pipes Two pipes were of unknown origin Monitored for the presence of caffeine & other indicator parameters Caffeine was detected at two of the sites: Site K and one unknown (Site TH5) A linear relationship was observed between E. coli and caffeine at these sites r2=0.95
  22. 22. Background Collected Data Study Aims Site Summary Results Conclusions Direct Discharges Caffeine was detected at two of the sites: Site K and one unknown (Site TH5) A linear relationship was observed between E. coli and caffeine at these sites r2=0.95 Faecal bacteria, Site K & TH5, Feb 12 E. coli TC (MPN/100 ml) (MPN/100 ml) E. coli, Site K, Feb 12 Min Max Site K 261.3 - > 2419.6 >2419.6 MPN day-1 MPN day-1 TH5 64.4 – 1,553 >2419.6 1,960 4.8 x 105
  23. 23. Background Collected Data Study Aims Site Summary Results Conclusions Surface Water QualitySummary of surface water quality adjacent to sites NH3+ (mg L-1- N) 0.08 ± 0.01 NO2-(mg L-1- N) 0.04 ± 0.009 NO3-- (mg L-1- N) 1.13 ± 0.1 SRP (PO43-- mg L-1-P) 0.01 ± 0.001 TP (PO43-- mg L-1-P) 0.02 ± 0.002 Total Coliforms 10 – 24,196 (MPN/100 ml) E. coli (MPN/100 ml) 0 – 17,329
  24. 24. Background Collected Data Study Aims Site Summary Results Conclusions Conclusions Parameters such as P were largely removed during the soil treatment process Some, such as indicator bacteria also experienced large reductions, nevertheless, max total coliform >2,420 MPN/100 ml within 1 m of a nearby water course (102 m from the tank) Nitrate experienced a low rate of reduction and was found at relatively high concentrations within 1 m of adjacent water course at one site (max 12.3 mg L-1 NO3-N) Problem of OSWTS, which may have their subsoil treatment systems either fully or partially by passed - This warrants further investigation - Correct identification of the source of contamination is vital An appropriate inspection system, which is capable of detecting pollution arising from OSWTS is needed
  25. 25. Background Collected Data Study Aims Site Summary Results Conclusions Conclusions Of the sites intrusively investigated: Site D and Site S had inappropriately designed percolation systems Site F had a suspected broken inflow pipe, concern that a portion of greywater maybe piped separately Sites J and K had pipes discharging directly to a watercourse. The system at Site D had never been switched on (Homeowner, pers. comm.) Therefore, there were issues relating to installation and maintenance even before the permeability and characteristics of the subsoil and soil were taken into account. Effective education of homeowners regarding the correct care and maintenance of their OSWTS is crucial.
  26. 26. Acknowledgements Patrick Rafferty1, Eddy Minet1, Suzanne Linnane1, Alison Orr2 & Raymond Flynn2 1 Centre for Environment & Freshwater Studies, DkIT 2 Queens University Belfast This work was funded by the Western River Basin District, ESB International and the Department of the Environment, Heritage and Local GovernmentMcCarthy, V., Flynn, R., Orr, A., Minet, E., Rafferty, P., Meehan, R. and Linnane S. (2010) A field study assessing the impact of onsite wastewatertreatment systems (OSWTS) on surface water in the Milltown Lake catchment, Co. Monaghan . valerie.mccarthy@dkit.ie www.valeriemccarthy.me
  27. 27. Acknowledgements The National Federation of Group Water Schemes and the Churchill and Oram Group Water Scheme The homeowners for allowing us access their land and OSWTS Eddy Minet, Michelle Reilly and other staff and students at the Centre for Freshwater and Environmental Studies, DkIT Jim O’ Donohue and Tom McGoldrick questionnaires and site investigation Robbie Meehan and Nevin Traynor for carrying out site assessments and percolation testsvalerie.mccarthy@dkit.ie www.valeriemccarthy.me

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