Site Assessment – Desk Study, Field Survey, Soil Structure

1. Site Assessment – Desk Study, Field Survey, Soil Structure • Dan Doody • Senior Engineer (Retired) • Monaghan County Council

2. Site Assessment – Key Issues • Environmental Function of ICW – Natural treatment processes. Minimum ‘hard engineering’. Low/zero energy requirements. • Social Considerations – Existing land use. Stakeholder interests in site and linked land and water resources. • Landscape fit – Integration into the environment - Detailed land survey. • Biodiversity – Complement local ecology. (Wetland plants, diverse habitats).

3. Site Assessment • Baseline information: • Can ICW be safely constructed? • Any negative impacts on environment/receiving waters? • Site data for appropriate design. • Info to regulators – planning/discharge licenses. • Info to contractors – Include ground conditions to allow cost estimate.

4. Site Assessment - General • Location of ICW • If in (or discharging to) a SAC, SPA, NHA – An Appropriate Assessment (Art 6 of Habitats Directive) will be required. • Otherwise - field visit to describe habitats in accordance with the Heritage Council’s guide to habitats in Ireland. • Generally favour sites with low current biodiversity value.

5. Site Assessment - General • Risk Based Approach: Hazard-Pathway-Receptor. • Hazard: water vectored pollutants, construction/operation of ICW. • Pathway: significant linkage (e.g. field drains, gravel seams, karst) between hazard and receptor. • Receptor: Surface Water, Groundwater, Natural/built heritage.

6. Site Assessment - General • ‘Absolute Protection is not possible’. • Mitigate risk by; • Low velocity/high residence time – wetland configuration of adequate functional area. • Subsoil of sufficient depth and of the required impermeability.

7. Site Assessment - General • ICWs afford additional protection: • High impedances to infiltration by biofilms, humus and organic matter. • Biological feedback mechanisms secure water retention. • Wetland soils provide an effective processing medium (e.g. for denitrification of nitrate-N and ammonium-N).

8. Site Assessment - General Terrestrial Soils v. Wetlands Soils

9. Typical ICW Influent - Farmyards

10. Typical ICW influent - Wastewater Domestic ICW Influent

11. Ammonium-N concentration • Sustained influent concentrations exceeding 100mg/l and flux concentrations in excess of 280mg/l may cause vegetation die-off.

12. Typical Discharges - Farmyards

13. Typical Discharges - Wastewater

14. Precipitation/Evapotranspiration • Rain related inflow may be many orders of magnitude greater than that originating from direct sources. • Conversely there are likely to be drought periods when there will be no surface water discharges.

15. Restrictions • ICWs should not be considered for sites: • Within 60m up-gradient of a potable well. • Within the inner protection zone of a public groundwater supply (300m up-gradient where protection zone not identified). • Within 25m of dwelling. • Under mature trees. • Where there is a risk of collapse (swallow holes/karst features). • Of Natural Heritage value (without an appropriate assessment).

16. Restrictions (contd.) • ICWs should not be considered for sites: • Where ICW may negatively impact Cultural Heritage value. • Where adequate land area not available. • Close to watercourses (10m from ponds 1&2, 5m from subsequent ponds). • Liable to flooding. • Where neither surface discharge nor exfiltration is possible (additional wet-woodland bunded area??)

17. Surface Water Protection • ICW should be of sufficient size and/or receiving water should have sufficient assimilative capacity (see below)

18. Groundwater Protection • 500mm thickness of subsoil under ponds with a max permeability of 1x10-8m/s underlain by a further 500mm of subsoil. • On a regionally important aquifer where the groundwater vulnerability is high/extreme, 750mm of soil enhanced to 1x10-8m/s underlain by a further 250mm. • On highly permeable sand/gravel/fractured rock in hydraulic contact with the water table – 750mm of low permeability subsoil with upper 500mm enhanced to provide a permeability of 1x10-8m/s.

19. Groundwater Protection (contd.) • Where a risk exists of catastrophic leakage (karst geology/mined areas) increase depth of subsoil to 1500mm – or reject the site. • Geomembrane-lined ponds to be underlain by 100mm of subsoil & 50mm of protective fine sand and overlain by 200mm of low to moderate permeability subsoil.

20. Competency of Assessor • To collect and interpret recorded and field info. • To make a visual assessment (Is a specialist needed?). • To assess the impact on aquatic receptors and site values. • To design the wetland (including understanding terrestrial and wetland soil ecology and their bio-geochemical processes).

21. Site Assessment - Practical • Desk Study & collation of information • Visual Assessment: • Characterisation of wastewater (farmyard inventory/PE and volumetric range). • Evaluate receptor sensitivity and location. • Site Tests: • Trial holes. • Soil characteristics and particle size analysis. • Decision Process/Recommendations.

22. Desk Study • Prelim. consultation with client: • Current wastewater practices. • Approx. volume and composition of waste. • Clients rationale for wastewater management. • Provide the client with an understanding of ICWs (incl. environmental benefits). • Budget costs and approx. land area. • See ‘Site Assessment Form’, Appendix C. of Guidance Document

23. Data Collation • Site Information. • Targets at risk? • Site Restrictions? – NPWS. • Location options? • Topography – OSI maps. • Weather/Climate data (www.met.ie)

24. Surface water receptors • Flow and quality data from EPA, OPW LA, otherwise calculate flow by: • Empirical formula or • CAD model. • Direct flow measurements.

25. Discharge from ICW • Discharge (m3/yr) = (A+B+C) – (D+E) where, • A = initial volume for treatment (m3/yr). • B = Intercepting (paved/roof) area (m2) x annual rainfall (m). • C = ICW area (m2) x annual rainfall (m). • D =ICW area (m2) x annual evapo-transpiration & interception (m). • E = ICW area (m2) x annual infiltration rate (to ground) (m).

26. Receiving Water Quality data • BOD,MRP,SS, Ammonium-N, Nitrate-N, Nitrite-N, (+ if available, Q-rating & WFD river body status). • May be available from EPA or LA – if not: • Min 3 sets of samples over 3 months (incl. July – Sept)

27. Mixing of discharge with river water • Cds = (Qu x Cu) + (Qd x Cd) (Qu + Qd) • Qu = river flow u/s. • Cu = pollutant concentration in river u/s. • Qd = discharge flow. • Cd = pollutant concentration in discharge. • Cds = pollutant concentration in river d/s. • Average flows (ICW discharge prop. to rainfall) • S.I. No.272 of 2009 surface water and S.I. No.9 of 2010 groundwater.

28. Groundwater • Limiting parameter – Ammonium-N • EPA and GSI – Aquifers & Vulnerability maps – groundwater protection zones. • National aquifer maps (GSI). • If Vulnerability maps not available check: • Relevant River Basin District project. • Soil & subsoil maps (Teagasc). • Outcropping bedrock & karst (GSI). • Groundwater Response Matrix – Appedix A (Guidance Document).

29. If Surface Discharge not available: • Consider discharge to ground. • If discharge less than 5m3/day detailed assessment not required. • If greater than 5m3/day – guidance on detailed assessment to be published by EPA in 2011.

30. Natural & Cultural Heritage • Designated (and candidate) NHAs, SPAs, SACs, protected structures, archaeological sites – consult with: • Client • LA • NPWS • DECLG

31. Visual Site Assessment • If no insurmountable problems from desk study carry out visual assessment to: • Verify (or amend) desk study. • Assess on-site hazards. • Evaluate surface/ground water receptors. • Location options for ICW.

32. Visual Assessment - Wastewater • Site visits – client present (on wet days): • Component sources of waste. • Estimate total volume of waste. • Discuss all water management activities with client. • Take Photographs.

33. Visual Assessment - Topography • Scope Topographical Survey to: • Aid design. • Examine discharge options. • Assess landscape fit. • Wet sites have advantages but: • Biodiversity impact/benefits? • Additional inflow? • N.B. Check for field drains.

34. Visual Assessment - Surface Waters • Identify receiving waters: • Channel width, depth, debris marks. • Est. assimilative capacity. • Water quality info – samples. • Other water features: • Lakes, wetlands, streams, ditches and N.B. land drains. • Photographs.

35. Visual Assessment - Groundwater • Check existing wells/boreholes within 300m (incl. direction of flow). • Groundwater levels (trial holes). • Any groundwater quality data? • Karst features – swallow holes, ‘dolines’ • Road cuttings, open excavations, river banks (ground conditions). • Photos.

36. Utilities, Natural & Cultural Heritage • Verify (or amend) desk study: • Archaeological input? • Trees, o/h lines, houses, schools, churches. • Set-back distances. • Downwind receptors. • Evidence of flooding. • Can ICW be constructed?

37. Trial Holes/Trenches • Trial Holes – min 2-3m below bases of ponds (plus depth to rock & water table). • No. of trial holes: • Area of ICW 0.5ha - min 3 • 0.5 – 1.0ha - min 4 • 1.0 – 1.5ha - min 5 • 1.5 – 2.0ha - min 6 • More than 2.0 ha - min 7 • Record soil data to BS 5930 (Ref. Appendix D, Guidance Document)

38. Soil Subsoil Characteristics

39. Particle Size Distribution Test • A PSDT indicates permeability: • Clay content – lab test to BS 1377 (particles greater than 20mm diameter removed) • Clay content 13% or greater for 1x10-8m/s. • If 10% - 13% clay content, enhance subsoil to achieve permeability of 1x10-8m/s. • No of PSDTs related to size of ICW (similar to trial hole scenario).

40. Summary – ICW Decision Issues

41. Discharges Glaslough ICW ‘The Pure Drop’ (Autumn 2010) No Discharge (1 May 2011)

42. Contact Information • danjdoody@gmail.com • Tel. 047 88811 • Mob. 087 6470832