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HomeMy WebLinkAbout2664 - Site Assessment Reportm OIV. CO. CO. ANNING SECTION 15 JUL Lc47J 64 IIIL Y �L�'i V�^i`...i tl"Ifd6ii ty� �; "j•. SITE CHARACTERISATION FORM COMPLETING THE FORM Note: This form requires the latest version of Adobe Acrobat Reader and on PC's Windows 7 or later. Windows XP produces errors in calculations Step 1: Goto Menu Item File, Save As and save the file under a reference relating to the client or the planning application reference if available. Clear Form Use the Clear Form button to clear all information fields. Notes: All calculations in this form are automatic. Where possible information is presented in the form of drop down selection lists to eliminate potential errors. Variable elements are recorded by tick boxes. In all cases only one tick box should be activated. All time record fields must be entered in twenty four hour format as follows: HH:MM All date formats are DD-MM-YYYY. All other data fields are in text entry format. This form can be printed out fully populated for submission with related documents and for your files. It can also be submitted by email. Section 3.2 In this section use an underline across all six columns to indicate the depth at which changes in classification / characteristics occur. Section 3.4 Lists supporting documentation required. Section 4 Select the treatment systems suitable for this site and the discharge route. Section 5 Indicate the system type that it is proposed to install. Section 6 Provide details, as required, on the proposed treatment system. APPENDIX A: SITE CHARACTERISATION FORM File Reference: Daniel & Ciara Finnegan, Cavan Moutry, Emyvale. Prefix: Mr El First Name: I Surname: Finnegan IDaniel Address: Site Location and Townland: j- Cavan Moutry, Emyvale, Co. Monaghan Number of Bedrooms: 4 E Maximum Number of Residents: Comments on population equivalent There are 4 double bedrooms which will equate to six adults. Proposed Water Supply: Mains jj Private Well/Borehole I Group Well/Borehole Soil Type, (Specify Type): Subsoil, (Specify Type): Poorly drained mineral soil. Gleys. AminPD Sandstone and shale till TLCSsS Bedrock Type: DMSSL Aquifer Category: Regionally Important I Locally Important Lm 0 Poor El Vulnerability: Extreme High LIModerate Low ❑✓ Groundwater Body: Aughnacloy Status Poor Name of Public/Group Scheme Water Supply within 1 km: Truagh GWS Source Protection Area: ZOC SI SO ❑ Groundwater Protection Response: R1 0 Presence of Significant Sites (Archaeological, Natural & Historical): Past experience in the area: Vone Raised mounds gererally required in this area. Comments: (Integrate the information above in order to comment on: the potential suitability of the site, potential targets at risk, and/or any potential site restrictions). The site is potentially suitable as there appears to be no restrictions to the on -site treatment of domestic effluent. Surface water and ground water could be targets at risk. NOTE: This site characterisation is for an existing house on the site that is for renovation. Note: Only information available at the desk study stage should be used in this section. 3.1 Visual Assessment Landscape Position: Elevated on a Northerly facing slope. Slope: Steep (>1:5) Shallow (1:5-1:20) Relatively Flat (<1:20) ❑✓ Slope Comment About 1:15 Surface Features within a minimum of 250m (Distance To Features Should Be Noted In Metres) Houses: Existing Land Use: Wasteground Vegetation Indicators: ass and some rushes. Groundwater Flow Direction: Expected North. Ground Condition: Firm to soft during a spell of wet weather. Site Boundaries: Mature hedges all around. 3.1 Visual Assessment (contd.) Roads: Local road along the Eastern boundary. Outcrops (Bedrock And/Or Subsoil): None Surface Water Ponding: None Lakes: Lough More 3.8km South-West. Beaches/Shellfish Areas: None Wetlands: None Karst Features: None Watercourses/Streams:* Rakelly river 271 m South-West. *Note and record water level 3.0 ON -SITE ASSESSMEN 3.1 Visual Assessment (contd.) Drainage Ditches:* None within 50m. Springs:* listed within 100m Wells:* None within 100m Comments: (Integrate the information above In order to comment on: the potential suitability of the site, potential targets at risk, the suitability of the site to treat the wastewater and the location of the proposed system within the site). The site was in fair condition underfoot with the assessment being carried out during a period of wet weather. `Note and record water level 3.2 Trial Hole (should be a minimum of 2.1m deep (3m for regionally important aquifers)) To avoid any accidental damage, a trial hole assessment or percolation tests should not be undertaken in areas which are at or adjacent to significant sites, (e.g. NHAs, SACs, SPAs, and/or Archaeological etc.), without prior advice from National Parks and Wildlife Service or the Heritage Service. Depth of trial hole (m): 2.1 Depth from ground surface Depth from ground surface to bedrock (m) (if present): to water table (m) (if present): 1.2 Depth of water ingress: 1.0 Rock type (if present): None Date and time of excavation: 09 -Jun -2026 11:00 Date and time of examination: 11 -Jun -2026 09:00 Depth of Surface and Subsurface Percolation Tests 0.1m II 0.2m II 0.3 m 0 0.4m 0 0.5m II 0.6 m 0.7 m I 0.8m ISS 0.9m II 1.0m I 1.lml lI 1.2m II 1.3 m L_J 1.4m ( I 1.5 m I 1.6m 0 1.7m 0 1.8m I 1.9m II 2.0m I 2.1m lI 2.2 m I I 2.3m II 2.4m II 2.5 m [_I 2.6 m 2.7 m 0 2.8m 0 2.9 m 3.0 m 3.1 m I 3.2 m 1I 3.3m II 3.4m II 3.5m Soil/Subsoil Texture & Plasticity and Soil Density/ Classification** dilatancy*** Structure Compactness SILT / CLAY TOP SOIL SILT / CLAY subsoil 50% clay SILT / CLAY subsoil with some sand 4 threads —80mm ribbons — dilatant 6 threads - 160mm ribbons - dilates with difficulty. 3 threads - 40mm ribbons - dilatant CRUMB BLOCKY / MASSIVE GRANULAR SOFT UNCOMPACT Colour**** Preferential flowpaths BROWN GRASS ROOTS NONE GREY/ ORANGE SOFT II DARK NONE BROWN II Likely Subsurface Percolation Value: 50 Likely Surface Percolation Value: I 40 Note: *Depth of percolation test holes should be indicated on log above. ('Enter Surface or Subsurface at depths as appropriate). See Appendix E for BS 5930 classification. 3 samples to be tested for each horizon and results should be entered above for each horizon. "" All signs of mottling should be recorded. 3.2 Trial Hole (contd.) Evaluation: The trial hole was 2.Om deep. There were three distinct layers. Silt / clay top -soil and below that sub -soil that was blocky / massive in nature with about 50% clay and below that grey subsoil that was soft and sandy in nature. The water table was at 0.5m 3.3(a) Subsurface Percolation Test for Subsoil Step 1: Test Hole Preparation Percolation Test Hole 1 2 3 Depth from ground surface I 400 400 400 to top of hole (mm) (A) Depth from ground surface 800 800 800 to base of hole (mm) (B) ii II Depth of hole (mm) [B - A] 400 400 400 Dimensions of hole 300 x 300 300 x 300 300 x 300 [length x breadth (mm)] Step 2: Pre -Soaking Test Holes Pre-soak start Date 09 -Jun -2026 09 -Jun -2026 Time 15:00 15:00 2nd pre-soak Date 10 -Jun -2026 10 -Jun -2026 start Time 14:30 14:30 Each hole should be pre-soaked twice before the test is carried out. Step 3: Measuring T100 Percolation Test Hole No. Date of test Time filled to 400 mm Time water level at 300 mm K 09 -Jun -2026 15:00 10 -Jun -2026 14:30 3 11-06-2026 11-06-2026 11-06-2026 09:00 09:00 09:00 12:40 13:00 13:10 Time (rain.) to drop 100 mm (T100) L 220.00 240.00 250.00 Average T100 If T100 > 480 minutes then Subsurface Percolation value >120 - site unsuitable for discharge to ground If T100 ≤ 210 minutes then go to Step 4; If T100 > 210 minutes then go to Step 5; 236.67 Step 4: Standard Method (where T,00 < 210 minutes) Percolation Test Hole 1 2 3 Fill no. Start Finish At (min) Start Finish At (min) Start Finish At (min) Time Time Time Time Time Time (at 300 (at 200 mm) mm) (at 300 (at 200 mm) mm) (at 300 (at 200 mm) mm) 1 000 I 0! 000 2 000 000 000 3 000 000 00I Average At 0.00 0.00 0.00 LI_J Value Average At/4 = [Hole No.1] 0.001(t1) Average At/4 = [Hole No.2] 0.001(t2) Average At/4 = [Hole No.3] 0.00 (t3) Result of Test: Subsurface Percolation Value = 0 (min/25 mm) Comments: Vith the sub -surface tests being slow I proceded to step 5 Step 5: Modified Method (where T100> 210 minutes) Percolation Test Hole No. 1 Fall of water Time Start Finish Time K, T— in hole (mm) Factor Time Time of fall = T, Value = T, hh:mm hh:mm (mins) / T = 4.45 =T / Krs 300 -250 I 8.1 12:40 13:20 40.0011 0.2011 21.98 250-200 I9.7 13:20 14:30 70.0011 0.1411 32.11 200 -150 I 11.9 14:30 16:50 140.00 0.0911 52.35 150-100 I 14.1 16:50 19:40 170.0011 0.0811 53.65 Average T- Value T- Value Hole 1 = (T1) I 40.02 Percolation Test Hole No. 3 Fall of water Time Start Finish Time K„ T— in hole (mm) Factor Time Tim§e of fall = T, Value =T, hh:mm hh:mm (mins) IT, = 4.45 = Tm 300 -250 I 8.1 13:10 14:00!!_50.00!!_0.16!!_27.47 250-200 I.7 14:00 15:5011110.0011 0.0911 50.46 200 - 150 I 11.9 15:50 18:10 140.0011_0.0911_52.35! 150-100 14.1 18:10 21:20!190.0011_0.07!!_59.96! Average I T- Value T- Value Hole 3 = (T2) 47.56 Percolation Test Hole No. 2 Fall of water in hole (mm) Time Factor =T, Start Time hh:mm Finish Time hh:mm Time of fall (mins) =Tm K„ = T /Tm T — Value =4.45 /Kh 300-250 8.1 13:001113:50 50.00 0.16 27.47 250-200 9.7 13:50!!15:20 90.00110.11! 41.29 200-150 11.9 15:20 17:50 150.00 0.08 56.09 150-100 I14.1 17:5011_21:4011230.001!_0.06 72.59 Average T- Value T- Value Hole 2 = (12) 49.36 Result of Test: Subsurface Percolation Value = 45.64862939291277 (min/25 mm) Comments: A raised mound will be required due to the amount of clay in the subsoil. 3.3(b) Surface Percolation Test for Soil Step 1: Test Hole Preparation Percolation Test Hole Depth from ground surface to top of hole (mm) Depth from ground surface to base of hole (mm) Depth of hole (mm) Dimensions of hole [length x breadth (mm)] Step 2: Pre -Soaking Test Holes 1 2 3 400 400 400 400 400 400 300 x 300 300x 300 300x 300 Pre-soak start Date 09 -Jun -2026 09 -Jun -2026 09 -Jun -2026 Time 19:35 I 19:35 I 19:35 2nd pre-soak Date 10 -Jun -2026 I 10 -Jun -2026 10 -Jun -2026 start Time 14:05 I 14:05 I 14:05 Each hole should be pre-soaked twice before the test is carried out. Step 3: Measuring T100 1 2 3 Percolation Test Hole No. I II II I 11 -Jun -26 II 11 -Jun -26 11 -Jun -2026 Date of test ii 09:0511 09:05 09:051 Time filled to 400 mm 10:50 10:40 10:401 Time water level at 300 mm 105.00 95.00 II 95.00 Time to drop 100 mm R ) 100 98.33 Average T100 If T100 > 480 minutes then Surface Percolation value >90 - site unsuitable for discharge to ground If T100 ≤ 210 minutes then go to Step 4; If T100 > 210 minutes then go to Step 5; Step 4: Standard Method (where T,00 ≤ 210 minutes) Percolation Test Hole 1 2 3 Fill no. Start Finish AT (min) Start Finish AT (min) Start Finish AT (min) Time Time Time Time Time Time (at 300 (at 200 mm) mm) (at 300 (at 200 mm) mm) (at 300 (at 200 mm) mm) 1 10:50 12:10 80.00 10:40I12:00 80.00110:401112:20 100.00 2 I 12:101p14:10 120.00 12:00 13:5011 110.00 I 12:201114:25 125.00 3 Average AT 14:101117:0011170.00113.50 16:40 170.00 14:25 17:2011175.001 123.33 120.00 133.33 Value Average AT/4 = [Hole No.1] 30.831(T1) Average AT/4 = [Hole No.2] 30.001(T2) Average AT/4 = [Hole No.3] I 33.331(T3 Result of Test: Surface Percolation Value = 31.39 (min/25 mm) Comments: 'he topsoil at this site is of fair quality and may be used to form a raised mound soil percolation area to polish treated effluent from an dvanced treatment system. Step 5: Modified Method (where T,Q0 > 210 minutes) Percolation Test Hole No. 1 Fall of water in hole (mm) Time Factor = T, Start Time hh:mm Finish Time hh:mm Time of fall (mins) = Tm K = T, / T T- Value = 4.45 /K, 300 - 250 8.1 0.00 =0 250 - 200 0.00 l ______ 200- 150 11.9 �0 0.0011 _ 150- 100 14.1 �� 0.00 �� Average T- Value T- Value Hole 1 = (T1) 0.00 Percolation Test Hole No. 3 Percolation Test Hole No. 2 Fall of water Time Start Finish Time K,s T — in hole (mm) Factor Time Time of fall =T, Value =T, hh:mm hh:mm (mins) /Tm =4.45 =T /K,� 300- 250 I 8.1 =� 0.00 l= 250 -200 I9.7 00 0.00 lI 200 - 150 P9 0.00 == 150- 100 I 14.1 =� 0.00 =I Average I T- Value T- Value Hole 2 = (T2) 0.00 Result of Test: Surface Percolation Value = o (min/25 mm) Fall of water Time Start Finish Time K,z T- Comments: in hole (mm) Factor Time Time of fall = T, Value = T, hh:mm hh:mm (mina) / T = 4.45 =T /K 300-250 I 8.1 I� 0.00 �I 250 - 200 9.7 00 0.00 =� 200-150 � 11.9 0.00 150-100 � 14.1 00 0.00 � Average T- Value T- Value Hole 3 = (T2) I 0.00 3.4 The following associated Maps, Drawings and Photographs should be appended to this site characterisation form. 1. Discovery Series 1:50,000 Map indicating overall drainage, groundwater flow direction and housing density in the area. 2. Supporting maps for vulnerability, aquifer classification, soil, subsoil, bedrock. 3. North point should always be included. 4. (a) Scaled sketch of site showing measurements to Trial Hole location and (b) Percolation Test Hole locations, (c) wells and (d) direction of groundwater flow (if known), (e) proposed house (incl. distances from boundaries) (f) adjacent houses, (g) watercourses, (h) significant sites (i) and other relevant features. 5. Site specific cross sectional drawing of the site and the proposed layout' should be submitted. 6. Photographs of the trial hole, test holes and site including landmarks (date and time referenced). 7. Pumped design must be designed by a suitably qualified person. The calculated percolation area or polishing filter area should be set out accurately on the site layout drawing in accordance with the code of practice's requirements. Integrate the information from the desk study and on -site assessment (i.e. visual assessment, trial hole and percolation tests) above and conclude the type of system(s) that is (are) appropriate. This information is also used to choose the optimum final disposal route of the treated wastewater. Slope of proposed infiltration / treatment area: 1:15 Are all minimum separation distances met? II Depth of unsaturated soil and/or subsoil beneath invert of gravel (or drip tubing in the case of drip dispersal system) 0.90 Percolation test result: Surface: 31.39 Not Suitable for Development I Identify all suitable options Septic tank system (septic tank and percolation area) (Chapter 7) Secondary Treatment System (Chapters 8 and 9) and soil polishing filter (Section 10.1) Tertiary Treatment System and Infiltration / treatment area (Section 10.2) Sub -surface: 45.65 Suitable for Development Discharge Route' No Groundwater Yes Yes Propose to install: Secondary Treatment System and soil polishing filter and discharge to: Lnd Water Invert level of the trench/bed gravel or drip tubing (m) 0.60 Site Specific Conditions (e.g. special works, site improvement works testing etc. Mechanical aeration system and a raised mound soil polishing filter measuring 1.2m in height to be installed and constructed to EPA 2021 specifications. The raised mound is required due to clay encountered at 0.6m. The raised mound shall be made up of the insitu topsoil. I recommend 60m of percolation trench in the soil polishing filter consisting of 6 lengths of trench each measuring 10m. The invert of the percolation trenches should be at 0.6m with 0.9m pervious unsaturated soil below to ensure proper polishing of the final effluent. The raised percolation area shall measure 13m x 13m and may be landscaped into the contours of the site. Ensure that the final effluent from the mechanical aeration system is distributed evenly to each of the six percolation trenches. It is important to ensure that the percolation trenches and related pipe work are put in at the correct slope. A surface water drain measuring 1 m deep shall be employed (min 2m away) up -slope from the raised mound soil polishing filter to divert surface water away from the percolation area and to prevent the water table rising in wet weather. NOTE: It is very important to ensure that the aeration pump remains on at all times on the mechanical aeration system or otherwise the system will revert to septic conditions causing odors and poorer quality effluent which may lead to clogging of the percolation trenches. ' A discharge of sewage effluent to "waters" (definition includes any or any part of any river, stream, lake, canal, reservoir, aquifer, pond, watercourse or other inland waters, whether natural or artificial) will require a licence under the Water Pollution Acts 1977-90. Refer to Section 2.4. SYSTEM TYPE: Septic Tank Systems (Chapter 7) Tank Capacity (m3) Percolation Area No. of Trenches Length of Trenches (m) Invert Level (m) 0 Mounded Percolation Area No. of Trenches 6.00 Length of Trenches (m) 10.00 Invert Level (m) 0.60 SYSTEM TYPE: Secondary Treatment System (Chapters 8 and 9) and polishing filter (Section 10.1) Secondary Treatment Systems receiving septic tank effluent Packaged Secondary (Chapter 8) Treatment Systems receiving raw wastewater (Chapter 9) Media Type Area (m2)* Depth of Filter Invert Level Type Sand/Soil BAF TREATMENT SYSTEM Soil Capacity PE 6 Constructed Wetland Sizing of Primary Compartment Other 2 90 m3 Polishing Filter*: (Section 10.1) r30.001 Option 3 - Gravity Discharge T60.00 Surface Area (m2)* Trench length (m) Option 1 - Direct Discharge Surface area (m2) Option 4 - Low Pressure Pipe Distribution Option 2 - Pumped Discharge Trench length (m) Surface area (m2) Option 5 - Drip Dispersal Surface area (m2) SYSTEM TYPE: Tertiary Treatment System and infiltration / treatment area (Section 10.2) Identify purpose of tertiary Provide performance information Provide design information treatment demonstrating system will provide required treatment levels DISCHARGE ROUTE: Groundwater ❑✓ Hydraulic Loading Rate * (I/m2.d) 30.00 Surface area (m2) r 30.00 Surface Water ** Discharge Rate (m3/hr) 0.04 Hydraulic loading rate is determined by the percolation rate of subsoil ** Water Pollution Act discharge licence required QUALITY ASSURANCE: Installation & Commissioning System to be signed off by a suitably qualified person and recommendations in section 5.0 to be adhered to. Package treatment system must conform to EN 12566-3 standard. Package treatment system to be properly installed and certified by company supplying the system in accordance with the EPA 2021 code of practice. Keep records of desludging for five years. On -going Maintenance Desludge tank as recommended by manufacturer and periodically inspect the system for damage or surface ponding. Maintenance contract to be agreed by company supplying the package treatment system and contract must be adhered to so as to ensure that the system continues to function properly. Company: Blolabs Prefix: Mr Q First Name: Michael Surname: Holohan Address: ITERERA, SCOTSTOWN, CO. MONAGHAN Qualifications/Experience: GSI / EPA CERTIFIED Date of Report: 13 -Jun -2026 Phone: I 08681691621 E-mail biolabsirl@outlook.com Indemnity Insurance Number: RPI-IE000946-00 Signature: CLONISUOYI V V / � / 111. NNAVI. 1l UFRRYGORRY MM I.AGIIMORF ESKER A RU(; IN NY AVAN IMouiray) I.I4NAVI:1) r WELLS AND BOREHOLES ADJACENT TO THE SITE Public Supply Source Protection Areas ■ SI-Inner Protection Area 11 DERRYGORRY SO -Outer Protection Area ESKEU e III NNAVI i1 MULL AI1I I"ICI' AVAN (Mont aY) SOURCE PROTECTION DATA (N/A) CLONIS©OYL1 l /RIIMRI'' Mll 1. I AG11MO11I RIVERS AND AQUIFER CATEGORY n,m VULNERA B D H u V LOW a BEDROCK DMSSL f��nt hornan n * / 3)' - .. " d/) ! f Corp' n ,,�•" "' lonisb �� D-) r' • � b ' er ny � I L ery a _.,..4, --- pavan outr ) +� Q nimbi 7 ', . a. t 2Q '1 �'4r Clank n ullar 1. ,� tu1ulia na ..�.> • Killyslavan 11b S TN J s4 NoasC ON TOE Si rE cqR R�No vrlo N� SKETCH OF PERCOLATION AREA INCLUDING SITE SURROUNDS VIEWS OF PERCOLATION SITE TRIAL HOLE ON DAY OF EXCAVATION TRIAL HOLE TWO DAYS AFTER EXCAVATION T1 +,ate 3 (►� � ,;t •: ��� �.�:r�, ,i �M eft +YI 3 -T TEST C=HOLES Ti T2 P1 P2 P3 P TEST HOLES OUTLINE SPECIFICATIONS FOR MOUNDED SOIL POLISHING FILTER 1. Treated effluent from the mechanical aeration sump unit shall be pumped intermittently or fed by gravity if the levels allow to the distribution chamber on the mound feeding the 6 percolation trenches. The raised mound shall be 1.2m in height throughout its area and consist of the topsoil from the site. The mound shall measure 13m x 13m. 2. The slope of the percolation trenches from the distribution chamber shall be 1 in 200 3. The length of each of the 6 percolation trenches shall be l0m. Total length 60m. 4. The separation distance between the percolation trenches shall be 2m (ie 2.5m centre to centre) 5. Percolation pipes shall be 100mm diameter smooth wall uPVC sewer pipes, perforated at 4, 6 and 8 o'clock. Perforations shall be 8mm diameter, at 75mm centre's along the pipe. Holes shall be checked before installation to ensure they are free from debris. 6. The width of each percolation trench shall be 500mm. 7. The depth of each percolation trench shall be 600mm below the mound surface. 8. Percolation pipes shall be laid on a 250mm bed of washed gravel, having particles in the range of 8 - 32mm. 9. Pipe surround shall be washed gravel, having particle size in the range 8 - 32mm. 10. Pipe cover shall be 150mm depth of washed gravel, having particle size in the range of 8 - 32mm. 11. Geotextile layer to be placed on top of this followed by 100mm topsoil to top of mound. 12. Geotextile shall be in accordance with EN ISO 10319. Access / inspection points and vents shall be provided for the ends of the percolation pipes. Covers shall be visible and installed to prevent the ingress of water. They shall be suitable for rodding and scouring purposes. 13. A surface land drain lm deep shall be employed upslope of the raised mound soil polishing filter and not closer than 2m to divert surface water away from it and to prevent the water table rising in wet weather. SCHEDULE OF SITE SEPARATION DISTANCES PACKAGE TREATMENT SYSTEM . Minimum distance to any dwelling = 7m . Minimum distance to site boundary = 3m . Minimum distance to trees = 3m . Minimum distance to roads = 4m . Minimum distance to slope breaks = 10m . Minimum distance to watercourse / streams = 10m . Minimum distance to soakaway = 10m . Minimum distance to open drain = 10m . Minimum distance to lake or foreshore = 50m able 6.3 EPA Code of Practice 2021 POLISHING FILTER . Minimum distance to any dwelling = 10m . Minimum distance to site boundary = 3m . Minimum distance to trees = 3m . Minimum distance to roads = 4m . Minimum distance to slope breaks = 10m . Minimum distance to water course / stream = 10m . Minimum distance to soakaway = 10m . Minimum distance to open drain =10m . Minimum distance to lake or foreshore = 50m Minimum distance to up gradient well = 15m Minimum distance well on same level = 30m . Minimum distance to down gradient well = 40m 6.31 EPA Code of Practice 2021 unless stated otherwise TOPSOIL 100MM GEOTEXTILE LAYER I150MM WASHED STONE ABOVE PIPE O 100MM PIPE I 0.6M 250MM WASHED STONE BELOW PIPE INVERT OF TRENCH SUITABLE SUBSOIL MINIMUM 0.9M Water table EACH TRENCH 500MM WIDE MOUNDED TOPSOIL 1.2M GROUND LEVEL SECTION THROUGH MOUNDED SUBSOIL PERCOLATION SYSTEM N