re: on-site wastewater management assessment lot 14, dp

18 May 2021 5QS Ref: 218009

Mr J Davies 140 Good Hope Road GOOD HOPE NSW 2582 Dear Mr Davies,

Re: On-site Wastewater Management Assessment Lot 14, DP 1132530 140 Good Hope Road, Good Hope

1 Introduction

An on-site wastewater dispersal geotechnical investigation has been undertaken on the

above property in accordance with AS/NZS1547:2012 ‘On-site Domestic Wastewater

Management’ and the Environment and Health Protection Guideline ‘On-site Sewage

Management for Single Households’.

This report provides details of the investigation and recommendations for on-site dispersal

of treated sewage wastewater at the subject site. A Site and Soil Evaluation and various

dispersal area calculation sheets that address specific matters as required by

AS/NZS1547:2012 ‘On-site Domestic Wastewater Management’ and the Environment and

Health Protection Guideline ‘On-site Sewage Management for Single Households’ have been

attached.

Details of the property and pertinent site features may be seen on the attached drawing

218009/EFD-1 and details of the site assessment and dispersal area calculations are set out

in the attached Site and Soil Evaluation and irrigation area calculation sheets.

YASS HARDEN CANBERRA SYDNEY GOSFORD NEWCASTLE

TM

5QS Consulting Group South is a division of Twelve20 Pty Ltd ABN 58 609 085 207

6226 5598 [email protected] PO Box 645 Yass NSW 2582

5QS Consulting Group 18 May 2021 Consulting Engineers 5QS Ref: 218009

2

On-site Wastewater Management Assessment 140 Good Hope Road, Good Hope

2 Project Description

The investigation was for the dispersal of aerated wastewater treatment system (AWTS)

treated domestic wastewater via surface irrigation.

The assessment has been based on;

a) A future 4 bedroom residence and a 2 bedroom cottage

b) The residence and cottage both being connected to tank water.

It is proposed to construct a new residence and cottage on the crest of a broad ridge trending

from east to west across the northern portion of the property. The property falls away from

the broad crest and very steep grades in excess of 50% to the south and lower grades of

between 10 and 20% to the west and north.

At the time of the investigation the site supported a good coverage of pasture grasses.

Isolated mature gum trees were scattered across the ridge. The remainder of the property

was cleared. A broad drainage depression traversed the midpoint of the property at the foot

of the ridge. A farm dam had been constructed across the drainage depression adjacent to

the western side boundary.

The surface grades in the vicinity of the proposed available dispersal area were convex

divergent with grades of approximately 5% to 15% downslope to the north and west.

The location of the proposed residence, pertinent site features are set out on the attached

drawing 218009/EFD-1.

3 Desktop Study

3.1 Soil Landscape

The site falls within the Cockatoo Soil Landscape as identified on the “Soil Landscapes of

the Goulburn 1:250 000 Sheet” published by the Department of Land and Water

Conservation.

The Cockatoo Soil Landscape lies within the Derringullen Formation which overlies the

Douro Volcanics and has shallow to moderately deep, brightly coloured red and yellow

gradationally textured soils with weak to occasionally moderate structure, neutral to slightly

alkaline reaction tends and occasional development of non-bleached A2 horizons are typical

on slopes. The soils are similar to better quality Red and Yellow Earths. Non-calcic Brown

Soils also occur on slopes with Lithosols on crests. Terra Rossa Soils are found on the

occasion limestone outcrops.

Rolling low hills. Relief 60-150m on elevations between 600 and 730m. Slope gradients 10-

20%. Permanent erosional stream patterns closely to very widely spaced form non-

directional tributary pattern.

Outcrops of tombstone-like rocks are usually aligned in a north–south direction along the

spines of hills.


3


Table 1 - Summary of Key Features

Red Earths Yellow Earths

Landform element Sideslopes Sideslopes

Surface condition Hardsetting Hardsetting

Drainage Moderate Moderate

Soil permeability Moderate Moderate

Watertable depth None None

Depth to bedrock 0.3m to 1m 0.5m to 1m

pH (topsoil) 5.5 5.5 - 6.0

Known nutrient deficiencies

N, P, K, S, Ca, Mo N, P, K, S, Ca, Mo

Soil salinity Not present Not present

Erodibility (topsoil/subsoil)

Moderate / Low Moderate / Moderate

USCS (subsoil) SC, CL SC, SL

Shrink-swell potential Low Low

3.2 Groundwater Bore Search

A groundwater bore search was undertaken using the NSW Government’s online search

facility at allwaterdata.water.nsw.gov.au.

There were no registered groundwater bores located within 500m of the proposed

development/dispersal area.

Provided wastewater treatment and dispersal options detailed in report are implemented it is

believed that the dispersal of treated wastewater on the site does not pose a risk to

groundwater at any groundwater bore.

3.3 Groundwater Vulnerability

Yass Valley Local Environment Plan 2013, cl 6.4 Groundwater Vulnerability, requires the

following matters set out in Table 2 to be addressed:

Table 2 - Groundwater Vulnerability Assessment

2 Is the site within land identified as

“Groundwater vulnerability” on the

Groundwater Vulnerability Map?

No

4 Methodology and Calculations

4.1 Fieldwork

The fieldwork undertaken on 19 February 2016 and 10 May 2021 consisted of a visual

assessment of the site and surrounding area, the driving 4 falling weight dynamic cone

penetrometer probes (DCP) to refusal or to 1.0m depth and the excavation of 2 augered


4


boreholes (BH) in order to assess the typical subsurface conditions in the vicinity of the

potential/proposed dispersal areas.

Soil samples were recovered from BH1 & BH2 and were examined for physical and chemical

characteristics.

All fieldwork was conducted generally in accordance with the methodology outlined in

AS/NZS1547:2012 ‘On-site Domestic Wastewater Management’ and the Environment and

Health Protection Guideline ‘On-site Sewage Management for Single Households’.

4.2 Subsurface Profile

The DCP probes encountered shattered shale rocks and cobbles, but managed to penetrate

to >1m, with effort.

The typical soil profile encountered on the site in the vicinity of the proposed dispersal area

was considered to be consistent with the non-calcic brown soils profile of the Cockatoo Soil

Landscape and could be generally described as:-

Table 3 – Typical Soil Profile

0 – 150mm brown, clay LOAM, topsoil, slightly moist with shattered shale

cobbles at 100mm depth.

150 – 1000+mm dark brown, sandy CLAY, slightly moist, increasing moisture with

depth. Moderately structured

The above sub-surface profile was anticipated to be representative of the natural sub-surface

soil profile across the proposed effluent dispersal area. The depth of strata and depth to

rock may be expected to vary across the site.

Neither groundwater nor surface water was encountered during the investigation.

4.3 Hydraulic Loading

The hydraulic loading has been estimated using methodology detailed in AS/NZS1547:2012

Table H1. The estimated hydraulic load from the combined residence and cottage using

town water is set out in Table 4, below.

Table 4 - Hydraulic loading (Tank water)

Accommodatuion Maximum Number

People

Hydraulic Loading

per Person

(L/day)

Total Hydraulic

Loading

(L/day)

4 bed residence +

2 bed cottage 10 persons 120 1200


5


4.4 Design Irrigation Rate

The rate at which the hydraulic load of the treated wastewater can be applied to an area is

the Design Loading Rate (DLR). The Design Loading Rate cannot exceed the Long Term

Acceptance Rate of the soil. The DLR is a function of the soil type, soil permeability, and

other environmental factors such as evaporation and transpiration (if applicable) and ability

for the plants or soil to absorb or bind the nutrients.

Textural assessment of the sandy CLAY subsurface stratum to 500mm below surface level

indicated the following characterisation and recommended DLRs for use in the calculation

of the required dispersal area for surface irrigation for the application of secondary treated

wastewater in accordance with AS/NZS1547:2012 Table 5.2, as shown in Table 5, below.

Table 5 – DLR for secondary treated wastewater (ie from an AWTS)

Soil

Category

Soil texture

Structure

Indicative

Permeability (Ksat)(mm/d)

Surface Irrigation

DLR ( mm/d)

5

Sandy Clay

Moderately structured

0.06 – 0.12

3

4.5 Dispersal Area Calculations

The following methods were used to calculate the required dispersal areas for AWTS

treated wastewater. They rely on the Hydraulic Loadings in Table 4 and the Design Loading

Rates in Table 5.

• Nominated Area Method

• Nitrogen Loading Method

• Phosphorus Loading Method

Each method uses different physical and chemical site characteristics to determine the

required wastewater dispersal area. The most suitable dispersal area sizing method will be

determined with consideration to site specific limitations. Typically, the method that

produces the largest area for a particular dispersal mechanism is selected to enable the

most effective on-site dispersal of wastewater. Each of the above methods is described in

Table 6, below.

Table 6 – Methodologies Used for Calculating Required Wastewater Dispersal Areas

Method Description

Nominated Area Method

Uses a combination of regional climatic records, design loading rate (ie wastewater volume) and the long-term acceptance rate

to determine, using a water balance, the minimum required surface irrigation dispersal area that will not require wet weather

storage.


6


Method Description

Nitrogen Loading Method

Calculations are based upon treated wastewater with a total

nitrogen content of 25mg/L, and an average maximum vegetation uptake rate of 32.9mg/m2/day. The average

maximum uptake rate for the vegetation is based on the ability of the vegetation to use the nutrient before it passes through the

root zone.

Phosphorus Loading Methods

Calculations are based upon treated wastewater with a total phosphorus content of 12mg/L, and an average maximum vegetation uptake rate of 3.3mg/m2/day. The phosphorus absorption capacity of the soil is also used to calculate the

required area with the soil absorption rate based on the ability of the soil to bind the phosphorus and prevent it being washed

through the soil profile (where it can become a source of pollution).

The irrigation areas calculated using the methods in Table 6, are presented as the minimum

required surface irrigation dispersal areas, in Table 7.

Table 7 - Minimum Required Dispersal Area(s) (m2)

Residence & Cottage

using Tank Water

Spray Irrigation or LPED (m2)


Nitrogen (25 mg/l)

Phosphorus (12 mg/l)

10 persons 550 950 750

4.6 Limitations to On-site Wastewater Dispersal

Table 6 of The Environment and Health Protection Guideline On-site Sewage Management for

Single Households and Table K1 of AS/NZS 1547:2012 provide soil assessment rating

systems for on-site wastewater dispersal systems. When the results from the site

investigations and soil analysis are compared with these tables, minor, moderate or major

limitations to the on-site irrigation of treated wastewater on the site can be identified. These

limitations are given in Table 8.

Table 8 – Minor, Moderate and Major Limitations to the On-site Dispersal of Treated Wastewater

Soil Feature Limitation

Slope Moderate

Depth to bedrock or water table Moderate

Permeability Minor


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EAT Minor

pH Minor

Electrical Conductivity (EC) Minor

The dispersal area for the site will not require remedial work to overcome any Major

limitations.

4.7 Shallow Depth to Rock

The shallow depth of rock will not adversely impact on the performance of surface spray

irrigation.

4.8 Slope Surface spray irrigation should not be applied where slopes exceed 15%.

5 Recommended Treatment and Dispersal Systems

Based on our evaluation of the site and the identified soil profile and site limitations, the site

is suitable for the on-site dispersal of wastewater from an AWTS via surface irrigation over

a minimum area of 950m2,

Examples of suitable AWTS systems include;

• Taylex ABS

• Econocycle ENC10 or ENP10

• Envirocycle NR10

5.1 Surface Spray Irrigation

Treated wastewater may be dispersed via a surface spray irrigation system comprising of a

trunk line installed within the dispersal area with several quick release connections to enable

the easy relocation of the lateral irrigation lines so that the wastewater is able to be easily

dispersed over the entire design dispersal area. Each lateral irrigation line should

incorporate 5 sprinklers.

5.2 Location of Dispersal Area(s)

The total suitable wastewater dispersal area and location are shown on drawing

218009/EFD-1. The indicative required surface irrigation area is also shown on drawing

218009/EFD-1. Sufficient area for reserve wastewater dispersal is available outside the

required surface irrigation area.

A reserve wastewater dispersal area is recommended by AS/NZS1547:2012 and should be

of equivalent size to the initial dispersal area(s) noted in Table 7. The purpose of the reserve

dispersal area is to rest the initial dispersal area, or for duplication of the dispersal area if

unforeseen circumstances require this at some time in the future. The reserve dispersal

area is not required to be utilised, however, it must be protected from any development that

would prevent its use in the future.


8


A potential location of the AWTS tank is shown diagrammatically on drawing 218009/EFD-1

and may be varied to suit site conditions, owner’s requirements and any restrictions imposed

by Yass Valley Council.

6 Other Considerations

6.1 Buffer Setbacks

The recommended buffer setback distance of the dispersal areas from surface features are

set out in Table 9, below.

Table 9 – Buffer Setback Distance Requirements for Surface Irrigation Dispersal Mechanisms

Feature Buffer Distance

(All distances in metres)

Where Dispersal Area is

Upslope

Where Dispersal Area is

Beside or Downslope

Dwelling 15 15

Driveway 6 3

Intermittent Drainage Line 40 -

Farm dam 40 -

Domestic Groundwater Bore 250 250

Property Boundary 6 3

Permanent waterway/creek 100 -

Potentially applicable buffer situations have been shown in Bold.

Yass Valley Council may relax or impose additional buffer or set back restrictions. Refer to

any conditions of approval for possible additional requirements, restrictions or guidelines.

6.2 Drainage

An uphill diversion drain should be constructed to protect the dispersal area from surface

run off from surrounding areas. Where site slopes allow, upslope subsurface seepage

should be intercepted and diverted away from the dispersal area by a subsoil drain.

6.3 Vegetation

The wastewater dispersal area(s) must be vegetated. The vegetation can include grasses

and shrubs. The proposed dispersal area supported an excellent coverage of grasses at the

time of the investigation. Vegetation should be regularly mowed and pruned to maintain the

rate of evapotranspiration.

6.4 Driveway(s)

All irrigation pipe(s) should be installed in a protective pipe/conduit where they cross driveways.


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6.5 Livestock

Allowing any livestock including; cattle, sheep and horses etc. to graze on active surface

irrigation area(s) is not recommended.

6.6 Wastewater Quality

It is important that the occupant makes a consistent effort to reduce the strength of the

treated wastewater.

Methods to reduce wastewater strength include:

i. Using the minimum recommended amounts of low phosphate, biodegradable

liquid detergents and cleaning agents;

ii. Avoiding large quantities of bleaches, disinfectants and whiteners;

iii. Minimising the amount of solid waste entering the septic system, especially non-

biodegradable items such as plastics.

6.7 AWTS and Dispersal System Maintenance

The proposed wastewater treatment system and the installed dispersal mechanism and area

should be regularly checked to ensure that they are operating correctly.

Most AWTS systems require to be serviced on a quarterly basis.

Signs of failure include surface ponding, wastewater run off, erosion, leaching of the soil,

poor vegetation growth including burnt vegetation, odours or the formation of surface crusts.

7 Report Limitations and Site Variations

The extent of testing associated with this assessment is limited to the activities referenced

in the report and variations in ground conditions may occur. 5QS Consulting Group should

be contacted immediately should subsurface conditions be found to differ from those

described in this report.

This On-Site Wastewater Management Assessment was not an investigation of the specific

subsurface profile at the location and is not intended to provide any comment on the

potential excavatability of the subsurface material.

For and on behalf of

5QS Consulting Group

Rob Barker FIE Aust CPEng NER (Civil/Structural)

Attachments

1. Drawing 208055/EFD1

2. Site and Soil Evaluation

3. Dispersal Area Calculation Sheets

5QS Ref:Date:Assessor:

1200 L/d L/wk

Climate: Climate Data Source:

mm

mm

Topography:

Groundwater:

m

500 mg/kg 0.00 0.0

dS/m 0.00% 0.0g/cm3 0.0 meq/100g 0.0

YESYES

Calcium

DLR - Irrigation:DLR - Trenches (Primary):

DLR - Mound:

Moderately Structuredsandy Clay5

Indicative Permeability:

Groundwater bores in the area and their current purpose:Horizontal distance to groundwater well used for domestic supply:Groundwater vulnerability:

N/A0

Not within GW vulnerability Area

0.75m to >1m

Soil Structure:

Lowsome visiblenil

Soil Texture:

0.06 - 0.12 (Ksat)(m/d)

mm/d

DLR - Trenches (Secondary): 10 mm/d

Soil Assessment

mN/ADepth to bedrock or hardpan: Depth to high soil watertable:

mm/d

mm/d

32.5

5

Run-on and Seepage: Site Filling:some expected

Site Aspect:Site Drainage:

Owner:Site Location:Client:

Site Landform:Landform Shape:Erosion Potential:Surface Rocks:

Intended Water Supply: Tank Water

Annual Rainfall:

Annual Evaporation: Evaporation:

5 - 15%goodNorth westModerately drained

Is there sufficient Land Area for Reserve Dispersal:Is there sufficient Land for a Primary Dispersal Area:

Phosphorous Sorption:Emerson Aggregate Test:Electrical Conductivity: 0.15

Dispersal Area

Soil Permeability Category:

6.5

0.0Bulk Density:ESP:

Soil Analysis on Sample BH1 - 100 to 350mm

meq/100g

pH:

Aluminium:

meq/100gmeq/100gmeq/100g

Cation Exchange Capacity:

Sodium:Magnesium:Potassium:3 - 6 (3)

convex divergent

1273

672.4

Site Information and Assessment

Rob Barker

The following is a Site and Soil Evaluation summary in accordance with AS 1547-2012 "On-site Domestic Wastewater Management" and the Environment & Health Protection Guidelines "On Site Sewerage Management for Single Households"

8400Wastewater Load:

Rainfall:Design Percentile: 50

Yass Valley Region Synthetic Record

Yass Valley Region Synthetic Record

Site Slope:Site Exposure:

Onsite Effluent Dispersal Assesment

SITE AND SOIL EVALUATION

J Davies140 Good Hope rd, Good Hope0

21800910-May-21

crest

1200 L/d8400 L/wk

0.25 0.7

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

31.0 28.0 31.0 30.0 31.0 30.0 31.0 31.0 30.0 31.0 30.0 31.0

50.5 46.1 45.9 38.7 54.0 60.0 64.2 67.5 63.2 62.5 67.4 52.4

220.0 156.0 130.0 76.0 48.0 33.0 35.0 51.0 75.0 114.0 147.0 188.0


37.9 34.5 34.4 29.1 40.5 45.0 48.2 50.7 47.4 46.9 50.6 39.3

70.2 63.4 70.2 67.9 70.2 67.9 70.2 70.2 67.9 70.2 67.9 70.2

108.0 97.9 104.6 97.0 110.7 112.9 118.3 120.8 115.3 117.1 118.5 109.5


154.0 109.2 91.0 53.2 33.6 23.1 24.5 35.7 52.5 79.8 102.9 131.6

93.0 84.0 93.0 90.0 93.0 90.0 93.0 93.0 90.0 93.0 90.0 93.0

247.0 193.2 184.0 143.2 126.6 113.1 117.5 128.7 142.5 172.8 192.9 224.6


-139.0 -95.3 -79.4 -46.2 -15.9 -0.2 0.8 -7.9 -27.2 -55.7 -74.4 -115.1

0.0 0.0 0.0 0.0 0.0 0.0 0.8 0.0 0.0 0.0 0.0 0.0

m2

m3

Total

504.3

826.4

1330.7

Total

891.1

1095.0

1986.1

0.4

530Required Wet Weather Storage:

Calculation Results

Total Irrigation Area:

Site Location:Client:

Owner: 5QS Ref:

1273.0

Total

365.0

672.4

Climate Data

21 mm/wk

Site Information and Assessment

J Davies140 Good Hope rd, Good Hope

0

Wastewater Load (Qw):Rainfall runoff coefficient

Calculation

Days in Month

Precipitation (mm)

Evaporation (mm)

Tank WaterIntended Water Supply:Design Loading Rate (Irrigation):

Crop Factor:

Wastewater Load (Qd):

Percolation

Total Water Outputs

Precipitation

Effluent Irrigation

Total Water Inputs



The following Nominated Area Method Calculation is a water balance which determines the wet weather storage requirement based on a nominated irrigation area.

Storage (mm/month)

Cumulative Storage (mm)

Date:Assessor:

21800910-May-21Rob Barker

Water Storage

Water Inflows (mm/month)

Water outflows (mm/month)

Evapotranspiration

5QS Ref:Date:Assessor:

1200 L/d8400 L/wk

includes 20% reduction for denitrificationLawn - unmanaged

Total Phosphorous Concentration (TPC): mg/LWastewater Load (Qd): L/d

Phosphorus produced:

Phosphorus sorption capacity of the soil:

=

= m2

Site Location:

m2

Nitrogen Loading Method

10-May-21Client: Rob Barker

mg/Lmg/m2/day

Site Information

Intended Water Supply: Tank Water

(TNC x Qd)/LR

140 Good Hope rd, Good Hope0

Wastewater Load (Qd):Wastewater Load (Qw):

Owner:


Nitrogen/Phosphorous Loading Method

J Davies 218009

Phosphorus Removed kg/m 2

262.8

kg (over 50 years)

Phosphorus Uptake by Plants

262.8

Phosphorus Removed = Phosphorus Absorbed by Soil + Used by Plants over 50 Years

Phosphorus uptake:

mg/kgkg/Ha (over 50 years)

kg/m2 (over 50 years)

Phosphorus Adsorbed by Soil500

2885

0.288

0.349

Dispersal Area =

Phosphorus Removed over 50 Years:

754

mg/m2/day

mg/m2 (over 50 years)

kg/m2 (over 50 years)

3.3

60225

0.060

0.349 kg/m2 (over 50 years)

Dispersal Area Required

kg

kg/m2

Phosphorus Applied kg

The Nitrogen Loading Method Calculations are based upon treated effluent with a total nitrogen figure of 25 mg/L, and a maximum vegetation take up rate (Critical loading rate) of 32.9 mg/m²/day.

Phosphorus applied to Dispersal Area over 50 Years

12

Total Nitrogen Concentration (TNC):Critical Loading Rate (LR):

Irrigation Area =

= 912

2532.90

Phosphorous Loading Method

Phosphorus Applied to Dispersal Area

The Phophorous Loading Method Calculations are based upon treated effluent with a Total Phosphorus Content of 12 mg/L, and an average maximum soil absoption rate (Sorption Capacity) of 500 mg/kg, and a plant take up rate (Phosphorous Uptake) of 3.3 mg/m²/day. The

average maximum take up rate for the soil is based on the ability of the soil to bind the phosphorus and prevent it being washed through the soil profile.

1200

re: on-site wastewater management assessment lot 14, dp

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