Hand out about

ENVIRONMENT WAIKATO’S RULES

FOR

ON-SITE WASTEWATER DISCHARGES

File No: 56 80 12

Document No: 598657

Enquiries to: Brent Fletcher

August 2002

Dear Sir/Madam

Some comments about the status Waikato Regional Council’s (Environment Waikato) permitted activity rules for onsite sewage treatment and disposal

Thank you for you inquiry about our rules for on-site sewage. Environment Waikato has permitted activity rules for the on-site treatment and disposal of domestic sewage. The rules have a number of criteria and if compliance with these criteria can be demonstrated then a resource consent (i.e. a specific discharge permit) is not required.

At present Environment Waikato has both a Transitional Regional Plan (July 1994) and an appeals version of the Proposed Regional Plan (February 2002). Both plans have rules about on-site sewage. The Regional Plan when fully operative will replace the Transitional Regional Plan.

The current status of the rules is that the Transitional Regional Plan is still relevant but so are the proposed rules. The appeals version of the Proposed Regional Plan is not yet fully operative because it has references (appeals) against it. It cannot be fully operative until the references have been decided in the Environment Court. At present it is partially operative.

In the meantime the way that the permitted activity rules for on-site sewage are applied is:

“The Transitional Regional Plan rules sets out the minimum requirements but we ask users to consider the direction set out in the appeals version of the Proposed Regional Plan. Rules or rule criteria that do not have references against them, are effectively available to be applied”.

We expect that the Proposed Regional Plan will become fully operative in about 12-24 months time.

For any inquiries about on-site sewage please phone 0800 800 402 in the first instance.

Yours faithfully

Brent Fletcher

Resource Officer,

Utilities Programme

Environment Waikato’s On-site Sewage Rules as provided for in the (proposed) Regional Plan

The Proposed Regional Plan is currently an appeals version of February 2002. This means that the plan is now in a form that Council wants to adopt, and staff will refer to the new plan for direction regarding resource use activities.

The new rules for on-site sewerage are much the same as those that existed under the Transitional Regional Plan.

The table below sets out the reference numbers of the new rules as they will appear in the Regional Plan as compared to the previous rules in the Transitional Regional Plan:

Previous	New
Transitional Regional Plan	Regional Plan
Permitted Activity Rule 3.3.1	Permitted Activity Rule 3.5.7.5
Permitted Activity Rule 3.3.2	Permitted Activity Rule 3.5.7.4
Permitted Activity Rule 3.3.3	Permitted Activity Rule 3.5.7.6
Discretionary Activity Rule 3.3.4	Discretionary Activity Rule 3.5.7.7
	Prohibited Activity Rule 3.5.7.8

Should you have any inquiries to make about the new rules, please contact the Waikato Regional Council (Environment Waikato) on 0800 800 401 or 402.

The four on-site sewage rules of the Transitional Regional Plan:

3.3.1 Permitted activity - discharge of domestic sewage from septic tanks

The discharge of domestic sewage effluent (including grey and sullage water but not including stormwater) into the ground from new on-site domestic sewage treatment and disposal systems designed, constructed, operated and maintained in accordance with New Zealand Standards Institute Standard Number 4610:1982 is a permitted activity, provided that the following conditions are met:

(a) The volume of effluent to be discharged shall not exceed 1.26 cubic metres per day averaged over any one month period.

(b) The discharge shall not cause or constitute a nuisance.

(c) There shall be no direct discharge of effluent into water.

(d) The minimum depth of unsaturated soil between the effluent disposal field and the water table shall be sufficient to ensure bacterial reduction so as to prevent adverse effects on the potability of any local ground water supplies.

(e) For discharges from systems installed after 11 July 1994 the property area or the effective disposal area for any one treatment and system discharge shall be no less than 2500 square metres.

The discharge from a new septic tank is a permitted activity, subject to the following conditions:

- volume up to 1.26 m³/d

- discharge shall not cause a nuisance

- no direct discharge to water

- minimum depth of unsaturated soil.

- minimum area for new systems.

Notes:

• Septic tank design standard

For the purposes of clarity, it is emphasised that non-compliance with Standard 4610:1982 constitutes non-compliance with this rule.

• Ground water supply

Where ground water is used for potable supply, due care needs to be taken in siting the sewage system.

• Definition of “effective disposal area”

For the purposes of this rule “effective disposal area” is defined as that area of land that is available for the infiltration and assimilation of effluent. The “effective disposal area” may extend beyond property boundaries provided an easement is registered on the title of the receiving property.

Notes are provided on:

- Septic tank design standard.

- Ground water supply.

- Definition of “effective disposal area”.

- Discharge volume.

- Nuisance.

- Areas where rule does not apply.

• Discharge volume

A maximum discharge volume of 1.26 cubic metres per day would allow for the discharge from a typically large household. It would also cater for many small, intermittently used systems for clubrooms, community halls, baches etc. Water saving devices can be installed to control the volume to be discharged.

• Nuisance

A “nuisnace” is any accumulation or deposit (that) is in such a state or is so situated as to be offensive or likely to be injurious to health. This is not in substitution of the Health Act 1956.

• Areas where rule does not apply

In accordance with Council resolution concerning the former General Authorisation for septic tanks, the following are noted:

- in the case of Cooks Beach, this rule shall expire on 1 June 1995

- this rule shall not apply to the Allans subdivision north of Whangamata being described as Lots 1 to 7 DPS 32132 Block XII Tairua SD.

3.3.2 Permitted activity - discharge of domestic sewage from existing septic tanks.

The discharge of domestic sewage effluent (include grey and sullage water but not including stormwater) into the ground from existing (installed before 11 July 1994) on-site domestic sewage treatment and disposal systems maintained in accordance with New Zealand Standards Institute Standard Number 4610: 1982 is a permitted activity provided that the following conditions are met:

(a) The volume of effluent discharged does not exceed 1.26 cubic metres per day averaged over any one month.

(b) The discharge shall not cause or constitute a nuisance .

The discharge from an existing septic tank is a permitted activity, subject to the following conditions:

- volume up to 1.26 m³/d

- discharge shall not cause a nuisance

- no direct discharge to water

- minimum depth of unsaturated soil

Notes

• Higher standard anticipated in future

Septic tank systems provide a minimal degree of effluent treatment. It is anticipated that a higher standard of discharge than that provided by septic tanks, will be required after the first review date of this plan.

• Survey of ground water problems

As part of the implementation of this rule Environment Waikato will undertake a survey of potential problem areas in conjunction with territorial local authorities, to determine where local ground water problems occur. Such a survey will be undertaken within five years of the operative date of this plan and in accordance with policy 3.2.4.

• Septic tank design standard

For the purposes of clarity, it is emphasised that non-compliance with Standard 4610:1982 constitutes non-compliance with this rule.

Notes are provided on:

- Higher standard anticipated in future.

- Survey of ground water problems.

- Septic tank design standard.

- Discharged volume.

- Nuisance.

- Areas where rule does not apply.

• Discharge volume A maximum discharge volume of 1.26 cubic metres per day would allow for the discharge from a typically large household. It would also cater for many small, intermittently used systems for clubrooms, community halls, bashes etc. Water saving devices can be installed to control the volume to be discharged. • *Nuisance* A “nuisance” is any accumulation or deposit (that) is in such a state or is so situated as to be offensive or likely to be injurious to health. This is not in substitution of the Health Act 1956. • *Areas where rule does not apply*
In accordance with Council resolution concerning the former General Authorisation for septic tanks, the following are noted: - in the case of Cooks Beach, this rule shall expire on 1 June 1995 - this rule shall not apply to the Allans subdivision north of Whangamata being described as Lots 1 to 7 DPS 32132 Block XII Tairua SD.
	*3.3.3 Permitted activity - discharge of domestic sewage from on-site domestic sewage treatment and disposal systems.*

The discharge of domestic sewage effluent (including grey and sullage water but not including storm water) into the ground from on-site domestic sewage treatment and disposal systems (excluding those designed and constructed in accordance with New Zealand Standards Institute Standard Number 4610 : 1982) is a permitted activity provided that the following conditions are met:

(a) The volume of effluent to be discharged shall not exceed 3 cubic metres per day averaged over any one month period.

(b) The discharge shall not cause or constitute a nuisance.

(c) The design and construction of the system shall achieve the following criteria:

- pre-treatment of effluent to a standard unlikely to cause clogging of the disposal system or soils

- isolation of the disposal field from direct contact with ground water

- no degradation of ground water quality such that, as a result of the discharge, or in combination with other discharges existing and reasonably foreseeable uses will be compromised

- no degradation of surface water quality as a result of the discharge, or in combination with other discharges

- no direct discharge of effluent into ground water or surface water.

This condition shall be satisfied by:

- certification by a suitably qualified and experienced practitioner that the system will consistently satisfy the criteria, or

- provision of appropriate documentation which demonstrates achievement of the criteria.

(d) The system shall be managed and maintained in accordance with good practice and in accordance with any requirements or recommendations specified in any relevant code or guidelines related to the particular system.

The discharge of domestic sewage from on-site domestic sewage treatment and disposal systems is a permitted activity, subject to the following conditions:

- volume up to 3 m³/d

- avoidance of nuisances

- design standards to be achieved

- management and maintenance requirements.

Notes:

Notes are provided on:

• Ground water supply

Where ground water is used for potable supply, due care needs to be taken in siting the sewage system.

• Discharge volume

A maximum discharge volume of 3 cubic metres per day would provide for the equivalent of approximately 15 persons average occupancy.

This will cater for many small amenities such as motels, clubrooms, etc. Water saving devices can be installed to control the volume to be discharged.

- siting

- discharge volume

- application of rule to communities

- suitably qualified and experienced practitioner

- appropriate documentation

- nuisance.

• Application of rule to communities

For the avoidance of doubt, this regional rule covers the situation where modern on-site sewage systems are proposed for a community, or other group of properties. In this case, a community or group as a whole could obtain an engineer’s certification, or provide information about its on-site sewage discharges, to meet the conditions of the rule. This means that property owners would not need to individually obtain engineering certification, or individually provide the required information.

· Suitably qualified and experienced practitioner

A “suitably qualified and experienced practitioner” is a person who is qualified and experienced in the field of on-site sewage treatment and disposal.

· Appropriate documentation

Documentation which demonstrates that the on-site effluent disposal system installed achieves the criteria. Documentation may be in the form of a letter or certificate outlining the specifications of a system and compliance with the criteria.

• Nuisance

A “nuisance” is any accumulation or deposit (that) is in such a state or is so situated as to be offensive or likely to be injurious to health. This is not in substitution of the Health Act 1956.

3.3.4 Discretionary activity - other on-site sewage discharges

The discharge of on-site domestic sewage effluent into the ground from a system or in a manner outside the scope of or unable to meet the conditions pertaining to rules 3.3.1, 3.3.2 and 3.3.3 is a discretionary activity.

Any discharge which is inconsistent with the “permitted activity” rules is a discretionary activity.

Note:

• Consent conditions and notification

Conditions for these consents, if granted, will be determined on a case by case basis. Notification requirements will be determined in accordance with s94 of the RMA.

3.4 ANTICIPATED ENVIRONMENTAL RESULTS

Consents for these activities will be determined on a case by case basis.

It is anticipated that the policies and rules for on-site domestic sewage discharges will have the following environmental results:

- ground water uncontaminated by sewage effluent in new areas of on-site domestic sewage system use

- avoidance of subsequent effects on surface waters

- reduced incidence of “public health” issues associated with on-site sewage disposal

- non-proliferation of septic tanks or systems similar to the provisions of NZS:4610:1982 in intensively developed areas

- appropriate solutions developed in areas where existing problems found to occur.

Anticipated environmental results are as follows:

- clean ground water

- no effects on surface waters

- fewer public health issues

- septic tanks not in developed areas

- solutions to problems.

Summary of On-site Rules

Rule 3.5.7.8 – Prohibited Activity – discharge of untreated human effluent to water

3.5.7.4 Permitted Activity Rule - Discharge of Domestic Sewage from Existing On-Site Systems

The discharge of domestic sewage effluent (including grey water but not including stormwater) into land from an on-site domestic sewage treatment and disposal system that was lawfully established or authorised before the date of notification of this Plan (28 September 1998), is a permitted activity subject to the following conditions:

a The volume of effluent to be discharged from any one system shall not exceed 1.3 cubic metres per day averaged over any one month period.

b There shall be no direct discharge of effluent into water.

c The minimum depth of unsaturated soil between the effluent disposal field and the water table shall be no less than 600 millimetres.

d The discharge shall not result in any objectionable effects from odour beyond the boundary of the subject property.

e For discharges from systems installed after 11 July 1994, the effective disposal area^* for any treatment and disposal system shall be no less than 2,500 square metres.

f For discharge from properties which, at the date of authorisation of the system, exceeded 2,500 square metres, this rule shall not apply where, subsequently, the effective disposal area^* is reduced to less than 2,500 square metres.

g For discharges from properties which, at the date of authorisation of the system, were less than 2,500 square metres, this rule shall not apply where, subsequently, the effective disposal area is reduced.

h The discharge shall not occur within 20 metres of a Significant Geothermal Feature.

i From 1 January 1 2006 the septic tank shall be fitted with an effluent outlet filter.

j There shall be no adverse change in ground water quality as a result of the discharge, or in combination with other discharges.

Advisory Notes:

· The process for assessing odour is specified under Section 6.4.1.3 of the Plan.

· Discharges of contaminants into or onto land within 20 metres of a Significant Geothermal Feature are addressed by the Rules 7.2.6.1 and 7.2.6.2 of this Plan.

· These existing systems will generally be adequate provided that land and soil conditions are suitable and that regular filter cleaning and desludging is undertaken.

· Should the treatment and/or disposal system fail to the extent that more than routine maintenance such as desludging and filter cleaning is required to reinstate the system, it will no longer comply with this rule and should be upgraded to meet the conditions of Rule 3.5.7.5 or 3.5.7.6.

[NB – italicised criteria are those subject to appeal]

Permitted Activity Rule 3.5.7.4 – existing on site systems

·        Volume of discharge not more than 1.3 m³/d

·        Min. soakage field separation distance

to g.w.t is 600mm

·        No direct discharge to water

·        Avoidance of nuisances

·        Systems installed after 11.7.94 section size

(effective disposal area) to be at least 2500m²

·        Should failure occur & more than routine

maintenance is required to reinstate the system,

then upgrading will be required.

·        Effluent filter fitted to tank by 01.01.06

3.5.7.5 Permitted Activity Rule - Discharge of Domestic Sewage From New On-Site Systems

The discharge of domestic sewage effluent (including grey water but not stormwater) onto or into land from an on-site domestic sewage treatment and disposal system lawfully established or authorised after the date of notification of this Plan (28 September 1998), is a permitted activity subject to the following conditions :

a The volume of effluent to be discharged from any one system shall not exceed 1.3 cubic metres per day averaged over any one month period.

b The minimum total septic tank size shall be no less than 3,000 litres.

c There shall be no direct discharge of effluent into water.

d There shall be a zone of unsaturated soil of no less than 600 millimetres between the base of the effluent soakage trench and the top of the water table at all times of the year.

e The discharge shall not result in any objectionable odour beyond the boundary of the subject property.

f The effective disposal area^* for any one treatment and disposal system discharge shall be no less than 2,500 square metres. The discharge shall no longer comply with this rule where the effective disposal area^* is subsequently reduced to less than 2,500 square metres.

g The sewage disposal system shall not be sited within 30 metres of a Natural State Water Body or Fisheries Class Water Body as specified in the Water Management Class Maps and 10 metres from any other surface water body.

h The sewage disposal system shall not be sited within 30 metres of a potable water supply well unless the well is drawing from a separate, confined aquifer.

i The discharge shall not occur within 20 metres of a Significant Geothermal Feature.

j The septic tank shall be fitted with an effluent outlet filter.

k There shall be no adverse change in ground water quality as a result of the discharge, or in combination with other discharges.

Advisory Notes:

· The process for assessing odour is specified under Section 6.4.1.3 of the Plan.

· It is recommended that on-site systems are designed, constructed, operated and maintained in accordance with (Auckland Regional Council 1994 On-site Wastewater Disposal From Households and Institutions – Technical Publication 58).

· Discharges of contaminants into or onto land within 20 metres of a Significant Geothermal Feature are addressed by the Rules 7.2.5.12 and 7.2.5.13 of this Plan.

[NB – italicised criteria are those subject to appeal]

Permitted Activity Rule 3.5.7.5 – new on site systems

·        Volume of discharge not more than 1.3 m³/d

·        Min. tank capacity is 3,000 litres

·        Effluent filter on tank outlet

·        Min. soakage field separation distance

to g.w.t is 600mm

·        No direct discharge to water

·        Avoidance of nuisances

·        Section size (effective disposal area)

to be at least 2500m²

·        Should failure occur & more than routine

maintenance is required to reinstate the system,

then upgrading will be required.

3.5.7.6 Permitted Activity Rule - Discharge of Domestic Sewage from New, Improved On-Site Domestic Sewage Treatment and Disposal Systems

Except as provided for by Rule 3.5.7.5, the discharge of domestic sewage effluent (including grey water but not including stormwater) onto or into land from an on-site domestic sewage treatment and disposal system is a permitted activity subject to the following conditions:

a The volume of effluent to be discharged shall not exceed three cubic metres per day averaged over any one month period.

b The design, construction, operation and maintenance of the system shall meet the following standards:

i. pre-treatment of effluent to a standard not to exceed concentrations of 20g/m³ of Biological Oxygen Demand and 30g/m³ of suspended solids

ii. there shall be a zone of unsaturated soil as measured vertically between the bottom of the soakage field discharge line and the top of the ground water table at all times of the year, which shall be no less than 600 millimetres for conventional trenches, beds and mounds, or 300 millimetres where dripper irrigation lines are used and the design loading rate for effluent disposal is less than five millimetres/day

iii. there shall be no adverse change of ground water quality as a result of the discharge, or in combination with other discharges

iv. there shall be no adverse change of surface water quality as a result of the discharge, or in combination with other discharges

v. there shall be no direct discharge of effluent into ground water or surface water.

c The discharge shall not result in any objectionable effects from odour beyond the boundary of the subject property.

d The sewage disposal system shall not be sited within 30 metres of a Natural State Water Body or Fisheries Class Water Body as specified in the Water Management Class Maps and 10 metres from any other surface water body.

e Written proof of compliance with this rule shall be provided to the Waikato Regional Council on request in the form of either:

i certification by a person who is qualified and experienced in the field of on-site sewage treatment and disposal that the system will consistently satisfy the above standards taking into account the relevant site constraints, or

ii documentation which demonstrates achievement of the standards.

f The discharge shall not occur within 20 metres of a Significant Geothermal Feature.

[NB – italicised criteria are those subject to appeal]

PERMITTED ACTIVITY RULE 3.5.7.6 - new on site systems

an advanced type of

sewage treatment and disposal system

· volume of discharge not more than 3.0 m³/d

· 20:30 BOD/SS effluent quality requirement

· avoidance of nuisances

· no direct discharge to water

· min soakage field separation distance to g.w.t is 600mm for conventional soakage lines (e.g LPED) or 300mm when dripper line irrigation is used.

· design standards to be achieved

· management and maintenance requirements

3.5.7.7 Discretionary Activity Rule - Other On-Site Sewage Discharges

The discharge of domestic sewage effluent from on-site domestic sewage treatment and disposal systems onto or into land and any subsequent discharges of contaminants into air, in a manner which does not comply with Rules 3.5.7.4, 3.5.7.5 and 3.5.7.6 is a discretionary activity (requiring resource consent).

Exclusion to Rule 3.5.7.7:
Discharges of contaminants within 20 metres of Significant Geothermal Features are excluded from this rule. The effects of these activities are managed by Rules 7.2.6.1 and 7.2.6.2 of the Plan.

3.5.7.8 Prohibited Activity Rule – Discharges of Untreated Human Effluent to Water

The discharge of untreated human effluent to water is a prohibited activity.

On site sewage - permitted activity compliance

What type of information should be provided to demonstrate that compliance with the permitted activity rule can be met?

The information provided should include but not be limited to the following:

· a description of the site where the disposal will take place, which should include:

· the topography of the site (e.g. slope, prevailing wind direction, whether the site is in the sun part of or all day).

· the depth of the spring ground water table level below the ground surface.

· a site sketch or plan should be included with this information.

· the size of the disposal field (m²) its proximity to a) any open waterways, and b) to any bores within 500 metres of the disposal field.

· a description of the sewage treatment and disposal system, and its operation.

· a description of the soil types that are located within the area of the property where the effluent is to be disposed of. This should include a soil profile description from at least three points within the soakage area proposed and also include the designed rate of effluent loading onto the soil in mm/day.

· cleaning and maintenance requirements.

· In areas where there is a already a number of septic tank discharges, any recent groundwater sampling results would be desirable particularly results that show the levels of nitrate and faecal coliforms present in local groundwater (if any). Of particular interest to Environment Waikato are areas where there are free draining soils, poor draining soils and/or where there is a high groundwater table.

It is strongly recommend that if you are likely to have difficulty in providing the type of information described above, that the assistance of an on-site wastewater treatment and disposal expert be sought. (This should be someone who is highly trained and informed in the principles, design and application of on-site sewage systems).

Improved types of wastewater treatment and disposal systems - what are they?

To alleviate some of the confusion over what type of systems are acceptable under the criteria of the Regional on-site sewage rules 3.3.3/(3.5.7.6), the following explains:

The rules envisage an improved type of treatment and disposal system which is typically a large multi-chambered unit incorporating an effluent filter and some sort of extra treatment stage to ensure that a high standard of wastewater treatment is attained. This type of system is considerably more advanced than a basic septic tank and its associated effluent soakage trench. Rule 3.5.7.6 requires that the effluent produced from these types of systems is to be of a quality in terms 20 mg/L of Biological Oxygen Demand and 30 mg/L Suspended Solids (i.e. 20:30 BOD/SS). This is a secondary standard of treatment. Septic tanks with filters are unlikely to be able to meet this treatment standard as it generally requires some form of secondary biological treatment to achieve – for example by active aeration (aerated system) or passing through a packed bed reactor (sand filter or textile filter or similar).

On particularly restricted sites where very tight soils (poor draining) or very sandy soils (fast draining) predominate, a very high standard of effluent treatment may be required. For example the system may need to incorporate a re-circulating sand contactor, or provide extended effluent treatment such as an activated system (aeration). On difficult soils the effluent soakage field provided should be larger rather than smaller. The effluent loading rate of the soil should be low (typically less than 10mm/day).

In situations where there is a seasonal or permanently high water table the effluent soakage field may also need to be mounded up in order to provide an appropriate separation distance of unsaturated soil. This is the distance required from the bottom of the soakage field distribution line to the top of the groundwater table. It is necessary to ensure final renovation of the effluent by the soil for protection of the groundwater table from harmful contaminants and to promote some further breakdown of undesirable nutrients that are contained in wastewater.

Generally effluent discharged from these types of systems should be pump dosed, although certain types of siphon dosing are also available.

Where doubt exists as to the applicability of a particular system, it is up to the applicant to provide information that demonstrates that the criteria of rule 3.3.3/(3.5.7.6) will be achieved by the system proposed. In many instances where compliance with rule 3.3.3/(3.5.7.6) is sought owners would be well advised to engage a wastewater treatment and disposal expert to carry out a full site evaluation and then to design an appropriate system for them.

Where upgrading of a basic single chambered septic tank system is being considered rather than total replacement, there are a number of options available, ranging from add on secondary chambers to the fitting of special filters (contactors) after the existing tank. Generally, if the septic tank was installed in line with the old New Zealand Standard NZS4610:1982 it will not be of sufficient treatment capacity compared to the types of systems envisaged in terms the criteria of the new rules.

Improved types of systems – examples

Some other information about:

§ wastewater flow design allowances

§ site soil types

§ soakage trench and soakage bed loading rates,

§ Long Term Acceptance Rates (LTAR)

i.e. how to work out how much soakage area is required

§ Some of the photocopied information is from:

The New Zealand Manual of Alternative Wastewater Treatment and Disposal Systems, Volume II Part A

ON-SITE WASTEWATER DISPOSAL FROM HOUSEHOULDS AND INSTITUTIONS, Auckland Regional Council, Technical Publication No. 58, November 1994 (written by Ian Gunn for ARC).⨪

Some comments about soakage fields

It is important that the soakage field is correctly set up. This can be done by considering the volume of effluent that is to pass through the field in line with the characteristics of the soil on/in which it is to be located.

Bernhart’s Design Principle is one method of working out the appropriate soakage field size in line with the long term acceptance rate of the soil (LTAR).

Example:

A = F x L where

S A = bottom of bed/trench area (m²)

F = daily wastewater flow (litres)

S = the bed loading rate (mm/day)

L = pollution factor (NZ = 1.0)

Assume:

· 5 person household with normal fixtures @ 180 l/pp/day.

· Soil type category 3 – medium fine and loamy sand (good drainage).

· Trench loading rate from table 8.1 (TP58), LTAR is 20 – 30mm/day.

· No obvious restrictions on-site, (i.e. groundwater is deep, soils are consistent and bore or stream in close proximity of soakage area).

Calculation to determine length of trench required: