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Septic tank to package treatment plant upgrades

Mitigation title
Nutrient neutrality: Small private foul water systems - Septic tank to package treatment plant upgrades (STU) in the River Lugg SAC catchment
Description

This information is prepared to assist homeowners, developers and planning agents with respect to upgrading existing Septic Tank foul water management systems to latest ‘best available technology’ (nutrient removal) package treatment plants – including, as a means to secure nutrient neutrality requirements of new overnight accommodation.

All required or requested drainage reports, information, technical reports, system specifications as relevant to demonstrate compliance with eligibility and upgrade requirement must be submitted to the LPA in a timely manner.

Any planning application required to enable the upgrade to happen has been submitted with all required reports and information and validated by the local planning authority.

Eligible septic tank systems

  • Septic tank currently serving a residential main dwelling (including holiday accommodation, B&B, small care homes and other dedicated self-contained overnight accommodation provision).
  • Located within the hydrological catchment of the River Lugg SAC (SSSI) *1.
  • Septic tanks that are demonstrated as not compliant with one or more of the following criteria:
  1. To ensure that there is no significant in combination effect, the discharge to ground should be at least 200m from any other discharge to ground
  2. The drainage field will not be subject to significant flooding, e.g. it is not in Flood Zone 2 or 3
  3. The drainage field is more than 40m from any surface water feature e.g. ditch, drain, watercourse
  4. The drainage field is more than 5 m from the designated site boundary (or sensitive interest feature).
  5. The drainage field is in an area with a slope no greater than 15%.
  6. There are no other known factors which would expedite the transport of phosphorus for example fissured geology, insufficient soil below the drainage pipes, known sewer flooding, conditions in the soil/geology that would cause remobilisation phosphorus, presence of mineshafts.
  7. The drainage field is in an area where the high groundwater depth is at least 2m below the surface at all times
  8. The percolation test has been performed on the proposed location of the drainage field with the resulting value lying within the required range under the Building Regulations 2010 and BS6297, which specify an average Vp value of between 12 and 100
  9. That are currently discharging to a failing drainage field or to a local watercourse

Upgrade requirements

  • The replacement PTP must demonstrate Best Available Technology in phosphate removal solely through a biologically achieved primary reduction in Phosphate at outfall to a certified level of <= 0.8mg/litre2.
  • No secondary or tertiary phosphate stripping/precipitation systems such as reed beds, chemical dosing, phosphate stripping mediums or electrical (ion) processes will be acceptable.
  • The PTP must be a unit accepted by Natural England as being suitable for use in Nutrient Neutrality catchments.
  • Where technically achievable and evidenced by percolation tests under Building Regulations 2010 and BS6297 showing a Vp of 12-100 is achievable a drainage field must be used to manage PTP outfall.
  • The future management, maintenance and any future replacement system will need to be legally certain for the lifetime of all developments the system supports or enables. (Minimum 100 years for HRA purposes)
  • The property owner(s) or other legally responsible party will be required to sign a legal agreement and/or accept a relevant condition in respect of any planning permissions required to secure the system as agreed and subject to the required HRA process.
  • The new PTP unit must be installed on land under the legal control of the property owner and comply with all other relevant regulatory requirements such as building control, General Binding Rules and obtaining any other required permits, licences, wayleaves. 

Upgrade to deliver Nutrient Neutrality

  • The upgrade must be in the same hydrological sub-catchment as the new nutrient pathway (effect) being mitigated; or create the mitigating benefit upstream of the new nutrient pathway impacting the Lugg SAC.
  • Where an existing septic tank system is compliant with General Binding Rules and discharging to a working drainage field the default phosphate discharge value in the statutory Nutrient Calculator – 11.60 mg/litre can be used.
  • Where an existing septic tank system is not compliant with General Binding Rules and discharges to a failing drainage field or watercourse (of any type) and so must in any case be upgraded to become compliant with current regulations the default phosphate discharge value in the statutory Nutrient Calculator based on a default PTP being installed – 9.7 mg/litre can be used *3.
  • All nutrient neutrality calculations must be completed using the statutory Nutrient Calculator.
  • The relevant standard occupation ‘person equivalent’ must be used.
  • The precautionary water usage of 120lpd must be used as water efficiency savings are uncertain.
  • All required legal certainty must be secured and the upgrade must be completed and be operational and existing septic tank fully decommissioned PRIOR to first use of any development relying on the upgrade for nutrient neutrality.

Upgrade to create Phosphate Credits for sale

  • Specific legal agreements will be required to secure the use of any reduction in phosphate loads delivered by a STU as Phosphate Credits for sale or legal allocation to separate developments or planning applications to deliver nutrient neutrality.

Informative notes

  • STU may also be considered as nutrient mitigation methodology where relevant in other nutrient sensitive catchments such as River Wye SAC and River Teme SSSI (species links to River Clun SAC)
  • The LPA may in future seek a Local Development Order specifically related to remove the need for a full Planning Application in respect of undertaking a STU.
  • The council, or Natural England through the developing Environmental Delivery Plan process, may establish a separate methodology or mechanism for supporting and delivering STU and managing Phosphate Credits that may be created.
  1. Can also apply to River Clun SAC hydrological catchment – but note Nitrogen also requires nutrient neutrality to be demonstrated.
  2. Currently the HABA Bio Easy Flow PTP unit has been demonstrated as acceptable BAT for phosphate reduction. Other compliant/acceptable PTP units may become available overtime. The HABA Bio Easy Flow is also compliant with BAT for Nitrogen at discharge in respect of the River Clun SAC catchment.
  3. The LPA has sought its own legal advice to confirm this is an acceptable baseline to use.