Generally, we operate in phosphorus affected catchments. We initially undertake a desk-based review of each tank to determine whether phosphorus has a pathway to the protected site. This is challenging for discharges to ground and we need to review each system against the Small Scale Threshold guidance. This is a set of requirements to determine whether phosphorus makes its way to the protected site or whether it gets stuck in the soil profile and has “no Likely Significant Effect”. This criterion includes:
Providing there is an impact pathway then the septic tank/low performing PTP is capable of providing mitigation. We also take a legal review of the tank against the Environment Agency’s General Binding Rules to see whether the tank is capable of generating credits and whether a permit is needed. This is a list of 23 rules which have been introduced in intervals, with notable changes happening in 2015 and 2023. Providing the tank does not need a permit and satisfies the rules, then it is capable of providing mitigation and no permit will be needed.
We then need to ensure the tank can be installed in compliance with the Building Regulations and the appropriate British Standards. Our principle is Approved Document H of the Buildings Regulations which gives spatial requirements and construction considerations for components such as:
The applicable British Standards are generally BS 12566 (PTPs) and BS 6297 (Drainage fields). Providing the tank is eligible after a review of all these requirements then we can undertake an initial legal check and invite the tank owner in to sign the necessary agreements. We then undertake our nutrient budget calculations. The calculations are based on:
Once the nutrient budget calculations are undertaken we can then determine how many credits can be delivered through the upgrade. We consult on every install to ensure that the works are compliant with the necessary requirements. We provide instructions on how to do percolation tests and undertake drainage field sizing calculations. We also undertake structural and floatation calculations for each tanks and issue standard details for the installation works to the contractor.
Once the installation is complete we compile all necessary documentation, including Building Control approval, commissioning report and post-installation survey and submit these to the council. We work with independent labs to test the effluent to ensure that it is performing as designed and also coordinate all of the onsite testing. Once the tank has reached a critical interval (1 year and 2 years post installation) we provide a final effluent monitoring report to the councils for review.