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The EPA issued a clarification in early Aug in relation to the design capacity requirements in Section 7 and Section 9 of the Code of Practice: Waste Water Treatment and Disposal Systems serving Single Houses (p.e. <10) (CoP).

In order to ensure consistency across all types of domestic wastewater treatment systems (including septic tanks) the following method of calculating the design capacity suitable for the dwelling should be followed:

For the purposes of the CoP the minimum house size is 2 bedrooms, which equates to a design capacity of 4 population equivalent (p.e.).

For every additional bedroom, irrespective of size, an additional 1 p.e. should be added.

2 bedrooms = 4pe
3 bedrooms = 5pe
4 bedrooms = 6pe
5 bedrooms = 7pe
etc

I think its fair to say the average size house in Ireland that have been granted planning over the last few years was previously calculated as 8PE. Under the calculations above the average size house in Ireland has now been reduced to 6PE.

This ties in nicely with the topic that was also clarified in relation to interpreting the EN12566:3 certs secondary Waste Water Treatment Units. If you need to figure out what is the population equivalent of the WWTU while inspecting the EN certs for a specific manufacturer then only focus your attention to the figures associated with the "Nominal Hydraulic Daily Load".

The EPA CoP assigns 150Ltrs (0.15cu.m) as a daily hydraulic load per person. The population equivalent is derived by dividing the figure associated with the Nominal Hydraulic Daily Load by 0.15.

 eg: 

 (Please Note: There is no official sizing-up/scaling standard in place by Irl. It is my understanding that this tedious & technical issue is currently trying to be resolved and clarification on this issue will be published within the next year.)

On a totally separate note if the average size house is now a 6PE system and assuming the site is suitable for a septic tank then the site requires 6no. 18m long trenches of percolation pipe. In the CoP pg. 49 the max no. of trenches that can exit a distribution box is 5.



Perhaps the powers that be in the EPA could re-look at this, as all the distribution boxes in the market have 06 outlets it would make more sense to just use one distribution box for 06 runs of pipe rather than have to introduce 02-way splitters etc.

The following image was submitted by a SiteAssessor.com member last April after he conducted a visual inspection of a distribution box located before a failing percolation area.



You can download the clarification doc here or access through the EPA website.

tim
087-9903697
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PS Thx to the Department of the Environment for the heads up on this clarification.