Response from Mr D G Wood (Individual)
1. Mr D G Wood (Individual) : 13 Jan 2016 13:09:00
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Dear Planners
AONB DPD Planning Consultation – Comments
I am a resident of Silverdale and a Chartered Civil Engineer with extensive experience in sewerage and sewage treatment. With my professional background I have a keen interest in the safe disposal of sewage and having lived here for 11 years I am aware of many problems with the existing “sewage disposal” arrangements. These include smell, discharge of crude sewage/sludge to groundwater and resulting pollution of the shore, all due to lack of understanding and poor maintenance. I am therefore extremely concerned about any proposal to build new houses in Silverdale. I am not against new development but these MUST have provision for safe treatment and disposal of sewage.
Of major concern is the cumulative damage to the environment - groundwater systems and the coastal margin. I also have concerns about possible non-compliance with Building Regulations.
Because the limestone bedrock is heavily fissured effluent from existing septic tanks is not retained for long enough in the immediate sub-surface zone for appreciable secondary treatment to occur. Virtually crude sewage quickly flows through fissures and merges with ground water to discharge in springs along the shore. This probably results in areas with high bacterial content posing a health risk to people and contamination of sea water.
Where new properties are too far away from the “public sewer system” then the only realistic options, acceptable under Building Regulations, for sewage disposal are packaged treatment plants or septic tank plus secondary treatment eg a drainage field.
Effluent from packaged treatment plants can be discharged to a watercourse (with EA consent) but as there are none to speak of in this area the only suitable discharge would be the same as for a septic tank ie a drainage field.
In general parlance people refer to septic tanks discharging to “soakaways” but a drainage field consisting of sub-surface perforated pipes is required by Approved Document H.
The siting requirements are that a septic tank should be at least 7m from the house and no more than 30m from heavy vehicle access. The drainage field should be at least 15m away from any building.
The size of a drainage field or its “floor area” is calculated from this formula:-
Area = population X percolation rate X 0.25 square metres
The minimum acceptable value of percolation rate is 12 so for a 4 person house the minimum floor area for the drainage field is 12 square metres. This assumes excellent percolation and in reality this value could be several times higher.
Considering these Building Regulation requirements any new property would need a back garden reaching at least 18m from the house and 5m wide. This is a considerable size of garden which is not achieved in most cases of new development.
In an unsewered area it would not therefore be possible to develop most sites at the density required for financial viability whilst complying with Building Regulations and not adversely affecting the environment. This does not consider proximity to other houses - which would make the situation even more difficult, the ground conditions or the topography.
In summary I do not believe any new houses can be built while Silverdale remains unsewered due to:
• Continuing contamination of ground water and coastal pollution
• Non-compliance with Building Regulations for new houses
• Potential proliferation of small, inefficient sewage treatment plants with no control on maintenance or performance
Yours sincerely
