Site Assessment
Why is Site Assessment Necessary?
It is essential in the interests of public health to ensure the safe disposal of wastewater from a development. A site assessment will determine whether or not a particular site can achieve this.
What does a Site Assessment Involve?
There are 5 key elements in the assessment
A desk study to provide information on soils, geology and groundwater vulnerability.
A field visit to look at site drainage, vegetation, levels, housing density, water uses in the area.
Trial hole to check the depth and type of sub-soils and depth to water table. If the trial hole indicates poor subsoil permeability- there may be little point in proceeding to the percolation test and/or application for planning permission.
Percolation testing (P/T tests). These tests determine the soil’s ability to filter and move the wastewater. A "T" test is normally done at 800mm below ground level, which is about the level where the pipe from the wastewater system enters the ground. A "P" test is undertaken on sites with shallow soils, at 400mm below ground level. The same test hole dimensions are used, and the same test procedure.
Recommendation on a wastewater treatment option. A good assessor will include a full wastewater treatment design with a cross section showing where the pipework enters the soil polishing filter.
Who can Undertake a Site Assessment?
Donegal County Council have set up a panel of site assessors, qualified to undertake site investigations using EPA methodology. The assessors have professional indemnity insurance, and are bound to present accurate information on the site characteristics. Assessors are contracted directly by the planning applicant.
How Much does the Assessment Cost?
The cost of the assessment should be agreed with the site assessor. Ideally, a cost could be negotiated for each part of the assessment described. This allows the applicant to decide whether or not to proceed to a full site assessment, and a full planning application. This approach should be agreed before starting any part of a site assessment. The fee does not include digging the holes. A desk study, together with the experience of the assessor, will indicate a site that is unlikely to pass the assessment. It is more appropriate to spend a smaller fee on this advice, than a larger fee on a full report for a failed site.
Appropriate Sites
Can all Sites be made Suitable for Development?
No, some sites cannot be made suitable. Both treatment and disposal of wastewater is required. One or other, (or both), may be a problem. This may be due to a number of reasons, including poor draining soils or groundwater use for drinking. The site assessment is a risk assessment. The assessor must identify the potential targets at risk, when wastewater is produced on site. This includes the risk of ponding (with impeded drainage), the risk of contamination of groundwater, and the risk of run off to surface water drains and rivers. Ultimately, the decision on the site suitability rests with the Planning Authority. The site must be capable of providing adequate treatment within the site and dispersion of the total water volume arising in the development. Outfall to surface waters (drains and rivers) is not permitted.
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