I have been discussing the hard standing drainage for Thanet earth with TDC and the EA, normally I am inclined to modify these communications into short posts for you all, but I am putting up my communications between TDC and me, pretty much in full, my emails in black and TDCs in red. For once it looks like a satisfactory outcome and a job properly done!
The reason that I am doing this is that it serves to emphasise how important interceptors are and why I feel that Manston Airport shouldn’t be operating without one on the main runway, positioned as it is on our essential drinking water aquifer and currently discharging into an internationally acclaimed wetland:
Could you kindly look into this one for me, or tell me who can, could you also tell me how big the interceptors are if any are installed?
A mixture of factors has come together making an aspect of Thanet Earth potentially very dangerous indeed.
When the planning application for Thanet Earth was approved there was no environmental impact study done, I don’t know if this was because it counted as an agricultural development or if it just slipped under the radar.
This means that the surface drainage of the car, lorry parks and loading areas have drains that run into soakaways not only are these on the aquifer, but they are very close to where Thanet Earth is pumping out water from a borehole for its irrigation and crop washing.
The recent disparity between diesel prices in different countries mean that lorries are being fitted with larger fuel tanks 1,000 litres is not uncommon.
I doubt that the driver would even notice if while he was manoeuvring his lorry a bollard or something caught and ruptured his fuel tank and as lorries often have two of these tanks it could be a considerable time before he noticed.
There is also a new crime spreading across Europe which is pertinent to lorry parks on the aquifer, below an extract from a news article.
On the 24th of June when the workmen arrived for a new day they found 3 lorries that have been filled up the last night with their tanks completely empty, having been pierced with a pickaxe. They didn't even take half of the diesel, with the remainder spilled on the ground. The company lost more than 4000 € that day from fuel theft in addition to the cost of repairing 3 fuel tanks.
One month later the smell of spilt diesel still engulfs the facility. Now the lorries are guarded during the night by a man with a licence to carry and use firearms. On the fence a sign warns: be wary of pitbull dogs.
Apologies for the delayed response, I have just returned from annual leave. The original consultation on this app predates my arrival, but I am chasing up the relevant info on this site and will get back to you once I am in possession of the facts. In the meantime, the Environment Agency may be a useful source of information regarding the history of this one.
I have from the EA, Lorry and loading areas do drain to soakaway but via Class 1 full retention interceptors with oil detector alarms and with pen-stop values up and down stream of the interceptor that can be used to stop any contaminated discharge to the interceptor or from the interceptor.
So the question I would like the answer to is; is the interceptor and surface containment area able to contain the spillage from these newly enlarged lorry tanks?
Chatting to a few lorry drivers that buy transport books from the shop I gather 2,000 litres isn’t an fuel unusual capacity.
I have now received a response from the RPS Principal Engineer working on the Thanet Earth project (vide infra) and visited the site to inspect progress of these works.
In answer to your question regarding a spill from a large tank on a lorry, the worst case scenario options have been calculated for the principal parking areas of the site as follows. I should add, that the site is also designed to restrict access to the buildings to designated areas, thus deterring lorries from parking anywhere else on the site (e.g. on the side of a roadway, where a spill could directly enter ground).
'The interceptors installed are Conder 'full retention' separators, are fitted with automatic closure devices that comprise a floating disc or ball and plate in a cylindrical shaft over the outlet duct. In major spillages, or when the maximum oil retention capacity is retained the
closure device is forced down over the aperture to prevent discharge.
Audio and visual alarms will action when the oil level is at 90% capacity.
With regard storage of accidental spills, I have calculated the storage volumes available at each of the separators based on a worst case of having 89.9% of the oil storage capacity full before the spillages i.e. just prior to alarm for emptying:
- Separator 1 (Pack house) = remaining capacity within the interceptor
of 400l + drainage system and above ground containment of 75,000l =
- Separator 2 (GH2/3)= remaining capacity within the interceptor of 80l
+ drainage system and above ground containment of 10,000l = 10,080l.
- Separator 3 (GH4) = remaining capacity within the interceptor of 40l +
drainage system and above ground containment of 4,000l = 4,040l.'
As you can see, the absolute worst case scenario would be for a lorry tank to be punctured in the vicinity of drainage running to separator 3, but this would still be able to offer protection commensurate with losing two entire large HGV tank loads of fuel, although the primary concern, should this ever occur, would obviously be the fire risk in the first instance
I will reply more coherently when I have discussed this with a friend who specialises in this area, sorry I can’t do it manu propria, initial thoughts have me wondering what happens with a fuel spillage in a rain storm round number 3, I will do some sums.