Following on from my posting a few days ago regarding the lovely clay sump that appears to be developing in my garden, I'm wondering if the best means of ensuring proper ground drainage (and the substantial roof draining which overflows from the rain harvester when it's full, as it has been all year!) would be to have a borehole drilled through to a permeable strata and remove the high water table from the clay in the vicinity of the rain harvester and soakaway (which are seven or so metres away from the house).Whittlesford (CB22) is in an area of patches of loam and gravel (and the courses of ancient rivers which have all gone apart from the Cam/Granta). There is apparently chalk down there somewhere, but I've got no idea how far. There are several former gravel pits around here but there may not necessarily be gravel in our garden.Has anyone here had experience of having a borehole soakway drilled for them?Michael

No, but I have a borehole for sale, if you're interested. Buyercollects, as it's too big to post.You could have a word with a farmer who will point you to awell-driller locally who will know the formations under your feet.Even they get it wrong though, so be prepared for a cost and more costif the first one doesn't work.

Any experience of borehole deep soakaways?

Oct 18, 2012 42 Replies

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boreholedriller1 12 years ago

Even in areas such as near the Thames. You need to bear in mind that the th e surrounding geology is alluvial deposits, over Terrace Gravels and then t he London Clay. Water within the terrace gravels is in continuity with the Thames, so with the recent rainfall the levels will be high, if not overflo wing. The water level within the Chalk aquifer is at a much lower level and is sealed from the aquifer in the terrace gravels by means of impermeable geology, namely the London Clay, Woolwich and Reading Beds and Thanet Sands . The two aquifers are therefore at different levels and not in direct cont inuity. It would therefore be possible to discharge into the chalk aquifer with the Environment Agency's permission.

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Onetap 12 years ago

The 'permeable media' that I meant is the permeable chalk strata into which you would be tipping ground water.

The ground water will contain suspended solid particles. I would expect the chalk to become blocked by this over some time, acting as a filter would.

I don't know how you could clear such an accumulation of material.

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boreholedriller1 12 years ago

ed". An example borehole would be 15 metres of impermeable clay overlying a permeable strata such as chalk.

ich you would be tipping ground water.

the chalk to become blocked by this over some time, acting as a filter wou ld.

A deep bore soakaway is fitted with a syphon head a metre above the base of the attenuation chamber. The soakaway intersects many fractures within the chalk and blocking up with silt is highly unlikely. In installations that are water bearing, the installation can be cleaned out with a borehole pump , but we have never found this to be needed.

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