Chapter 9: Road drainage and the water environment

M1 JUNCTION 19 IMPROVEMENT
ENVIRONMENTAL STATEMENT VOLUME 2
CHAPTER 9 – ROAD DRAINAGE AND THE WATER ENVIRONMENT
would be below 1% for each drainage zone, and would be 0.5% for all drainage zones
combined. This means that the do-minimum scenario would present an acceptable risk of a
pollution incident occurring.
Surface Water Discharges
9.4.19 In addition to the highway discharges described earlier, which are currently exempt from
licensing, there are a number of consented discharges to the various watercourses in the
area. The majority comprise treated sewage / storm effluent from both water companies
and private residences. There are also a few site drainage trade effluent discharges.
Groundwater
9.4.20 Published geological and ground investigation information form the basis of the geological
baseline conditions. The geology is described in more detail in Chapter 5 Materials.
9.4.21 The general geological sequence is of Glacial Till overlying Jurassic Lower Lias Group
mudstones, which has been dissected by the River Avon and its tributaries causing erosion
and removal of the Glacial Till cover in places and deposition of overlying younger river
terrace gravels and alluvium. Thus there are small outcrops of Glacial Till along the
western extent of the M6, the most northern and southern extents of the M1 (although the
cuttings have exposed the underlying solid strata in places) and also beneath part of the
area of the Junction. Extensive deposits of river terrace gravels and alluvium are
associated with the River Avon and Clay Coton Yelvertoft Brook. There are lesser fluvial /
alluvial deposits associated with the Swinford Lodge Brook and tributary and also some unnamed
watercourses which are crossed by the M6.
9.4.22 There are some areas of made ground (described in more detail in Chapter 5 Materials),
mainly associated with borrow pits from various earlier phases of road construction, which
appear to have been infilled with ‘inert’ construction waste. There is a former Cleanaway
landfill site (Catthorpe Landfill, NGR SP 553 787) located adjacent to the south of the M6,
which was licensed between 1977 and 1986 to receive domestic and industrial wastes.
9.4.23 The alluvium generally comprises soft to firm alluvial clay and silt up to about 5m deep in
the vicinity of the River Avon. The river terrace gravels comprise interbedded very gravelly
clay, gravelly sand, and gravel (mainly of flint) between about 1 to 3m thickness. The
Glacial Till, varying between gravelly clay to firm to still clay is up to 10m thick. The Lower
Lias strata comprise a sequence of horizontal to sub-horizontal, predominantly ‘hard’ clays
/ mudstones with occasional thin limestone and (separate) ironstone bands. The Lower
Lias is between 140-170m thick.
9.4.24 The river terrace and fluvio-glacial / alluvial deposits are classified as minor aquifers. The
distribution of the minor aquifer is shown on Figure 9.1. Minor aquifers are usually of only
local importance for supporting abstractions or providing baseflow to surface waters. The
Lower Lias strata and Glacial Till deposits are generally classified as non-aquifers,
although specific units within the former can have minor aquifer status. Non-aquifers
usually do not support any abstractions or provide significant baseflow to surface waters.
However, some of the thin limestones within the Lias can yield significant quantities of
water. The proportion of water-bearing limestones increases towards the base of the Lower
Lias Group, forming the Blue Lias or Scunthorpe Mudstone Formation, which can be
classified as a minor aquifer. On the basis of interpretation of the published geological map,
the strata below the proposed scheme are towards the top of the Lower Lias Group
sequence, and therefore would indicate non-aquifer status.
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