Chapter 9: Road drainage and the water environment

M1 JUNCTION 19 IMPROVEMENT
ENVIRONMENTAL STATEMENT VOLUME 2
CHAPTER 9 – ROAD DRAINAGE AND THE WATER ENVIRONMENT
9.6 ENVIRONMENTAL IMPACT
9.6.1 The potential impacts of both the construction and operation of the junction improvement
are considered for surface waters and groundwaters respectively below, together with
proposed mitigation measures where necessary.
9.6.2 Highway runoff and accidental spillages present the most significant risk. The Design
Manual for Roads and Bridges (DMRB), Volume 11, Section 3, Part 10 2 identifies ranges of
pollutant concentrations in highway runoff. It lists 39 different pollutants which may arise in
road runoff. DMRB states that, in broad terms, metals and hydrocarbons affect water
quality and impair biological functions, and sediments affect aquatic habitat by smothering
feeding and breeding grounds and by physically altering the habitat.
9.6.3 Potential impacts on flood risk are also dealt with below, and in more detail in the Flood
Risk Assessment.
Catthorpe Viaduct Replacement
9.6.4 As set out in the introduction, there are proposals to replace the Catthorpe Viaduct in
advance of the junction improvement.
Surface Water
9.6.5 During construction EA Pollution Prevention Guidelines (PPG’s) 22 will be followed and
control measures included in a project CEMP similar to the junction improvement as set out
under Section 9.5 Mitigation above. The main concern at this stage will be run-off
containing high concentrations of suspended solids into the River Avon and temporary silt
traps may be required to prevent this. If a pollution event were to occur to the River Avon,
despite the measures in place, it would have a Moderate Adverse impact.
9.6.6 In operation any impacts will be Negligible compared with the existing junction. There will
be some reduction in the amount of run-off as the surface area of highway will be reduced.
Groundwater
9.6.7 The viaduct replacement is over an area of non-aquifer and there is no known source of
contaminated land, although there is always a risk of leaks and spills during construction.
This would be controlled by the CEMP. The risk of adverse impacts is considered to be
Negligible.
9.6.8 During operation there would be no change in risks to groundwater compared with the
existing road. Run-off from the carriageway would not be discharged to groundwater.
Flood Risk
9.6.9 The viaduct replacement is not within a flood zone. There would be a reduction in the
quantity of surface run-off.
Summary for Catthorpe Viaduct
9.6.10 At construction there would be a risk of a Moderate Adverse effect. In operation, the
drainage measures will match the existing arrangements as far as possible resulting in a
Neutral effect.
B0531000_ID_70-EIA Vol 2 Chap 9 Road Drainage and the Water Environment Final Rev 4.doc Page 27