Chapter 9: Road drainage and the water environment

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M1 JUNCTION 19 IMPROVEMENT ENVIRONMENTAL STATEMENT VOLUME 2 CHAPTER 9 – ROAD DRAINAGE AND THE WATER ENVIRONMENT runoff on water quality in the receiving watercourses has been estimated (see Appendix A) for dissolved copper and total zinc, in accordance with DMRB guidance 2 . Copper and zinc are two of the most important pollutants present in soluble form, and have been selected as a proxy for other dissolved pollutants, serving as an indicator of whether there is sufficient dispersion and dilution within the receiving water. 9.6.24 As set out in the DMRB, the simple assessment (method A) is used to determine whether the routine runoff is likely to have an impact on the receiving surface watercourses. If it shows that an impact is possible, further assessment is required using the detailed assessment (method B). Where two or more outfalls discharge to the same reach or adjacent reaches, their runoff volumes are combined for the purposes of assessment. 9.6.25 The results are summarised in tables 9.10 and 9.11. More detailed results are shown in Appendix A, Pollution and Spillage Risk Calculations. Table 9.9 Summary Results of Simple Assessment of Pollution Impacts from Routine Runoff (DMRB Method A) Junction Option Drainage Zones 1 and 2 combined 3, 4 and 5 combined 6 and 8 combined 7 and 9 combined All zones combined 2029 Do Minimum X X 2029 Do Something X X X = DMRB Method A calculations show that required dilution is achieved X = DMRB Method A calculations show that detailed assessment (Method B) is required Drainage zones are combined according to the location of the relevant discharge points – see Figures 9.2 and 9.3 Table 9.10 Summary Results of Detailed Assessment of Pollution Impacts from Routine Runoff (DMRB Method B) Zones 1 and 2 combined Zones 3, 4 and 5 combined Zones 6 and 8 combined Zones 7 and 9 combined All zones combined 2029 Do Minimum 2029 Do Something Downstream Downstream Zinc (µg/l) Copper (µg/l) (EQS < 200 (EQS < 22 µg/l) µg/l) µg/l) Downstream Copper (µg/l) (EQS < 22 µg/l) Downstream Zinc (µg/l) (EQS < 200 24 94 21 81 n/a n/a 6 18 35 143 32 131 n/a n/a 6 18 n/a n/a 13 45 B0531000_ID_70-EIA Vol 2 Chap 9 Road Drainage and the Water Environment Final Rev 4.doc Page 30
M1 JUNCTION 19 IMPROVEMENT ENVIRONMENTAL STATEMENT VOLUME 2 CHAPTER 9 – ROAD DRAINAGE AND THE WATER ENVIRONMENT 9.6.26 The estimations indicate that the discharges from the proposed junction improvement would cause the concentration of copper in an un-named tributary of the River Avon to exceed the EQS. This watercourse would receive runoff from drainage zones 6 and 8. All other receiving watercourses would continue to meet the standards for copper and zinc. Under the do minimum scenario in 2029, the EQS for copper would also be exceeded in the tributary receiving runoff from drainage zones 6 and 8. In addition, under the do minimum scenario for 2029, Swinford Lodge Brook, receiving discharges from drainage zones 1 and 2, would fail to meet the EQS for copper. 9.6.27 The routine runoff estimations are conservative as they do not include for mitigation measures. The proposed arrangement of treatment ponds and other precautionary pollution prevention measures, including penstocks and petrol interceptors, would further reduce the potential for pollution from surface water discharges. Given that there is little treatment available for the existing discharges, there is potential for the water quality to improve within the receiving watercourses. 9.6.28 The probability of pollution from an accidental spillage reaching a receiving watercourse has been assessed for the proposed junction improvement, using DMRB methodology (method D). The pollution risk is expressed as the probability of an incident in any one year. The acceptable risk of a serious pollution incident occurring is where the annual probability is predicted to be less than 1%. 9.6.29 The results are summarised in Table 9.11 below. More detailed results are shown in Appendix A. Table 9.11 Summary Results of Assessment of Pollution Impacts from Accidental Spillages (DMRB Method D) Annual Probability of Pollution Incident (%) Drainage Zones 2029 Do Minimum 2029 Do Something Zones 1 and 2 combined 0.29 0.06 Zones 3, 4 and 5 0.13 0.27 combined Zones 6 and 8 combined 0.06 0.07 Zones 7 and 9 combined 0.07 0.18 All zones combined 0.55 0.68 9.6.30 Where two or more outfalls discharge to the same reach (section of river) or adjacent reaches, their runoff volumes are combined for the purposes of assessment – see Figures 9.2 and 9.3. 9.6.31 The calculations indicate that, for all drainage zones, both for the do minimum scenario and for the proposed junction improvement, the annual probability of a serious pollution incident is less than 1%. Therefore, the risk of pollution is assessed as being acceptable. 9.6.32 While the serious spillage calculations assume some risk reduction due to emergency response (use of booms, absorbent pads etc), the initial calculations do not take into account the mitigation measures of the proposed treatment and attenuation ponds. DMRB guidance states that the inclusion of ponds within a scheme can reduce the pollution incident risk by 50%. B0531000_ID_70-EIA Vol 2 Chap 9 Road Drainage and the Water Environment Final Rev 4.doc Page 31
Page 1: M1 Junction 19 Improvement Environm
Page 4 and 5: M1 JUNCTION 19 IMPROVEMENT ENVIRONM
Page 71 and 72: Appendix A - Pollution and Spillage
Page 73: Method D - Assessment of Pollution
Page 78 and 79: Groundwater: Hydrocarbons Hydrogeol
Page 83 and 84: Non Technical Summary Skanska Const
Page 85 and 86: Contents 1 Introduction 1 1.1 Overv
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1 Introduction 1.1 Overview Jacobs
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2 Policy Review 2.1 Planning Contex
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When the both the ‘Flood Zone’
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3 Flood Risk to the Proposed Develo
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3.2 Fluvial Flooding - Ordinary Wat
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Major earthworks affecting surface
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3.7 Flooding from Infrastructure Fa
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3.9 Summary of Risks to Site Table
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4 Impacts of the Proposed Developme
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4.6 Summary of Flood Impacts from D
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5 Proposed Mitigation Measures 5.1
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The extents of this problem are cur
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5.7 Summary of Recommended Mitigati
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6 Residual Risks The level of flood
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7 PPS25 Sequential and Exception Te
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8 Conclusion The M1 Junction 19 Imp
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Appendix A Existing Layout, Environ
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Appendix B Contractor’s Proposals
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Appendix C Hydrogeological Assessme
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Memorandum Fairbairn House, Ashton
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Memorandum (Continued) Page 3 of 6
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Memorandum (Continued) Page 5 of 6
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Appendix D Volume Distribution for
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Floodplain compensation area - elev
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Depth Bands (m) TOTAL (m³) Area Re
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Chapter 9: Road drainage and the water environment

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