Highways Agency

• 1. introduction
• 2. scheme proposals
• 3. engineering assessment
• 4. environmental assessment
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 5. traffic and economic assessment

4. environmental assessment (continued)

4. Environmental Assessment (continued)

4.8 Water Quality and Drainage

4.8.1 Introduction

The Environmental Appraisal Report evaluated the potential environmental impacts of a number of proposed alternative route options for the proposed A 14 Improvements. This report provides the evaluation of the Alternative Proposal and compares it with the environmental impacts associated with the CHUMMS Strategy. This section of the report addresses the difference in potential impacts to the water environment between the two options.

4.8.2 Study Area

The study area was defined within Part I of this Report.

4.8.3 Method of Assessment

The offline alignment of the Alternative Proposal is the same as that for the identified CHUMMS Strategy, so in many respects the potential impacts to the water environment are the same as those already identified within the main Stage 2 Environmental Appraisal Report. There are, however, some key differences between the Alternative Proposal and the CHUMMS Strategy and these are identified below.

• North-south traffic will continue along the existing A14 alignment to the north of the Trinity Foot junction.
• East-west traffic ONLY will use the new A14 alignment between the Trinity Foot junction and Ellington.
• The offline alignment will be four lanes in the Alternative Proposal compared to the six lanes in the CHUMMS Strategy.
• The railway viaduct at Huntingdon will be replaced by a similar structure in the Alternative Proposals, whilst a smaller crossing is proposed within the CHUMMS Strategy.

The reduction in developed area and traffic volumes along the new offline section associated with the Alternative Proposal has potential benefits to the watercourses that will receive drainage it. The potential benefit was evaluated using the methodologies identified within the TAG framework.

Within the TAG framework, the potential impacts on water quality were assessed using the established methodologies for routine runoff and spillage risk outlined in the Design Manual for Roads and Bridges Volume 11 Section 3 Part 10 (DMRB 11.3.10). The methodology for routine runoff involves tests to predict future concentrations of zinc and copper in receiving watercourses. The spillage risk assessment methodology provides the return period of a serious accident based on road length, presence of junctions, annual average daily traffic (AADT), percentage of heavy goods vehicles (%HGV), serious spillage rates, emergency services response time and River Ecosystem (RE) Target of the receiving watercourse.

The DMRB assessment has only been undertaken for those watercourses for which appropriate supporting data were available (either from the Environment Agency or through baseline water quality monitoring). An evaluation of the potential impacts to Ellington Brook has not been undertaken in this assessment as the drainage from the A14 will enter into the same drainage channel that serves the A1 at present. No data were available for the A1 with which to evaluate the combined impact downstream of the outfall.

Whilst there are potential benefits to the watercourses that will receive drainage from the new alignment, in the Alternative Proposal north-south traffic will continue to use the existing alignment. As such in the Alternative Proposal, this section of the existing A14 will continue to drain into the same watercourse with the associated risks to the quality and quantity of water from routine runoff and accidental spillages. In the time available, an evaluation of the existing drainage system has not been possible and therefore a DMRB assessment has not been undertaken. The potential impacts and associated mitigation are, however, discussed qualitatively.

4.8.4 Criteria for Magnitude and Significance of Impacts

These have been identified within Part I of this Report.

4.8.5 Existing Conditions

These have been identified within Part I of this Report.

4.8.6 Assessment of Proposed Routes

The water environment is important in terms of water supply, transport and dilution of wastewater, biodiversity, aesthetics, recreation, value to economy and conveyancing of flow and flood waters. The predicted impacts, and their significance, to these attributes of the water environment, for the Alternative Proposal have been formally summarized in the TAG Worksheet and Appraisal Summary Table (AST).

PREDICTED IMPACTS AND SIGNIFICANCE

During Construction

The predicted impacts associated with the construction of the Alternative Proposal are considered to be not significantly different from those associated with the construction of the CHUMMS Strategy. The offline alignment of the improvements is the same for each option, so they both have the potential to impact the same watercourses. The difference between constructing a dual lane two-way rather than a three lane two-way is considered to be insignificant in terms of potential impacts to the water environment.

Furthermore it is considered that the replacement of the railway viaduct with a similar structure within the Alternative Proposal has a similar potential to impact upon the groundwater environment as the construction of the smaller crossing required as part of the CHUMMS Strategy.

During Operation

The output of the DMRB surface water and spillage risk modelling that was conducted for each of the two routes is included in a table (located at the end of this chapter).

The analysis shows that there would be no significant benefit to water quality within watercourses receiving routine runoff from the Alternative Proposal compared to that predicted for the CHUMMS Strategy. The analysis did however show a more adverse impact in the watercourse that would receive drainage closest to the eastern interchange of the offline alignment and the existing alignment. This is because of the increased road area that will drain to this watercourse with the more complex interchange required with the Alternative Proposal.

The analysis did show that there would be some reduction in the spillage risk in a number of watercourses associated with the Alternative Proposal compared to the CHUMMS Route. The reduction in risk was not so significant, however, that there would be a change in the mitigation required to reduce potential impacts to receiving watercourses. There was an increased risk from spillages identified for the watercourse identified in paragraph 9.14, associated with the addition of slip roads within the Alternative Proposal layout that would drain into it.

In the Alternative Option a significant proportion of the traffic would continue to use the existing alignment in order to gain access to the A1 to the north of Huntingdon along the existing eastern A1/A14 Interchange (Ref to appropriate Traffic Section in the Technical Appraisal Report). As such watercourses that receive drainage from the existing alignment would continue to receive runoff under the Alternative Proposal therefore there would be no potential improvement to water quality within these under this option.

No evaluation of the existing drainage system as part of this Stage 2 assessment It is possible, however, that the drainage system that serves the current A14 would not be acceptable, both in terms of the quality and quantity of run off, under current standards. The existing drainage system along the A14 would need to be evaluated to assess the suitability of current mitigation, if the Alternative Proposal was progressed.

4.8.7 Potential Mitigation Measures

The potential mitigation measures the Alternative Proposal are the same as those proposed within Section 13 of the main Stage 2 Environmental Appraisal Report. In addition, a thorough assessment would be required of the compatibility of the existing A14 drainage system with current drainage standards along the stretch that is to be retained.

4.8.8 Summary

The quantitative and qualitative assessment of the CHUMMS Strategy and the Alternative Proposal suggests there is no significant difference between the two options in terms of potential impacts to the water environment. The most significant difference is that in the Alternative Proposal a significant proportion of the traffic would continue to use the existing A14 alignment; the drainage of which may not be appropriate to current drainage standards in terms of the quality and quantity of runoff.

Table 4.33 - Comparison of the Results of the DMRB Water Quality Assessment Modelling for the CHUMMS Strategy and the Alternative Proposal

Note: Concentrations are for Total zinc and Dissolved copper. Watercourses have been assigned a River Ecosystem target of RE2 unless there were data available to the contrary. See text of main EAR for other assumptions made for modelling.

Note: Concentrations are for Total zinc and Dissolved copper. Watercourses have been assigned a River Ecosystem target of RE2 unless there were data available to the contrary. See text of main EAR for other assumptions made for modelling.