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25/10017/AIR PLANNING OFFICER REPORT AND RECOMMENDATION

Application No. : 25/10017/AIR Applicant : Mr Mike Davies Proposal : Information in relation to condition 9 of PA 23/01407/B detailing works of site clearance and ground preparation, details of surface water drainage works at Land West Of Glenfaba Road Site Address : Land West Of Glenfaba Road Fields 311835, 311836 And 311785 Glenfaba Road Peel Isle Of Man

Planning Assistant: Charlotte Gatt

Recommended Decision: Permitted

Date of Recommendation: 24.03.2025

Conditions and Notes for Approval

C : Conditions for approval N : Notes attached to conditions

NOTE. In this instance of the submitted documentation and after consultation with the Case Officer confirming that they are happy with the level of detail, it is deemed sufficient to achieve the desired outcome and would be considered satisfactory for the planning condition 9 of application 23/01407/B, under the understanding that the development shall not be carried out unless in accordance with the approved details.

Plans/Drawings/Information; This decision hereby approved relates to drawings and documents submitted to the Department titled: APPLICATION FORM, CONDITION 9 SURFACE WATER RESPONSE, 10057112-ARC-XX-XX-RP-C-8100 - PEEL DRAINAGE STRATEGY C01, all recorded as being electronically received by the Department on 10.01.2025

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Officer’s Report

1.0 Description 1.1 The proposed application 23/01407/B for the construction of a new Sewage Treatment Works and creation of new vehicular access was approved at appeal on 16.07.2024 subject to 19 conditions, some of which required submission of additional information prior to the commencement of works.

1.2 This report is specific to Condition (9) which the applicants are seeking to satisfy.

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25/10017/AIR 1.3 Specific wording of the condition is as follows:

Prior to the commencement of development, including works of site clearance and ground preparation, details of surface water drainage works shall be submitted to and approved in writing by the Department. The details to be submitted, which shall accord with the principles set out in the drainage strategy at Section 8.2 of Volume 3 of the Environmental Statement, shall: i) provide information about the design storm period and intensity, the method employed to delay and control the surface water discharged from the site and the measures taken to prevent pollution of the receiving groundwater and/or surface waters; ii) include a timetable for implementation; and iii) provide a surface water management and maintenance plan for the lifetime of the development. Development shall be carried out in accordance with the approved details.

REASON: In order to reduce the risk of creating or exacerbating flood risk and to minimise the risk of pollution

2.0 Proposal 2.1 The applicants have submitted details providing information for the surface water drainage, site clearance and ground preparation along with a detailed plan and word document along with a duly completed AIRC form on the 10.01.2025.

2.2 The Drainage Strategy document includes comprehensive details for the location, existing site (covering Land Use and Topography, Catchment, Geology and Hydrogeology, Flood Risk, Existing Surface Water, Existing Runoff Rates, Existing Drainage Infrastructure, Ground Conditions, Ground Infiltration Rates and Ground Water).

2.3 The document then goes on to highlight details for the SURFACE WATER DRAINAGE STRATEGY. This covers, Planning Policy Requirements, Climate Change, Proposed Strategy, Storage Requirements, Water Quality Design Criteria, Site Specific Drainage Design Considerations, Maintenance, Typical SuDS Maintenance Schedules and Overland Flow Paths.

2.4 The Drainage Strategy document then summarises all of the details that have been provided and outlines the following: The Greenfield Runoff Rate for the site has been provided by the Isle of Man Government Flood Management and Drainage division at a rate of 7 l/s/ha for a 1 in 100 year + 40% climate change rainfall event and is based on a site area of 3.3ha. This rate has therefore been used as the maximum allowable discharge rate from the site. The proposed surface water drainage system can effectively control all runoff generated within the site to the required runoff rates without increasing flood risk elsewhere.

Regular maintenance of all drainage features will be required to ensure they work efficiently during the lifetime of the development. Surface water runoff from the development is split into conventional surface water runoff and that which is contaminated from potential sewage spillage within the sewage treatment works. Separate attenuation is to be provided for each as below.

2.4.1 Conventional Surface Water - The below ground attenuation pipe will attenuate surface water runoff from building roofs and selected areas of the roadway up to and including a 1 in 100 year + 40% climate change rainfall event. This attenuation pipe will discharge to the River Neb via an oil separator to manage oil and hydrocarbons. The rate of

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25/10017/AIR discharge to the river will be limited to 23.1 l/s with the use of a flow control device. A headwall with a non-return valve will be constructed adjacent to the river.

Surface water runoff from cut slopes and where applicable, the natural slopes beyond created by the construction of the new access road and the sewage treatment works will be collected and managed in a way that mimics the natural drainage methods that occurred prior to development.

2.4.2 Contaminated Surface Water - The attenuation pipe will attenuate surface water runoff that has been potentially contaminated from spillage up to and including a 1 in 100 year + 40% climate change rainfall event. The contaminated water will discharge back into sewage treatment process at a controlled rate of 6 l/s. This below ground attenuation pipe has been designed to accommodate a 1 in 100 year + 40% climate change rainfall.

2.5 Details plans and tables have then been provided in relation to the drainage that is to be implemented. Drawing No. 10057112-ARC-XX-XX-DR-C-0 Rev C02 can be viewed alongside all of the other documentation that has been provided.

2.6 Appendix B covers all of the Microdrainage Calculations, which have been provided in depth.

2.7 Appendix C covers the Greenfield Runoff Rate alongside Appendix D.

3.0 Consultation 3.1 The Department's Inland Fisheries Officers were consulted for advice on the satisfaction of condition. The advice received 07.03.2025, after their review of the submitted and updated documents, concludes that they are pleased to confirm that the information satisfies the relevant clauses.

3.1.1 The comments state: "DEFA Fisheries have no objection as long as defined conditions set out in the Section 18 consent are imposed. The Neb River contains fish, including salmon (Threatened species), trout and eels (Protected species) and have concerns due to the nature of the proposed works and potential impacts to this fishery. Having met with the project management and contractors on site, proposed controls of surface water are deemed adequate, with daily monitoring required to ensure these measures are effective. If ineffective, further mitigating controls must be employed due to the sensitive timing (migratory fish spawning season protection from October to June - inclusive) and valuable fishery this development may impact on. Conditions imposed via Section 18 consent include;

-Place effective sediment controls below the working area to control pollution entering the Neb River and millrace and ensure --NO direct pumping of contaminated water from the works to any watercourse at any time, nor any filtered or dried sediment to be disposed of in any watercourse.

-Fisheries Division ask that all surface water is pumped to the filter/run off drain at its highest point to allow dirty water the greatest amount of filtering before reaching the "silt buster" before allowed to enter the Neb River.

-Harmful substances toxic to aquatic life (such as unset concrete) are isolated within the working area and do not enter the watercourse.

-The working area is effectively isolated, ensuring continuous river water flows below the working area at all times.

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25/10017/AIR -Ensure DEFA Fisheries are notified to carry out fish removals before development of utilities crossing the millrace as fish inhabiting the raceway must be removed from the working area before work begins." 07.03.2025

3.2 The Department's Environmental Protection Unit were consulted for advice on the satisfaction of condition. The advice received 20.03.2025, after their review of the submitted and updated documents, concludes that they are pleased to confirm that the information satisfies the relevant clauses 3.2.1 "EPU are satisfied with the proposed discharge control measures and monitoring proposed in relation to condition 9. The utilisation of sustainable drainage systems (SuDs) and separate attenuation systems for conventional and contaminated surface water run-off has been proposed in line with best practice. A site visit should be conducted in conjunction with Fisheries prior to commencement of works." 20.03.2025

3.3 DOI Highways Drainage were consulted regarding the details and their comments are as follows: "MU decided not to build their access road to adoptable standards so it will remain in their ownership as will the drainage system serving it. MU will provide a BN3 kerb with 30mm upstand across the vehicular entrance to the site to prevent runoff from the highway draining into it. This will mimic the current situation. Whilst we have no comment to make on their drainage proposals, FMD might as the proposed discharge route is to a watercourse, in this case a main river (Neb)." 19.03.2025

3.4 The Flood Risk Management Division were consulted for advice on the satisfaction of condition. The comments received on 24.03.2025, after their review of the submitted and updated documents, concludes that they Do Not Oppose.

4.0 Recommendation 4.1 In this instance of the submitted documentation and after consultation with the case officer confirming that they are happy with the level of detail, it is deemed sufficient to achieve the desired outcome and would be considered satisfactory for the planning condition 9 of application 23/01407/B, under the understanding that the development shall not be carried out unless in accordance with the approved details.

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I can confirm that this decision has been made by the Director of Planning and Building Control in accordance with the authority afforded to that Officer by the appropriate DEFA Delegation and that in making this decision the Officer has agreed the recommendation in relation to who should be afforded Interested Person Status.

Decision Made : Permitted Date : 24.03.2025

Determining officer Signed : J CHANCE

Jennifer Chance

Director of Planning and Building Control