FOUL AND SURFACE WATER MEANS OF DISPOSAL

REPORT

AT

STONER HOUSE, LONDON ROAD CRAWLEY, WEST SUSSEX, RH10 8BL

FOR

AXIOM STRUCTURES LTD

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CONTENTS 1.0 Introduction 2.0 Investigation 3.0 Calculations 4.0 Drawings 5.0 Thames Water Correspondence 6.0 Appendices 7.0 Summary Compiled by: Date: 29th April 2016 Revision: -

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1.0 Introduction

1.1 This report has been prepared in connection with the above development and no responsibility is accepted to any third party for all or part of this study in connection with this or any other development.

1.2 The location, size, depth and identification of existing services that may be shown

or referred to in this report have been assessed from non-intrusive observations, record drawings and the like. Any Contractor shall safely carry out intrusive investigations, trial holes or soundings prior to commencing any works, to satisfy himself that it is safe to proceed and that the assessments are accurate. Any discrepancies shall be notified to the Client prior to the commencement of any works.

1.3 JDH Consulting Engineers LLP was appointed by Alan Bowling, Director of Axiom

Structures Limited, on the 21st April 2015.

1.4 The purpose of this report is to evaluate the means of surface water disposal and SuDS requirements to satisfy the Crawley District Planning Condition (Recommendation RE: CR/2015/0463/FUL Section 14).

1.5 It is proposed to convert the multi-storey office building into 111 apartments. This will include the creation of ground floor accommodation, (through infilling the existing car parking area, under the building) plus additional 4 storeys to the existing building. The site is currently fully developed with very little soft landscape.

1.6 A Pre-Development enquiry was made to Thames Water. Lance Cooper, Development Engineer – Waste, confirmed by letter on 18th March 2016 (copy contained in this report) that the foul water of 12.5 litres per second and the surface water of 25 litres per second would not be detrimental to their system and recommended that a Section 106 connection consent application should be made. A Section 106 application has not yet been submitted to Thames Water.

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2.0 Investigation

2.1 Surface Water Disposal

2.2 The surface water drainage system has been designed in accordance with CIRIA

C697 The SUDS Manual. The SuDS system shall accommodate the 1:100 year return period + 30% global warming.

2.3 Surface water disposal should be directed to ground (through infiltration) as the

first option; the second option being directly to a watercourse (with an agreed restricted discharge) and the third option to surface water sewer (with an agreed restricted discharge).

2.4 The first option to discharge to ground using conventional soakaways is not

practical, due to the Crawley clay.

2.5 The second option to discharge to a watercourse is not viable, as there is no watercourse on the site boundary.

2.6 Therefore, the restricted surface water discharge of 25 litres per second (as

agreed with Thames Water) is to be directed to sewer, via a new lateral drain laid across the London Road into the 1350mm diameter surface water sewer manhole No. 8253.

2.7 25 litres per second represents a 50% reduction in the existing volumetric

discharge from the site.

2.8 Attenuation Storage Volume MicroDrainage source control 2015.1 software was used to calculate the storage volume required to accommodate the 1:100 year return period + 30% global warming, without the tank and/or drainage system overflowing. The area draining from the site is 0.34 ha. The calculation shows that the required attenuation storage is 83.6m3, peaking at 60 minutes during a winter storm. This volume equates to a 155m2 by 600mm deep attenuation tank. The MicroDrainage calculations sheets 1 to 5 supporting the above statements are contained within section 3.0 Calculations, of this report.

2.9 Foul Water Disposal 2.10 The waste water flow rate was calculated in accordance with BSEN 12056

Drainage Inside Buildings by KUT LLP Building Services Consultancy, responsible for developing the above ground sanitation design. A copy of KUT’s calculation sheet is contained at the end of section 3.0 Calculations, of this report.

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3.0 Calculations

Summary Results for 100 year return period (+ 30%) page 1 of 5

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Summary Results for 100 year return period (+ 30%) page 2 of 5

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Summary Results for 100 year return period (+ 30%) page 3 of 5

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Summary Results for 100 year return period (+ 30%) page 4 of 5

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Summary Results for 100 year return period (+ 30%) page 5 of 5

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KUT LLP Summary results for the waste water flow rate (Foul Water)

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4.0 Drawings Site drainage areas

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Proposed External Foul and Surface Water Drainage

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5.0 Thames Water Correspondence

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6.0 Appendices

The following drawings are pdf copies of the drawings contained within this report (Section 4.0) and are attached, so that they can be viewed at a larger scale. Site Drainage Areas Drawing number 300/Study/05 P1 External Drainage Drawing number 15026/DR/601 T1

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7.0 Summary

7.1 The surface water drainage system shall be designed in accordance with CIRIA C697 The SUDS Manual. The SuDS system shall accommodate the 1:100 year return period + 30% global warming.

7.2 The surface water volumetric discharge from the site has been agreed with

Thames Water as 25 litres per second. This is a 50% reduction of the existing discharge.

7.3 The above calculations demonstrate that 83.6m3 of storm water storage is

required when the surface water runoff is restricted to 25 litres per second. This storage is contained within a 155m2 by 600mm deep attenuation tank, with a Hydro-Brake flow control.

7.4 Thames Water also confirmed that the waste water flow rate of 12.5 litres per

second can be accommodated within their public foul water sewer.