VERSION 1

DATE 21-12-18

BY RL

AMENDMENT

REASON - issued for consultation

Thurne Bungalows & Repps S101A – Technical Report Page 1 of 21

1.0 Introduction

This assessment has been undertaken in response to the appeal lodged against the S101a application rejection for the provision of sewerage to Thurne Bungalows & Repps. The purpose of this document is to provide information for a review of the application. This document provides an outline definition of a technically feasible solution along with indicative costs.

Please be aware that the contents of this report, including the summary of costs, are an estimate based on solutions generated by a desktop assessment. The solutions set out within this document are indicative and should not be relied upon without further detailed investigations. These are considered to be feasible solutions for the purposes of evaluating the S101a application. A detailed design would be required to investigate and validate the solution

2.0 Areas to be served

For the purposes of defining notional solutions the properties have been divided into areas grouped by proximity and potential access points as follows:

1. Staithe Road, Repps: application comprising 4 traditional residential properties.

Potential for connecting 27 residential properties and a holiday camp site

2. South Bank – West: 1570 metre river-side stretch with application comprising 33 bungalows. Potential for connecting 48 bungalows

3. Potter Heigham Bank: 480 metre river-side stretch on north bank with application comprising 3 bungalows. Potential for connecting 7 bungalows

4. South Bank – East: 650 metre river-side stretch with application comprising 1 bungalow. Potential for connecting 16 bungalows

5. Martham Bank: 810 metre river-side stretch on south bank with application comprising 19 bungalows. Potential for connecting 32 bungalows

Plot 11 Ludham bank - “Toad Hall”

The single property at Plot 11 on the Ludham bank, “Toad Hall” is too remote from existing sewerage infrastructure and neighbouring property for a viable connection to the public sewerage system. Therefore, this property has not been considered further in this assessment.

There are a range of small package treatment plants available that may provide an alternative provision for foul water disposal from this property. The available products tend to use either a rotating biological contactor (RBC) or a small aeration unit, both of which require a reliable power supply. The RBC type would be expected to require less power to operate; typically using 50w motor to drive the rotation in a single property installation.

Although generally considered low maintenance, the sump would still need to be emptied once every 9-12 months depending on occupancy.

3.0 General sewerage strategy options

The areas comprising this study are not sufficiently close for a single integrated strategy, although there are potential linked strategies for Areas A & B and separately also for Areas C & D.

Standalone solutions

Areas assessed as distinct and separate schemes and are summarised as follows:

Area A: Gravity sewerage to new pumping station in agricultural land off Staithe Road in vicinity of NGR TG4167317072. A rising main connecting to the existing sewerage network at the REPPS with BASTWICK TOWER RD pumping station (RETRSP). Network reinforcement required at RETRSP.

Area B: A vacuum main laid adjacent to footpath, connecting to a pump station in pasture off Staithe Road in the vicinity of NGR TG4144217428. A rising main conveying flows to the existing sewerage network at the RETRSP pumping station. Network reinforcement required at RETRSP. The footpath will be up-graded to enable suitable vehicle access to service the vac pots.

Area C: Avacuum main laid adjacent to footpath, connecting to a pump station in pasture at rear of Mill House in the vicinity of NGR TG4297819079. The existing track will be up-graded to provide suitable vehicle access. A rising main conveying flows to the existing 225mm diameter sewer at manhole TG41187602 in Bridge Road (NGR TG4179618638). The footpath will be up-graded to enable suitable vehicle access to service the vac pots.

Area D: A vacuum main laid adjacent to footpath, connecting to a pump station in land at rear of the footpath in the vicinity of NGR TG4312318953. New access road required. A rising main conveying flows to the existing sewerage network at the RETRSP pumping station. Network reinforcement required at RETRSP. The footpath will be up-graded to enable suitable vehicle access to service the vac pots.

Area E: A vacuum main laid adjacent to footpath, connecting to a pump station in private land adjacent boat house at Cess Road, in the vicinity of NGR TG4390819152. A rising main conveying flows to the existing sewerage network at MARTHAM-CESS ROAD pumping station (MARCSP). Network reinforcement required at MARCSP. The footpath will be up-graded to enable suitable vehicle access to service the vac pots.

Thurne Bungalows & Repps S101A – Technical Report Page 4 of 21 Integrated or optimised solutions

Combined solutions have been considered that make use of relative proximity and explore potential efficiencies by grouping more properties to a conveyance route. The potential combined schemes and are summarised as follows:

Areas A & B combined: vacuum system and pump station serving area B discharging via a short rising main to the gravity sewer serving area A gravity. All flows connecting via a new pumping station in agricultural land off Staithe Road in vicinity of NGR TG4167317072. A rising main conveying flows to the existing sewerage network at the RETRSP pumping station. Network reinforcement required at RETRSP.

Areas C & D combined: gravity sewerage system laid adjacent to footpath of Area C, connecting to the new conveyance pumping station serving Area D via crossing beneath the river. A vacuum system laid adjacent to footpath, connecting to a new pump station in land at rear of the footpath in the vicinity of NGR TG4312318953. A rising main conveying flows to the existing sewerage network at the RETRSP pumping station. Network reinforcement required at RETRSP.

4.0 Notional solution composition

Area A – Standalone

• 400m of 150mm diameter sewer at depth up to 3.0 metres.

• 430m of 150mm diameter sewer at depth range to 4.0 metres

• 4nr 100mm diameter connecting laterals

• Pump station: 18kW MEICA with septicity control

• 1.7km of 100mm nb rising main in type 3/4 carriageway, at depth 1.5 metres

• Reception chamber and 40m of 225mm sewer connecting to the connection point at manhole TG4217 3800; depth of 1.5 metres. This provides up to 2m3 of additional storage at RETRSP

Area B - Standalone

• 1790m of 125mm diameter vacuum main at depth not exceeding 2.0 metres.

• 33 vacuum pots

• 33nr 100mm diameter connecting laterals

• Pump station: 17kW MEICA with septicity control

• Upgrade footpaths and track to enable tanker access along line of the vac main

• 170m of 100mm nb rising main at depth 1.5 metres

• Reception chamber and 40m of 225mm sewer connecting to the connection point at manhole TG4217 3800; depth of 1.5 metres. This provides up to 2m3 of additional storage at RETRSP

Area C – Standalone

• 480m of 100mm diameter vacuum main at depth not exceeding 2.0 metres.

• 3 vacuum pots

• 3nr 100mm diameter connecting laterals

• Pump station: 17kW MEICA with septicity control

• Upgrade footpaths and track to enable tanker access along line of the vac main

• 1.4km of 100mm nb rising main at depth 1.5 metres

• Reception chamber and 5 metres of 150mm sewer connecting to manhole

TG41187602; depth of 1.5 metres

Area D - Standalone

• 830m of 100mm diameter vacuum main at depth not exceeding 2.0 metres.

• 4 vacuum pot

• 4nr 100mm diameter connecting laterals

• Pump station: 19kW MEICA with septicity control

• Upgrade footpaths and track to enable tanker access along line of the vac main

• 1.1km of 100mm nb rising main at depth 1.5 metres

• Reception chamber and 40m of 225mm sewer connecting to the connection point at manhole TG4217 3800; depth of 1.5 metres. This provides up to 2m3 of additional storage at RETRSP

Area E

• 810m of 100mm diameter vacuum main at depth not exceeding 2.0 metres.

• 19 vacuum pots

• 19nr 100mm diameter connecting laterals

• Pumping station: 17kW MEICA with septicity control

• Upgrade footpaths and track to enable tanker access along line of the vac main

• 1.95km of 100mm nb rising main at depth 1.5 metres

• Reception chamber and 40 metres of 225mm sewer connecting to the wet well at MARCSP; depth of 1.5 metres. This provides up to 2m3 of additional storage at

MARCSP

Area A & B Combined

• 400m of 150mm diameter sewer at depth up to 3.0 metres.

• 430m of 150mm diameter sewer at depth range to 4.0 metres

• 1790m of 125mm diameter vacuum main at depth not exceeding 2.0 metres.

• 33 vacuum pots

• 37nr 100mm diameter connecting laterals

• Pump station A: 18kW MEICA

• 1.7km of 100mm nb rising main at depth 1.5 metres

• Pump station B: 17kW MEICA with septicity control

• 170m of 100mm nb rising main at depth 1.5 metres

• Upgrade footpaths and track to enable tanker access along line of the vac main

• Reception chamber and 40 metres of 225mm sewer connecting to the connection point at manhole TG4217 3800; depth of 1.5 metres.

Area C & D Combined

• 310m of 300mm diameter micro-bore tunnel, at depth circa 2.0 metres.

• 3nr 100mm diameter connecting laterals

• River crossing formed by 120m directional dig, nominal bore 600mm; 2nr shafts each of 2.4m diameter and 6.0m depth

• 10m of 300mm diameter sewer linking the south bank shaft to the conveyance pumping station wet well in Area D main

• 830m of 100mm diameter vacuum main at depth not exceeding 2.0 metres.

• 4 vacuum pot

• 4nr 100mm diameter connecting laterals

• Vacuum station: 10kW MEICA

• 50m rising main discharging to adjacent conventional conveyance pumping station (also receiving flows from Area C)

• Conveyance pumping station: 19kW MEICA with septicity control

• 1.9km of 100mm nb rising main, at depth 1.5 metres

• Upgrade footpaths and track to enable tanker access along line of the vac main

• Reception chamber and 40m of 225mm sewer connecting to the connection point at manhole TG4217 3800; depth of 1.5 metres. This provides up to 2m3 of additional storage at RETRSP

Factors common to all:

• Land purchase for pumping stations

• High water level, requiring dewatering and piling

• Crossing significant infrastructure (flood walls and watercourses)

• Environment mitigation measures

• Archaeology

• Modelling (for network impact)

• Statutory power upgrade

• Temporary access arrangements (diverting footpaths)

• Extensive planning required (raised structures in flood plain)

Additional factors not costed:

• Aesthetic enhancements to new pumping stations in land adjacent the river banks

• Disruption / curtailment of public foot path

• Disruption due to seasonally constrained works

5.0 Cost estimates

Please note that our cost estimates are based on a solution generated by a desktop assessment. The solution set out above is indicative and not final. As such it should not be relied upon without further detailed investigations. A detailed design would be required to investigate and validate the solution.

Our estimates have been compiled using the AMP7 price base and will need to be revised accordingly if delivery is scheduled after 2025.

Whole life cost (WLC) is based on a discount rate of 2.3% for AMP 7 in lieu of OFWAT’s final determination and a period of 40 years.

It should be noted that the full potential is estimated at c.130 new connections. While the cost of provision for these additional properties will increase the total costs, a substantial reduction in the cost per connection could be expected in areas B and E.

The costs ought to be reviewed in reference to that of providing a privately owned cess pool solution as defined in Table 4 below.

The individual cess pool comprises a tank capacity of 22.5m3, OPEX based on seven tank emptying per year.

No assessment has been made of the practicality of installing larger cess pool tanks in the areas, although it is noted that the physical constraints at many of the properties would pose technical difficulties for this option.

Cost estimate confidence

AWS cost models are derived from the out turn costs of similar projects and activity types, dating back to the AMP5 period (2010 to 2015). While the majority of the items and activities that comprise this estimate are common, some elements are under represented in terms of either scale or quantity and consequently there are some areas of low confidence in the values generated.

Further detailed assessment will be required to raise the cost estimate confidence in these areas to an acceptable level.

6.0 Factors limiting practicability

While the purpose of this report is to outline a technically feasible solution, broader assessment of its practicability will need to take into consideration factors that are not readily predictable and not directly under the control of AWS. The following factors will need to be addressed:

1. Implications of seasonal restrictions to construction. Winter and the wetter months pose difficult working conditions (and therefore slow progress) and greatly increase the potential for environmental damage. During summer the amenity demand will impose constraints on access for construction traffic. The construction will be highly disruptive and will inevitably restrict (and temporarily remove) access to properties.

2. Temporary access routes for construction activities is unfeasible in some areas, such as the western extents of Area B. Providing a safe footpath, segregated from construction activity is not possible in some areas.

3. Above ground structures in the flood plain will need to be elevated to address flood risk. This may not be acceptable on aesthetic grounds. Cost estimates will need to be revised if additional measures are required to mitigate the visual impact. This may meet with challenges in the planning process as would the provision of suitable vehicle roadways along the footpaths, which will be essential for maintenance.

Figure 9: Indicative profile for a vacuum pump station

4. The raised structures and embankments required to provide maintenance access to them will displace flood storage volume. Further consultation will be required to determine whether this is feasible.

5. The solution requires deep excavations, in excess of 5m deep and will need dewatering; however, the capacity of standard provision apparatus (eg. silt buster) may not be suitable or capable for the conditions and circumstances of these solutions. There is a high risk of pollution that may not be possible to mitigate.

6. There is a heightened risk of inundation from flood water and infiltration that will need to be managed with particular attention to the type of configuration of the lateral connections. A more proscriptive approach to this will be necessary, which will be an invasive exercise for many of the properties, potentially resulting in some alterations in order to make a sound connection.

7. As the operation of vacuum sewer systems relies on the air drawn in from the collection chambers, the system will be inoperable if the land in which the collection chambers are located becomes inundated with flood water. There would be no service while this condition prevails.

7.0 Conclusions

Anglian Water has an obligation to achieve the best value from our investments and the conclusions that we have drawn from this assessment will reflect the need to direct investment to where the risk reduction is greatest. Investment in this application will have implications for the investment programme as a whole and we’ll need to demonstrate that the benefits can be justified against the programme requirements.

While noting that the installation of a 22m3 cess pool may not be practicable for many of the properties in the assessment area, it remains an indispensable metric for affordability on a wider scale.

With the exception of the Area A Standalone, all of the remaining solutions outlined above lie on the periphery of typical sewerage schemes. As such there are elements of the envisaged works, for which the programme and cost cannot be confidently estimated without more detailed analysis.

It should be noted that the installation of sewerage along the river bank will create a profound change in appearance, particularly with regard to upgrading footpaths to enable vehicle access for tankers, which may not be acceptable to the local planning authority.

Similarly, the practicability of the solutions outlined in this report depend upon the acquisition of private land for siting pump stations and creating easements for pipelines. Therefore, the successful outcome will be subject to negotiation and cannot be relied on at this stage.

The resolution of these matters is not entirely in Anglian Water’s control and the agreement of statutory bodies and third parties will be required before greater certainty can be achieved.

While taking into consideration these uncertainties, the cost estimates at this stage would indicate that the provision of sewerage to Areas B and E could be a viable alternative to upgrading the serviceability of the existing private cess pool provision. Subject to assurances with regard to planning acceptability and the availability of private land to site the necessary infrastructure, the solutions for Areas B and E would merit further detailed evaluation.

This conclusion recognises the reasonable probability that non-applicant properties in areas B & E will also seek to connect if a sewerage system is offered.

The same assumption could not be made for properties in Area A, where the conventional private cess pool installation is likely to be more serviceable. Combining areas A and B does not sufficiently reduce the unit cost to a level where additional connections would be expected to bring it in broad parity with the private cess pool option. In this instance the standard cess pool provision would be considered practicable. Therefore, provision of sewerage is Area A is not currently considered a supportable investment option.

This assessment concludes that the areas C and D are too remote from existing infrastructure to achieve affordable units cost even with the potential for additional connections taken into consideration.

In drawing this conclusion we have borne in mind the sustainability of the existing boat service. The pollution risk and amenity limitations are in part related to the physical capacities of the existing boat.

It would seem reasonable to assume that a utility provision via boat will continue to operate in some form. The more remote properties such as Toad Hall will still require a service. Therefore, a significant reduction in the number of cess pools served would enable an enhanced service to the remainder and bring about a tangible reduction in the risks and amenity associated with them.

It should be noted that among the most prominent areas of uncertainty with the river bank solutions is in forming a permanent vehicle access way, suitable for a 13m3 tanker.

This roadway is essential for the sewerage system, particularly for a vacuum system. However, the roadway in itself would significantly enhance the serviceability of the existing cess pool provision. This would reduce a number of the current amenity concerns, as it would lessen reliance on the boat and offer alternative services for property owners.

The provision of more options for servicing the properties by simply improving vehicle access or enabling an additional service boat and/or operator are viable alternative approaches that ought to be explored further.

Anglian Water Evaluation of Sewerage Options 2018

Project title; Thurne Bungalows and Repps Evaluation of Potential Sewerage Options

The cost tables are missing on this transcription. You can download a copy of the full report here.