INVESTIGATION, COMMENTS & RECOMMENDATIONS ON THE SEWER SYSTEM IN GRYFFE VALLEY 

Background to drainage infrastructure 

Waste water (sewage) from properties passes through the drains into the local waste water sewers and from there into the trunk waste water sewers to be directed to waste water treatment works. In the past the waste water network was used to capture both surface water runoff and foul water in one pipe. Since the 1950s the conventional approach to drainage has been to take the rainfall runoff from buildings, roads and pavements and directly discharge to a watercourse.  For all new developments, sustainable drainage schemes (SuDS) are required for surface water systems which provide attenuation and treatment prior to return, by natural dissipation where possible, to the water environment. Having separate systems frees capacity for waste water and reduces emergency overflows.  Waste water is transported to treatment works where gross solids and grit are removed and the remaining water treated. The organic solids which are removed from the water in the form of sludge are utilised in recycling outlets. Once the water has been treated to an acceptable standard it can be discharged back to the river or the sea. The drainage infrastructure described above can be split into four parts: 

• Part 1 assets:  connections from individual properties to a sewer;
• Part 2 assets: sewers that connect developments to trunk sewers, and some sustainable drainage systems ( SuDS);
• Part 3 assets: local bulk infrastructure, such as trunk sewers, waste water pumping stations and some SuDS; and
• Part 4 assets: strategic assets such as waste water treatment works.

 We are told that this main sewer, which generally follows the course of the River Gryffe serves Kilmalcom, Quarriers, Bridge of Weir, Houston and Brookfield.  Apart from the newer houses in Bridge of Weir and Houston all of these villages have what is called combined systems of Part 1 and 2 assets.  That is the foul and rainwater discharge into a single pipe.  Many of these pipes are old and there will be an increasing amount of infiltration into the system.  Where the surface and foul system are separate, it is not clear just to what extent they join together later and connect into the main sewer.   

Comments from the public 

HALL has received a substantial amount of information from members of the public who have knowledge of the Gryffe Valley Interceptor Sewer which is by definition Part 3 assets.  From this information HALL can deduce what the problems may be. Members of the public are expressing astonishment that the authorities claim that they have only just become aware of the problem.  It is alleged that in 1981, when Kilmacolm became the final village to be connected to the main Sewer, the instant the plug was pulled on the old sewage works the storage tank at the top end of the sewer immediately filled up and started spilling into the river.  The rate of spill is said to have been massive (in the order of 500 - 600 litres/second.)  To the man in the street it would seem that the water authority had made a major mistake in its calculations and that the system hasn’t been corrected.  The response seems to have been to allow the main sewer to overflow and permit more and more development to connect to it without any thought for the risks that this may entail. 

It appears that a specialist consultant, Bullen and Partners, were commissioned in the late 1990’s to carry out what is referred to as a Drainage Area Plan.  It is alleged that the plan was drawn up using sophisticated computer modelling and the Phase 3 Report recommended an increase in sewer diameter in various locations because the existing sewers was under sized.  Other methods of on-line and off-line storage of sewage were also recommended. The fact that the sewer overflows seems to confirm these conclusions. 

SEPA admits to permitting Scottish Water to allow the Interceptor Sewer to overflow into the River Gryffe at times of excessive rainfall, but on the understanding that there will be minimum impact.  We understand that this permission is officially termed emergency overflow consent, not combined sewer overflow consent. We are told that there is a great difference.  There is concern that SEPA apparently ignore the fact the Consent to Discharge they have granted at the emergency overflow at Auchans pumping station only permits Scottish Water to discharge to the river at times of "emergency". ie only during power or mechanical failures. Neither have they explained why they have never insisted on emergency storage at the pumping station for these emergency purposes. We assume that SEPA are relying on any sewage which overflows being highly diluted and flushed away by the force of the river in spate.  They did not anticipate overflow being allowed to flood onto open space and contaminate it.  They certainly don’t admit to knowing about it.   

We understand that work has started at Auchans and that there is no additional storage of sewage proposed. Therefore it seems reasonable to conclude that these works will have no effect whatsoever on the disturbing problems being experienced in Houston and that the public would have good grounds to regard them as a red-herring when used as palliative comment by the authorities. 

Members of the public attended a public display in late 1999 to explain proposed River Protection works.  It was put on by the Roads Authority at the River Inn in Crosslees.  From that there seems to be an impression that SEPA would not permit any sewer overflow to the Gryffe downstream of Bridge of Weir.  Was the intention at that time that Scottish Water would work with the Roads Authority (now Renfrewshire Council) in protecting properties at Crosslee Park?  

We understand that Scottish Water's Flood Register has properties in Broomfield, Houston listed as suffering from internal sewer flooding.  Surely, this in itself was sufficient to get something done? 

We are told that SEPA instigated proceedings against West of Scotland Water after a “fish kill” on Locher Burn at 2:00pm, on 6 June 2000.  Allegedly the incident was caused by a contractor employed by the water authority allowing tannery effluent to spill into burn.   SEPA should have records of the fish kill which allegedly affected 8km of burn and River Gryffe, but was not reported to them until the 5 July 2000.  The incident was evidently featured in the  Paisley Daily Express on the 12 July 2000.  There are claims that other incidents have taken place which have been witnessed by SEPA.   

Contrary to what appears to have been Bullen and Partners recommendations, Scottish Water has not carried out any major works to increase the capacity of the Part 3 assets. What they have done is put a lining into most of the main sewer (the Interceptor Sewer).  No doubt this has been done because the system was in such a poor state that either ground water was infiltrating into the sewer or effluent was leaking out.  A lining will reduce the internal diameter of the sewer and thereby reduce its capacity.  On the other hand if it is thought that ground water is infiltrating the system, by stopping it, the systems capacity to carry effluent will increase.  The lining also stops leaking out of the system which will have the effect of decreasing the systems capacity.   C

ritically, the last length of sewer before the Auchans Pumping Station has not been lined.  This length of sewer has no connections into it and is therefore the determining length as far as capacity is concerned.  HALL has been informed that it is this length that is the major cause of the problem.  It lies in the flood plain and allegedly Scottish Water has no knowledge of the rate of infiltration that takes place into this water logged section of sewer.  It is said that even in dry weather the system copes with 3 times its designed loading. 

Overflow storage at Auchans is said to be woefully inadequate and that even if the capacity was increased at this point in the system, by increasing pipe and pump sizes, the pumping main which carries the effluent to Linwood also is too small.  It appears that the Linwood Treatment Works, a Part 4 asset, is to close and that the effluent then will be pumped from Linwood to the Erskine Waste Treatment works at Inchinnan.  It is not known if or why this will make any difference to the deficiencies of the system in Gryffe Valley. If all of this is true then Scottish Water apparently knows more about the problem than they have admitted.  Their representative says their investigations “may highlight that there is a hydraulic incapacity within the sewer system”. Is it official speak for “we think the system is too small, but we don’t know by how much”?  Given this and what we report above, it seems to HALL that it is credible when members tell us that employees of Scottish Water say that the Gryffe Valley should be a “Constrained Area”.   

What Scottish Water and SEPA say. 

In letters to HALL and its members: S

cottish Water says that they have “highlighted problems with the waste water network which will require further investigation”.  . 

SEPA has said “proposals to up-grade the main sewage pumping station at Auchans (about 2km downstream of Houston) will help to relieve pressure on the Houston section of the Trunk main, if ‘backing up’ in the main is part of the problem. 

Scottish Water has also said their investigations “may highlight that there is a hydraulic incapacity within the sewer system”. 

What can Scottish water do? 

We can sympathise with them in this.  Do they play safe and build in a large factor of safety at great cost, or do they try and get it just right? At the end of the day the public pays. 

What can Scottish Water do?  The solution to upgrading the mains sewer will not emerge quickly – but they must take steps to eliminate risks to public health.  They have a duty to do so.  Where the mains sewers overflow they should be able to build controlled overflow arrangements that will screen out solids and channel liquid effluent into the river.  These overflows could be in enclosed concrete structures, suitably camouflaged to blend in with their surroundings.  The outlet pipes could be trained into the centre of the river and below the surface to ensure that the effluent receives maximum aeration, breaking up the harmful contaminants.   The cost of such measures would be likely to be measured in the low £millions and could be designed and built before next winter.   

SEPA have suggested that proposals to replace pumps and construct a macerator (solids mincer) at Auchans PS in Spring 2008 will cure the overflow problems.  But, is there any evidence that it will?  It seems strange to us that works of such a minor nature haven’t been carried out before if they are the solution to the overflow problem. 

All works to Part 3 and 4 assets will be funded by Scottish Water and ultimately the public at large through water charges. 

The Planning Context 

How does this affect new development like the proposal to develop houses on the Manse Field site? Planning Advice Note (“PAN”) 79, Water & Drainage, outlines the rules to be followed when considering a planning application.  Sections 10 and 11 state that sites identified as appropriate for development can sometimes be constrained by a lack of water and waste water infrastructure or capacity, or be deemed to be constrained by service deficiencies which require to be overcome before new development can be accommodated. Constraints can include: 

• insufficient capacity in the strategic assets e.g. water treatment works or waste water treatment works;
• communities at risk of, or existing properties having experience of,sewer flooding;
• communities at risk of, or existing properties experiencing, poor pressure;
• watercourses at risk of detrimental impact from waste water discharges; and
• communities at risk of supply interruption below a minimum desired service level.

 Whilst the optimum use of existing capacity is an important consideration, there is a need for the provision of expanded water supply and drainage networks to be responsive to demographic changes and new demands. Development planning has an important role to play in influencing and addressing these requirements. 

If a proposed development is considered acceptable in a location where the current water or drainage infrastructure would be insufficient, stakeholders should work together to identify the best practicable option to accommodate the development.  

The above requirements presuppose that the proposed new development has been identified during development plan process and that rectification of the deficiencies which are deemed to be constraints will have taken place before the new development takes place.  In the case of any new development in Houston it would be necessary on this basis to eliminate the risk of sewer flooding and detrimental discharge to watercourses and the resultant risk to public health. In respect of Houston, the stakeholders, at the time of drawing up the development plan (Local Plan) had no need to work together to find the best practicable solution because the development plan does not envisage new residential development in Houston beyond March 2006. 

Inter alia the provisions of Sections 26-28 of PAN 79, the intention of planning guidance is that development plans will provide clarity and certainty about the way communities will change and evolve over the longer term.  It is imperative that issues relating to water and drainage should not be viewed in isolation but considered in relation to the plan's objectives. 

Scottish Water is mandated to advise planning authorities, to the best of its knowledge, on the current and programmed capability to accommodate development.  SEPA are mandated to provide the planning authority with advice on the requirements of environmental legislation, the content of drainage policies and on strategic environmental issues, such as areas vulnerable to cumulative impact from waste water discharges.   

Planning authorities, Scottish Water and SEPA are not expected to wait until the formal consultation stages of the development plan preparation process to discuss water and drainage issues.  Working together is important throughout the process to ensure that, as they are prepared, development plans reflect an up-to-date and accurate picture of drainage capacity and are informed by a shared understanding of how new development can be accommodated.  An awareness of such things as available capacity, demographic changes, economic objectives, regulatory controls and a practical and efficient investment programme will assist in making informed choices.  The plan should evolve with all parties satisfied that the development strategy is achievable within the desired time period through the removal of any constraints.

SEPA can decide where there are definite plans to address a constraint to the sewer system to permit new development being provided with an interim, temporary measure until such time as the upgrade works are completed.  Such measures can include individual/private systems even in settlements of over 2,000 people where they would not be permitted.  The developer would have to make a pro-rata contribution to enable work to start to remove the constraint.

In accordance with Sections 42 – 45, the planning authority should be satisfied that an applicant’s proposals would not have an adverse impact on water quality, public health or the environment. Neither should proposals impede the development of a sustainable drainage network. Where the applicant has stated their intention to connect to Scottish Water's network, and Scottish Water has not made an objection, there should be no barrier to granting planning permission in relation to water or waste water infrastructure. Where applicable, the applicant should be advised of the requirement to seek consent from Scottish Water to connect to its network and comply with the environmental regulations stipulated by SEPA.

The granting of planning permission does not secure connection to public water and waste water infrastructure. It is the responsibility of the developer to liaise with Scottish Water directly to ensure the necessary consent to connect to its network is secured.  Scottish Water generally operates on the basis of consent to connect being granted following their design approval of a proposal, which already has obtained planning permission. Where there is spare capacity, it will allow a developer to connect. However, it is possible that between the time an earlier assessment of capacity is made and the time when the developer is ready to connect, Scottish Water will have granted consent for another developer to connect to its network. There is, therefore, no guarantee that capacity identified will remain. Scottish Water will, however, manage the ongoing provision of capacity based on the emerging demand for connections as agreed with developers. This will rely on robust development programmes and effective early engagement.

Should there be any infrastructure upgrades required to support new development, Scottish Water will meet part of the costs, but only up to a limit based on the future income that the new connection will bring.

Inter alia Section 46, where a development proposal is not anticipated in the development plan and would be likely to take up drainage capacity required for other sites allocated in the development plan, the planning authority should give careful consideration to the implications for the delivery of the development plan strategy.  The planning authority may wish to seek the advice of Scottish Water should this situation arise.

How the planning context affects Planning Application 071084/PP 

What HALL believes is that there is no certainty to what extent the Part 2 assets, the local sewers connecting to the main sewers, are overloaded at times of high rainfall.  On the basis of probability it must be assumed that when properties flood they do so because the system is constrained and that by adding between 35 and 45 new properties into a local system which is relatively small will exacerbate the problems caused by the constraint.   

Whilst the development at Manse Crescent might be connected to a separated foul sewer it would be connected to a combined mains sewer and must suffer from backing‑up until the main sewer overflows.  In accordance with the natural laws of hydraulics the local sewers will “back up” to the level of the overflow.  This would certainly lead one to conclude that this could be a constraint on new development.  

The applicant has proposed that surface water would be collected in an open SuDS pond.  It isn’t clear whether they expect that it would dissipate naturally or whether they intend that it would be released into the sewer system at times of low rainfall.  The Council requires such a system to be contained in an underground tanking system, which would have to release water into the sewer system.  In the circumstances neither option appears to HALL to be desirable.  The risk of the system failing is that it would cause additional flooding of the properties in Manse Crescent and in the Crosslees area.  It is difficult to see how any underground tanked surface water storage system, which would be in most part below the ground water table, could be built in a way which would eliminate this risk.  The lack of a SuDS system for groundwater and rainwater which would not present a risk of flooding is another constraint on this site. 

Scottish Water says that they have “highlighted problems with the waste water network which will require further investigation”.  . 

SEPA has said “proposals to up-grade the main sewage pumping station at Auchans (about 2km downstream of Houston) will help to relieve pressure on the Houston section of the Trunk main, if ‘backing up’ in the main is part of the problem. 

Scottish Water has also said their investigations “may highlight that there is a hydraulic incapacity within the sewer system”. 

Neither SEPA nor Scottish Water offer any explanation what causes the constraint or how it can be solved.  As this area is not recognised as a constrained area the developer cannot be permitted to make use of an interim solution.  Therefore the connection of any new development into the existing sewer system has to be part of or come after completion of the works which will remove the constraints in all not in part (as the Auchans PS work may only achieve).

Section 46 supports HALL’s assertion that it would for a mistake for the planning authority to grant planning approval assuming consent afterwards from Scottish Water and agreement from SEPA.  This proposed development is simply not part of the development plan because its potential existence has never been part of the discussions between the planning authority and Scottish Water when they considered the development plan's objectives.   In drainage capacity terms the proposal does not exist – it cannot be incorporated into the development plan until Scottish Water can be satisfied that the sewer system will cope.  In these circumstances Section 46 clearly supposes in these circumstances that the planning authority will seek Scottish Water’s advice on the impact on development plan strategy– not the same as consulting on an application which accords with the development plan.

SEPA also have a part to play in so far as they are bound to ensure that developments do not compromise environmental quality or fragment the public sewerage system.  They also have a mandate to engage with the planning authority and Scottish Water to review development constraints and available environmental capacity.  We are told that SEPA haven’t yet made up their mind not to object to this application.

A conditional consent would require acceptance that it was either in accordance with the development plan or that the development plan had been revised.  The planning authority can only revise a development plan by them consulting with interested parties – they cannot delegate that responsibility.

Even if the application did conform to the development plan it would not be possible for Scottish Water to assess the developer’s contribution if the cost of any upgrade works is unknown.  Also, they could not give consent to connect to the drainage system because they could not approve the developer’s design.

HALL’s recommendations

·         No new development which will connect to the Gryffe Valley Interceptor Sewer until such time that the planning authority and Scottish Water, in consultation with SEPA and the public agree a strategic plan which will be the basis of future development plans.

·         Scottish Water to instigate a short term programme of constructing overflow equipment which removes solids and aerates liquid effluent which is channelled directly into water courses capable of sustaining overflow during periods of heavy rainfall.

·         SEPA and HSE prosecute Scottish Water each and every time overflow causes a public health risk, causes damage or flooding to property or pollutes a water body.

·         Renfrewshire Council takes steps to protect the public from harm by erecting fences and cleaning up contaminated ground which is open to the public.

·         SEPA and HSE take enforcement measures against Renfrewshire Council if it does not take measures to protect the public.

·         A Gryffe Valley Liaison Committee which will monitor action and progress by the authorities.  The committee should include representatives of the public other than the Local Community Councils.

Houston Amenity Land Limited - 1 March 2008