AI’s Hillhead surface water management plan – more dodgy assumptions?

Flooding can have a devastating impact on communities. Not only can it cause damage to property and possessions, it can cause injury and death. The Met Office says we should expect an increasing frequency of extreme rain: 

…research, published in Nature Communications, found that under a high emissions scenario (RCP 8.5) rainfall events in the UK exceeding 20mm/hr could be four times as frequent by 2080 compared to the 1980s.

Managing flood risk is therefore an important business. Council’s trust consultants to get the figures right. 

Last month, Aggregate Industries submitted further information to Devon County Council in relation to its planning application DCC/4399/2024 for Hillhead Quarry near Uffculme, which is in part to deal with the quarry’s ponding problems.

 

In its revised surface water management plan for the site – where "all surface water will be managed in the former extraction area, with Houndaller Pond only acting as an exceedance route" – Aggregate Industries’ water consultants BCL Hydro – the same crew working on Straitgate – made a big assumption: 

The fact that [Houndaller Plantation] pond can sustain long-term and regular abstraction… means that it would be similarly effective as a soakaway.

We questioned this claim in the post AI sense-checks AI... and its soakaway assumptions at Hillhead, and wrote to Devon County Council saying: 

There remains, therefore, no cogent evidence – measurements or otherwise – of the soakaway capacity at Houndaller Plantation Pond. It is wrong to assume that Houndaller Pond would be “similarly effective as a soakaway”, and therefore it does not necessarily ‘follow’ that Houndaller Pond could cope with exceedance flows from a storm event.

But there appeared to be other wild assumptions put forward by Aggregate Industries’ water consultants too. As we set out to Devon County Council:

... it appears that the applicant’s revised plans have not allowed sufficient storage space within the extraction area for the design storm event: 

The applicant claims “the ASV [Attenuation Storage Volume] requirement equates to 3,350 m3 during the design event (1 in 100-yr + 45% allowance for storm intensity due to climate change)” and that “the revised surface water management plan for Houndaller (by incorporating 3,416.60 m3 within the former extraction area) will provide sufficient storage space for the design event.” 

The applicant claims runoff rates and attenuation requirements were computed using “the assumption that 12.75 hectares [127,500m2] of the catchment area would possess runoff characteristics analogous to that of an impermeable paved surface.” The applicant has not provided any output from those computations to substantiate the conclusions. 

An ASV of 3,350m3 divided by the impermeable catchment area of 127,500m2, implies the applicant has modelled for a rainfall event of 0.0263m or 26.3mm. 

This would seem to be an inadequate figure, given the historic records for nearby areas: 

“June 1946 In Cullompton, 2.35 in [60 mm] of rain fell in 45 minutes and ... in the lower part of the town flooding was 3 ft deep in houses.”

“22 October 1960 Flooding occurred in Crediton, following a total of 64 mm of rain on 20 and 21 October (recorded in Exeter)” 

“21 November 2012 Between 20mm to 39mm (0.8in to 1.5in) fell in 12 hours overnight on already saturated ground.” 

https://www.middevon.gov.uk/media/345917/appendix-j-historic-records-of-flooding.pdf 

The University of Exeter Weather Observation Records has the Highest Daily Rainfall at 47.20 mm on 4 September 2024.

https://empslocal.ex.ac.uk/uoeweather/records/ 

The UK’s wettest day, in records back to 1891, was 3 October 2020. The average rainfall across the entire UK was calculated at 31.7mm. The Met Office says record-breaking rainfall like that seen on 3 October 2020 could be 10 times more likely by 2100.

https://www.metoffice.gov.uk/about-us/news-and-media/media-centre/weather-and-climate-news/2021/record- breaking-rainfall-more-likely-due-to-climate-change 

Using the FEH22 rainfall depth-duration-frequency model for that area, 26.3mm is less than a 1-hour, 30-year event; by contrast, a 12-hour, 100-year event would exceed 90mm.

https://www.ceh.ac.uk/sites/default/files/2023-05/FEH22_rainfall_depth-duration_frequency_%28DDF%29_model.pdf 

A 90mm rainfall event, with the same impermeable catchment area of 127,500m2, would require a much larger storage capacity of 11,475m3...

When it came to Straitgate Farm, consultants Amec Foster Wheeler, writing Aggregate Industries’ Flood Risk Assessment, modelled for a lesser 1 in 100-yr storm event + 10% climate change, and reckoned that across the 25.61ha (256,100m2) site, a total volume of 19,054m3 was required to attenuate runoff. Dividing the latter by the former implies a 74.4mm rain event was modelled for, or 67.6mm excluding the 10% climate change uplift. Assuming Hillhead, 23 miles away, is prone to the same level of storms as Straitgate, then adding back a +45% climate change allowance, means that the surface water management plan for Hillhead needs to accommodate runoff from a 98mm storm event – or in old money, nearly 4 inches of rain. 

So why BCL Hydro has only modelled for a not-uncommon 1-inch rain event is anybody’s guess. 

Given that there are now a series of questionable conclusions from BCL Hydro – here, here and here – local people would be forgiven for having little faith in whatever surface water management plan eventually emerges for Straitgate Farm.

EDIT 17.1.25 Devon County Council issues Planning Permission for DCC/4399/2024 with conditions 

Officer Delegated Report

AI’s ponding problem at Hillhead – enough water to fill 15 Olympic pools!

Any quarry Aggregate Industries ends up digging at Straitgate Farm must not introduce water bodies, because of aircraft safeguarding considerations at Exeter Airport: 

25. No water body shall be created within the site other than the approved weigh bridge lagoon.    

But Aggregate industries is not very good at controlling surface water. 

If it were, it would not be suffering a "surface water ponding issue" at its Hillhead Quarry near Uffculme. We’ve already posted about this – here, here, here and here. 

Aggregate Industries has recently lodged a planning application with Devon County Council for Hillhead Quarry near Uffculme – DCC/4399/2024:

Variation of conditions 2, 4, 6, 7, 12, 19, 22 and 25 of ROMP permission DCC/3655/2014... to vary the phasing; landform; drainage; and restoration of the site.

The Planning Statement for the application reads:  

3.4.1 Houndaller Extension Area is currently facing surface water ponding issues in Phase 6 which is preventing completion of restoration of this section of the quarry. It is considered that a similar situation will occur once extraction operations cease in Phase 7. During 2023 and to date in 2024, in excess of 1m dept [sic] of water has collected over much of the Phase 6 area. The consented final restoration landform does not allow for effective drainage. Therefore, Aggregate Industries are proposing a long-term solution for surface water ponding issues on site.  

Just how wrong has Aggregate industries got things at Hillhead? 

There may be in excess of 1m depth of water, but how far does that water extend? Fortunately, Google Earth has recently provided new imagery for the area – and the answer is 9.27 acres or 3.75 ha, giving a volume of water in excess of 37,500 cubic metres, or enough to fill 15 Olympic-sized swimming pools. 

Where is all this water to go, now and in the future? According to the Hydrological & Hydrogeological Impact Assessment for the above application: 

5.8.8.1 ... ingress waters (rainfall runoff and groundwater seepage) will be captured by the perimeter drainage ditch and directed into Houndaller Plantation Pond, which will recharge the groundwater system in the BSP Aquifer. 

5.8.8.2 An infiltration rate of 50 m/d has been used in the calculations, which is the worst-case value for hydraulic conductivity derived from falling head tests (as used for calculating the worst-case ingress rates in the extraction area). 

5.8.8.3 The design storm would raise the water level (injection head) in the pond by 0.5 m.

5.8.8.4 The mean surface area (through which the outflow occurs in the recharge / soakaway feature) is taken to be the sides of the pond when accommodating 0.5 m change in water level. 

5.8.8.5 The unlined flanks of the pond have a total length of 400 m and have an effective depth of 0.5 m; therefore, the total surface area for infiltration would be 200 m2. 

5.8.8.6 Based on Darcy’s Law, applying an injection head of 0.5 m and an infiltration rate of 50 m/d, and with the mean surface area for infiltration set at 200 m2, the soakaway rate (recharging the BSP Aquifer) equates to 5,000 m3/d. 

5.8.8.7 This is equivalent to circa 150% of the storm ingress ASV indicated at section 5.8.7.14. Therefore, it is concluded that Houndaller Plantation Pond has sufficient soakaway capacity for the design storm. 

However, this calculation doesn’t look right: a soakaway rate of 5000 cubic metres of water per day through an infiltration area of just 200 square metres seems impossibly large.

What do we find? Firstly, the author of the report has not assumed "the worst-case value for hydraulic conductivity" they have in fact assumed the best: 

3.5.9.1 The hydraulic conductivity of the BSP has been determined from falling head tests undertaken in the area; and typically varies between 5.8x10-4 and 7.3x10-6 m/s, equivalent to 0.6-50 m/d. 

Secondly, the author has omitted the length of the flow path (l) from their calculations. Darcy’s Law relates the flow of groundwater through the saturated aquifer (Q) to the cross section of the aquifer (A) and the hydraulic gradient (h/l) and is written as Q = -kAh/l, where k is the hydraulic conductivity. 

Using the worst case of 0.6m/d for hydraulic conductivity (k), with 200m2 (A), 0.5m (h) and, for example, a 1000m flow path (l), the soakaway rate would fall from the incredible 5,000 m3/d to just 0.6 x 200 x 0.5/1000 = 0.06m3/day – almost 100,000 times less. 

Which means that it’s not at all clear that Houndaller Plantation Pond does have "sufficient soakaway capacity for the design storm." 

The Hydrological & Hydrogeological Impact Assessment for the above application was authored by the same team that will, either this month or next*, be trying to work out infiltration rates at Straitgate Farm. Hardly instills confidence does it?

EDIT 25.6.24 *Infiltration tests now postponed by Aggregate Industries until "end of July/early August". 

EDIT 12.7.24 Objection from Devon County Council Flood Risk Team

EDIT 2.8.24 Regulation 25 Request

Run-off problems at Venn Ottery. Would AI’s legacy at Straitgate be the same?

Aggregate Industries' surface water management plan for Straitgate Farm has yet to be approved. In 2016, we posted: 

Watercourses originating from Straitgate pass through four communities downstream; communities that are prone to flooding. Any quarrying at Straitgate Farm must not make the situation worse, either during work or afterwards. DCC has requested that any plans make the situation better. How this could be so, with the loss of millions of gallons of groundwater storage capacity in the unsaturated layer of sand and gravel on top of the hill above these communities, remains to be seen.

Pre-Commencement Condition 6 states: 

No development hereby permitted shall commence until a Construction and Environmental Management Plan... has been submitted to and approved in writing by the Mineral Planning Authority. The Plan shall include... (d) details of the management of surface water during the construction and soil stripping phases 

The plan is still up in the air because the company has yet to produce any reliable infiltration rates. Condition 13 states:

(b) Updated infiltration tests shall be carried out using an infiltrometer and shall be undertaken in strict accordance with BRE Digest 365 Soakaway Design (2016) and must be undertaken within the Budleigh Salterton Pebble Beds. A representative number of tests shall be conducted in order to provide adequate coverage of the site, with particular focus placed on the locations and depths of potential infiltration devices; 

The results of these tests will inform the size of attenuation ponds required to stop downslope flooding, remembering Condition 25 which states:

No water body shall be created within the site other than the approved weigh bridge lagoon.  

Why is it important to get these infiltration tests right? Look at the problems at Venn Ottery, with fingers being pointed towards Aggregate Industries' worked-out sand and gravel quarry, uphill and nearby. 

More than a million tonnes of material were removed between 2011 and 2016, material that would have previously acted as a 'sponge' for rainfall above a downstream community. 

We’ve posted about surface water run-off problems from this site before. 

Back in 2015, Devon County Council admitted in correspondence that flooding in Venn Ottery was "to do with the quarrying activities". Newton Poppleford and Harpford Parish Council minutes also reported: 

Cllr Cole reported that the Quarry Manager was taking further remedial action to create a better settlement ponding system and other works to alleviate the problem of the Neighboring fields being washed out. A new pipe was to be placed under Green Lane where it had washed out. 

In 2016, Devon County Council's monitoring report for the quarry reported: 

Significant amount of run off was present in the waterbodies at the time of the visit.

In the same year, local people – in response to the company's planning application to restore the quarry to a higher level than was previously approved following "an error with the previous estimated amount" – reported "ongoing issues with surface water run-off from the quarry". The Council responded, saying: 

6.22 It is accepted that there have been a few occasions when surface water has discharged from the site, but in these instances the operator has acted quickly to remedy the situation and it is considered that the final restoration of the site (which includes water storage features) will adequately deal with any surface water issues.

Clearly, it hasn't, and the problem has become worse.

 

Last year, Venn Ottery "experienced its worst flooding event", according to the Venn Ottery & Southerton Residents Association. A Devon County Council report says nine properties were flooded internally. VOSRA claims: 

The increased run-off from the (now closed) Venn Ottery Quarry brought a river of water along the track from the Otterdene area to Venn Ottery green, where it crossed along 2 routes to join the stream that runs alongside the green and through the back gardens of 1-5 Barton Mews.

VOSRA compiled an extensive dossier of previous flooding events – including the map below – which was sent to East Devon District Council, Devon County Council, the Environment Agency, and the local MP. The dossier claims: 

From about 2012 onwards residents in the houses on west side of Venn Ottery green have noticed an increase in the volume of water running along the unmetalled road and across the green. Within a couple of years of starting quarrying in 2010, water from the quarry site caused the track that runs westeast from the Otterdene (Happy Valley) area towards Venn Ottery to become impassable, and the field nearby to (behind Dartwood, Brookdell) to be waterlogged. Similarly, ’Puddle Lane’ became even more muddy. When requested by the local community, Aggregate Industries provided quantities of pebbles to improve the drainage and raise the level of the track to some extent. 

The quarrying ceased and in 2017-18 the land was ‘restored’. An area on the northeast was formed into an attenuation lake to hold back excess water run-off. The lake is not very large so cannot always retain all the water, which then runs downhill and into VO. 

VOSRA is calling for action: 

The attenuation pond at the eastern corner of the closed quarry site is undersized and has no controls on overflow. Extension of the pond and the installation of a sluice to control the outflow could greatly reduce the speed at which water flows. 

How did this attenuation pond come to be so undersized, when such important details should have been scrutinised by Aggregate Industries’ expert consultants, as well as the relevant statutory bodies?

Could it be that infiltration rates in this material – the Budleigh Salterton Pebble Beds, the same material as at Straitgate – were assumed to be higher than in reality? At Straitgate, Aggregate Industries assumed inflated infiltration rates of 1m/d to size attenuation features, ignoring results of soakaway tests, which showed "Insufficient drop in water level".

The problems at Venn Ottery, however, don’t stop at downslope flooding. 

A bridleway was provided by Aggregate Industries on the eastern side of the site as a condition of the S106 agreement associated with processing the material at Blackhill, to "provide a safe alternative for part of the HGV route". 

Last month, part of the bridleway was washed away. Water running off the site has left a deep, unsafe canyon, and the bridleway has been closed.

Once upon a time, in answer to critics of the Venn Ottery plans, Aggregate Industries claimed:

We shall be putting back a lot more than we're taking away.

Locals, bailing water out from their houses, having their PROW swept away, might not be so sure.

Hedgerows

🌳 💦Hedgerows planted on steep contours & high densities can reduce runoff rates up to 50%, preventing flooding &improving the water quality of our rivers & streams. This is by improving hydrological soil processes: increasing percolation, filtration & evapotranspiration 🌳 💦 pic.twitter.com/85J6DZIO9g

— Hedgelink (@Hedgelink_UK) March 4, 2024

Groundwater levels continue to rise at Straitgate

This week, the groundwater level at PZ2017/02 – a borehole that sits on the eastern boundary of the proposed extraction area – was 30cm higher than reported here last week.

It now sits just 0.90m below ground level – a new maximum. 

As previously posted, the sand and gravel that Aggregate Industries wants at Straitgate Farm starts on average 2.3m below ground level. 

The company’s permission only permits quarrying above the maximum water table. 

Another borehole showing ZERO depth of available resource

The sand and gravel that Aggregate Industries wants at Straitgate Farm starts on average 2.3m below ground level.

The company’s permission only permits quarrying above the maximum water table. 

Clearly, therefore, in areas where the maximum groundwater level is closer than 2.3m below the ground surface, there is likely to be no sand and gravel available for the company to recover. 

In practice, to make it at all worthwhile – bearing in mind the costs, ecologically or otherwise, involved in stripping, storing, restoring more than 2.3m of 'best and most versatile' topsoil, subsoils and overburden – the maximum groundwater would need to be no nearer than 3.3m below ground level to be able to extract even 1 metre’s worth of sand and gravel. 

Earlier this month we posted how the water level at borehole PZ2017/03 has risen to ground level, and how Aggregate Industries has been pulling the wool over everybody’s eyes – planning inspectors included. 

Obviously, there is no resource available to the company for an indeterminate area around this borehole on the eastern boundary of the extraction area. It's now the same for the area around another borehole. 

Last week, the groundwater level at borehole PZ2017/02 was just 1.19m below ground level. This is again on the eastern boundary - as shown below:

   

This groundwater level is higher, by our estimation, than the borehole’s previously recorded maximum on 18/02/2020. It is notable that levels in this location have only been monitored between 2017 and 2022, and not, like a number of the other locations, during the wet winter of 2013-2014. 

It’s not altogether surprising that the previous maximum has been exceeded, given the recent rainfall:

Last February was one of the driest on record for England & Wales with many locations seeing less than 10% of normal rain.

This February will be one of the wettest, many places will record more than 200%.

Extremes driven by climate change and things will get more extreme. pic.twitter.com/3xPTqh8soj

— Dave Throup (@DaveThroup) February 18, 2024

This all ties in with what we said in 2021, when we posted Depth of available resource at Straitgate is in places ZERO. 

Borehole PZ2017/02 is where Aggregate Industries plans to locate infiltration trenches to stop downslope flooding. Clearly, with water levels this high, those trenches can't work as intended. Again, as we posted in 2021, Infiltration areas to stop flooding couldn't be 3m deep – without breaching MWWT and in 2018, AI’s infiltration plans can’t work either – with groundwater this close to the surface. 

Ordinarily, if Aggregate Industries were monitoring the site, another calculation of the extrapolated maximum winter water table, the MWWT, would now be triggered, the company’s permitted base of extraction would have to be moved upwards and the available tonnage moved downwards. 

For reasons we can all guess, the company is not currently monitoring groundwater levels across the site.

Water level at borehole PZ2017/03 rises to GROUND LEVEL

Following the post AI has been pulling the wool over everybody’s eyes – planning inspectors included, the water level in PZ2017/03 was last week found sitting at ground level. 

The water level has no doubt reached ground level in this location before – but is not something that has been disclosed by Aggregate Industries.

Remember, the sand and gravel that Aggregate Industries wants starts about 2.3m on average below this level. 

What are groundwater levels doing in other boreholes across the site? Have maximum levels been exceeded again, given all the recent rainfall? 

No one has any idea because Aggregate Industries is not monitoring them. 

This matters, because the maximum water table across the site – the MWWT, guesstimated using previously recorded levels from this borehole and others – will not only form the base of the permitted excavation, to protect the groundwater supplying nearby private water supplies, but will also determine how surface water is managed, to avoid flooding and maintain stream flows.

Last month, Aggregate Industries made clear that it only intended to monitor the boreholes across the excavation site once a month using manual dipping. 

Groundwater levels can rise quickly at Straitgate Farm. Borehole readings show that even from a low base they can reach maximum levels in just 4 weeks. Continuous data loggers, as Aggregate Industries and its consultants have used in the past, are therefore essential for capturing these movements. Clearly, the company doesn’t want to do any more than the barest minimum. It certainly doesn’t want to discover that the MWWT has been exceeded again.

AI has been pulling the wool over everybody’s eyes – planning inspectors included

Nowhere in the mountain of documentation – either for the planning application to quarry Straitgate Farm, or the subsequent 2-week public inquiry – did Aggregate Industries make known that groundwater on the east of the proposed extraction area – an area designated a soakaway for flood mitigation – can at times sit just 16 cm or less? below the surface. 

Fancy omitting such a crucial piece of information. 

Aggregate Industries has not monitored groundwater at Straitgate Farm since March 2022. A curious lack of inquisitiveness, you might think, given how wet the last few months have been. 

But Aggregate Industries doesn’t want to know about any elevated water levels that might reduce the amount of recoverable material. 

However, curiosity can get the better of some people. 

At borehole PZ2017/03 – shown on this map, on this hydrograph, and below – groundwater was found this week to be sitting just 16 cm below the ground surface. 

16 cm.

We have been warning about this issue on multiple occasions – including here, here, here, here, etc – but even we didn't realise just how close the groundwater actually sits below the ground surface*. 

Aggregate Industries’ consultants, on the other hand – who, in addition to relying on an automatic data logger, have been manually dipping this borehole quarterly since 2017 – would have known. They would have seen with their own eyes how close the water sat below the ground surface, but chose not to share the information more widely – not with Devon County Council, not with the Environment Agency, not with the Planning Inspectors at the Public Inquiry. 

Having been alerted to the elevated groundwater levels in this location, Devon County Council raised the issue with the company back in 2018, when PZ2017/03 recorded its maximum height of water of 138.68 mAOD on 27/04/2018. In a now superseded document, Aggregate Industries wrote:

Results from routine quarterly monitoring in April 2018 identified groundwater levels in localised piezometers on the eastern extraction area boundary higher than those depicted by the existing MWWT contour plot. Consequently, Devon County Council has determined this to be a material matter in that it has requested that the effects of these results be assessed to determine the effects on the quantity of mineral resource. Its position is defined in the following extract from an email dated 1st August 2018 (S Penaluna, Devon CC) as a: “......need to know exactly which areas might be excluded for reasons of groundwater protection and these would need to be indicated on a plan.” 

But the Council was misled, fobbed off, or lied to, when the company claimed: 

1. The extraction area, as shown on the Wood E&IS plan, remains unchanged... 

4. The change [in mineral resource], moreover, results in no area being “excluded for reasons of groundwater protection” but merely a localised effect on the depth of working in a localised (eastern) part of the site. 

What’s the big deal? Condition 28 of the permission allows the design of the base of the quarry to be changed to reflect revised estimations of the maximum water table: 

Prior to the commencement of any soil stripping on any phase of the development, a review of the Maximum Winter Water Table (MWWT) grid (being the hydrogeologically modelled surface of the maximum winter water table based on the highest recorded winter groundwater levels) shall be submitted to the Mineral Planning Authority for its approval in writing.

In Aggregate Industries' latest resource assessment for the site: 

The MWWT will ultimately form the base of the workable deposit, and any variation will impact the potential resource. 

But what’s most concerning is that borehole PZ2017/03 is in an area designated for flood mitigation, an area where it is intended to dig a trench, with a 1m buffer above the maximum groundwater level, to hold back surface water runoff and allow it to soak away.

   

Surface water will not soak away as designed with groundwater sitting just 16 cm below the surface. 

Why is it important to get the management of surface water right? You only have to look at the ponding problems at Aggregate Industries' Houndaller site for the answer.

There can therefore be no confidence that the planned trenches to stop downslope flooding will act as intended, and every confidence a water body will be created. 

As we have already posted, quarrying at Straitgate can only be permitted if: 

25. No water body shall be created within the site other than the approved weigh bridge lagoon.   

Without drilling another borehole further into the site, and implementing another period of monitoring, no one has any idea where the maximum groundwater levels are in the area surrounding PZ2017/03 – Aggregate Industries’ MWWT is at best a guesstimate. 

What should be done? 

In 1967 they knew exactly what to do – they left this area alone. Aggregate Industries should be forced to do the same.

*The exact depth to water from the ground surface could not previously be calculated using piezometer groundwater level data in mAOD, because a precise surface elevation figure for the borehole had not been supplied by Aggregate Industries.

AI introduces new ‘MWWT +1m criteria’ to comfort LLFA

It would appear that Aggregate Industries has given up 1 metre of resource in its plans to quarry Straitgate Farm – according to emails sent by the company to persuade Devon County Council's Flood Risk Management Team in its capacity as Lead Local Flood Authority to withdraw its objection. 

Last month we posted DCC’s Flood Risk Team withdraws objection – WITHOUT sight of ‘a plan indicating how exceedance flows will be safely managed’, WITHOUT knowing whether a drainage scheme is even ‘feasible’. 

Following an FOI request, and the release of a number of redacted emails, we can now see the reasons behind the LLFA's volte-face.  

On 19 July 2021, Aggregate Industries told the LLFA: 

The objection you have received shows a fundamental misunderstanding of our scheme, one of the reasons why we are monitoring the MWWT is to inform the depth of extraction so that a minimum of 1m unsaturated zone is maintained over the MWWT.

  

On 28 July, the LLFA confirmed their understanding: 

My query is that if the MWWT keeps getting higher (closer to the ground) will there be enough depth (the report says 1.45 m) to accommodate the required volume for infiltration? Bearing in mind no excavation within 1 m of the MWWT and the fact that in some places the BSPB is as thin as 3 m (although I’m not sure where these places are).

  

On 18 August, Aggregate Industries told the LLFA: 

Regarding depth of void excavation for runoff storage above unworked material to protect MWWT:… Effectively, the eastern downslope edge of the extraction void for phases 1 and 2 will be shifted upslope, on account of the MWWT +1m criteria limiting the ability to extract from the downslope-most edge of these phases.” 

One hour later, the LLFA wrote: 

I am happy with the response. Essentially they are shifting the void upslope to account for the MWWT and 1 m stand off to ensure there is sufficient depth/capacity for the runoff which is reassuring.

With reference to the "void", on 30 June Aggregate Industries explained: 

The void created by mineral extraction acts as the infiltration basin so there is not a single cross section as this will change as extraction progresses... 

   

On 7 September, the LLFA withdrew its objection. 

Of course, "a minimum of 1m unsaturated zone... maintained over the MWWT" is brilliant news; we have been campaigning for material to be left unquarried above the maximum water table for years. 

Given that the Updated Resource Assessment claims: 

The MWWT will ultimately form the base of the workable deposit, and any variation will impact the potential resource.

we have suggested that Devon County Council ask for the resource to be recalculated taking the new "MWWT +1m criteria" into account. 

Or is all this just another big misunderstanding?

Has Aggregate Industries misunderstood its own scheme again?

Has Aggregate Industries – either intentionally or unintentionally – misled the LLFA officer?

WHPC voice flooding concerns

AI’s proposal would PERMANENTLY alter the landscape – so why has the flood risk assessment only assumed a 10-12 year lifespan and 10% climate change uplift?

Aggregate Industries’ Flood Risk Assessment says: 

The development lifespan will be 10 to 12 years, so it is proposed that an allowance for a 10% increase in extreme rainfall is considered, according to NPPF guidance on climate change which states that an allowance of 10% is made for development with a lifetime extending to 2039 respectively;  

The change to the landform would not, however, be for just 10 to 12 years – it would be FOREVER. 

In our response in 2017, we wrote: 

114. The applicant has used an uplift of +10% in its runoff calculations to reflect climate change. However, since this proposal would result in a permanent change upon the landscape this uplift is inadequate. The EA forecasts peak rainfall intensity increasing by 20% in 2055-2085 and 30% in 2085-2115. 

We pointed to the LLFA’s response to Aggregate Industries’ ROMP application for Hillhead, which said: 

Following the publication of the Flood Risk Assessments: Climate Change Allowances document (dated 19th February 2016) by central government, the applicant will be required to use a climate change uplift value of 40% when sizing the proposed surface water drainage management system for this development.

40%, not 10%. 

In May this year, Devon County Council's Flood Risk Team, in its role as Lead Local Flood Authority, objected to Aggregate Industries' proposal, but was comfortable with what it understood to be the allowance for climate change: 

In terms of the concerns relating to climate change, the applicant has proposed a surface water management strategy which includes an allowance of 40% for climate change in terms of rainfall within the attenuation calculations. This is inline with the most up to date guidance from the Environment Agency: Flood Risk Assessments - Climate Change Allowances (July 2020).

Which would be brilliant – if 40% were true. The LLFA had either misread, or not read, Aggregate Industries' FRA. We wrote to the LLFA pointing out the discrepancy in their understanding.

Nevertheless, the LLFA has since withdrawn its objection, obviously still comfortable with the uplift for climate change even though it is only 10%. The statutory consultee pointed to the access road and holding area, and to national policy:  

The applicant has provided calculations to indicate that the proposed surface water drainage system for the access road and holding area has been designed to manage the 1 in 100 year event plus climate change which is in line with local and national policy.

Indeed, the access road and holding area may have a more limited lifetime, for which drainage calculations may be in line with national policy, but what about the 56 or more acres that would be permanently changed?

National policy considers the lifetime of development in terms of flood risk, and says: 

The lifetime of a non-residential development depends on the characteristics of that development. Planners should use their experience within their locality to assess how long they anticipate the development being present for. Developers would be expected to justify why they have adopted a given lifetime for the development, for example, when they are preparing a site-specific flood risk assessment. The impact of climate change needs to be taken into account in a realistic way and developers, the local planning authority and Environment Agency should discuss and agree what allowances are acceptable. Paragraph: 026 Reference ID: 7-026-20140306 

National policy also says: 

Indeed, for Aggregate Industries' proposal to construct an asphalt plant at Hillhead, the LLFA specified: 

MicroDrainage model outputs will be required to demonstrate that the proposed surface water drainage system is designed to the 1 in 100 year (+40% allowance for climate change) rainfall event. 

So why – when a 40% uplift was required at Hillhead for both the quarry and the asphalt plant, and when flooding has been acknowledged as such an important issue for communities downstream of Straitgate Farm – did the LLFA in all its flooding wisdom think that a 10% allowance for climate change would be acceptable, for a development that would not only leave a PERMANENT scar on the landscape, but would also PERMANENTLY change the way surface water runs off the site?

Has the LLFA not seen the news this year, the death and destruction that can happen when 150 mm of rain falls in 24 hours?

Events that were once in 100 years are becoming commonplace. Freak weather is increasingly normal.

Has DCC forgotten its Scoping Opinion?

In 2015, Devon County Council issued a Scoping Opinion: PRE/0953/2015 Proposed extraction of Sand and Gravel at Straitgate Farm, Ottery St Mary. We posted about it at the time.

Devon County Council said the Scoping Opinion was:

...a formal opinion as to the information that the applicant will need to include in the Environmental Statement to accompany the planning application for the proposal described above PRE/0953/2015. 

Given the LLFA's recent response, let’s remind ourselves what the Scoping Opinion said on flood risk:

 

In brief, emphasis added, the Scoping Opinion told Aggregate Industries that "as a minimum" it should – amongst other things – demonstrate that "it will be feasible to balance surface-water runoff to the greenfield rate for all events up to the 1 in 100 year storm plus an allowance of 30% for climate change"; that "Where SuDS are proposed, it must be demonstrated that they are feasible..."; that a site plan should show "exceedance flow paths". 

Pretty normal stuff. But obviously not for Aggregate Industries, who has so far been unable to show that its surface water management plans are feasible. 

Despite that, the LLFA has withdrawn its previous objection, on the basis that a pre-commencement planning condition is imposed: 

The conditions should be pre-commencement since it is essential that the proposed surface water drainage system is shown to be feasible... 

Amazingly, the proposed condition – to be resolved after determination, when 6 years have not been enough to resolve matters before determination – shows that the LLFA has not even seen "a plan indicating how exceedance flows will be safely managed at the site." Clearly, without such a plan – and a raft of other information too – Aggregate Industries has NOT demonstrated either feasibility or the safe management of flood risk. 

Has Devon County Council forgotten its Scoping Opinion, and its request that there should be "proper consideration of all of the likely effects of the project"? 

Has Devon County Council forgotten Regulation 18(4)(b) of The Town and Country Planning (Environmental Impact Assessment) Regulations 2017 that says "An environmental statement must... include the information reasonably required for reaching a reasoned conclusion on the significant effects of the development on the environment..."?

EIA, planning conditions, and the law

When the planning application to quarry Straitgate Farm is determined, it will be accompanied by a raft of proposed conditions – conditions that, in the case of flood risk, would attempt to sort out after determination what Aggregate Industries and Devon County Council have failed to resolve over the past 6 years before determination, conditions that would negate any further public scrutiny.

As previously posted, the Council's Flood Risk Team, in its role as Lead Local Flood Authority, has withdrawn its objection to Aggregate Industries’ proposal on the proviso that a pre-commencement planning condition (sometimes referred to as a 'Grampian' condition) is imposed – a condition that would amongst other things include procuring a design for how surface water would be managed on the restored site i.e. in perpetuity. 

It is unclear whether the LLFA fully understands what is proposed. 

What is clear is that the LLFA does not know whether a scheme to control flooding – whilst maintaining stream flows, whilst maintaining groundwater recharge for drinking water supplies, whilst avoiding the creation of permanent bodies of water and an airport safeguarding hazard – would even be feasible: 

The conditions should be pre-commencement since it is essential that the proposed surface water drainage system is shown to be feasible

Nevertheless, the LLFA has clearly decided that it wants no further public involvement in the matter, and that the significant, thorny and as yet unresolvable issue of flood risk management should be sorted out behind closed doors at some future date. 

However, reliance by the Local Planning Authority on the LLFA’s recommendation would not only be reckless, considering the number of problems local people have already highlighted, but according to legal advice would also be unlawful. 

Let’s look behind that advice. 

Aggregate Industries’ planning application has been the subject of Environmental Impact Assessment. According to government planning guidance: 

The aim of Environmental Impact Assessment is to protect the environment by ensuring that a local planning authority when deciding whether to grant planning permission for a project, which is likely to have significant effects on the environment, does so in the full knowledge of the likely significant effects, and takes this into account in the decision making process... The aim of Environmental Impact Assessment is also to ensure that the public are given early and effective opportunities to participate in the decision making procedures. Paragraph: 002 Reference ID: 4-002-20140306

Why is that important? The EIA contains the applicant's own assessment of the environmental impact of the proposal, which may be – and definitely has been in Aggregate Industries’ case – inaccurate, inadequate or incomplete. According to R (Blewett) v Derbyshire CC [2004] the EIA regulations: 

...recognise that an environmental statement may well be deficient, and make provision through the publicity and consultation processes for any deficiencies to be identified so that the resulting ‘environmental information’ provides the local planning authority with as full a picture as possible. 

If the LPA considers that further information is required, planning guidance says: 

...they must ask the applicant, in writing, to provide it (regulation 25). All information provided must be publicised, and consulted on. Paragraph: 047 Reference ID: 4-047-20170728

The legal advice we have received points to the recent case of R (Swire) v Secretary of State for Housing, Communities and Local Government [2020] which itself draws on other cases. Here are three paragraphs from that case: 

...the underlying purpose of the Regulations in implementing the [EIA] Directive is that the potentially significant impacts of a development are described together with a description of the measures envisaged to prevent, reduce and, where possible, offset any significant adverse effects on the environment. Thus the public is engaged in the process of assessing the efficacy of any mitigation measures... 70

...it was not right to approach the matter on the basis that the significant adverse effects could be rendered insignificant if suitable conditions were imposed. The proper approach was to say that potentially this is a development which has significant adverse environmental implications: what are the measures which should be included in order to reduce or offset those adverse effects? 70

...It is clear that a planning authority cannot rely on conditions and undertakings as a surrogate for the EIA process. It cannot conclude that a development is unlikely to have significant effects on the environment simply because all such effects are likely to be eliminated by measures that will be carried out by the developer pursuant to conditions and/or undertakings. 78

Of course, it’s not just the public that should be "engaged in the process of assessing the efficacy of any mitigation measures." Such a condition also deprives councillors on the planning committee of the opportunity to assess mitigation measures. In R (Jones) v Mansfield District Council [2003]: 

The purpose of the Regulations was to allow an opportunity to debate the environmental impact of a proposal so that full account of both the impact and the proposed mitigation could be taken into account in the eventual decision. 

It’s common sense. The LLFA’s condition plainly indicates the Council is without significant information to enable it to make an informed decision about surface water management. In R (Jones) v Mansfield District Council [2003]: 

Without the results of the surveys, they were not in a position to know whether they had the full environmental information.

In the case of Aggregate Industries’ proposal, for example, the LLFA has conditioned that "Soakaway testing must be undertaken... in accordance with BRE 365." Aggregate Industries has already had a go at soakaway tests. What happened? The results were inconclusive, several tests "were not undertaken due to slow infiltration rates." For each one of the six test pits: 

TP1 Unable to calculate infiltration rate 

TP2 Unable to calculate infiltration rate 

TP3 Unable to calculate infiltration rate 

TP4 Unable to calculate infiltration rate 

TP5 Unable to calculate infiltration rate 

TP6 Unable to calculate infiltration rate 

Aggregate Industries' document admits: 

The soakaway tests did not allow an infiltration rate to be determined using the BRE approach...

But there’s another reason why the Council cannot leave something as significant as flood mitigation to be resolved by condition, post determination. A planning application can either be allowed, allowed with conditions or dismissed. There is no power to modify an application other than by condition, but the Planning Inspectors’ Handbook makes clear that:

...care should be taken that a condition does not substantially alter the nature of the development applied for. In the case of Wheatcroft v SSE [1982] JPL p37 the judge formulated a test to define what a "substantial alteration" is. If the change is such that third parties would be likely to want to comment on it then the condition should not be imposed, as to do so would deprive those people of the opportunity for comment. 

Clearly, if the LLFA has no idea whether a surface water management scheme is even feasible, then the proposed condition could obviously throw up a requirement for significant alterations. Since a quarry at Straitgate Farm would permanently alter the landscape, and thereby surface water drainage characteristics, stakeholders should of course be entitled to comment on alterations – particularly if such alterations had the capacity to impact third party land beyond the site for evermore. 

Why would Devon County Council think otherwise, other than to stitch the whole thing up?