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Phosphorous Budget Calculator v3.1
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Introduction
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Following the Dutch
Nitrogen Case which ruled that where a site is failing to achieve condition
due to pollution, the potential for a new development to add to the nutrient
load is "necessarily limited". Ramsar sites are classified as
'European Sites' under the National Planning Policy Framework (NPPF)
Paragraph 176. As such, Natural England's view is that any development
proposal that adds phosphorous into the catchment of Ramsar sites, such as
the Somerset Levels and Moors, is likely to have a significant effect.
Proposed developments likely to affect European Sites should be subject to
Habitats Regulations Assessment to assess the Likely Significant Affect on
the Ramsar. Application with a Likely Effect will require an Appropriate
Assessment to assess the implications of the proposal on the designated site.
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This tool
is designed to quantify the phosphorous loading of an area of land subject to
a change of land use and population, in order to identify is proposed
developments will be 'Phosphorous neutral'. Where the proposed development
will create additional phosphorous into the system, solutions in how to
offset this excess phosphorous and achieve phosphorous neutrality are
presented.
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This tool is only
necessary for proposed developments that have the potential to increase
phosphorous loading to rivers that flow into the Somerset Levels and Moors
Ramsar site. Developments that are located outside of the hydrological
catchment but will connect to a Wastewater Treatment Works (WwTW) that drains
to a river within the catchment should not complete Stages 2 and 3.
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The methodology
employed within this tool was, in part, guided by Natural England's advice on
nutrient neutrality in relation to the Stodmarsh designated sites, published
in November 2020.
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This tool
consists of seven main worksheets:
Stage 1 - Identifies the additional phosphorous as a result of changes in
the population
Stage 2 - Calculates the phosphorous load from current land use
Stage 3 - Calculates the phosphorous load from future land uses
Stage 4 - Calculates the total change in phosphorous loading as a result of
the proposed development
Stage 5 - Calculates the required solutions to achieve phosphorous
neutrality under current wastewater permit limits
Stage 6 - Calculates the required solutions to achieve phosphorous
neutrality under AMP7 wastewater permit limits
Stage 7 - Calculates the difference in mitigation solutions between current
wastewater permit limits and AMP7 permit limits
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About
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This Phosphorous
budget calculator is designed to allow the user to:
- Calculate the phosphorous budget for a proposed development and if, in
its current form, the proposed development is phosphorous neutral; and
- Assess the various mitigation options if the proposed development is not
phosphorous neutral.
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The tool has been designed so that the user is
able to update the data and methods in light of any new research or
understanding
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The information
supplied in this tool is for guidance purposes only and is not intended to
provide an exact budget calculation due to the limitations and assumptions of
the model. The user is responsible for ensuring the accuracy and completeness
of all data entered, be it manually or automatically, and used by this tool.
The user is also responsible for any commercial decisions taken on any of the
outputs of this tool.
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Royal HaskoningDHV
will not be liable for any of the following arising from the use of this tool
(including from any negligence on the part of Royal HaskoningDHV):
(i) loss of anticipated profits or expected future business;
(ii) damage to reputation or goodwill;
(iii) damages, costs or expenses payable by the user to any third
party;
(iv) loss of any order or contract; or
(v) indirect or consequential loss of any kind.
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This Phosphorous budget calculator has been
developed by Royal HaskoningDHV on behalf on Somerset West and Taunton
District Council.
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Phosphorous budget calculator, v3.1 (released
March 2021)
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General help
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The Tool uses the following colour coding to
indicate the functionality to the user. These colours are:
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The user needs to input a value here
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This contains fixed or calculated values and the
user does not need to input a value
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Stage 1
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This stage
calculates the change in phosphorous loading as a result of changes in the
population of a site.
Step 1: The user should input the additional number of units that are
proposed by the development. This is then multiplied by the occupancy rate
per dwelling.
Step 2: The user has the option to select whether sewage from the proposed
development will be handled by Wastewater treatment works or by Package
treatment plants. The user must select one or the other, both options cannot
be used.
Step 2a: If the proposed development is to use Wastewater
Treatment Works (WwTW), then the user should select 'Yes' from the drop down box.
Following this, the user should select the WwTW that the development will
connect to.
Step 2b: If the proposed development is to use
Package Treatment Plants (PTPs), then the user
should select 'Yes' from the drop down box. Following this, the user should
input the reduction efficiency of the package treatment plant. If the
efficiency is unknown then the user should input a precautionary efficiency
of 90%.
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Stage 2
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This stage calculates the
phosphorous load from the current land use.
Step 2: The user should input the area (hectares) of the current land uses
that make up the total area of the development site. A GIS viewer can be used
to identify the land uses on a coarse scale
(https://gridreferencefinder.com/). However, if more detail is known about
the site land uses then this should be manually inputted by the user.
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Stage 3
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This stage
calculates the phosphorous load from the current land use.
Step 2: The user should input the proposed land uses that make up the total
area of the development site. Any pre-determined on-site mitigation should
also be inputted here.
Bespoke banking coefficients should be inputted for constructed wetland
that can be evidenced
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Stage 4
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This stage provides
a summary of the phosphorous loads calculated in stages 1-3 and presents the
phosphorous budget for the proposed development.
A 20% precautionary buffer is included to account for uncertainties in the
runoff coefficients used. The User has the option to change this buffer
should this be appropriate.
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Stage 5
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This stage
calculates the area and land uses of the mitigation site required for the
proposed development to be phosphorous neutral, under current WwTW permit
limits.
Step 4: The user has the option to select the amount of phosphorous load to
be offset by the various land uses, which will then calculate the relevant
area of land (Hectares) that needs to be changed.
Step 5: The user has the option to input the required area of land
(hectares) to be mitigated until the project is phosphorous neutral, which
will then calculate the equivalent phosphorous load for each land use.
The banking coefficients for wetlands uses a value of 8 kg/ha/yr for
guidance purposes only. A site bespoke site-specific value will need to be
calculated
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Stage 6
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This stage
calculates the area and land uses of the mitigation site required for the
proposed development to be phosphorous neutral, under AMP7 WwTW permit
limits.
Step 4: The user has the option to select the amount of phosphorous load to
be offset by the various land uses, which will then calculate the relevant
area of land (Hectares) that needs to be changed.
Step 5: The user has the option to input the required area of land
(hectares) to be mitigated until the project is phosphorous neutral, which
will then calculate the equivalent phosphorous load for each land use.
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Stage 7
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This stage provides
a summary in the differences in mitigation land use area between the current
WwTW permit limits and the AMP7 WwTW permit limits
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Land Use Definitions
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The land uses presented in this tool followed the
CORINE 2018 land use data. Definitions of key land uses are presented below:
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Land Use
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Description
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Urban
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Development which encompasses the built form,
gardens, pathing, roads, hardstanding's, parks and small areas of open space,
ponds and SuDS. The phosphorous load results from sewer overflows and from
drainage that picks up phosphorous on the urban land. Agricultural barns used
for storage of materials, farming supplies and temporary livestock can be
classified as Urban. However, barns used for a specific farming type (e.g.
piggeries and chicken farms) should be classified under the relevant farming
land use.
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Mineral
Workings and Quarries
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An open or surface mineral working, usually for
the extraction of building stone, as slate, limestone, etc.
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Allotment and
City farms
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Wholly or mainly cultivated for the production
of vegetable or fruit crops for consumption by the tenant or local community.
In some cases the land will also be used for ornamental plants and the
keeping of hens or bees.
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Sports and
Leisure facilities
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Facilities used for recreational purposes such
as managed sports pitches, athletic fields, gymnasiums, swimming pools
etc.
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Transport
tracks and ways
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Encompasses large infrastructure such as
motorways and significant rail infrastructure. Small scale roads and tracks
are covered under the Urban land use
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Transport
terminals
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A large scale facility where passengers and
freight are assembled or dispersed
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Cereals
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Holdings on which cereals, combinable crops and set-aside account for
more than two thirds of the total standard output.
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Dairy
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Holdings on which dairy cows account for more than two thirds of their
total standard output.
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Cropping
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Holdings on which arable crops (including field
scale vegetables) account for more than two thirds of the total standard
output, excluding holdings classified as cereals; holdings on which a mixture
of arable and horticultural crops account for more than two thirds of their
total SO excluding holdings classified as horticulture and holdings on which
arable crops account for more than one third of their total standard output
and no other grouping accounts for more than one third.
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Horticulture
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Holdings on which fruit (including vineyards),
hardy nursery stock, glasshouse flowers and vegetables, market garden scale
vegetables, outdoor blubs and flowers and mushrooms account for more than two
thirds of their total standard output.
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Pig Farming
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Holdings on which pigs account for more than two thirds of their total
standard output.
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Lowland grazing / Paddock
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Holdings on which cattle, sheep and other
grazing livestock account for more than two thirds of their total standard
output except holdings classified as diary. A holding is classified as
lowland if less than 50% of its total area is in the Less Favoured Area
(LFA). A paddock is classified as a small enclosures used for grazing horses.
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Mixed livestock
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Holdings for which none of the other categories
account for more than two thirds of total standard output. This category
includes mixed pigs and poultry farms as wells as farms with a mixture of
crops and livestock (which neither accounts for more than two thirds of
standard output.
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Poultry farming
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Holdings on which poultry account for more than two thirds of their
total standard output.
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General Arable
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Use this option if unsure of the breakdown of arable land.
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Improved grass
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Land used for grazing (other than arable land)
where over one third of the sward comprises, singly or in a mixture,
ryegrass, cocksfoot or timothy, or land that has been improved by management
practices such as liming and top dressing, where there is not a significant
presence of sensitive plants species indicative of native unimproved
grassland.
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Unimproved grass
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Land used for grazing or mowing which is not
normally treated with mineral fertiliser or lime and contains a significant
presence of sensitive plant species indicative of native unimproved
grassland.
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Open Space /
Greenfield
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Greenfield areas that have not been in
agricultural use for at least 10 years and are not subject to unmanaged
recreational use.
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Woodland
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Tree-covered areas which either arose naturally
or as a result of plantations. This includes conifer woodland, mixed
woodlands and broad-leaved woodlands etc.
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shrub /
heathland / bracken / bog
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Land that contains extensive areas of either
shrubs, heath or bracken A bog refers to land that is a wetland area of muddy
ground that can accumulate peat.
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Freshwater
marsh
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Non-tidal, non-forested marsh wetland that
contains fresh water, and is continuously or frequently flooded.
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Meadow / semi
natural grassland
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A meadow is a field habitat vegetated by grass
and other non-woody plant that has an open character and is not grazed by
livestock
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Wetland
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Land use specific to constructed wetland only
and does not include ponds or SuDS.
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Wastewater Permit Limits
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Current WwTW permit limits Vs AMP7 WwTW permit
limits
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The Water
industry is looking to update and bring in new final effluent phosphorous
consent which should come in before 2025, as part of the Water Industry
National Environment Programme (WINEP). The enhancements are required to meet
more onerous environmental permit requirements. Many WwTW in Somerset do not
currently have a permit limit. However, following plans by Wessex Water, a
large number will operate to a new permit level under AMP7. Further
information regarding AMP7 permit limits can be found in the following
documents:
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0501C Atkins
Phosphorus removal technology review
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Representation
C3 WINEP - Phosphorus removal
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Soil Drainage
Criteria
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The drainage characteristics of
soil has a control over the dominant flow pathways for pollutant losses and
as such controls the loading of Phosphorous into surface water bodies.
Therefore the runoff coefficients from various land uses are different in freely
draining soil compared to impermeable soil. For impermeable soil under Arable
land use, it is assumed that man made drainage systems would be in place,
whereas rough grazing and woodland areas would not be drained. For
free-draining soil, the majority of the flow would be to groundwater, and it
is assumed that drainage would not be required. The user should use the
Soilscapes tool (Cranfield soil and Agrifood insitute, 2020) to determine the
dominant soil type on their site. Soilscapes can be found at
http://www.landis.org.uk/soilscapes/index.cfm
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The following table
is used to identify the dominant drainage type of the proposed development
from the soil type identified above. The drainage type should then inform
Stage 2 of the calculator
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Free draining
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Impermeable
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Colour
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ID
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Name
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Colour
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ID
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Name
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3
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Shallow lime-rich soils over chalk or limestone
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1
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Saltmarsh soils
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4
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Sand dune soils
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2
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Shallow very acid
peaty soils over rock
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5
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Freely draining lime-rich loamy soils
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8
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Slightly acid loamy
and clayey soils with impeded drainage
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6
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Freely draining slightly acid loamy soils
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9
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Lime-rich loamy and
clayey soils with impeded drainage
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7
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Freely draining slightly acid but base-rich soils
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15
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Naturally wet very acid sandy and loamy soils
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10
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Freely draining slightly acid sandy soils
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16
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Very acid loamy
upland soils with a wet peaty surface
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11
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Freely draining sandy Breckland soils
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17
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Slowly permeable
seasonally wet acid loamy and clayey soils
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12
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Freely draining floodplain soils
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18
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Slowly permeable
seasonally wet slightly acid but base-rich loamy and clayey soils
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13
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Freely draining acid loamy soils over rock
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19
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Slowly permeable wet
very acid upland soils with a peaty surface
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14
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Freely draining very acid sandy and loamy soils
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20
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Loamy and clayey
floodplain soils with naturally high groundwater
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21
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Loamy and clayey
soils of coastal flats with naturally high groundwater
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22
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Loamy soils with
naturally high groundwater
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23
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Loamy and sandy soils
with naturally high groundwater and a peaty surface
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24
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Restored soils
mostly from quarry and opencast spoil
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25
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Blanket bog peat
soils
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26
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Raised bog peat soils
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27
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Fen peat soils
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HaskoningDHV UK Ltd.,
a company of Royal
HaskoningDHV
Stratus House, Emperor Way, Exeter, Devon EX1 3QS
Registered Office: Rightwell House, Bretton, Peterborough PE3 8DW
Registered in England 1336844
W: www.royalhaskoningdhv.com
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