statement of evidence of robert john potts
TRANSCRIPT
Statement of Evidence of Robert John Potts
Dated: 12 May 2017
REFERENCE: Ben Williams ([email protected])
Jessie Cross ([email protected])
under: the Resource Management Act 1991
and: submissions and further submissions in relation to the
proposed Southland Water and Land Plan
and: Dairy Holdings Limited
Submitter
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STATEMENT OF EVIDENCE OF ROBERT JOHN POTTS
INTRODUCTION
1 My full name is Robert John Potts.
2 I hold the following qualifications: New Zealand Certificate in
Engineering (Civil), Bachelor of Engineering (Honours) Agricultural,
(University of Canterbury); Graduate Diploma in Hydrology
(Groundwater) (University of New South Wales), Making Better
Decisions (RMA) (University of Auckland) and am a Chartered
Professional Engineer (CPEng). I am a Member of the Institute of
Professional Engineers NZ (MIPENZ), Water NZ (ex-Chairman of
Small Wastewater and Natural Systems Group), NZ Land Treatment
Collective (ex-President) and Irrigation NZ. I am currently
Chairman of the Management and Audit Group for On-site Effluent
National Testing Programme and am on the Industry Review Panel
for Unit Standards in On-site Wastewater Training.
3 I am currently employed by Lowe Environmental Impact Limited as
a Senior Environmental Engineer.
4 I have worked in the area of Agricultural Engineering since 1977,
firstly with Ministry of Agriculture and Fisheries, then from 1989
until 1994 with Lincoln University, and from 1994 I have worked in
private practice. I have assessed the effects of irrigation
development and farm intensification in NZ, Australia, Pakistan,
Algeria and Vietnam.
5 My roles have included: project management, assessing
groundwater resources, impacts of farm intensification, land
treatment of wastes (solid and liquid), erosion and sediment
mitigation design, and assessing impacts of infrastructure
installation and operation.
SCOPE OF EVIDENCE
6 My evidence will deal with the following:
6.1 Physiographic zone mapping;
6.2 Effluent storage certification requirements;
6.3 Mapping of sub-surface drains;
6.4 Solid animal waste discharge restrictions; and
6.5 Silage storage facilities and associated stormwater flows.
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7 Although this is a Council hearing, I have read the Expert Witness
Code of Conduct set out in the Environment Court’s Practice Note
2011. I have complied with the Code of Conduct in preparing this
evidence and I agree to comply with it while giving oral evidence
before the hearing committee. Except where I state that I am
relying on the evidence of another person, this written evidence is
within my area of expertise. I have not omitted to consider material
facts known to me that might alter or detract from the opinions
expressed in this evidence.
8 I have also reviewed:
8.1 Other publications referenced in various sections of my
evidence;
8.2 The evidence of Mr Colin Glass on behalf of Dairy Holdings
Limited (DHL);
8.3 The relevant Officers’ reports and submissions on the
proposed Southland Water and Land Plan (Plan) by
interested parties.
PHYSIOGRAPHIC ZONES
9 The proposed Plan seeks to manage activities according to
physiographic zones, which have been developed based on common
landscape attributes that influence water quality, such as climate,
topography, geology and soil type.1
10 While I agree that there is merit in managing areas in zones as the
Plan attempts to do, it is important that the zones are accurately
defined and delineated on planning maps, so that land is not
improperly classified. Otherwise, landholders will be left in a position
where they are restricted from carrying out activities on their land
based on arbitrary zones, rather than on environmental outcomes.
11 The Peat Wetlands zone is described as being “characterised by
highly acidic peaty soils and a naturally high water table.” DHL
raised a concern in its submissions on the Plan that part of its Valley
Views farm is incorrectly zoned Peat Wetlands.
12 I have reviewed photos of the soil profile and overhead aerial photos
of the relevant area. I have also had a colleague (Sarah Smith of
Enviranz) visit the farm to independently verify the soil type.
13 The Plan showing the peat area is shown in Figure 1 and an aerial
photo showing the land use on the area in Figure 2. Photos taken
by Sarah Smith are shown as Figure 3 – these show the paddock
1 Proposed Plan, page 18.
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currently in swede. Based on these photos and the description
provided by Mrs Smith (Annexure A), I do believe that this area
has been incorrectly classified.
Figure 1: Extract from LWP Physiographic Zone Map 22
Figure 2: Valley Views Farm boundary (indicated by orange lines)
and area of Peat Land outside of farm boundary. Black circle
indicates the area in Paddock 6 that is incorrectly recorded as Peat
Land
Peat Wetland Area shown
extending into paddock 6.
Paddock 6 – no peat
land in area
indicated in Map 22
(see Fig. 1)
Peat
Land
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In Paddock 6 – Site 2 currently swede
Corner of Paddock 6 – Site 1 in trees
Paddock 6 – view to east of swedes
Paddock 6 – Test Pit Site 2
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Figure 3: Soil profile in corner of Paddock 6 Valley View Farm (indicated
by black circle in Figure 2) and further out in turnip paddock, as well as
Paddock 4
14 The Environment Southland supporting fact sheet describes the key
environmental feature of peat soils as having high organic carbon
content. Figure 3 shows the soil profile from the DHL Valley Views
Farm Paddock 6 and on inspection this soil profile does not match
that description. The soil appears to be a silt loam, with low organic
matter content.
15 Figure 4 shows an example of a typical southland peat soil for
comparison. They are formed by the decomposition of organic
matter in anaerobic conditions. Peat soils also typically have low
bulk densities, pH and phosphorus retention.
16 The fact sheet also describes peat wetland soils as occupying lower‐
lying parts of the landscape. However, the corner of Paddock 6
shown as having peat soils is an elevated area.
17 The physiographic area surrounding the peat wetland area is classed
as an oxidising soil. These soils are typically found at low elevation,
on flat to gently undulating land or elevated terraces along the outer
margins of the major river systems. This explanation matches the
description of the location of soil in Paddock 6.
Paddock 4 – Test Pit
Paddock 4 – Soils
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18 Soils on the other side of the road and in different parts of Paddock
6 have a different physiographic class in the Plan (Oxidising) but
from aerial photos and the site walkover by Sarah Smith, there
doesn’t appear to be any significant change in land form or use.
Figure 4: Typical Southland Peat Soil Profile
19 I have not conducted a thorough review of all of the zones, however
it is certainly possible that similar errors of zoning have been made
elsewhere. This is perhaps inevitable given the large area to be
zoned, however it highlights the need for a mechanism in the Plan
for landholders to appeal the zoning of their land, and have this
amended based on site-specific surveys where necessary.
EFFLUENT STORAGE
20 The Plan in Rule 32 requires that the design and build process of all
agricultural effluent storage must be certified by a Chartered
Professional engineer (CPEng). DHL seek to change this to “by a
suitably qualified person”
21 As a Chartered Professional Engineer, I have had lots of experience
with these types of effluent systems and the ponds are almost
always constructed below, or near below ground with engineered
liners (clay, HDPE or rubber). Only when the ponds are above
ground and the embankments are above a certain height (4 m) and
storage above a certain volume (20,000 m3) is a building consent
required that would require CPEng sign-off. Under these
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circumstances, I consider CPEng sign-off is required, i.e. if a
building consent is required.
22 IPENZ Practice Note 21: Farm Dairy Effluent Pond Design and
Construction (2013) states the following, with emphasising
provided by me:
6.4 Records and Sign-Offs It is important that pond owners be given a full set of records for their clay lined pond as they may be requested by their Regional Council for information on the sealing and/or seepage rate for the constructed pond. Also note that in some regions a Chartered Professional Engineer (CPEng) or a Suitably Qualified Person (SQP) may be required to sign off on a clay lined storage pond, so it is essential that these people are actively involved in the design and construction work. Rules and consent conditions should be sighted before construction begins to confirm any specific requirements.
23 Likewise, in IPENZ Practice Note 27: Dairy Farm Infrastructure
(2013), CPEng sign off is only required for retaining walls and other
specialist engineering/geotechnical structures that require a building
consent.
24 I therefore support DHL’s submission that for effluent pond design
and construction not requiring a building permit, sign-off by a
“Suitably Qualified Person” is sufficient.
SUB-SURFACE DRAINS
25 Under the proposed Plan, when developments are made or winter
grazing is undertaken, land owners must supply Council with details
of all existing drains, as well any new developments (Rule 35(a)(xii)
and Rule 23(b)(vi)). DHL wishes to make a minor amendment so
that these rules are in line with wording in Rule 13(a)(v), so that
only a map of any new or upgraded drain developments need be
provided.
26 I note that the Reporting Officer in the Tracked-changes version of
the Plan has added that the requirement is any “known” drains.2 I
support this addition but consider it needs to be modified further, as
outlined below.
27 I agree with the intent of the rule. Drainage under effluent
application areas has the potential to shortcut contaminants to
surface and groundwater. The type of drain and its construction
method is important to reducing this potential short cut, as outlined
in the clauses below:
2 Proposed Southland Water and Land Plan: Part A – Version showing
recommendations from the Hearing Report prepared under section 42A of the Resource Management Act 1991, at page 71.
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27.1 Subsurface drainage is required to remove water from the
rootzone. This is accomplished using deep open drains or
buried pipe/mole drains. They are needed in areas like
Southland where there is relatively high rainfall and soils
that commonly have poor drainage, and groundwater is
seasonally close to the surface in some areas. Drainage will
ensure that plant growth is not restricted by constant
waterlogging.
27.2 There are two main types of drains:
(a) A linear pattern of deep drains (30 – 100 m intervals)
with porous material near the surface to intercept
surface runoff and mole-plough drains to drain water-
logged soils or lower groundwater; and
(b) Intermittent drains located to pick up seeps/springs
from the hill country or to drain topographical low spots
to stop ground pugging.
27.3 Mole-ploughing as a method of sub-surface drainage has
added risk because the fracturing of the soil profile and
creation of macropores can provide a rapid channel for
contaminants to bypass soil and enter the drain. DHL farms
in Southland do not incorporate this type of drainage
system.
27.4 The DHL farms in Southland have intermittent drains
constructed using best practice. These do not follow straight
lines. As shown in Figure 5, the gravel around the drainage
pipe (150 mm diameter corrugated plastic perforated pipe
(Draincoil)) is placed to 100 mm above the pipe, then the
natural soil is replaced, giving at least 400 mm of topsoil and
subsoil for drainage water to pass through before entering
the drain. These drains are not there to intercept overland
flow and discharge it without treatment through the soil
profile to open drains. Therefore, the concerns usually
associated with drains are significantly reduced at the DHL
farms.
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Figure 5: Construction of DHL Subsurface Drain showing pea gravel at
depth and soil backfill prior to compaction
28 It can be difficult to map existing sub-surface drains, particularly
ones that do not follow a straight path upgradient from the outlet.
Drainage systems can be buried deep below ground and this can
cause great difficulty when trying to trace pipework and source
drainage problems. Recently installed drains may still be visible on
the surface due to a localised depression or slightly different
vegetation, however, older drains are not visible. So even though
drains may be known to exist, locating them to map may be
extremely difficult.
29 I support the Officer’s recommended change to remove the
requirement to locate sub surface drains from Rule 23(b)(vi), and
include only known drains in Rule 35(a)(xii), but with the following
additional amendments shown in bold:
(xii) the location of any known sub-surface drains that are identifiable by surface features within the discharge area, and their outlet position and relative depth, is mapped and provided to Environment Southland upon request.
SOLID WASTE DISCHARGE
30 DHL seeks to amend Rule 38 (d)(iv) to allow for discharges of solid
waste during winter when soil and weather conditions allow.
Currently there is a blanket ban on any discharge from May to
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September. DHL proposes management that restricts discharging
solid waste when the ground is at field capacity (as is already
provided for by Rule 38(d)(iii).
31 The reasons for restricting solid waste discharge between May and
September are due to relatively high rainfall and colder
temperatures in Southland area during this period. As solid waste
remains on the surface longer than liquid effluent, there is a higher
risk that it can be mobilised by surface runoff. Many soils will be at
field capacity throughout this time, making the risk of runoff higher.
A blanket ban of solid waste discharge during these months ensures
that there is zero chance of any contaminant entering waterways.
32 However, by refusing the spreading of waste from 1 May to 30
September when conditions allow, farmers will be forced to apply
potentially up to 365 days of waste over 212 days. This increases
the nutrient loading and risk of runoff of contaminants during other
periods of the year. As weather is not predictable and no season the
same, there is a chance that in wet spring/summers, there would be
limited time available when soil conditions allow for safe application.
Similarly, there will be times during winter when conditions to apply
solid waste without any significant adverse effects are possible and
this needs to be taken into account.
33 The Officer’s Tracked-change version of the Plan has recommended
that this condition be removed. The section 42A report considers
that the risk of solid waste being applied in inappropriate conditions
is currently managed by the clause that restricts the application of
solid waste when soil moisture exceeds field capacity. I agree with
the section 42A report and the recommended amendment to Rule
38.
34 Farmers need flexibility to respond to the conditions to optimise the
management of nutrients. Managing animal solid waste discharge to
land using sound management practices implemented through Farm
Environment Management Plans3 and by removing the May to
September application ban would provide this flexibility and ensure
that risks are minimised.
SILAGE STORAGE FACILITIES
35 The Plan in Rule 40 (a)(vii) states that a silage storage facility must
not be on land that is permanently or intermittently wet by the
presence of springs, seepage, high groundwater, ephemeral
streams, or flows of stormwater. DHL seek to include “other than
3 For example, not discharging waste when heavy rainfall is forecast, not discharging
waste to land with slopes greater than 15 degrees, and not discharging waste when soil temperatures are below 5 degrees.
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those flows coming off the silage covers in rainfall, which cannot be
avoided”.
36 Because of the nature of many silage storage facilities there is a
chance that the facility itself may cause minor ponding or overland
flow. There is potential for stormwater runoff because silage covers
are made from waterproof plastic to ensure that silage does not
become wet and remains in an anaerobic environment. Silage is
usually stored in a dome shape. In high rainfall events it is unlikely
that all the rainfall coming off the cover is absorbed by the soil, so it
is expected that there would be some ponding and overland surface
flow. However, the domed shape does direct the runoff away from
the stack. This runoff needs to be directed away from the base of
the stack to minimise risk of contaminants being transported to
waterways.
37 Provided that a common-sense interpretation of Rule 40 (a)(vii) is
applied, and the above-mentioned realities of silage storage facilities
are taken into account, in my view no amendment to Rule 40
(a)(vii) is necessary. However, to be safe, I support the suggested
changes in the DHL submission, as outlined in bold below:
40(a)(vii) no part of the silage storage facility is on land that is made permanently or intermittently wet by the presence of springs, seepage, high groundwater, ephemeral streams, or flows of stormwater (other than those flows coming off the silage
covers in rainfall, which cannot be avoided).
SUMMARY AND CONCLUSIONS
38 The physiographic zones need to be mapped correctly so that
landowners are not unfairly restricted from carrying out farming
activities. Where better soil classification is known, it should be
used.
39 Suitably qualified people with experience in designing effluent
storage facilities should be allowed to certify the design, as required
by the IPENZ practice notes. Should a building consent be required,
then CPEng sign-off should be required.
40 I support the proposed change to the rule on mapping drainage
systems to known drains only, but consider in addition that mapping
should be restricted to drains that are identifiable on the surface.
41 I support the proposed change to the restrictions on solid spreading,
i.e. the deletion of the winter restriction condition of the rule. I
consider that restrictions on slope, soil moisture status, soil
temperature and forecast rain reduce the risk of contamination
(however, these can be implemented through Farm Environment
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Management Plans, and do not necessarily need to be included as
conditions in Rule 38).
42 The intent of the restrictions on silage storage is to ensure that
water is not flowing into or through the stack. Stormwater that
comes off silage covers should not be caught by the proposed rule
conditions regarding stormwater, providing it is directed away.
Robert Potts
12 May 2017
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Annexure A – Envira Consulting Limited Memo on Site Soils
MEMORANDUM To: Rob Potts, LEI From: Sarah Smith, Envira Consulting Limited Date: 10 May 2017 Subject: DHL Valley Views Farm Soil Assessment Notes Dear Rob, As discussed, outlined below are notes to accompany the photos taken on the DHL Valley Views farm during a site visit on 10 May 2017. The sampling locations referred to are shown in the figure below. Weather conditions at the time of the visit were fine and sunny with little wind.
Paddock 6 This paddock is currently cultivated, with a swede crop in-situ at the time of the site visit. The farm manager commented that about 800 m of Novaflo drainage was installed to address drainage issues. Two sampling locations were examined in this paddock as shown on the Figure, with notes as follows:
Sampling Location 1
• Dug at the edge of the swede crop, about 15 m from the entrance gate in the NW corner of the paddock. The pit dug was about 25 – 30 cm deep. There were numerous tree roots present as the site was near the boundary where a line of trees is present.
• The soil type appears to be in two layers, a slightly darker brown/grey silty loam upper layer (down to 80 mm bgl) overlying a lighter brown/grey silty loam layer with occasional darker brown patches/mottles. The soil is thought to also contain some clay, but there were no obvious clay layers noted.
• The soil conditions were dry. The soil structure was crumbly. • No peat material was encountered in the test pit.
Sampling Location 2
• Dug at a location about 5 m from the edge of the crop within the paddock itself, at a location about 250 m from the paddock’s entrance gate. The pit dug was about 20 cm deep.
• The soil type appears to be a dark brown silty loam with a little clay possible. The soil conditions were moist (but not wet), and the structure appeared crumbly.
• No mottling or peat material was observed in the test pit. Paddock 4 This paddock is currently under pasture, with the farm manager commenting that the pasture present in this paddock is relatively new (sown in a 60:40 ryegrass/clover mix). One sampling location was examined in this paddock as shown on the Figure, with notes as follows:
• Dug at a location about 5 m from the edge of the paddock, within the pasture present in the paddock. The pit dug was about 20 cm deep.
• The soil type appears to be a dark brown silty loam. The soil conditions were moist (but not wet), and the structure appeared granular.
• No peat material was observed in the test pit. • A few orange mottles were noted on the wall of the excavation and present
within the excavated material (as orange particles). Yours sincerely
Sarah Smith Principal Scientist Envira Consulting Limited