Statement of Evidence of Robert John Potts

Dated: 12 May 2017

REFERENCE: Ben Williams (ben.williams@chapmantripp.com)

Jessie Cross (jessie.cross@chapmantripp.com)

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