SECTION 87F REPORT OF ROBERT ALLEN DOCHERTY … · Prepared by Robert Docherty, Pattle Delamore...

Section 87F Technical Hearing Report

Application No. APP-2006012045.03 Horowhenua District Council Prepared by Robert Docherty, Pattle Delamore Partners Limited, 14 June 2016

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IN THE MATTER of the Resource Management Act

1991

AND

IN THE MATTER of applications by Horowhenua

District Council to Manawatu-Wanganui Regional

Council and Horowhenua District Council for

resource consents associated with the operation of

the Foxton Wastewater Treatment Plant.

SECTION 87F REPORT OF ROBERT ALLEN DOCHERTY – WASTEWATER

TREATMENT AND IRRIGATION SYSTEM



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A. QUALIFICATIONS / EXPERIENCE

1. My full name is Robert Allen Docherty. I am a Technical Director and Senior

Environmental Engineer in the Auckland office of Pattle Delamore Partners Ltd. I have

a Bachelors Degree in Civil Engineering from the University of Auckland and a Masters

of Engineering Science (Waste Management) from the University of New South Wales.

I am a member of the Institution of Professional Engineers of NZ and have been a

member since 1987. I am contracted by the Manawatu-Wanganui Regional Council

(Horizons Regional Council) to provide expert advice on the consent application by

Horowhenua District Council (HDC) to discharge Foxton’s wastewater to land.

2. I have over 30 years of experience in the consenting, design, construction and

operation of wastewater treatment and disposal systems handling municipal and

industrial wastewater. Many of these systems have included treatment pond systems

and land irrigation systems similar to the proposed Foxton scheme.

3. In assessing the information provided in the AEE documents I have used staff in my

engineering team to assist me who have experience in the application of wastewater to

land, nutrient loading rates and use of the Overseer model.

4. I have read the Code of Conduct for Expert Witnesses in the Environment Court

Practice Notes. I agree to comply with this Code of Conduct. This report is given

within my area of expertise. I have not omitted to consider material facts known to me

that might alter or detract from the opinions that I express.

5. I have visited the WWTP site and the proposed land disposal area on 21 March 2016.

B. BACKGROUND

6. HDC has applied for a variety of resource consents, (including an air discharge

consent) for its existing Foxton WasteWater Treatment Plant (WWTP) at Matakarapa

including the proposed spray irrigation of treated wastewater to ground on 54 hectares

of farm land adjacent to the Foxton WWTP. This consent application also covers the

construction of a possible new treated wastewater storage pond and/or alterations to

the existing ponds to provide flow balancing storage of 47,000 cubic metres (m3) to

service the irrigation scheme.



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7. HDC submitted the application for consents in October 2015. The Assessment of

Environmental Effects (AEE) was prepared by Lowe Environmental Impact Limited

(LEI) on behalf of HDC.

8. As of 12 June 2016 HDC has provided additional information in a number of responses

to a Sec 92 request, which has discussed some of the issues raised by PDP,

particularly the issues around de-sludging of the ponds.

C. PROPOSED ACTIVITIES

9. HDC operates the Foxton WWTP at Matakarapa approximately two kilometres

southeast of central Foxton. The WWTP services the Foxton community and currently

discharges into the Foxton Loop of the Manawatu River. Due to poor water quality

within the Foxton Loop and the desire to improve the quality of the Manawatu River

HDC has reviewed possible options to improve this situation, and has decided that the

most appropriate solution is to have a land based disposal system and cease direct

discharges of treated wastewater into the Foxton Loop.

10. As described in Section 6 of the AEE, at a conceptual level the application seeks to

change the existing WWTP system from a discharge to water (currently the Manawatu

River via Foxton Loop) to a discharge to land.

11. HDC is understood to have a preliminary agreement with the Knight Family who own

farm land to the south of the WWTP for wastewater disposal, as shown on Figure A2 in

the Application. Figure A2 also identifies the location of the existing WWTP and that it

is surrounded on three sides by land owned by Mr Jarvis. Figure A15 shows a

proposed rising main which would need to be constructed across the Jarvis property to

pump treated wastewater (effluent) to the Knight property.

12. Land-based effluent disposal to a crop (and the crop in NZ is typically trees or grass) is

a common approach for many communities in New Zealand and is generally the

preferred disposal method where the alternative is to discharge into a surface water

body.



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13. Land disposal usually provides additional treatment of the effluent as it passes through

the soil provided it is applied in the correct manner and enables at least some of

the nutrient value (nitrogen and phosphorous particularly) contained in the effluent to

be utilised as a resource for grass growth. In addition, it obviously applies irrigation

water to the grass. The key to minimising any adverse environmental effect is to

manage the rate of application of the effluent to achieve the desired nutrient removal

uptake rate by the grass.

14. Based on information contained in the AEE, it is understood the wastewater entering

the WWTP (mean inflow of 1307 m3/day) is not currently screened. It enters a large

69,000 m3 oxidation pond followed by two 12,000 m3 maturation ponds in which

wastewater is naturally aerated with no mechanical aerator assistance. The ponds

have a normal water depth of about 1.5 metres and it is understood the ponds were

constructed using the insitu sandy soils and that no specific pond lining was installed to

minimise leakage (either plastic or low permeability clay) at the time of construction.

The primary (large) pond was constructed in 1974 and the two smaller ponds in 1997.

It is understood that there is presently no electricity supply to the WWTP site.

15. It is understood these ponds have not been desludged since they were built and a

sludge survey in 2013 estimated there was about 14,400 m3 of sludge in the three

ponds. The Applicant estimates that this sludge has reduced the combined residence

time to about 61 days based on existing flows. This residence time is still quite long for

this type of treatment plant which is good as it will be assisting the treatment capability

of the WWTP. HDC plans to de-sludge the ponds in 2017/18 and this will have a

temporary detrimental effect on the effluent quality whilst this is undertaken. The

desludging will also likely lead to an increase in leakage from the ponds once the

sludge layer above the floor has been reduced in thickness, but any increase in

leakage can be minimised by applying good engineering practice during the de-

sludging process. This is discussed later in my report.

16. Nutrients and pathogens are the key contaminants in terms of the potential for the

wastewater to affect surface and groundwater quality. The median and 95th percentile

concentrations of key wastewater (effluent) parameters presented by the Applicant for

the period 2010 to 2015 and by HRC for the period 2007 to 2016 are given in Table 1

below.



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Table 1: Foxton WWTP Treated Wastewater (Effluent) Water Quality Data

Parameter Unit

Horowhenua District Council (Applicant) Monitoring Data

1

Manawatu- Wanganui Regional Council Monitoring Data

2

Median 95

th

Percentile Median

95th

Percentile

Soluble Carbonaceous five day Biochemical Oxygen Demand (ScBOD5)

g/m3 4.0 8.0 4.3 16.1

Total Suspended Solids (TSS)

g/m3 75 160 73 158

Total Kjeldhal Nitrogen (TKN)

g/m3 23 34.3 na na

Ammoniacal-Nitrogen (NH4-N)

g/m3 11.8 21.4 12.6 24.2

Nitrate Nitrogen (NO3-N) g/m3 0.08 3.5 na na

Nitrite Nitrogen (NO2-N) g/m3 0.09 3.1 na na

Total Nitrogen (TN) g/m3 22 33 na na

Dissolved Reactive Phosphorus (DRP)

g/m3 2.5 4.5 2.8 4.8

Total Phosphorus (TP) g/m3 4.0 6.4 na na

Escherichia coli (E. coli) cfu/100mL 400 6,100 520 10,600

Notes:

na = not available as data not provided by Manawatu-Wanganui Regional Council.

1. Based on values reported in the Foxton Wastewater Discharge – Resource Consent Application and AEE (Table 6.2)

2. MWRC monitoring data as provided by Logan Brown and supplied in the report Section 87F Report of Logan Arthur Brown on behalf of the Manawatu-Wanganui Regional Council.

3. For E coli. the data provided by Logan Brown and supplied in the report “Section 87F Report of Logan Arthur Brown on behalf of the Manawatu Wanganui Regional Council” is representative of the 2010 to 2015 period, as data prior to 2010 was not considered representative of the current Foxton WWTP effluent quality.

17. I agree with the Applicant’s summary that these treated wastewater concentrations are

typical for a functioning oxidation pond system. In fact, I consider that they indicate

‘quite well treated effluent’ compared with many other oxidation pond based systems

within New Zealand.



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18. Based on the Applicants data shown in Table 1 above, the WWTP is providing

reductions in total nitrogen, phosphorous and E.Coli which are a little better than I

would have expected. I consider that at least part of the reason for this will be due to

the relatively long residence time in the ponds and also that there are three separate

ponds working in series which reduces short-circuiting.

19. The treated wastewater (effluent) from the ponds currently discharges into a drain

which flows directly into the Foxton Loop. The key changes proposed by this

application are the move to a 100% discharge of effluent to land (albeit staged to occur

incrementally over a 3 year period) and the addition of storage at the WWTP to

temporarily store wastewater when it cannot be irrigated at the rate at which it is

entering the WWTP due to factors such as wet weather.

20. The current discharge to surface water consent (Discharge Permit 103925) has a

condition requiring that the treated wastewater discharge shall not cause certain

conditions to occur in the Foxton Loop at the reasonable mixing distances outlined in

the consent. These conditions are, inter alia;

a. the ammonia (NH4-N) concentration to exceed 0.4 grams per cubic metre; or

b. the carbonaceous BOD5 concentration due to dissolved organic compounds

(that is, material passing through a GF/C filter) to exceed 2.0 grams per cubic

metre; or

c. the Escherichia coli (E. coli) concentration to exceed 550 cfu/100 ml.

The consent also notes that the above conditions shall be considered to be breached

only when:

The concentration of any parameter recorded or measured at the site 200m

downstream of the discharge is above the standards set in Conditions; and

The increase between the upstream and downstream concentration is equal to

or exceeds 20%.



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21. According to the Foxton WWTP Consent Compliance Summary report (LEI 2015:B2)

provided as part of the consent application there have been occurrences of

noncompliance with ammoniacal nitrogen concentrations (five breaches between

2009-2015) and E coli levels (21 breaches between 2009-2015) in the receiving

Foxton Loop. In the Consent Compliance Summary report the Applicant has identified

that it is likely that only six of the 21 E coli. non-compliance events are likely to be a

result of the Foxton WWTP discharge as E coli. levels monitored in the Foxton WWTP

discharge at the same date were lower than the non-compliant E coli. levels monitored

in the Foxton loop. I note that Logan Brown has identified seven ammonia breaches

comprising five downstream and two upstream (as Foxton Loop flow direction can vary

with tidal influence) in his report and has not discussed E. coli breaches.

22. The applicant has proposed to move away from the present system of having Consent

Limits for water quality imposed in the Foxton Loop water and instead proposes

consent limits for the treated wastewater discharge as it leaves the WWTP. We

understand that Mr Logan Brown is in agreement with this approach. These proposed

effluent quality limits will cover the discharge to surface water (for three years from

commencement of the new consent) and to land thereafter. I discuss this further later

in this report.

23. The requirement to provide flow balancing storage of 47,000 m3 for the irrigation

system has been calculated by LEI and may be comprised of partially treated

wastewater or treated effluent or a combination of both depending on the method of

providing the storage which has yet to be decided on by HDC. There are four

alternative options put forward in the AEE which are; (a) constructing a new lined

effluent storage pond located to the west of the existing WWTP which would store

treated effluent, or (b) constructing additional volume within the existing oxidation pond

by raising the embankments (which would store partially treated effluent), or (c)

converting one of the maturation ponds into a storage pond (which would store partially

treated effluent), or (d) a combination of the above. Note that for the treatment

efficiency of the existing WWTP to not be reduced then this storage volume of

47,000 m3 must be over and above the existing 93,000 m3 of treatment pond volume.

I discuss issues related to storage later in this report.



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24. The average volume of wastewater inflow to the ponds between 1993 and 2015 has

been calculated by the Applicant to be 1,307 m3/day. The Applicant has assessed

current leakage from the existing wastewater treatment ponds to be approximately

156 m3/d based on flow meter measurements. This calculates to be about 12% of the

daily inflow.

25. The Applicant has assessed population growth to be about 0.4% per year. Such a low

growth rate will be unlikely to have a significant effect on flow and load into the WWTP

over a 10 year period as it is less than a 5% increase. However, as with all land

disposal systems, it is imperative that an annual check be kept on flow and growth to

ensure the treatment and storage unit processes as well as the land irrigation system

have sufficient capacity.

26. The Applicant has divided the proposed land discharge areas (totalling 145 ha) into

Land Management Units (LMU) based on soil type and topography. Within each LMU

there is an Irrigation Management Area (IMU) that will receive irrigated treated

wastewater. The total area of the IMU areas is 54 ha. The description of each LMU

and IMU is presented in the Conceptual Design Report1. Each IMU will be subject to

different irrigation management practices.

27. Wastewater is proposed to be irrigated to three irrigation areas with irrigation

management practices as follows:

a. IMU1: 18 ha of deficit irrigation (15 mm per event without exceeding field

capacity)

b. IMU2: 30 ha of non-deficit irrigation (20 mm irrigation depth per event without

exceeding field capacity by more than 8 mm)

c. IMU3: 6 ha of high rate application (20 to 50 mm per event to occur only when

the Manawatu River flow is above the upper 20th percentile flow)

28. It is my understanding that Mr David Horne has checked these proposed loading rates

and considers them to be acceptable.

1 Lowe Environmental Impact Limited, Foxton Wastewater Treatment Plant, Conceptual Design, 2015



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29. The average nutrient leaching from the three LMU areas (which total 145 ha) has been

assessed by the Applicant to be 28 kg-N/ha/yr and 1.6 kg-P/ha/yr using the agricultural

industry standard Overseer modelling program (Nutrient Loss and Farm

Intensification2). Although higher than expected for bull beef farm operations,

I consider these nutrient leaching rates to be in line with typical nutrient losses from a

dairy farm operation. As a comparison, the Applicant calculates the N leaching from

the present farming operation over the entire LMU of 145 ha to be 7 kg/ha/yr.

30. Whilst my staff have not undertaken any checks of nutrient leaching using the

Overseer model they have checked the range of parameters used by LEI in the

Overseer model and in general, consider them to be reasonable.

31. A concern I have is around the leaching from specific IMU areas which are under

irrigation. This leaching has been calculated by the Applicant to be 18 kg-N/ha/yr for

IMU 1 (Deficit irrigation), 77 kg-N/ha/yr for IMU 2 (non-deficit irrigation) and

132 kg-N/ha/yr for IMU 3 (high rate irrigation). My concern relates to the potential for

overloading these areas, and in particular IMU 3, and I will discuss this in more detail

later in this report.

32. The Applicant has identified a reduced nutrient loading on surface water based on

changing from direct discharge to surface water to a land discharge system of between

53 and 77% nitrogen reduction and between 87 and 97% phosphorus reduction

(Surface Water Considerations 3). Whilst I have not undertaken any calculation checks

on these proposed reductions in nutrient loading there is no doubt that significantly

reduced nutrient loading of surface water can be achieved through discharge to land

provided the irrigation system as proposed is operated in accordance with the

operating regime as described in the AEE and can be managed effectively and I

strongly support this.

D. SCOPE OF REPORT

33. My report focuses on an assessment of the design and management and the effects of

the proposed wastewater treatment pond system and the proposed irrigation disposal

system.

2 Lowe Environmental Impact Limited, Foxton Wastewater Treatment Plant Discharge, Nutrient Loss and Farm Intensification,

2015 3 Lowe Environmental Impact Limited, Foxton Wastewater Treatment Plant Discharges, Surface Water Consideration Design,

2015



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34. The exact effects of the proposed activity are not a key focus of this report, as this has

been discussed in detail in other Section 87F reports. My report will focus on;

a. the design and management of the system and whether this will result in the

proposed effects outlined in the application.

b. identify any gaps in the Applicants proposed design and management which

may impact the magnitude of the resulting effects.

E. EFFECTS OF THE PROPOSAL

Wastewater Treatment Plant and Irrigation Effluent Storage

35. Given the non-compliances with existing consent conditions discussed above (in

Cl. 21), it seems reasonable that no relaxation of treatment or effluent quality should

be permitted. I understand that Logan Brown concurs with this and even though the

effects on the water quality in the Loop are significant Logan’s approach is to make

sure the effects do not get any worse given that the discharge into the Loop will be

removed in 3 years time once the effluent discharge to land is enacted.

36. As a minimum, in order to maintain the current level of treatment the physical layout

and residence time (based on the present total volume of the WWTP being 93,000 m3)

should be maintained and additional mechanical aeration would need to be provided in

future as flows increase or as necessary to maintain the WWTP effluent quality. Note

that for the treatment efficiency of the existing WWTP to not be reduced then this

storage volume of 47,000 m3 must be over and above the existing 93,000 m3 of

treatment pond volume. I discuss issues related to storage later in this report.

37. The Applicants proposed WWTP effluent water quality consent limits are outlined in

Table 2 below. The representative WWTP effluent quality, (as determined by Logan

Brown by taking the higher of the results from the Applicant’s monitoring data and the

Horizons Regional Council’s monitoring data) have been provided by Logan Brown

and are also shown in Table 2.



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38. The method of establishing the WWTP effluent water quality compliance/non-

compliance proposed by the Applicant and as shown in Table 2, is consistent with

methods outlined in the New Zealand Municipal Wastewater Monitoring Guidelines

(NZWERF, Sep 2002) Table 13.2, which outline that for a monitoring period during

which 12 samples are taken (consistent with monthly sampling within annual

monitoring period proposed for Foxton WWTP) eight out of 12 samples can exceed the

median effluent quality limit and two out of 12 samples can exceed the 95th percentile

limit. This method of establishing compliance/non-compliance allows statistically for

risks around the collecting of unrepresentative samples rather than samples reflecting

actual effluent water quality.

39. PDP considers this method of establishing effluent water quality compliance/non-

compliance is acceptable and it is acceptable to apply it to the Foxton WWTP.

However, the water quality values proposed by the Applicant (shown as the

“Applicants Proposed” values in Table 2) are not representative of the existing median

and 95th percentile Foxton WWTP effluent water quality.

40. I consider that the consent limits for the treated wastewater discharge should be based

upon the actual existing wastewater discharge quality of the Foxton WWTP (shown as

the “Representative” values in Table 2) as this then makes it consistent with the

NZWERF method described above and also aligns with the values used by the

Applicant in the Assessment of Environmental Effects.

41. The effect on water quality within the Foxton Loop based on the continued discharge of

current Foxton WWTP effluent water quality is covered in the evidence of Logan Brown

(Section 87F Report of Logan Arthur Brown on behalf of the Manawatu Wanganui

Regional Council).

42. I consider the Representative Foxton WWTP effluent water quality values, as outlined

in Table 2 are reasonable for the proposed discharge to land activity. In addition, I

consider the existing WWTP to be capable of achieving the effluent water quality

presented in Table 2 in the future provided the WWTP configuration and residence

time is maintained and provided additional aeration is added to account for any

increase in organic loads.



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Table 2: Applicants proposed discharge quality limits versus the existing discharge

quality from the Foxton WWTP.

Parameter Applicants Proposed WWTP

Effluent Water Quality

Consent Limit

Representative Foxton WWTP

Effluent Water Quality

(8 out of 12

samples)

(2 out of 12

samples)

Foxton

WWTP

Effluent

Water

Median

Foxton WWTP

Effluent 95th

Percentile

Soluble

carbonaceous

Biological Oxygen

Demand (g O2/m3)

35 45 4.3 16.1

Total suspended

solids (g/m3)

100 150 75 160

Ammoniacal

nitrogen (g/m3)

17 25 12.5 24.2

Dissolved reactive

phosphorus (g/m3)

4 5 2.8 4.8

E. coli (median)

(cfu/100ml)

5,000 12,000 520 10,600

Notes:

1. Based on the higher of the Horowhenua District Council (Applicant) monitoring data and the

Horizons Regional Council monitoring data outlined in Table 1 above.



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43. Screening of Influent: The Applicant has identified that the screening of influent

wastewater is not proposed due to power limitations onsite at the wastewater

treatment plant. Whilst there is presently no power supply to the site this will be

rectified as the proposed irrigation system will require a power supply in order to run

the irrigation pumps. The power demand from a mechanical screen is relatively very

small and I consider that the provision of the new power source to the WWTP could

easily be sized to include capacity to operate a screen. Without influent wastewater

screening, gross solids (particularly plastic) will enter the wastewater treatment ponds

and float on the surface potentially causing offensive odours and provide an attractant

for vermin. A screen will also reduce potential gross solids loading on any effluent

screening which will need to occur prior to the irrigation pump station.

44. I have been shown some photographs taken by Mr Logan Brown of Horizons (see

photos in Appendix A) of gross solids at the water’s edge of the ponds and also on the

waveband and caught in the boundary fence around the WWTP. Apparently wind

blown material is frequently seen deposited around the site and it is likely that some of

this enters neighbouring properties and waterways. It is typical and good practice to

have an inlet screen in place to control these gross solids and I consider it good

practice to provide such a screen at this plant to ensure the issues outlined above do

not occur.

Proposed Effluent Storage Volume

45. The Applicant has identified the need for 47,000 m3 of effluent storage for the

proposed irrigation activity. The storage volume is a key parameter which is very

important to calculate correctly for any land disposal scheme. If the volume is under

calculated then it will result in more effluent being applied to land at certain times when

the land and /or crop is not able to assimilate or treat it. The net effect of this will be a

greater flux of nutrients leaching into groundwater and ultimately into the surface water

than has been calculated by the Applicant. The volume of storage required must

carefully consider rainfall, evaporation, crop evapotranspiration, soil assimilative

capacity, groundwater mounding, wet weather inflows to the WWTP, expected

population growth and inflow volume increase, irrigation scheduling as well as farm

management practices by the farmer.



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46. To elaborate on this, there is quite a complex set of interacting factors to consider

when calculating the storage volume required not least of which is the interaction

between the daily volume to be irrigated to comply with the Consent Conditions,

available volume in the storage pond, wastewater inflows and farm management

practices.

47. The storage volume of 47,000 m3 will need to be provided prior to the land disposal

scheme becoming operational and the volume will need to be over and above the

present volume provided within the WWTP in order to maintain the same treatment

plant efficiency and quality of effluent.

48. It is fundamental that the storage volume is correctly calculated in order to correctly

assess the effect on the irrigation scheduling and therefore, also to assess the effect

on the environment. I have not checked the storage volume calculation and it is the

responsibility of the Applicant to calculate this correctly. The Applicant has provided

information in the AEE discussing various irrigation scenarios and storage volumes but

it is not clear how the specific volume of 47,000 m3 has been determined.

49. Either way, given the importance of calculating the volume correctly, I recommend that

the storage volume modelling calculation be peer reviewed at the detailed design

stage and I have recommended a Consent Condition be included to cover this. The

volume of storage required and how it is to be physically provided could also have a

significant impact on the Capital Cost of this scheme. In my view this is another reason

why the storage volume should be accurately calculated at the consent application

stage of the project.

Storage Pond Concerns

50. The Applicant has not confirmed the dimensions of the new storage pond or whether a

new pond will be constructed in order to provide the overall storage requirement of

47,000 m3. The Applicant has also specifically identified that another option could

include turning one of the existing WWTP maturation ponds into a storage pond

(Conceptual Design Report)4.

4 Lowe Environmental Impact Limited, Foxton Wastewater Treatment Plant Discharge, Conceptual Design, 2015



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51. The absence of specificity about how the new storage will be provided makes it more

difficult to assess the effects. For example, if a new pond was constructed with an

impermeable liner (one option proposed by the Applicant) and if this was used to

temporarily store treated effluent then there would be no change to the performance of

the existing WWTP, no leakage from the new storage pond and probably no adverse

effects.

52. On the other hand if one of the maturation ponds was to be taken out of service and

used for storage purposes, and/or if all the existing ponds were to have their

embankments raised and used to provide temporary storage then this raises other

concerns. I will now discuss my concerns:

a. Increased leakage to groundwater. Increasing the water depth in the existing

unlined ponds will result in increased leakage from the ponds to groundwater

as acknowledged in the Applicants Section 925 response. In the Section 92

response the Applicant identifies that an anticipated pond depth increase of 0.5

metre may result in an increase in pond leakage from the present 156 m3/d to

230 m3/d. Leakage of 230 m3/d would equate to about 18% of the daily inflow.

I have not seen details as to how this extra seepage has been calculated, but it

should be carefully considered, particularly in view of the proposed desludging

of the ponds within the next two years. While not part of the current application,

the action of desludging alone (irrespective of any addition to the hydrostatic

head in the ponds if the banks are raised) will likely increase the leakage above

the existing rate of about 156 m3/d. The effects of the hydraulic and nutrient

impact on groundwater has been assessed only for the 156 m3/d (I discuss this

further below). Furthermore the anticipated increase in pond depth of 0.5 m

has not been confirmed.

In my view further information should be provided about how the exact storage

requirements will be provided within the existing pond or ponds. Further, the

effects of this additional pond depth should be included in groundwater effects

assessments.

5 Lowe Environmental Impact Limited, Foxton Wastewater Treatment Plant Discharge, Resource Consent Application – Section

92 Response, 15 Dec 2015



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b. Decreased treatment capacity. The Applicant has asserted that effluent

storage within the existing wastewater treatment ponds (e.g. by taking one of

the maturation ponds out of service or by temporarily increasing the water

depth in all the ponds) will not affect the treatment capacity of the system.

Given that the Applicant has not confirmed the volume to be stored in the

existing ponds or how storage will be achieved I consider that the Applicant has

not provided sufficient information to demonstrate that the current treatment

plant capacity will be maintained. Removing one of the maturation ponds from

the treatment train will almost certainly result in some treatment reduction as it

would reduce the hydraulic retention time by 11% (based on present flows) and

so result in worse quality effluent which may adversely impact the receiving

environment. (Note that a single maturation pond only has a volume of 12,000

m3 so a further 35,000 m3 would need to be provided by some other means).

c. Geotechnical Instability: It is unclear from the Application whether or not the

geotechnical aspects of increasing the water depth in the ponds, or fluctuating

the water level in one of the maturation ponds (from pond empty up to at least

1.5 metres water depth), has been considered. What I am concerned about

here is whether or not either of these options is practicable given that it could

create a situation of geotechnical instability of the pond embankments. Such

instability could arise due to changes in the phreatic surface in the pond

embankments. This is a particular concern given that it is my understanding

that the embankments are not lined and are constructed from insitu sandy soils.

Desludging of the Existing Ponds

53. The Applicant has excluded any assessment of effects related to desludging of the

wastewater treatment ponds from this resource consent application on the grounds

that it is not directly related to the proposed activity. However, desludging of the

wastewater treatment ponds in 2017/2018 may result in increased leakage to

groundwater and therefore in my view is relevant to this resource consent application.

For this reason I consider that the impact of desludging the wastewater treatment

ponds on leakage to groundwater should be assessed so as to enable a full

understanding of the potential effects of the discharge to groundwater through

operation of the WWTP.



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54. Following on from my discussion above, the Applicant has provided a S92 response to

the issue of pond desludging and related leakage (Fluent Solutions Ltd, letter dated 17

May 2016). I have read this report and I am in general agreement with it, although I still

have some reservation around the quantum of leakage increase and potential for

embankment damage that could occur given the sandy nature of the soils at this site. I

acknowledge that this can be minimised by using good engineering practice as

indicated in the Fluent report. Accordingly, I recommend taking a conservative

approach and that there is a Condition included in the Consent around this as follows;

a. An engineer familiar with pond desludging prepare contract documents

requiring applicable desludging methods be used which will not lead to

increased leakage or pond floor or embankment damage.

b. Monitoring of leakage rates before, during and after desludging is undertaken.

If leakage increases then HDC discusses mitigation methods with Regional

Council.

Land owner lease arrangement

55. There is no doubt that in the case of the Foxton WWTP a discharge to land is a

preferred method of discharge compared to discharge to surface water as it will have a

significantly reduced effect on the aquatic environment especially in terms of mass flux

of nutrients into the surface water. However, this relies entirely on there being land

available on which to irrigate. There will no longer be the option available to HDC of

discharging to surface water.

56. It is common practice (although not exclusively the case) for a Council to own the land

on which irrigation of effluent is to take place. This places maximum control in the

hands of the Consent holder (the Council). In the Foxton situation HDC will have no

other means of disposing of the effluent other than onto the Knight Family property,

albeit that there is provision to use the 47,000 m3 of temporary storage which is

equivalent to 36 days of storage (47,000 m3/d / 1,300 m3/d = 36 days).

57. Given that HDC will be leasing the irrigation site from the Knight Family, I consider it is

imperative that HDC has in place a very robust long term lease agreement (at least

equal to the term of the consent) which will enable HDC to irrigate at any time in

accordance with its consent. This agreement needs to be operable even if it does not

match the farm management practices of the farm owner.



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Irrigation System Design

58. I consider the concept of the proposed irrigation system to be appropriate for a system

designed to achieve 100% discharge to land, with discharge to typically well drained

sandy soils and identified areas of high rate irrigation to receive treated wastewater

during wet weather conditions.

59. The assessed average nutrient losses from the proposed irrigated pasture system of

28 kg-N/ha/yr and 1.6 kg-P/ha/yr, although higher than expected for bull beef farm

operations, are in line with typical nutrient losses from dairy farm operations.

60. The Applicant has assessed that the effects on the receiving environment will be

reduced which is to be expected when the discharge of 100% of treated wastewater is

proposed to replace an existing direct discharge to surface water.

61. However, the specific details and the management and operability of the proposed

system will determine the actual effects that will result from the proposed activity if

implemented. As a result I consider that the Applicant needs to address a number of

concerns relating to the design, management and operation of the proposed irrigation

system in order to provide confidence that the actual observed effects are in keeping

with those assessed in the application.

62. Overall I consider that the Applicant needs to provide additional technical information

relating to the scheme to provide confidence that it will operate as outlined. This

information needs to relate to details around how the balancing storage volume will be

provided.

Irrigation System Management

63. The ability for the Applicant to manage and operate the irrigation disposal system in

accordance with the proposed discharge regime described in the application will have

a significant bearing on the actual observed effects of the discharge to land. The

existing Land Application Management Plan is currently a table of contents, which

does not provide the necessary information required for the operability of the proposed

irrigation system to be assessed. There are some key points around nutrients and

environmental effects of the system which are being considered as part of this

Application and these technical matters need to be incorporated into the consent either

through conditions or in a more detailed Management Plan at this stage of the process.



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This enables MWRC to understand (among other things) with greater certainty what

the effects of the proposal are, what limits should be placed on the proposal through

conditions, and how these limits will be met through implementation of a management

plan. Leaving these matters to be included in a Plan prepared at a later date by a third

party who may not necessarily be familiar with all the technical issues runs the risk of

not correctly capturing the full importance of the issues. It is my understanding that a

more detailed Management Plan will provided in evidence by the Applicant.

64. To elaborate further, there are some practical details about how the system will be

managed and operated which have not been thought through which could lead to an

increase in nutrient leaching above the masses discussed in the Application. For

example, if the irrigation system is operated so that more irrigation water is disposed of

to IMU 3 than calculated by the Applicant, then the mass of nitrogen which will leach

into the groundwater will be greater than the 132 kg-N/ha/yr and consequently the

average nutrient mass from the overall 145 ha LMU area will exceed the calculated 28

kg-N/ha/yr.

65. It is proposed that the operation of the irrigation scheme will be undertaken and

controlled by the farm owner as part of the owner’s larger farming operation. I find it

very difficult to understand how this will not conflict with HDC’s requirement to

discharge effluent on a daily basis (albeit that there is some ability to flow

balance/store effluent on some days) and also maintain compliance with the HDC’s

resource consent. The Applicant needs to demonstrate that sufficient and very robust

management controls and guidance will be put in place so that the farmer will irrigate

on a daily basis and also operate in accordance with the resource consent and not

operate the land solely for maximum farming return.

66. I am not convinced that the irrigation system is going to be simple to operate. In fact I

believe it will be complex to operate as it requires the farmer/operator to decide on a

daily basis which IMU is to be irrigated, which block in that IMU is to be irrigated and

how much irrigation can be applied, and at the same time determining how much

effluent needs to be irrigated so as to balance the water level in the storage pond (and

prevent it becoming too full) at the same time as understanding the implications of

pond inflows (e.g. increased flows due to wet weather) and rainfall whilst also running

a working farm.



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67. My view is that, particularly in winter when the ground in IMU1 and IMU2 is wet, in

order to simplify the coordination between his farming operation and the requirement

for effluent irrigation it is likely the farmer will end up applying a greater volume to the

HIGH RATE land disposal area (IMU3) than is presently allowed for. This will be the

easiest and least complicated option for the farmer to choose when he is under

pressure from the competing interests of his farming activities versus disposal of

effluent. If increased loading of the high rate area does occur it will result in increased

leaching of nutrients to groundwater and surface water. The Applicant needs to provide

some convincing details in the Application that he has considered and modelled these

types of scenarios.

68. The Applicant has identified that the use of fertiliser will continue for non-irrigated

areas within the LMU1 and LMU2 land area but has not identified what controls will be

in place. As the Applicant has assessed that the nutrient leaching from non-irrigated

areas will not change, comprehensive guidance and controls for the application of

fertiliser by the farm manager/operator will need to be in place. There is a

recommended Consent Condition to cover this.

69. The Application has not addressed how compliance with the proposed field capacity

controls of irrigation to IMU1 and IMU2 will be achieved. I consider that a combination

of weather monitoring and soil moisture probe monitoring will be required in order for

the applicant to maintain compliance with the proposed field capacity controls. The

procedures for the use of such monitoring equipment and data to operate the irrigation

system will need to be clearly laid out in order for compliance with these controls to be

achieved. There is a recommended Consent Condition to cover this.

70. The Applicant has identified that there may be some hydrophobicity in the proposed

high rate irrigation IMU3 areas but that this can be addressed. I agree that it can be

adequately addressed by ensuring the irrigation application rate is kept at a relatively

low rate per hour. The Applicant needs to cover this in the Management Plan to be

produced in evidence.

71. The Applicant has not addressed the issue of groundwater mounding due to irrigation

of IMU3 and the impact this could have on the low lying land areas adjacent to IMU3.

My concerns here relate to the potential for increased groundwater levels to reduce the

ability of the low land (currently shown as IMU 1 and IMU2) to accept the proposed

amount of irrigation. I am also concerned that if this were to occur, the farmer may



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elect to install some land drainage to overcome this which could lead to ‘short-

circuiting’ of irrigated effluent to surface water. Accordingly, I recommend a Consent

condition be included which will prohibit the construction of any land drainage in the

irrigated areas unless a hydrogeological assessment is first undertaken to assess the

effects.

72. In my experience irrigation of wastewater which has been retained in pipework

between irrigation events has the potential to cause offensive odours. As more than

one to two days is sufficient time for anaerobic conditions to occur I consider it likely

that the proposed irrigation will result in the discharge of some odours. However,

without details being provided by the Applicant as to the volume of effluent that could

become anaerobic it is hard to quantify the effects. I consider that a Consent condition

requiring there to be “no offensive odour to be produced” would be satisfactory. In the

event that offensive odour is produced, there are mitigation measures which can be

implemented by the Applicant such as, flushing lines with fresh water or draining the

lines of effluent after use. This is addressed further in the section 87F report of Mr

Curtis for MWRC and HDC.

F. DISCUSSION

73. I consider that a resource consent condition requiring the screening of influent

wastewater to the wastewater treatment plant should be included in the resource

consent.

74. The Applicant needs to ensure that the volume of effluent storage has been modelled

correctly and given that this is a key parameter, I consider that it should be peer

reviewed at the time of detailed design. Accordingly, I recommend a Consent

Condition to this effect.

75. Based on the confirmed storage requirements for the existing wastewater treatment

ponds, it is my view that the Applicant should advise how this storage will be achieved

and provide an assessment of how this augmentation will affect the treatment capacity

of the pond system and the leakage of wastewater from the pond system to

groundwater. Alternatively, since this information has not been provided by the

Applicant, I recommend Consent Conditions be included to cover it.



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76. While not part of the current suite of consent applications, it is my view that desludging

the wastewater ponds in 2017/2018 is relevant to the assessment of the leakage to

groundwater from the WWTP (the discharge for which consent is being sought) and

any impact on leakage rates and the resulting effect on the receiving environment

should be considered as part of the effects assessment. The Applicant has stated that

leakage will not exceed 160 m3/d and accordingly I recommend a Consent Condition to

this effect.

77. I believe there would be a definite benefit for the Applicant to provide some details as

to the lease agreement with the farm owner, particularly around how irrigation is going

to be managed and the potential conflict with farming activities, long term leasing

surety and mitigation options in the case of issues arising with the irrigation regime.

Land Application Management Plan

78. The Applicant will need to produce a Land Application Management Plan which will

discuss methodology of management and provide guidance and instruction to the

irrigation system and farm operator to ensure that compliance with the resource

consent is maintained. Accordingly, details about what the Management Plan shall

cover have been included in the Consent Conditions. I understand that the Land

Application Management Plan will be produced as part of the Applicant’s evidence and

not as a Section 92 response.

Monitoring Reports

79. It is good practice for any land irrigation scheme disposing of effluent to have a

monitoring report prepared by the operator and reviewed by an independent party

experienced in effects assessments and design and operation of land disposal

schemes. These reports shall be sent to the Regional Council Regulatory manager for

review.

Annual Monitoring Report; This report shall include( but not be limited to); inflows,

outflows, volumes irrigated to individual IMUs, nitrogen loading to each IMU,

groundwater and surface water quality data, effluent quality data, daily rainfall,

information around the daily measurements made by the operator to determine

irrigation scheduling, daily storage pond volume, comparison against consent

conditions, consideration/evaluation of the data and the relevance of it in terms of

effect, a description of any issues and how these have been/will be mitigated, any

proposed improvements or changes.



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Five Yearly Trend Report; This report shall include all the data from the preceding

4 years of data plus the 5th year information and analyse the data looking for trends

and effects. Preparation of this report should include a walk-over site visit by the

independent reviewer and onsite discussion with the operator to review how well the

system is operating.

Consent Conditions have been included which require these reports to be produced by

the Applicant.

G. CONCLUSIONS

80. Although the concept of complete discharge to land utilising the existing WWTP (plus

storage) is sound, I consider that the concerns with design and management/operation

of the proposed system identified in this report need to be addressed to ensure that the

proposed activity does not fail or become non-complying.

H. CONSENT CONDITION REVIEW AND RECOMMENDATIONS

81. My recommendations about Consent Conditions have been incorporated into the

proposed Conditions presented by Mr Mark St Clair.



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I. RELEVANT SUBMISSIONS ADDRESSED

Submission Summary Comment

5 Oppose application because of cultural and environmental impacts. States that TRToNW is under-represented. Specifically opposes consent term as “HDC have proven to exhibit poor compliance and initiatives”.

PDP will not address this submission as it is outside the scope of our assessment.

However, PDP has suggested a reduced consent term for the consent based on different concerns.

21 Has concerns around:

Lack of improvement to the treatment plant.

Lack of attention to reducing the volume of wastewater generated.

PDP has addressed need for improvements to Foxton WWTP.

PDP consider the concern around the lack of attention to reducing wastewater volumes to be reasonable and this has been addressed in the Consent Conditions.

41 Opposes discharge to surface water over three years. Suggests temporary land disposal system in interim 3 years.

Acknowledged that the applicant identified that the lining of existing ponds not practical, but suggests condition allowing 10 years for financing and construction of new pond.

PDP has not addressed this submission directly:

PDP does not consider the use of a temporary interim land disposal system to be practical.

Lining of existing ponds is related to effects on groundwater on surface water and therefore falls within other specialists assessments.

45 Calls for:

Term to comply with Common Catchment Renewal timing.

Review conditions requiring mitigation or cessation of discharges (land, water) if monitoring shows that the modelled effects on groundwater, soil, surface water, are significantly different to those actually measured.

PDP will not address this submission directly:

PDP will suggest a reduced term for the consent, but for different reasons to these.

The modelling of effects and conditions around this falls within other specialists assessments, however, PDP have outlined conditions requiring review of the land irrigation system and rigorous monitoring and reporting of land irrigation system operation.

58 Generally supports application but wants:

IMU2 to be deficit irrigation

IMU3 to be amended to resolve delayed groundwater effects.

WWTP inlet screening.

Treatment pond aeration

PDP will not address this submission directly:

IMU2 irrigation method and IMU3 irrigation and groundwater modelling is being assessed by other specialists.

PDP has addressed WWTP inlet screening.

PDP has addressed the need for improvements to WWTP (such as aeration) to maintain existing effluent quality.



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APPENDIX A: Photos of scum and gross solids build up within the Foxton WWTP and as

deposited in surrounding area (as provided by Logan Brown of MWRC on 19 April 2016).



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SECTION 87F REPORT OF ROBERT ALLEN DOCHERTY … · Prepared by Robert Docherty, Pattle Delamore...

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Transcript of SECTION 87F REPORT OF ROBERT ALLEN DOCHERTY … · Prepared by Robert Docherty, Pattle Delamore...