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SECTION 87F REPORT OF ROBERT ALLEN DOCHERTY … · Prepared by Robert Docherty, Pattle Delamore...
Transcript of 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
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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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.
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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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.
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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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.
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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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.
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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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%.
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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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.
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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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
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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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
Section 87F Technical Hearing Report
Application No. APP-2006012045.03 Horowhenua District Council Prepared by Robert Docherty, Pattle Delamore Partners Limited, 14 June 2016
10
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.
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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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.
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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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.
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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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.
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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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
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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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
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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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.
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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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.
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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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.
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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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.
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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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
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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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.
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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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.
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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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.
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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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.
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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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).
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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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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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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