Foxton Wastewater Treatment Plant

Prioritisation of Land for Wastewater Land Treatment

(LEI, 2014:A2)

Prepared for

Horowhenua District Council

Prepared by

November 2014

Foxton Wastewater Treatment Plant Prioritisation of Land for Wastewater Land Treatment (LEI, 2014:A2)

Horowhenua District Council

This report has been prepared for the Horowhenua District Council by Lowe Environmental Impact (LEI). No liability is accepted by this company or any employee or sub-consultant of this company with respect to its use by any other parties.

Quality Assurance Statement

Task Responsibility Signature

Project Manager: Hamish Lowe

Prepared by: Katie Beecroft, Sian Cass, Phil Lake Reviewed by: Hamish Lowe

Approved for Issue by: Hamish Lowe

Status: Final

Prepared by :

Lowe Environmental Impact Ref: Foxton_WWTP -A2_Land_Prioritisation - P O Box 4467 FINAL.docx Palmerston North 4442 Job No.: 10 172 | T | [+64] 6 359 3099 | E | [email protected] Date: November 201 4 | W| www.lei.co.nz

TABLE OF CONTENTS

TABLE OF CONTENTS ...... 2

1 EXECUTIVE SUMMARY ...... 1

2 INTRODUCTION ...... 3

2.1 Purpose ...... 3

2.2 Background ...... 3

2.3 Scope ...... 3

3 DESIGN PARAMETERS FOR WASTEWATER DISCHARGES ...... 4

3.1 General ...... 4

3.2 Resource Assessment ...... 4

3.3 Land Application Area for Assessment Purposes ...... 4

4 LAND APPLICATION ASSESSMENT METHODOLOGY ...... 5

4.1 Process Overview ...... 5

4.2 Parameters ...... 5

4.3 Development of Zones ...... 6

4.4 Aggregation of Rating Results ...... 8

5 ASSESSMENT PARAMETERS ...... 9

5.1 General ...... 9

5.2 Land Use Attributes ...... 9

5.3 Soil Attributes ...... 9

5.4 Hydrological and Hydrological Attributes ...... 10

5.5 Summary ...... 12

6 PARAMETER ASSESSMENT ...... 13

6.1 General ...... 13

6.2 Nutrient Uptake Potential ...... 13

6.3 Soil Drainage and Permeability ...... 13

6.4 Soil Depth to Restrictive Layer ...... 13

6.5 Soil Slope and Stability ...... 14

6.6 Mounding Risk ...... 14

6.7 Flood Return Interval ...... 14

6.8 Rating Summary ...... 14

7 ASSESSMENT SUMMARY ...... 15

8 FOXTON ...... 16

8.1 General ...... 16

8.2 Land Near Foxton WWTP ...... 16

8.3 Land for Further Investigation ...... 16

9 CONCLUSIONS AND RECOMMENDATIONS ...... 17

9.1 Assessment Conclusions ...... 17

9.2 Recommendations ...... 17

10 REFERENCES ...... 18

11 APPENDICES...... 19

1 EXECUTIVE SUMMARY

Horowhenua District Council (HDC) operates the Foxton wastewater treatment plant (FWWTP). The FWWTP currently discharges its treated effluent to Foxton Loop, a former meander of the Manawatu River, and requires resource consents to replace the existing discharge consents.

In 2012, HDC examined potential land treatment options for the wastewater discharges from each of the district’s municipal WWTPs. Lowe Environmental Impact (LEI) were engaged to identify a prioritised list of land treatment and potential storage areas for the general areas of Levin, Shannon, Foxton and Foxton Beach; this resulted in a report (LEI 2012) containing maps showing the land treatment suitability of the land within a 10 km radius of each Horowhenua township. As part of the re-consenting process for the FWWTP, this report presents the land prioritisation details relevant to the FWWTP from that report, and includes a more focussed desk top assessment of land within a 5 km radius of FWWTP.

The process undertaken to determine the ability of areas around Foxton to receive wastewater is summarised as follows:

The parameters selected for assessment of land application sites in the Foxton area are given below. The parameters are all weighted equally and include:

• Land use; o Nutrient uptake. • Soil attributes; o Soil drainage and permeability. o Depth to restrictive layer. o Slope and stability. • Hydrological and hydrogeological attributes;

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o Mounding risk. o Flood return interval.

This desktop assessment method has been used as a first step in the design process for a wastewater application to land scheme(s). Additional stages are required to supply detail about preferred land areas and project engineering considerations, such as reticulation routes and costs. The additional information contains a level of detail which is not considered feasible or appropriate for a desktop assessment of regional suitability for land application of wastewater. Recommendations are given below for the progression of additional work to determine an appropriate location and application regime.

The investigation undertaken as part of this report concluded that, in general, there is suitable land available for the establishment of a land treatment system for the Foxton discharges. Extensive areas of land in the vicinity of Foxton and Foxton Beach indicate that pursuing land within the Zone A areas should be the first choice for HDC, subject to consideration of the impact of groundwater levels on land application feasibility.

This report provides a large scale view of land treatment suitability near Foxton and Foxton Beach. The next step in selecting land to pursue for the development of a land treatment system is to limit the land areas examined. In selecting the areas for further investigation, information from the preceding reports (land assimilative capacity, discharge scenarios) should be incorporated. Within the selected areas the following should be considered: • Land parcel sizes and ownership; • The impact of shallow groundwater limitations; • Special use considerations i.e. known heritage sites; and • Approximate reticulation routes.

From the completion of this stage the project moves from a desktop investigative approach to incorporation of design and cost elements. It is recommended that stakeholders are consulted, in particular Horizons, to enable the approach taken to date to be discussed and in-principle agreement with the approach to be sought.

Based on the outcomes of this report it is recommended that land adjacent to the FWWTP be examined. Land directly south of the Manawatu River mouth and north to north-east of Foxton should also be examined further.

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2 INTRODUCTION

2.1 Purpose

The purpose of this report is to: • Identify locations in the general area of Foxton and Foxton Beach which are theoretically suitable for land application; • Determine limitations to land application in the areas; • Map land areas showing their prioritisation for land application suitability; and • Identify preferred locations for land application of Foxton wastewater for further detailed investigation.

2.2 Background

Horowhenua District Council (HDC) is responsible for the provision, operation and maintenance of reticulated wastewater treatment systems for Levin, Shannon, Foxton and Foxton Beach.

HDC have been examining potential options for the long-term improvement of its wastewater discharge including the establishment of land application schemes. Lowe Environmental Impact (LEI) was engaged in 2012 to investigate the suitability of sites within a 10 km radius of each town’s WWTP for land application of treated municipal wastewater.

2.3 Scope

This report presents the results of a desktop investigation of existing land resource information to establish priorities for consideration of land treatment options. The key considerations for land treatment prioritisation include limitations resulting from soil types, slopes, and proximity to water. The report details:

• Section 3 summarises the land treatment system design parameters; • Section 4 describes the methodology for evaluating the suitability of areas; • Section 5 details the assessment parameters; • Section 6 summarises the assessment for the key parameters; • Section 7 details the results of the investigation and identifies suitable areas for land treatment within a 10 km radius of Foxton and Foxton Beach; • Section 8 examines the area within a 5 km radius of FWWTP in more detail; and • Section 9 gives conclusions and recommendations for the direction of further investigations.

No consideration has been given to land availability, and no field investigations to verify the accuracy of the mapped information have been undertaken.

This investigation is to identify if land is potentially suitable for land treatment, prior to further investigation. Prior to final selection suitable locations identified in this report should be subject to a site investigation to verify the characteristics pertaining to that site and required of a land application system.

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3 DESIGN PARAMETERS FOR WASTEWATER DISCHARGES

3.1 General

The use of land application for wastewater discharge can be an alternative to WWTP upgrades, such that the land is used as a form of treatment reducing the extent of any treatment plant upgrade required. It is therefore considered appropriate to base the land treatment assessment on current wastewater characteristics. Characteristics considered in the design include: • Flow parameters; • Population growth and flow projections; and • Wastewater quality.

Relevant characteristics for wastewater from the FWWTP are summarised in: • Land and Water Discharge Scenarios – LEI, 2012.

3.2 Resource Assessment

Typically a broad scale assessment of the investigation area, including discussion of the underlying geology, climate, topographical assessment and hydrology, amongst others, would be undertaken to give information about the setting for a land treatment scheme. Due to the scale of the investigation area this step has been excluded. It is recommended that a resource assessment is included as part of subsequent investigation stages following the narrowing of the search area.

3.3 Land Application Area for Assessment Purposes

The scenarios previously reported for the Foxton and Foxton Beach discharges identified approximate land areas needed for each discharge scenario. This report focuses on land treatment as distinct from land disposal. Land areas required for each community range from:

• Foxton, 20 – 125 ha; and • Foxton Beach, 2 – 43 ha.

These areas include an allowance for boundary setbacks.

It should be noted that the land areas given above are for assessment purposes only. There may be other parameters, such as nutrients and land use which may influence this land area requirement, but this depends on the system design and management.

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4 LAND APPLICATION ASSESSMENT METHODOLOGY

4.1 Process Overview

The process undertaken to determine the ability of areas within an initial 10 km radius of Foxton and Foxton Beach and then within a more focussed 5 km radius of the FWWTP to receive wastewater is outlined as follows:

Details of the process are given below.

4.2 Parameters

There are a wide range of parameters which influence the ability of a land treatment site to receive wastewater. The selection and interpretation of assessment parameters may vary due to location specific challenges or advantages.

The relative importance of the various parameters varies and in many cases is subjective. However, there is a need to consider the collective suitability of a particular site based on the merits of each parameter, and this is achieved using a weighted scoring system whereby each parameter is given a percentage (the weighting), which indicates its importance relative to other parameters. Each location within the investigation area is given a score for each parameter from 1 to 5 based on suitability, with 1 being least preferred for land application and 5 being most preferred. This then enables sites to be compared.

Land within a radius of 10 km from each of the communities has been identified and is referred to as the Investigation Area. The characteristics of land in this Investigation Area is variable, and can be broadly described as having the following landforms:

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• Peat Country - in isolated pockets east of Foxton are areas of peat, which has been made available for cultivation following the draining of flax swamps. Surface drains allow these areas to be used for dairy farming and the growing of root vegetables; in particular potatoes. • Alluvial Flats – are areas where silt material has settled following Manawatu River flooding. These areas occupy an area to the between Shannon and the eastern and southern sides of Foxton. Surface and subsurface drainage is used to lower the shallow groundwater and allow them to be used for dairy farming and the production of vegetable crops. Some cereal is also grown, including green feed maize. • Sand Country – is typically coastal areas confined by State Highway 1 and the Tasman Sea. However, large long dunes exist some 13 km inland, occupying an area north-east of Foxton. Within 1 km of the coast the soils are poorly developed and free draining. Further inland drainage limitations occur in interdune locations, giving rise to coastal dune lakes between the coast and State Highway 1. These areas are used for forestry, low producing animal grazing, and when irrigated, dairy farming.

A range of parameters can be applied to the land forms as listed below.

• Land use; o Nutrient uptake. • Soil attributes; o Soil drainage and permeability. o Depth to restrictive layer. o Slope and stability. • Hydrological and hydrogeological attributes; o Mounding risk. o Flood return interval.

The parameters are described in more detail in Section 6.

The weighting applied may be altered based on feedback from HDC and stakeholders, but at this stage an equal weighting has been applied. Consultation regarding the weightings could be undertaken with stakeholders. This will help to identify the highest and lowest rated issues for stakeholders and may assist to stimulate discussion regarding the most feasible outcomes. However, the technical aspects of the parameters may not be fully understood by the stakeholders.

As part of a more detailed examination which includes some field investigation the following parameters should also be considered:

• Reticulation requirements (distance and elevation); • Land area available; and • Special use locations (archaeological, historic, water take, etc.).

Following the addition of these parameters it may be more appropriate to consult with stakeholders and modify the weighting system used. However, the analysis required to complete these layers is substantial and it is considered that these parameters should be examined following initial identification of preferred areas.

4.3 Development of Zones

When the weighted scores from individual parameters are grouped they provide a total that can be compared with totals of parameters from different locations. To help rank the suitability of

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the parameter totals at individual locations they can be grouped, and in this case the groupings are called Zones. Five Zone groupings have been used and are:

• Zone A – No significant limitations are experienced within areas of this rating zone. Zone A represents the preferred zone for siting of a land treatment system; • Zone B – Minor limitations are experienced within areas of this rating zone. Zone B is likely to be well suited for land treatment; • Zone C – Some limitations are experienced within areas of this rating zone. Zone C is suitable for land treatment when appropriately managed; • Zone D – Significant limitations are experienced within areas of this rating zone. Land treatment is likely to be possible within Zone D however costs and management requirements are expected to be greater than other zones; and • Zone E – Severe limitations to land treatment are experienced within areas of this rating zone. It is likely that cost and management requirements would be prohibitive to the establishment of land treatment in Zone E.

A GIS based approach has been used to develop zones, effectively resulting from an aggregation of the parameter scores. In GIS terms this is known as combining layers. This allows a continuous assessment of individual points on a map to be compared; which may not necessarily reflect a transition between any one individual parameter score (layer).

Table 1 summarises the implications of the Zones for land application system design.

Table 1: Zone Suitability Zone Suitable for A Requires smaller land area High value and/or short rotation crops Non-deficit irrigation Greater number of irrigable days High rate of nutrient removal Routine cultivation and harvest B High value and/or short rotation crops Non-deficit irrigation or partially deficit irrigation Can irrigate in shoulder seasons (April, May, September, October) for drier than average years Moderately high rate of nutrient removal Short withholding period for grazing or cultivation and harvest C Pasture or restricted range of annual crops Predominantly deficit irrigation Larger land area requirement Withholding period prior to grazing or cultivation and harvest is extended D Plantation forestry, pasture, shallow rooting crops Deficit irrigation over summer months Low nutrient loading Limitation to cultivation and harvest Extended withholding period for stock trafficking E Requires largest land area Conservation plantings Low deficit irrigation for short season No cultivation, infrequent harvest.

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4.4 Aggregation of Rating Results

As mentioned above, a score has been applied to each parameter (as represented by GIS layers). This allows a graduated map to be produced which shows how the individual parameter score varies over an area. The maps for each parameter are presented in Appendix A, Figures 1 to 7.

The individual parameter maps can be aggregated to produce a map which shows the summation of the combined parameters. Rather than a continuation of totals over a map, the totals are grouped into Zones, as discussed above. The combined Zone map, indicating greatest to least preference for land application, is shown in Appendix A, Figure 8. A map of the combined results for a more focussed 5 km radius of the FWWTP is shown in Appendix A, Figure 9.

The limits assigned for each zone are based on a judgemental estimate of suitability for land application of wastewater.

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5 ASSESSMENT PARAMETERS

5.1 General

The parameters listed in Section 4 are described below and the method for rating the land within the Horowhenua District investigation areas are given.

5.2 Land Use Attributes

The land use of any site indicates both: a) The potential for nutrient removal from the site; and b) Limitations for the establishment of a land treatment system due to the acceptability of certain crops and land management practices receiving wastewater from a municipal source.

The existing land use of sites within the investigation area was determined from the LINZ land use database. The data was current at June 2010. It is acknowledged that some change in land use is likely to have occurred in the ensuing time but the data used is considered to provide sufficient certainty for this desktop assessment. Land use parameters considered are as follows.

Nutrient Uptake The land cover type and land management practices adopted on any site are an indicator of the sites ability to remove nutrients applied as wastewater. Sites in the investigation area are scored as given in Table 2.

Acceptability Food safety issues and public health perceptions create limitations to land treatment of wastewater. The intention of HDC is that land will be purchased, rather than leased. This means HDC have the ability to change the land use in accordance with land use acceptability for receiving wastewater. This parameter has therefore not been included in the assessment of suitability.

Table 2: Land use parameter scores Land Use Class Nutrient uptake score 71 – Natural forest 2 72 – Pre-1990 planted forest 2 73 – Post 1989 forest 2 74 – Grassland with woody biomass 3 75 – Grassland, high producing 5 76 – Grassland, low producing 3 77 – Cropland, perennial 4 78 – Cropland, annual 4 79 – Wetland, open water 0 81 - Settlements 1, 4 (reserves)

5.3 Soil Attributes

The soil is the primary receiving environment for applied wastewater and is the final treatment process for renovating the wastewater. The capability of the soil to:

a) Avoid transmittance of wastewater derived contaminants to the wider environment; and

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b) Effectively recover the nutrient resource within the wastewater for plant and biota use is key to the successful development of a land treatment scheme. For the purpose of rating the land in the investigation area soil parameters assessed are given below.

It should be noted that a number of the data sets were created in the 1970s and 1980s and so may have changed due to drainage schemes and other large scale works. Following the prioritisation of land areas, it may be necessary to confirm or review data on-site.

Soil Drainage and Permeability Soils ability to drain is a function of soil texture and soil structure. Data for the investigation area comes from the Fundamental Soil Layer (FSL, LRIS portal) and has a scale of 1:50,000. Areas are scored as follows:

• 5 – Well drained; • 4 – Moderately well drained; • 3 – Imperfectly drained or excessively drained; • 2 – Poorly drained; and • 1 – Very poorly drained.

Depth to Restrictive Layer Restriction to water passage may be due to soil pans, rocks or groundwater. Data is from the FSL and has a scale of 1:50,000. Areas are scored as follows:

• 5 – >1.50 m; • 4 – 1.20 – 1.49 m; • 3 – 0.90 – 1.19 m • 2 – 0.60 – 0.89 m; • 1 – 0.45 – 0.59 m; and • 0 – <0.44 m.

Soil Slope and Stability In the absence of suitable flat land, steeper land may be used for wastewater irrigation, it requires specific design to manage the risk of slope movement under moist soil conditions. Data for the investigation area comes from the Land Resource Inventory (LRI, LRIS portal) and has a scale of 1:50,000. Areas are scored as follows:

• 5 – Slope class A (0-3°); • 4 – Slope class B (4-7°); • 3 – Slope class C (8-15°); • 2 – Slope class D (16-20°) and E (21-25°); and • 1 – Slope class F (26-35°) and G (>35°).

5.4 Hydrological and Hydrological Attributes

The prevention of wastewater derived contaminants entering water (surface or ground) is a key environmental objective of land treatment system design. It is of lesser concern in a land disposal system. The main mechanisms for transport to water are drainage to groundwater and direct surface water discharge i.e. by overland flow or flooding. The system should be designed to avoid overland flow and ideally excessive drainage volumes if land disposal is to be avoided. The likelihood of insufficiently treated wastewater entering water is reduced by:

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a) Avoidance of sites with a high groundwater table; and b) Avoidance of sites with a high risk of flooding.

In addition, the hydraulic properties of the shallow groundwater can influence the impact that the increased drainage volume can have and so must be considered. Land areas have been assessed as follows.

Depth to Seasonal High Groundwater Table The ability to treat and disperse applied wastewater is limited by the available unsaturated soil volume i.e. depth to groundwater. The investigation area can been scored based on piezometric surface data from Horizons Regional Council (HRC). A map of the piezometric surface across the investigation area indicates that seasonal high groundwater levels are unlikely to be a limiting factor over most of the investigation area.

However, field experience within the general area suggests that seasonal saturation at comparatively shallow depths occurs in the parts of the investigation area but is not reflected in the HRC piezometric surface mapped. As a result the information available for review is considered to be of a scale which is insufficient for this assessment. Consequently scores for the depth to seasonal high groundwater parameter have not been included in the aggregated mapping.

Depth to restrictive layer (Section 7.1.4) is considered to adequately describe the depth to a saturated layer since it includes saturation due to a perched water table where that occurs.

Mounding Risk The rate at which groundwater moves, both horizontally and vertically influences the mixing and transport of drainage from soil. If the rate of movement is slow there is a potential for mounding of the piezometric surface to occur. This may cause a localised elevation of the groundwater table and may influence the flow of groundwater beyond the application site. The investigation area has been scored for mounding risk as follows:

• 5 – Transmissivity of groundwater >2000 m2/day; • 4 – Transmissivity of groundwater 1000-2000 m2/day; • 3 – Transmissivity of groundwater 500-1000 m 2/day; • 2 – Transmissivity of groundwater 200-500 m2/day; • 1 – Transmissivity of groundwater 50-200 m2/day; and • 0 – Transmissivity of groundwater <50 m2/day.

Flood Return Interval Flooding of a land treatment site causes: • Loss of soluble applied nutrients; • Potential loss of nutrient laden sediment; • Damage to crops and soil quality; • Damage to irrigation infrastructure; and • Reduction in number of irrigable days.

The areas are scored based on the FSL Flood Return Interval as follows:

• 5 – Nil risk; • 4 – Slight risk = <1 in 60 y; • 3 – Moderate risk = 1 in 20 y to 1 in 60 y;

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• 2 – Moderately severe risk = 1 in 10 y to 1 in 20 y; • 1 – Severe risk = 1 in 5 y 1 in 10 y; • 0 – Very severe risk = >1 in 5 y.

5.5 Summary

The described parameters when combined are considered to give a qualitative assessment of areas suitable for land application of wastewater at any point within the investigation area.

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6 PARAMETER ASSESSMENT

6.1 General

Assessment of each parameter has been undertaken as described in Section 5. Maps for each parameter and for the aggregated maps are provided in Appendix A and the results and trends shown are detailed below. Figure 1, Appendix A defines the Investigation Area.

6.2 Nutrient Uptake Potential

Figure 2, Appendix A, gives a map of nutrient uptake potential based on current land use. Extensive areas, from the base of the Tararua Ranges westward to the sea, excluding directly along the coast, are well suited to wastewater application for the purpose of nutrient removal.

It is unlikely that a land application scheme will be limited by nutrient loading if a high removal cropping regime is managed on a site within these areas. Areas scored as 2 (green areas) are predominantly forested corresponding to a lower rate of nutrient removal. Yellow areas occur in cropping locations and are based on the seasonality of nutrient removal and fallow or low uptake periods during cropping.

6.3 Soil Drainage and Permeability

Figure 3, Appendix A, gives a map of soil drainage for the investigation area. Well drained areas (orange) occupy land around Levin corresponding to the Ohau gravels, and to the coastal dunes. Well drained areas also occur along parts of the Tokomaru terrace land above the communities. Imperfectly drained areas (blue) occur where the Tokomaru Terrace finishes, in the steep and incised drop to the Manawatu surface.

Extensive areas of the Manawatu River plain have poorly drained soils, due largely to the fine soil texture and poor structure. Very poorly drained soils occur in the Opiki Basin which is dominated by Peat.

Coastal sand country south of the Manawatu River mouth is typically well drained. At the boundary of the coastal sands and inland sediments springs occur leading to the formation of the coastal peat lakes, and these areas are imperfectly drained.

North of the Manawatu River mouth the coastal sand country is less well suited to land treatment of wastewater due to the presence of excessively drained dune sand interspersed with low lying areas of high groundwater, forming in some cases, coastal lakes.

Areas directly adjacent to water ways typically are more free-draining, however these areas may be discounted for other reasons such as risk of discharge to the waterway.

6.4 Soil Depth to Restrictive Layer

Figure 4, Appendix A gives a map of soil depth to a restrictive layer. In general the sand country is not limited by depth. Foxton and Foxton Beach have extensive areas surrounding them which have no depth restrictions.

It is important to recognise the purple areas around Foxton and close to the Manawatu River that are likely to have a high water table and be flood prone.

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6.5 Soil Slope and Stability

Figure 5, Appendix A, gives a map of slope. Extensive areas of the Horowhenua are classified as stable having flat to undulating slopes. There is no risk for adverse effect such as overland flow, due to slope and very little risk due to stability issues such as gullying or sheet erosion as a result of material grading and continuous land cover. Some sandy areas identified in green may experience movement due to poor aggregation and structural stability of the soils.

Areas corresponding to low slope are present near to all the communities. Therefore land slope is unlikely to be limiting for land treatment design.

6.6 Mounding Risk

Figure 6, Appendix A, indicates the rate of subsurface water movement in the investigation area. In general the risk of mounding occurring at a site follows the same trend as for the depth to a restrictive layer.

Water moves quickly in the sand country and the risk of mounding is not likely to be limiting if there is sufficient depth to groundwater. However, if groundwater is close to the surface and has a flat hydraulic gradient then mounding may be a problem.

6.7 Flood Return Interval

Figure 7, Appendix A, gives a map of the flooding risk in the investigation area as indicated by the flood return interval. In general most of the area has a low flooding risk. Higher levels of flooding exist around the Manawatu River with some areas designated as spillways when the Manawatu River reaches high river levels.

It is noted that drainage schemes have been initiated or extended in the period since the data used in this assessment was compiled, and so the flooding risk may be less in some cases than indicated on the map. It is recommended that this is assessed in further detail for preferred land areas.

6.8 Rating Summary

The parameters examined indicate that there are areas likely to be suitable for land treatment of wastewater. Different areas are constrained by different parameters. The relative suitability of areas for wastewater land treatment can be determined by aggregating the scores for each parameter as described in Sections 4.3 and 4.4 above.

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7 ASSESSMENT SUMMARY

As described above, the scores for the parameters can be combined to create zones representing the suitability of the land in the Investigation Area for land treatment of wastewater. It should be noted that the key parameters that have been combined are considered to be intrinsic, or unable to be altered easily and include: • Soil drainage; • Soil depth to restrictive layer; • Dominant slope; and • Flood return interval.

The land use parameter (nutrient uptake potential) has the potential to be altered by land management factors i.e. crop choice, irrigation rate, and so that parameter has not been included in determination of zones.

Figure 8 shows the aggregated zones. There are significant areas of Zone A land, having properties that are well suited to land treatment of wastewater, within the Investigation Area. The Zone A land typically corresponds to the coastal sand country. Foxton and Foxton Beach have a large amount of suitable land near to the settlements. This includes land between the Moutoa Spillway and the River, and the spillway itself.

Areas of Zone A land have the fewest limitations for design of a land application system, and can be expected to support higher rates of irrigation for a greater number of days annually than in other zones. Restrictions to plant growth are typically absent in Zone A land and so the choice of crops to grow, and correspondingly the ability to sequester or remove applied nutrients is high. As a result smaller land areas are typically needed to discharge a volume of wastewater as compared to other land Zones.

Areas of Zone D land are limited in their capacity to receive and treat applied wastewater. Where the limitation is slope, Zone D land is suitable for low input crops such as plantation forestry and extensive pasture. In the lower Manawatu the predominant limitation for Zone D land is wetness, whereby soil drainage is slow and the depth to saturation is less than 1 m over winter. This Zone D land is best suited to shallow rooting crops such as pasture. Deficit irrigation is recommended, and where cultivation and harvest is undertaken irrigation should be stopped sufficiently prior to vehicle traffic on the site to allow soil to attain a moisture deficit.

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8 FOXTON

8.1 General

The maps originally produced evaluate a large area based on 10 km radius circles around each Horowhenua community. A more detailed look at land within a 5 km radius of the FWWTP has also been undertaken.

8.2 Land Near Foxton WWTP

Within a 5 km radius of the FWWTP there is a mix of land as represented by different zones. Figure 9 shows a 5 km area surrounding the FWWTP and includes cadastral boundaries of each lot.

Zone A (green) land is predominant. This land is well suited to land treatment with few limitations, but the low lying nature of the coastal Foxton area is often associated with shallow groundwater that is not described or mapped with certainty by the parameters used for this desktop assessment; care will be required to assess groundwater and any other restrictions for land parcels when undertaking more detailed site investigations. Zone B occupies most of the remaining land close to the Manawatu River. The limitations are often relative to the shallow groundwater and poor drainage. These conditions would have to be carefully managed with wastewater applications.

The land parcels directly adjacent to the FWWTP range between 85 to 130 hectares. Two parcels would more than accommodate the maximum land requirements for both Foxton and Foxton Beach with low costs associated to the small reticulation distance.

8.3 Land for Further Investigation

Areas of Zone A land are most preferred and should be investigated in greater detail. The primary location would be close to the FWWTP, however land directly south of the Manawatu River mouth and north to north-east of Foxton should also be examined further.

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9 CONCLUSIONS AND RECOMMENDATIONS

9.1 Assessment Conclusions

In general there is suitable land available for the establishment of a land treatment system for each of the Horowhenua communities. Extensive areas of land in the vicinity of Foxton and Foxton Beach indicate that pursuing land within Zone A areas should be the first choice for HDC, subject to consideration of the impact of groundwater levels on land application feasibility.

Foxton Foxton and Foxton Beach have plenty of options to select suitable land for wastewater application. Land zoned both A and B, although identified with minor limitations, may have a high water table and poor drainage that makes some areas less desirable when better options are close by.

9.2 Recommendations

This report provides a large scale view of land treatment suitability near Foxton and Foxton Beach. The next step in selecting land to pursue for the development of a land treatment system is to limit the land areas examined. In selecting the areas for further investigation information from the preceding reports (land assimilative capacity, discharge scenarios) should be incorporated. Within the selected areas the following should be considered: • Land parcel sizes and ownership; • The impact of shallow groundwater limitations; • Special use considerations i.e. known heritage sites; and • Approximate reticulation routes.

From the completion of this stage the project moves from a desktop investigative approach to incorporation of design and cost elements. It is recommended that stakeholders are consulted, in particular Horizons, to enable the approach taken to date to be discussed and in-principle agreement with the proposed forward approach.

Based on the outcomes of this report it is recommended that land adjacent to the FWWTP is examined in further detail.

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10 REFERENCES

Lowe Environmental Impact (2012). Horowhenua District Prioritisation of Land for Wastewater Land Treatment

Lowe Environmental Impact (2012). Land and Water Discharge Scenarios

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11 APPENDICES

Appendix A Figures

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APPENDIX A

Figures

Figure 1: Investigation area and sites for further investigation Figure 2: Land use – Nutrient uptake potential Figure 3: Soil – Drainage Figure 4: Soil – Depth to restrictive layer Figure 5: Soil – Slope and stability Figure 7: Hydrological – Flood return interval Figure 8: Land treatment suitability zones Figure 9: Foxton land treatment suitability zones

FIGURE 9 LAND TREATMENT SUITABILITY FOXTON WWTP