of applications pursuant to the Resource Management Act 1991 Matamata Metal Supplies

Transcription

1 IN THE MATTER of applications pursuant to the Resource Management Act 1991 BY Matamata Metal Supplies FOR Stormwater discharge consent for a quarry operation at Barton Road, Okauia STATEMENT OF EVIDENCE (Stormwater Infrastructure) Chris Hardy 7 November 2018

2 INTRODUCTION 1. My full name is Christopher Allington Hardy. 2. I hold the qualification of BE (Civil) from the University of Auckland, 2003, and NZCE (Civil) from the Waikato Polytechnic, I am a Associate Director at AECOM Hamilton. I have held a position with AECOM since Prior to that I worked as a civil engineer with MWH NZ Ltd. I have 18 years of experience as a civil engineer working on stormwater, water and wastewater (three waters) networks. 4. I have read the Code of Conduct for Expert Witnesses contained in the Environment Court Practice Note 2014 and have complied with that practice note in preparation of this evidence. I agree to comply with it in presenting evidence at this hearing. The evidence that I give is within my area of expertise, except where I have stated my reliance on other identified evidence. I have considered all material facts that are known to me that might alter or detract from the opinions that I express in this evidence. SCOPE OF EVIDENCE 5. I have been retained by J Swap Contractors Ltd. to provide stormwater infrastructure advice relating to the consent applications by Matamata Metal Supplies Limited (the applicant). 6. I have been involved in stormwater planning at a number of J SWAP and other quarries in the Waikato in the past 10 years including Osterns Quarry (J Swap), Hyndmans Quarry (J Swap), Waitawheta Quarry (HG Leach) Tahuna Quarry (HG Leach) and Matatoki Quarry (HG Leach). I have been involved in the development of an updated stormwater management plan for the Matamata Metal Supplies site since The purpose of this statement of evidence is to outline the application relating to stormwater infrastructure at the site and consideration of submissions in this regard. 8. My evidence covers: a. Overview of the key aspects of the site stormwater system b. Proposed infrastructure and operational improvements c. Response to the Officer s report d. Response to submissions Page 2

3 9. In preparing this evidence I have reviewed the following: a) s42 Officers report received 29 October 2018 (inclusive of submissions received) OVERVIEW 10. The quarry site is located on the western side of the Kaimai Range. Topography at the site is steep and characterised by a number of small tributary streams of the Mangapiko Stream. 11. The quarry features three distinct stormwater management areas in terms of location and elevation from highest to lowest as follows 1 : a) Quarry pit b) Quarry haul road c) Processing and stockpiling area 12. The quarry also operates a number of overburden areas. The overburden areas are separate from the main operation in terms of stormwater and are implemented using temporary and adaptable stormwater measures in accordance with Waikato Regional Council sediment control guidelines. 13. The quarry pit is bypassed by three stream diversions that minimise the catchment to the pit. Runoff into the pit is contained and discharges to ground via soakage. 14. The upper haul road and adjacent closed overburden areas discharge to a stormwater settlement pond (Pond A) located adjacent to a farm access road that runs beside the haul road. The farm access road formation provides a flat bench on which Pond A is located. Topography above and below the pond is very steep and limits the extent to which Pond A can be expanded or relocated. Pond A discharges downslope through open paddocks into the Mangapiko Stream. 15. Pond A is currently a long and narrow pond with multiple weirs separating the pond into five sections. The pond currently has two inlets, one of which is some distance down the length of the pond, and no inlet forebays or chemical 1 Refer to plan CI-0003 as Attachment A for the location of the management areas, stormwater subcatchments, and diversions. Page 3

4 treatment. The pond outlet structure has a low level orifice outlet that does not decant water from the top of the pond. 16. In its current configuration as outlined above Pond A may only operate adequately during initial rainfall and very low flows. During higher runoff or sustained rainfall the pond is likely to have high velocities due to its narrow width and also turbulent flow at the downstream inlet and across the weirs. High velocities and turbulence will keep sediment mobilised (or remobilise it). The low level orifice outlet will not discharge water from the optimal surface level of the pond if the outlet is submerged. 17. The lower haul road falls to a roadside drain with intermittent sediment pits that remove coarse sediment prior to discharge into grassed paddocks via two cross culverts. 18. The processing area is bypassed by an ephemeral stream diversion that is piped under the site. A natural tributary passes the processing area to the north and has several access road culverts associated with the quarry haul road and an adjacent farm access road. 19. Runoff from the upper processing area discharges to a holding pond that also receives process wash water. Holding pond water is treated in a Lamella treatment unit which uses gravity settlement with the addition of chemical flocculants to remove sediment from the stormwater and discharge it to a holding pond as concentrated slurry from the base of the unit. Clean water is siphoned off the top of the Lamella unit and discharged into Tributary C adjacent to the Processing Area. 20. When the holding pond is full it is emptied and disposed of in the quarry pit or in the overburden disposal areas where it is confined and dried. 21. Runoff from the lower processing area discharges to a stormwater settlement pond (Pond B) located at the lowest point in the quarry site near the site entrance. Pond B formerly discharged into a minor overland flow path crossing farmland and eventually discharging to a tributary of the Mangapiko Stream. The pond has recently been reconfigured to discharge to the Lamella holding pond as part of upgrades discussed below. 22. Quarry pit stormwater catchment is not covered further in my evidence because runoff is captured and retained without discharge from the pit. Runoff entering the pit is stored and is only discharged by soakage so all sediment is retained within the pit. Page 4

5 23. The proposed improvements discussed below relate to the Haul Road and Processing Area catchments and discharges. EXISTING OPERATION AND PROPOSED IMPROVEMENTS 24. The quarry stormwater system has been operated mainly using simple sediment ponds and sediment pits. Such simple types of measures suited the quarry operation because the steep nature of the site results in rapid changes in landform with development over short periods. Ponds and sediment pits could be moved or added to reasonably easily. 25. The processing operation was a fixed installation so a permanent mechanical treatment facility (the Lamella Treatment Plant) could be installed at that location without the need to move it. 26. The location and operation of the two main sediment ponds (Pond A and Pond B) and the haul road drains have not changed since I first visited the site in Changes in the quarry landform during the period since 2012 have been either contained within the quarry pit water shed or associated with new overburden areas away from the main operational areas. Remote overburden areas are serviced by their own temporary sediment treatment devices. 27. Clean water diversions divert clean water away from dirty water areas to minimise contaminated runoff volumes and reduced the volume load on treatment devices. Clean water stream and overland flow diversions have been used for the quarry pit and processing areas but are more difficult to achieve for the haul road due to topography. 28. Wet weather sampling was undertaken by Waikato Regional Council on 10 July The results of the sampling showed that discharges from Pond A (1520 mg/l) and Pond B (410 mg/l) are not complying with current consent requirements for suspended solids concentration which is required to be less than 100 mg/l. 29. Transitional changes to the operation of Pond B were undertaken following the wet weather sampling and are outlined in Section 48 and 49 below. 30. Further upgrades and changes in the operational regime of both ponds are proposed to improve their performance. The proposed upgrades are described in the Site Stormwater Management Plan and are summarised below. HAUL ROAD Page 5

6 31. The upper quarry haul road discharges to Pond A and will continue to do so. 32. The lower quarry haul road will be diverted direct to the Lamella Plant which will eliminate two existing culverted discharges to pasture and a direct discharge to Tributary C Clean water diversions are proposed to be implemented for both the upper and lower haul roads. The diversions will remove clean water runoff from the respective discharges and will reduce the volume load on Pond A (Upper Haul Road) and the Lamella Plant (Lower Haul Road). 34. Clean water diversions in the Upper Haul Road catchment are associated with a completed overburden area that is now finished as established pine plantation and vegetated surfaces. Clean water diversions from this area will discharge to an existing culvert servicing the adjacent farm access track. 35. Clean water diversion associated with the Lower Haul Road is associated with existing areas of pasture not used in the quarrying operation. Clean water diversions from the Lower Haul Road area will discharge to two existing culverts noted in Paragraph 32. POND A 36. All clean water catchments (reinstated overburden areas and sections of clean, lightly trafficked farm access tracks) will be diverted away from Pond A where practical. This will reduce the contributing catchment area from 6.5 hectares to 1.9 hectares which will lower velocities in the pond and improve settlement performance. 37. There are currently four inlets into Pond A. Two of the inlet points are from clean water catchments which will be diverted. The remaining two inlet points are primary dirty water runoff inlets from the quarry upper haul road. 38. The existing Pond A primary inlets will be consolidated by making redundant one inlet that currently discharges mid-way along Pond A 3. Diversion of the midpoint inlet to a location at the head of the pond will allow for better inlet control and will prevent the pond from being disrupted. 39. The existing Pond A outlet structure orifice will be replaced with two floating decants. This change will increase the available operational volume of the pond and will result in water being discharged from the surface of the pond as 2 Refer to plan CI-0003 as Attachment A for the location of the existing discharges to pasture to be diverted. 3 Refer to plan CI-0011 as Attachment B Page 6

7 opposed to the base of the pond. An improvement in discharge quality can be expected as a result of this change. 40. A rainfall activated chemical dosing system will be installed at the proposed common inlet to the improved Pond A. The potential effectiveness of a chemical dosing system is outlined in the site Chemical Treatment Management Plan Pond A currently has four concrete weirs which discharge by overtopping. The four existing concrete weirs will be removed to form a single uninterrupted pond. A sediment forebay of approximately 10 % of the total pond volume will be constructed at the inlet end of the pond with a level spreader to aid even distribution into the settlement section of the pond. These changes will improve the settlement performance of Pond A by removing disruptive elements which could otherwise cause sediment to be re-suspended. 42. The width of Pond A will be increased from 3 m to 5.5 m and the overall length will remain the same. As a result the pond volume will increase from approximately 420 m³ to approximately 900 m³. 43. The proposed volume of Pond A is equivalent to 4.5 % of the proposed catchment area which exceeds the typical 3 % requirement. A larger pond volume should improve settlement performance and is appropriate given the sensitive nature of the sediments at the site. 44. It is my opinion that the proposed changes to the scale and operation of Pond A will improve the discharge quality at that location. The changes maximise the use of the existing pond location as far as practical and within the topographical constraints of the site which include: a) Steep overburden slopes of about 30 to 35 degrees above the pond, b) Steep slopes of about 15 to 30 degrees below the pond, and c) The Farm Access Road adjacent to the pond that is being narrowed as far as practical to allow for a greater pond width. 45. It is also my opinion that it is not practical to relocate Pond A downslope because the existing steep topography will require a significant amount of earthworks to exceed what is currently proposed at the existing location. The expansion of Pond A as far as practical at its current location, and the addition of chemical treatment, is the best practical option for a sediment pond solution without mechanical treatment. 4 Chemical Treatment Management Plan (CTMP), Prepared by Erosion Control Co. Ltd, 21st September 2018 Page 7

8 46. The performance of Pond A cannot be linked to a design storm event for the purpose of consent conditions. Pond A has been designed as a conventional sediment retention pond for which design parameters are not based on a design storm event, rather a number of minimum dimensional and volume requirement of which the latter (volume) is exceeded in the proposed design. 47. The design storm event level of service of Pond A, as a conventional pond, cannot be determined. The performance of the upgraded pond will be optimised via the dosing system and dosing will also increase with inflow rate. It should however be expected that Pond A s treatment performance could deteriorate above a certain inflow threshold. POND B 48. Pond B was formerly operating as a settlement pond. Recent operational changes have removed the outlets and implemented a transitional pumped system discharging to the Lamella Plant. Additional upgrades are proposed to increase the level of service provided in a greater range of storm events. 49. The current level of service of the transitional solution has not been assessed because the proposed upgrades will be implemented as soon as practical. The operational changes undertaken to date have maximised the storage volume of the Pond B in its current footprint. Pond B does not yet meet the required storage volume for long term operation so the transitional solution has a higher chance of overflow than the proposed permanent solution. 50. It is proposed that the upper and lower processing areas are combined and treated in the existing Lamella Plant which historically has a more reliable discharge quality than conventional settlement ponds. The existing Lamella water treatment plant will be modified to utilise its full design capacity to treat 140 m³/hr. 51. It is my understanding that conventional pond systems are designed approximately for a level of service storm event of no more than a 50% Annual Exceedance Probability (AEP). The actual level of service is difficult to determine because performance is dependent on a number of factors including sediment load and type, and the duration of an event. 52. The AEP represents the annual percent chance of the design storm occurring or being exceeded. A 50% AEP event statistically has a 50% chance of being exceeded in any given year but could occur less or more frequently. Page 8

9 53. Sediment pond treatment performance typically reduces progressively with larger inflows. The maximum capacity of the Lamella Plant is fixed so events in excess of the level of service could discharge at or close to the untreated runoff quality. 54. A treatment service level storm event of 20 % AEP is proposed for the Lamella Plant and Pond B so that the onset of untreated overflow is greater than a 50 % AEP level of service. 55. The upper processing area will continue to discharge directly to the Lamella Plant inlet pond. 56. Buffer storage is required so that the upgraded Lamella Plant has sufficient capacity to cope with the additional catchment for the proposed 20 % AEP level of service. It is proposed that the upgraded Pond B will supplement the live storage volume already available in the Lamella Plant inlet pond. 57. Pond B will therefore operate as a runoff storage pond which is pumped up to the Lamella Plant for treatment prior to discharge or temporarily held back via automated level controls when the Lamella inlet pond is near full. 58. The capacity of Pond B will be increased from about 370 m³ to about 2,184 m³ and will be provided in two separate pond cells. This is the maximum volume that can be practically achieved within the existing site constraints which include underground power cables and the main quarry access. The resulting combined storage volume of Pond B and the Lamella Plant inlet pond is sufficient to meet the proposed 20 % AEP level of service. 59. The existing service outlet at Pond B will blocked off and provision only for emergency spill in excess of the service level event will be provided. Water currently being discharged from Pond B will now pass through the Lamella Plant prior to discharge. 60. It is my opinion that the changes proposed in the upper processing area and at Pond B reduce the risk of a non-complying discharge as far as practical. The changes also reduce the number of lower quarry discharge locations from four to one through the elimination of two haul road culverts and the Pond B discharge in favour of the Lamella discharge. 61. I note that all systems have a limitation on treatment based on their design level of service. Design levels of service are typically set based on a practical level of treatment that can be reasonably and cost effectively achieved in relation to the Page 9

10 benefit. Although treatment performance of conventional ponds typically decreases with increasing inflows above a certain threshold, the receiving environment also experiences greater flows (i.e. more dilution) as well as higher levels of sediment and debris from natural and farm sources. 62. In my opinion the performance of the Lamella Treatment Plant and Pond B should be linked to a design storm event of 20 % AEP. Unlike conventional ponds which yield diminishing treatment with high inflow rates, the Lamella system has been designed to have a minimum buffer volume based on a specific design event. 63. The proposed increased level of service from 50 % AEP to 20 % AEP accounts for the change from a settlement pond system to a mechanical treatment system which has a more abrupt degradation in discharge quality during overflow conditions. CULVERTS 64. This section of my evidence addresses the upgrade of existing culverts located on the major tributary streams and diversions. 65. The Stormwater Management Plan identifies a number of culverts that have been in place for a long period and may require upgrade to meet a 50 year (2 % AEP) storm event level of service in accordance with Waikato Regional Plan rule I note that the assessment method used to determine design flow rates in the Stormwater Management Plan is typically conservative and does not account for storage and interaction which will typically reduce peak flow rates below those calculated. 67. The culverts have been in place for a long period of time and the associated upstream and downstream channels are observed to be stable and typical of other tributaries in the area. J Swap has advised that none have ever been seen to overtop. 68. The recommended culvert sizes presented in the Stormwater Management Plan are preliminary. Detailed design will need to be undertaken where upgrades are deemed to be required and will at that stage consider fish passage and erosion protection design. 69. I note that earthworks to upgrade the culverts and the associated upstream and downstream channels could increase the risk of erosion and instability. The Page 10

11 existing stream character and vegetation will be difficult to replicate in a high energy (steep) environment and could take a long time to normalise. 70. It is my opinion that the need for culvert upgrades and any subsequent culvert upgrade design should be considered in more detail in conjunction with historic performance, effect on the waterway and the overall potential impact of construction activities. 71. Given that the existing culverts have not shown any issues of capacity or adverse effects during normal flows I support retaining the existing culverts until such a time as they have reached the end of their useful life. Periodic inspection and maintenance will provide evidence of culvert condition and will ensure that inlet and outlet conditions are mainted for fish passage and erosion as required. SECTION 42 REPONSE 72. This section of my evidence addresses the Section 42A report inclusive of the submission information contained within. 73. The Raukawa Charitable Trust submission recommends daily monitoring at the discharge points when discharges are occurring. In my opinion weekly monitoring of suspended solids from the Lamella plant and during large isolated events for pond discharges is sufficient to monitor the performance of the system. 74. The operation of established sediment ponds should not vary to a degree which would warrant daily monitoring during low or average rainfall. I also note that the Lamella Plant will discharge daily regardless of rainfall (due to aggregate processing) so testing every day would be required which is excessive for the same reason noted above for ponds. Testing of the Lamella Discharge can be carried out even if it is not raining so a reliable weekly schedule can be achieved. 75. Schedule 1 conditions require a stormwater management plan that includes continuous monitoring at a number of remote sites and adaptive management in the event of flow trigger levels being met. 76. Although it is not expressly stated I assume that the flow trigger level is intended to provide an indication that the quarry stormwater system will be discharging which will then trigger the requirement for monitoring and adaptive management to be undertaken. Page 11

12 77. The proposed continuous monitoring system is complicated, particularly in regard to the spatial separation of the sites both in terms of distance from the quarry and time of flow. I note the following in this regard: a) Permanent monitoring stations remote from the site are likely to be costly to implement due to power and telemetry requirements. The ability for a telemetry signal could be limited by the steep terrain and may be an unavoidable limitation. b) Flow measuring equipment could be susceptible to damage in the steep high energy flow environment and are most likely to fail or be damaged during such events as a result of rocks and debris from the steep upstream forested catchments. c) The proposed downstream monitoring locations are sufficiently remote from the site that they could be influenced by other discharges or catchment changes such as slips or earthworks at other sites. 78. A similar outcome could be achieved using a single real time rain gauge at the quarry site to identify that discharge will likely occur from the site. Manual monitoring could then be implemented and undertaken in order of location (upstream first) and priority (pond discharge points). 79. I note that a rainfall gauge will be required to determine when rainfall occurs above the trigger level stated in proposed condition 2 of the Stormwater Discharge Permit (AUTH ) 80. The proposed monitoring locations in the vicinity of the Quarry are the most representative of quarry discharges. The nearby sites are also immediately accessible for visual inspection and monitoring. Remote downstream site monitoring can follow the critical quarry sites if required. 81. I agree that a process to actively manage the system could be beneficial to limit adverse effects as far as practical in some unforeseen circumstances. However I note that issues are only likely to be seen during overdesign events once the stormwater treatment system is upgraded and complying. 82. In overdesign events there will be limited options to provide further reactive intervention or improvement provided periodic inspection and maintenance requirements are adhered to. Shutting off of the discharge during extreme events could result in an uncontrolled overflow without the benefit of partial treatment through the treatment devices. Page 12

13 83. Adaptive management approaches are likely to be limited to equipment inspections and the proactive removal of sediment to maximise storage in advance of predicted rainfall, or performance monitoring during large events including real time removal of sediment from the Lamella Plant waste storage pond. Only the latter will benefit from real time rainfall or flow monitoring with the former being achievable based on weather forecasts. 84. It is my opinion that temporary continuous monitoring or more frequent manual monitoring will provide the most benefit during upgrade and optimisation. Once the site is complying and optimised, scheduled weekly and event based monitoring should be sufficient to identify issues and determine compliance against a baseline that could be defined using data collected up to that point. 85. I support the inclusion of consent condition 33 (Schedule 1) requiring detailed engineering design of culvert upgrades in accordance with Waikato Regional Council requirements inclusive of erosion control and fish passage 5. This requirement is consistent with my evidence in paragraphs 66 to 70. I however note my evidence paragraph 71 stating my preference for upgrades to be deferred until the useful life of the existing culverts has been reached. 86. Schedule 1 recommended condition 15 6 requires that flocculation is included in all sediment retention devices at the site. I agree with this requirement based on the nature of the materials at the site and the difficulty of settlement of suspended solids by gravity only. 87. Table 5 7 recommends a resource consent term of 15 years for the discharge of stormwater. I understand that MMS accept this length of consent. 88. I note that stormwater structures (e.g. culverts and pipelines) typically have a useful life in excess of 50 years. Mechanical items typically have lifespans of years (or more in some cases) with periodic maintenance and replacement of wearable parts. 89. In my opinion, a consent duration of 35 years is normally appropriate in terms of stormwater infrastructure provided performance is monitored and new technologies are considered when the useful lifespan of mechanical components is reached. Normally a 35 year consent duration would provide Matamata Metal Supplies with certainty of investment in technology and 5 S42A report reference page 29 and 31 (Schedule 1 Condition 33) 6 S42A report reference page 31 (Schedule 1 Condition 15) 7 S42A report reference page 52, Table 5 Page 13

14 infrastructure over the remaining lifespan of the quarry and more in line with the expected lifespan of the associated infrastructure. However, it is understood that MMS are prepared to accept a lesser period. Page 14

15 Attachment A

16 Printed on % Post-Consumer Recycled Content Paper Last saved by: HARDYC( ) Last Plotted: Filename: P:\605X\ \400_TECH\431_MMS SWMP UPDATE SEPTEMBER 2018\CAD\ SHT-CI-0003(2).DWG ISO A1 594mm x 841mm N PROJECT Matamata Metal Supplies CLIENT J Swap Contractors CONSULTANT AECOM 121 Rostrevor Street Hamilton tel fax PROJECT MANAGEMENT INITIALS CH DESIGNER CHECKED APPROVED ISSUE/REVISION 3 3/10/2018 CATCHMENT UPDATES 2 3/07/2018 LOWER HAUL ROAD CHANGES 1 9/01/2017 FOR CONSULTATION I/R DATE DESCRIPTION PROJECT NUMBER SHEET TITLE Drainage Catchment Plan SHEET NUMBER CI-0003

17 Attachment B

18 ISO A1 594mm x 841mm NOTES 1. Dimensions are in millimeters unless stated otherwise. 2. Dimensions of existing features are approximate only. 3. All proposed works are to be designed and constructed in accordance with Waikato Regional Council Erosion and Sediment Control standards and guidelines. Existing wier 1 Existing wier 2 Approx. 120m Existing wier 3 Existing wier 4 Manhole riser with orifice outlet and secondary spill over riser PROJECT Matamata Metal Supplies POND A - EXISTING PROFILE Scale 1:200 CLIENT J Swap Contractors Approx. 120m Existing discharge pipeline CONSULTANT 4500 AECOM 121 Rostrevor Street Hamilton tel fax Existing inlet Existing inlet POND A - EXISTING PLAN Scale 1:200 Rainfall activated chemical dosing Approx. 120 m Level Spreader Proposed manhole riser outlet with primary decant outlets (3 No.) and secondary spill over riser Forebay Inlet manhole to provide mixing for chemical dosing Last saved by: HARDYC( ) Last Plotted: Filename: P:\605X\ \400_TECH\431_MMS SWMP UPDATE SEPTEMBER 2018\CAD\ SHT-CI-0011.DWG Rainfall activated chemical dosing Existing inlet Approx. 12 m Level Spreader Forebay - approx. 10% of total pond volume Existing culvert to be blocked and flow diverted further upstream to the pond inlet POND A - PROPOSED PROFILE Scale 1:200 Approx. 108 m POND A - PROPOSED PLAN Scale 1:200 Existing discharge pipeline Proposed manhole riser outlet with primary decant outlets (2 No.) and secondary spill over riser 5.5 m PROJECT MANAGEMENT INITIALS CH GE GE DESIGNER CHECKED APPROVED ISSUE/REVISION 1 9/08/2018 FOR CONSULTATION I/R DATE DESCRIPTION PROJECT NUMBER SHEET TITLE Pond A Details SHEET NUMBER CI-0011 Printed on % Post-Consumer Recycled Content Paper