8. Monitoring and maintenance

In addition to the Water Quality Discharge Monitoring Programme (WQDMP) (Section 9 of this FTMP), the following monitoring and maintenance specific to the flocculation management practices is required.

8.1 Monitoring

Monitoring will include:

Certification of all ESC devices; Inspection after rainfall event; Weekly audits; and Pre and post rain event audits, including significant weather events.

The specific monitoring of the flocculation system will be undertaken by the Site Foremen and Site Engineers with regular checks of this monitoring made by the Environmental and Sustainability Manager.

This monitoring will be undertaken weekly and following heavy rain events of the following items:

Rainfall in previous 24 hours; Depth of water in displacement tank; Volume of flocculent used (added); pH of the pond; Initial header tank level; Any changes in degree of stabilisation of the site; Appearance of pond (relative turbidity); and Estimated level of accumulated sediment within pond.

The frequency of this testing may be increased during extended periods of heavy rainfall or reduced during dry periods.

Additionally, prior to any forecast heavy rain or if the site is to be unattended for more than 48 hours the flocculent reservoir tank will be filled to ensure that chemical treatment will occur through the following (or potential) 50mm of rainfall.

The results of pH sampling will be used to determine if any modifications are required to the dosage rate. The acceptable limits for the pH is between 5.0 and 9.0. If the pH levels fall outside these ranges the Environmental and Sustainability Manager will determine appropriate actions which could include decommissioning the flocculation unit or adding alternate chemicals, such as sodium carbonate or sodium bi-sulphate, to alter the pH.

Monitoring of pH will be a key indicator of the potential for residual aluminium discharges. Specifically, overdosing of PAC may cause a reduction in pH, raising the potential for aluminium within the PAC to react, forming toxic aluminium compounds that are bioavailable to fresh and marine water organisms.

8.2 Maintenance

Page 25 | Mt Eden Enabling Works The Site Foreman will have responsibility for the maintenance of the chemical treatment devices on their site.

The maintenance of the chemically treated sediment retention devices will be similar to that of nonchemically treated devices. The exception will be that the devices will require removal of the accumulated sediment more frequently. This accumulated sediment will be removed, dried and placed in fill areas of the site when this volume exceeds 20% of the pond storage volume or otherwise decreases the efficiency of the pond.

For a rainfall activated system the maintenance will include checking that the catchment tray is kept clear of leaves etc., and that the outlet point of the delivery hose is encouraging adequate mixing of the flocculant with inflows. All hoses, connections etc. will be checked to ensure they are sound and that there is no leakage. Flocculant levels etc. will be topped up and the displacement tank emptied at this time.

The daily maintenance of the system will also include the setting of the header tank level. This level allows a degree of rainfall to take place prior to dosing occurring. This initial level will be set to the following parameters:

When the site is dry, the header tank will be left empty so that 12mm of rain will fall prior to discharge of flocculent During extended periods of rainfall or if the site is already saturated (i.e., runoff will occur as soon as rain begins) the header tank will be filled to the level of the low rate outlet.

As the area of the contributing catchment and the degree of stabilisation within the contributing catchment alters the area of the catchment tray will be altered to account for these changes.

The catchment tray area will also be used as a method of controlling the pH and dissolved aluminium levels.

The results of the daily and weekly inspections and sampling will be retained for inspection as requested.

8.3 Transportation of flocculation chemicals

The transportation of flocculation chemicals (including chemicals for pH balance) to and from the Project will be undertaken in accordance with the required Hazardous Goods, Traffic and Transport regulations.

On site the chemicals will be transported in sealed containers, securely retained within the site vehicle. These containers will be small enough to be easily handled and only the expected required volume will be transported.

The use of these chemicals will be in accordance with the Construction Health and Safety Management Plan.