U:\2021\BM210482_IBo_Waihi_North_Project\Documents\WNP_Freshwater_Report_May_2022\FINAL_Freshwater_Report_FOR DELIVERY_June 2022\FINAL DELIVERED 17 JUNE 2022\WAI-985-000-REP-LC-0007_Rev0_Freshwater_20220621_FINAL.docx 20.4.1.3 Ammoniacal Nitrogen in the treated water discharge In their modelling of the treated water discharge for WNP, GHD (2022b) predicted that maximum daily mean concentration of ammonia at the most downstream site at Waihi (site OH6) would be 0.89 g/m3 and the maximum concentration would be 1.93 g/m3 and would be within current consent limits. 20.4.1.4 Effects of Ammoniacal Nitrogen on aquatic ecological values We have noted above that the water quality of the Ohinemuri River falls from Attribute band A above the treated water discharge to Attribute band B at sites below the discharge for annual median for ammoniacal nitrogen but falls below the NBL below the discharge for the annual maximum (Table 35). NOF Attribute band B is set for the 95% species protection level (starts impacting occasionally on the 5% most sensitive species); Attribute band A is set at the 99% species protection level. We note that the results for the annual maximum for ammoniacal nitrogen downstream of the treated water discharge all fall within the Attribute band C (below NBL), providing 80% species protection (i.e., starts impacting regularly on the 20% most sensitive species, but not at acute level (Attribute D). We also note that the NPS-FM numeric attribute state for each band for ammoniacal nitrogen is based on a pH 8 and a temperature of 20⁰C. The data reported above and provided in Table 35 has not been adjusted for these parameters. 20.4.2 Nitrate 20.4.2.1 Background Nitrate nitrogen is a nutrient that is necessary for algae and macrophyte (plant) growth. In excessive concentrations in freshwater, it can result in nuisance growths of these plant forms, especially where phosphorus is also in excess. At higher concentrations, nitrate can be toxic to aquatic life. 20.4.2.2 NOF limits The NOF sets out limits for nitrate for ecosystem health for freshwaters (rivers) in New Zealand. These limits relate to nitrate toxicity limits and are set out in attribute bands for condition of water quality for ecosystem health. The limits for each attribute band are set out for the protection of species in the community (e.g., 99% species protection; no observed effect on any species tested). The NOF attribute bands for nitrates are set out in Appendix 12. 20.4.2.3 Nitrate in the Ohinemuri River We have set out the concentrations of nitrate recorded from the Ohinemuri River at Waihi as the numeric attribute state limits of the NOF (i.e., annual median and annual maximum) (Table 36). It is evident that for the most part over the record of data available that water quality of the Ohinemuri River meets Attribute A for the annual median and annual 95th percentile for nitrate at all sites of the river at Waihi. The treated water discharge is not contributing to any changes in the nitrate concentrations in the Ohinemuri River.
RkJQdWJsaXNoZXIy MjE2NDg3