4 June 2020 Horizons Regional Council Private Bag 11025 Manawatu Mail Centre PALMERSTON NORTH 4442 Attention: Sara Wescott Senior Consents Planner Dear Sara RESOURCE CONSENT APPLICATION NO. 107258, 107259 and 107260 RANGATAUA WWTP Please find attached a table and associated attachments providing our response to the request for further information on the above consent applications. I trust the attached satisfies your request, however, should you have any follow up questions please contact myself or Deborah Kissick on [email protected] or 02102651357. Yours sincerely Stuart Watson ENVIRONMENTAL MANAGER Attachment One: Table 1: Response to s.92 request for further information Attachment Two: Memo from Aquanet Consulting re: Potential effects of discharge load increases (dated 29 October 2019) Attachment Three: Proposed draft load conditions Resource Consent Application No. APP-107258, 107259 and 107260 – Rangataua Wastewater Treatment Plant Attachment One: Table 1: Response to s.92 Request for Further Information Page | 2 Resource Consent Application No. APP-200008943.02 – Rangataua Wastewater Treatment Plant Horizons Information Request / Comment RDC response Email from Sara Wescott, 30 August 2017 1 Has there been any changes to the system, volumes and There have not been any major changes in the treatment process at the Rangataua WWTP since management of the plant since 2014? 2014. Discharge volume has been monitored since January 2012. Data does not indicate any marked trend. Data indicates: • Regular, prolonged periods of time when the discharge volume is very low or nil, typically in summer; • The dataset also contains a large number of unexplained “0” values during periods when discharge is expected to have occurred. This is thought to be due to equipment failure (solar power), and the operator (Veolia) advised that they should be considered with caution and are unlikely to represent actual “no discharge” days. These were replaced in the dataset by the average of previous/next day; • There are gaps in the dataset (12/06/2015-25/07/2015 and 6/12/2015 – 13/11/2016) • Wet weather flows are in the order of 150 m3/day, but with occasional peaks over 200 m3/d (August 2015) and up to 600 m3/day (June/July 2014); • 12-months rolling median flow varied between 3 and 53 m3/day; • 24-months rolling median flow varied between 5 and 42 m3/day; • 12-months rolling 95th percentile flow varied between 26 and 194 m3/day; • 24-months rolling 95th percentile flow varied between 70 and 171 m3/day. Any limits placed on effluent flow should incorporate typical error of measurement, expected to be in the 10-15% range. If limits were to be placed on effluent discharge volumes, the upper end of the above ranges (plus 10-15% to account for error of measurement) may be considered as representative of the existing discharge. However, as explained later in this response, it is considered preferable to set “end of pipe” controls based on effluent loads rather than effluent Page | 3 Resource Consent Application No. APP-107258, 107259 and 107260 – Rangataua Wastewater Treatment Plant Horizons Information Request / Comment RDC response volumes to provide for flexibility in response to growth, whilst providing long-term certainty with regards to in-stream effects. 2 Can you please confirm the ecological status of the One Plan Schedule F defines criteria for “Rare”, “Threatened” or “At Risk” Habitats. Schedule F2b wetland (both at the site of the WWTP and downstream defines exclusions. to the confluence with the Mangaehuehu Stream) – is this a Schedule F habitat? Page | 4 Resource Consent Application No. APP-107258, 107259 and 107260 – Rangataua Wastewater Treatment Plant Horizons Information Request / Comment RDC response The “wetland” to which the treated effluent is discharged is a depression between the wastewater plant and a grazed paddock, and vegetation is dominated by exotic wetland grass species with a few relatively small willows (refer to Attachment 1A). It is considered that it falls under the Schedule F2b exclusions (e.g. damp gully heads, or paddocks subject to regular ponding, dominated* by pasture or exotic species in association* with wetland^ sedge and rush species), and therefore does not constitute a Rare, Threatened or At Risk Habitat as defined in One Plan Schedule F. It is also noted that the construction of the wetland was authorised by consent 4926 (variation 2), granted on 14 December 2000. Schedule F2b specifically excludes “Areas of wetland^ habitat maintained in relation to the implementation of any resource consent^ conditions^”, i.e. any planting of native species undertaken by or on behalf of Ruapehu District Council will not result in the “wetland” falling under the Schedule F definitions of “Rare”, “Threatened” or “At Risk” Habitats. It is RDC’s position that the wetland does not constitute a Schedule F habitat. 3 With respect to the treatment of the effluent – has the It is unclear what is meant by this question. impact of the entire length of the wetland been assessed The current consent conditions identify the Mangaehuehu Stream as the receiving environment for or just the portion of the wetland adjacent to the ponds? the discharge and require sampling upstream and downstream of the point where the wetland flows into the Mangaehuehu Stream. The assessment of in-stream effects provided in the AEE is based on comparison of upstream/downstream data and thus de facto includes the whole length of the “wetland” (and any contaminant inputs to the wetland downstream of the discharge). 4 Since the application was lodged in 2014, Accelerate25 The exact impact of Accelerate 25, or other growth-related initiatives, on permanent or visitor has been developed. Can you please advise if this will population is difficult to predict; however, it is considered essential that the resource consent impact predicted growth rates and therefore effluent conditions do not unnecessarily preclude growth opportunities. To achieve this, it is suggested that volume and loading rates? conditions should focus on controlling actual effects on stream water quality/ecology and the risk of effects from the discharge. The risks of effects posed by a point-source discharge on water quality/ecology are primarily associated with the contaminant loads in the discharge (as opposed to the discharge volume or concentration of contaminants in the discharge). Page | 5 Resource Consent Application No. APP-107258, 107259 and 107260 – Rangataua Wastewater Treatment Plant Horizons Information Request / Comment RDC response In-stream data shows that effects of the discharge on water quality and ecology have generally been undetectable, thus well within the One Plan targets since 2013. In principle, as long as the contaminant loads in the discharge do not increase, the effects on water quality/ecology should remain similar to what they currently are. Given that effects are currently undetectable, and that the treatment wetland will be improved to follow the recommendations of Mr McGibbon (refer to Attachment 1A), it is also likely that some increase in loads coming out of the oxidation ponds could occur without effects on the receiving environment (the Mangaehuehu Stream) becoming more than minor. On the basis of the above, RDC proposes conditions requiring: • Triggers based on daily loads of contaminants in the discharge, based on rolling 24-months median and 95th percentile values calculated on the basis of historical data, as follows: o A 24-month rolling median load of no more than X kg/day th o A 24-month rolling 95 percentile load of no more than Y kg/day; o X and Y values for each parameter are given in the table below TSS Ammoniacal-N ScBOD DRP 5 (kg/day) (kg/day) (kg/day) (kg/day) 24 month rolling 1.5 0.5 0.4 0.1 Median 24 month rolling 95th 6.5 2.5 0.8 0.3 %ile NB: numbers are based on combined Horizons and RDC data, for the period January 2012 to October 2019 Page | 6 Resource Consent Application No. APP-107258, 107259 and 107260 – Rangataua Wastewater Treatment Plant Horizons Information Request / Comment RDC response • Alternatively, the load triggers could be based on actual data, using the NZ wastewater monitoring guideline approach (i.e. no more than X out of Y consecutive samples exceeding Z kg/day (e.g. The daily load of TSS shall not exceed 2.3 kg/day in more than 15 out of any 24 consecutive calculated daily loads, and shall not exceed 6.5 kg/day in more than 3 out of any 24 consecutive calculated daily loads) • Comparison with the load triggers to be based on daily loads calculated monthly, on the basis of daily discharge volume and monthly discharge quality samples • To keep track of any increase in contaminant loads from the discharge, a condition requiring: o An assessment of the impact of any changes and/or trends over time in contaminant loads from the WWTP; o Whether those changes / trends indicate a risk to meeting the load triggers over the following 12-month period, including the identification of any contributing factors to those risks (e.g. expectations of growth in visitor numbers, industry, residents etc); and o Whether or not the Permit Holder considers that WWTP treatment improvements are necessary to avoid ongoing exceedance of the load triggers, including a Best Practical Option Assessment should improvements be identified as necessary. • To date, in stream monitoring has not detected any effect of the discharge. On this basis, we consider further in-stream monitoring should only be required in the instance where the load triggers are exceeded. We welcome discussion with Horizons on this point. 5 With respect to Accelerate25, has this resulted in any No, this alternative has not been considered specifically. RDC considers this option would have very other alternatives being considered, such as piping the limited environmental benefits (given the lack of measurable environmental effects from the effluent to Ohakune? Rangataua WWTP on the receiving environment, i.e.