Water, Wastewater & Nitrogen

The application material puts the wastewater volume at approximately one million litres a day and the associated nitrogen load at 2.8 tonnes a year. Both are the applicant’s own figures. Neither has been independently verified in public. This page takes them at face value and asks the only question that matters once you do: where does it all go?

One million litres a day is not an abstraction. It is a volume that must be collected every day, treated every day, and disposed of every day, for as long as 1,200 dwellings stand at Arrow Junction. It does not pause for a dry summer, a wet winter, a plant shutdown or a pump failure. Whatever the system is, it has to work on its worst day, not its average one.

Where does every litre go?

This is the question the whole application turns on, and it deserves a full answer rather than a schematic. Here is the pathway, stage by stage, with the question each stage has to survive.

1 · The household

Every litre begins in a kitchen, a bathroom, a laundry or a toilet in one of 1,200 dwellings. It arrives as potable water — which itself has to be sourced, treated and delivered, a separate problem of the same size — and leaves as wastewater carrying nitrogen, phosphorus, pathogens, household chemicals and whatever else goes down a drain. The volume is a function of how many people live there and how much water each one uses, which is why the occupancy assumption behind the figure matters and should be published.

2 · The reticulated sewer network

From the dwelling it enters a piped network of gravity mains, pump stations and rising mains that has to convey the full daily flow, plus peaks, plus whatever stormwater and groundwater finds its way in through joints and manholes. Infiltration is not a hypothetical: it is the normal behaviour of buried pipe, and it is why wet-weather flow is larger than dry-weather flow. A network is also a chain of single points of failure. When a pump station loses power or a rising main breaks, the wastewater does not stop being produced — it overflows, and it overflows to the nearest low point, which is usually a watercourse.

3 · The wastewater treatment plant

The network delivers the flow to a treatment plant. The plant has a design capacity, a design load and a consented discharge. All three are finite. A plant sized for the average day is undersized for the wet day; a plant sized for the finished development is oversized on day one and undersized if the development grows. The plant’s capacity, its ownership, and whether it is new, existing or expanded are therefore first-order questions, not detail.

4 · Treatment

Treatment removes solids, reduces organic load, and — to the extent the process is designed and operated to do so — removes nutrients. This is the stage where nitrogen is either converted and removed or passed through into the treated effluent. Nutrient removal is the most demanding thing a plant does: it is sensitive to temperature, to loading rate, to hydraulic shock and to operator skill, and its performance in a cold-climate, seasonally variable, tourism-influenced catchment is not the same as its performance on a design sheet. Treated effluent is cleaner than raw sewage. It is not clean water.

5 · Land application at Morven Hill

The treated effluent is then applied to land — in this proposal, disposal at Morven Hill. Land application is not disposal in the sense of disappearance. It is a transfer: the water and the nutrients left in it are placed onto a defined area of ground, at a defined rate, for the soil and the plants growing in it to take up. The area available, the rate applied and the capacity of that ground to accept it are what determine whether this works or fails.

6 · Soil and vegetation

In the soil, some of the nitrogen is taken up by plants, some is held temporarily, and some is converted by soil processes. Uptake is seasonal — plants take up far less in winter, exactly when soils are wettest and least able to hold water. Uptake also has a ceiling: past a certain loading rate, soil and vegetation simply cannot take up any more, and the excess keeps moving. In free-draining soils it moves quickly.

7 · Groundwater and the receiving environment

What is not taken up drains below the root zone and into groundwater, and groundwater moves — toward bores, springs, and eventually surface water. This is the end of the pathway and the beginning of the consequences: drinking-water sources, the nutrient status of rivers and lakes, and the ecology that depends on both. Groundwater also has a long memory. Nitrogen that reaches it does not arrive at the receiving environment on the day it is applied, and it does not stop arriving on the day the discharge stops.

Every stage above transfers the problem to the next one. Only two stages actually remove nitrogen from the system: treatment, and plant uptake. Everything else moves it. That is why the four nitrogen figures below are different numbers, and why publishing only one of them is not an answer.

Nitrogen: four quantities, one label

Nitrogen is discussed in this application as though it were a single number. It is not. There are at least four distinct quantities, each larger or smaller than the next, and a figure is meaningless until you know which one it is.

1 · Nitrogen entering the plant

The total load arriving from 1,200 dwellings in raw wastewater. This is the largest of the four. It is a function of population and per-person nitrogen production, and it is the figure the treatment process has to work on.

2 · Nitrogen remaining in treated effluent

What survives treatment. This is entirely determined by the treatment process chosen and how well it is operated, and it is the figure that is actually applied to land. The gap between quantity 1 and quantity 2 is the plant’s nutrient removal performance, and it should be stated as a design value and as a consented limit, not as an aspiration.

3 · Nitrogen applied to land

The load placed on the disposal area — quantity 2, expressed against the area it lands on. This is where a total becomes a loading rate, and it is the point at which the physical capacity of Morven Hill becomes the binding constraint.

4 · Nitrogen predicted to reach groundwater or surface water

What is left after soil and plant uptake: the load that leaves the disposal area downward and reaches the receiving environment. This is the smallest of the four and the only one that describes the environmental effect. It is also the one that depends most heavily on modelling assumptions, and therefore the one that most needs an independent check.

2.8 tonnes a year

The figure in the record is 2.8 tonnes of nitrogen a year. We publish it because it is in the application material. We also publish the problem with it, which is this: the record as we have it does not state which of the four quantities above it refers to.

That is not a pedantic point. If 2.8 tonnes is the load entering the plant, the environmental effect is much smaller than the number sounds. If it is the load predicted to reach groundwater, the effect is very much larger than the number sounds. The same three digits describe a manageable discharge and a serious one depending on a single unstated definition — and a reader cannot tell which without being told.

We are not asserting that 2.8 tonnes a year is wrong. We are asserting that it is unusable until the applicant states which of the four quantities it measures, over what area, under what treatment performance, and on what occupancy assumption. Publishing one number without its definition is not transparency.

Phosphorus: the figure that is not there

Wastewater carries phosphorus as well as nitrogen, and in lake and river systems phosphorus is frequently the nutrient that governs algal growth. The application material we have seen quantifies nitrogen. It does not quantify phosphorus.

We are not claiming the phosphorus load is large. We are recording that it is unstated, which means neither we nor anyone else can say whether it is significant. An assessment that quantifies one nutrient and is silent on the other is incomplete on its face. Phosphorus load entering the plant, remaining in treated effluent, applied to land, and predicted to reach water — [Awaiting client evidence]

Morven Hill: the capacity question

Morven Hill is the proposed disposal location. Land disposal works or fails on a small number of physical facts about the specific piece of ground, and they are the facts we are asking for:

• Area. How many hectares are actually available for application, as distinct from how many hectares exist? — [Source to be added]
• Soil. Soil type, depth and drainage characteristics across that area — free-draining soils move water and nitrate downward quickly. — [Source to be added]
• Depth to groundwater. How far is it from the base of the root zone to the water table, and how does that vary seasonally? — [Source to be added]
• Slope and runoff. A hill is not flat ground; what prevents surface runoff toward watercourses during application or heavy rain? — [Source to be added]
• Storage. Effluent cannot be applied to saturated or frozen ground. How many days of storage exist, and what happens when storage is full? — [Source to be added]
• Vegetation and management. What is grown, who harvests it, and what happens to the nutrient taken up if it is not removed? — [Source to be added]
• Tenure. What legal instrument secures the disposal area for the life of the development? A disposal system with no permanent right to its disposal land is not a disposal system. — [Source to be added]

Nitrogen loading per hectare

This is the number that decides it, and it is not published.

A total annual load tells you nothing on its own. The same load spread over a large area may be absorbed; concentrated onto a small one it will not be. Land-treatment systems are assessed on loading rate — nitrogen applied per hectare per year — because that is the quantity that can be compared against what soil and plants at a given site can actually take up, and against the limits set for the catchment.

We cannot calculate it. To do so we would need the disposal area, and the application area at Morven Hill is not in front of us. We will not estimate it, because an invented denominator would produce a precise-looking number with no basis, which is exactly the kind of claim this site exists to avoid. Nitrogen loading rate per hectare per year, and the application area it is calculated on — [Source to be added]

What we will say is this: until that figure and its supporting soil and groundwater assessment are public, nobody — including the applicant — can demonstrate that this disposal system works.

The limits this has to be measured against

A discharge is not assessed in the abstract. It is assessed against limits, and the relevant ones here are:

• Drinking-water standards for nitrate in any groundwater used as a drinking-water source, and the location of every bore and spring within the affected groundwater path. — [Source to be added]
• National and regional freshwater limits for nitrogen and phosphorus in the receiving surface water, and whether the catchment is already at or over them. — [Source to be added]
• The consented discharge conditions for the treatment plant and the land application system, including monitoring, reporting and the consequences of exceedance. — [Source to be added]
• Cumulative effect — this discharge added to every other nutrient source already in the same catchment, which is how the receiving environment actually experiences it. — [Source to be added]

What has not been answered

• Which of the four nitrogen quantities the 2.8 tonnes a year figure describes.
• The occupancy and per-person water-use assumptions behind approximately one million litres a day — [Awaiting client evidence]
• The treatment process proposed, its design nutrient-removal performance, and its consented limits.
• The wet-weather flow, the infiltration allowance, and what happens to overflow when the network or the plant is at capacity.
• The disposal area at Morven Hill, and therefore the loading rate per hectare.
• Depth to groundwater, groundwater flow direction, and the bores and springs downgradient of the disposal area.
• The phosphorus load, at every one of the four stages.
• Where the potable water for 1,200 dwellings comes from, and what taking it does to the same catchment.
• Whether the assessment is against current catchment nutrient loads or against loads that already include other consented growth.

Our position

Approximately one million litres a day, every day, permanently, at a rural site, disposed of to land above groundwater that feeds the receiving environment, is the largest single environmental question this proposal raises. The applicant’s own figures establish the scale of it. They do not establish that it can be managed, because the quantities that would show that — the definition behind 2.8 tonnes, the disposal area, the loading rate, the depth to groundwater, the phosphorus load — are not on the record.

We think a proposal of this size should not proceed on an undefined nitrogen figure and an unpublished loading rate. If the applicant publishes them and they stand up to independent review, we will publish that too, in the same place and with the same prominence.

Evidence statement

Classification: Applicant Evidence

Status: Applicant-supplied figures (approximately 1,000,000 litres per day; 2.8 tonnes of nitrogen per year), reproduced as stated and not independently verified. The pathway description and the four-way nitrogen distinction are our analysis of what those figures must mean, not additional measurements.

Author: Ridgeburn Press · Evidence Desk

Last reviewed: 16 September 2026

Sources

1. Application material — wastewater volume (approximately 1,000,000 litres per day), applicant — [Source to be added]
2. Application material — nitrogen load (2.8 tonnes per year), applicant — [Source to be added]
3. Wastewater treatment and land-application design, including the Morven Hill disposal area, applicant’s engineer — [Source to be added]
4. Groundwater and nutrient-transport assessment for the disposal area — [Source to be added]
5. Regional discharge consent conditions and catchment nutrient limits, regional council — [Source to be added]

Assumptions

• That approximately 1,000,000 litres per day describes the completed 1,200-dwelling development at full occupancy; the occupancy and per-person water-use assumptions are not published — [Awaiting client evidence]
• That 2.8 tonnes per year is an annual total for the same development. Which of the four nitrogen quantities it measures is not stated — [Awaiting client evidence]
• That treated effluent is applied to land at Morven Hill; the available application area is not published, so no loading rate per hectare is calculated anywhere on this page — [Source to be added]

What is not established

• Which of the four nitrogen quantities the 2.8 tonnes a year figure refers to.
• The nitrogen loading rate per hectare per year at the disposal area.
• The phosphorus load at any stage of the pathway — it is unquantified in the material we hold.
• The treatment process, its design nutrient-removal performance and its consented limits.
• Depth to groundwater, groundwater flow direction, and the drinking-water sources downgradient of the disposal area.
• Wet-weather flow, infiltration allowance and overflow behaviour when the network or plant is at capacity.
• Whether the receiving catchment is already at or over its nutrient limits.

Right of response

Ridgeburn Limited, Queenstown Lakes District Council and any person named here may respond in full. How to respond.