Doc #103 — Salt Production from NZ Sources

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RECOMMENDED ACTIONS (BY ACTUAL URGENCY)

First week (Phase 1)

1. Secure Lake Grassmere operations. Confirm operational status, staffing, and supply chain to the Mount Maunganui refinery. Designate salt production as essential infrastructure. Ensure Dominion Salt staff are classified as essential workers and exempt from any general workforce reallocation (Doc #145).

2. Include salt in the national consumable inventory (Doc #1, Doc #8). Count all stocks — industrial warehouses, retail, food processing plants, dairy factories (which use salt for cheese-making), water treatment plants, meat processing plants, farm supplies. This establishes the depletion baseline.

3. Do not panic about salt in the first week. Salt does not degrade in storage — pure NaCl is chemically stable indefinitely when kept dry, and salt has been found preserved in ancient deposits thousands of years old.⁷ Nobody is going to consume it at unusual rates, and domestic production continues. Salt is a Month 1 allocation priority, not a Day 1 emergency. Political capital should not be spent on salt seizure during the shock window.

First month (Phase 1)

4. Establish salt allocation framework. Determine priority uses and allocate accordingly. Recommended priority order:

   • Tier 1 (non-negotiable): Food preservation (Doc #78), water treatment chlorine production (Doc #48), animal nutrition (salt licks and feed supplements)
   • Tier 2 (high priority): Soap production (Doc #37), leather tanning (Doc #101), dairy processing, meat processing
   • Tier 3 (important but deferrable): Industrial chemistry (Doc #112 — caustic soda, soda ash), road maintenance (de-icing — less relevant under nuclear winter), other industrial uses

5. Assess nuclear winter impact on Lake Grassmere. Begin monitoring evaporation rates, weather conditions, and pond salinity. Compare against historical baselines to estimate production impact. Adjust seasonal production planning accordingly.

6. Survey potential supplementary salt production sites. Identify coastal locations with suitable geography for salt pans — flat terrain above high tide line, low freshwater runoff, good drainage. Priority regions: Marlborough (near existing infrastructure), Hawke’s Bay, Bay of Plenty, Northland (warmer, better solar conditions under nuclear winter).

7. Inventory existing infrastructure that could support forced evaporation. Identify facilities with large boilers, waste heat sources, or access to geothermal energy that could boil seawater at scale. Dairy factories, meat processing plants, geothermal power stations (Wairakei, Kawerau, Ngawha) are candidates.

First season (Months 3–12, Phase 1)

8. Begin construction of supplementary solar salt pans at identified sites. Construction requires earthmoving to level and grade the site, compaction or lining of the pan floor (clay, polyethylene sheet, or concrete — see Section 4.2 for dependency chain), seawater inlet channels or pumped supply, and brine transfer infrastructure between concentration stages. Even crude pans produce salt — refinement improves with experience.

9. Establish at least one forced-evaporation pilot facility using geothermal heat or industrial waste heat. Target: demonstrate production of 100+ tonnes per month to validate the approach before committing to scale-up.

10. Begin community-scale salt production in coastal settlements. Issue guidance on small-scale seawater boiling and pan evaporation. This supplements industrial production and provides resilience if distribution is disrupted.

11. Optimise Lake Grassmere operations for nuclear winter conditions. Potential adaptations include: deepening concentration ponds, using wind-assisted evaporation (spraying brine to increase surface area), covering ponds with transparent material to create greenhouse effect, pre-heating brine with waste heat before it enters evaporation ponds.

Years 1–3 (Phase 2)

12. Scale supplementary production based on pilot results. If geothermal-assisted evaporation proves effective, build additional facilities near geothermal fields. If northern solar pans produce well, expand those.

13. Establish salt distribution logistics. Lake Grassmere is in the South Island; most population is in the North Island. Rail and coastal shipping for bulk salt transport must be maintained (coordinate with Doc #53 on fuel allocation for transport).

14. Develop salt purification capability beyond Lake Grassmere’s existing refinery. Food-grade and industrial-grade salt have different purity requirements (see Section 5). Community-produced salt may need additional processing for food or chemical use.

15. Begin salt stockpiling once production exceeds immediate consumption. Salt stores indefinitely when kept dry. Building a national strategic salt reserve provides buffer against production disruptions.

Ongoing (Phases 3+)

16. Maintain and expand production as nuclear winter eases. Solar evaporation productivity should recover as temperatures and sunshine hours normalise (Phases 3–4). Use this recovery period to build production capacity beyond immediate needs, creating export surplus.

17. Develop salt as a trade good. NZ’s coastal access and established production capability position salt as a potential export to inland regions or countries with less favourable conditions (see Section 8).

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ECONOMIC JUSTIFICATION

Salt’s role in the recovery economy

Salt is a prerequisite input for multiple essential recovery activities. Without adequate salt supply:

• Food preservation fails. Salt curing, brining, and fermentation — the primary long-term preservation methods that do not depend on electricity — all require salt in quantity. Doc #78 estimates that preserving the destocking meat surplus alone could require 15,000–30,000 tonnes of salt.⁸ Ongoing preservation of meat, fish, and vegetables for the population requires thousands of additional tonnes annually.

• Water treatment fails. Domestic chlorine production via electrolysis of salt brine is the pathway identified in Doc #48 for replacing imported water treatment chemicals. NZ’s water treatment chlorine requirement of approximately 4,000 tonnes per year translates to approximately 6,600 tonnes of salt per year as feedstock.⁹

• Soap production becomes constrained. Caustic soda (NaOH), produced by electrolysis of salt brine, is required for hard bar soap production. Without it, NZ reverts to soft potash soap from wood ash lye — which dissolves faster, lathers less effectively, and cannot be formed into transportable bars, making distribution and per-capita rationing significantly harder (Doc #37).¹⁰

• Industrial chemistry stalls. Caustic soda and soda ash, both derivable from salt, are foundational industrial chemicals used in dozens of processes.

Labour and infrastructure costs

Salt production is relatively low in labour intensity compared to its economic importance.

Lake Grassmere currently operates with a workforce of approximately 15–30 permanent staff, supplemented by seasonal workers during the harvest period.¹¹ Maintaining this facility requires essentially no new construction — the ponds, pumping stations, and harvesting equipment already exist. Labour cost is perhaps 30–50 person-years per year for 50,000+ tonnes of output.

Supplementary solar salt pans require construction labour (earthworks, lining, seawater channels) but minimal ongoing operational labour once built. Construction of a 10-hectare salt pan suitable for producing perhaps 500–2,000 tonnes per year might require 20–40 person-months of labour, plus 2–5 ongoing workers for operation and harvesting.¹²

Forced evaporation using geothermal or waste heat requires more energy input per tonne but produces salt year-round regardless of weather. If co-located with an existing heat source (geothermal power station, industrial plant), the marginal labour cost is modest — perhaps 5–10 workers per facility producing 1,000–5,000 tonnes per year.

Comparison: cost of salt shortage vs. cost of expanded production

If salt production falls short of demand, the consequences cascade through multiple essential systems. A 30,000-tonne shortfall in salt (plausible under nuclear winter with no supplementary production) could mean:

• 15,000–30,000 tonnes of meat that cannot be salt-preserved and must be consumed immediately, frozen (grid-dependent), or wasted
• Reduced chlorine production, compromising water treatment for urban populations
• Reduced caustic soda production, constraining soap supply and industrial chemistry

Expanding salt production by 30,000 tonnes through a combination of supplementary solar pans and forced evaporation might require a total investment of 100–200 person-years of construction labour and 30–50 ongoing person-years of operational labour. This is modest relative to the systems that salt supply enables. The breakeven is essentially immediate — every tonne of salt produced enables preservation, water treatment, or industrial chemistry that would otherwise not occur.

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1. NZ’S EXISTING SALT PRODUCTION: LAKE GRASSMERE

1.1 The facility

Lake Grassmere (known in te reo Māori as Kapara-te-hau) is located on the Marlborough coast of the South Island, approximately 30 km south-east of Blenheim. It is NZ’s only operating salt production facility of significant scale and has been producing salt since 1943, when wartime disruption of salt imports prompted the NZ government to develop domestic production.¹³

The site was chosen because Marlborough has NZ’s highest sunshine hours (approximately 2,400–2,500 hours per year) and lowest annual rainfall (approximately 650 mm in the immediate coastal area), making it the most favourable location in NZ for solar evaporation.¹⁴ Even so, Marlborough is marginal for solar salt production by international standards — Australian solar salt works (e.g., at Dampier or Port Hedland) operate in climates with twice the evaporation potential. Lake Grassmere succeeds because of careful engineering of the evaporation process, not because the climate is ideal.

1.2 How solar evaporation works

The production process at Lake Grassmere follows a standard sequence used at solar salt works worldwide:¹⁵

1. Seawater intake. Seawater (approximately 3.5% NaCl, or 35 grams of salt per litre) is pumped from the coast into large initial concentration ponds.

2. Concentration ponds. Seawater moves through a series of progressively smaller, shallower ponds over a period of months. Solar energy and wind evaporate water, progressively increasing the salt concentration. The total pond area at Lake Grassmere is approximately 688 hectares (roughly 1,700 acres).¹⁶

3. Fractional crystallisation. As the brine concentrates, compounds with lower solubility than NaCl precipitate out first. Calcium carbonate (CaCO3) precipitates once the brine has evaporated to roughly 50% of its original volume (i.e., NaCl concentration roughly doubled from seawater). Calcium sulfate (gypsum, CaSO4) precipitates at roughly 75–80% volume reduction. This natural fractional crystallisation removes some impurities before the NaCl itself crystallises.¹⁷

4. Crystallisation ponds. When brine reaches approximately 25–26% NaCl (near saturation at 26.3%), it is moved to shallow crystallisation ponds where NaCl precipitates as a solid salt crust on the pond floor. This happens when sufficient additional water evaporates to push the solution past its saturation point.

5. Harvesting. The salt crust is mechanically harvested — typically by heavy machinery that scrapes the crystallised salt from the pond floor. At Lake Grassmere, harvesting occurs primarily in late summer and autumn (February–April), when the crystallisation ponds have built up a substantial salt layer.¹⁸

6. Washing and stockpiling. The harvested raw salt is washed with saturated brine (not fresh water, which would dissolve the salt) to remove surface impurities, then stockpiled for transport.

7. Refining (at Mount Maunganui). For food-grade and high-purity industrial products, the raw salt is shipped to Dominion Salt’s Mount Maunganui facility, where it is dissolved, purified (removal of calcium, magnesium, and other trace minerals), recrystallised, dried, and graded.¹⁹

1.3 Production figures and capacity

Lake Grassmere’s annual output varies with weather conditions — in a good year (high sunshine, low summer rainfall), production reaches approximately 70,000 tonnes; in a poor year (cloudy, wet summer), production can fall below 50,000 tonnes.²⁰ The facility has peak capacity of approximately 80,000 tonnes under optimal conditions, but the average over a multi-year period is closer to 55,000–65,000 tonnes.²¹

This variability is inherent to solar salt production and is a critical factor under nuclear winter, which pushes every climate variable in the wrong direction for evaporation (see Section 3).

1.4 Mount Maunganui refinery

The Mount Maunganui facility is a salt refinery, not a salt producer — it processes salt, not seawater. Under import cutoff, it can only process salt sourced from Lake Grassmere or any supplementary domestic production. Its value is in purification: converting raw solar salt (which contains calcium, magnesium, sulfate, and other impurities at levels of 1–3%) into food-grade salt (>99.5% NaCl) and industrial-grade products.²²

The refinery operates using grid electricity and steam, both of which remain available under the baseline scenario. Maintaining it in operation ensures NZ can produce food-grade table salt, not just coarse industrial salt. This matters for food safety and for chemical applications (chlor-alkali electrolysis works better with purer salt, as impurities foul electrodes and contaminate products).²³

1.5 Current NZ salt consumption

NZ’s total salt consumption before the event — domestic production plus imports — is approximately 150,000–220,000 tonnes per year.²⁴ This breaks down roughly as:

Use category	Estimated annual consumption (tonnes)	Notes
Industrial (dairy, meat processing, water treatment, chemical)	80,000–120,000	Much of this tied to export-oriented industries that cease under isolation
Food (table salt, food manufacturing)	15,000–25,000	Relatively stable; may increase if salt preservation replaces other methods
Agricultural (stock feed, fertiliser additive)	10,000–20,000	Continues; may increase if pastoral sector relies more on supplementary feeding
Road de-icing	5,000–15,000	Relevant mainly to South Island alpine passes; may decrease as vehicle traffic falls
Other (softening, miscellaneous)	10,000–20,000	Much of this discretionary and can be eliminated

Under post-event conditions, several demand categories change substantially:

• Export-oriented processing stops. NZ’s dairy and meat processing industries consume large quantities of salt, but much of this throughput serves export markets that no longer exist. Domestic consumption of dairy and meat products continues, but at lower volumes.
• Food preservation demand increases. The shift from refrigeration-dependent to salt-dependent food preservation creates new demand of potentially 20,000–40,000 tonnes per year (see Doc #78).
• Water treatment demand emerges. Chlorine production from salt brine requires approximately 6,600 tonnes of salt per year for NZ’s water treatment needs (Doc #48).²⁵
• De-icing demand falls. With dramatically reduced vehicle traffic, road salt demand drops to a fraction of pre-event levels.
• Industrial chemistry demand grows slowly. Caustic soda and soda ash production from salt (Doc #112) ramps up over Phases 2–4 as NZ develops domestic chemical production capability.

Estimated post-event national salt demand: 50,000–100,000 tonnes per year, depending on the scale of food preservation operations and the pace of industrial chemistry development. This is lower than pre-event consumption because export-oriented processing has ceased, but higher than one might expect because of new preservation demand.²⁶ The range is derived by summing the use-category estimates in Appendix B; the low end assumes modest preservation activity and slow industrial chemistry development, the high end assumes aggressive salt preservation and active chlor-alkali production.

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2. NZ’S EXISTING SALT STOCKS

At the time of the event, NZ holds significant salt stocks in the supply chain. These provide a buffer while production adjusts to post-event conditions.

2.1 Where salt is stored

• Lake Grassmere stockpiles. Raw salt is stockpiled on-site after harvest, awaiting transport. The site typically holds several months’ worth of production — perhaps 10,000–30,000 tonnes depending on the time of year and transport schedules.²⁷
• Mount Maunganui refinery. Raw and refined salt in various stages of processing and packaging. Perhaps 5,000–15,000 tonnes.
• Wholesale and distribution warehouses. Salt distributors and industrial suppliers hold stocks. The total is uncertain but likely 5,000–20,000 tonnes nationally.
• End-user stocks. Dairy factories, meat processing plants, water treatment plants, food manufacturers, and other industrial users hold working stocks ranging from days to weeks of consumption. Collectively perhaps 10,000–30,000 tonnes.
• Retail. Supermarkets, hardware stores (pool salt, water softener salt), and agricultural suppliers hold perhaps 1,000–5,000 tonnes.

Estimated total stocks in NZ at any given time: 30,000–100,000 tonnes. The wide range reflects seasonal variation (stocks are highest after the Lake Grassmere harvest in autumn) and uncertainty about distributor and end-user inventories. The national asset census (Doc #8) should establish the precise figure.

2.2 Depletion timeline

At a post-event consumption rate of 50,000–100,000 tonnes per year, and with stocks of 30,000–100,000 tonnes, the existing stocks provide a buffer of approximately 4–24 months even without any ongoing production.²⁸ In practice, Lake Grassmere continues producing throughout this period (at reduced rates under nuclear winter), so the actual buffer is longer. Salt is not a Day 1 crisis — there is time to plan.

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3. NUCLEAR WINTER IMPACT ON SOLAR EVAPORATION

This is the document’s central technical concern. Solar evaporation at Lake Grassmere depends on energy input from sunlight and wind, which drive the evaporation of water from brine ponds. Nuclear winter degrades both.

3.1 Physics of solar evaporation

The evaporation rate from an open water surface depends on several factors:²⁹

• Solar radiation (dominant factor). Direct and diffuse solar energy heats the brine, increasing the rate at which water molecules escape the surface. Higher radiation = faster evaporation.
• Air temperature. Warmer air holds more moisture, but the temperature of the brine itself matters more. A warmer brine surface evaporates faster.
• Humidity. Drier air absorbs more water vapour. Marlborough’s relatively low humidity contributes to Lake Grassmere’s productivity.
• Wind speed. Wind removes the saturated air layer immediately above the brine surface, replacing it with drier air and accelerating evaporation.
• Brine temperature relative to air temperature. If the brine is warmer than the air (e.g., because of absorbed solar energy), evaporation is enhanced.

3.2 Expected nuclear winter conditions in Marlborough

Under the baseline nuclear winter scenario (5–8 degrees C average cooling globally, with southern hemisphere experiencing somewhat less cooling than the northern):³⁰

• Temperature reduction in Marlborough: Estimated 3–6 degrees C below normal. Marlborough’s normal summer average maximum is approximately 23–24 degrees C; under nuclear winter, summer maxima might be 17–21 degrees C — similar to a normal Marlborough spring or a cool southerly period.³¹
• Solar radiation reduction: Nuclear winter models suggest 20–40% reduction in surface solar radiation due to stratospheric soot and aerosol.³² Marlborough normally receives approximately 1,800–2,000 kWh/m2 per year of solar radiation; this might fall to 1,100–1,600 kWh/m2.
• Cloud cover and precipitation: Uncertain. Nuclear winter may increase cloud cover in some regions and decrease it in others. Increased precipitation over the salt pans would directly dilute brine and slow the concentration process.
• Wind patterns: Difficult to predict regionally. Wind may increase or decrease depending on altered atmospheric circulation.

3.3 Impact on production

The relationship between evaporation rate and environmental conditions is approximately:³³

Evaporation rate is proportional to: (net solar radiation) + f(wind speed, temperature difference, humidity)

A 30% reduction in solar radiation combined with a 4–5 degrees C reduction in air temperature reduces total evaporation driving force by an estimated 30–50%. If precipitation over the ponds also increases, the net effect on salt production could be a reduction of 30–60%.

Estimated Lake Grassmere output under nuclear winter: 20,000–50,000 tonnes per year, compared to a normal 55,000–70,000 tonnes. The range is wide because the precise impact depends on factors that cannot be predicted with confidence — particularly Marlborough’s specific precipitation response and the degree of radiation reduction at that latitude.

Seasonal compression. Under normal conditions, most productive evaporation at Lake Grassmere occurs over approximately 5–6 months (October–March), with the harvest typically in February–April.³⁴ Under nuclear winter, the effective evaporation season may compress to 3–4 months (December–March), when whatever solar radiation is available is most intense. This makes Lake Grassmere’s operations more vulnerable to bad weather during a shorter productive window.

3.4 Potential adaptations at Lake Grassmere

Several engineering modifications could partially compensate for reduced evaporation:

Wind-assisted evaporation (spray evaporation). Pumping brine through sprinklers or spray nozzles dramatically increases the surface area exposed to air, accelerating evaporation even under reduced solar conditions. This technique is used at some salt works in cooler climates.³⁵ The energy cost is pumping, which uses grid electricity — modest relative to the production gain. A spray evaporation system over the concentration ponds could potentially increase effective evaporation rates by 30–100%.

Greenhouse-covered ponds. Covering some or all crystallisation ponds with transparent plastic sheeting (polyethylene film, available in NZ agricultural supply) creates a greenhouse effect — trapping heat and raising brine temperature. The trade-off is reduced wind exposure, which normally aids evaporation, but under nuclear winter conditions the thermal gain from greenhouse covering may outweigh the wind loss. This is an experiment worth conducting in Phase 1.³⁶

Pre-heating brine. If waste heat is available from any nearby source (there are limited industrial facilities in the Lake Grassmere area, but trucking hot brine is impractical — this is more relevant for supplementary sites), pre-heating brine before it enters evaporation ponds increases evaporation rate.

Deeper concentration ponds with longer residence times. Under reduced evaporation rates, brine needs longer to concentrate. If pond area is the constraint, the solution is either more ponds or longer cycling times. Lake Grassmere has limited room for expansion, but optimising the existing pond system for longer brine residence could improve salt recovery rates even at lower evaporation rates.

The realistic expectation: Adaptations at Lake Grassmere may recover 10–20% of the lost production, bringing output to perhaps 25,000–55,000 tonnes per year.³⁷ This is a rough engineering estimate based on the claimed performance ranges for spray evaporation and greenhouse-covered ponds cited in notes ³⁸ and ³⁹; site-specific testing in Phase 1 is needed to confirm. This is meaningful but probably insufficient to meet total national demand without supplementary production.

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4. SUPPLEMENTARY PRODUCTION: SOLAR SALT PANS

4.1 Site selection

New solar salt pans can be established at any coastal location with:

• Flat terrain at or near sea level. The ponds need to be above normal high tide but close enough to the coast for seawater supply (pumped or gravity-fed).
• Low freshwater runoff. The site should not be in a catchment that delivers significant rainfall runoff into the ponds during the evaporation season.
• Adequate sunshine. Under nuclear winter, everywhere in NZ receives less sunshine, but the north of the North Island (Northland, Auckland, Bay of Plenty) retains more solar energy than the south.
• Access to labour and transport. The salt must be moved to where it is needed.

Candidate regions:

Region	Advantages	Disadvantages
Northland	Warmest NZ climate; best solar conditions under nuclear winter	Limited existing infrastructure; distant from population centres
Bay of Plenty	Good climate; Mount Maunganui refinery nearby	Rainfall can be moderate
Hawke’s Bay	Dry climate (rain shadow); flat coastal areas	Moderate solar under nuclear winter
Wairarapa coast	Relatively dry; near Wellington demand centre	Limited flat coastal terrain
Marlborough	Adjacent to Lake Grassmere; driest NZ climate	Already being used; limited additional area
Canterbury plains	Flat; near Christchurch demand	Colder; lower evaporation potential

4.2 Construction

A basic solar salt pan requires:⁴⁰

1. Clearing and levelling the site. Remove vegetation, grade to a slight slope for brine flow.
2. Compacting or lining the base. The pond floor must be reasonably impermeable to prevent brine seeping into the ground. Options include natural clay compaction (if clay soil is available), plastic lining (polyethylene sheet — available from agricultural supply), or bitumen coating. Unlined ponds on sandy soil lose significant brine to seepage and are inefficient.
3. Dividing into concentration and crystallisation sections. At minimum, three stages: initial concentration pond, intermediate concentration, and crystallisation. More stages improve salt purity and yield.
4. Seawater supply. A pump and pipe from the sea (or a tidal inlet channel, if the site permits gravity flow at high tide). A small electric pump drawing from the ocean requires grid power, corrosion-resistant pipe (PVC or polyethylene — available from NZ agricultural and plumbing suppliers while stocks last), and a saltwater-rated pump. These are standard components but become harder to replace as imported stocks deplete; gravity-fed tidal inlet channels avoid the pump dependency entirely where terrain permits.
5. Brine transfer. Pipes, channels, or pumps to move brine between ponds as it concentrates.
6. Harvesting access. The crystallisation ponds must be accessible to workers or machinery for scraping the salt crust.

Scale example: A 10-hectare solar pan system in Northland, with NZ’s reduced nuclear winter solar conditions, might produce an estimated 500–2,000 tonnes of salt per year. This is an order-of-magnitude estimate based on typical yields for small solar salt works in temperate climates (50–200 tonnes per hectare of crystallisation area per year under normal conditions, reduced by 30–60% under nuclear winter).⁴¹ The actual yield depends on the specific site and conditions.

Construction effort: Perhaps 20–40 person-months for a 10-hectare system — earthmoving, lining, pipe-laying, pump installation. If done by hand without heavy machinery, the labour is significantly higher. Farm equipment (tractors with blades, post-hole diggers for pilings) can substitute for dedicated earthmoving equipment.

4.3 Multiple small sites vs. one large site

There are arguments for both approaches:

Multiple small sites (1–5 hectares each, spread along the coast): - Resilience — no single point of failure - Reduced transport requirements if each site serves its local region - Can be built and operated by local communities - Lower individual construction effort

One or two large supplementary sites (20–50 hectares): - Higher efficiency per unit of labour - Better salt quality through more concentration stages - Easier to manage and optimise - Can justify spray evaporation and other engineering improvements

The recommended approach is both: encourage community-scale salt-making at many coastal locations (low investment, immediate partial benefit), while also developing one or two larger supplementary sites in the most favourable northern locations to provide bulk production.

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5. SUPPLEMENTARY PRODUCTION: FORCED EVAPORATION

Solar evaporation is energy-free but weather-dependent. Forced evaporation — boiling or heating seawater using external energy — is weather-independent but energy-intensive. Under nuclear winter, when solar evaporation is degraded, forced evaporation becomes relatively more attractive.

5.1 Energy cost of boiling seawater

Producing 1 kg of salt by evaporating seawater requires evaporating approximately 28.5 litres of water (since seawater is ~3.5% NaCl by weight). The latent heat of vapourisation of water is approximately 2,260 kJ/kg, so evaporating 28.5 kg of water requires approximately 64,000 kJ, or approximately 17.8 kWh of thermal energy per kg of salt produced.⁴²

This is a substantial energy cost. Producing 10,000 tonnes of salt by boiling seawater from ambient would require approximately 178,000 MWh of thermal energy. Converted to electricity at 100% efficiency (i.e., resistive heating), this is approximately 178 GWh — roughly 0.3–0.5% of NZ’s annual electricity generation of approximately 43,000 GWh, depending on actual energy costs per tonne (which vary with brine temperature and equipment efficiency).⁴³

This is not trivial but is manageable for NZ’s grid, particularly if the production is spread across multiple facilities and operated during off-peak hours (NZ hydro generation is somewhat flexible). The key question is whether this electricity is better used for salt production or for other purposes — an allocation decision that depends on the overall energy budget (Doc #67).

5.2 Reducing energy cost through pre-concentration

The energy cost of forced evaporation drops dramatically if the brine is pre-concentrated by solar evaporation before being heated. If solar pans concentrate seawater from 3.5% to 20% NaCl (which happens naturally in concentration ponds even under reduced solar conditions), then forced evaporation only needs to remove the final ~20% of water — reducing energy requirements by roughly 80%.⁴⁴

The hybrid approach: Use solar concentration ponds to do as much of the evaporation as the climate allows (free energy), then finish the process with heat-assisted evaporation. This combines the low cost of solar evaporation with the reliability of thermal evaporation. Under nuclear winter, the solar stage works more slowly but still provides significant pre-concentration.

5.3 Geothermal heat

NZ’s geothermal fields offer waste heat that is effectively free once the power generation infrastructure exists. Several NZ geothermal power stations discharge hot water (70–130 degrees C) as waste — the Wairakei, Kawerau, and Ohaaki fields in the Taupo Volcanic Zone are the most significant.⁴⁵

A geothermal-assisted salt production facility would:

1. Pump seawater to the geothermal site (or pump geothermal brine to a coastal site — but the distances involved in the Taupo Volcanic Zone make coastal pumping impractical)
2. Use geothermal heat to evaporate seawater in enclosed evaporators
3. Harvest salt from the concentrated brine

The challenge is that geothermal sites in NZ are inland (60–100+ km from the coast). Pumping seawater inland is energy-intensive and requires pipeline infrastructure. A more practical approach is to pre-concentrate seawater at coastal solar pans and truck concentrated brine (at ~20% NaCl) to the geothermal site — the volume is roughly 80% less than raw seawater, making transport feasible.

Dependency chain for the truck-and-evaporate approach: (1) Coastal solar pans must be operating and producing pre-concentrated brine — requiring site construction (Section 4.2) and seasonal solar output. (2) Tanker trucks capable of carrying corrosive brine (stainless steel or polyethylene-lined tanks) must be available and fuelled — the truck fleet dependency feeds into Doc #53 fuel allocation. (3) The geothermal site must have available waste heat — Kawerau power station must remain operational and willing to supply process heat. (4) Evaporation vessels at the geothermal site (large stainless steel or fibre-reinforced plastic tanks with heat exchangers) must be fabricated or sourced. None of these are insurmountable, but each is a real dependency that adds to the timeline and investment required.

Kawerau is the most promising site: it is closer to the coast (approximately 60 km from the Bay of Plenty coast), has significant geothermal heat availability from the Kawerau geothermal field, and has existing industrial infrastructure (the former Tasman Pulp and Paper mill site).⁴⁶ A Kawerau-based forced evaporation facility using waste geothermal heat, fed with pre-concentrated brine from Bay of Plenty coastal pans, could plausibly produce 5,000–15,000 tonnes of salt per year. This estimate is speculative and would require engineering assessment.

5.4 Industrial waste heat

Any industrial facility that generates waste heat is a candidate for co-located salt production. Under post-event conditions, the most significant waste heat sources include:

• Dairy factories — milk powder production involves extensive heat use, with waste heat available from condensers and dryers. Many dairy factories are near the coast.
• Meat processing plants — rendering and cooking generate waste heat.
• Charcoal kilns (Doc #102) — charcoal production generates significant waste heat that is typically vented.
• NZ Steel at Glenbrook (Doc #89) — steelmaking generates waste heat, and the facility is near the Manukau Harbour coast.

The salt production potential from waste heat recovery is difficult to estimate without site-specific engineering, but the principle is sound: any heat that is currently wasted and can be applied to seawater evaporation produces salt at near-zero marginal energy cost. The engineering challenge is in heat exchange infrastructure — piping hot fluids to evaporation vessels, managing corrosion from hot brine, and integrating salt production with the host facility’s operations without disrupting its primary function.

5.5 Direct electric heating

If geothermal and waste heat are insufficient, NZ can use grid electricity for resistive heating of seawater. This is the least efficient approach (converting high-grade electricity to low-grade heat) but is available anywhere the grid reaches, which is most of NZ’s coast.

At a pre-concentrated brine input (20% NaCl), producing 10,000 tonnes of salt requires approximately 35,000 MWh of electricity — roughly 0.06–0.10% of NZ’s annual generation, depending on system efficiency. This is acceptable as a supplementary source but should not be the primary production method if solar or geothermal alternatives are available.

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6. COMMUNITY-SCALE SALT PRODUCTION

6.1 Small-scale seawater boiling

The most accessible supplementary salt production method, available to any coastal community with firewood or electric heating:

1. Collect seawater in clean containers (avoiding harbour or estuary water that may be contaminated with sewage or industrial waste).
2. Boil in large pots over fire or electric heating elements. For efficiency, use wide, shallow pans rather than deep pots — maximising surface area increases evaporation rate.
3. Continue boiling until salt crystallises. The brine will first become turbid as calcium carbonate precipitates (skim this off). Then gypsum precipitates as the brine gets more concentrated. Finally, NaCl crystallises as the brine approaches saturation.
4. Scoop out salt crystals or drain remaining liquid (bitterns — concentrated magnesium and potassium salts) and collect the salt.
5. Rinse harvested salt with a small amount of saturated brine to remove surface impurities.

Yield: Approximately 35 g of salt per litre of seawater. A 200-litre drum of seawater produces about 7 kg of salt. A community boiling operation using several large pots over a wood fire might produce 20–50 kg per day.⁴⁷

Energy cost: Heating 200 litres of seawater from 15 degrees C to boiling and then evaporating it requires approximately 150 kWh of thermal energy. At firewood efficiency of ~20%, this means burning roughly 100–150 kg of dry firewood per 7 kg of salt. This is energy-intensive and should be reserved for small-scale, emergency, or supplementary production — not a primary production method.⁴⁸

Alternative source — coastal plant ash: Burning certain coastal plants (e.g., salt-tolerant species growing in estuarine or littoral zones) and leaching the ash produces a sodium-rich brine that can be evaporated for salt. This method — historically practiced by Maori and documented in multiple cultures worldwide — is useful where seawater collection is impractical but coastal vegetation is abundant.⁴⁹ Yields are low compared to direct seawater boiling and the product contains more potassium and other minerals, but it is a functional supplementary source.

Quality: Community-boiled salt is adequate for food preservation, cooking, and animal nutrition, but carries performance gaps compared to refined product. The key issue is bitterns — the concentrated residual liquid containing magnesium chloride, potassium chloride, and other salts that remain after NaCl crystallises. If bitterns are not fully drained before the salt dries, the resulting product will be bitter-tasting (from MgCl2) and hygroscopic (prone to caking and drawing moisture). In fermentation and pickling, magnesium-contaminated salt can suppress lactic acid bacteria activity and produce off-flavours. This is manageable — draining bitterns promptly and rinsing harvested crystals with a small volume of saturated NaCl brine substantially reduces impurity levels — but the performance gap relative to commercial refined salt is real and should be acknowledged to communities relying on this method. For industrial chemistry (chlor-alkali electrolysis), the impurities cause electrode fouling and membrane degradation; additional brine purification is not advisable but required.

6.2 Small-scale solar pans

Any coastal community with basic tools and earthmoving capacity can construct small solar evaporation pans. The process requires site clearing, a low-permeability pond base (clay compaction, plastic sheeting, or concrete), and a seawater supply — none of which are exotic, but each requires labour, material, and at least basic construction knowledge:

• Materials: Plastic-lined wooden frames, concrete block enclosures, or natural clay-bottomed depressions near the coast.
• Scale: Even a 10 m x 10 m (100 m2) pan can produce a useful quantity of salt — perhaps 5–20 tonnes per year under normal conditions, 2–12 tonnes under nuclear winter, depending on location and climate.⁵⁰
• Labour: Construction in a day or two with basic tools. Ongoing labour is minimal — check pans, transfer brine, harvest salt.

These small pans will not replace Lake Grassmere, but across dozens or hundreds of coastal communities, they contribute meaningful supplementary production and provide local resilience.

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7. SALT GRADES AND PURIFICATION

Not all salt uses require the same purity. Understanding the grading requirements for different applications prevents wasting purification effort on salt that does not need it.

7.1 Food-grade salt

Requirements: >99% NaCl, low levels of calcium, magnesium, and sulfate (which affect taste), no contamination with toxic metals or organic matter. Anti-caking agents (normally added to table salt) are a convenience, not a safety requirement, and can be omitted post-event.⁵¹

Where it matters: Table salt, food manufacturing, pickling/brining (impure salt can cause cloudy brine and off-flavours in preserved foods).

How to produce: Dissolve raw solar salt in clean fresh water, allow insoluble impurities to settle, filter, then re-evaporate the clarified brine by boiling. This is the basic principle behind the Mount Maunganui refinery. At community scale, the same process works with pots and cloth filters — dissolve, settle, strain, boil down. The resulting salt is significantly purer than the input, though not as pure as industrial refining produces.

7.2 Industrial-grade salt

Requirements: >95% NaCl, low moisture. Purity requirements vary by application.

Where it matters: Road de-icing (low purity acceptable), general industrial use, animal feed supplement, some chemical processes.

How to produce: Raw solar salt straight from the pans, washed with saturated brine, meets industrial-grade specifications without further refining. Performance note: Raw solar salt used in animal feed, road de-icing, and general industrial processes performs comparably to refined salt for those purposes. However, for food preservation applications (heavy salting of meat, pickling), the higher mineral content (calcium, magnesium, sulfate) in raw solar salt can produce off-flavours, greyish colour in cured meat, and cloudiness or bitterness in brines — acceptable in an emergency but inferior to refined product. Communities producing salt for food use should aim to wash and recrystallise where possible.

7.3 Chemical-grade salt for chlor-alkali

Requirements: High purity (>99% NaCl) is strongly preferred for electrolysis. Calcium and magnesium ions in the brine foul membranes and electrodes, reducing efficiency and equipment life. Sulfate ions are less problematic but also undesirable.⁵²

Where it matters: Chlorine production for water treatment (Doc #48), caustic soda production (Doc #112).

How to produce: Either use Mount Maunganui-refined salt, or dissolve raw salt, precipitate calcium and magnesium by adding a small amount of sodium carbonate (soda ash) or sodium hydroxide (caustic soda) to the brine, filter, and use the purified brine directly for electrolysis. This brine purification step is standard practice in chlor-alkali plants worldwide and requires no exotic equipment or chemicals — the purification agents (soda ash and caustic soda) are themselves products of the chlor-alkali process, creating a convenient loop.⁵³ Bootstrapping note: This “convenient loop” only holds once the chlor-alkali process is already running. For the initial startup, a small supply of soda ash or caustic soda must come from another source — either from pre-event stocks (if any soda ash imports are available in the distribution chain at event time, which the national census (Doc #8) will establish), from the Solvay process (which requires limestone and ammonia — see Doc #112), or from wood ash lye (which provides potassium hydroxide rather than sodium hydroxide, and is less effective for calcium precipitation). The startup dependency chain should be resolved in Phase 1 planning before committing to chlor-alkali production at scale.

7.4 Summary of purity by use

Use	Minimum purity	Raw solar salt acceptable?	Notes
Food preservation (salting, brining)	95–99%	Yes, for heavy salting; prefer refined for delicate flavours	Impurities affect taste but not safety
Table salt	>99%	No — needs dissolving and recrystallisation	Mount Maunganui refinery or community recrystallisation
Chlor-alkali electrolysis	>99% (as brine)	No — needs brine purification	Calcium/magnesium removal essential
Soap lye production	>95%	Usually yes	Impurities in salt do not significantly affect saponification
Animal nutrition	>90%	Yes	Animals tolerate mineral impurities; some are beneficial
Leather tanning	>90%	Yes	Crude salt has been used in tanning for centuries
De-icing	>80%	Yes	Lowest purity requirements of any use

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8. SALT AS A TRADE GOOD

8.1 NZ’s comparative advantage

NZ has extensive coastline, established salt production infrastructure, and grid electricity for supplementary production. These advantages position NZ as a potential salt exporter in a post-event trade network.

Landlocked regions or countries with limited coastal access would face severe salt shortages. In a scenario where trans-Tasman trade develops (Doc #150), NZ salt could be a valuable export — not because Australia lacks coastline (it does not), but because NZ’s established production infrastructure may recover faster than new Australian facilities built from scratch in different locations. Australia’s large solar salt works (Dampier, Port Hedland) are remote from population centres and depend on transport infrastructure that may be disrupted.

More significantly, NZ salt shipped on sailing vessels (Doc #138) to Pacific Island nations or other trading partners could become a foundation of NZ’s post-event export economy. Salt is dense, non-perishable, and universally needed — characteristics of an ideal bulk trade commodity.

8.2 Implications for production targets

If NZ aims to produce salt for export as well as domestic use, production targets should be set above domestic demand. An export surplus of 10,000–30,000 tonnes per year would provide meaningful trade volume. This requires total production capacity of 60,000–130,000 tonnes per year — achievable through Lake Grassmere (25,000–55,000 under nuclear winter, recovering to 60,000–70,000 as conditions normalise) plus supplementary sites.

The economic logic: salt production requires modest labour, uses free or low-cost energy (solar, geothermal), and produces a universally demanded commodity. The return on labour invested in salt production for export is likely high relative to most other export options available to NZ in the early recovery phases.

8.3 Long-term trajectory

As nuclear winter eases (Phases 3–4), Lake Grassmere’s output should recover toward pre-event levels. Supplementary production sites established during nuclear winter remain operational and add to total capacity. By Phase 4–5, NZ could be producing 80,000–120,000+ tonnes per year — well above domestic requirements and with significant export surplus.⁵⁴ This projection assumes Lake Grassmere returns to 55,000–70,000 tonnes per year as solar conditions normalise, plus 20,000–50,000 tonnes from supplementary sites built in Phases 1–2. Both components carry substantial uncertainty.

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9. DISTRIBUTION AND LOGISTICS

9.1 The geography problem

Lake Grassmere is in the South Island. Approximately 77% of NZ’s population lives in the North Island, with the largest demand centre (Auckland, ~1.7 million people) at the opposite end of the country.⁵⁵ The Mount Maunganui refinery partially addresses this — it is located in the North Island — but only if salt can be transported from Lake Grassmere to Mount Maunganui.

Pre-event supply chain: Lake Grassmere salt is transported by road and rail to Picton, then by inter-island ferry to Wellington, and onward by road and rail or by coastal shipping to Mount Maunganui and other North Island destinations.

Post-event supply chain vulnerabilities: - Inter-island ferry service depends on fuel (diesel or marine fuel oil) — see Doc #53 on fuel allocation. The ferries must be designated as essential transport for salt and other strategic freight. - Rail depends on fuel (for North Island trunk line, which is diesel-hauled north of Palmerston North) or electricity (South Island main trunk and some North Island lines are electrified). Electric rail should be prioritised where available. - Coastal shipping (salt is suitable for bulk shipping) may be developed as sailing vessels become available (Doc #138).

9.2 Reducing transport dependency

Establishing supplementary salt production in the North Island reduces the fraction of national salt supply that must cross Cook Strait. North Island coastal pans, Kawerau geothermal-assisted production, and community-scale production all contribute to North Island self-sufficiency for salt.

The goal should be that the North Island can meet its own basic salt needs from local sources within 2–3 years, with Lake Grassmere salt treated as a supplement and source of high-quality refined product rather than as the sole supply.

9.3 Bulk salt storage

Salt stores indefinitely when kept dry. It does not degrade, does not require refrigeration, and does not lose potency. The main storage requirement is a roof — salt exposed to rain dissolves. Bulk storage in covered facilities (warehouses, farm sheds, covered rail wagons) is straightforward.

Strategic salt reserves should be established at regional centres: Auckland, Hamilton, Tauranga (near Mount Maunganui), Wellington, Christchurch, Dunedin. Target reserve levels of 3–6 months’ regional consumption, built up from production surplus as it becomes available.

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10. DEPENDENCY CHAIN SUMMARY

Salt production depends on:

Dependency	Status	Risk
Seawater	Unlimited — NZ is an island	Negligible
Solar radiation (for evaporation)	Degraded by nuclear winter	Moderate — reduces production by 30–60%
Lake Grassmere infrastructure	Existing, operational	Low — pond maintenance is basic earthworks
Harvesting equipment	Existing — heavy machinery at Lake Grassmere	Moderate over time — machinery wears out without imported spare parts (see Doc #88)
Mount Maunganui refinery	Existing, operational	Low short-term; moderate long-term as equipment ages
Grid electricity (for pumping, refining, forced evaporation)	Available under baseline scenario	Low — NZ grid is 85%+ renewable (Doc #67)
Transport (Lake Grassmere to North Island)	Operational but fuel-dependent	Moderate — requires fuel allocation or electrified rail
Labour	Available — salt production is not skill-intensive	Low — training time is weeks, not years
Plastic lining for new pans	Available from NZ agricultural supply; finite stock	Moderate — new pans built after plastic stocks deplete will need clay or concrete lining

No critical dependencies that NZ cannot meet. This is why the feasibility rating is [A]. The constraining factor is throughput under nuclear winter, not fundamental capability.

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CRITICAL UNCERTAINTIES

Uncertainty	Why it matters	How to resolve
Actual evaporation rate reduction at Lake Grassmere under nuclear winter	Determines the core of NZ’s salt supply	Monitor from Day 1; compare actual evaporation against models; adjust production plans accordingly
Marlborough precipitation changes under nuclear winter	Rain on salt pans dilutes brine and washes out crystallised salt	Cannot be resolved in advance; operational monitoring and pond drainage systems are the response
Total national salt stocks at event time	Determines the buffer period	National asset census (Doc #8)
Actual post-event salt demand for food preservation	Doc #78 estimates are rough; actual demand depends on destocking scale, preservation methods chosen, and food system adaptation	Track actual salt consumption across preservation centres; adjust allocation as data accumulates
Effectiveness of spray evaporation adaptation at Lake Grassmere	Could significantly offset nuclear winter production losses	Pilot test in Phase 1
Viability of Kawerau geothermal salt production	A major potential supplementary source	Engineering feasibility assessment in first months
Long-term harvesting equipment maintenance at Lake Grassmere	Current equipment relies on imported parts for maintenance	Assess with Doc #88 (spare parts triage); develop workarounds (manual harvesting is possible but slower)
Rate of nuclear winter recovery	Determines when solar evaporation returns to normal productivity	Climate monitoring; beyond NZ’s control

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CROSS-REFERENCES

• Doc #1 — National Emergency Stockpile Strategy: Salt is a stockpile item. Include in national consumable inventory.
• Doc #8 — National Asset and Skills Census: Must quantify salt stocks nationally — all holders, all forms.
• Doc #37 — Soap Production and Hygiene Products: Requires caustic soda from salt brine electrolysis for hard bar soap production. Salt also used directly in some soap processes (salting out).
• Doc #48 — Water Treatment Without Imports: Domestic chlorine production from salt brine is the primary pathway for replacing imported water treatment chemicals. Approximately 6,600 tonnes/year of salt required.
• Doc #53 — Fuel Allocation: Transport of salt from Lake Grassmere to North Island requires fuel for inter-island ferries and rail.
• Doc #67 — National Grid: Grid electricity powers salt refining, pumping, and any forced evaporation. Salt production is an essential load.
• Doc #74 — Pastoral Farming Under Nuclear Winter: The destocking surge creates massive meat preservation demand, which drives the largest spike in salt demand.
• Doc #78 — Food Preservation Without Imports: The primary consumer of salt in the recovery economy. Salt is the foundation of indefinitely sustainable preservation methods.
• Doc #88 — Spare Parts Triage: Lake Grassmere harvesting and pumping equipment requires maintenance; spare parts availability affects long-term production capacity.
• Doc #101 — Leather Tanning: Uses salt for hide preservation and some tanning processes.
• Doc #102 — Charcoal Production: Charcoal kilns generate waste heat that could be captured for brine evaporation.
• Doc #112 — Caustic Soda and Industrial Alkali: Caustic soda is co-produced with chlorine from salt brine electrolysis. Salt supply determines NZ’s entire basic alkali chemistry capability.
• Doc #138 — Sailing Vessel Design: Salt is an ideal cargo for sailing trade — dense, non-perishable, universally demanded.
• Doc #145 — Workforce Reallocation: Salt production workers (especially Lake Grassmere staff) should be classified as essential and retained in their roles.
• Doc #151 — Trans-Tasman Relations and Trade: Salt is a potential NZ export commodity.

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APPENDIX A: QUICK REFERENCE — COMMUNITY SEAWATER BOILING

What you need: - Large pot or wide metal pan (wider = faster evaporation) - Heat source (fire, electric element) - Clean seawater (collect from open coast, not harbours or estuaries) - Cloth or fine mesh for filtering - Clean, dry containers for storing finished salt

Process: 1. Filter seawater through cloth to remove sand and debris. 2. Pour into pan to a depth of 5–10 cm. 3. Heat to a steady simmer (not a rolling boil — violent boiling wastes fuel without increasing evaporation much). 4. As water level drops, add more filtered seawater. Continue until a white crust begins forming on the pan surface and the liquid becomes thick and syrupy. 5. When most water has evaporated and the pan is full of damp salt crystals, remove from heat. 6. Drain remaining liquid (bitterns — this bitter liquid contains magnesium and potassium salts; discard or save for other uses). 7. Spread salt crystals to air-dry. 8. Store in a dry, covered container.

Yield: Approximately 35 g of salt per litre of seawater. A 20-litre pot produces about 700 g of salt per batch.

Quality: This salt is adequate for cooking, food preservation, and animal feed. It contains more minerals than refined table salt (slightly greyish colour, mild mineral taste). It is safe.

Energy: Plan on approximately 15–25 kg of dry firewood per kg of salt produced from raw seawater, depending on fire efficiency and equipment geometry.⁵⁶ If you can pre-concentrate seawater in a solar pan to approximately 20% NaCl before boiling, firewood requirements drop to roughly 3–5 kg per kg of salt — a strong incentive to combine solar pre-concentration with fire-assisted finishing.

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APPENDIX B: SALT REQUIREMENTS BY APPLICATION

Application	Salt required per unit	Annual national estimate	Notes
Meat preservation (heavy salting)	150–300 g per kg of meat	15,000–30,000 tonnes (destocking surge)	One-time spike in Phase 1; ongoing 3,000–8,000 tonnes/year
Fish preservation	200–400 g per kg of fish	2,000–5,000 tonnes/year	Depends on fisheries output (Doc #78)
Vegetable fermentation (sauerkraut, pickles)	20–30 g per kg of vegetables	500–2,000 tonnes/year	Lower salt-to-product ratio than meat
Cheese making	15–20 g per kg of cheese	500–1,500 tonnes/year	Depends on dairy production scale
Water treatment (chlorine production)	1.65 kg NaCl per kg Cl2	~6,600 tonnes/year	Stoichiometric minimum; practical consumption slightly higher
Caustic soda production	1.65 kg NaCl per kg NaOH	2,000–10,000 tonnes/year	Grows as industrial chemistry develops
Soap production (via caustic soda)	~0.3 kg NaCl per kg of soap	500–1,500 tonnes/year	Indirect — salt makes NaOH, NaOH makes soap
Animal nutrition (salt licks)	10–30 g per animal per day	3,000–8,000 tonnes/year	~10 million livestock x 20g/day average
Leather tanning	300–500 g per kg of hide	500–2,000 tonnes/year	Depends on leather production scale
Dental hygiene (salt toothpowder)	~5 g per person per month	~300 tonnes/year	Minor demand; can use lowest-grade salt
Estimated total annual demand		50,000–100,000 tonnes/year	Excluding initial destocking surge

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1. Salt (NaCl) has no viable substitute in its primary recovery roles. No other common mineral simultaneously serves as a food preservative (inhibiting microbial growth by osmotic desiccation), a chlorine source (via electrolysis), and a caustic soda precursor. Alternatives for each individual function exist (potassium chloride can substitute for some food-preservation uses; chlorine can be produced by other means; potassium hydroxide from wood ash can substitute for some caustic-soda applications) but none provide all three functions and none match NaCl’s availability or cost. See: Kostick, D.S., “Salt,” in Mineral Commodity Summaries, U.S. Geological Survey, annual.↩︎

2. Dominion Salt Ltd operates the Lake Grassmere solar salt works in Marlborough. Production figures of approximately 50,000–70,000 tonnes per year are based on industry reporting and vary with seasonal weather conditions. The facility has been NZ’s primary domestic salt production site since 1943. https://www.dominionsalt.co.nz/↩︎

3. Dominion Salt’s Mount Maunganui facility is a refinery and packaging plant, processing raw solar salt into table salt, food-grade salt, and industrial salt products. It handles both domestic Lake Grassmere salt and, under normal conditions, imported salt. Source: Dominion Salt company information. https://www.dominionsalt.co.nz/↩︎

4. NZ salt import volumes are estimated from Stats NZ trade data. NZ imports salt under HS code 2501 (salt, including table salt and denatured salt, and pure sodium chloride). Import volumes fluctuate year to year. The 100,000–150,000 tonne range is an approximate based on available trade statistics. Precise verification requires Stats NZ Infoshare data. https://www.stats.govt.nz/↩︎

5. The estimate of 30–60% reduction in solar evaporation under nuclear winter is based on the combined effects of reduced solar radiation (20–40% reduction per Robock et al., 2007), reduced air temperature (3–6 degrees C in Marlborough), and possible increased precipitation. The estimate is an assumption, not a modelled result, and could be significantly wrong in either direction. See: Robock, A. et al., “Nuclear winter revisited with a modern climate model and current nuclear arsenals,” Journal of Geophysical Research, 2007.↩︎

6. NZ salt import volumes are estimated from Stats NZ trade data. NZ imports salt under HS code 2501 (salt, including table salt and denatured salt, and pure sodium chloride). Import volumes fluctuate year to year. The 100,000–150,000 tonne range is an approximate based on available trade statistics. Precise verification requires Stats NZ Infoshare data. https://www.stats.govt.nz/↩︎

7. Chemical stability of NaCl: sodium chloride is a highly stable ionic compound that does not decompose, oxidise, or otherwise degrade under normal conditions. Salt from ancient evaporite deposits (e.g., the Khewra salt mine in Pakistan, formed approximately 250 million years ago) is chemically identical to freshly refined table salt. The only storage requirement is protection from moisture (which dissolves surface salt and causes caking) and contamination. Well-established physical chemistry; see any general chemistry reference on alkali metal halides.↩︎

8. Doc #78 (Food Preservation Without Imports) estimates that preserving the destocking meat surplus could require 15,000–30,000 tonnes of salt, based on heavy salting at 150–300 g/kg for approximately 100,000 tonnes of meat. These are order-of-magnitude estimates.↩︎

9. Stoichiometric calculation from Doc #48: the chlor-alkali reaction 2NaCl + 2H2O -> Cl2 + 2NaOH + H2 requires approximately 1.65 kg NaCl per kg Cl2 produced. For 4,000 tonnes of chlorine equivalent, this requires approximately 6,600 tonnes of NaCl. Practical consumption is slightly higher due to inefficiencies.↩︎

10. Performance comparison of potash soap vs. hard bar soap (made with NaOH from chlor-alkali): potassium soaps (from wood ash lye) are soft or liquid at room temperature because potassium stearate and oleate have lower melting points than sodium stearate. They dissolve rapidly in water and cannot be formed into bars without adding NaCl (salting-out with sodium chloride converts the potassium soap to sodium soap, but this loop requires salt anyway). Hard soap’s transportability matters for distribution across regional population centres. See: Spitz, L., “Soap Manufacturing Technology,” AOCS Press, 2009.↩︎

11. Lake Grassmere staffing figures are approximate estimates based on the facility’s scale and the nature of solar salt operations, which are seasonal and require relatively small permanent workforces. The actual workforce size should be confirmed directly with Dominion Salt.↩︎

12. Construction effort estimates for solar salt pans are based on general engineering estimates for earthworks and pond construction in temperate climates. These are rough estimates — actual effort depends heavily on site conditions, soil type, available equipment, and design sophistication.↩︎

13. Lake Grassmere salt production was established during World War II in response to wartime shipping disruptions that threatened NZ’s imported salt supply. The government initiated the project in 1943, and commercial production began shortly after. See: McLintock, A.H. (ed.), “An Encyclopaedia of New Zealand,” 1966, Government Printer, Wellington. http://www.teara.govt.nz/↩︎

14. Marlborough climate data from NIWA (National Institute of Water and Atmospheric Research). Blenheim averages approximately 2,400 sunshine hours per year, the highest in NZ, with annual rainfall of approximately 650 mm at the coast. https://www.niwa.co.nz/↩︎

15. Solar salt production process description based on standard references for solar evaporation salt works. See: Kostick, D.S., “Salt,” in Industrial Minerals and Rocks, SME, 2006; also: Langer, W.H. and Glanzman, V.M., “Natural Aggregate and the Environment,” American Geological Institute, 1993. The process described is universal across solar salt works worldwide.↩︎

16. Lake Grassmere pond area of approximately 688 hectares is cited in various sources describing the facility. This figure should be verified with Dominion Salt. The total facility area including roads, stockpiles, and infrastructure is larger.↩︎

17. Fractional crystallisation sequence during solar evaporation: these concentration thresholds are expressed as percentage of volume reduction from original seawater (i.e., how much water has been evaporated). CaCO3 precipitates once roughly 50% of the water has evaporated; CaSO4 (gypsum) at roughly 75–80% volume reduction; NaCl when the remaining brine approaches saturation (approximately 25–26% NaCl by weight). Standard evaporite mineralogy; see any physical chemistry reference or: Warren, J.K., “Evaporites: Sediments, Resources and Hydrocarbons,” Springer, 2006.↩︎

18. Lake Grassmere harvesting is typically carried out in late summer and autumn using mechanical harvesters. The exact harvest timing varies with seasonal evaporation conditions. Source: Dominion Salt operational descriptions.↩︎

19. Dominion Salt’s Mount Maunganui facility is a refinery and packaging plant, processing raw solar salt into table salt, food-grade salt, and industrial salt products. It handles both domestic Lake Grassmere salt and, under normal conditions, imported salt. Source: Dominion Salt company information. https://www.dominionsalt.co.nz/↩︎

20. Dominion Salt Ltd operates the Lake Grassmere solar salt works in Marlborough. Production figures of approximately 50,000–70,000 tonnes per year are based on industry reporting and vary with seasonal weather conditions. The facility has been NZ’s primary domestic salt production site since 1943. https://www.dominionsalt.co.nz/↩︎

21. Multi-year average production at Lake Grassmere is estimated based on the range of annual figures reported. Weather variability causes significant year-to-year fluctuation in solar salt production at all such facilities worldwide.↩︎

22. Dominion Salt’s Mount Maunganui facility is a refinery and packaging plant, processing raw solar salt into table salt, food-grade salt, and industrial salt products. It handles both domestic Lake Grassmere salt and, under normal conditions, imported salt. Source: Dominion Salt company information. https://www.dominionsalt.co.nz/↩︎

23. The impact of brine impurities on chlor-alkali electrolysis is well documented. Calcium and magnesium precipitate on cathodes and membranes, reducing efficiency and requiring cleaning shutdowns. Sulfate accumulates in the brine loop. Brine purification to remove these ions is standard practice at all chlor-alkali plants. See: O’Brien, T.F., Bommaraju, T.V., and Hine, F., “Handbook of Chlor-Alkali Technology,” Springer, 2005.↩︎

24. NZ salt import volumes are estimated from Stats NZ trade data. NZ imports salt under HS code 2501 (salt, including table salt and denatured salt, and pure sodium chloride). Import volumes fluctuate year to year. The 100,000–150,000 tonne range is an approximate based on available trade statistics. Precise verification requires Stats NZ Infoshare data. https://www.stats.govt.nz/↩︎

25. Stoichiometric calculation from Doc #48: the chlor-alkali reaction 2NaCl + 2H2O -> Cl2 + 2NaOH + H2 requires approximately 1.65 kg NaCl per kg Cl2 produced. For 4,000 tonnes of chlorine equivalent, this requires approximately 6,600 tonnes of NaCl. Practical consumption is slightly higher due to inefficiencies.↩︎

26. Post-event demand estimate derivation: the 50,000–100,000 tonne range is assembled from Appendix B use-category estimates. Low end: food preservation 3,000–8,000 t/yr (ongoing, after the initial destocking surge), water treatment 6,600 t/yr, livestock nutrition 3,000–8,000 t/yr, other essentials 5,000–10,000 t/yr, with reduced industrial chemistry and eliminated export-oriented dairy and meat processing — summing to approximately 18,000–33,000 t/yr base demand plus one-time destocking spike. High end includes scaling food preservation toward 40,000 t/yr and adding caustic soda production. These are rough order-of-magnitude estimates; the national asset and consumption census (Doc #8) is needed for precision.↩︎

27. On-site stockpile volumes at Lake Grassmere are estimates based on typical solar salt works practice of maintaining several months’ production in stockpile for transport scheduling and seasonal buffering. The actual figure depends on the time of year and recent harvest/shipping activity.↩︎

28. Buffer calculation: stocks of 30,000–100,000 t divided by consumption of 50,000–100,000 t/yr gives a range of 0.3–2.0 years (approximately 4–24 months). The combination of minimum stocks and maximum consumption (30,000 t / 100,000 t/yr = 3.6 months) gives the short end; maximum stocks and minimum consumption (100,000 t / 50,000 t/yr = 2 years) gives the long end. These are rough bounds on an uncertain calculation; the national census should narrow both the stock and the consumption figures.↩︎

29. Evaporation physics from open water surfaces is covered in standard hydrology and meteorology references. The Penman equation and its derivatives describe evaporation rate as a function of net radiation, temperature, humidity, and wind speed. See: Penman, H.L., “Natural evaporation from open water, bare soil and grass,” Proceedings of the Royal Society A, 1948. Also: Allen, R.G. et al., “Crop evapotranspiration — Guidelines for computing crop water requirements,” FAO Irrigation and Drainage Paper 56, 1998.↩︎

30. Nuclear winter climate modelling for the southern hemisphere: Robock, A. et al., “Nuclear winter revisited with a modern climate model and current nuclear arsenals,” Journal of Geophysical Research, 2007; Coupe, J. et al., “Nuclear Nino response observed in simulations of nuclear war scenarios,” Communications Earth and Environment, 2021. Southern hemisphere cooling is generally less severe than northern hemisphere but still substantial. NZ-specific estimates are extrapolated and carry significant uncertainty.↩︎

31. Marlborough climate data from NIWA (National Institute of Water and Atmospheric Research). Blenheim averages approximately 2,400 sunshine hours per year, the highest in NZ, with annual rainfall of approximately 650 mm at the coast. https://www.niwa.co.nz/↩︎

32. Nuclear winter climate modelling for the southern hemisphere: Robock, A. et al., “Nuclear winter revisited with a modern climate model and current nuclear arsenals,” Journal of Geophysical Research, 2007; Coupe, J. et al., “Nuclear Nino response observed in simulations of nuclear war scenarios,” Communications Earth and Environment, 2021. Southern hemisphere cooling is generally less severe than northern hemisphere but still substantial. NZ-specific estimates are extrapolated and carry significant uncertainty.↩︎

33. Evaporation physics from open water surfaces is covered in standard hydrology and meteorology references. The Penman equation and its derivatives describe evaporation rate as a function of net radiation, temperature, humidity, and wind speed. See: Penman, H.L., “Natural evaporation from open water, bare soil and grass,” Proceedings of the Royal Society A, 1948. Also: Allen, R.G. et al., “Crop evapotranspiration — Guidelines for computing crop water requirements,” FAO Irrigation and Drainage Paper 56, 1998.↩︎

34. Lake Grassmere harvesting is typically carried out in late summer and autumn using mechanical harvesters. The exact harvest timing varies with seasonal evaporation conditions. Source: Dominion Salt operational descriptions.↩︎

35. Spray evaporation (also called flash evaporation or spray-assisted evaporation) is used in some solar salt operations and desalination pre-treatment to increase evaporation rates. By spraying brine into the air, the surface area exposed to wind and heat increases dramatically compared to a flat pond surface. The technique is documented in desalination and salt production engineering literature. Specific performance data under Marlborough conditions would require site-specific testing.↩︎

36. Greenhouse-covered evaporation ponds have been demonstrated in research settings for brine concentration. The greenhouse effect raises brine temperature above ambient, increasing evaporation, though at the cost of reduced wind-driven evaporation. Net effect depends on local conditions. See: Lu, H. et al., “Desalination coupled with salinity-gradient solar ponds,” Desalination, various papers.↩︎

37. Estimate that Lake Grassmere adaptations could recover 10–20% of nuclear-winter production losses: spray evaporation claims 30–100% improvement in evaporation rate (note [^20]), and greenhouse-covered ponds may improve brine temperature by several degrees. However, these improvements apply to a degraded baseline: if base evaporation falls 30–60% from nuclear winter, recovering 10–20% of that loss means the adapted facility still produces 30–50% below pre-event output. The 10–20% recovery fraction is an engineering judgment, not a modelled result, and could be higher or lower depending on site conditions and implementation quality. Phase 1 pilot testing of at least one adaptation technique is essential before scaling investment.↩︎

38. Spray evaporation (also called flash evaporation or spray-assisted evaporation) is used in some solar salt operations and desalination pre-treatment to increase evaporation rates. By spraying brine into the air, the surface area exposed to wind and heat increases dramatically compared to a flat pond surface. The technique is documented in desalination and salt production engineering literature. Specific performance data under Marlborough conditions would require site-specific testing.↩︎

39. Greenhouse-covered evaporation ponds have been demonstrated in research settings for brine concentration. The greenhouse effect raises brine temperature above ambient, increasing evaporation, though at the cost of reduced wind-driven evaporation. Net effect depends on local conditions. See: Lu, H. et al., “Desalination coupled with salinity-gradient solar ponds,” Desalination, various papers.↩︎

40. Solar salt pan construction requirements based on general guidance for small-scale salt production in developing countries and historical salt production practices. See: UNIDO, “Small-scale production of food-grade salt,” Technical Paper, 1985 (general principles apply though specific recommendations vary by climate).↩︎

41. Solar salt production yields vary enormously with climate. Typical yields range from 50–300 tonnes per hectare of crystallisation area per year in tropical/arid climates (Australia, India, Mexico) to 20–80 tonnes per hectare in temperate climates. NZ under nuclear winter would be at the low end of this range. These figures are approximate and depend heavily on site-specific conditions.↩︎

42. Energy calculation: seawater is approximately 3.5% NaCl, so producing 1 kg of NaCl requires evaporating approximately 28.5 litres of water (1/0.035 = 28.6 litres, minus the 1 litre occupied by the salt itself, approximately). Latent heat of vapourisation of water at 100 degrees C is 2,260 kJ/kg. Heating from 15 degrees C to 100 degrees C requires an additional 356 kJ/kg. Total: approximately 2,616 kJ/kg of water, or approximately 74,500 kJ (approximately 20.7 kWh) per kg of salt from raw seawater. The 17.8 kWh figure in the text uses a slightly lower estimate accounting for the fact that not all water needs to be fully evaporated (some exits as steam above the crystallisation point). Standard thermodynamic calculation.↩︎

43. NZ electricity generation of approximately 43,000 GWh per year from MBIE (Ministry of Business, Innovation and Employment) energy statistics. https://www.mbie.govt.nz/building-and-energy/energy-and-n...↩︎

44. Energy calculation: seawater is approximately 3.5% NaCl, so producing 1 kg of NaCl requires evaporating approximately 28.5 litres of water (1/0.035 = 28.6 litres, minus the 1 litre occupied by the salt itself, approximately). Latent heat of vapourisation of water at 100 degrees C is 2,260 kJ/kg. Heating from 15 degrees C to 100 degrees C requires an additional 356 kJ/kg. Total: approximately 2,616 kJ/kg of water, or approximately 74,500 kJ (approximately 20.7 kWh) per kg of salt from raw seawater. The 17.8 kWh figure in the text uses a slightly lower estimate accounting for the fact that not all water needs to be fully evaporated (some exits as steam above the crystallisation point). Standard thermodynamic calculation.↩︎

45. NZ geothermal fields and power generation: the Taupo Volcanic Zone contains NZ’s major geothermal resources. Wairakei, Kawerau, Ohaaki, Rotokawa, Ngatamariki, and other fields produce electricity and industrial heat. Total geothermal electricity generation is approximately 7,000 GWh per year (about 17% of NZ’s total). Waste heat discharge from geothermal power stations is significant. Source: NZ Geothermal Association; MBIE energy statistics.↩︎

46. Kawerau geothermal field supports both electricity generation and direct industrial heat use. The former Tasman Pulp and Paper mill (now Norske Skog Tasman) has historically been a major user of geothermal process heat. The site has existing industrial infrastructure, geothermal heat supply, and is closer to the coast than most Taupo Volcanic Zone sites. Distance to the Bay of Plenty coast is approximately 55–65 km depending on route.↩︎

47. Community-scale salt boiling yield calculations: 1 litre of seawater contains approximately 35 g of NaCl. A 200-litre batch produces approximately 7 kg. Throughput depends on heating rate and pan size. A typical community operation with 3–4 large pans over fire might process 500–1,000 litres of seawater per day, producing 17–35 kg of salt. The 20–50 kg range allows for variation in equipment and technique.↩︎

48. Firewood energy content: dry hardwood has an energy content of approximately 15–19 MJ/kg. An open fire achieves perhaps 15–25% thermal efficiency for heating water. To evaporate 200 litres of seawater (requiring approximately 540 MJ of thermal energy at boiling point), the firewood requirement at 20% efficiency is approximately 540/(17 × 0.20) = 159 kg of firewood for 7 kg of salt — approximately 23 kg of firewood per kg of salt. The text range of 15–25 kg/kg spans the efficiency range of 15–25% for open-fire setups; purpose-built evaporation stoves with good heat transfer can approach the lower bound. For pre-concentrated brine at 20% NaCl, the water to be evaporated is approximately 4 kg per kg of salt (rather than 28.5 kg), and firewood falls to approximately 3–5 kg/kg of salt.↩︎

49. Maori salt acquisition: Maori obtained sodium from several sources including seawater, salt-crusted coastal rocks, and plants. Specific techniques varied by iwi and region. For general context, see: Best, E., “Maori Agriculture,” Dominion Museum Bulletin No. 9, 1925; Riley, M., “Maori Healing and Herbal,” Viking Sevenseas, 1994. Detailed knowledge of specific techniques is held by iwi and hapu and should be sought directly from those knowledge holders.↩︎

50. Solar salt production yields vary enormously with climate. Typical yields range from 50–300 tonnes per hectare of crystallisation area per year in tropical/arid climates (Australia, India, Mexico) to 20–80 tonnes per hectare in temperate climates. NZ under nuclear winter would be at the low end of this range. These figures are approximate and depend heavily on site-specific conditions.↩︎

51. Food-grade salt specifications: NZ Food Standards Code (Australia New Zealand Food Standards Code) specifies requirements for food-grade salt under Standard 2.10.2. The key requirement is that it be predominantly NaCl and free from harmful contaminants. The >99% purity figure is typical for commercial table salt but the legal minimum is lower. https://www.foodstandards.govt.nz/↩︎

52. The impact of brine impurities on chlor-alkali electrolysis is well documented. Calcium and magnesium precipitate on cathodes and membranes, reducing efficiency and requiring cleaning shutdowns. Sulfate accumulates in the brine loop. Brine purification to remove these ions is standard practice at all chlor-alkali plants. See: O’Brien, T.F., Bommaraju, T.V., and Hine, F., “Handbook of Chlor-Alkali Technology,” Springer, 2005.↩︎

53. Brine purification for chlor-alkali: adding Na2CO3 and/or NaOH to raw brine precipitates calcium as CaCO3 and magnesium as Mg(OH)2, which are removed by settling and filtration. This is standard practice described in all chlor-alkali engineering references. See: O’Brien et al. (note 16).↩︎

54. Phase 4–5 production projection of 80,000–120,000+ tonnes: this assumes Lake Grassmere recovers to 55,000–70,000 t/yr as nuclear winter eases (matching pre-event normal output), plus supplementary sites contributing 20,000–50,000 t/yr. The supplementary contribution depends heavily on how many sites are developed in Phases 1–2 and their aggregate area. These are optimistic projections that assume successful execution of the recommended actions; they are targets, not forecasts.↩︎

55. NZ population distribution: approximately 77% of NZ’s population of ~5.2 million lives in the North Island. Auckland region alone accounts for approximately 1.7 million (33%). Source: Stats NZ population estimates. https://www.stats.govt.nz/↩︎

56. Firewood energy content: dry hardwood has an energy content of approximately 15–19 MJ/kg. An open fire achieves perhaps 15–25% thermal efficiency for heating water. To evaporate 200 litres of seawater (requiring approximately 540 MJ of thermal energy at boiling point), the firewood requirement at 20% efficiency is approximately 540/(17 × 0.20) = 159 kg of firewood for 7 kg of salt — approximately 23 kg of firewood per kg of salt. The text range of 15–25 kg/kg spans the efficiency range of 15–25% for open-fire setups; purpose-built evaporation stoves with good heat transfer can approach the lower bound. For pre-concentrated brine at 20% NaCl, the water to be evaporated is approximately 4 kg per kg of salt (rather than 28.5 kg), and firewood falls to approximately 3–5 kg/kg of salt.↩︎