Spread

Silicate rock weathers when rain and soil carbonic acid dissolve Ca/Mg-bearing minerals, converting atmospheric CO2 into dissolved bicarbonate that eventually reaches the ocean. Spreading finely crushed basalt on cropland accelerates that geology. Beerling et al. (Nature 2020) estimated a theoretical global cropland upper bound of ~2 Gt CO2/year at roughly $80–180/t; that number is not a county public-works rate and is not a Midwest rate. The paycheck-novum uses a named field result: Beerling, Kantola and colleagues ran a four-year maize/soy trial at the University of Illinois Energy Farm south of Urbana, Champaign County (40.063°N, 88.196°W), applying Blue Ridge metabasalt (Specialty Granules, Blue Ridge Summit, PA) at 50 t/ha/year with a grain-size p80 of 267 µm. Cumulative CDR on maize/soy was 10.5 ± 3.8 tCO2/ha over four years, about 2.6 tCO2/ha-year (Beerling, Kantola et al., PNAS 2024, doi:10.1073/pnas.2319436121); a companion GCB analysis of the same site reports improved net carbon budgets under that loading (Kantola et al., Global Change Biology 2023, doi:10.1111/gcb.16903). That is a four-year cumulative on a tile-drain / cation mass-balance quantification period, not a weekly print. Isometric Enhanced Weathering in Agriculture is the same class of instrument: drainage chemistry plus cation mass-balance over a named vintage, not this week's rain. A wet week in Tazewell moves existing soil bicarbonate, lime, fertilizer, and tile-drain lag. It does not newly weather Blue Ridge metabasalt at p80 267 µm. Overtime therefore attaches to a named multi-year Isometric vintage; rain is a spreading-hours problem (too wet to get the trucks out), not a weekly carbon meter. 50 t/ha/year is the Energy Farm research rate, applied with lime equipment on a few hectares. It is not a county public-works rate. Agricultural lime in Illinois is typically 2–5 t/ha. Operational Spread from 2031 is 10 t/ha/year — one extra lime-adjacent pass county spreaders can actually run. CDR is scaled linearly from the named trial as an upper-bound assumption: ~0.5 tCO2/ha-year at 10 t/ha. Non-linearity (surface-area and pH saturation) would only lower that number. Tazewell County, on the Illinois River, has more lime-history and higher-pH soils; expected drainage-alkalinity there sits toward the low end of the scaled band. Coarser quarry sand can fail to print at all (a 2025 midwestern trial on Chengwatana basalt sand showed no detectable CDR). Grain size is therefore the gate. The same crush curve that weathers also dusts: p80 267 µm means 80% of mass is finer than 267 µm, and the <10 µm tail is respirable. Blue Ridge metabasalt is not a silica rock, but Lewis, Beerling et al. (Applied Geochemistry 2021) measured 5.2 wt% free quartz in it; cristobalite is not the driver. OSHA's respirable crystalline silica PEL is 50 µg/m³ (8-hr TWA) with an action level of 25 µg/m³ (29 CFR 1910.1053). That standard does not apply to agricultural operations (explicit exemption; agriculture is 29 CFR 1928). A 2029 advisory-not-a-ban is therefore about spread yards that sit outside the quarry PEL, not a new mineral. Yard total dust can sit in the mg/m³ range during dry loading; RCS from the 5.2% quartz tail can approach the 25 µg/m³ action level. Pediatric 'fines week' is household PM10 from that tail, not occupational silicosis. Rock supply is named, not assumed. Specialty Granules' Blue Ridge Summit, PA plant is a roofing-granule operation (~300 tph, capability ~450 tph; Rock Products 2019). The 2026 Champaign pilot at 50 t/ha on ~3,000 ha is ~150,000 t/year — a fines/undersize stream from that plant, not the whole US crushed-stone market, railed ~700 miles on Norfolk Southern into Champaign and trucked to the Energy Farm and SWCD yards. Grinding energy to p80 267 µm from a typical quarry F80 ~5 mm uses Bond's equation with a basalt work index ~17 kWh/t: additional grind ~8 kWh/t plus ~5 kWh/t crushing, about 13–20 kWh/t total (Beerling 2020 Extended Data Fig. 10; Zhang et al., Frontiers in Climate 2024, doi:10.3389/fclim.2024.1380651). That is the cost Beerling already named, paid on a named crush, not waved away. From 2031 the 12-county Illinois program cannot live on Pennsylvania roofing fines. Operational rock is Midwest traprock: Dresser Trap Rock, Polk County, WI (Keweenawan metabasalt, already shipping railroad ballast and chips) and Specialty Granules Pembine, WI, barged and railed down the Mississippi/Illinois to the Pekin yard on the river. Whatcom County does not import Blue Ridge; it grinds local Cascade basalt at existing road-aggregate pits (Cowden-class operations already crushing in Whatcom/Skagit) and trucks it under 50 miles. USGS crushed stone is on the order of 1.5 Gt/year of all sizes. 2046 at 10 t/ha on 3 million ha is ~30 Mt/year of p80-267 traprock fines — about 2% of that total, a dedicated fines industry, not a climate sticker on lime trucks. Lime crews remain a labor pool for spreading hours; they are not the grind. The named tonne is maize/soy drainage alkalinity. Mouth-side is not baker's patent. The Pekin mill on the east bank of the Illinois River is a corn wet mill (historic Corn Products / CPC site, 1904; Pekin Energy / Aventine / Alto as of the 2020s), measuring ash on corn gluten feed and other wet-mill coproducts, not Minolta color on wheat flour. ADM's big Illinois wet mill is Decatur, not Pekin; Tazewell wheat is not in the practice code. Grey flour as baker's patent was a category error and is out. Feed ash can be real without being the Kantola tonne: atmospheric deposition of a <10 µm tail onto maize during Spread Week is a particle-load pathway, not tile-drain bicarbonate. MRV is already a private protocol: Isometric's Enhanced Weathering in Agriculture v1.1 (cation mass-balance plus drainage chemistry over a quantification period); Microsoft's 2024 Lithos offtake was 11,400 t over three years; Frontier buyers contracted Lithos for 154,240 t / $57.1M (2024–2028). USDA NRCS can add a conservation practice code. A state DOT does not carry agricultural MRV — it owns trucks. Additionality: substituting basalt for agricultural lime is not a new tonne (lime is CaCO3 and dissolving it releases CO2). The tonne is extra quarry-byproduct basalt on top of an unchanged lime contract, verified ex-post by Isometric on a named vintage, paid by the offtake. Two honest labs can disagree when they are not measuring the same analyte: tile-drain alkalinity is carbon; corn-gluten-feed ash is milling.