I’m an environmental consultant on a greenfield pit in Nevada, pushing to lock in concurrent reclamation and a zero‑discharge water balance (GoldSim) before first blast. We’re modeling 1.2 m store‑and‑release covers and geomorphic landforms for waste rock, and using paste backfill to cut the TSF footprint. What’s worked for you on keeping pit‑lake chemistry stable — circulation, upstream diversions, or just getting recharge routing right?
We kept a Nevada pit lake steady by cutting a 2 m‑deep density‑current trench to a lined sump on the floor and rigging a flexible riser; during fill we skimmed the first flushes (high sulfate/Fe) with a 100–150 gpm pump back to the plant, then shut it off once profiles flattened — no mixers needed. Caveat: with that 1.2 m store‑and‑release your inflow pulses, so set a simple ‘Cl-’ trigger in GoldSim to pull a periodic sump drawdown if evaporative creep gets ugly; @mark39’s embedded alkalinity helps, but don’t bet the lake on it.
Quick example: we blended about 1–2% dolomite fines into the upper lifts of backfill and built a small woodchip PRB at the main inflow so early runoff carried alkalinity and sulfate/Fe got knocked down. During rise, a 3 in. venturi on the transfer pump gave just enough mixing to keep redox in check; rule of thumb was “dose early, dose small.” Minor caveat: watch scaling/DOC pulses, and if it spikes, pair it with @carlos_m87’s floor‑sump setup for short‑term skimming.
Since you’ve got paste backfill, @OP, we plumbed a small sidestream from the paste plant’s high-alkalinity bleed into the final void during first fill (about 5–10 gpm for about 12 months) and tied dosing to a simple pH/alkalinity trigger in GoldSim — it flattened the early acid pulses without movers. Caveat: watch for CaCO3/ettringite scaling in the line and shut it off once sulfate plateaus. For context on reactive buffering strategies, the GARD Guide is handy: http://gardguide.com.
But building on @smith32, we went underwater with a submerged “alkaline runway” along the main ramp — coarse calcitic riprap and baffled drops — so first‑fill inflows cascaded across it and loaded alkalinity before reaching depth; antacid on the way in. Small caveat: we throttled flow to limit fines carryover and ran two small solar mixers the first summers to keep early stratification from locking in — do you have power near the rim?
On a Nevada pit we kept the lake steady by pre‑treating inflows with an anoxic limestone drain and a small vertical‑flow cell — a big ‘Brita’ upstream — so alkalinity bumped and Fe/Al dropped before it reached the lake (design ref: https://osmre.gov/sites/default/files/inline-files/PassiveTreatment_01.pdf). It’s cheap to run, but only works if feed is low‑DO and fairly clear, so we added a small presed basin and a storm bypass. Do you have space in the ramp catchment to tuck one in?