Jason,

We use iodine (added as sodium iodine) as a conservative (does not break down), mobile (does not get hung up on soils) tracer in environmental projects. Downside is you would be adding iodine in parts per million concentration, so you need to take samples of the downstream water and send to an analytical lab to measure the low concentrations. Not difficult but there's a bit of a cost. Other option might be a dye. We use dyes from brightdyes.com for tracers, although dye might get lost during migration through aquifer soils.

Dale

They've gone to plaid.
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