Measurables?
Like raw material to waste?
Solid waste totals and projected reductions?
Emissions?
Discharges?
Waste water generation?
Power usage?
Water usage?
Paper usage?
Consumable materials usage?
Alternate materials usage?
Recyclable material usage?
Do these sound OK for a start?
Look at your "ASPECTS". They each should have some data that could be tracked.