[Hugh R]

Quote from Cummins Cal Pacific LLC is $47,179.49 for four DCL International Mine-X Sootfilters.

It's a CA requirement for standby generators within 100 meters of a K-12 school (SCAQMD Rule 1470). Since these are schools, they have to comply with the rule.

My wife is the purchasing manager for the school district and I'm trying to help them out gratis

I've given them several suggestions including selling them outside of CA and buy gasoline ones under 50 HP (exempt from permitting).

Don't know about exhaust filters on diesel trucks other than that they are requiring older ones to be phased out in CA and replaced with much cleaner ones. Going the same way with cargo ships.