Within 4VAC50-60-85 Section E: "impoundment structures or facilities shall only be constructed in karst features after completion of a geotechnical investigation..."  This should be changed to apply to karst areas instead of specific features. I hope never, if rarely, would a stormwater basin be built in a sinkhole; but there are many cases of basins being built in close proximity to a sinkhole which have failed due to underlying soluble bedrock.

Also in Section E: "The person responsible for the land-disturbing activity is encouraged to screen for known existence of heritage resources in the karst features." From my time on the TAC, I believe this was intended to require screening for Natural Heritage Resources (rare, threatened, or endangered animals, plants, or natural communities) that could be impacted by a project.

Finally, a definition for karst areas would be helpful in 4VAC50-60-10 Definitions.

Thanks and good luck,