Bare soil means soil or sand not covered by grass, sod, other live ground covers, wood chips, gravel, artificial turf, or similar covering. The levels of lead in bare soil which are defined to be hazardous and should be documented and addressed in risk assessment are defined:

24 CFR 35.1320(b)(2) (ii) Soil. (A) A soil-lead hazard for play areas frequented by children under 6 years of age shall be bare soil with lead equal to or exceeding 400 micrograms per gram.
  (B) For other areas, soil-lead hazards shall be bare soil that totals more than 9 square feet (0.8 square meters) per property with lead equal to or exceeding 2,000 micrograms per gram.

Interpretive Guidance:
Soil Testing
Soil Testing and Clearance