(b) Prime farmland soil productivity shall be restored in accordance with the following provisions:

1. (1) Measurement of soil productivity shall be initiated within 10 years after completion of soil replacement.
2. (2) Soil productivity shall be measured on a representative sample or on all of the mined and reclaimed prime farmland area using the reference crop determined under Paragraph (b) (6) of this Section. A statistically valid sampling technique at a 90-percent or greater statistical confidence level shall be used as approved by the Department in consultation with the U.S. Soil Conservation Service.
3. (3) The measurement period for determining average annual crop production (yield) shall be a minimum of 3 crop years prior to release of the operator's performance bond.
4. (4) The level of management applied during the measurement period shall be the same as the level of management used on nonmined prime farmland in the surrounding area.
5. (5) Restoration of soil productivity shall be considered achieved when the average yield during the measurement period equals or exceeds the average yield of the reference crop established for the same period for nonmined soils of the same or similar texture or slope phase of the soil series in the surrounding area under equivalent management practices.
6. (6) The reference crop on which restoration of soil productivity is proven shall be selected from the crops most commonly produced on the surrounding prime farmland. Where row crops are the dominant crops grown on prime farmland in the area, the row crop requiring the greatest rooting depth shall be chosen as one of the reference crops.

7. (7) Reference crop yields for a given crop season are to be determined from:

   1. (A) The current yield records of representative local farms in the surrounding area, with concurrence by the U.S. Soil Conservation Service; or
   2. (B) The average county yields recognized by the U.S. Department of Agriculture, which have been adjusted by the U.S. Soil Conservation Service for local yield variation within the county that is associated with differences between nonmined prime farmland soil and all other soils that produce the reference crop.

8. (8) Under either procedure in Paragraph(b) (7) of this Section, the average reference crop yield may be adjusted, with the concurrence of the U.S. Soil Conservation Service, for:

   1. (A) Disease, pest, and weather-induced seasonal variations; or
   2. (B) Differences in specific management practices where the overall management practices of the crops being compared are equivalent.