(a) A rural city or a rural county, which has received, or is eligible for, a reduction in diversion requirements pursuant to Section 41787, may become a member of a rural regional agency for the purpose of complying with the diversion requirements of Section 41780, in which case the region’s maximum disposal tonnage allowable shall be calculated as follows:

1. (1) Determining the regional maximum disposal tonnage allowable, excluding members with reduced diversion requirements.
2. (2) Determining the maximum disposal tonnage allowable for those members authorized to meet reduced diversion requirements.
3. (3) Adding the calculated maximum disposal tonnages determined pursuant to paragraphs (1) and (2) to determine the regional maximum disposal tonnage allowable.

(b)

1. (1) A rural regional agency may not assume responsibility for compliance with diversion requirements upon formation pursuant to subdivision (b) of Section 41787.1, and for compliance with Article 1 (commencing with Section 41780), if the rural regional agency is comprised of more than two rural counties, unless authorized by the board pursuant to paragraph (2).
2. (2) The board may authorize the assumption of responsibility for compliance with diversion requirements by a rural regional agency upon formation, which is comprised of more than two rural counties, if the board finds that the rural regional agency’s assumption of responsibility will not adversely affect compliance with this part.