9VAC25-900-91. (Reserved.) Exchange of credits.

A. Exchange of a credit released by the department is subject to the provisions of § 62.1-44.15:35, 62.1-44.19:15, or 62.1-44.19:21 of the Code of Virginia.

B. Where necessary to ensure compliance with local water quality requirements, the exchange of a credit released by the department is conditioned as follows:

1. Within the Chesapeake Bay Watershed, the exchange of credits within an area subject to an approved local TMDL for total phosphorus or total nitrogen with allocations more stringent than the Chesapeake Bay Watershed TMDL shall be limited to those credits generated upstream of where the discharge reaches impaired waters.

2. Within the Southern Rivers watersheds, the exchange of credits within an area subject to an approved local TMDL for total phosphorus or total nitrogen shall be limited to those credits generated upstream of where the discharge reaches impaired waters.

3. Within an area with waters impaired for dissolved oxygen, benthic community, chlorophyll-a, or nutrients but with no approved local TMDL, the exchange of credits shall be limited to those credits generated in accordance with the following hierarchy:

a. Upstream of where the discharge reaches impaired waters if credits are available;

b. Within the same 12-digit HUC if credits are available;

c. Within the same 10-digit HUC if credits are available;

d. Within the same 8-digit HUC if credits are available;

e. Within an adjacent 8-digit HUC within the same tributary if credits are available; or

f. Within the same tributary.

C. The hierarchy of subdivision B 3 of this section shall not apply when:

1. The department determines through issuance of a VPDES permit that local water quality cannot be protected unless exchange of credits are restricted to upstream of where the discharge reaches impaired waters; or

2. It has been demonstrated to the department's satisfaction that:

a. The water quality impairment is not likely caused by nutrients; or

b. The use of credits would not reasonably be considered to cause or contribute to the impairment.