SECTION 252:690-3-11. Receiving water background characterization requirements

(a)   Long term average. Where required, the DEQ will calculate a LTA background level of a substance as a geometric mean unless otherwise specified.

(b)   Background data sources. Background data must be defensible analytical data and be representative of the receiving water's current upstream conditions. The DEQ will use data collected and reported in accordance with a background monitoring requirement in a previous permit where available.

(c)   Unavailability of background data. Where no background data is available, the background is assumed to be zero.

(d)   Size of background data set. At least 10 data points are required for a background data set to be considered complete. The DEQ may use a partial background data set for reasonable potential purposes if the data is the only defensible analytical data available. Where the use of a partial background data set results in demonstration of reasonable potential, the permit will include effluent limitations based on a zero background level, which may have a delayed effective date of no more than two years. The permit will require the permittee to complete the background monitoring, at which time the DEQ will reopen the permit, if necessary, to adjust permit limitations according to the background level determined from a complete background data set.

(e)   Alternative Method for Determination of 7Q2.

(1)   A permittee may use an alternative method for determining a 7Q2 as allowed by OAC 785:46-1-6 (c). The 7Q2 calculated from the historical record may be modified to incorporate anticipated upstream flow releases provided the source of water is owned or controlled by a federal governmental entity and the following information is submitted to the DEQ:

(A)   a determination that a reliable source of upstream flow exists;

(B)   documentation that the upstream source of water:

(i)   includes water quality improvement as an authorized use, or

(ii)   includes allocated storage for water quality improvement;

(C)   documentation that the upstream source of water is governed by a water control plan developed and implemented pursuant to 33 CFR § 222.5; and

(D)   a demonstration that the alternative 7Q2 is identified in the most recently published State Water Quality Management Plan.

(2)   The DEQ will include any approved alternative 7Q2 as a permit limit in any discharge permit. Said limit shall be stated as a minimum daily flow measured at the nearest upstream flow gage.

(3)   In the event that the alternative 7Q2 is not consistently attained, the DEQ may re-open the permit and re-calculate the effluent limitations using the actual receiving stream flows.

[Source: Added at 19 Ok Reg 1721, eff 6-13-02; Amended at 22 Ok Reg 1477, eff 6-15-05]