Human Use Allowance 63

The temperature standard provides for temperature increases, above applicable criteria, through a human use allowance (HUA): “Following a temperature TMDL or other cumulative effects analysis, wasteload and load allocations will restrict all NPDES sources and nonpoint sources to a cumulative increase of no greater than 0.3 degrees Celsius (0.5 degrees Fahrenheit) above the applicable criteria after complete mixing in the water body, and at the point of maximum impact” (OAR 340-041-0028(12)(b)(B)). It follows that the TMDL allocations of this chapter are based on the applicable criteria described earlier in this section (Section 2.1.3.1), plus the portion of the human use allowance allotted to any given source. The HUA is apportioned as indicated in Table 2.1-2 for all waters in the John Day Basin except for parts of Long Creek (drains into lower Middle Fork) and the John Day River upstream of the North Fork where waters are thermally influenced by point sources. The HUA for the waterbodies potentially impacted by existing point sources (John Day River above the North Fork, Long Creek) is apportioned as indicated in

Table 2.1-3. This apportionment was based on general consistency with other basins and on John Day

Basin community input. Potential future sources may draw on the reserve capacity. The general HUA of 0.3 ºC applies throughout the Basin and this TMDL prohibits human-related warming in excess of 0.3 ºC at any given location.

59

64

69

74

79

84

89

94

15

17

19

21

23

25

27

29

31

33

35

0

20

40

60

80

100

120

Te

m

p

er

at

u

re

(ºF

)

Te

m

p

er

a

tu

re (

C )

river kilometer

Current Condition

Flow

Restored

Vegetation

Natural Thermal Potential

30% Width

Reduction

OREGON DEPARTMENT OF ENVIRONMENTAL QUALITY 64

Table 2.1-2. HUA apportionment for reaches not having existing point sources (up- or down-stream reaches not exhibiting thermal overlap with point sources)

Application Portion of HUA Notes

Load Allocation 0.10 °C All nonpoint sources Reserve Capacity 0.20 °C

Table 2.1-3. HUA apportionment – areas of potential influence from existing point sources (part of Long Creek and the upper John Day River)

Application Portion of HUA Notes

Load Allocation 0.10 °C All nonpoint sources Wasteload Allocation

0.10 °C

Combined increase in temperature associated with effluent from Long Creek WWTP, Dayville WWTP,

Mt. Vernon WWTP Specific Reserve

Capacity John Day WWTP

General Reserve Capacity

0.20 ºC outside reaches with cumulative effect relating to _{existing point sources} 0.10 °C within reaches with cumulative effect relating to _{existing point sources} Table note: the HUA apportionment above reflects an allowance of 0.1 ºC for cumulative effects of all point sources, including the existing WLA and the John Day WWTP specific RC. Note that the tabulated HUA portions are not necessarily additive – while the apparent sum of the HUA portions here exceeds the general maximum of 0.3 ºC, this is not allowed at any given location. To clarify that the HUA apportionment of Table 2.1-2 and Table 2.1-3 does not provide for exceedance of 0.30 ºC warming, examples at different locations are included here:

John Day River upstream of the City of John Day. If a new point source upstream of the City of John Day would not result in any overlapping thermal influence with the John Day WWTP, then:

 NPS HUA = 0.10 ºC

 new source (WLA) maximum HUA = 0.20 ºC (assuming authorization of the new sources usage of the entire general reserve capacity)

 this would deplete the General RC HUA to zero  total HUA used = 0.30 ºC

This scenario would not change the current apportionment in the downstream reach, because the river temperature increase from the new source did not extend downstream to the City of John Day WWTP.

John Day River from the City of John Day WWTP to below Dayville at a point where point source influence has attenuated to zero. This TMDL prescribes the following current HUA

apportionment:

 NPS HUA = 0.10 ºC

 Mt Vernon, Dayville WWTP (WLA) and John Day WWTP collective HUA = 0.10 ºC (it is shown in Section 2.1.7.2.1 that with 0.10 ºC river warming from the John Day WWTP and with Mt Vernon and Dayville WWTP effluent temperatures maximized, the cumulative allowed temperature increase for all point sources would not exceed 0.10 ºC at any location.

 this usage of the specific RC depletes the general RC HUA to 0.10 ºC in this reach  total HUA used = 0.30 ºC (at any location in the reach)

OREGON DEPARTMENT OF ENVIRONMENTAL QUALITY 65 If a new point source requests to access the general reserve capacity, DEQ will evaluate the discharge and assign the appropriate reserve capacity HUA so that the overall HUA threshold of 0.3 ºC is not exceeded.

2.1.3.4.1 Effluent Mixing Proportions

Following TMDL development, the HUA applies after complete mixing and at the point of maximum impact [OAR 340-041-0028(12)(b)(B)]. This allowance for complete mixing extends to all applicable criteria. As well, it extends throughout the year, given that the TMDL addresses the entire year. We note also that permitted mixing zones may be more restrictive.

2.1.3.4.2 Spawning Waters Cold Water Protection Allowance

The HUA is generally set at 0.3 ºC for all sources combined [OAR 340-041-0028(12)(b)(B)]. However, under certain conditions, heating of up to 0.5 ºC to 1.0 ºC is allowed and stream temperatures are

assessed at 60-day, instead of seven-day, averages. The greater allowance and 60-day averaging apply via the cold water protection criteria [OAR 340-041-0028(11)(b)] when point sources are discharging into spawning area waters that are cooler than the spawning criterion.

2.1.3.4.3 Point of Maximum Impact

Along the modeled corridor, the warm season “point of maximum impact” (POMI) is where the greatest difference between existing and NTP 7DADM temperatures occur. The existing points of maximum impact, along modeled rivers during the maximum 7DADM, are identified in Table 2.1-4. In addition, it is noted that the location of the POMI may change seasonally and with changes in human impacts.

Table 2.1-4. Points of maximum impact

(longitudinal maximum difference between current and estimated natural conditions with the location of the maximum difference – recall of Table B-1, Appendix B)

Waterbody Greatest excursion from NTP (maximum 7DADM, Δ °C) Current point of Maximum Impact (river km) John Day River (summer 2004) 10.8 (19.4 °F) 327.00 North Fork John Day River (summer 2002) 3.6 (6.5 °F) 168.70 Middle Fork John Day River (summer 2002) 7.6 (13.7 °F) 2.55 Note: to convert km to river-specific river miles, refer to Table 1.4-3 through Table 1.4-5