For each individual facility NPDES source, the John Day Basin temperature WLA is here defined as the maximum heat loading from the facility that will restrict the source to an increase of no greater than the portion of the HUA assigned, above specified temperature targets after complete mixing in the receiving waterbody. Addressing the entire year, these ‘specified temperature targets’ are as follows:
(1) Warm season targets for modeled streams: In order to address the natural conditions criterion of the temperature water quality standard, the target is the warm season maximum NTP or ambient background temperature, whichever is less. This target supersedes the warm season biologically based criterion when waters are warmer than the superseded criterion.* This occurs during the periods identified below, for the upper mainstem – the only modeled waterbody with individual NPDES permitted discharges.
i. Between the North Fork and Canyon Creek: May 16-December 31 or when stream temperature is greater than 18 ºC (64.4 ºF)
ii. Between Canyon Creek and Indian Creek: June 16-December 31 or when stream temperature is greater than 16 ºC (60.8 ºF)
iii. Between Indian Creek and just below Reynolds Creek: June 16-August 31 or when stream temperature is greater than 16 ºC (60.8 ºF)
iv. From just below Reynolds Creek to the headwaters: when stream temperature is greater than 12 ºC (53.6 ºF)
(2) For all other times and for un-modeled streams, the normally applicable criteria (e.g.
biologically based or cold water protection) of the temperature standard are targeted via this TMDL.
* Capping the target at maximum NTP temperature ensures that natural peak temperatures of a relatively normal year’s climate and flow (the 2004 model calibration year), will not be exceeded at any time during the warm seasons to come. Integrating background into the target ensures that ultimately, as surrounding conditions become more natural, natural temperatures will be targeted by point sources throughout the warm season.
As used herein, the NTP targets are derived from simulation of natural conditions based on the climate of 2002 (North and Middle Forks) and 2004 (mainstem). With further analysis for subsequent TMDL development, NTP estimates could be updated, particularly as climate change is better understood. In the interim, as these years were not abnormal flow or climate years (and note that only 2004 is used as the basis for point source targets), the simulated NTP temperatures are considered a suitable target to apply as an annual maximum temperature limit that approximates natural conditions. We note that while daily maximum temperature fluctuates substantially through the year and within any season, the reducing trend of annual 7DADM maxima will exhibit much less variance.
According to the Basin WLA definition above, the applicable HUA for each source must be determined in order to calculate WLA temperature limits. Cumulatively, point sources may not impact stream
temperatures more than 0.1 ºC, above the portion of the HUA established in Section 2.1.3.4. In order to determine the HUA for each individual facility, a cumulative effects analysis was carried out and is summarized below.
OREGON DEPARTMENT OF ENVIRONMENTAL QUALITY 73 2.1.7.2.1 Cumulative Effects Analysis
This section addresses the three individually permitted NDPES sources in the Basin and the City of John Day WWTP. Table 2.1-7 lists these four facilities, their discharge periods and the current condition summer maximum background temperature of the River just upstream from the outfalls (the temperature model is calibrated to 2004 conditions). The John Day, Mt. Vernon and Dayville WWTPs are located adjacent to the John Day River. The Long Creek WWTP has the capability of discharging to Long Creek, which flows to the Middle Fork, which flows to the North Fork, which flows to the John Day River at km 282.2 (river mile 185). For Long Creek and Mt. Vernon, lagoon evaporation and infiltration occur at rates such that their direct discharge outfalls are not utilized. The Dayville WWTP episodically discharges treated effluent directly to the John Day River from Nov 1 – May 31. All three NPDES sources have provisions in their permits to allow direct discharges during part or all of the year. The John Day WWTP discharges effluent to lagoons under a Water Pollution Control Facility (WPCF) permit (WQF#43569). Assimilative capacity is held as Reserve Capacity (Section 2.1.11) specifically for the John Day WWTP, to be used as needed through current or future permitting mechanisms.
Table 2.1-7. Facility discharge periods and stream maximum 7DADM temperature
Common Name WQ File Number Receiving Water Direct Discharge Permitted Period Comments 2004 Modeled Maximum 7DADM CITY OF
DAYVILLE 23560 John Day R November 1 - May 31 27.1 LONG
CREEK
WWTP 51180 Long Creek November 1 - May 31 outfall not utilized Not modeled MT
VERNON
WWTP 59065 John Day R Year round outfall not utilized 26.7 John Day
WWTP 43569 discharges year round to lagoons adjacent to John Day River 26.0 Given the HUA breakdown described previously in this chapter, the point sources may not cause a cumulative temperature increase of more than 0.1 °C. The Long Creek WWTP is the only NPDES permitted source in the North and Middle Forks Subbasins. Given the geographic separation, overlapping thermal effects are not feasible between Long Creek and the mainstem WWTPs. The cumulative effects analysis for the upper John Day River sources shows that each of the point source’s potential temperature impacts dissipates before causing an instream increase of 0.1 ºC. This was assessed based on maximizing discharge and temperature from the three point sources, starting with the current condition calibrated model and increasing flow to potential. We simulated an up to 0.1 ºC river temperature increase associated with each point source discharge, added to potential flow conditions (which represents higher flow than 7Q10, increasing the likelihood of thermal overlap between sources) and followed the resultant temperature departure downstream to complete attenuation. For the purpose of testing worst-case effluent temperatures prior to mixing with the River, the effluent discharge
temperatures were capped at 32 ºC (thermal plume rule limits exposure inside mixing zone at or above this temperature – refer to Section 2.1.3.6).
OREGON DEPARTMENT OF ENVIRONMENTAL QUALITY 74 Explanatory notes:
32 ºC is not necessarily an allowable maximum effluent temperature for the facilities. Rather it is an extreme value used to conservatively test cumulative effects. Other thermal plume and post-mixing limits criteria will be factored in to the permit limit-setting process.
While low-stage river flow will be more thermally influenced by individual point sources, downstream retention of a given river temperature increase is maintained for further distances at high flow. At low flow, rivers quickly equilibrate to their surroundings. At high flows, the receiving volume is such that point sources are not capable of causing HUA exceedances. The optimal test flow for cumulative impacts is obtained by increasing flow to the upper range of where individual point sources can make a significant difference in stream temperature. Summer NTP flow served as a balancing point to test this.
Figure 2.1-7 plots both the maximum 7DADM temperatures under the potential flow scenario, and the potential flow scenario with the three point source discharges added. The difference is difficult to discern at this scale. To better illustrate, this graph is zoomed in to the area around the John Day WWTP at river km 384.0 (river mile 248, Figure 2.1-8). The graph shows the point source causing an up to 0.1 ºC increase in temperature, relative to the potential flow condition without point sources. Figure 2.1-9 shows that the maximized temperature increases (either 0.1 ºC or the maximum river temperature increase resultant from facility design flow at 32 ºC) from all three point sources rapidly decrease before the next point source in-flow. In combination, the three maximized thermal impacts do not cause the river temperature to increase above 0.1ºC.
Figure 2.1-7. Point sources’ effluent simulated to increase river temperature by up to 0.1 ºC (John Day River, using the current condition model with natural potential flow)
OREGON DEPARTMENT OF ENVIRONMENTAL QUALITY 75
Figure 2.1-8. Zoom of previous graph around John Day WWTP at river km 384.
Figure 2.1-9. Difference between potential flow scenario with and without point sources (point source effluent simulated to increase John Day river temperature by up to 0.1 ºC)
OREGON DEPARTMENT OF ENVIRONMENTAL QUALITY 76