WSP10769

• File Number: 8220.105
• Description: Colorado River-Water Projects-Navajo
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 7/1/2001
• Author: BOR
• Title: Revised Draft Environmental Assessment for the Jicarilla Apache Nation Water Subcontract-aka USBR/PNM Water Contract Renewal and Extension
• Water Supply Pro - Doc Type: Report/Study

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zero flow periods were eliminated (Holden 1999). Implementation of the SJRRJP flow recommendations
are intended to restore flows in the river to pre-Navajo Dam characteristics. The average annual flow of
the San Juan River as measured at Shiprock, NM is about 1.5 million AF per annum.

Shumway Arroyo discharges into the San Juan River No water from SJGS is discharged into Shumway
Arr(\V{) Thp IInnpr ponn O{)Wl>: in fp,nnm:p. tn nrf"C'.inifMinn f::lllincr in its. w;::!ff'.r,hf':n Thf" InWf"f end is a
'" _. - u_ --r,., - - __ - __ - - n_ - - -,- -. _.. '-'
perennial stream fed by irrigation return flow as well as precipitation.

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6.2.1 San Juan River Water and Sediment Quality

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The only impact on water quality from SJGS is the depletion of the San Juan River. No water is
discharged from SJGS into the San Juan River.

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6.2.1.1 Effect of Diversion on San Juan River Water Selenium Concentrations

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Concern was raised by representatives of the Navajo Nation and Southern Ute Indian Tribe that
consumption of San Juan Riverwater by the SJGS contributes to the problem of high selenium
concentrations in the river by withdrawing water that would otherwise be available for dilution of the
element. In order to address this concern, calculations were made using several pumping volume
scenarios in order to determine if it was likely that the amount of water diverted by SJGS had an
appreciable impact on selenium concentrations downstream of the SJGS weir. The calculations relied on
a number of assumptions as well as empirical data taken from Blanchard el af. (1993). The assumptions
and calculations are provided in Appendix B of this document. The result of the calculations
demonstrates that, given the assumptions involved, the amount of water diverted by SJGS has no
significant effect on downstream selenium concentrations.

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Data on dissolved selenium concentrations in the San Juan River acquired since the collection of data
used in the Blanchard report are included in the Final Supplemental Environmental Impact Statement
(FSElS) for the Animas-La Plata Project (USBR 2000). FSEIS Technical Appendix 3, Water Quality
Analysis, tabulates historic water quality measurements in the San Juan River (Table 3-7, p. 3-14).

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The average selenium concentration in 277 samples taken from the San Juan River at Shiprock is 1.0
(~g/I as dissolved Se). The study in Appendix B of this document is based on three samples taken at the
Shiprock station, which are not substantially different from the data contained in the FSEIS. The data in
Table 3.7 of the FSEIS indicate that the long-temllevels of dissolved selenium at Shiprock are similar to
the selenium levels collected for the Blanchard report, which would confirm the validity of the data used
in the Blanchard report and support the conclusions in the study in Appendix B of this document.

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6.2.1.2 History of Past Discharges

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Until May 1983, SJGS discharged wastewaters to the Shumway Arroyo via an outfall permitted by the
EPA under the National Pollutant Discharge Elimination System (NPDES). The wastewaters contained a
variety of wastes from the plant pollution control and process operations. The wastewaters discharged to
the Shumway Arroyo ultimately flowed into the San Juan River, approximately 3 miles south of the
SJGS.

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