TACOMA HYDROELECTRIC PROJECT PROJECT EFFECTS ON THE WATER QUANTITY AND QUALITY OF THE ANIMAS RIVER

Transcription

1 TACOMA HYDROELECTRIC PROJECT PROJECT EFFECTS ON THE WATER QUANTITY AND QUALITY OF THE ANIMAS RIVER Prepared for: PUBLIC SERVICE CO. OF COLORADO Durango, Colorado Prepared by: DEVINE TARBELL & ASSOCIATES, INC. Portland, Maine NOVEMBER 27

2 TACOMA HYDROELECTRIC PROJECT PROJECT EFFECTS ON THE WATER QUANTITY AND QUALITY OF THE ANIMAS RIVER TABLE OF CONTENTS Section Title Page No. 1. PURPOSE AND BACKGROUND SYNTHETIC UNIMPAIRED HYDROGRAPH OF CASCADE CREEK PROJECT OPERATIONS POTENTIAL REFERENCE WATERSHEDS DEVELOPMENT OF HYDROLOGY USING SELECTED REFERENCE SITES WATER QUALITY ASSESSMENT SUMMARY OF RESULTS REFERENCES...2 APPENDICES APPENDIX A - POR SYNTHESIZED HYDROLOGY FLOW EXCEEDANCE TABLES AND GRAPHS APPENDIX B - REPRESENTATIVE WET YEAR (1997) SYNTHESIZED HYDROLOGY FLOW EXCEEDANCE TABLES AND GRAPHS APPENDIX C - REPRESENTATIVE DRY YEAR (22) SYNTHESIZED HYDROLOGY FLOW EXCEEDANCE TABLES AND GRAPHS APPENDIX D - REPRESENTATIVE NORMAL YEAR (24) SYNTHESIZED HYDROLOGY FLOW EXCEEDANCE TABLES AND GRAPHS APPENDIX E - REPRESENTATIVE WET, DRY AND NORMAL HYDROGRAPHS APPENDIX F - COMPARISON OF FLOW DATA FOR CASCADE CREEK ABOVE CASCADE CREEK DIVERSION DAM AND CDWR S RECORDS FOR PSCO S CASCADE CREEK DIVERSIONS i

3 TACOMA HYDROELECTRIC PROJECT PROJECT EFFECTS ON THE WATER QUANTITY AND QUALITY OF THE ANIMAS RIVER LIST OF FIGURES Figure Title Page No. 1 EFFECTS OF PROJECT OPERATIONS ON TRACE METAL CONCENTRATIONS IN THE ANIMAS RIVER BELOW TACOMA POWERHOUSE (22) CASCADE CREEK AT THE CASCADE CREEK DIVERSION DAM UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) CASCADE CREEK ABOVE THE CONFLUENCE WITH THE ANIMAS RIVER UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) ANIMAS RIVER ABOVE CASCADE CREEK UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) ANIMAS RIVER BELOW CASCADE CREEK UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) ANIMAS RIVER ABOVE TACOMA POWERHOUSE UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) ANIMAS RIVER BELOW TACOMA POWERHOUSE UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24)...19 ii

4 TACOMA HYDROELECTRIC PROJECT PROJECT EFFECTS ON THE WATER QUANTITY AND QUALITY OF THE ANIMAS RIVER LIST OF TABLES Table Title Page No. 1 USGS GAGES IN THE PROJECT VICINITY COMPARISON OF CASCADE CREEK AT THE CASCADE CREEK DIVERSION DAM BASIN AND USGS GAGE VALLECITO CREEK NEAR BAYFIELD COMPARISON OF CASCADE CREEK ABOVE THE CONFLUENCE WITH THE ANIMAS RIVER BASIN AND VALLECITO CREEK NEAR BAYFIELD GAGE COMPARISON OF ANIMAS RIVER ABOVE CASCADE CREEK AND ANIMAS RIVER BELOW SILVERTON GAGE COMPARISON OF ANIMAS RIVER ABOVE TACOMA POWERHOUSE AND ANIMAS RIVER BELOW SILVERTON GAGE COMPARISON OF ANIMAS RIVER BELOW TACOMA POWERHOUSE AND ANIMAS RIVER BELOW SILVERTON GAGE EFFECTS OF PROJECT OPERATIONS ON TRACE METAL CONCENTRATIONS IN THE ANIMAS RIVER BELOW TACOMA POWERHOUSE (22)...14 iii

5 Section 1 Purpose and Background This report describes the development of hydrologic data for certain watersheds associated with the Tacoma Hydroelectric Project. This study was performed in support of an analysis of the potential effects of the Tacoma Project on the water flows and water quality of the Animas River. The Tacoma Project is located approximately 2 miles north of Durango, Colorado, on a high intermountain plateau west of the Animas River in La Plata and San Juan counties. The Project is owned and operated by Public Service Company of Colorado (PSCo). This report includes discussion of methods used to evaluate and develop the unimpaired hydrology of the Animas River and the influence of the Project operations on that unimpaired hydrology as it might effect specific water quality parameters, specifically dilutional effects on organics, metals, and nutrient loadings. The hydrology of the Project area was developed using a straight-line or linear proration methodology. The proration method estimates unimpaired flows for a region of interest using unimpaired streamflow measurements from one or more reference basins. The equation below estimates unimpaired flows based on an area-weighted correlation to flows at a reference site: Q target A = A target reference Q reference where: Qtarget is the flow (cfs) for the basin of interest, Qreference is the flow (cfs) for the reference basin, Atarget is the drainage area (square miles) for the basin of interest, Areference is the drainage area (square miles) for the reference basin. Drainage areas were taken directly from U.S. Geological Survey (USGS) records where available, or by using Geographic Information Systems (GIS) based calculations. 1

6 Section 1 Purpose and Background Once the basin hydrologic data are established, the dilutional effects of Project operations on the Animas River related to metals, organics, or nutrient concentrations can be estimated as follows: Q A = Q N + Q P TM A = Q A x C 1 C 2 = TM A / Q N where Q A = Animas River average daily flow below Tacoma powerhouse Q N = Animas River average daily unimpaired flow below Tacoma powerhouse Q P = Net Tacoma plant flow (Q Out Q In ) TM A = Total parameter loading in the Animas below Tacoma powerhouse C 1 = Parameter concentration in Animas River below Tacoma powerhouse C 2 = Parameter concentration in Animas River under unimpaired flow conditions The Cascade Creek drainage above PSCo s diversion dam is an undeveloped watershed located virtually entirely within the boundaries of the San Juan National Forest. Relative to the Animas River drainage, very little mining or development activity has occurred in the Cascade Creek drainage. The waters of Cascade Creek above the diversion dam have excellent physical and chemical water quality characteristics. It is generally agreed that the water quality of Cascade Creek related to the parameters of organics, metals, and nutrient loading is significantly better than that of the Animas River. This being the case, then the following also holds true: when: Q A > Q N; C 1 < C 2 Q A < Q N ; C 1 > C 2 2

7 Section 2 Synthetic Unimpaired Hydrograph of Cascade Creek The proration methodology requires hydrologic similarity between the basin of interest and the reference drainage. Hydrologic similarity implies that the Project and reference sites possess comparable physical characteristics such as climate, land cover, elevation, aspect, and geology. If the features of the watershed of interest deviate from that of the reference site, the prorated unimpaired stream flows may deviate accordingly; therefore, when the character of the Project and reference sites differ significantly, application of the proration method provides less reliable results. For hydrologically similar unimpaired watersheds, it has been shown that drainage area correlates well with flow rate. Consequently, to estimate the unimpaired streamflow of a regulated drainage, the reference site should be unregulated and have a sufficiently long period of record. If, however, a completely natural reference site is not available, a site with limited regulation should be chosen to minimize the effects of cumulative errors. The high mountains of southwestern Colorado experience a relatively large amount of meteorological variation due largely to the effects of orographic lift and precipitation shadowing. Indeed, these processes can occur on very small spatial scales leading to equally significant variability in basin runoff response. While the mechanisms of lift and shadowing cannot easily be measured, the aforementioned watershed characteristics (e.g., climate, topography, land cover, elevation, aspect, and geology) influence these processes. To minimize this variability and provide accuracy to the streamflow estimates for the Project basin, a reference site in close proximity to Cascade Creek with reasonably comparable precipitation, elevation, aspect, slope, and percent water body was selected. 3

8 Section 3 Project Operations The Tacoma Project is located about 2 miles north of Durango, Colorado, on a high intermountain plateau west of the Animas River in La Plata and San Juan Counties. The Project was constructed in 195 and 196. Water supply for operation of the facilities originates in three drainage basins: Cascade Creek, Little Cascade Creek, and Elbert Creek. The Project consists of the Cascade Creek diversion facilities and four dams Cascade Creek Diversion Dam, Aspaas Dam, Stagecoach Dam, and Terminal Dam which impounds the main storage reservoir, Electra Lake. The Cascade Creek diversion facilities deliver the major water supply component for the Tacoma Project. These facilities consist of an approximately 1-foot-high concrete diversion dam on Cascade Creek with a normal water level at approximately 8,9 feet 1 ; 4,2 feet of 1-footdiameter, semi-circular, elevated wooden flume; a 1,4-foot-long, 6-inch-diameter steel inverted siphon crossing Cascade Creek; and a 14,5-foot-long, 64-inch-diameter steel pipeline. The Cascade Creek Diversion Dam is located 3.9 miles upstream of the confluence of Cascade Creek and Lime Creek at Purgatory Flats. After its confluence with Lime Creek, Cascade Creek flows approximately another 2.8 miles to where it enters the Animas River. Water from Cascade Creek is transported through the Cascade Creek diversion facilities and then released into Little Cascade Creek. A gaging station recording flows exiting the Cascade Creek diversion pipe is located at the outlet of the pipe before the flow enters Little Cascade Creek. The open channel of Little Cascade Creek carries the water to Aspaas Lake located just north of Electra Lake. Flows in Little Cascade Creek are then diverted at Aspaas Dam into Electra Lake, which is formed by Terminal Dam on the main channel of Elbert Creek. An 11,4-foot-long steel penstock extends from Electra Lake to the Tacoma powerhouse. The maximum static head between Electra Lake and the Tacoma powerhouse is 1,77 feet. 1 All elevations are provide in mean sea level (msl) datum. 4

9 Section 3 Project Operations Aspaas Lake impounds approximately 24 acre-feet of water at the normal maximum operating level of 8,377 feet. The corresponding reservoir surface area is approximately 4 acres. Columbine Lake is located within the Project Boundary along the flowline that delivers Project water diverted from Cascade Creek into Electra Lake. The small timber dam at the downstream end of Columbine Lake has been breached. There are no plans to rebuild the dam as it serves no Project purpose. The pond is roughly.5 miles long with a surface area of approximately 4 acres. The lake is generally less than 5 feet deep and has no usable storage. The normal water surface elevation of Columbine Lake is approximately 8,8 feet. Terminal Dam impounds Electra Lake, a reservoir with about 2,6 acre-feet of active storage at its normal maximum water surface elevation of 8,377 feet. The corresponding surface area is approximately 8 acres. During normal water years, Electra Lake is filled by runoff during the spring and early summer. Runoff from snowmelt typically occurs from late April through July, with peak flows occurring in late May to mid-june. During the spring runoff period, the plant is operated at a constant daily output, otherwise known as a base-load schedule. Over a number of weeks, generation is increased gradually to balance outflow with inflow into Electra Lake. Once plant capacity is reached, excess inflow is used to fill Electra Lake. Beginning in August, the plant is operated at a reduced capacity in order to maintain the level of Electra Lake to within several feet of its normal high water level (elevation 8,377 feet). In August and September, the output of the plant is reduced as snowmelt is exhausted and streamflows subside. In anticipation of next spring s runoff, the plant output is increased in late November or early December, operated on a peaking schedule, to gradually drawdown the reservoir to its winter settings with a normal minimum operating level of 8,357 feet. 5

10 Section 4 Potential Reference Watersheds The development of reference basins for the watersheds related to the Tacoma Project began with a compilation of the available USGS gages in the vicinity of the Project area (Table 1). This list of gages was reviewed for applicability based on the period of record, drainage area size, elevation, and average annual precipitation. The color-coding provided in Table 1 shows the first step in the process of searching for a reference basin based on initial screening selection criteria. The three screening methodologies employed are described below: Period of Record - Gages were excluded that had less than 1 consecutive years of hydrology, or a Period of Record (POR) which did not include recent years due to the potential for changes in watershed characteristics resulting from development and/or recent land use practices. Drainage Area - Gages with a drainage area greater than 5 square miles or approximately two times the drainage area of the Animas River above Cascade Creek were excluded from the list to avoid inaccuracies due to dissimilarities in watershed characteristics such as the tendency for larger basins to have lower slopes while typically encompassing a larger range of elevations. Basin Characteristics - Basin characteristics such as elevation, geographic orientation, average annual precipitation and water transfers were reviewed to identify gages with significantly different characteristics. Representative hydrology for Cascade Creek at the PSCo diversion dam was previously estimated in the Cascade Creek Hydrology report developed by Devine Tarbell & Associates, Inc. ([DTA] 26) wherein the reference gage selected was the USGS stream gage at Vallecito Creek near Bayfield

11 Section 4 Potential Reference Watersheds TABLE 1 USGS GAGES IN THE PROJECT VICINITY Gage Site USGS Gage ID Elevation, feet above msl Drainage area, mi 2 Period of Record Animas River above Tacoma , /1/1945-9/3/1956 Animas River at Durango , /1/ Present Animas River at Howardsville , /1/1935-9/3/1982 Animas River at Silverton , /1/ Present Animas River below Silverton , /1/ Present Beaver Creek near Norwood , /1/1941-9/3/1981 Cimarron River near Cimarron , /1/ Present Cebolla Creek near Lake City , /1/1946-9/3/1954 Cement Creek at Silverton , /1/ Present Cow Creek near Ridgway , /1/1955-9/3/1973 Dolores River at Dolores , /1/1895-9/3/25 Dolores River below Rico , /1/ Present Dolores River near Mcphee , /1/1938-9/3/1952 East Fork Dallas Creek near Ridgway , /1/1947-9/3/197 E. Fork San Juan R ab Sand Ck, nr Pagosa Spgs , /1/1956 3/3/23 East Mancos River near Mancos , /1/1937-9/3/1951 Fall Creek near Durango , /1/1959-9/3/1965 Fall Creek near Fall Creek , /1/1941-9/3/1959 Florida River below Lemon Reservoir , /1/1955-9/3/1963 Florida River near Durango , /1/1967-9/3/1982 Florida River near Durango , /1/191-9/3/196 Hermosa Creek near Hermosa , /1/192-9/3/198 Junction Creek near Durango , /1/1959-9/3/1965 La Plata River at Hesperus , /1/1917-9/3/25 Lake Fork below Mill Gulch near Lake City , /1/1981-9/3/1986 Lightner Creek near Durango , /1/1927-9/3/1949 Legend For Table 1: Short Period of Record / No Recent Hydrology Large Drainage Area Dissimilar Basin Characteristics 7

12 Section 4 Potential Reference Watersheds Gage Site USGS Gage ID Elevation, feet above msl Drainage area, mi 2 Period of Record Lime Creek near Silverton , /1/1956-9/3/1961 Los Pinos River near Bayfield , /1/1927-9/3/1986 Lost Canyon Creek at Dolores , /1/1941-9/3/1948 Lost Canyon Creek near Dolores , /1/ Present Mancos River near Manco 937 7, /1/1931-9/3/1938 Middle Fork Piedra River near Pagosa Springs , /1/1969-9/3/1975 Middle Fork Piedra River near Dyke , /1/1977-9/3/1983 Middle Mancos River near Mancos , /1/1938-9/3/1951 Mineral Creek above Silverton , /1/1968-9/3/1975 Mineral Creek near Silverton , /1/1936-9/3/1949 North Clear Creek below Continental Reservoir , /1/1929-9/3/1998 Piedra River near Pagosa Springs , /1/1936-9/3/1954 Piedra River near Piedra , /1/1939-9/3/1973 Red Mountain Creek above Ironton , /1/ /31/1955 Rio Grande River near Creede , /1/199-9/3/1998 San Miguel River near Placerville ,3 31 1/1/191 - Present Turkey Creek near Pagosa Springs , /1/1937 9/3/1949 Uncompahgre River below Ouray , /1/1913-9/3/1929 Uncompahgre River near Ridgway , /1/ Present Vallecito Creek near Bayfield , /1/ Present Weminuche Creek near Pagosa Springs , /1/1937-9/3/1949 West Dolores River near Stoner , /1/1941-9/3/1944 West Fork San Juan R, near Pagosa Springs , /1/1937 9/3/1953 Williams Creek near Pagosa Springs , /1/1937-9/3/1949 Wilson Gulch near Durango , /7/1995-9/3/25 Legend For Table 1: Short Period of Record / No Recent Hydrology Large Drainage Area Dissimilar Basin Characteristics 8

13 Section 5 Development of Hydrology Using Selected Reference Sites An analysis of the potential sites listed in Table 1 according to basin characteristics lead to the following selections of reference basins for the watersheds associated with the Tacoma Project: Cascade Creek at the Cascade Creek Diversion Dam reference basin is Vallecito Creek near Bayfield Cascade Creek above the confluence with the Animas River reference basin is Vallecito Creek near Bayfield Animas River above Cascade Creek reference basin is Animas River below Silverton Animas River above Tacoma Powerhouse reference basin is Animas River below Silverton Animas River below Tacoma Powerhouse reference basin is Animas River below Silverton Using the Proration Method discussed in Sections 1 and 2, the unimpaired hydrology for the Project-related sites was estimated using the reference basins identified above. Each of the Project-related sites are discussed below. Cascade Creek at the Cascade Creek Diversion Dam - Impaired and unimpaired hydrology data was developed for Cascade Creek at the Cascade Creek Diversion Dam (37 39'37"N, 17 48'43"W). Based on a comparison of significant watershed characteristics, the USGS Gage Vallecito Creek near Bayfield was selected as the reference site for Cascade Creek at the Cascade Creek Diversion Dam. An unimpaired hydrology set for the Cascade Creek basin was developed by a straight drainage area proration of the Vallecito gage dataset. A comparison of selected basin parameters is presented in Table 2. 9

14 Section 5 Development of Hydrology Using Selected Reference Sites TABLE 2 COMPARISON OF CASCADE CREEK AT THE CASCADE CREEK DIVERSION DAM BASIN AND USGS GAGE VALLECITO CREEK NEAR BAYFIELD Cascade Creek at the Cascade Creek diversion dam Vallecito Creek Drainage Area (mi 2 ) Gage Elevation (msl) 8,97 7,96 Maximum Elevation (msl) 13,72 14,38 Average Elevation (msl) 11,179 11,35 Average Basin Slope (%) Percent of Basin Area covered by Water bodies.6%.62% Area-Weighted Average Annual Precipitation (in) The regulated streamflows for Cascade Creek below the Cascade Creek diversion dam were calculated using the Annual Water Diversion Reports for Cascade Creek published by the Colorado Division of Water Resources (Office of the State Engineer). The Cascade Creek diversion dam is operated in a run-of-river mode utilizing available flows up to the maximum capacity of the diversion facilities. The maximum capacity of the diversion facilities is not precisely known, but is reported to be approximately 275 cfs (Tacoma Project, May 25 Pre- Application Document). Accordingly, the impaired streamflow at Cascade Creek diversion dam was defined as the unimpaired flows minus the flows diverted into the conveyance facilities. This approach does not account for leakage from the conveyance facilities or dam. Leakage at the diversion dam has been roughly estimated at about 1 cfs, but varies seasonally. Cascade Creek above the confluence with the Animas River - Natural and regulated hydrology data were also developed for Cascade Creek above its confluence with the Animas River (37 36'1"N, 17 46'16"W) using the USGS Gage Vallecito Creek near Bayfield. A comparison of significant watershed characteristics is presented in Table 3. 1

15 Section 5 Development of Hydrology Using Selected Reference Sites TABLE 3 COMPARISON OF CASCADE CREEK ABOVE THE CONFLUENCE WITH THE ANIMAS RIVER BASIN AND VALLECITO CREEK NEAR BAYFIELD GAGE Cascade Creek above confluence with Animas River Vallecito Creek Gage Drainage Area (mi 2 ) Gage Elevation (msl) 7,693 7,96 Maximum Elevation (msl) 13,72 14,38 Average Elevation (msl) 1,721 11,35 Average Basin Slope (%) Percent of Basin Area covered by Water bodies.51%.62% Area-Weighted Average Annual Precipitation (in) The incremental drainage area between Cascade Creek above its confluence with the Animas River and Cascade Creek at the Cascade Creek diversion dam was estimated to be 59.7 mi 2. The incremental unimpaired hydrology for Cascade Creek above its confluence with the Animas River was developed by prorating the Vallecito USGS gage data to this incremental drainage area and then adding the unimpaired hydrology for the Cascade Creek at the Cascade Creek diversion dam unimpaired hydrology yielding a cumulative Cascade Creek unimpaired hydrology. It should be noted that neither travel time nor attenuation between locations were taken into account. The impaired hydrology for Cascade Creek above its confluence with the Animas River was developed by adding the Cascade Creek at its Cascade Creek diversion dam impaired hydrology to the incremental unimpaired hydrology of Cascade Creek above its confluence with the Animas River. Animas River above Cascade Creek - Based on the initial screening criteria and a comparison of significant watershed characteristics, USGS gage 93592, Animas River below Silverton, was selected as the reference site for the Animas River above Cascade Creek (37 36'1"N, 17 46'16"W). Watershed characteristics for the two basins are identified in Table 4. 11

16 Section 5 Development of Hydrology Using Selected Reference Sites TABLE 4 COMPARISON OF ANIMAS RIVER ABOVE CASCADE CREEK AND ANIMAS RIVER BELOW SILVERTON GAGE Animas River above Cascade Creek Site Animas River below Silverton Gage Drainage Area Gage Elevation (msl) 7,684 9,199 Maximum Elevation (msl) 14,35 13,871 Average Elevation (msl) 11,427 11,441 Average Basin Slope (%) Percent of Basin Area covered by Water bodies.47%.52% Area-Weighted Average Annual Precipitation (in) Unimpaired hydrology for the Animas River above Cascade Creek was estimated by prorating the Animas River gage data to the drainage area of the Animas River above Cascade Creek. The Animas River above Cascade Creek is upstream of any Project influence. Consequently, the impaired and unimpaired hydrology are identical related to any Tacoma Project effects. Animas River above Tacoma Powerhouse - Based on similarities in watershed characteristics, USGS gage 93592, Animas River below Silverton, was also selected as the reference site for the Animas River above Tacoma Powerhouse (37 31'24 N, 17 46'58 W). A comparison of characteristics for the two basins is presented in Table 5. TABLE 5 COMPARISON OF ANIMAS RIVER ABOVE TACOMA POWERHOUSE AND ANIMAS RIVER BELOW SILVERTON GAGE Animas River above Tacoma Powerhouse Site Animas River below Silverton Gage Drainage Area (mi 2 ) Gage Elevation (msl) 7,287 9,199 Maximum Elevation (msl) 14,35 13,871 Average Elevation (msl) 11,17 11,441 Average Basin Slope (%) Percent of Basin Area covered by Water bodies.59%.52% Area-Weighted Average Annual Precipitation (in) Unimpaired hydrology for the Animas River above the Tacoma powerhouse was created by prorating the Animas River below Silverton USGS gage streamflow record to the drainage area of the Animas River above the Tacoma powerhouse minus the Cascade Creek drainage area. The unimpaired hydrology of Cascade Creek at its confluence with the Animas River was then 12

17 Section 5 Development of Hydrology Using Selected Reference Sites added to this drainage area. Time of travel and attenuation between the locations were not taken into account. The impaired hydrology for the Animas River above Tacoma powerhouse drainage area was created by summing the unimpaired hydrology for the Animas River above Cascade Creek and the impaired hydrology for Cascade Creek. Again, time lag and attenuation between the locations were not taken into account. Animas River below Tacoma Powerhouse - Based on similarities in relevant watershed characteristics, USGS gage 93592, Animas River below Silverton, was also selected as the reference site for the Animas River below Tacoma powerhouse (37 31'24 N, 17 46'58 W). The overall similarities of the two basins are summarized in Table 6. TABLE 6 COMPARISON OF ANIMAS RIVER BELOW TACOMA POWERHOUSE AND ANIMAS RIVER BELOW SILVERTON GAGE Animas River below Tacoma Powerhouse Site Animas River below Silverton Gage Basin Drainage Area (mi 2 ) Gage Elevation (msl) 7,287 9,199 Maximum Elevation (msl) 14,35 13,871 Average Elevation (msl) 11,17 11,441 Average Basin Slope (%) Percent of Basin Area covered by Water bodies.59%.52% Area-Weighted Average Annual Precipitation (in) Impaired or regulated hydrology for Animas River below Tacoma Powerhouse was developed by summing the impaired hydrology developed for the Animas River above Tacoma powerhouse and the historic water releases from the Tacoma powerhouse. The unimpaired hydrology for the Animas River below Tacoma powerhouse is identical to that of the Animas River above Tacoma powerhouse. 13

18 Section 6 Water Quality Assessment Water quality data in the form of the concentration of the trace metals cadmium, copper and zinc for the Animas River below Silverton during the months of February, May, June, July and September were obtained from the USGS report entitled Using Water-Quality Profiles to Characterize Seasonal Water Quality and Loading in the Upper Animas River Basin, Southwestern Colorado. A correlation was developed between river flow and the total metal loading in the Animas River. This correlation was used to determine the trace metal concentration for each month of the year which was subsequently used to estimate the effects on water quality in the Animas River due to the operations at Tacoma powerhouse. For purposes of this study, a total metal load was estimated by summing the concentration of the three trace metals. The concentration of trace metals at the gaging station on the Animas River below Silverton was assumed to be equal to the concentration at the Animas River above the confluence with the Cascade Creek site. A total metal concentration for the impaired and unimpaired hydrology data set for above and below the Tacoma powerhouse was created assuming the trace metal concentrations in Cascade Creek are significantly lower than those of the Animas River. Combining the unimpaired and impaired hydrology data with these metal loadings, the effects of Project operations on total metal concentrations in the Animas River below Tacoma powerhouse are summarized below in Table 7 and shown graphically in Figure 1 for a low-flow year (22). TABLE 7 EFFECTS OF PROJECT OPERATIONS ON TRACE METAL CONCENTRATIONS IN THE ANIMAS RIVER BELOW TACOMA POWERHOUSE (22) Month Trace Metal Concentration (mg/l) Unimpaired Impaired Percent Change January February March April May June July August September October November December

19 Section 6 Water Quality Assessment FIGURE 1 EFFECTS OF PROJECT OPERATIONS ON TRACE METAL CONCENTRATIONS IN THE ANIMAS RIVER BELOW TACOMA POWERHOUSE (22).7.6 Total Metal Concentration,milligrams per liter Jan 1 Jan 15 Jan 29 Feb 12 Feb 26 Mar 12 Mar 26 Apr 9 Apr 23 May 7 May 21 Jun 4 Jun 18 Jul 2 Jul 16 Jul 3 Aug 13 Aug 27 Sep 1 Sep 24 Oct 8 Oct 22 Nov 5 Nov 19 Dec 3 Dec 17 Dec 31 Date Analysis of water quality in the Animas River below the Tacoma powerhouse during a dry year shows that Project operations tend to have a minor adverse impact on water quality during months when the facility is operated in a base-load schedule (higher flow months), typically from mid-april through November, and a considerable positive impact when the facility is in a peaking schedule (low flow months), typically December through mid-april. 15

20 Section 7 Summary of Results Two reference gages were used in the development of hydrology data sets for Project watersheds: Vallecito Creek near Bayfield gage (USGS No ) and Animas River below Silverton gage (USGS No ). Other data sources included the historic operation records for the Cascade Creek diversion dam gage and the Tacoma powerhouse. The gages were selected based on basin characteristics and POR. Appendices A through D include tables and figures showing comparisons of the unimpaired and impaired hydrology sets for representative wet, dry, and normal years and the POR. Figures 2 through 7 show the synthetic hydrographs developed for each site of interest for the representative normal year (24). Appendix E includes the synthetic hydrographs developed for each site for the representative wet, dry, and normal years. Appendix F shows annual and monthly comparisons of the CDWR record of the Cascade Creek diverted flows and the estimated flows above the Cascade Creek diversion dam using the Vallecito Creek synthesized flow record for the period of November 1, 198 through October 31, 24. As discussed in Section 6, the analysis of water quality in the Animas River below the Tacoma powerhouse for a dry year shows that the Project typically has a minor negative impact on the water quality in the Animas River below the Tacoma Powerhouse during higher river flow periods and a considerable positive impact during lower flow periods. This is due to the relative importance of either net storage or net releases during these time periods given the water in Electra Lake which has significantly better water quality than the water in the Animas River. Given that other dilution-related parameters (e.g., organics, nutrient loading) would be affected in the same manner as that identified as metals, it can be concluded that Project effects related to organics and nutrient loading are very similar to the effect predicted for metals. 16

21 FIGURE 2 CASCADE CREEK AT THE CASCADE CREEK DIVERSION DAM UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) January February March April May June July August September October NovemberDecember Unimpaired Impaired FIGURE 3 CASCADE CREEK ABOVE THE CONFLUENCE WITH THE ANIMAS RIVER UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) 1,8 1,6 1,4 1,2 1, January February March April May June July August September October NovemberDecember Unimpaired Impaired 17

22 FIGURE 4 ANIMAS RIVER ABOVE CASCADE CREEK UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) 3,5 3, 2,5 2, 1,5 1, 5 January February March April May June July August September October NovemberDecember Unimpaired Impaired FIGURE 5 ANIMAS RIVER BELOW CASCADE CREEK UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 January February March April May June July August September October NovemberDecember Unimpaired Impaired 18

23 FIGURE 6 ANIMAS RIVER ABOVE TACOMA POWERHOUSE UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) 5, 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 January February March April May June July August September October NovemberDecember Unimpaired Impaired FIGURE 7 ANIMAS RIVER BELOW TACOMA POWERHOUSE UNIMPAIRED AND IMPAIRED HYDROLOGY FOR REPRESENTATIVE NORMAL YEAR (24) 5, 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 January February March April May June July August September October NovemberDecember Unimpaired Impaired 19

24 Section 8 References Devine Tarbell & Associates, Inc Tacoma Hydroelectric Project Cascade Creek Hydrology. August 26. Leib, Kenneth J.; Mast, M. Alisa; Wright, Winfield G. 23. Using Water-Quality Profiles to Characterize Seasonal Water Quality and Loading in the Upper Anima River Basin, Southwestern Colorado. Public Service Company of Colorado. 25. Pre-Application Document, Tacoma Hydroelectric Project (FERC Project No ). May 25. U.S. Department of Agriculture; Natural Resources Conservation Service. Undated. Colorado Precipitation Data/Maps. [Online] URL: products/datasets/climate/data/precipitation-state/co.html. (Accessed August 26.) U.S. Geological Survey. National Water Information System Surface -Water Data for Colorado. [Online] URL: (Accessed August 3, 26.) P:\Xcel\132.1\WP\6-OtherStds&Rpts\Project Effects\T-Proj Effcts on WQ-7114.doc AS/JB/elt /8. November 4, 27 2

25 APPENDICES

26 APPENDIX A POR SYNTHESIZED HYDROLOGY FLOW EXCEEDANCE TABLES AND GRAPHS

27 Synthesized Unimpaired and for the POR of the Animas River Above Cascade Creek Percent Annual January February March April May June July August September October November December 1.% % % % % % % % % % % % % % % % % % % % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % ,9 1, % ,46 1, % ,67 1, % ,86 1, % ,13 1, % ,128 1, % ,157 1, % ,179 1, % ,232 1, % ,244 1, % ,251 1, % ,28 1, % ,296 1, % ,39 2, % ,323 2, % ,356 2, % ,378 2, % ,399 2, % ,431 2, % ,461 2, % ,52 2,295 1, % ,544 2,333 1, % ,576 2,362 1, % ,63 2,416 1, J:\Projects\Xcel Energy\132.1-Tacoma\6-OtherStdspts\Basin Hydrlgy\ Appendix A-1-1 OrigGraphics\Appendix A.xls

28 Synthesized Unimpaired and for the POR of the Animas River Above Cascade Creek Percent Annual January February March April May June July August September October November December 26.% ,632 2,492 1, % ,657 2,531 1, % ,722 2,57 1, % ,749 2,598 1, % ,765 2,665 1, % ,82 2,74 1, % ,926 2,739 1, % ,944 2,774 1, % ,52 2,84 1, % ,13 2,894 1, % ,169 2,933 1, % ,246 3,4 1, % 1, ,297 3,63 1, % 1, ,368 3,12 1, % 1, ,43 3,141 1, % 1, ,469 3,197 1, % 1, ,546 3,234 1, % 1, ,617 3,257 1, % 1, ,723 3,322 1, % 1, ,845 3,393 1, % 1, ,952 3,479 2, % 2, ,4 3,537 2,275 1, % 2, ,182 3,645 2,386 1, % 2, ,234 3,746 2,615 1, % 2, ,435 3,828 2,833 1, % 3, ,729 3,92 3,34 1,272 1, % 3, ,6 4,5 4,69 1,361 1, % 4, ,27 4,63 4,144 1,37 2, Appendix A-1-2 J:\Projects\Xcel Energy\132.1-Tacoma\6-OtherStdspts\Basin Hydrlgy\ OrigGraphics\Appendix A.xls

29 Animas River Above Cascade Creek Annual Flow for the POR 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Animas River Above Cascade Creek January Flow for the POR % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Appendix A-1 graphs - 1

30 Animas River Above Cascade Creek February Flow for the POR % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Animas River Above Cascade Creek March Flow for the POR % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Appendix A-1 graphs - 2

31 Animas River Above Cascade Creek April Flow for the POR 1,2 1, % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Animas River Above Cascade Creek May Flow for the POR 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Appendix A-1 graphs - 3

32 Animas River Above Cascade Creek June Flow for the POR 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Animas River Above Cascade Creek July Flow for the POR 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Appendix A-1 graphs - 4

33 Animas River Above Cascade Creek August Flow for the POR 1,6 1,4 1,2 1, % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Animas River Above Cascade Creek September Flow for the POR 2,5 2, 1,5 1, 5 % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Appendix A-1 graphs - 5

34 Animas River Above Cascade Creek October Flow for the POR % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Animas River Above Cascade Creek November Flow for the POR % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Appendix A-1 graphs - 6

35 Animas River Above Cascade Creek December Flow for the POR % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% Appendix A-1 graphs - 7

36 Synthesized for the POR of the Animas River Below Cascade Creek Percent Annual January February March April May June July August September October November December 1.% % % % % % % % % % % % % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % ,17 1, % ,27 1, % ,45 1, % ,13 1, % ,143 1, % ,163 1, % ,181 1, % ,29 1, % ,233 1, % ,247 1, % ,263 1, % ,289 2, % ,331 2, % ,372 2, % ,398 2, % ,448 2, % ,478 2, % ,54 2, % ,563 2, % ,63 2, % ,632 2, % ,652 2, % ,68 2, % ,691 2,343 1, % ,733 2,358 1, % ,762 2,44 1, % ,799 2,467 1, % ,827 2,516 1, % ,836 2,572 1, % ,846 2,637 1, % ,865 2,713 1, % ,96 2,738 1, % ,972 2,832 1, % ,36 2,89 1, % ,63 2,924 1, % ,99 2,966 1, % ,137 3,39 1, % ,172 3,98 1, % ,225 3,134 1, J:\Projects\Xcel Energy\132.1-Tacoma\6-OtherStdspts\Basin Hydrlgy\ Appendix A-2-1 OrigGraphics\Appendix A.xls

37 Synthesized for the POR of the Animas River Below Cascade Creek Percent Annual January February March April May June July August September October November December 26.% ,235 3,187 1, % ,298 3,232 1, % ,359 3,285 1, % ,386 3,327 1, % ,459 3,364 1, % ,556 3,415 1, % ,661 3,481 1, % ,792 3,55 1, % 1, ,882 3,62 1, % 1, ,92 3,698 1, % 1, ,959 3,798 1,882 1, % 1, ,36 3,833 1,899 1, % 1, ,116 3,928 1,914 1, % 1, ,226 3,999 2,1 1, % 1, ,334 4,73 2,3 1, % 1, ,424 4,115 2,9 1, % 1, ,446 4,151 2,156 1, % 1, ,511 4,183 2,257 1, % 2, ,623 4,233 2,44 1, % 2, ,75 4,34 2,56 1, % 2, ,879 4,52 2,648 1, % 2, ,965 4,674 2,798 1, % 3, ,18 4,795 2,985 1,556 1, % 3, ,52 4,261 4,895 3,213 1,66 1, % 3, ,125 4,66 4,941 3,619 1,677 1, % 4, ,223 5,194 5,13 4,41 1,789 1, % 5, ,345 5,65 5,253 5,99 2,86 3, % 5, ,363 5,669 5,278 5,193 2,129 3, Appendix A-2-2 J:\Projects\Xcel Energy\132.1-Tacoma\6-OtherStdspts\Basin Hydrlgy\ OrigGraphics\Appendix A.xls

38 Synthesized for the POR of the Animas River Below Cascade Creek Percent Annual January February March April May June July August September October November December 1.% % % % % % % % % % % % % % % % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % , % ,4 1, % ,44 1, % ,6 1, % ,86 1, % ,1 1, % ,112 1, % ,129 1, % ,161 1, % ,177 1, % ,227 1, % ,241 1, % ,261 1, % ,314 1, % ,353 1, % ,372 2, % ,427 2, % ,467 2, % ,57 2, % ,528 2, % ,536 2, % ,544 2, % ,59 2, % ,619 2,238 1, % ,65 2,296 1, % ,661 2,357 1, % ,68 2,423 1, % ,73 2,466 1, % ,722 2,532 1, % ,745 2,563 1, % ,82 2,655 1, % ,862 2,711 1, % ,911 2,745 1, % ,944 2,82 1, % ,97 2,845 1, % ,2 2,917 1, % ,5 2,971 1, J:\Projects\Xcel Energy\132.1-Tacoma\6-OtherStdspts\Basin Hydrlgy\ Appendix A-2-3 OrigGraphics\Appendix A.xls