3.4.1.5 Water Quality

Initial Fill and Make-up Water

Because the North Platte River drainage is fully appropriated, securing a water supply for the Project requires temporary or permanent agreements from existing water right holders. Black Canyon is currently in discussions over various permitting paths for water usage with the State Engineer and Reclamation. As a further consideration, the water uses in the North Platte drainage are subject to the terms of the North Platte Decree and the 2001 Stipulation. In addition, the PRRIP and compliance with the ESA constrain the development of any new water projects in the North Platte Basin that exceed 20 ac-ft per year in water depletions (Wyoming Water Development Commission 2016).

The State Engineer has broad discretion in how to permit water usage at the Project, but has indicated the following permits and agreements will likely be necessary:

(i) A new water storage right associated with the upper reservoir; (ii) An excess capacity storage contract with Reclamation to hold water in Seminoe Reservoir; (iii) A water service contract with Reclamation to purchase the initial water fill; (iv) A temporary water authorization allowing the purchased water to be diverted for use at the Project; (v) A contractual arrangement with the Casper Alcova Irrigation District for their consent to water being diverted from Seminoe for the initial fill; (vi) A memorandum of operation or understanding regarding how spilled water at Seminoe that is accounted for as Project water can be captured downstream and exchanged.

Black Canyon is consulting on water permitting with the State Engineer and has undertaken actions to secure the above agreements and permits. A new water storage right for the upper reservoir will be sought after FERC licensing is complete and construction of the upper reservoir begins. Black Canyon has initiated a basis of negotiations with Reclamation in order to secure the excess capacity storage contract(s) and water service contract. A temporary water authorization will be sought from the State Engineer, pursuant to Wyo. Stats. Ann. §41-3-110. In addition, Black Canyon is in negotiations with the Casper Alcova Irrigation District to secure the contractual arrangement to allow for the initial fill and, potentially, long-term, make-up water for the Project. The Project may, if necessary, seek to engage with other water right holders and/or parties as becomes necessary to secure water supply and usage. As the State Engineer is still making final determination on permitting, the agreements for the water supply and plans for its availability may be further developed and finalized as the licensing process advances.

3.4.1.5 Water Quality Federally Approved Water Quality Standards

Wyoming’s surface water quality standards include designated uses, water quality criteria, and antidegradation provisions to protect and restore Wyoming’s surface waters. The standards are developed to be consistent with the Wyoming Environmental Quality Act

and the Federal CWA. Wyoming’s Surface Water Quality Standards are included in Chapter 1 of the Water Quality Rules and Regulations and were updated in April 2018 (Wyoming Department of Environmental Quality [WDEQ] undated-b). The North Platte River is considered a Class 1 water from the headwaters of Pathfinder Reservoir upstream to Kortes Dam and from Natrona County Road 309 bridge (near the confluence with Poison Spider Creek) upstream to Alcova Dam (WDEQ/Water Quality Division [WQD] 2007a). The remainder of the segment, including all reservoirs, is considered Class 2AB (WDEQ/WQD 2007a). Water quality standards for temperature, dissolved oxygen (DO), pH, turbidity, suspended solids, and taste, odor, and color are presented in Table 3.4-5. Table 3.4-6 details the minimum DO criteria for Class 1, 2AB, 2B, and 2C waters.

Table 3.4-5. Narrative Water Quality Standards for Class 1, 2AB, 2B, and 2C Waters

Parameter Standard

For Class 1, 2, and 3 waters, pollution attributable to the activities of man shall not change ambient water temperatures to levels which result in harmful acute or chronic effects to aquatic life, or which would not fully support existing and designated uses.

Temperature When ambient temperatures are above 60°F (15.6°C) in all Class 1, 2AB, and 2B waters which are cold water fisheries, pollution attributable to the activities of man shall not result in an increase of more than 2ºF(1.1ºC) in existing temperatures.

Dissolved Oxygen

pH When ambient temperatures are above 60ºF(15.6ºC) in all Class 1, 2AB, 2B, and 2C waters which are warm water fisheries, pollution attributable to the activities of man shall not result in an increase of more than 4ºF(2.2ºC) in existing temperatures. In all Class 2A, 2D, and 3 waters, pollution attributable to the activities of man shall not deplete DO amounts to a level which will result in harmful acute or chronic effects to aquatic life, or which would not fully support existing and designated uses.

In all Class 1, 2AB, 2B, and 2C waters, pollution attributable to the activities of man shall not result in a DO content of less than that presented in Table 3.4-6 below. For all Wyoming surface waters, pollution attributable to the activities of man shall not be present in amounts which will cause the pH to be less than 6.5 or greater than 9.0 standard units.

For all Class 1, 2, and 3 waters, pollution attributable to the activities of man shall not change the pH to levels which result in harmful acute or chronic effects to aquatic life, directly or in conjunction with other chemical constituents, or which would not fully support existing and designated uses.

Parameter Standard

Turbidity In all cold water fisheries and/or drinking water supplies (Classes 1, 2AB, 2A, and 2B), the discharge of substances attributable to or influenced by the activities of man shall not be 1-20 present in quantities which would result in a turbidity increase of more than ten (10) nephelometric turbidity units (NTUs).

Suspended Solids In all warm water or nongame fisheries (Classes 1, 2AB, 2B, and 2C), the discharge of substances attributable to or influenced by the activities of man shall not be present in quantities which would result in a turbidity increase of more than 15 NTUs.

In all Wyoming surface waters, floating and suspended solids attributable to or influenced by the activities of man shall not be present in quantities which could result in significant aesthetic degradation, significant degradation of habitat for aquatic life, or adversely affect public water supplies, agricultural or industrial water use, plant life or wildlife.

Taste, Odor, Color

No Class 1, 2, or 3 waters shall contain substances attributable to or influenced by the activities of man that produce taste, odor, and color or that would: (a) Of themselves or in combination, impart an unpalatable or off-flavor in fish flesh; (b) Visibly alter the natural color of the water or impart color to skin, clothing, vessels, or structures; (c) Produce detectable odor; or (d) Directly or through interaction among themselves, or with chemicals used in existing water treatment processes, result in concentrations that will impart undesirable taste or odor to public water supplies. Source: WDEQ/WQD 2007a.

Table 3.4-6. Minimum DO Criteria for Class 1, 2AB, 2B and 2C Waters (milligrams per liter [mg/L])

30 Day Mean 7 Day Mean 7 Day Mean Minimum(4)

1 Day Minimum(4)

Cold Water Criteria Early Life Stages(1)(2) Other Life Stages

N/A(3) 6.5

9.5 (6.5)

N/A(3) N/A(3)

5.0

8.0 (5.0) 4.0

Notes: 1. These are water column concentrations recommended to achieve the required inter-gravel DO concentrations shown in parentheses. For species that have early life stages exposed directly to the water column, the figures in parentheses apply. 2. Includes all embryonic and larval stages and all juvenile forms to 30 days following hatching. 3. N/A (Not Applicable). 4. All minima should be considered as instantaneous concentrations to be achieved at all times.

Source: WDEQ/WQD 2007a.

Previous Water Quality Data Collection

U.S. Environmental Protection Agency

Seminoe Reservoir was surveyed three times in 1975 by U.S. Environmental Protection Agency’s (USEPA) National Eutrophication Survey. The final report issued in 1977 concluded that the reservoir was eutrophic in the North Platte and Medicine Bow arms, moderately eutrophic in the upper basin, and mesotrophic at two sample stations nearest Seminoe Dam. The limiting nutrient was determined to be phosphorus in May and October, and nitrogen in August. It was believed that light might also be a limiting factor during times of high turbidity. A year of monthly tributary sampling indicated that the North Platte River contributed 60.7 percent of the annual phosphorus loading and 62.8 percent of the annual nitrogen loading, while the Medicine Bow River contributed 23.0 percent of the annual phosphorus input and 17.8 percent of the annual nitrogen input (USEPA 1977 as cited in Reclamation 1981).

U.S. Bureau of Reclamation

The baseline limnology of Seminoe, Kortes, Pathfinder, and Alcova Reservoirs on the North Platte River was studied by Reclamation limnologists during 1976-1979. The study period included two years of severe drought followed by two years of higher-than-average runoff in the North Platte basin (Reclamation 1981). Limnology of the Upper North Platte reservoir system is typical in many ways of the High Plains Region of the Western U.S.; i.e., the reservoir waters are dimictic and alkaline, with salinity averaging 369 mg/L and calcium carbonate hardness averaging 184 mg/L. Study results showed that blue-green algae blooms are common in late summer and that this annual bloom depends on a shift from phosphorus-limiting conditions in early summer to more nitrogen-limiting conditions by late summer. The study also indicated that nutrient dynamics, and hence primary production in the system, are heavily influenced by the interaction of three main factors: system operating criteria, annual runoff variations in the three major tributaries, and the presence of deep outlets in all four dams (Reclamation 1981).

All the reservoirs in the study were characterized as alkaline, hard, and somewhat saline bodies of water. Measured hydrogen ion concentrations (pH) were always greater than 7.0, mean calcium carbonate hardness was approximately 184 mg/L, mean total dissolved solids approximately 318 mg/L, mean salinity (sum of anions and cations) approximately 369 mg/L, and conductivity readings during the study ranged from 240 to 577 microsiemens per centimeter (μS/cm) (Reclamation 1981).

All four reservoirs are dimictic, with isothermal conditions in both spring and fall and ice covers in the winter. Study results showed that maximum observed summer water temperatures ranged from about 17 to 20C at the surface, and 14 to 18C at the bottom.

Light penetration in the North Platte and Medicine Bow arms of Seminoe Reservoir is greatly reduced by the turbidity of the runoff in early summer. The water clears by midsummer, but a turbid underflow apparently passes through Seminoe Reservoir,

causing reduced light availability in Kortes Reservoir and the Miracle Mile in the late summer and fall. Study results showed that bottom DO concentrations in the deep-water study stations in the reservoirs reach their minimum by late August; however, the brevity of summer thermal stratification seems to prevent the development of any serious anaerobic, reducing conditions. Minimum observed bottom DO concentrations were reported as 0.2 mg/L in Seminoe Reservoir (Reclamation 1981).

Heavy metals (i.e., iron, manganese, zinc, copper, and lead) did not appear to constitute a biologic hazard in the system, although the study reported total concentrations of iron often, and manganese sometimes, exceeded USEPA quality criteria for domestic water supplies. The percent organic content and the concentration of heavy metals in the bottom sediments of the reservoirs are strongly positively correlated with the percentage of claysized fines (Reclamation 1981).

The study indicated that the high production of epilithic algae and benthic organisms in the Miracle Mile of the North Platte River seems directly attributable to the deep discharges from Seminoe and Kortes Dams, which supply nutrients and ensure a relatively constant physical environment. This instream production, in turn, appears to provide a food base for trout moving into the Miracle Mile from the North Platte arm of Pathfinder Reservoir (Reclamation 1981).

Existing Water Quality Data

Wyoming Department of Environmental Quality/Water Quality Division

There is limited water quality data available in the immediate Project vicinity. The Monitoring and Assessment Program of the WDEQ/WQD conducted stream assessments on the North Platte River from 1996 through 2005, where chemical, physical, and biological information were collected. The objectives of these assessments were to: 1) document baseline conditions and 2) evaluate water quality conditions to determine whether designated uses were supported on their dates of sampling. The WDEQ/WQD completed one-time assessments at 26 stations on the North Platte River. The primary objective of this study was to evaluate the water quality conditions of the North Platte River with respect to Wyoming water quality standards to determine whether designated uses of the North Platte River were supported (WDEQ/WQD 2007b).

Segment 2 of this study was the river reach from Seminoe Reservoir to Casper, Wyoming. In this reach of the North Platte River, there were six sample locations (WB175, WB181, WB179, WB176, WB177, and WB1178). Sampling location WB175 is the first location downstream of Seminoe Reservoir and, therefore, the closest sampling location to the proposed Project. All the sample locations in Segment 2 are depicted in Figure 3.4-2. Segment 2 receives inflows from Segment 1 and streams within Seminoe-Pathfinder (HUC 10180003), Medicine Bow (HUC 10180004), Little Medicine Bow (HUC 10180005), Sweetwater (HUC 10180006), and Middle North Platte-Casper (HUC 10180007) subbasins (WDEQ/WQD 2007b). This segment drains a watershed comprised largely of sedimentary formations and marine shales common to the Wyoming Basin and Northwestern Great Plains with some granitics and metamorphic materials in the mountains (USGS 1985). The North Platte River is considered a Class 1 water from the

headwaters of Pathfinder Reservoir upstream to Kortes Dam and from Natrona County Road 309 bridge (near the confluence with Poison Spider Creek) upstream to Alcova Dam (WDEQ/WQD 2007b). The remainder of the segment, including all reservoirs, is considered Class 2AB (WDEQ/WQD 2007a).

Water temperatures in this segment of the North Platte River were below the WDEQ/WQD (2007b) maximum criteria of 20°C for a cold-water fishery on the dates sampling occurred. Throughout the segment, DO concentrations were above the acceptable one-day minimum criterion of 8 mg/L that is considered protective of early aquatic life stages in Class 1 and 2AB waters (WDEQ/WQD 2007a). Turbulent reservoir releases combined with dense beds of aquatic vegetation resulted in supersaturated DO concentrations >10 mg/L at some sites. Temperature and DO concentrations at these sites may vary depending on upstream reservoir conditions. All of the pH values throughout the segment, except for station WB175, were within the state standards of 6.0-9.0 (WDEQ/WQD 2007b). The pH at WB175 was >9.0, which was probably the result of elevated photosynthetic rates from the thick stands of aquatic macrophytes on the channel bed (WDEQ/WQD 2007b).

Recent guidance by the USEPA (2000) recommends maximum total phosphorous and nitrate-nitrogen concentrations of 0.022 mg/L and 0.025 mg/L, respectively, to protect aquatic life uses for streams in the Wyoming Basin ecoregion. Concentrations of these nutrients at most stations were below detection (<0.1 mg/L). This information is not particularly informative since the detection limit was greater than the recommended concentration. However, the presence of thick aquatic macrophyte stands in the North Platte River below the reservoirs suggests nutrient enrichment may be occurring at lower concentrations. This is expected since hypolimnetic reservoir releases can contain nutrients that when oxidized, become bioavailable. For example, station WB181 (Figure 3.4-2) exhibited a nitrate-nitrogen concentration of 0.1 mg/L that exceeded the recommended maximum concentration for the Wyoming Basin. The source of this nutrient was likely hypolimnetic water releases from Pathfinder Dam, immediately upstream of the sampling location (WDEQ/WQD 2007b).

This page intentionally left blank.