Water Quality - Fort Randall.pdf

Figure 9-6. Relative abundance of zooplankton in samples collected along Lake Francis Case during

2018.

9.4 WATER QUALITY AT THE FORT RANDALL POWERPLANT

9.4.1 STATISTICAL SUMMARY AND COMPARISON TO APPLICABLE WATER QUALITY STANDARDS

CRITERIA

Plate 9-19 and Plate 9-20 summarize the water quality conditions that were monitored on water discharged through the Fort Randall Dam powerplant during the 5-year period 2014 through 2018. A review of these results seemingly found no significant water quality concerns. However, the 0.18 ug/L human health criterion for total arsenic was exceeded on all five occasions. The highest total arsenic concentration measured was 3 ug/L.

9.4.2 TEMPERATURE, DISSOLVED OXYGEN, AND DAM DISCHARGE TIME-SERIES PLOTS

Hourly temperature and dam discharge recorded at the Fort Randall powerplant during 2018 were used to construct an annual time-series plot (Plate 9-21). Monitored water temperatures showed seasonal cooling and warming through each calendar year. Daily water temperatures remained fairly stable during the winter, early spring, and fall and exhibited considerable variability during the late spring and summer.

When thermal stratification becomes established in Lake Francis Case during the late spring, the temperature of the water discharged through the powerplant becomes highly dependent upon the discharge rate of the dam. This indicates that the vertical extent of the withdrawal zone in the reservoir is dependent upon the discharge rate of the dam. This is believed to be a result of the design of the intake structure (i.e. bottom withdrawal) and the presence of the submerged approach channel leading to the intake structure. Water is likely drawn from an extended vertical zone in Lake Francis Case year-round, but is only evident in the temperatures monitored at the powerhouse during reservoir thermal stratification during the summer. When thermal stratification breaks down in the summer, the high correlation between dam discharge and the temperature of the discharged water no longer occurs.

Hourly dissolved oxygen and dam discharge recorded at the Fort Randall powerplant during 2018 were used to construct an annual time-series plot (Plate 9-22). Dissolved oxygen levels remained relatively high and stable during the winter, steadily declined through the spring and summer, and steadily increased during the fall. The lowest dissolved oxygen levels occurred during mid-summer. The higher winter, declining spring, and increasing fall dissolved oxygen concentrations are attributed to decreasing dissolved oxygen solubility with warmer water temperatures. The decreasing dissolved oxygen in the summer is attributed to degradation of dissolved oxygen in the hypolimnion as the summer progressed.

Water is withdrawn from Lake Francis Case into the dam’s power tunnels approximately 2 feet above the reservoir bottom. During the summer when Lake Francis Case is thermally stratified, dissolved oxygen levels degrade near the reservoir bottom. Under such conditions, low dam discharge rates pull water with low dissolved oxygen concentrations from the near-bottom region of the hypolimnion.

As seen in the time series plots, dissolved oxygen levels monitored during the summer of 2018 approached the 5 mg/L criterion established for the protection of the Warmwater Permanent Fish Life

Propagation use, but never fell below it. Lower dissolved oxygen levels at the powerplant are likely associated with lower discharge conditions when water is drawn into the penstocks along the reservoir bottom. Seemingly, the low dissolved oxygen levels are related to oxygen degradation in the reservoir hypolimnion during the summer. During periods of lower discharge, water is drawn along the bottom of the submerged approach channel to the dam’s intake tower. This is where low dissolved oxygen would occur in the hypolimnion during mid- to late summer. To further evaluate this situation a Special Water

Quality Study was conducted during the summer of 2010 to evaluate how low dissolved oxygen levels in the powerplant discharges impact the Missouri River tailwaters of Fort Randall Dam (see Section 9.6).

9.4.3 NUTRIENT FLUX CONDITIONS OF THE FORT RANDALL DAM DISCHARGE TO THE MISSOURI

RIVER

Nutrient flux rates for the Fort Randall Dam discharge to the Missouri River over the 5-year period 2014 through 2018 were calculated based on samples taken from the Fort Randall powerplant (i.e.

site FTRPP1) and the dam discharge at the time of sample collection (Table 9-4). The samples collected in the powerplant are taken from the raw water supply line and are believed to be unbiased regarding particulate-associated constituents. Therefore, the flux rates calculated for the Fort Randall Dam discharge give an unbiased estimate of the flux rates for all the constituents, including total phosphorus and total organic carbon. The maximum flux rates for all the constituents are believed to be attributed to higher dam discharges.

Table 9-4. Summary of nutrient flux rates (kg/sec) calculated for the Fort Randall Dam discharge to the Missouri River (i.e. site FTRPP1) during January through December over the 5-year period 2014 through 2018.

Statistic

Flow

(cfs)

Total

Ammonia N

(kg/sec)

Total

Kjeldahl N

(kg/sec)

Total

NO3-NO2 N

(kg/sec)

Total

Phosphorus

(kg/sec)

Dissolved

Phosphorus

(kg/sec)

Total Organic

Carbon

(kg/sec)

No. of Obs. 59 59 59 59 59 59 59

Mean 19,280 0.0188 0.1926 0.0586 0.0060 0.0038 2.2673

Median 18,300 n.d. 0.1576 0.0153 n.d. n.d. 2.1693

Minimum 1,600 n.d. n.d. n.d. n.d. n.d. 0.1993

Maximum 46,100 0.3171 0.6527 1.8122 0.0307 0.0408 6.0047

Note: Nondetectable values set to 0 for flux calculations.

Plate 9-19. Summary of water quality conditions monitored on water discharged through Fort Randall Dam (i.e. site

FTRPP1) during the 5-year period of 2014 through 2018.

Parameter

Monitoring Results Water Quality Standards Attainment

Detection

Limit(A)

No. of

Obs.

Mean(B)

Median

Min.

Max.

State WQS

Criteria(C)

No. of WQS

Exceedances

Percent WQS

Exceedance

Dam Discharge – Powerplant

(Mean Daily, cfs)

59 19,629 20,200 1,600 35,300

Water Temperature (C) 0.1 58 12.0 10.6 1.2 25.5 27(1,4) 0 0%

Dissolved Oxygen (mg/L) 0.1 58 10.7 11.1 6.1 14.4 5(1,5) 0 0%

Dissolved Oxygen (% Sat.) 0.1 58 99.2 101.0 76.7 124.0 ----- ----- -----pH (S.U.) 0.1 58 8.2 8.2 7.9 8.5 6.5(1,2,5), 9.0(1,2,4), 9.5(3,4) 0 0%

Specific Conductance (uS/cm) 1 58 903 906 743 1,004 ----- ----- -----

Oxidation-Reduction Potential (mV) 1 58 392 383 306 517 ----- ----- -----

Turbidity (NTU) 1 58 ----- 1 n.d. 16 ----- ----- -----

Alkalinity, Total (mg/L) 7 50 171 172 161 182 ----- ----- -----

Carbon, Total Organic (mg/L) 0.05 50 4.27 4.40 3.00 5.10 ----- ----- -----

Chloride, Dissolved (mg/L) 1 50 13 13 11 15 438(2,4), 250(2,6) 0 0%

Colorized Dissolved Organic Matter (ug/L) 10 50 19.18 18 12 28 ----- ----- -----

Dissolved Solids, Total (mg/L) 5 50 625 616 530 740

1,750(2,4), 1,000(2,7), 3,500(3,4), 2,000(3,6) 0 0%

Nitrogen, Ammonia Total (mg/L) 0.02 50 ----- n.d. n.d. 0.37 5.7 (1,4,7), 1.7 (1,6,7) 0 0%

Nitrogen, Kjeldahl Total (mg/L) 0.1 50 0.36 0.37 0 0.66 ----- ----- -----

Nitrogen, Nitrate-Nitrite Total(mg/L) 0.04 50 ----- 0.05 0 1.90 10(2,4) 0 0%

Nitrogen, Total (mg/L) 0.1 50 0.46 0.43 0.05 2.21 ----- ----- -----

Phosphorus, Dissolved (mg/L) 0.008 50 ----- n.d. n.d. 0.060 ----- ----- -----

Phosphorus, Orthophosphate (mg/L) 0.005 42 ----- n.d. n.d. 0.060 ----- ----- -----

Phosphorus, Total (mg/L) 0.008 50 ----- n.d. n.d. 0.080 ----- ----- -----

Sulfate (mg/L) 1 50 294 292 257 334 875(2,4), 500(2,6) 0 0%

Suspended Solids, Total (mg/L) 4 50 ----- 5 n.d. 136 158(1,4), 90(1,6) 1 2% n.d. = Not detected, b.d. = Criterion below detection limit.

(A) Detection limits given for the parameters Streamflow, Water Temperature, Dissolved Oxygen (mg/L and % Sat.), pH, Specific Conductance, and

Oxidation-Reduction Potential are resolution limits for field measured parameters.

(B) Nondetect values set to 0 to calculate mean. If 20% or more of observations were nondetects, mean is not reported. The mean value reported for pH is an arithmetic mean (i.e. log conversion of logarithmic pH values was not done to calculate mean).

(C) Criteria given for reference – actual criteria should be verified in appropriate State water quality standards.

(1) Criteria for the protection of warmwater permanent fish life propagation waters.

(2) Criteria for the protection of domestic water supply waters.

(3) Criteria for the protection of commerce and industry waters.

(4) Daily maximum criterion (monitoring results directly comparable to criterion).

(5) Daily minimum criterion (monitoring results directly comparable to criterion).

(6) 30-day average criterion (monitoring results not directly comparable to criterion).

(7) Total ammonia criteria pH and temperature dependent. Criteria listed are for the median pH and temperature conditions.

Plate 9-20. Summary of annual metals and pesticide levels monitored on water discharged through Fort Randall

Dam (i.e. site FTRPP1) during the 5-year period of 2014 through 2018.

Parameter

Monitoring Results Water Quality Standards Attainment

Detection

Limit

No. of

Obs.

Mean(A)

Median

Min.

Max.

State WQS

Criteria(B)

No. of WQS

Exceedances

Percent WQS

Exceedance

Aluminum, Dissolved (ug/L) 40 4 ----- n.d. n.d. n.d. ----- ----- -----

Aluminum, Total (ug/L) 40 4 110 95 80 170 ----- ----- -----

Antimony, Dissolved (ug/L) 0.5 4 0.65 0.70 0.30 0.90 ----- ----- -----

Antimony, Total (ug/L) 0.5 4 ----- 0.45 0 0.80 5.6(3) 0 0%

Arsenic, Dissolved (ug/L) 1 4 ----- 2 n.d. 2 340(1), 150(2) 0 0%

Arsenic, Total (ug/L) 1 4 ----- 2 n.d. 2 0.018(3) 4 100%

Barium, Dissolved (ug/L) 5 4 36 36 33 40 ----- ----- -----

Barium, Total (ug/L) 5 4 37 37 34 41 ----- ----- -----

Beryllium, Dissolved (ug/L) 2 4 ----- n.d. n.d. 0.0 ----- ----- -----

Beryllium, Total (ug/L) 2 4 ----- n.d. n.d. 0.0 4(3) 0 0%

Cadmium, Dissolved (ug/L) 0.2 4 ----- 0.1 n.d. 0.1 4.8(1), 0.46(2) 0, 0 0%, 0%

Cadmium, Total (ug/L) 0.2 4 ----- 0.1 n.d. 0.2 5(3) 0 0%

Calcium, Dissolved (mg/L) 0.01 4 61.08 58.88 57.57 69.00 ----- ----- -----

Chromium, Dissolved (ug/L) 10 4 ----- n.d. n.d. n.d. 1,191(1), 1809(2) 0 0%

Chromium, Total (ug/L) 10 5 ----- n.d. n.d. n.d. ----- ----- -----

Copper, Dissolved (ug/L) 6 4 ----- n.d. n.d. 8 31(1), 20(2), 0 0%

Copper, Total (ug/L) 6 4 ----- 6 n.d. 10 1,300(3) 0 0%

Hardness, Dissolved (mg/L) 1 4 259.73 259.55 235.40 284.40 ----- ----- -----

Iron, Dissolved (ug/L) 7 4 ----- n.d. n.d. 0 ----- ----- -----

Iron, Total (ug/L) 7 4 98 90 60 150 ----- ----- -----

Lead, Dissolved (ug/L) 0.5 4 ----- 0.05 n.d. 0.20 169(1), 6.6(2) 0 0%

Lead, Total (ug/L) 0.5 4 ----- 0.05 n.d. 0.30 ----- ----- -----

Magnesium, Dissolved (mg/L) 0.01 4 25.96 26.81 23.02 27.21 ----- ----- -----

Manganese, Dissolved (ug/L) 2 4 5 5 4 6 ----- ----- -----

Manganese, Total (ug/L) 2 4 40 40 10 70 ----- ----- -----

Mercury, Dissolved (ug/L) 0.05 4 ----- n.d. n.d. 0.004 1.4(1) 0 0%

Mercury, Total (ug/L) 0.05 4 ----- n.d. n.d. n.d. 0.77(2), 0.05(3) 0 0%

Nickel, Dissolved (ug/L) 10 4 ----- n.d. n.d. n.d. 1,003(1), 111(2) 0 0%

Nickel, Total (ug/L) 10 4 ----- n.d. n.d. n.d. 610(3) 0 0%

Selenium, Dissolved (ug/L) 1 4 3.00 3.00 2.00 4.00 ----- ----- -----

Selenium, Total (ug/L) 1 4 2.25 2.00 2.00 3.00 4.6(2), 170(3) 0 0%

Silver, Dissolved (ug/L) 1 4 ----- n.d. n.d. 6 15(1) 0 0%

Silver, Total (ug/L) 1 4 ----- n.d. n.d. 1 ----- ----- -----

Sodium, Dissolved (mg/L) 0.01 4 95 98 86 100 ----- ----- -----

Thallium, Dissolved (ug/L) 0.5 4 ----- n.d. n.d. 0.05 ----- ----- -----

Thallium, Total (ug/L) 0.5 4 ----- n.d. n.d. 0.05 0.24(3) b.d. b.d.

Zinc, Dissolved (ug/L) 10 4 ----- 4.00 n.d. 10 251(1,2) 0 0%

Zinc, Total (ug/L) 10 4 ----- n.d. n.d. 0 7,400(3) 0 0%

Pesticide Scan (ug/L)(C) 0.08(D) 4 ----- n.d. n.d. n.d. ----- ----- -----n.d. = Not detected, b.d. = Criterion below detection limit.

(A) Results for iron (dissolved and total) and manganese (dissolved and total) include some monthly samples.

(B) Nondetect values set to 0 to calculate mean. If 20% or more of observations were nondetects, mean is not reported. The mean value reported for pH is an arithmetic mean (i.e. log conversion of logarithmic pH values was not done to calculate mean).

(C) Criteria given for reference – actual criteria should be verified in appropriate State water quality standards.

(1) Acute (CMC) criterion for the protection of freshwater aquatic life.

(2) Chronic (CCC) criterion for the protection of freshwater aquatic life.

(3) Criterion for the protection of human health.

Note: Some of South Dakota’s criteria for metals (i.e. cadmium, chromium, copper, lead, nickel, silver, and zinc) are based on hardness. Criteria shown for those metals were calculated using the median hardness value.

(D) The pesticide scan includes: acetochlor, alachlor, ametryn, atrazine, benfluralin, bromacil, butachlor, butylate, chlorpyrifos, cyanazine, de-ethylatrazine, de-isopropylatrazine, dimethenamid, diuron, EPTC, ethalfluralin, fonofos, hexazinone, isophenphos, metolachlor, metribuzin, pendimethalin, phorate, prometon, prometryn, propachlor, propazine, simazine, terbufos, triallate, and trifluralin. Individual pesticides were not detected unless listed under pesticide scan.

(E) Detection limits vary by pesticide – 0.08 ug/L is a median detection limit for the pesticides in the pesticide scan.