ML20085M458
| ML20085M458 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 06/30/1988 |
| From: | CAROLINA POWER & LIGHT CO. |
| To: | |
| References | |
| RTR-NUREG-1437 AR, NUDOCS 9111110017 | |
| Download: ML20085M458 (72) | |
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- I H. B. Robinson Steam Electric Plant lI
[I Environrnental Monitoring Program
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- I Interpretive Report ,
lI June 1988 ~l I !I lI I lI !', CD&L c._.,_ . . _ ,. , .g ig99u o~ PDR
l l H. B. ROBINSON STEAM ELECTRIC PLANT ENVIRONMENTAL MONITORING PROGRAM INTERPRETIVE REPORT JUNE 1988
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I l^I This copy of this report is not a controlled docusment as detailed in Environmental Services Sect ion Procedures. Any changes made to the original of this report subsequent to the date of issuance can be obtained frewt
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I Manager Environmental Services section Carolina Power & Light Company Shearon Harris Energy & Environmental Center rI
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Routo I, Don 327 beew HiiI, Marth Carolina 27%2 I
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I Table of Contents Page I list of Tab 1es...................................................... ii List of Figures..................................................... iii LXECUTIVE
SUMMARY
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1.0 INTRODUCTION
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- g 2.0 SITE DESCRIPT10N............................................ 2
- g 3.0 POWER PLANT OPERATIONS AND PERMIT LIMIYS.................... 3 3.1 Plant Modif1:ations.........................................
l 3 3.2 Operating History........................................... 3 1 3.3 Requested Changes in Permit Limits.......................... 8 3.3.1 Cc/ rent Permit Description.................................. 8 i 3.3.2 Paposed Permit Limits...................................... 9 I. 4.0 BIOLOGICAL STU0lES ON ROBINSON IMPOUNDMENT.................. 12 a 4.1 Historical Review........................................... 12
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g 4.2 Results and Discussion of the Biological Studies............ 13 4.2.1 Water Chemistry............................................. 13 4.2.E Water Temperatures and Dissolved 0xygen..................... l 4.2.3 4.2.4 Meteorological and Hydrologic Conditions.................... Plankton and Benthos Communities............................ 14 16 18 , Phytoplankton............................................... 10
,E Zooplankton................................................. 20 LE Benthic Macroinvertebrates.................................. 21 4.2.5 6 qu at i c Veg eut i on. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 73 4.2.6 fisheries................................................... 23 l3 Larval Fish..u.............................................. 24 Adult Fish..................................................
27 Status of Copper and the Fishery............................ 30 'l
..I 5.0 EVALUATION OF THERMAL EFFLUENT EFFECTS ON FISH.............. 31 j 6.0
SUMMARY
...................................................... 34 7.0 L I T E PA T U R E C I T E D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 e I I I '
I List of Tables Table M 1 H.B. Robinson Plant gross generation, 197L-1987............. 4 2 Honthly average discharge temperature at the weir from Robinson Impoundment, 1976-1987........................ 7 I 3 H.B. Robitison discharge temperatures and heat rejection, 1985-1987........................................ 11 4 Proposed new H.B. Robinson NPDES temperature limits......... 12 5 Typical Robinson Impoundment water quality parameter ranges......... ............................................ 13 !- 6 Summaries of analysis of variance and Duncan's multiple range test on monthly water temperature data from Robinsa.) Impoundment........................................ 15 7 Flow in Black Creek at U.S. I above the Robinson Impoundment ranked by years (listed lowest to highest).................. 17 8 Summaries of analysis of variance and Duncan's multiple
,g range test on organism density data from ig Robinson Impoundment........................................ 19 9 Relative abundance of fishes collected by cove rotenone sampling from Robinson Imooundment..........................
. 24 10 Larval fishes coiletted from Robinson Impoundment, 1974-1987................................................... 25 11 Analysis of varience and Duncan's multiple range test for differences in mean larval fish densities............... 26 12 Comparison of cove rotenone data from Robinson Impoundment and other blackwater lakes in the region.................... 30
.I 13 Copper concentrations in livers from 'ish collected in the middle and lower impoundment......................... 31 I
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3 List of Figures Figures Py 1 Robinson impoundment sampling stations..................... 43 2 Gross generation of H.B. Robinson Units 1 and 2
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197S-1987................................................... 44 3 Monthly average discharge temperatures at Robinson l impoundment, 1976-1987...................................... 47 4 Actual daily discharge temperatures and permit limits for 1 the H.B. Robinson Plant, 1985-1987.......................... 49 3 5 Compar. son of current NPDES temperature limits and g proposed temperature limits................................. 52 6 Mean copper concentrations in Robinson Impoundment. l 1977 1987................................................... 53 7 Tempersture and dissolved oxygen in Robinson Impoundment d u r i ng A' 1 y 15 , 19 8 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 8 Phytoplankton and zooplankton density by month and year from Robinson Impoundment, 1980-1987........................ 56 9 Biomass of Eleocharfs baldwinil from Transects A and E in Robinson Impoundment, 1983-1986.......................... 57 10 Mean log density of total larval fish, Lepomis larvae, and largemouth bass larvae in Robinson Impoundment, 1977-1987................................................... 58 11 Total number and weight per hectare of all fish by transect in Robinson Impoundment, 1977-1987................. 59 12 Total number and weight per hectare of all fish, I bluegiil > 60 mm, and bluegill < 60 mm from Robinson Impoundment, 1977-1987...................................... 60 J 13 Total number and weight per hectare of largemouth bass by transect and year in Rooinson Impoundment, 1977-1987..... 61 14 Isotherms and dissolved oxygen from Robinsor Impoundment during August 1985, 1986, 1987, indicating areas optimal for fish.................................................... 62 iii
I Executive Summary 1
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The current NPDES permit for Carolina Power & Light Company's (CP&L) Robinson Steam Electric Plant has limits for temperature of once-through cooling water at the discharge point into the Robinson Impoundment. These current temperature limits were determined from a successful 316a Demon-stration submitted by CP&L in 1976. Since those limits were imposed in 1977, the plant has occasionally exceeded the limits for short periods due primarily to more adverse meteorological conditions than those experienced during the short (approximately 1 year) 316a Demonstration study. Based on this operating experience and the results of concurrent biolcgical monitoring, CP&L believe; that some of the current limits are lower than necessary. Also, the current changes in monthly temperature limits do not i keep pace with the rate of natural seasonal changes in impoundment temper. atures and, therefore, ':ause restrictions on the operation of the plant
.I that are not necessary to maintain a balanced and indigenous community of fish and wildlife in and on the impoundment.
Biological studies which have been conducted continuously on the impoundment since the mid-1970s, especially during adverse meteorological ~ conditions when the temperature limits were exceeded, have documented the environmental effects of the heated water discharge to the Robinson Im-poundment. These data show: l'
- 1. The impcundment can be divided into two biological areas:
(1) the upper impoundment, which is shallow and narrow with abundant aquatic vegetation and affected by Black Creek inflow and (2) the middle and lower impoundment, which is wider and deeper with fewer areas of aquatic vegetation. l~ 2. The thermal discharge has the greatest impact in the middle L impoundment, especially near tne point of discharge. The upper impoundment receives only minimal thermal impact. The lower impoundment is also affected by thermal discharge; however, cooling of discharge aaters occurs as waters are recirculated through the impoundment. iv
F k p 3. When the poner plant circulating water pumps are operating, L there is a good mixing of the water column minimizing the areas of low-dissolved oxygen despite elevated water temperatures. Thermal stratification generally is weak during all seasons, and a thermocline is rarely established except in the middle im-( poundment area over the old Black Creek Channel. ( 4 Meteorological and hydrological conditions at the Robinson Im-poundment were more severe during 1986 than any other year of the 1977-1987 period. Record low rainfall and resulting low { Black Creek inflow were noted for 1986.
- 5. Low impoundment water levels during 1986 had the greatest impact 1 in the upper reservoir due to the narrow, shallow morphometry.
Higher ambient water temperatures, zooplankton, larval large-mouth bass, and lower standing crop of juvenile and adult fish were recorded in the upper impoundment during 1986.
- 6. Annual mean water temperatures in the upper and lower impound-ment were not statistically different over years. The middle impoundment was statistically warmer between certain years.
1 7. Phytoplankton, and zooplankton densities were higher in the mid-die and lower impoundment than the upper impoundment. This is due to lake-like conditions providing more favorable conditions for plankton,
- 8. Copper concentrations were elevated in the middle and lower impoundment during 1977 1982 period and were lower from 1983 to 1987 after the removal of the brass condenser tubes in Unit 2.
- 9. Thirty-seven species of fish, typical of black water habitats in the region, have been collected from the impoundment. Sun-fishes, largemouth bass, and bullhead catfish are the primary sport fishes.
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I I 10. Larvae of 21 taxa of fishes have been collected in the impound-ment. Larval fish densities were highest in the upper impound-ment and were not different between the middle and lower impoundment. Fewest larval fish were collected during 1977-1979.
- 11. Fish standing crops were lowest during 1977-1981 and higher during 1982-1985. Standing crops during 1986 and 1937 were 4 I
lower than 1982-1985 but were higher than 1977-1981.
- 12. Elevated copper in the impoundment reduced fish reproduction and recruitment and caused deformities in fish. Since removal of i the source of copper in 1982 by power plant modifications, copper concentrations have decreased in impoundrrent water and fish tissues.
Fish deformities were eliminated and standing I crops returned to normal levels. [ 13. Expansion of the fishery from 1982 to 1985 was rapid, especially bluegill and largemouth bass. Declines in bluegill since 1985 l probably reflect a stabilization of the fishery after rapid expansion.
- 14. During periods of maximum thermal discharge, much of the im-
; poundment, especially the upper and lower impoundment, remain
'l favorable for fish and other aquatic biota.
- 15. No major fish kills have occurred in Robinson Impoundment.
, 16. The standing crop of fish is above that expected for blackwater systems such as the Robinson Impoundment. }
L- Based on these findings, the H.B. Robinson Steam Electric Plant is believed by CP&L to have had no appreciable harm to the balanced and in-digenous community of fish and wildlife in and on the impoundment. The impoundment supports a higher than expected standing crop of fish and offers good sport fishing. vi
{ in conclusion, CPt.L proposes that the temperature limits in the re-7 newed NPDES permit be revised to reflect the increased understanding cf L the effects of heated water discharged to the Robinson impoundment. The limits for the spring months, specifically Hay, could be increased 7 slightly to those temperatures experienced in 1986 and not cause an unac-J ceptable adverse effect, in addition, the distharge temperature of the once-through cooling water can vary greatly over a 30-day period in re-sponse to the natural warming and cooling of the impoundment in the spring and f all months, respectively. Temperature limits set at approximately 15-day intervals would more closely parallel actual conditions. Semi-monthly limits could be determined by a simple averaging method to make the transition between months with different limits. The operation of the plant and biological monitoring over the past several years offers ample empirical evidence that the proposed limit changes are ccceptable and I appropriate. The proposed minor changes would not allow the discharge temperature to be any higher than those that have been experienced before when biolo-gical monitoring has demonstrated the impoundment can maintain a balanced l and indigenous fish population. vii
ll u l.0 INTRODUCTION Carolina Power & Light Company (CP&L) owns and operates the Robinson r Nuclear Project that consists the H.B. Robinson Steam Electric Plant and Robinson impoundment, the cooling reservoir for the power plant, k CPLL has conducted environmental studies on the Robinson Impoundment since the mid-1970s and submitted a successful 316a Demonstration in 1976 that documented a balanced and indigenous fish population in the reser-voir. The discharge temperature limits of the current National Pollutant Discharge Elimination System (NPDES) permit are a result of the initial 316a Demonstration and are essentially the satme temperatures experienced during the initial 316a Demonstration period of 1975-1976. On a few occasions since that time, due primarily to more severe meteorological conditions than those experienced during the demonstration period, the heated water discharge temperature has exceeded the limits in the NPDES permit for short periods, s In support of the NPDES permit, biological studies have been con-ducted since 1973 to determine what impact, if any, the thermal discharge from the H.B. Robinson Steam Electric Plant has had on the Robinson Im-poundment. Reports summarizing the results of the many studies conducted on the biota of the impoundment have been submitted to the South Carolina Departreent of Health and Environmental Control. These reports have usu-ally covered a one- to three-year period with occasional comparisons to longer periods. This report will give a broader perspective of the bicta of the im-poundment over the 15 years of study and will evaluate the effect of the proposed temperature limits. The objectives of this report are to (1) propose changes to the NPDES permit limits on temperatures of once-through cooling water, (2) provide an overview of the biological studies conducted on the Robinson Impoundment, and (3) assess the impact of the proposed limits. 1
I 2.0 SITE DESCRIPTION Carolina Power & Light Company (CF&L) constructed the Robinson Im-
,I poundment (Figure 1), a 911-hectare (2,250-acre) cooling impoundment, on Black Creek in Darlington and Chesterfield Counties, South Carolina, in the late 1950s to provide cooling water for the H.B. Robinson Steam Elec-tric Plant. The impoundment is located in the Sandhills region with a watershed of approximately 44,800 ha (173 mi2 ). Much of the watershed is in the Sandhills National Wildlife Refuge with the remainder being either forested or in agricultural production.
The power plant consists of the 183-MWe coal-fired Unit I and the 665-MWe nuclear-fueled Unit 2. These generating units are operated with pg once-through cooling, discharging waste heat to the impoundment via a [.E four-mile-long discharge canal. The waste heat enters the middle area of the impoundment designated as Transect E (Figure 1). Unit 2 (86% of the total generating capacity) contributes the primary heat load, while Unit 1 (14% of the gentrating capacity) contributes a lesser heat load to the impoundment. Several transects and stations have been derignated throughout the impoundment to identify biological sampling locations (Figure 1). In some j cases in this report, specific sites or stations will be identified while L in other cases, transects or areas are noted. Generally, the Transect G area is referred to as the upper impoundment, Transect E as the middle { impoundment at or near the point of the thermal discharge, and Transect A as the lower impoundment. Stations are a specific location on a transect and are designated by both a transect and station code such as A1. fl
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3.0 POWER PLANT OPERATION AND PERMIT LIMITS I 5 3.1 Plant Modifications Since the 1975 to 1976 period during which the 316a Demonstration J took place, there have been numerous modifications to the Robinson Plant resulting in a slight increase in heat rejected to the impoundment. As a result of the replacement of the steam generators in 1984 and a subsequent Nuclear Regulatory Commission approval, the Unit 2 reactor began operation l in 1985 at a higher output 2300 MWt as compared to 2200 MWt. This higher thermal rating resulted in a net increase in heat rejection to the 19poundment of approximately 65 MWt during full-load operation of the plant. Howevet, there have been several equipment upgrades to Unit 2 in the past few years which have reduced heat rejected to the impoundment. Tnese include replacement of the condenser in 1982; replacement of the feedwater heaters, some reheater bund 1?s, and steam generators in 1984; and the replacement of the low-pressure turbine in 1987. These changes reflect a continuing effort to improve the efficiency of Unit 2 and have reduced the heat rejected to the impoundment by 30 MWt. Therefore, there has only been a net 35 MWt of additional heat rejected to the impoundment due to power plant modifications during the past several years. It should be noted that it has been the Company's intention to oper-ate Unit 2 at 2300 MWt since the early 1970s. In fact, the heat rejection limit in the current permit, as described later, already reflects this higher thermal rating and has not been exceeded by the modifications dis-cussed above. 3.2 Operating History Throughout most of its history, the Robinson Plant has operated at or above the industry average capacity f actor for similar units. Whenever possible, major outages for maintenance or refueling have been scheduled in the spring or fall months when higher system peak loads are not j expected. After approximately 10 years of oper ation, Unit 2 developed corrosion problems with the steam generators, and as a result, Unit 2
generation was reduced in 1982 and 1983 to allow preparation for replace-ment of the steam generators in 1984. Ur.it 2 as shut doan from February ( 1984 until January 1985 for replacement of the steam generators and I several other major improvements. During 1984 Unit 1 provided virtually ( all of the heat 'oad to the impoundment. Beginning in early 1985, Unit 2 returned to service and was operating at full capacity with the extra thermal upgrade of the reactor discussed above and the many efficiency improvements that reduced the heat rejection / gross generation ratio. Both units operated near full capacity during most of the 1986 drought that brought higher than normal ambient temperatures and much lower than normal inflow to the impoundment. A summary of monthly average gros 5 generation for each unit for the years 1975 through 1987 (Table 1) provices an indication of the relative heat load for any specific year. Monthly gross generation values for the power plant are plotted in Figure 2. y The resulting monthly average discharge temperature from the genera-tion loads are recorded by the continuous recorder at the disch trge weir in Tahle 2. A plot of this data (Figure 3) provides a visual comparison of the monthly discharge temperatures. Table 1 H.B. Robinson Plant gro;S generation (Xio0C MWH). 1975-1987 1975 1976 Unit I unit 2 Plant Unit 1 Unit 2 Plant January 71 500 571 44 454 498 February 43 487 530 15 507 522 March 46 518 564 17 525 542 April 79 184 263 0 493 493 May 103 71 174 0 460 460 June 93 402 495 61 502 563 July 105 472 577 65 475 540 August 95 509 604 73 494 567 September 74 475 549 95 493 5B8 October 39 508 547 94 476 570 November 93 0 93 113 0 113 Dece:hber 73 271 344 104 250 354 Total 914 4397 5311 681 5129 5810 4
I Table 1, continued 1977 1978 I Unet i Unit 2 Plant Unit i Unit 2 Plant January 92 52i 613 83 425 508 feeruary 62 253 315 102 0 102 I March April Mar June 94 129 131 475 399 511 569 528 642 77 22 19 46 487 0 77 68 506 81 471 552 24 487 511 I July August September 101 90 96 452 359 218 553 449 314 28 70 77 393 494 342 421 564 419 October 96 250 346 6 !21 527 November 104 63 167 63 307 570 Decemoer 40 508 548 43 507 550 Total 1816 4480 55 % 5 4209 4823 1979 1980 Unit I unit 2 Plant Unit i M U Plant Januar* 68 491 559 67 527 594 FeDruary 60 433 493 97 484 581
,- March 71 521 592 103 285 388 'f AprIi 103 157 360 93 208 301 ki Msy 110 0 110 85 327 412 June 104 0 104 100 461 561 I July August September 90 66 65 114 517 474 204 583 539 121 118 104 261 52 0
382 170 104 October 86 503 589 67 55 122 i'~ Povember 69 497 566 23 442 465 December 53 515 [ 568 96 300 39b Total 5 4222 5167 1074 3402 4476
!W 1981 1982 Unit Unit 2 Plant "Jnit ) Unit 2 Plant l; January 104 480 584 86 436 522 February 63 417 480 36 362 398 March 0 525 525 83 0 8t jI Apri1 0 495 495 112 0 112 L May 3 251 254 101 0 101 June 85 256 341 99 0 99 l
I July August September 94 87 68 459 213 0 553 87 281 108 118 88 318 0 73 108 191 407
- October 45 253 298 74 420 494 Novemoer 59 55 114 4 405 409
,l December 87 332 419 18 416 434 I Total 695 3681 4376 927 2431 3358
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l Table 1, continueo 1983 '994 Unit 1 Unit ? Pfent Unit t Unit 2 Plant January 43 395 438 58 246 304 February 38 367 404 30 0 30 March 30 423 452 73 0 73 April 54 303 357 84 0 84 May 80 46 126 103 0 103 June 71 402 473 93 0 93 July 76 400 476 75 0 75 August 86 413 499 75 0 75 september $1 174 224 52 0 52 October 14 428 422 59 0 29 November 10 29 39 111 0 111 December 73 211 284 67 0 67 total 625 3590 4215 910 246 1156 1985 ~ 1986 unit 1 Unit 2 Plent Unit t unit 2 Plent January 79 43 122 95 318 413 February 43 261 304 80 0 80 March 2 513 515 93 76 169 April 42 514 556 62 529 592 May 42 535 576 48 555 603 June 75 538 613 44 507 551
.uly 69 529 598 74 553 627 August 72 508 580 55 431 485 Sept entier 44 479 523 29 447 476 October 60 514 573 35 567 602 l November 7 530 537 14 547 561 l Decemoer 67 551 618 21 524 345 Totel I0I 5515 6116 649 505) 5704 1987 unit 1 untt 2 Plant January 46 572 618 February 42 509 551 March 46 350 396 April 53 0 53 May 61 0 61 June 79 186 265 l July 55 442 496 l August 56 408 463 September 38 346 385 October 0 561 561 Novemoer 19 525 544 Decemoer 28 571 600 Total 523 4469 4992 NOT2: All columns and rows may not +otal esa:tly due to rounding, 4
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l 7aDie 2 Nonthly average temperature at the discharge canal me6r frtwn Robinson impounement, 1976-1987 L Degrees r enrenh,i t enth 1976 1977 1978 1979 1980 1981 1982 1983 _1984 1985 1986 1987 Jan 69.5 66.6 64.9 72.1 74.3 69.2 66.8 70.0 58.8 50.7 67.0 72.6 Feb 78.2 64.6 49.8 69.8 71.0 69.9 72.1 70.1 52.7 58.8 51.4 7 3 . ', Mar 84.8 85.1 55.0 82.0 68.1 78.8 67.9 75.3 56c6 77.5 64.6 71.7 ( r Apr May 88.9 92.J 90.5 97.4 68.2 92.0 30.6 76.5 87.8 74.8 75.0 65.7 88.1 87.6 67.8 78.9 88.5 82.1 79.6 75.5 80.0 102.2 96.0 77.3 Jun 99.1 103.6 105.0 81.9 96.5 96.7 84.0 94.0 85.6 95.0 104.0 102.8 Jul 102.7 105.9 101.3 80.0 95.5 101.0 84.9 97.8 87.0 103.5 109.7 102.6 Aug 103.3 100.6 104.8 104.6 89.8 95.6 86.1 99.3 87.7 103.2 102.5 101.2 Sep 100.9 95.2 98.4 99.9 85.6 91.2 87.8 96.5 78.3 101.3 94.9 94.5 Oct 87.9 81.8 90.7 93.3 73.8 83.6 87.2 86.3 71.3 94.2 94.1 89.0 h 58.5 67.5 86.4 86.4 77.6 67.0 77.4 61.7 62.8 86.3 85.1 84.2 I Dec 58.8 73.0 76.7 78.7 64.5 67.4 72.7 61.2 "3.0 76.9 77.1 79.8 Degrees Celsius Month 1976 1977 1978 197C 1980 1981 1982 1983 1984 1985 1986 1987 l nn 20.9 19.2 18.3 22.3 23.5 20.7 19.3 21.1 14.9 10.4 19.5 22.6 B Feb 25.7 18.1 09.9 21.0 21.7 21.1 22.3 21.2 11.'s 14.9 10.8 23.1 Mar 29.4 29.5 12.3 27.8 20.1 26.0 20.0 24.1 13.6 25.3 18.1 22.1 Apr 31.6 32.5 20.1 27.0 24.7 31.0 23.8 2J.9 18.7 31.2 30.9 19.9 May 33.5 36.4 33.4 26.1 31.4 27.9 26.5 24.2 26.7 39.0 35.6 25.2 Jun 37.3 39.8 40.6 27.7 35.9 36.0 28.9 34.5 29.8 35.0 40.0 39.4 Jul 39.3 41.1 38.3 31.7 35.3 38.4 29.4 36.6 30.6 39.8 43.2 39.3 Aug 39.6 38.1 405 40.4 32.1 35.4 30.1 37.4 31.0 39.6 39.2 38.5 Sep 38.3 35.1 36.? 37.8 29.8 32.9 31.0 35.9 26.1 38.5 35.0 34.8 Oct 31.1 27.) 32.6 34.1 23.2 28.7 30.7 30.2 21.9 34.6 34.5 31.7 Wiv 14.7 19.7 30.2 30.2 25.4 19.$ 25.2 16.5 17.1 30.3 29.5 29.0 Dec 14.9 22.8 18.9 26.0 18.1 19.7 22.6 16.2 11.7 25.0 25.1 26.6 l l l l l I I 7
3.3 Requested Changes in NPDES Permit Limits i 3.3.1 Current Permit Description The current NPDES permit issued on December 1, 1983, has the follow. ing temperature limits on Outfall 001, once-through cooling water: Month Daily Average 'F ('C) Daily Maximum 'F (*C) June-September 108.7 (42.6) 111.2 (44.0) l October 95.9 (35.9) 99.5 (37.5) November 86.0 (30.0) 91.4 (33.0) December-February 78.8 (26.0) 85.1 (29.5) March 86.0 (30.0) 89.6 (32.0) April 89.6 (32.0) 95.0 (35.0) May 93.2 (34.0) 98.6 (37.0) These temperature limits, applied at the end of the discharge canal weir just prior to entering the impoundment, were originally assigned by l the U.S. Environmental Protection Agency (EPA) af ter a review of the 316a Demonstration (CP&L 1976a, 1976b) and largely reflect temperatures l experienced during the 1975-76 demonstration study period. In addition to the above limits, there is a gross heat rejection 'imit
. of 9 9 5.5 x 10 BTV/hr and 6.29 x 10 BTV/hr for daily average and daily maxi-mum, respectively.
Table 3 compares the actual experienced discharge temperatures during 1985-87 to the limits specified in the permit. This is shown graphically in Figure 4. The primary problem experienced with the current temperature limits is the abrupt char.ge in daily maximum average limits at the beginning and end of certain months, especially during spring and fall. This sudden change in temperature reflects neither actual plant operating conditions, r ambient water temperatures, or conditions optimal for aquatic life. The spring and f all months are usually a time of relatively rapid, steady
change in the natural impoundment water temperature. Permit linits that [ impose a constant maximum limit for 30 continuous days during these pe-L riods are inherently dif ficult to meet while providing adequate environ-mental protection during the entire period. The daily maximum limit for May, for example, is higher than necessary on the first day of the month and lower than necessary during the final days. A similar but reverse situation occurs in October. Assigning a long-term (30-cay) average limit for an arbitrary period l of a calendar month, especially in the rapidly changing spring and fall months, has inherent problems. Just a few days of unusually high dis-charge water temperatures in the final days of a month can result in an exceedance of the monthly average and, therefore, a violation for those 30 days. Compliance with the current monthly average limits might force 1 the plant tu severely cut back generation for the last ftw days in a month to meet temperature requirements. Then at the beginning of a next month, I the new limits would allow a rapid increase in power and discharge temper-ature output. This type of situation is not advantagous to either the aquatic environment or the efficient operation of the plant. In addition, recent operating experience indicates a cor.sistent pro-blem with the present May limits. The incremental change on both daily average and dily maximum limits from May to June is 15.5'F (8.f,'C) and 12.6*F (7.0*C), respectively. This is the largest such change during the year. 3.3.2 Proposed Permit Limits In the original 316a Demonstration, CP&L had requested and presented justification for daily average and daily maximum limits of 96.8'F (36.0*C) and 100.4*F (38.0'C) for May. However, the limits assigned (93.2*F [34.0*Cl and 98.6*F [37.0*C)) were based on the temperatures actu-ally observed during the biological study period. Since then CP&L has conducted regular monitoring studies on the various aspects of the biology of the impoundment. In 1985 the daily average and daily maximum discharge temperatures for May were 95.0*F (35.0*C) and 98.9'F (37.2*C), 9
s 4 respectively, and in 1986 these values were 96.0'F (35.6*C) and 102.0*F ' (38.9*C), respectively. DHEC was timely notified when these temperatures were anticipatad and when they occurred. Accordingly, CP&L believes that in May a daily average limit of 96'F (36.6*C) and a daily maximum of 102*F (38.9"C) are appropriate. CP&L also pronoses that the temperature limits for the transitional spring and f all months be revised from monthly to an approximately 15-day interval. The current daily average and maximum, with the exception of May as discussed above, would continue but would include two limit changes per month. This arrangement would allow several intermediate steps that are not now included. These intermediate steps would be determined by averaging the current permit limits (except for May) to include the final week of the month and the first week of the following month. The result-ing average value would provide a new limit midway between the two pre-vious limits. This technique would raise the limit for a cooler month a I moderate amount but also cause a corresponding reduction for a portion of the adjacent hotter month. The change would result in no net differerce in allowable temperature discharged. For example, the current daily maximum limits for September and October are 111.2* and 99.5'F, respec-l tively. For the middle 15 days of those months, the limit would remain the same.. For the period from September 24 through October 8, the new limit would be (111.2 + 99.5)/2 = 105.4*F. The daily average limits would be revised in the same mar.ner. Table 2 lists the proposed new limits and Figure 5 compares the proposed limits to the current permit limits. By allowing for semimonthly limit changes during the spring and fall 1 months, the proposed limits more closely correspond to the actual tempera-ture changes occurring in the impoundment. These requested changes in-clude higher limits for May. This will provide limits that are no higher than necessary for operation of the plant nor needlessly restrain plant operation when higher discharge temperature; are environmentally accept-able. Further, biological data collected over several years and summa-rized in this report support these proposed limits. g
Table 3 M.B. Robinson discharge temperatures and heat rejection. 1985-1987 0 h tmly evers;e 'I DslIy manimum *[ Hest (u10 Bru/nr1 Actual Limit ActuSI Limit Average Maximum
= January 87 72.6 78.8 75.6 85.1 4.7 5.6 February 87 73.5 78.8 77.6 85.1 4.6 5.6 March 87 71.7 86.0 81.1 89.6 3.0 4.5 April 87 67.8 89.6 75.4 95.0 0.3 0.6 May 87 77.3 93.2 83.2 98.6 0.5 0.7 June 87 85.0 108.7 102.8 111.2 1.0 4.8 July 87 102.6 108.7 107.8 111.2 4.0 5.3 August 87 101.2 i08.7 107.6 (11.2 3.7 S.1 September 87 94.5 108.7 104.3 111.2 3.0 5.1 October 87 89.0 95.9 96.4 99.5 4.1 4.4 November 87 84.2 86.0 89.0 91.4 4.4 5.3
, December 87 79.8 78.8 83.6 85.1 5.0 5.6 January 86 67.0 78.8 75.4 85.1 2.0 4.8 February 86 59.6 78.8 65.2 85.1 0.4 0.5 Maren 86 64.6 86.0 82.3 89.6 1.0 4.2
,. April 86 87.6 89.6 93.8 95.0 4.3 5.0 May 86 96.0 93.2 102.0 98.6 4.4 5.3 June 86 104.0 108.7 106.8 111.2 4.8 5.6 July 86 109.7 108.7 112.9 111.2 5.4 6.0 August 86 102.5 108.7 111.3 111.2 4.2 5.9 September 86 94.9 108.7 103.6 111.2 3.9 5.4 October 86 94.1 95.9 104.6 99.5 4.3 5.3 November 86 85.1 86.0 90.2 91.4 4.0 4.7 December 86 77.1 78.8 82.2 85.1 4.2 5.3 January 85 50,7 78.8 57.0 85.1 1.0 3.1 February 85 $8.2 70.8 76.0 85.1 3.0 5.1 1 March 85 77.5 86.0 85.8 89.6 4.0 5.4 April 85 88.1 89.6 97.0 95.0 4.3 5.0 May 63 95.0 93.2 99.9 98.v 4.4 5.2 June 65 102.2 104.6 5.2
-I July 85 103.5 108.7 108.7 107.6 111.2 111.2 4.9 5.9 5.6 August 85 103.2 108.7 108.3 Itl.2 4.9 5.8 September 85 101.3 108.7 106.8 111.2 4.2 5.0 October 85 94.2 95.9 97.5 99.5 3.9 4.6
., November 85 83.5 86.0 90.7 91.4 3.9 4.7 December 85 76.9 78.8 85.8 85.1 4.2 4.7
_ limit: 5.5 6.29 Temperature limit exceecances are uncertined.
~
13 I 11
I I Table 4 Proposed new H.B. Rooinson NPDES temperature Iimits. 24th of Previous Month Through 9th ' irouv., I wan t h Dail, Ave. the 8th of Current Month Daily Man. 23rd o' Current Month Dai's Ave. Daily 43a. January 78.B*F 85.1*F 78.8'F 65.lar February 78.8'F B5.1*F 78.B'F $5.1*F
-I warch 82.4*F 87.4*F B6.0*F 89.6*F Apr1i 87.8'F 92.3*F 89.6*F 95.0*r May 92.B'F 99.5'r I
96.0*F 102.0*F
.'une 102.4*F 106.6*F 108.7'F 111.2*r Jute 108.7'T 111.2*F 108.7'F 111.2**
August 108.7'F 111.2*F 108.7*F 111.2*8 I September lob.7'F 111.2*F 108.7'r 111.2*F october 102.3*F 105.4*F 95.9'r 99.5*F November 91.0*r 95.5*F e6.0*F 91.4*r oeces. oar 82.4 r 8s.3 F 78.s*r 85.i r I 4.0 BIOLOGICAL STUDIES ON ROBINSON IMPOUNDMENT 4.1 Historical Review I Many reports addressing the biota of the impoundment have been is-sued. The initial 316a Demonstration (CP&L 1976a.1976b) showed that the operation of the H.B. Robinson Plant resulted in no appreciable harm to the balanced and indigenous community of fish and wildlife in and on the impoundment. Since 1979, environmental reports have been issued summariz-ing the results of environmental monitoring programs (CP&L 1979a, 1979b, I 1980, 1982a, 1983a, 1983b, 1984, 1985, 1986, 1987). Additional studies have been conducted addressing reduced fish recruitment and bluegill de-formitics (LMS 1980; CP&L 1981, 1982b, 1983c; CP&L and LMS 1981; Wo.'ck 1985), and trace elements (Harr-ison 1984; Harrison et al.1983; Harrison and Lam 1982: Smart 1985; Smart 1986).
, These studies have all added to the knowledge and understanding of the effects of power plant operations on the biological communities in Robinson impoundment. They have shown the continuation of the balanced biological connunities over the years of study. Certain problems, such as the effects of elevated copper and zinc on fish populations, bave also I been addressed and the follow-up studies have indicated recovery from these problems. The various chemical, physical, biological, and 12
l I ! climatological conditions experienced during these studies are analyzed in this report. 4.2 Results and Discussion of the Biological Studies
' 4.2.1 Water Chemistry The impoundment water is darkly stained, acidic, and has low conduc-tivity, alkalinity, and hardness (Table 3). This " blackwater" is con-sidered low in primary productivity and nutrients. Due to the limited
[ size of the SanJhills region and the lack of impoundments with similar
.{
topography and water chemistry, comparisons of Robinson impoundment to other water bodies are difficult to make. Table 5 Typical Robinson impowner.ent =ater chemistry parameter ranges. 'll Parameter Ranoe pH 4.o-6.o r i ., W Conductivity 15-31 umhos Total Hardness 1.2-lo.o eg/l
- Alkalinity < o.5-1.4 mg/l Total organic cardon 2.3-9.3 mg/l L Total nitrogen (as N) 0.02-o.53 mg/l Total phosphate (as P) < o.ol-o.04 mg/l p Copper < 20-57 ug/l
.r i j, Concentrations of sodium, calcium, sulf ate, and magnesium typically
- increase from the upper impoundment to the lower impoundment, probably a result of evaporation. Trace element concentrations have not been signif-icantly different from those found in Black Creek above the impoundment except for copper and zinc. Turbidity has been lower in the middle and N lower impoundment than in the upper impoundment and Black Creek above the impoundment indicating deposition of fine particles due to reduced flow.
Elevated copper concentrations were recorded from 1977 to 1982 and reached peak annual values of 61 ug/l at Station E2 and 44 ug/l at Sta-tion A2 in 1979 -(Figure 6). These increases were determined to be a I 13 i'I ,
l I
'I result of the erosion and corrosion of the brass condenser tubes. To remedy this, in 1982 the brass tubes were replaced with stainlest; steel g tubes, after which impoundment copper concentrations diminished to an 'E annual average of 4-6 ug/1. !
4.2.2 Water Temperatures and Dissolved Oxygen During biological studies, water temperature and dissolved oxygen (00) were measured. Thermal stratification in the middle impoundment is [ increased by power plant operations and is most prominent over the Black Creek channel (Figure 7). However, the impoundment remains well mixed
; (CP&L 1987) with adequate dissolved oxygen (> 4.0 mg/1) for aquatic life.
g The 00 may drop below 4.0 mg/l but usually only in the lowest tE 2-3 meters of the impoundment, usually corresponding to the narrow former Black Creek channel. This occurs only during the warmer months of certain
, years and influences only a limited part of the impoundment. Boyd (1979) reports a D0 of 5.0 mg/l as the minimum desirable level in ponds but that fish can survive in the ranqe of 1.0-5.0 mg/1. While the USEPA states
~
5.0 mg/l as a minimum for good fish populations (USEPA 1986), they also indicate fish vary in their tolerance (by spacies, age, activity, etc.) and fish can survive for a while in concentrations considerably below that c suitable for a thriving population. Fisheries biclogists often use E 4.0 mg/l 00 as the minimum value for fish growth. F' Approximately 13 days are required for the thermal plume to reach the intake af ter being discharged (CP&L 1979b). During this period thermally induced stratification decreases with distance downstream f rom the dis-charge (Swartley 1987). Little or no stratification occurs in the lower impoundment (Figure 7). jg i Occasionally a narrow wedge of thermally influenced water is pushed by southerly winds northward through the bridge at the SR 346 causeway, and on rare occasions, this wedge reaches Transect G. However, thermal flow is usually restricted to the upper 0.5 m of the water column and results in only minimal thermal enhancement at Transect G. 14
The analyses of impoundment water temperatures (Table 4) were based on monthly temperatures taken at 1-m depth at Stations A2, E2, and G? during biological monitoring programs. Water temperature data were not taken during 1984. Stations were significantly different from each other for all tests (E2>A2>G2). Table 6 surnroerles of analysis of variance and Duncan 's mul t ip le range test e on monthly water temperature data frca Robinson I rt pow nctnen t . Items are listed in descencing order, All Moait hs ADril-June June-Aucust 1 A2 E2 G2 *2 E2 G2 A2 E2 G2 Jul 8 Aug 8 Jul 8 Jun 8 Jun a jyn a jyg a Aug Jul Aug ab jyg a Aug a May D Mar b y,y b gyg a Jul Aug W Jun D Jun ab jyn ab Apr C ADr C ADr C Jue D Jun Jun sep D Sep ab g,,bc May C May D c Mar Oct d oe,b Oct C u Ape de Apr e App ed Mbv' Nov C Nov de Mac I e g,p ef Dec I Dec Feb9 Mar Febd ' Dec Feb9 Jan9 Jan' Jen D I Ai1 Months ADri1-June Juns. August I A2 E2 G2 A2 E2 G2~ A2 E2 G2
'77 '85a '86 a 77a 77a 81a '86 '86a 86
'85 '86ab 77ab .giab ,86a ,77a 77 ,gga 77 1 e86 79
'77ab
'76ade
,7 gab iggab 78 "
.ggabc
'85a
$76ab
'86a '78
.g3
',7 7 a 76ab
.go
,g7
,86abe igj ab
,' 8 7 a 73 79abe 8 tab 73a '85 '78 8D '95
'87 '87ade ,62ab 80abe 73abc .gga '81 '83ab iy9
'76 'Blae eg7eb '76abe 80abc '80ab .go 87ab ,33 83 '78abe '80ab 79abc 79ded '82 80 37 00ab 73
'81 '83 DC '79 8D '87 DC '83 Cd '79ab 76 '79 80 '82
.go sgo c '76ab .g3c ,$7cd '76ab ,79 .giab ,g3
'82 '32 C '83 D '82 C '82 d '83 D '82 '82 D '76 I
' I te< tis e i t h dlfferent superscripts are significantly different (P 5 0.05),
all otr.ers are net s!gnificantly different. The warmest water temperatures occurred during the midsummer months of July and August. This is expected since discharge temperatures are based on an increase in temperature over intake water temperatures. 15
I The highest annual mean water temperatures occurred during the 1985 to 1987 period, the 1977-78 period, and 1981. The coolest temperatures were during 1980 and 1982. No significant differences among years were I detected at A2 or G2, but significant differences between years were noted at E2 (Table 4). During the larval fish sampling months of April, May, and June, there were differences among water temperatures the years at each station (Ta-ble 4). Temperatures during certain years (1977,1978, 1981, 1985, and 1986) were generally warmer than other years. Likewise, there were some years (1979, 1980, 1982, and 1983) where temperatures were generally cooler than the other years. These differences were mainly a result of power plant operations and occurred when Unit 2 was out of service. Analysis of water temperatures during the summer months of June, July, and August found few significant differences (Table 4). This indi-cates that while there were station differences (E2>A2>GE), there was no year when the water was significantly warmer than the others during the 1977-87 period. {_ 4.2.3 Meteorolgical and Hydrologic Conditions The effectiveness of Robinson Impoundment for cooling is influenced i by several climatological f actors including, among others, surf ace area, meteorological conditions, and inflow from the Black Creek watershed. In
; order to quantify the effect of the 1986 drought conditions, rainfall, air temperature, and Black Creek inflow were examined.
According to meteorological data from the Robinson power plant site, Florence and Darlington, South Carolina, 1977-86 was relatively dry except for 1979, 1982, and 1983. Average annual departure from normal precipita-tion for the area was approximately 3 inches below normal with 1982-83 precipitation 2-10 inches above normal and 1986 precipitation 8-12 inches below normal. The most significant aspect of these conditions on the impoundment was the below normal rainfall, especially during 1986. I te g.
I Air temperatures were at or slightly below normal for the 1977-86 period. The most extreme departure from normal was in 1986 when tempera. tures were greater than 2 degrees above average for the year. Since the largest inflow to the impoundment is from Black Creek, l stream flow data from the U.S. Geological Hydrologic Ststion on Black Creek at U.S. 1 above the impoundment (Table 5) were examited. 8 1 7able 7 rio, in Black Creek at U.S. I above the Robinson impoundment ranked by I years (listed lowest to highest).
'I I
Jan Feb Mar Apr wya Jun Jul* sug* Sep* oct W oec Ave.' 'I '86 '85 '85 -'81 '86 '86
'81 '83 '86 '84 '82 '85 '86 !
'86 '81 '81 '86 '86 '81 '77 '80 '80 '82 '95 '91 '81
'85 '77 '86 '81 '85 '85 '80 '82 '83 '87 879 '79 '85
'83 '87 '82 '82 'S7 '77 '83 '77 '77 '79 '84 '78 '82 I '79
'80
'84
'80
'78
'82
'78
'79
'84
'87
'78
'77
'77
'82
'83
'80
'78
'83
'85
'82
'81
'79
'86
'84
'82
'84
'78
'78
'86
'95
'87
'83
'81
'80
'87
'82
'83
'78
'77
'77. '84 '87 '79 '80 '84 '78 '78 '81 '83 '78 '83 '80
'87 '85 '77 '84 '79 '87 '79 '81 '85 '81 '77 '96 '84
.B '73 '83 '83 '83 '78 '82 '84 '85 '79 '77 '86 '84 '79
'82 '79 '80 '80 'S$ '79 '80 '80 '77
' Iv Jata unevaliable During tha 1961 to 1986 period, 1986,1985, and 1981 ranked first, second, and third, respectively, in having the lowest recorded flows.
During the 1977-86 period, the five lowest flow years were all since 1981. While annual values for rainfall and Black Creek flow give an overall
- . indication of precipitation, the data may mask seasonal extremes. For
, example, the monthly ranking of Black Creek flow data in Table 5 shows 1981 was low during the first six months of the vear. But beginning in July and continuing through November, the flow was among the highest for the 1977 to 1987 period. Flow for 1986 followed a similar pattern but was low longer into the year. This was further compounded by the overall low- ; flow conditions during 1985.
Good inflow during the spring and summer months is important since normal imocundment water levels are needed for maximum cooling. Low flows and low-water levels during this time of year also reduce available 17
I fish-spawning habitats, particularly in the upper impoundment, and limit I the protected habitats. With limited areas of aouatic vegetation in the middle and lower impoundment, fish may be more likely to migrate out of normal hat,itats making them harder to sample with current methods. 4.2.4 Plankton and Benthos Communities Phytoplankton have been monitored since 1973, Zooplankton have been monitored since 1980, while benthic macroinvertebrates have been monitored since 1974. Analysis of variance (ANOVA) on phytopicnkton ard zooplankton data was performed to test for differences between stations, years, and months over the 1980-1987 period (Table 6). ANOVAs were run with Sta-tions A2, E2, and G2 and also with G2 omitted. This was done because of
, habitat similarities at A2 ar.d E2 and their dissimilarity to G2. Because of improvements in taxonomy and sampling methodology, statistical tests were inappropriate for certain data.
I I I 3 i I I I I a g
l I 1 Table 8 summaries of analysis of variance and Duncan's multiple range test
- on }
organism censity cata free 6binson impounement. Items are listed in j coscending order. Data unavailable for 1984, q t Phytoplankton Zooolamaton Benthos (w/o G2) ( ro G2)
. i station Analysis A2a A2 A2a apa gia ,
?- E2* E2 E2* E2* A1D l D 1 El b C2 D G2 veer Analysis a a gia , Bo Bo go a 85a
= D D gia 81 81 80ab gyab D DC D 87 87 82abe 82a B6 D l 86 DC 86be 83 D 82 !
85 0 86 DC 83 8 86 DC 82 D 85 C 55 C 85 C C d
, 13 83 87 C B7 C
Month Anglysis ,. Aug 8 Jula jyn a Mar 8 Feb 8
- i. sep ab gyg ob jy;ab g,7.b jun a Julab 5,,b ogg ab pay abe Aor ab oct DC oct D sep abc gy abe ge ab Jun kd jyn b g,y abc Febabe gyg ab
,.I Nov bcd Feb cd gy b g,y b g ,abc Apr obc octabc Jun abcd gg9 b Dec ed gg b Aug abc j,n bcd Jan ed p,3 b ge be 5,, bed L May ed Apr D Mar be Dec ed I. Mar d 3,n b 7g bc gyi cd Apr d y,7 0 J r,n C Aug d i,
' Items with different superscripts are signifIcentay difforent (P 5 0.05). ~
all others are not significantly different. Phytoplankton e phytoplankton community composition in the impoundment is deter-mined by the sof t, acid, low-nutrient water. Organism abundance is ccn- !;I sidered to be low to moderate in abundance and species composition is typical of oligotrophic (dystrophic) waters. Light limitations frcm the stained water could influence rhytoplankton abundance and composition. Green algae have been numerically dominant at all three stations. I 19
Analysis of variance of phytoplankton density data indicates there were no statistical differences between densities at Stations A2 and E2 I but they were higher than densities at G2 (Tabic 6). Phytoplankton densities varied monthly with relatively large varia-tion at G2 followed by E2 and A2 (Figure 8). Highest phytoplankton den-sities occurred during August at A2 and E2 and June at G2. Lowest phytoplankton densities occurred during March at G2 and April at A2 and E2 following periods of high inflow from Black Creek. This high inficw may have flushed the phytoplankton from this narrnwer ' of the impoundment. l g Significant differences in phyteplankton . tes were seen among years with 1980 having the highest densities, 4 A , IN: lowest, and the 1985-87 falling in between (Figure 8). Zooplankton The zooplankton community has been characterized as having slightly fewer taxa but with densities and biomass values equal to or greater than Cr&L Piedmont reservoirs (Hallin 1986). The most abundant zooplankters are copepods (3 taxa) and rotifers (24 taxa) with cladocerans (12 taxa) less abundant. Seasonal abundance follows a bimodal spring-fall peak pattern, especially in the middle and lower impoundment (Figure 5). Cope-pods and c16docerans contribute the most biomass whi .h also follows a bimodal spring-fall peak pattern. Densities at G2 were lower than at A2 and E2. When compo -ing only A2 and E2, a significant difference in den-sity was found between these stations. Tnis indicates that there is less zooplankton near the discharge but there is still greater zooplankton abundance at E2 and A2 than at G2 (Figure 8). Zooplankton densities were significantly different between the upper impoundment (G2) and the lower impoundment (A2 and E2) (Table 6). Den. sities at Station G2 fluctuated during the year and followed phytoplankton density patterns (Figure 8). Low densMies occurred in March, the month of highest Black Cretk inflow, and high densitics occurred in June and July corresponding to the months of highest phytoplankton densities. 1 20
I ! i Differences in zooplankton densities were observed over years (Fig. ure 8). Fran 1980 to 1982, organism densities at A2 and E2 were higher l than the 1983-87 period. This decrease in zooplankton density may have I been a result of increased predation by larger numbers of larval and juve-l nile bluegill. Zooplankton @nsities in the lower and middle Gmpoundment were lowest during 1983, 1985, 1986, and 1987 (Table 6). ! During 1985 discrete depth sampling was conducted to determine if there were any effects from thermally induced stratification. Samples were taken at 1-meter (thermally enhanced) and 3-meter depth from April chrough September. In most cases there were no significant differences in densities between depths at each station. The only difference was for
- opepods at E2 where there were fewer individuals at the cooler 3-meter depth t":n at 1 meter. Vertical stratification is probably not an impor-
..I tant factor influencing the vertical distribution of zoopla,kton in the impoundment. Benthic Macroinvertebra+.es ~I The benthic macroinvertcbrate community has been dominated by chironomids and oligochaetes, especially in the middle and lower impound-ment. Taxa richness has been similar at Station G2 during the years, l while at Stations A2 and E2, taxe. richness has increased. This increase in taxa richness at A2 and E2 may be a result of improved field and labor-techniques which allow better retrieval of small, delicate I atory oligochactes and chironomids that dc,minate these stations. The increcse in submerged aquatic vegetation may provide better habi-tats for benthic organisms (see Section 4.2.5). Aquatic vegetation also
. provides an area for detritus deposition. Both cf these factors increase the benthic community. Areas couposed mostly of exposed sand are less f avorable to benthic organisms. As aquatic vegetation has spread in the middle and lower impoundment, the benthic organisms that utilize these plants will also increase in abundance and kinds.
I 21
Benthic macroinvertebrate densities during 1985-87 were not signif-
'I icantly different between Al and El but both stations were different from G1 (Table 6). No significant differences were seen between years.
Spatial density by months indicated no significant differences among most months. I 4.2.5 Aquatic Vege T. ion I The Robinson Impoundment has supported a diverse population of native aquatic vegetation consisting of emergent, floating leaf, and submergent plants. There have been differences in aquatic vegetation composition betveen the upper and the middle and lower areas of the impcundment. I-The upper impoundment contains the highe,t diversity of aquatic veg-etation. Haidencane Panicum hemitomon is the most common emergent plant, water lilies Nymphaea odorata are the most common floating leaf plant, and milfoil Myriophyllum heterophyllum 15 the m.;st common submerged plant. The middlt and lower impoundment have few areas of floating leaf plants as a result of fewer protected areas, increased wave action, and greater depth. Emergent vegetation, mostly maidencane, has spread in undisturbed riparian areas awa) from houses and swimming beaches and often forms a ' band 1-2 70ters 'de. Submerged vegetation, mostly spike-rush I Eleochcr!s baldwinil and rush Juncus repens, has also increased in the lower impoundment over the period. Most of the changs in aquatic vegetation observed over the study period are due to natural succesion. These changes include increased floating-leaf vegetation in the upper impoundment, increased areas of emergent vegetation throughout the imp'.u ndment , and increasec areas of submerged vegetation in the lower impoundment. I Submerged vegetation in the middle impoundment has been affected by pcwer plant operations in the immediate discharge area. Both discharge I flow and temperature appear to determine patterns of submerged vegeta-tion. Spike-rush was the most abundant submerged plant in the middle 1 22 l
I [ impoundment during 1983, covering much of the bottom near the discharge weir. During 1984 when Unit 2 was out of service, the biomass of i spike rush increased. When Unit 2 returned tc Service in 1985 and throughout 1986, spike-rush was eliminated from the area immediately in front of the discharge weir (Figure 9). Populations of spike-rush across the impoundment from the discharge and in the lower impoundment experi-enced no decrease in biomass during this period indicating that the impact of the power plant discharge was limited to the immediate discharge area (Figure 9). 4.2.6 ...heries i / Fisheries studies in the Robinson Impoundment have charecterized the
,- fish populations as typical of other sandhills and regional lakes. Blue-
! gill, warmouth, and largemouth bass were the dominant fish throughout the impoundment, especially in the middle and lower impoundment (E2, A2).
Many of the other species (i.e., chubsuckers, suckers, and blackbanded and dollar sunfishes) were more common in the upper impoundment (G2) (Ta-ble 7). LI A I I f I I I I - - - - - - - - - - --- -- - - - - - - - - - - - - - - - - - _ - _ - - - - - - _ - - - - - 23
1'
- g. .
; Table 9 Relative abundence of f ishes collectec by cove rotenone sampling f rom Robinson impoundment 1977-1987,
( Species Trans. A Trans. F Trans, G
!.l
+
3 Ek>ufin + + Eastern medminnow + + + Redfin pickerel + + +
;- Chale pickerel + + +
Golden shiner * * ++ troncolor thiner - + +
, Dusky shiner + + .
Creek chubsucker + + + Lake chubsucker + + + spotted sucker + + + Wh!te catfish ++ + ++ l Yellow bullhecd + ++ + Flat bullhead + + + Tadpole mastom - - + bg Margined madtom swampfish
- - +
l g - + + Pirate Perch + + ++ Lined topainnos + + ++ MosQuitoflsh ++ + +
' .I Mud sunfish + + +
+
Flier - - Banded pigmy sunfish + + Blackbanded sunfish + +- ++ Bluespotted sunfish ++ +++ +++ Redbreast sunfish + + + I Redear sunfish + + + Warmouth ++ ++ ++ Bluegill +++ +++ ++ collar sunfish + + ++ Largemouth bass ++ + + White crappie + + + Black crappie + + + susto darter ++ + ++
! E Ll Tessellated darter saucneek darter
+
+
+
+
j
~
- = absent , + = 1-too/ha, ++ = 101-1000/ha +++ * >1000/he g Variations in the fishery of the impoundment have been noted over the E years including increases and decreases in the total population as well as in numbers of certain species. The following sections address the fisher-ies of Robinson Impoundment including larval and adult fishes.
I Larval Fish Larval fish studies have examined both the planktenic and littoral larval fish habitats. The larvae of 21 taxa have been col'lected from the impoundment (Table 8) (McGowan 1985). Since bluegill and largemouth bass I 24
.are the dominant sport fish in the impoundment, they will be discussed in r addition to the total larval fish community. A nongame taxa present L throughout the impoundment, Etheostoma, also is discussed.
Table 10 Larval fishes collected from Robinson impoundment, 1974-1987 Scientific Name Commor. Name Amildne I g e calve bowfin Esocidae E3 500. pickereis Cyprir.idae Notemigonus crysoleucase golden shiner Notropis chalvbteus ironcolor shiner Catostomidoe Erimvron spp.' chubsuckers l Minytrema melanops' spotted sucker letaluridae letalurus natal!S yellow bullhead g h platycephalus flat bullhead Amblyopsidae Cholog6 ster cornuta swempfish Aphredoderidea Aphredederus sayanus pirate perch Cyprinodontidae Fundulus lineolatus lined topainnow Poecillidae Gambusla affinis mosquitotish Centrarchidae I Enneaeanthus chaetodon' E blackbanded sunfish g gloriosus* blutscotted sunfish Lepomis auritus redbreast sunfish h gulosus* warmoJth I h macrochirus' bluegill Lepomis spp.' unidentifled sunfish Micropterus salmoides* largemouth bass Pomoxi.s 500 crappies Percidae Etheostrea fusiforme' swamp darter
. . - , - , o,,e.,ed ta.a I
l 25
I Data for total larval fish, Lepomis, and Etheostoma were collected using push nets (571 u mesh), while largemouth bass were collected using Plexiglas
- littoral traps. Larval fish were not sampled during 1984.
Analysis of variance of log-transformed larval fish density of each of the major species and total larval fish indicates significant differ-ences between Transects A, E, and G (Table 9). Larval fish densities at G I. were higher and significantly different from E and A which were not signi- , ficantly different from each other. At Tr nsect G. larval fish densities have been consistently higher than A and E (Figure 10). Table 11 Analysis of variance and Duncan's multiple range test
- for differences in mean terval fish densities (ranked highest to lowest). Data un-
, available for 1983 and 1984 Largemoutn ! Total Lepomis bass Etheostoma 8 ga ga G Ga D D D E E Eab E A
b gb gb gb j 1982a igg $a 1986a 1982a
, 1985a 1986 D 1987ab 1987 D < 1987ab iggi be 1982abc i9gi b 1986abc DC D 1987 1985abc 1980 1981b c 1980 DC 1981 DC 1979 D 198obe 1982bcd b 1980 c 1985 D 1979 Cd 1977 DCd 1979 C
1986 D d ed j977c ig77c 1977 i979 8 1978 1978 8 1978 C 1978 C May a Jun a u,y s Apr a Apr D May a Jun ab May a b Apr D Apr D b Jun Jun altems with different superscripts are significantly different (P 5 0.05).
's For total larval fish collected during 1977-87, there were signifi-cant differences between years with many overlapping annual means. Gener-ally, larval fish densities during the 1980-87 period were higher than the 1977-79 period, especially in the middle and lower impoundment. The years of the lowest larval fish densities were also the years of the highest conper levels in the impoundment (Figure 6).
E i l 26 l l
Larval Lepomis abundance was highest during 1985 (Table 9). Differ-ences between the other years were less clear at A and E where Lepomis i larvae were lowest in 1978 and then gradually increased through 1985. Lepomis density at A and G then declined from 1985 to 1987 (Figure 10). At Transect E, density declined from 1985 to 1986 but increased from 1986 3 to 1987. Larval Lepomis densities peaked in May and June for the impound-ment as a whole. I There wert no differences in largemouth bass larval densities between G and E or E and A, but G was higher than A. The highest density occurred in 1986 but was not significantly different from all other years (Ta-ble 9). Generally there has been a gradual increase in largemouth bass larvae in the impoundment since 1977 (Figure 10). This was most evident at Transects A and E. Etheostoma larvae were more abundant at G than at E and A and were
, more abundant during April and May than June. Temporal differences indi- j cate 1982 had higher densities than all other years. The lowest larval 4 densities were during 1977 and 1978.
i Larval fish densities in the middle and lower impoundment have been relatively high since 198? ,..gure 10). Lepomis accounted for much of this increase in abundance, especially during 1985. During 1986 and 1987, however, Lepomis abundance has decreased. Largemouth bass has also in-creased, especially during 1987. The increase in largemouth bass may have resulted in decreased abundance of bluegill larvae because of predation. The lower larval fish densities of 1977-1980 appear to be a result of increased copper concentrations in the middle to lower impoundment. After copper concentrations decreased in the impoundment, larval fish abundance
! increased.
Adult Fish During the 1977-87 period, there were fluctuations in fish standing crop. Analysis of cove rotenone data indicates significant differences among years for both density and weight. The 11 years can be grouped into g 27
I three periods: (1) 1977-81, (2) 1982-85, and (3) 1986-87 based on abund-ance. T Ouring the 1977-1981 period, there were low numbers of fish in the middle and lower impoundment (Figure 11). The lowest numbers occurred in
*l 1979 with standing crops improving after that time. The upper impoundment had higher numbers of fish during these years and did not experience a similar decline. The weight of fish per hectare variad between the middle
- and lower impoundment stations. Fish weights from the middle impoundment declined from 1977 to 1979 when they reached the lowest level observed (Figure 11). During this period, fish weights from lower impoundment ~ increased and was similar to the upper impoundment. This indicates there were few large fish in the lower impoundment, near normal fish populations , in the upper impoundment, and few small fish in the middle impoundment. From 1980 to 1981, there was a gradual increase in the total number of fish in the middle and lower impoundment. The weight of fish per hect-are became more similar in these areas. The upper impoundment continued to .aaintain its fishery. [ Beginning in 1982, the middle and lower impoundment experienced dra-matic increases in the number of fish. The weight of fish per hectare also increased but with less rapidity. The upper impoundment did not ex- - perience similar increases but stayed within the ranges previously ob-served. The , umber of fish per hectare in the lower impoundment peaked in [ 1983, then declined, but remained above 1977-81 levels. The high numbers of fish in the middle impoundment varied during 1S82-85 but were still the hichest of any area in the impoundment. d
~
From 1985 to 1987, fish populations in the middle impoundment de- . creased in both number and weight per hectare. Fish in the lower impound-ment decreased in number while increasing in weight during 1985. During J 1986 fish increased in number but decreased in weight. The number and g weight of fish per hectare in the upper impoundment decreased in 1986 then W increased in 1987. I
The increase in fish standing crops during the 1981-83 period re.
- I flects an increase in bluegill abundance (Figure 12). Tl.is followed a period of lower fish abundance, especially bluegill, attributed to elevated copper (CP&L 1982b, 1983c, Woock 1985). While bluegill populations have declined since their peak in 1983, their density and standing crops currently *emain above the levels of the late 1970s.
Since 1979 most bluegill were under 60 mm (Figure 12) representing a significant change from 1979 when there were very few small bluegill. The abundance of bluegill < 60 mm in the rotenone samples indicates survival through the summer following successful reproduction in spring. An abund-ance of small bluegill also provides prey for predators such as largemouth bass and chain pickerel. Largemouth bass also made significant population increases since 1981 (Figure 13). This was especially evident at Transect E. After reaching a
. peak in 1983, the number of largemouth bass decreased to numbers similar to those at Transect G. While the number of largemouth bass dropped at !l Transect E, the weight of fish per hectare remained high. Transect A also experienced an increase in largemouth bass since 19?9. Transect G popula-l' tions remained fairly constant over the 1977 to 1987 period with increases occurring from 1985 to 1987. Both total number and weight per hectare of largemauth bass in the middle and lower impoundment have generally in-LI creased since 1981 (Figure 13).
Overall, the lower Robinson Impoundment fishery experienced a period of low numbers and poor recruitment (1977-1979) due to elevated copper concentrations. This was followed by a period of high reproductive suc-cess (1982-1985). The current status appears to be one in which the fish
,. population is becoming stabilized after several years of fluctuation.
During 1985 to 1986 plant operations and severe climatic conoitions re-sulted in the worst environmental conditions noted to date in the impound-ment, yet the fishery was at or above the levels of the 1977 to 1981 period. I 29
l When comparing Robinsor. Impoundment to other regional blackwater is lakes, the total number and weight of fish per hectare in the imooundment I
- was higher than most other lakes (Table 12) Although many of the compar- l isons were to natural lakes and not impoundments, all referenced bodies of water are considered blackwater.
Table 12 Comparison of cove rotenone data from Robinson impoundment and other blackwater lakes in the region.
.g
~
Total number of weight (kg) of . Sampiino locat ion fish oer hectare fish per hectare . Robinson impoundment 1974-75 14,978 81.6 Robinson impoundment 1979 13,257 89.4 Robinson impoundment 1982 55,641 151.9 Robinson impoundment 1955 60,150 163.2 Robinson impoundment 1986 24,783 107.9 Robinson impoundment 1987 23,188 100.0 Robinson impoundment average 1974-1987 (w/o 1976) 29,336 120.4 Singletary Lake (Louder 1961) 709 6.3 Lake Waccamas (Louder 1961 Davis 1966) 1,100 141.3 AtIigafor Lake (Croweli 1966) 285 10.9 catfish Lake (Bayless 1966) 241 1.9 Status of Copper and the Fishery The fishery reductions of the late 1970s and early 1980s were related to elevated copper levels in the impoundment (CP&L 1982b, 1983c, Woock 1985). Since the removal of the brass condenser tubes, copper con-centrations have declined. This has resulted in lower liver copper core-centrations in largemouth bass, bluegill, and spotted sucker compared to I the early 1980s (Table 13). During the period of declining liver copper concentrations, the fishery, especially bluegill and largemouth bass, improved. The 1987 liver concentrations were at or approaching background levels for fish in the region. Concentrations of copper in fish livers I 30
I are expected to be similar to or less than those reported in 1987 in the coming years, f W Table 13 Ccuper concentrations in livers f rom fish cotiected in the middle and
,_ tower impounoment. Concentrations are in ug/g wet weight.
b Largemouth bass Bluegill Scotted sucker
, Year Mean n Raege Mean n Range Mean n Range 1980 72 9 7.1-220 26 17 1o-280 68 2 55-81 1981 35 17 7.9-150 191 43 < 1-860 51 19 14-100 1982 28 20 7.8-124 21 25 < 0.4-92 92 19 < 2-78 ~
1983 25 5 12-34 4.7 5 < 2-15 37 5 25-65
'= 1987 3.5 3 o.9-6.7 1.8 2 1.7-1.9 21 3 0.6-35 4.
5.0 EVALUATION OF PROPOSED THERMAL EFFLUENT EFFECTS ON FISH Monitoring of the fish populations in Robinson Impoundment over the years has shown that fish have been well distributed throughout the im-poundment including the discharge area. Catch rates have been lower at
. times in the immediate discharge area, particularly during midsummer when discharge temperatures are highest. Once the discharge area temperatures become more f avorable to fish, it has been demonstrated that fish return to the discharge area. It has also been shown that fish are attracted to this area during the winter months.
Conditions unf avorable to fish occur only during the warmest summer months (i .e. , July and August). Even during this period, the area of impact is limited to the middle impoundment allowing much of the impound-ment to be available for fish. This midsummer period is after the primary breeding season, and since fish are not behaviorally tied to a .et site, they would be able to avoid any unfavorable conditions.
~
Jensen et al. (1969) found breeding adults to be the most sensitive to temperature extremes. Most fish in the impoundment breed during March, April, May, and June prior to the months of highest thermal discharges. Even though Lepomis spawn throughout the summer, most reproduction ocuurs 31
'I during spring and early summer prior to the maximum impoundment tempera-I tures.
E Larval fish capture rates are generally highest in late May and early June when temperatures are well within tolerances for breeding adults. At Transect A, the highest measured temperatures during biological sampling
, were 31.0*C (87.8'F) and 31.2*C (88.2*F) during June 1977 and June 1981, 'l respectively, and 30.4*C (86.7'F) at Transect G during June 1981. Other sampling temperatures at these transects during April, May, and June did j not exceed 30*C (86*F). Larval Lepomis catch rates are highest in late May and early June when temperatures are near 30*C (86*F) wh'ch is con-sidered optimal for bluegill (Lemke 1977). Largemouth bass typically "I spawn when water temperatures are around IB*C (64.4*F) to 23*C (73.4*F) r (April and May in the impoundment). Again, no extreme temperatures occur during these months when the more vulnerable spawning adults are pre-sent. Tl.e temperature preference range for young-of-year bass is from 30*C (86*F) to 32*C (89.6*F) (Ferguson 1958).
I Water temperatures in the upper and lower impoundment are cooler than the middle impoundment when the power plant is operating. During the drought conditions of 1986, Station G2 was, on average, 9.6*C (17.3*F) cooler than Station E2 (midway across the middle impoundment) for May,
,, June, and July. A differerce was also seen between the Station E2 and Station A2 whert. during the same three-month period, A2 was 6.9'C
. (12.4*F) cooler than E2, While the temperatures at the discharge weir l were averaging 35.6*C (96.0*F), 40.0*F (104.0*F), and 43.2*C (109.8'F) during May, June, and July 1986, respectively,. much of the impoundment was suitable for spawning and growth.
t l Following the peak spawning period, temperatures during sampling at T"ansect E normally approach 38'C (100.4*F) during July and August. The lowest elevated temperature between 1977 and 1987 was 34*C (93.2*F) (Sep-tember 1982), while the highest was 39.6*C (103.3*F) (August 1979) at the middle transect station. Highest temperatures at Transect G exceedeo 30*C (86*F) only five times during the 11-year period with the highest tempera-ture, 32.3*C (90.1*F), occurring in August 1979. The highest temperature 1 I
' at Transect A was 33.1*C (91.6*F) during the same month and year. There-fore, only Transect E temperatures ever reach values that may cause fish mortality, even though no fish kills have been reported in the impound-ment. Furthermore, the highest temperatures occur during times when fish ( are best able to tolerate extremes. Most young-of-year and adult fish are of sufficient size by August to migrate to preferred environments. Only late spawned larval fish in the discharge area may be unable to escape temperature extremes. However, this life stage is more tolerant of hot water than older fish. Coutant (1975) found that small largemouth bass are more eurythermal than larger bass. According to the literature, fish acclimated to higher temperatures I have higher critical thermal maximums (Banner and Van Arman 1973; Cox 1974). Cairns (1956) showed that bluegill " tempered" to a 2*C/ day (3.6*F/ day) increase can tolerate temperatures up to 39.2*C (102.6*F) for at least a day. Siler and Clugston (1975) found that largemouth bass were collected from water with temperatures at or above those (36.4'C = 97.5'F) reported by Hart (1952) as the upper lethal limit. Bennett (1979) measured internal temperatures of bass from a heated impoundment as high as 36.2*C (97.2*F) and concluded that bass can successfully reproduce, hatch, grow, and become sexually mature in heated waters. Guest (1985) found LT50 values closer to 39'C (102.2*F) for both :lorida and northern g strains largemouth bass. Siler and Clugston (1975) also found that bass p were capable of finding and migrating to " refuge" areas whenever water temperatures became elevated. In Robinson Impoundment, cool water zones exist in heated areas due to feeder springs and seeps and the narrow fomer Black Creek channel, but it has not been determined if these areas function as thermal refuges for large numbers of fish. The authors referenced above report upper thermal lethal limits for bluegill and largemouth bass of 36.4*-39'C (97.5*-102.2'F). If one con-siders a maximum " desirable" temperature (one at which fish will leave an area, if possible) of 32*C (89.6*F), which is considerably less than the lethal limit, then during most years fish would have free pcssage of the entire impoundment. When addressing low 00 limitations if one assumes 4.0 mg/1, a value of ten used by fisharies biologists, to be the lower j l 1 33
I
" desirable" limit, then there is abundant available habitat for fish.
I While 1986, the worst drought year on record for the area, showed the impoundment " blocked" by water temperatures of 32*C or higher and D0 of 4 mg/l or lower, large "f avorable zones" were still available for fish both in the upper impoundment and the lower impoundment (Figure 14). This
" blocked" condition only lasted for two weeks and then improved with lower temperatures and higher 00 near the bottom.
I Based on measured maximum temperatures in Robinson impoundment during 1985-1987, the thermal effluent should not produce impoundment tempera-tures significantly detrimental to fish except in the immediate discharge vicinity and only during a relatively short time. Further, the impound-I- ment contains a reproducing indigenous population of fish with a higher than expected standing crop for blackwater systems. 6.0
SUMMARY
The current NPDES permit for Carolina Power & Light Company's Robin-l son Steam Electric Plant has limits for temperature at the discharge point for once-through cooling water into Robinson Impoundment. These current temperature limits were derived from a successful 316a Demonstration sub-mitted by CP&L in 1976. Since the limits were imposed in 1977, the plant I has occasionally exceeded the limits for shcrt periods due primarily to - more adverse meteorological and hydrologic conditions than those exper-ienced during the short (approximately 1 year) 316a Demonstration study. Biological monitoring during these exceedances has shown no adverse effects on the biota of the impoundment. Thus, it has become apparent that some of the current temperature limits are lower than necessary. The current method of monthly changes in iimits does b . keep pace with the natural seasonal change in impoundmert temperatures and, therefore, may cause needless restrictions on the operaticn of the plant. CP&L proposes that the temperature limits in the renewed NPDES permit be revised to reflect the increased understanding of the effects of heated I water discharged to Robinson Impoundment. The limits for the spricg months, specifically May, could be increased to those experienced in 1986 and not cause an unacceptable adverse effect. 34
L In response to the natural warming and cooling of the impoundment in the spring and f all months, respectively, the discharge temperature of the once-through cooling water can vary greatly over a 30-day period such that I temperature limits set at approximately 15-day intervals would more closely rarallel actual conditions. Semimonthly limits could be deter-mined by a simple averaging method to mak2 the transition between months with different limits. Studies to monitor the biological conditions of Robinson Impoundment have been conducted under a variety of environmental conditions and ther-mal loadings since 1973. By observing conditions over these years, over-all trends in the oiota are evident. The thermal discharge has the greatest impact in the middle impound-ment, especially near the point of discharge. The upper impoundmi nt re-ceives only minimal thermal discharge. The lower impoundment is also affected by thermal discharge; however, cooling of discharge waters occurs as waters are recirculated through the impoundment. I The impoundment can be divided into two biological areas: (1) the upper impoundment, which is shallow and narrow with abundant aquatic veg-etation and affected by Black Creek inflow and (2) the middle and lower impoundment, which is wider and deeper with fewer areas of aquatic vegeta-tion. During 1985 and 1986, water temperatures throughout the impoundment were higher than they have been since 1980. This was a result of Unit 2 returning to service with a slightly greater heat cutput (< 2%) at maximum power levels, improved reliability, and the occurrence of record low rain-fall and other climatological effects. The higher than normal ambient water temperatures, reduced rainfall and associated inflow from Black Creek, low impoundment water levels, and improved operation characteris-tics of Unit 2 during 1986 resulted in thermal conditions more severe than experienced during prior studies, l 35
When the plant pumps are operating, there is a good mixing of the , water column minimizing the areas of low-dissolved oxygen despite elevated water temperatures. Thermal stratification generally is weak durir.g all J seasons and a thermocline is rarely seen except in the middle impoundment i area over the old Black Creek Channel. I The impact of the thermal discharge on the lower trophic levels (phy-toplankton, zooplankton, benthos) appeared to be minimal over time, even though declines in all plankton were observed during certain years. Com-parisons of annual densities of phytcplankton between Stations A2 and E2 from 1980 to 1987 indicate A2 was not different from E2. Zooplankton densities, however, at these two stations during this same period were i higher at A2 than E2. Predation on zooplankton by the increasing number of larval fish is the probable reason for these differences since thermal discharges were lower than normal during much of this period. Low fish reproduction (1977-1981), which was linked to elevated cop-per concentrations, increased rapidly during the 1982-85 period. This increase occurred mainly in the middle and lower impoundment and included all fish, especially bluegill and largemouth bass. The slight drop in total larval fish, including larval bluegill, during 1985 and 1987 occurred during a period of increased largemouth bass abundance and resultant predation which contributed to the drop in smaller fish. Fish standing crops varied from low (1978 and 1979) to high (1982 to 1985). While there was a reduction in the overall number of fish per hectare as well as the weight of fish per hectare during 1986 and 1987, the total standing crop of fish was similar to or above the levels seen in 1977. i The expansion of the fishery in the impoundment during 1982 is simi-lar to that which occurs in new impoundments when there are many habitats unoccupied in the system. The fishery expands to fill these habitats. In the case of Robinson Impoundment, there were underutilized habitats avail-able following the fishery reductions of 1978 and 1979. When the stress of copper was removed fram the impoundment, the fishery responded to occu-py these habitats. , 1 36
I Af ter several years of an expanding fishery, it is not unexpected to I have a period of reduced recruitment while a system adjusts to a sustain-able carrying capacity. Robinson Impoundment currently has a fishery above that expected for a dystrophic blackwater impoundment. The diver-sity of fishes in the impoundment and the dominance of bluegill and large-
. mouth bass in the impoundment indicate a balanced and indigenous fishery with abundant sport fishes.
I Thers was an imoact from the tharmal discharge on the fishery in the immediate discharge area of the impoundment during summer months, but this area was able to recover during the rest of the year. The thermal dis-
~; charge may even enhance the fishery during the winter months by attracting fish such as largemouth bass into the area and extending the growing ,
season. The importance of other areas of the impoundment as cefuge and nurs-ery areas noted in the original 316a study are still important to the biota of the impoundment. The upper impoundment has maintained a rela-tively constant biological community. The lower impoundment was temporarily af fected by elevated copper but has been unaffected by the thermal discharge. The severe drought (1986) affected the impoundment in several ways, - including increased ambient water temperatures and lower impoundment water levels. These conditions, along with the modification and improvements of Unit 2, resulted in thermal conditions more severe than previously exper-ienced. These conditions, along with a normal decline :n the fishery often observed after a period of rapid expansion, were he probable causes of the decrease in the fishery observed from 1985 to 1986. While there was a decrease in the fishery in 1986 and 1987, it was still at or above levels observed during the middle 1970s. Any delayed response resulting from the drought conditions may become evident in the coming years. Fluc- _ tuations in the biota, especially the fishery, are a normal response to changing environmental conditions. With a return to a more norcal pattern I of rainf all, the fishery should remain balanced and indigemus. I 37
l In Robinson Impoundment, a variety of environmental conditions have been observed over the past 15 years. These proposed temperature limit changes would not allow the plant'3 discharge temperature to be any higher than temperatures that have been expe.-lenced before when biological moni-toring has demonstrated the impoundment can maintain a balanced and indigenous fish population. The operation of the plant and biological monitoring over the past several years offers ample empirical evidence that the proposed limit changes are acceptable and appropriate. pB' 9 38
- I 7.0 LITERATURE CITED
( Banner, A., and J. A. Van Arman. 1973. Thermal effects on eggs, larvae, and juveniles of bluegill sunfish. USEPA, EPA-R3-73-041, 111 pp. . Bayless, J. D. 1966. Coastal Lakes I--1965 surveys. North Carolina Wildlife Resources Commission, Raleigh, NC. June 30, 1966. Bennett, D. H. 1979. Behavioral thermoregulation of largemouth bass
- (Micropterus salmoides) in a reservoir receiving thermal effluent.
- Arch. Hydrobiol. 86:193-203.
Boyd, C. E. 1979. Water quality in warmwater fish ponds. Auburn Univer-sity Agricultural Experiment Station, Auburn, AL. Cairns, J. 1956. Effects of heat on fish. Indust. Wastes, 1:180-183. 4 !B Coutant, C. C. 1975. Responses of bass to natural and artificial temper-atore regimes, p. 272-285. I_n R. H. Stroud and H. Clepper (ed.). Black bass biology and management. Cox, D. K. 1974. Effects of three heating rates on the critical thermal
- a maximum of bluegill, p. 158-163. I_n J. W. Gibbons and J' R. R. Sharitz (ed.) Thermal Ecology.
sion. U.S. Atomic Energy Commis-CP&L. 1976a. H.B. Robinson Steam Electric Plant, 316 demonstration.
- Summary. Carolina Power & Light Company, Raleigh, NC.
I
}g . 1976b. H.B. Robinson Steam Electric Plant 316 demonstration.
;3 Volume II. Carolina Power & Light Company, Raleigh, NC.
- g : 1979a.. H.B. Robinson Steam Electric Plant 1976-78 environmental J monitoring program results. Volume I. Summary. Carolina Power &
Light Company, New Hill, NC.
. 1979b. H.B. Robinson Steam Electric Plant 1976-78 environmental monitoring program results. Volume II. Carolina Power & Light Company, New Hill, NC.
_ _ ,_,. -1980. H.B. .;inson Steam Electric Plant environmental monitoring program, 1979 annual report. Carolina Power & Light Company, New Hill, NC. ~
. 1981. Robinson Impoundment 1981 laboratory bioassej studies on bluegill deformities progress report. Carolina Power & Light Com-pany, New Hill, NC.
____. 1982a. H.B. Robinson Steam Electric Plant environmental monitoring program, 1980 annual report. Carolina Power & Light Comoany, New Hill, NC.
.B 39 ,I
I g . 1982b. 1981 studies of bluegill deformities and recruitment in 5 Robinson impoundment final report. Carolina Power & Light Company,
- w Hill, NC.
. 1983a. H.B. Robinson Steam Electric Plant annual environmental monitoring report, 1981. Carolina Power & Light Company, New Hill, NC.
. 1983b. H.B. Robinson Steam Electric Plant annual environmental monitoring report 1982. Carolina Power & Light Company, New Hill, NC.
_ _. 1983c. Laboratory bicassay studies on bluegill deformities and recruitment at Robinson Impoundment during 1983. Interim Report. I Carolina Power & Light Company, New Hill, NC.
. 1984. H.B. Robinson Steam Electric Plant 1983 environmental moni-toring report. Carolina Power & Light Company, New Hill, NC.
. 1985. H.B. Robinson Steam Electric Plant 1984 environmental mon-itoring report. Carolina Power & Lignt Company, New Hill, NC.
. 1985. RobinsonSteamElectricPlantI cnnual monitoring report.
Jan Carolina Power & Light Company, New H/, NC.
'y y
. 1987. Robinson Steam Electric Plant 2 5 annual monitoring report.
Carolina Power & Light Company, New Hill, NC. I CP&L, and LMS. 1981. Investigations of deformities and lowered recruit-ment of bluegill (Lepomis macrochirus) in Robinson Impoundment.
.E Lawler, Matusky, & Skelly Engineers and Carolina Power & Lignt iE Company, New Hill, NC.
g Crowell, T. E. 1966. Coastal Lakes 11--1965 surveys. North Carolina
,) Wildlife Resources Commission, Raleigh, NC. June 30, 1966. , Davis, J. R. 1966. Lake Waccamaw--1965 survey. North Carolina '!ildlife Resources Commission, Raleigh, NC. June 30, 1966.
Ferguson, R. G. 1958. The preferred temperature of fish and midsummer distribution in temperature lakes and streams. J. Fish Res. Bd.
.l Can. 15:607-624.
g Guest, W. C. 1985. Temperature tolerance of Florida and northern large-15 mouth bass: effects of subspecies, fish size, and season. Texas, J. Sci. Vol. 37:75-84
~
Hart, J. S. 1952. Geographic variations of some physiological and mor-phological characters in certain freshwater fish. University Toranto, Toranto, Ontario. Biol. Ser. 60. Harrison, F. L. 1984. Chemicals in effluent waters from nuclear "wer stations: The distribution, fate, und effects of copper. Lawrence Livermore National Laboratory, Livermore, CA. 40
I Harrison, F. L., D. J. Bishop, D. W. Rico, Jr., and J. P. Knezovich. 1983. Concentration and distribution of copper in effluents from the H.B. Robinson Stea'n Electric Plant. NUREG/CR-3132 VCRL 53047. Lawrence Livermore National Laboratory, Livermore, CA. 7 Harrison, F. L., and J. R. Lam. 1982. Concentrations of copper-binding g proteins in livers of bluegills from the cooling lake at the H.8. m Robinson Nuclear Power Station. NUREG/CR-2822 VCRL-53041. Lawrence Livermore National Laboratory, Livermore, CA. Jensen, L. D., R. M. Davies, A. S. Brooks, and C. D. Meyers. 1969. The effects of elevated temperature upon aquatic invertebrates. Cool-ing water studies for Edison Electric Institute. Report No. 4,
.I Research Project RP-49. The Johns Hopkins University.
Lemke, A. E. 1977. Optimum temperature for growth of juvenile blue-gills. Prog. Fish-Lult. 39:55-57. LMS. 1980. Experimentation to determine the cause(s) of the reduced 3 recruitment and incidence of abnormality in the Lake Robinson blue-E gill population. Repcrt to Carolina Power & Light Company. Lawler, Matusky, & Skelly Engineers, Pearl River, NY. Louder, D. E. 1961. Coastal plain lakes of southeastern North Carolina. Ln inventory of fish population in lentic water. L. B. Tebo ed., North Carolina Wildlife Resources Commission, Fed. Aid in Fish Restoration Project F5R and F6R Job No. 1. Mallin, M. A. 1986. Zooplankton community comparisons among five south-l eastern United States power plant reservoirs. J. Elisha Mitchell Sci. Soc. 102:25-34.
.g McGowan. E. G. 1985. An identification guide for selected larval fishes J from Robinson Impoundment, South Carolina.
Company, New Hill, NC. Carolina Power & Light Siler, J. R., and J. P. Clugston, 1975. Largemouth bass under conditions of extreme thermal stress, p. 333-341. Ln R. H. Stroud and H. Clepper (ed.). Black bass biology and management. Smart, M. M. 1985. Trace element monitoring at Robinson Impoundment during 1983. Carolina Power & Light Company, New Hill, NC.
. 1986. Mercury in muscle tissue of fish at Robinson Impoundment in 1985. Carolina Power & Light Company, New Hill, NC.
Swartley, W. A. 1987. Physical properties and flow dynamics of Robinson Impoundment. Carolina Power & Light Company, New Hill, NC. USEPA. 1986. Quality criteria for water. U.3. Environmental Protection Agency, EPA 440/5-86-001, Washington, DC.
. 41
s a Woock, S. E. 1985. Laboratory bioassay studies on bluegili deformities and recruitment at Robinson Impoundment during 1983. Carolina r Power & Light Company, New Hill, NC. k l I I I I I I I I l l l l l u
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E k 500 - 400 - 1975 300 - {=x o 3: 200 - .I i E 100 - 0 . . . . . . . . . . . . Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Doc 700
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[ . 1978 g 300 - 0 $ 200 - E 100 - c ; , O i i . . i i . . . . . . J s.1 Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 2. Gross generation of II. B. Robinson Units 1 and 2,1975-1987. l 44
- 700
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s 8 500 - 3==" 400 - 1979 5 = 300 - 0-l 0 . . . . . . . . . . . . Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 700
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eo S 8 500 - E " 400 - Ew 1982 g 300 - 0 =M 200 - 2 E 100 - - - - 0 . . . . , , , . . . . . Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 2. Cont'd.
. 45
I 700 e g 600 -
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;I Figure 5. Comparison of current NPDES permit temperature limits and proposed temperature limits.
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I O DISTANCE (m) Figure 7. Cont'd. g ss
PHY'i O PL ANKTON 9 9 I 4 8-S- E - e E 47-y i p a " I 7-6- N
---G--- A2 7 + E2 ---o--- E2 A G2 ---*- G2
$ , , , , , , , , . . , , 6 . . . > ' ' '
Jan Feb Mar Apr MayJun Jul Aug Sep Oct Nov Dec 1980 1981 1982 1983 1985 1986 1987 hth ' i ZOOPLANKTON 12 12 g3 ~ ~ N LI . 1 "-
. 10 -
' =
%4 %
9- 10 - en p L a 3 , r g-
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7-
---#~~ A2 ___g _ A2
---0--- E2 -.- o E2 A G2 A G2 6 , i i i > > + ' ' ' ' ' 8 ' ' ' ' ' '
Jan Feb Mar Apr MayJun Jul Aug Sep Oct Nov Dec 1980 1981 1982 1983 1985 MB N Month -I Figure 8. Phytoplankton and zooplankton density by month (all years combined) and year fall I months combined) from Robinson Impoundment,19801987, I 56
I !! Transect A i 80 = = ! ._ ; 60 - , il 1983 1904 1985 1906 ' Years Transact E g y 60 - 7g
,. b 20 -
1 1983 1984 1985 1986 Years W Spnng O Sumrner 23 Figure 9. Illomass of Elcocharis baldwinil from Transer's A and E in Robinson Impoundment,19831986, S7
Total larval fish
; Trarsect A g n'E ; Trar. sect E lW g 8- a Transact G E '
E6 2 " g j '- D Wl a 2I ; O O - . . E i 1977 1979 1981 1983 1985 1987 Year I Lepomis larvao a n = Transect A E o Transed E g 8- A Transed G 5 E 6-2 - a 3 k _ f.f s! I
- 0. u , , ,
1977 1979 1981 1983 1985 1987 Year Largemouth bass larvae 0.S I # Z 0.4 - c,
- Transact A Transect E Transsct G
)
I _E 0.3 - 0.2-c a 0.1-j a-- n
~
0.0 b 1977 1979 1981 1983 1985 1987 Year Figure 10. Mean log density of total larval fish, Lepomis larvae, and largemouth bass larvae in Robinson Impoundment,19771987. 58
I 140000
~
--o-- Transect A I 120000* w Transect E Transect G A
E 100000-I i
.c S0000-60000-E -
h40000- . i I 20000 l'Q 0 r
.e i i i Y- ,
1977 1979 1981 1983 1985 1987 Year I 400
--*-- Transect A
- Transect E
- Transect G g 300-e E
I u 8, 200-
= -
x 100 y-4 0: . l 1977 1979 1981 1983 1985 1987 Year l Figure 11. Total number and weight (Kg) per hectare af all Ush by transect in Robinson impoundment, 1977-1987. I 59
i l
! l
$ D To'al Fish y,. . )
g Blu0 gill > 60 mm 3., 4 c 0 Bluegili < so mm - 1+
, w ,
m
.I $1 40000-c.
+
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Year b 6 [' 300
;ii O Total Fish Ue E Bluegill > 60 mm c D Bluegin < 60 mm l^ a 200-0- Ajb.
gr) -
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.c cn
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->> 34
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i-I 3: 0- , , , 1977 1979 1981 1963 1985 1987 L Year L a m Figure 12. Total number (above) and weight (below) per hectare of all fish, bluegill > 60 mm, and bluegill < 60 mm from Robinson Impoundment, 1977-1987. 60 I
7 r I 1200
! ;; Transect A e 1000.'
i 3 . : Transect E W BOO- A Transect G
, c ,
E 3 COO-g a , y, 3 400- _ 200 ' L 0 7 - y - I 1977 1979 1981 1983 1985 1987 Year
.I 50 -
I
--o- Transect A j 40 - ; Transect E
.I '
a Transect G g 30 - /
'I m 5 .O-M I g
L- ) ~ l 1977 1979 1981 1983 1985 1987 Year LI 600 30 o iI
- $ 500 - --o-- Total nurrber 5 g
- - Total wog51 j
.c 400" -20 ,
.$. 300 - g4 1 ,
$ 200 -10 e _ -
i.I $ '**)F ? ? O , , , , go 1977 1979 1981 1983 1985 1987 [-
!.:. Year Figure 13. Total number and weight (Kg) per hectare oflargemouth bass by transect and year in Robinson Impoundment,19771987. ~
I 61
. ~ ,
~ A2 82 C2 D1 E1 F2 G2 ~ 1- ,- ,
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2./ ,' /N ' 3 s.
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[ 5- / P, ~ ~ U so e- _ JAugust 14,1985 - 10 - 11-12 - 13 A2 82 C2 01 E1 F2 f f f G2 f ? 1 t
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13
-ff l h area optimal for fish Figure 14. Isotherms (32" 38 C) and dissolved oxygen (4.0 mg/l) from Robinson Impoundment during August 1985,1986, and 1987, indicating areas optimal for fish.
62 _ . _ _ - - _ - _ _ ______-__- -_ - - - - -}}