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HomeMy WebLinkAboutNC0004979_Assessment Report_20100311PDuke CORPORATE EHS SERVICES Energy® Duke Energy Carolinas, LLC Carolinas 526 SOUTH CHURCH STREET CHARLOTTE, NC 28202 Mailing Address: EC13K / P. 0. BOX 1006 CHARLOTTE, NC 28201-1006 March 11, 2010 Mr. Jay Sauber Environmental Sciences Section North Carolina Department of Environment MAR 15 2010 and Natural Resources 1621 Mail Service Center D6_NR-YeATER QUA Raleigh, NC 27699-1621 POINT Sfli3RC� �F3� Subject: Allen Steam Station NP�)5ES Permit No. NC0004979 Balanced and I.ndigenous Populations (BIP) Assessment Report Dear Mr. Sauber: In your letter dated January 13, 2010, you noted during review of the Allen Steam Station BIP Assessment Report one concern regarding the benthic macroinvertebrate community with respect to the variability of the mean and total abundance of the burrowing mayfly Hexagenia spp. between three sample locations near Allen Steam Station. Attached is a written response to further address the benthic macroinvertebrate community and Hexagenia populations in Lake Wylie near Allen Steam Station. The frequency and timing of sampling (mid -summer) is likely a factor influencing the variability of the Hexagenia population data, while substrate between sample locations and water quality from the South Fork River could have also influenced Hexagenia populations. Thus, selection and monitoring of an additional macroinvertebrate sample location between the Upper Armstrong Bridge and Allen Steam Station condenser cooling water discharge at least once during the next five-year monitoring period to document the presence/absence and density of Hexagenia in an upstream area of the South Fork River is recommended. Clarification of water quality statements in Chapter 3 of the BIP report is also included in the attached response with respect to water quality action levels and nutrient standards. If in agreement with the response, please advise a convenient time to coordinate selection of the additional macroinvertebrate sample location with the NCDENR staff. If you have any questions, please contact me at (980)-373-5710. Sincerely, 47.x" ZL't�� Ron Lewis Water Management Attachments xc w/att: Mr. Charles Weaver, NCDENR-DWQ, 1617 Mail Service Center, Raleigh, NC 27699-1617 www.duke-energy.com Response to the North Carolina Department of Environment and Natural Resources (NCDENR) regarding Duke Energy report: "Assessment of balanced indigenous populations in Lake Wylie near Allen Steam Station". November 2009. Addressing concerns regarding Hexazenia populations Overall, mean macroinvertebrate densities within reservoirs may vary substantially among years, locations, and replicates within locations. The observed variability in Lake Wylie macroinvertebrate data during the entire study range (1994 — 2008) is fairly indicative of the inherently variable nature of reservoir macroinvertebrate data (Figure 1). It is important to note that there can be substantial variability in density data among replicates at the same location (Figure 2). This within -location variability is an important consideration when comparing density data among years and locations and assessing community changes relative to induced or naturally occurring effects. High within -location variability diminishes the ability to discern real (or significant) location -to -location differences. The primary variables used in making reservoir assessments are: Total mean densities, total numbers of taxa and, densities of the primary constituents of these benthic communities (Oligochaeta, Diptera, and Corbicula). These three groups were found to comprise from >70% to 100% of benthic macroinvertebrate communities at sampling locations in Lake Wylie. Total numbers of taxa were used as a general indication of overall diversity. Maximum numbers of taxa were most often observed at Location C, downlake from Allen Station (AS), while minimum taxa numbers were generally noted at Location B in the mouth of the AS condenser cooling water discharge canal (Figure 3). As an indicator of diversity, total taxa numbers show minimum impacts from AS thermal discharge at downlake Location C. Densities of the three major constituents also showed substantial spatial and temporal variability (Figures 4 through 6). Diptera were most often dominant at Location A, while Oligochaeta were generally predominant at Locations B and C. Concerning the presence and abundance of Hexagenia, it should be noted that these forms also showed considerable annual, spatial, and within -location variability and were often not found in the discharge (Figures 7 and 8). Looking at historical data back to 1994, Hexagenia showed comparatively low densities at all locations from 1994 through 1996. At Location A, densities increased through 1999, declined substantially in 2000, and then peaked again in 2002. During the most recent study period (2004 — 2008), Hexagenia were collected during three sampling periods at Location C and, on two of those occasions, densities were higher than at Location A, uplake of the station. Also, over a fifteen -year span, Hexagenia numbers showed a substantial decline at both Locations A and C since 2001 — 2002, and during 2004 — 2008 they were generally within historical ranges observed during 1994 —1997. We are aware that Hexagenia do demonstrate sensitivity to a variety of environmental factors including temperature, dissolved oxygen concentrations, and nutrients. We acknowledge that thermal impacts from the operation of AS would have an impact on Hexagenia at Location B. In studies conducted in the 1970's (Industrial Bio -test 1974), sampling was conducted at several locations in the South Fork of the Catawba River, two of which were upstream of the AS discharge. During eight sampling periods over one year (September 1973 — August 1974), Hexagenia were never collected at any location in the South Fork. Additionally, Lenat and Weiss (1973) did not report Hexagenia from the South Fork during their monitoring in 1972. Bio -test investigators also noted that mass emergence at a number of locations in the Catawba River arm of Lake Wylie occurred between May and early July. It is therefore possible, that since our sampling is conducted during mid -summer under "worst case" thermal conditions (i.e., high ambient temperatures), emergence of mayflies downstream of AS could have already occurred resulting in lower numbers, or the absence of Hexagenia in the substrates. Higher numbers and greater frequencies of Hexagenia upstream at Location A may have resulted in later emergence of Hexagenia due to cooler water in this riverine section influenced by the discharge from the Mountain Island Hydroelectric Station. The statement in the macroinvertebrate report that "Substrates were similar at all locations during 2004 — 2008" may have been misleading. Although "varying proportions of silt, sand, and organic matter" were observed, it was noted that "Sand was more prevalent at Locations B and C than at Location A". Therefore, less suitable substrate may also have played a role in lower densities and less frequency of Hexagenia downlake of AS in the Catawba River. In the water quality section of the report, it was stated that Lake Wylie has consistently been classified as eutrophic, as documented by NCDENR (2008a, 2008b) and Mecklenburg County Department of Environmental Protection (Buetow 2008), particularly in certain tributaries such as the South Fork River. Comparatively high nutrient levels may have also played a role in influencing Hexagenia densities not only in the South Fork River, but at Location C just outside the mouth of the tributary. Conclusions We respectfully submit the following conclusions based on the discussion above: 1) The high degree of spatial and temporal variability in macroinvertebrate densities may have been largely due to high levels of within -location variability which tended to mask significant differences among locations and over time; 2) Total numbers of taxa indicated reasonably diverse communities at Locations A and C; 3) The frequency and timing of sampling (mid -summer) is likely a factor influencing Hexagenia populations with respect to overall temperature effects and time of emergence; 4) Substrate variability and suitability, particularly between Locations A and C, would also have an impact on the numbers of Hexagenia at these locations; and 5) The impacts of water quality from the South Fork River could have also influenced populations of Hexagenia at Location C, at the confluence of the South Fork River and Catawba River arms of Lake Wylie. Suggested short -tem change in the study design While thermal inputs from AS would clearly have some impact on Hexagenia populations in the discharge, an effort should be made to determine if viable populations of Hexagenia exist in areas of the South Fork River outside of the influence of the AS discharge. We suggest that an additional macroinvertebrate sampling location between the Upper Armstrong Bridge and the AS discharge (Figure 9) be selected and monitored at least once during the next five-year monitoring period to document the presence/absence and density of Hexagenia in an upstream area of the South Fork River. Comment regarding lake water quality We appreciate your input and acknowledge that the referenced passage (first paragraph on page 3-2) was not adequately clear to the reader. Specifically, the question of the waterbody's (or portions thereof) status over time regarding specific water quality standards (i.e., NC standards for fecal coliform bacteria and chlorophyll a) as well as Mecklenburg County action levels for major nutrients, was combined into a single statement, which would have been more clearly treated as separate but related issues or comparisons. Incidences of excessive chlorophyll and fecal coliform concentrations were indeed documented in the referenced 2008 lake and reservoir assessment document authored by NCDENR (NCDENR 2008a); the other nutrient action level exceedances were documented in a Mecklenburg County DEP staff report (Buetow 2008). Furthermore, we agree that use of the term "nutrient -impaired", should have been avoided, given its common linkage to 303(d) assessments performed exclusively in light of State water quality standards and use attainment. In retrospect, further development of this subsection, including reference to the 2008 Catawba River Basin Ambient Monitoring System Report (NCDENR 2008b) datasets might have helped to further clarify. References Buetow, D. 2008. 2007 Lake Monitoring Report: Mecklenburg County Water Quality Program, SWIM Phase I Part 2 -CO. Mecklenburg County Department of Environmental Protection. Charlotte, NC. Industrial Bio -Test Laboratories, Inc. 1974. A Baseline/predictive environmental investigation of Lake Wylie, Catawba Nuclear Station and Plant Allen. September 1973 — August 1974. Report to Duke Power Company. 743 p. Lenat, DR, and CM Weiss. 1973. Distribution of benthic macroinvertebrates in Lake Wylie, North Carolina — South Carolina. School of Public Health, University of North Carolina at Chapel Hill. ESE Publication No. 311. 75p. NCDENR. 2008a. Lake & reservoir assessments: Catawba River basin. NCDENR, Division of Water Quality, Intensive Survey Unit. June 23, 2008. Raleigh, NC. NCDENR 2008b. Catawba River Basin Ambient Monitoring System Report, January 1, 2003 through December 31, 2007. NCDENR, Division of Water Quality. 83 p. 9,000 8,000 7,000 6,000 {is 5,000 as IM 4,000 12 3,000 2,000 1,000 0 ■ Location A ■ Location B © Location C 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Years Figure 1. Mean densities (no./m2) of macroinvertebrates collected annually at Locations A, B, and C from Lake Wylie near Allen Steam Station from 1994 — 2008. 45,000 40000 35000 cv3000'0 © 25000 r. . 20000 15000 10000 .5000 Macro invertebrate Densities Among Replicates 4 i_ocation A O i_ocation IB &LocationC 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Figure 2. Densities of macroinvertebrates among replicates from sampling locations in Lake Wylie from 1994 — 2008. .I 33 -0 30 ov U a� 0 25 ~ 20 15 10 ■ Location A ■ Location B ❑ Location C 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Years Figure 3. Total number of taxa collected annually at Locations A, B, and C from Lake Wylie near Allen Steam Station from 1994 —2008. Location A Figure 5. Density (no./m) of Oligochaeta, Diptera, and Corbicula collected annually at ■ Corbicula N Diptera o Oiigochaeta 2000 ---------- ------------------------------------------ ------------------------------------------------------- 2,254 2,426 I 3,365 1 800 S -- --------I ---------------------------------------- ------------------------------------------------------- 1 600 S-- -------- ------------------------------------------ ------------------------------------------------------- I.---------------------------------- 1 400 -- -------I ---- ------------------------------------------------------- 1 200-- �°---- I ---- I.--- ----- ------------ ---------- - ----- - - ---------------------- ------------------------- Z, 1 000 - ----- ----- ----- ------ ---------------------------- -------------------- -- 1---- 800 ---- --- ---- ----- ---- ----- 600 -- -- ---- I.--- ---- -- --- ------ ----- --------------------- ----- -------- ---- - �- I------------ 400 -- --- ---- --- - --- �.--- -- ------ ----- ------- -------- - - 200 - -- - l---- G- -- - -- ------- ----- I---- ------ - 1 1 1 1 1 11 !� 1 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Years Figure 4. Density (no./m2) of Oligochaeta, Diptera, and Corbicula collected annually at Location A from 1994 — 2008. Location B ■ Corbicula ■ Diptera © O(igochaeta 2000 ------------------------6,04 ---- -----------6,716 ---� qqq - -- ------------13,94 ------f 6,044---- I i----4,132--- � i 4,873--- 1800 ---- -------------------- -----------' ------------13,947 160o S-- ----------------------------------------------------------------- 1------------- --------------------------------- - 1400 -- ------------------------------ I- --------------------( II I---------- - 1200 -- ------------- --------------- I-------------------- ------------ I---------- --------------- ----- - �.----------- 1 000 -- ------ ---- ----- ------- ------ ------------ ------------------------- - -- - 0 800 -- ------------- --- ------- --- ----- ;--- ------------ -----a -------------------- I--- - 600 - ----- ----- ----- ----- --- ----- !-- ------------ ------ ----------------- I--- 400 --- ----- ----- --------------- ----------- - --- -- ------------- - 200 1---- ----- ---- --- I----- -- (- ►----1-- - ------------ - N.w - ►�� - 0 o 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Years Figure 5. Density (no./m) of Oligochaeta, Diptera, and Corbicula collected annually at Location B from 1994 — 2008. Location C ■ Corbicula ■ Diptera o Oligochaeta 4500 --------------------------------------------=-------------------------------------- 13,432 9,368 I 15,550 Ii 4000 ------------------------------------------------- --------------------------------------------- 3500 ------------------------------------------------- I•-------------------- II---------------------------------- - 3000 ---------------- -------------------------------- I --------------------------- 2500 ------------------------------------------------ I•------------- --- E I--------------------------- ----- - ami 2000 ------------------------------------------------- I.-------------------- ------------------------- i 1 500 ------------------------------------------------- I.--- --- ---- ------------------------ --- - ---- - 1 000 -------------------------------- ------------- I• -- ---- II-- ----------- ---- -- 500-- ----- ------------- -- ----- --- -- �- -- ---- I- ---- -- -- , - 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Figure 6. Density (no./m2) of Oligochaeta, Diptera, and Corbicula collected annually at Location C from 1994 — 2008. Figure 8. Densities of Hexagenia among'replicates at sampling locations in Lake Wylie from 1994 —2008. 9 0 1 2 Niles 0 1 2 3 Kilometers 255.0) i Steam Station Figure 9. Current macroinvertebrate sampling locations (A, B, C) and proposed location upstream of Allen Station (D). r '',