ROXBORO STEAM ELECTRIC PLANT RISK CLASSIFICATION

Transcription

1 ROXBORO STEAM ELECTRIC PLANT RISK CLASSIFICATION Apprx. lcatin f Unnamed Eastern Extensin Impundment Rxbr Steam Electric Plant Overall Risk Classificatin DEQ has prpsed the risk classificatin fr the East Ash Pnd as LOW TO INTERMEDIATE. Grundwater Key Factr. If either it is determined that n receptr is impacted by the cal ash impundments r alternate water is made available t all residents whse wells are being impacted by cal ash impundments, the verall grundwater risk wuld be lw. Based n the infrmatin received t date, there appears t be n dwngradient receptrs lcated 1,500 feet dwngradient f the impundment cmpliance bundary. The fllwing data gaps related t grundwater uncertainty include: Additinal areas adjacent t the current impundment may cntain CCR and wuld therefre require additinal assessment. Incmplete capture zne mdeling in fractured bedrck fr upgradient and side-gradient supply wells in the immediate vicinity f the impundment Incmplete gechemical mdeling Rxbr Steam Electric Plant Page 70 f 148 January 29, 2016

2 Incmplete backgrund cncentratin determinatin (It shuld be nted that the data gaps are currently being addressed by Duke Energy and their findings will be presented t the DEQ in supplemental reprts.) Surface Water Key Factr. The impundment is nt lcated within the 100-year fldplain. Dam Safety Key Factr. The impundment received a lw risk ranking befre any repairs are made. DEQ has prpsed the risk classificatin fr the West Ash Pnd as LOW. Grundwater Key Factr. Based n the infrmatin received t date, there appears t be n dwngradient receptrs lcated 1,500 feet dwngradient f the impundment cmpliance bundary. Surface Water Key Factr. The impundment is nt lcated within the 100-year fldplain. Dam Safety Key Factr. The impundment received a high risk ranking befre any repairs are made and a lw risk rating nce repairs are made and the impundments have been dewatered. DEQ has prpsed the risk classificatin fr the Unnamed Eastern Extensin Impundment as INTERMEDIATE. Grundwater Key Factr. If either it is determined that n receptr is impacted by the cal ash impundments r alternate water is made available t all residents whse wells are being impacted by cal ash impundments, the verall grundwater risk wuld be lw. Based n the infrmatin received t date, there appears t be n dwngradient receptrs lcated 1,500 feet dwngradient f the impundment cmpliance bundary. The fllwing data gaps related t grundwater uncertainty include: This impundment was just recently identified by Duke Energy and assessment is currently underway. The lcatin f the impundment is in clse prximity t ptential receptrs. (It shuld be nted that the data gaps are currently being addressed by Duke Energy and their findings will be presented t the DEQ in supplemental reprts.) Surface Water Key Factr. The impundment is nt lcated within the 100-year fldplain. Dam Safety Key Factr. This impundment des nt have a dam and was therefre nt given a rank with respect t dam safety. Rxbr Steam Electric Plant Page 71 f 148 January 29, 2016

3 Cal Ash Plant, Operatins, and CCR Impundment Descriptin Summary (frm CSA Reprt) NPDES Permit N.: NC Cunty: Persn Plant Status: Operating Number f Impundments: 3 (East Ash Pnd, West Ash Pnd, Unnamed Eastern Extensin Impundment) The Site is a cal-fired electrical pwer generatin facility lcated n a 6,095 acre parcel in nrth-central Nrth Carlina near Semra, in Persn Cunty, Nrth Carlina. The Site is lcated between McGhees Mill Rad t the east and Hyc Reservir. A large part f the Plant area encmpasses the east bank f Hyc Reservir. Plant peratins began at the Site in 1966, and additinal units were added in 1968, 1973, and Thrughut its peratinal histry, the Site has emplyed cal-fired units t prduce steam. Ash generated frm cal cmbustin has been stred n-site in ash basins and lined and unlined landfills. CCRs have been sluiced t the ash basins r cnveyed in its dry frm t the landfills. Tw ash basins areas have been used at the Rxbr Plant and are referenced using the dates f cnstructin and relative lcatin: the 1966 semiactive East Ash Basin and the 1973 active West Ash Basin. The East Ash Basin is lcated sutheast f the pwer generatin facilities, and the West Ash Basin is lcated suth f the pwer generatin facilities. An unlined landfill was cnstructed n the East Ash Basin in the late 1980s. A lined landfill was subsequently cnstructed ver the unlined landfill in The ash basins are impunded by earthen dams. Surface water runff frm the East Ash Basin and the lined landfill are ruted int the West Ash Basin t allw settling. Currently, the East Ash Basin and lined landfill are cvered with vegetatin where the landfill is nt active (grasses and shrubs). The West Ash Basin has sme grass cver and pnded water, mstly alng the suthern and eastern edges f the basin. A FGD System is present within the 1973 Active Ash Basin ftprint. The FGD system directs flue gas int an absrber where limestne (calcium carbnate) slurry is sprayed. Sulfur dixide in the flue gas reacts with the limestne slurry t prduce calcium sulfate, r gypsum. The system reclaims the un-reacted limestne slurry t be reused in the absrber. A small blwdwn stream is used t maintain the chlride cncentratin in the reactin tank. The blwdwn stream is discharged t a lined gypsum settling pnd where suspended slids are settled ut prir t entering a bireactr. The bireactr utilizes micrbes t reduce targeted sluble cntaminants t insluble frms that then precipitate frm slutin. The treated wastewater enters the ash basin effluent channel prir t Internal Outfall 002. Wastewater discharges frm the facility are permitted by the DWR under NPDES Permit NC In late 2015, Duke Energy identified a new basin just east f the East Ash Basin. DEQ has temprarily named this basin the Unnamed Eastern Extensin Impundment. This basin appears t be a frmer extensin f the East Ash Basin Rxbr Steam Electric Plant Page 72 f 148 January 29, 2016

4 that was cut ff when the landfill was created ver the East Ash Basin. Duke Energy is currently in the prcess f addressing this new basin. Surce Characterizatin Summary (frm CSA Reprt) Cal Ash. The ash samples frm bth basins were fund t cntain barium, beryllium, cpper, lead, mercury and selenium abve the RSL Prtective f Grundwater. Cncentratins f aluminum, cbalt, irn, manganese and vanadium were detected in ash basin samples abve the residential health RSL; hwever irn and manganese were nt detected abve RSLs in the West Ash Basin. Ash Leachate. Leachate cncentratins exceeding 2L Standard r IMAC fr antimny, arsenic, chrmium, cbalt, irn, manganese, nitrate, and vanadium in samples frm bth ash basins. Ash Pre Water. Antimny, arsenic, brn, cbalt, irn, manganese, sulfate, thallium, ttal disslved slids, and vanadium were detected in ash pre water samples frm bth the ash basins abve the crrespnding 2L Standard r IMAC. Grundwater Risk Classificatin Key Factr Based n the data prvided in CSA Reprt and results f the grundwater mdeling results presented in the CAP Reprt, the number f dwn-gradient receptrs (well users) 1500 feet frm the cmpliance bundary that are ptentially r currently knwn t be expsed t impacted grundwater frm surce(s) r migratin pathways related t the CCR impundments: East Ash Pnd. LOW RISK. There are n reprted supply wells within 1500 feet dwngradient f the impundment cmpliance bundary. West Ash Pnd. LOW RISK. There are n reprted supply wells within 1500 feet dwngradient f the impundment cmpliance bundary. Unnamed Eastern Extensin Impundment. LOW RISK. There are n reprted supply wells within 1500 feet dwngradient f the impundment cmpliance bundary. Rxbr Steam Electric Plant Page 73 f 148 January 29, 2016

5 Surface Water Risk Classificatin Key Factr The NC fldplain map depicts a 100-year fld elevatins within the west CCR impundment. The west CCR impundment and Hyc Lake fld elevatins are predicted t be 462 and 413 feet abve sea level, respectively. Hwever, this ash basin is cntained by a stream valley embankment (dam) with a discharge canal that cnveys wastewater frm the ash basin t Hyc Lake. This canal als cnveys ffsite (upstream) water arund the west ash basin and int Hyc Lake. Because the basin ftprint is nt lcated alng a run f a river fldplain the risk classificatin is Lw fr the Landscape Psitin and Fldplain criteria [Nte: Dam Safety Risk Classificatin sectin addresses hydrlgy, hydraulics parameters and ther factrs as they relate t dam safety.] Landscape Psitin and Fldplain: East Ash Pnd. LOW RISK. The CCR impundment is sited in a natural drainage way, it is sited alng a reservir and it is nt lcated within a 100 year fldplain. West Ash Pnd. LOW RISK. The ftprint f the CCR impundment is in Sargents Creek a natural drainage way. The NC fldplain map depicts a100-year fld elevatin t ccur within the ash impundment. (The CCR impundment and Hyc Lake fld elevatins are predicted t be 462 and 413 feet abve sea level, respectively.) This West Ash Pnd CCR impundment is sited alng a reservir, is in drainage way, has a 70 ft tall embankment, has an utfall and is designed t discharge int Hyc Lake, a reservir. Rxbr Steam Electric Plant Page 74 f 148 January 29, 2016

6 Unnamed Eastern Extensin Impundment. LOW RISK. The CCR impundment is sited in a natural drainage way, it is sited alng a reservir and it is nt lcated within a 100 year fldplain. Dam Safety Risk Classificatin Key Factr State f Structural Stability and Maintenance: East Ash Pnd (PERSO-033). LOW RISK. This impundment received a ntice f inspectin. The fllwing mdificatins/repairs t the dam have been submitted and shuld be cmpleted, as a minimum: tree remval and pipe remval. West Ash Pnd (PERSO-038 & PERSO-039). HIGH RISK befre repairs are made. LOW RISK after repairs are made. This impundment received a ntice f deficiency with structural deficiencies. The fllwing mdificatins/repairs t the dam have been submitted and shuld be cmpleted, as a minimum: tree remval, slpe repair, slpe mdificatin, grut pipe, and installatin f a new spillway. Unnamed Eastern Extensin Impundment. N/A. This impundment des nt have a dam and was therefre nt given a rank with respect t dam safety. Rxbr Steam Electric Plant Page 75 f 148 January 29, 2016