duke energy carolinas, llc dan river steam ...
February 21, 2013
Via email: [email protected]
Mr. Sean DeNeale Duke Energy Carolinas, LLC 400 South Church Street Charlotte, NC 28201-1006 Subject:
Duke Energy Carolinas, LLC Dan River Steam Station Ash Basin - NPDES Permit NC0003468 Proposed Groundwater Assessment Work Plan
Dear Mr. DeNeale: As requested by Mr. Ed Sullivan, P.E., of Duke Energy Carolinas, LLC (Duke Energy), HDR Engineering, Inc. of the Carolinas (HDR) presents the proposed groundwater assessment work plan. The proposed work plan presents the tasks for performing the assessment of the exceedances of the North Carolina Administrative Code Title 15A Chapter 02L .0202 (g) groundwater quality standards measured in groundwater monitoring wells located at the Dan River Steam Station ash basin, located near Eden, North Carolina. The tasks presented in the proposed groundwater assessment work plan were developed from discussions and information provided by Duke Energy personnel and from a meeting on November 19, 2012, between personnel from Duke Energy, the North Carolina Department of Environment and Natural Resources Division of Water Quality Aquifer Protection Section, and HDR. HDR appreciates the opportunity to assist Duke Energy with this project. Should you have any questions regarding this submittal or need further information, please do not hesitate to contact me at (828) 891-6296 or [email protected]. Respectfully submitted, HDR Engineering, Inc. of the Carolinas
William M. Miller, P.E. Senior Engineer Attachments: Duke Energy Carolinas, LLC, Dan River Steam Station Ash Basin, NPDES Permit NC0003468, Proposed Groundwater Assessment Work Plan
DUKE ENERGY CAROLINAS, LLC DAN RIVER STEAM STATION ASH BASIN NPDES PERMIT NC0003468 PROPOSED GROUNDWATER ASSESSMENT WORK PLAN
Prepared for: DUKE ENERGY CAROLINAS, LLC Charlotte, North Carolina
Prepared by: HDR ENGINEERING, INC. OF THE CAROLINAS Charlotte, North Carolina
FEBRUARY 21, 2013
DAN RIVER STEAM STATION ASH BASIN NPDES PERMIT NC0003468 PROPOSED GROUNDWATER ASSESSMENT WORK PLAN TABLE OF CONTENTS Section
Title
Page No.
1.
INTRODUCTION ................................................................................................... 1
2.
SITE DESCRIPTION .............................................................................................. 2 2.1 Plant Description ..........................................................................................................2 2.2 Ash Basin System Description .....................................................................................2
3.
REGULATORY REQUIREMENTS ............................................................................ 3
4.
SITE HYDROGEOLOGY ........................................................................................ 4
5.
DESCRIPTION OF GROUNDWATER MONITORING SYSTEM .................................... 6
6.
GROUNDWATER MONITORING RESULTS ............................................................. 8
7.
GROUNDWATER ASSESSMENT WORK PLAN ........................................................ 9
8.
GROUNDWATER ASSESSMENT REPORT AND PROPOSED SCHEDULE .................. 13
9.
REFERENCES ..................................................................................................... 14
Figures 1
SITE LOCATION MAP
2
SITE LAYOUT MAP
DAN RIVER STEAM STATION ASH BASIN NPDES PERMIT NC0003468 PROPOSED GROUNDWATER ASSESSMENT WORK PLAN LIST OF TABLES Table
Title
TABLE 1 - GROUNDWATER SAMPLING REQUIREMENTS TABLE 2 - EXCEEDANCES OF 2L STANDARDS APPENDIX APPENDIX A - EMAIL FROM SHUYING WANG, HYDROGEOLOGIST, NCDENR DIVISION OF WATER QUALITY TO KIM HUTCHINSON, DUKE ENERGY CORPORATION, DATED NOVEMBER 30, 2012
iii
Section 1
Introduction Exceedances of the North Carolina Administrative Code (NCAC) Title 15A Chapter 02L (g) groundwater quality standards (2L Standards) have been measured in groundwater samples collected from groundwater monitoring wells at the Dan River Steam Station ash basin. In a meeting on November 19, 2012, the North Carolina Department of Environment and Natural Resources (NCDENR) Division of Water Quality (DWQ) Aquifer Protection Section (APS) requested that Duke Energy Carolinas, LLC (Duke Energy) perform an assessment of groundwater exceedances of the 2L Standards at their Dan River Steam Station ash basin. The email summary of this meeting is included as Appendix A.
Duke Energy requested that HDR Engineering, Inc. of the Carolinas (HDR) prepare a groundwater assessment work plan for the Dan River Steam Station ash basin on their behalf. This document presents a proposed work plan for performing the groundwater assessment at the monitoring wells with measured exceedances of the 2L Standards.
1
Section 2
Background Duke Energy owns and operates the Dan River Steam Station, near the town of Eden, in Rockingham County, North Carolina (see Figure 1). The steam station has historically generated electricity by burning coal. The station operates two interconnected ash basins as part of its wastewater treatment system. Coal ash from the coal combustion process has historically been sluiced to the station’s ash basin. The discharge from the ash basin is permitted by the National Pollution Discharge Elimination System (NPDES) Permit No. NC0003468 issued September 1, 2010.
Condition A (11) of the NPDES permit requires groundwater monitoring to be performed around the ash basin. Attachment XX to the NPDES permit lists the groundwater monitoring wells that are required to be sampled, the constituents to be analyzed, and requirements for the sampling frequency and reporting of sampling results. The NPDES permit requires these monitoring wells be sampled three times a year with the analytical results submitted to the DWQ. Groundwater monitoring has been performed since January 2011 in accordance with the permit conditions.
1
Section 3
Site Description 3.1
Plant Description
Dan River Steam Station is a coal-fired generating facility located near the town of Eden in Rockingham County, North Carolina.
The three-unit station began commercial operation in
1949. All three coal-fired units, along with three oil-fired combustion turbine units were retired in 2012. The Dan River Combined Cycle Plant, a 620-megawatt natural gas facility that was recently constructed at the site, has began commercial operations December 10, 2012. The site is located on the north bank of the Dan River, as shown on Figure 1.
3.2
Ash Basin System Description
The ash basin system is located adjacent to the Dan River and consists of a Primary Cell, a Secondary Cell, and associated embankments and outlet works, as shown on Figure 2. The ash basin is impounded by earthen dikes and an earthen/ash divider dike separates the Primary Cell from the Secondary Cell. The Primary Cell lies at an elevation of approximately 535 feet and has a surface area of approximately 21.8 acres. The Secondary Cell lies at an elevation of approximately 527 feet and has a surface area of approximately 12.2 acres. The approximate elevation of the Dan River, adjacent to monitoring well MW-22, is 482 feet. The original ash basin was constructed in 1956 and laterally expanded in 1967. In 1980 the height of the earthen dikes was raised and an intermediate dike was constructed to form the current Primary Cell and Secondary Cell.
The ash basin is an integral part of the station’s
wastewater treatment system. During operation of the coal-fired units, the ash basin received inflows from the following:
Ash removal system
Station yard drain sump
Stormwater flows
The discharge from the ash basin is conveyed to the Dan River through the Secondary Cell discharge tower. 2
Section 4
Regulatory Requirements The NPDES program regulates wastewater discharges to surface waters to ensure that surface water quality standards are maintained. The Dan River Steam Station operates under NPDES Permit No. NC0003468, which authorizes discharge of cooling water (Outfall 001) and ash basin discharge (Outfall 002) to the Dan River in accordance with effluent limitations, monitoring requirements, and other conditions set forth in the permit. In addition to surface water monitoring, the NPDES permit requires groundwater monitoring to be conducted. Permit condition A(11), Attachment XX, Version 1.1, dated June 15, 2011, to the NPDES permit lists the groundwater monitoring wells to be sampled, the parameters to be analyzed, and the requirements for sampling frequency and reporting the results.
These
groundwater monitoring requirements are listed in Table 1. The groundwater monitoring wells, required by the NPDES permit, were installed by Duke Energy in 2010 and 2011.
The locations for the monitoring wells were approved by the
NCDENR DWQ APS. These monitoring wells are sampled three times a year and the analytical results are submitted to the DWQ. The compliance boundary for groundwater quality at the Dan River Steam Station ash basin site is defined in accordance with NCAC Title 15A Chapter 02L .0107(a) as being established at either 500 feet from the waste or at the property boundary, whichever is closest to the waste. The location of the monitoring wells, the waste boundary, and the compliance boundary are shown on Figure 2.
3
Section 5
Site Hydrogeology Dan River Steam Station and the ash basin are located within the Dan River Triassic Basin in the Piedmont physiographic province (Piedmont). The bedrock in Triassic Basin generally consists of conglomerate, sandstone, and mudstones with intrusive diabase dikes and sills. The following generalizations on the site hydrogeology are taken from A Master Conceptual Model for Hydrogeological Site Characterization in the Piedmont and Mountain Region of North Carolina (LeGrand 2004).
Piedmont bedrock primarily consists of igneous and metamorphic bedrock.
The fractured
bedrock is overlain by a mantle of unconsolidated material known as regolith. The regolith includes, where present, the soil zone, a zone of weathered, decomposed bedrock known as saprolite, and alluvium, where present. Saprolite, the product of chemical and mechanical weathering of the underlying bedrock, is typically composed of clay and coarser granular material up to boulder size, and may reflect the texture of the rock from which it was formed. The weathering product of granitic rocks may be quartz-rich and sandy-textured, whereas rocks poor in quartz and rich in feldspar and other soluble minerals form a more clayey saprolite. The regolith serves as the principal storage reservoir for the underlying bedrock (LeGrand 2004).
A transition zone may occur at the base of the regolith between the soil-saprolite and the unweathered bedrock. This transition zone of partially weathered rock is a zone of relatively high permeability compared to the overlying soil-saprolite and the underlying bedrock (LeGrand 2004).
Groundwater flow paths in the Piedmont are almost invariably restricted to the zone underlying the topographic slope extending from a topographic divide to an adjacent stream. LeGrand describes this as the local slope aquifer system. Under natural conditions the general direction of groundwater flow can be approximated from the surface topography (LeGrand 2004).
4
Section 5
Site Hydrogeology
Groundwater recharge in the Piedmont is derived entirely from infiltration of local precipitation. Groundwater recharge occurs in areas of higher topography (i.e., hilltops) and groundwater discharge occurs in lowland areas bordering surface water bodies, marshes, and floodplains (LeGrand 2004).
The site is bounded to the southeast by the Dan River, which flows from southwest to northeast along the ash basin dike. Two unnamed tributaries of the Dan River are located along the eastern and western sides of the site property.
A surface water divide is located generally along
Edgewood Road, with surface water on the east side of Edgewood Road draining towards the unnamed tributary located on the east side of the property and surface water on the west side of Edgewood Road draining towards the unnamed tributary located to the west of the property. The ground surface elevations at the site range from approximately 600 feet along Edgewood Road along the northern property line to approximately 482 feet along the Dan River.
5
Section 6
Description of Groundwater Monitoring System As discussed in Section 3, groundwater monitoring is performed in accordance with the requirements of the NPDES permit. The groundwater monitoring system for the ash basin system consists of the following monitoring wells: MW-20S, MW-20D, MW-21S, MW-21D, MW-22S, MW-22D, and MW-23D. These wells are sampled in January, May, and September. The locations for the monitoring wells were selected in consultation with the NCDENR DWQ APS. The location of the monitoring wells, waste boundary, and compliance boundary are shown on Figure 2. Monitoring wells MW-20S and MW-21S were installed to monitor the surficial aquifer. These wells were installed by rotary drilling methods using hollow stem augers, with the well screen installed above auger refusal to monitor the shallow aquifer within the saprolite layer. These wells were installed with screen lengths of 15 feet and 5 feet, respectively. The wells were installed with the screen interval for MW-20S from 4 feet to 19 feet below ground surface (bgs) and the screen interval for MW-21s from 3.5 feet to 8.5 feet bgs. Monitoring wells MW-20D and MW-21D were installed to monitor the transition zone of the surficial aquifer. These monitoring wells were installed by rotary drilling methods using hollow stem augers and by rock coring techniques (HQ diameter barrel) with the well screen installed in the uppermost region of the fractured rock transition zone. These wells were installed with 5foot-long screens. The wells were installed with the screen interval for MW-20D from 36.5 feet to 41.5 feet bgs and the screen interval for MW-21D from 13.6 feet to 18.6 feet bgs. Monitoring wells MW-22S and MW-22D are located at the toe of the earthen dike impounding the Primary Cell, where large diameter stone prevented installation by the drilling techniques used for the wells mentioned above. These wells were installed by using an air-powered ODEX drilling system. Well MW-22S was installed to monitor the surficial aquifer with a 10-foot-long screen from 12.35 feet to 22.35 feet bgs. MW-22D was installed to monitor the transition zone and was installed with a 5-foot-long screen from 31.95 to 36.95 feet bgs.
6
Section 6
Description of Groundwater Monitoring System
Monitoring well MW-23D is located approximately 3,100 feet northwest of the ash basin and is considered (by Duke Energy) to represent background water quality at the site. MW-23D was installed by rotary drilling methods using hollow stem augers and by rock coring techniques (HQ diameter barrel) with the well screen installed in the uppermost region of the fractured rock transition zone. This well was installed with a 10-foot-long screen from 6.7 to 16.7 feet bgs. Monitoring wells MW-20S and MW-20D are located north of the ash storage area. Monitoring wells MW-21S and MW-21D are located east of the Secondary Cell. Monitoring wells MW-22S and MW-22D are located south of the Primary Cell. Duke Energy installed monitoring wells MW-8, MW-9, MW-9D, MW-10, MW-10D, MW-11, and MW-11D prior to the installation of the compliance monitoring wells as part of a voluntary monitoring system. These wells are not shown on Figure 2. No samples are currently being collected from these wells.
7
Section 7
Groundwater Monitoring Results With the exception of MW-22S and MW-22D, the monitoring wells at the Dan River Steam Station have been sampled a total of seven times. These monitoring wells were sampled:
January 2011
May 2011
September 2011
January 2012
May 2012
September 2012
January 2013
Sampling at monitoring wells MW-22S and MW-22D began in January 2012. These wells have been sampled a total of four times.
With the exception of antimony, arsenic, boron, iron, manganese, total dissolved solids, sulfate, and pH, the results for all monitored parameters and constituents were less than the 2L Standards.
Table 2 lists the monitoring wells and the range of analytical results for the wells with exceedances of the 2L Standards.
8
Section 8
Groundwater Assessment Work Plan As presented in Table 2, exceedances of 2L Standards for antimony, arsenic, boron, iron, manganese, total dissolved solids, sulfate, and/or pH have been measured at the following monitoring wells: MW-20S, MW-20D, MW-21S, MW-21D, MW-22S, MW-22D, and MW-23D.
The proposed groundwater assessment work plan will evaluate the exceedances of the 2L Standards to determine if the exceedances are naturally occurring, if they are caused by particulate matter which is preserved in the sample as a result of well construction and/or sampling procedures, or if the exceedances can be attributed to impacts from the ash basin.
The groundwater assessment work plan report will include the following tasks: Task 1
Develop a Site Hydrogeologic Conceptual Model - Available reports and data on site geotechnical, geologic, and hydrologic conditions will be reviewed and used to develop a site hydrogeologic conceptual model.
The NCDENR document,
Hydrogeologic Investigation and Reporting Policy Memorandum, dated May 31, 2007, will be used as general guidance. Task 2
Discuss Site History and Land Uses – A discussion of the site history and land uses will be developed.
Task 3
Review Available Data on Ash Basin Water Quality- Available data on ash basin water quality will be reviewed to determine if a suitable “fingerprint” of ash basin water quality can be determined. If a suitable “fingerprint” of ash basin water quality can be determined, the parameters and constituents associated with the “fingerprint” will be used with the analytical results from the monitoring wells to determine if the exceedances in the monitoring wells can be attributed to impacts from the ash basin. This data will be provided by Duke Energy and will include NPDES-related monitoring data and additional data collected by Duke Energy from the ash basin during the May 2013 sampling event.
9
Section 8
Groundwater Assessment Work Plan
The ash basin data will be reviewed relative to groundwater sampling results for constituents included in the ash basin groundwater monitoring program and for major anion and cation data also collected during the May 2013 groundwater sampling event. The groundwater monitoring results at the monitoring wells with exceedances will be compared to the ash basin water quality data by utilizing water quality plots (i.e., Piper diagrams, Stiff diagrams, or others) to understand the possible influence of the ash basin on the groundwater quality at the monitoring wells with exceedances. Task 4
Review Available Ash Leaching Data – Existing results for leaching tests on ash will be reviewed to determine if the existing data can be used as input to the assessment or if additional leaching tests need to be performed. Additional leaching tests will be performed if needed and the results will be included in the assessment.
Task 5
Evaluate Well Construction Information – Well installation records will be reviewed to determine if well construction methods are contributing to the exceedances.
Task 6
Evaluate Exceedances Against Background Well Results – The analytical results from the wells with exceedances will be evaluated against results from the site background well to determine if the exceedances can be attributed to background water quality conditions.
Task 7
Evaluate Exceedances Against Turbidity Values – Exceedances will be evaluated against turbidity values measured during sampling to determine if the exceedances are a result of sediment or particulate matter which is preserved in the sample as a result of well construction or sampling methods.
Task 8
Evaluate Sampling Flow Rates – Sample collection flow rates will be evaluated to determine if the flow rates are affecting results. The use of low flow sampling techniques will be evaluated for selected wells.
10
Section 8
Task 9
Groundwater Assessment Work Plan
Collect and Analyze Filtered and Unfiltered Samples – Groundwater samples collected for compliance monitoring are not filtered in the field. In order to provide additional information for the assessment of exceedances, both unfiltered and filtered samples will be collected and analyzed for antimony, arsenic, iron, and manganese. The field filtration will be performed with an in-line, sealed, 0.45 micron filter.
Task 10
Collect Reduction/Oxidation Field Parameters – Reduction/oxidation (redox) processes can alternately mobilize or immobilize metals associated with naturally occurring aquifer materials. Iron and manganese are commonly associated with lakes and the associated sediments. The redox conditions associated with the aquifer/lake system may be a factor in the concentrations of iron and manganese observed at selected monitoring well locations.
Additional field parameters (i.e., dissolved
oxygen and redox potential) will be collected at selected wells to characterize the redox conditions at these locations. A discussion of the redox conditions at the wells will be provided in the assessment. Task 11
Collect Soil Samples - Analyze for Iron and Manganese Content - Soil samples will be collected from soil borings performed adjacent to monitoring wells MW-20S and MW-21S. One soil sample in each boring will be collected from above the observed water level in the adjacent monitoring well. Up to two soil samples in each boring will be collected from the depth of the screened interval in the adjacent well (within the shallow aquifer). The samples will be collected from different soil types where applicable. The borings will be logged for soil lithology by a Professional Geologist. The soil samples will be analyzed for total concentrations of iron and manganese, cation exchange capacity, redox potential, nitrate, sulfate, and pH. A discussion of the iron and manganese concentrations measured in the soils will be provided.
Task 12
Collect Surface Water Samples from the Dan River – Surface water samples will be collected from the Dan River and will be used in the evaluation of the exceedances in MW-22S and MW-22D. These samples will be collected from two locations; one
11
Section 8
Groundwater Assessment Work Plan
location will be upstream of MW-22S and MW-22D and the other location will be adjacent to the wells. Task 13
Collect Surface Water Samples and Sediment Samples from the Unnamed Tributary near MW-21S and MW-21D – Surface water and sediment samples will be collected from the unnamed tributary near MW-21S and MW-22D. The surface water and sediment samples will be used in the evaluation of the exceedances in MW21S and MW-21D. These samples will be collected from two locations; one location will be upstream of MW-21S and MW-21D and the other location will be adjacent to the wells.
Task 14
Perform Statistical Data Analyses of the Sampling Results – Statistical analyses of groundwater monitoring results will be performed to determine if the exceedances can be attributed to the ash basin water quality or if the exceedances can be attributed to naturally occurring background concentrations.
The NCDENR document,
Evaluating Metals in Groundwater at DWQ Permitted Facilities: A Technical Assistance Document for DWQ Staff, dated July 2012, will be used as general guidance. In addition to these tasks, HDR understands that Duke Energy will add total suspended solids to the list of analysis parameters for groundwater samples and will continue to analyze groundwater samples for total dissolved solids.
12
Section 9
Groundwater Schedule
Assessment
Report
and
Proposed
The groundwater assessment report will present results of the work proposed in Section 8.
After NCDENR has approved this proposed plan, the proposed schedule is to submit the groundwater assessment report approximately 120 days after the next scheduled groundwater sampling event at Dan River Steam Station.
The groundwater assessment report will be
submitted 150 days after the next scheduled groundwater sampling event if redevelopment of one or more of the monitoring wells is required. The next sampling event at Dan River Steam Station will occur in May 2013.
13
Section 9
References Harry E. LeGrand.
2004.
A Master Conceptual Model for Hydrogeological Site
Characterization in the Piedmont and Mountain Region of North Carolina, A Guidance Manual, North Carolina Department of Environment and Natural Resources Division of Water Quality, Groundwater Section.
14
FIGURES
Dr
600
60 0
600
600
Eden
S Edgewood Rd
um
600
E
i S ta d
0 60
60 0
600 600
60 0
50 0
500
0 60
Ash Basin 500
500 600
Dan River Steam Station
S Van Buren Rd
500
600
0 50
600
600
Ri
ve
r
600
600
an D 0 50
600
0
1,000
600
500
600
600
Notes: 1. Sources: US Topo; 2011, USGS National Map Aerial Imagery; 2010 North Carolina Statewide Orthoimagery, NC Geospatial & Technology Management Office SCALE (FEET)
600
600
500
500
600
600
50 0
0 60
14 U V
1,000
0 50
0 60
60 0
2,000 DATE
0 60
HDR Engineering, Inc. of the Carolinas License Number: F-0116 440 South Church Street, Charlotte, NC 28202
SITE LOCATION MAP DAN RIVER STEAM STATION DUKE ENERGY CAROLINAS, LLC ROCKINGHAM COUNTY, NORTH CAROLINA
1
February21, XX,2013 2013 February FIGURE
600
TABLES
TABLE 1 - GROUNDWATER SAMPLING REQUIREMENTS Well Nomenclature
Monitoring Wells: MW-20S, MW-20D, MW-21S, MW-21D, MW-22S, MW-22D, MW-23
Parameter Description
Frequency
Antimony
Chromium
Nickel
Thallium
Arsenic
Copper
Nitrate
Water Level
Barium
Iron
pH
Zinc
Boron
Lead
Selenium
Cadmium
Manganese
Sulfate
Chloride
Mercury
TDS
January, May, September
TABLE 2 - EXCEEDANCES OF 2L STANDARDS 2L Standard
Well ID
Antimony*
Arsenic
Boron
Iron
Manganese
TDS
Sulfate
pH
1 µg/L
10 µg/L
700 µg/L
300 µg/L
50 µg/L
500 mg/L
250 mg/L
6.5 - 8.5 SU
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
µg/L
µg/L
µg/L
µg/L
µg/L
µg/L
µg/L
SU
MW-20S
1.04
No Exceedances
No Exceedances
2,350 - 3,190
864 - 945
No Exceedances
No Exceedances
5.9 - 6.2
MW-20D
No Exceedances
No Exceedances
No Exceedances
No Exceedances
489 - 519
No Exceedances
No Exceedances
No Exceedances
Comments Concerning Exceedances
Iron and Manganese concentrations have been generally consistent over the period of monitoring. Antimony has been below the 2L and MRL of 1.0 µg/L except during one (May 2012) sample event. pH has been generally consistent over the period of monitoring. Manganese concentrations have been generally consistent over the period of monitoring.
MW-21S
1.02 - 1.33
25.2 - 44.7
No Exceedances
No Exceedances
306 - 668
No Exceedances
No Exceedances
No Exceedances
Arsenic concentrations have been generally consistent. January 2013 sample event (25.2 µg/L) is the lowest arsenic concentration measured over period of monitoring. Manganese concentrations have generally increased from a low concentration in January 2011 (306 µg/L) to 668 µg/L in January 2013. Antimony has been >2L during four events and <MRL during three events including the last 2 sample events.
MW-21D
No Exceedances
No Exceedances
No Exceedances
No Exceedances
901 - 1,050
643 - 770
310 - 350
No Exceedances
Manganese, TDS, and sulfate concentrations have been generally consistent over the period of monitoring.
No Exceedances
Iron concentration in January 2013 sample event (13,900 µg/L) is the lowest concentration measured over period of monitoring. Manganese results have been generally increasing over the period of monitoring.
MW-22S
No Exceedances
No Exceedances
No Exceedances
13,900 - 19,400
701 - 806
No Exceedances
No Exceedances
MW-22D
1.06 - 1.60
No Exceedances
711 - 793
829 - 1,010
145 - 261
No Exceedances
No Exceedances
No Exceedances
MW-23D
No Exceedances
No Exceedances
No Exceedances
326 - 1,700
192 - 468
No Exceedances
No Exceedances
5.9 - 6.3
* Interim Maximum Allowable Concentration.
Boron concentrations have been generally consistent over the period of monitoring. Three out of the four sample results for Boron >2L. Iron and Manganese concentrations may be affected by turbidity. The two iron and manganese 2L exceedances are coincident with the high turbidity readings in January 2012 (80 NTU) and September 2012 (53.5). The two sampling events with turbidity
Via email: [email protected]
Mr. Sean DeNeale Duke Energy Carolinas, LLC 400 South Church Street Charlotte, NC 28201-1006 Subject:
Duke Energy Carolinas, LLC Dan River Steam Station Ash Basin - NPDES Permit NC0003468 Proposed Groundwater Assessment Work Plan
Dear Mr. DeNeale: As requested by Mr. Ed Sullivan, P.E., of Duke Energy Carolinas, LLC (Duke Energy), HDR Engineering, Inc. of the Carolinas (HDR) presents the proposed groundwater assessment work plan. The proposed work plan presents the tasks for performing the assessment of the exceedances of the North Carolina Administrative Code Title 15A Chapter 02L .0202 (g) groundwater quality standards measured in groundwater monitoring wells located at the Dan River Steam Station ash basin, located near Eden, North Carolina. The tasks presented in the proposed groundwater assessment work plan were developed from discussions and information provided by Duke Energy personnel and from a meeting on November 19, 2012, between personnel from Duke Energy, the North Carolina Department of Environment and Natural Resources Division of Water Quality Aquifer Protection Section, and HDR. HDR appreciates the opportunity to assist Duke Energy with this project. Should you have any questions regarding this submittal or need further information, please do not hesitate to contact me at (828) 891-6296 or [email protected]. Respectfully submitted, HDR Engineering, Inc. of the Carolinas
William M. Miller, P.E. Senior Engineer Attachments: Duke Energy Carolinas, LLC, Dan River Steam Station Ash Basin, NPDES Permit NC0003468, Proposed Groundwater Assessment Work Plan
DUKE ENERGY CAROLINAS, LLC DAN RIVER STEAM STATION ASH BASIN NPDES PERMIT NC0003468 PROPOSED GROUNDWATER ASSESSMENT WORK PLAN
Prepared for: DUKE ENERGY CAROLINAS, LLC Charlotte, North Carolina
Prepared by: HDR ENGINEERING, INC. OF THE CAROLINAS Charlotte, North Carolina
FEBRUARY 21, 2013
DAN RIVER STEAM STATION ASH BASIN NPDES PERMIT NC0003468 PROPOSED GROUNDWATER ASSESSMENT WORK PLAN TABLE OF CONTENTS Section
Title
Page No.
1.
INTRODUCTION ................................................................................................... 1
2.
SITE DESCRIPTION .............................................................................................. 2 2.1 Plant Description ..........................................................................................................2 2.2 Ash Basin System Description .....................................................................................2
3.
REGULATORY REQUIREMENTS ............................................................................ 3
4.
SITE HYDROGEOLOGY ........................................................................................ 4
5.
DESCRIPTION OF GROUNDWATER MONITORING SYSTEM .................................... 6
6.
GROUNDWATER MONITORING RESULTS ............................................................. 8
7.
GROUNDWATER ASSESSMENT WORK PLAN ........................................................ 9
8.
GROUNDWATER ASSESSMENT REPORT AND PROPOSED SCHEDULE .................. 13
9.
REFERENCES ..................................................................................................... 14
Figures 1
SITE LOCATION MAP
2
SITE LAYOUT MAP
DAN RIVER STEAM STATION ASH BASIN NPDES PERMIT NC0003468 PROPOSED GROUNDWATER ASSESSMENT WORK PLAN LIST OF TABLES Table
Title
TABLE 1 - GROUNDWATER SAMPLING REQUIREMENTS TABLE 2 - EXCEEDANCES OF 2L STANDARDS APPENDIX APPENDIX A - EMAIL FROM SHUYING WANG, HYDROGEOLOGIST, NCDENR DIVISION OF WATER QUALITY TO KIM HUTCHINSON, DUKE ENERGY CORPORATION, DATED NOVEMBER 30, 2012
iii
Section 1
Introduction Exceedances of the North Carolina Administrative Code (NCAC) Title 15A Chapter 02L (g) groundwater quality standards (2L Standards) have been measured in groundwater samples collected from groundwater monitoring wells at the Dan River Steam Station ash basin. In a meeting on November 19, 2012, the North Carolina Department of Environment and Natural Resources (NCDENR) Division of Water Quality (DWQ) Aquifer Protection Section (APS) requested that Duke Energy Carolinas, LLC (Duke Energy) perform an assessment of groundwater exceedances of the 2L Standards at their Dan River Steam Station ash basin. The email summary of this meeting is included as Appendix A.
Duke Energy requested that HDR Engineering, Inc. of the Carolinas (HDR) prepare a groundwater assessment work plan for the Dan River Steam Station ash basin on their behalf. This document presents a proposed work plan for performing the groundwater assessment at the monitoring wells with measured exceedances of the 2L Standards.
1
Section 2
Background Duke Energy owns and operates the Dan River Steam Station, near the town of Eden, in Rockingham County, North Carolina (see Figure 1). The steam station has historically generated electricity by burning coal. The station operates two interconnected ash basins as part of its wastewater treatment system. Coal ash from the coal combustion process has historically been sluiced to the station’s ash basin. The discharge from the ash basin is permitted by the National Pollution Discharge Elimination System (NPDES) Permit No. NC0003468 issued September 1, 2010.
Condition A (11) of the NPDES permit requires groundwater monitoring to be performed around the ash basin. Attachment XX to the NPDES permit lists the groundwater monitoring wells that are required to be sampled, the constituents to be analyzed, and requirements for the sampling frequency and reporting of sampling results. The NPDES permit requires these monitoring wells be sampled three times a year with the analytical results submitted to the DWQ. Groundwater monitoring has been performed since January 2011 in accordance with the permit conditions.
1
Section 3
Site Description 3.1
Plant Description
Dan River Steam Station is a coal-fired generating facility located near the town of Eden in Rockingham County, North Carolina.
The three-unit station began commercial operation in
1949. All three coal-fired units, along with three oil-fired combustion turbine units were retired in 2012. The Dan River Combined Cycle Plant, a 620-megawatt natural gas facility that was recently constructed at the site, has began commercial operations December 10, 2012. The site is located on the north bank of the Dan River, as shown on Figure 1.
3.2
Ash Basin System Description
The ash basin system is located adjacent to the Dan River and consists of a Primary Cell, a Secondary Cell, and associated embankments and outlet works, as shown on Figure 2. The ash basin is impounded by earthen dikes and an earthen/ash divider dike separates the Primary Cell from the Secondary Cell. The Primary Cell lies at an elevation of approximately 535 feet and has a surface area of approximately 21.8 acres. The Secondary Cell lies at an elevation of approximately 527 feet and has a surface area of approximately 12.2 acres. The approximate elevation of the Dan River, adjacent to monitoring well MW-22, is 482 feet. The original ash basin was constructed in 1956 and laterally expanded in 1967. In 1980 the height of the earthen dikes was raised and an intermediate dike was constructed to form the current Primary Cell and Secondary Cell.
The ash basin is an integral part of the station’s
wastewater treatment system. During operation of the coal-fired units, the ash basin received inflows from the following:
Ash removal system
Station yard drain sump
Stormwater flows
The discharge from the ash basin is conveyed to the Dan River through the Secondary Cell discharge tower. 2
Section 4
Regulatory Requirements The NPDES program regulates wastewater discharges to surface waters to ensure that surface water quality standards are maintained. The Dan River Steam Station operates under NPDES Permit No. NC0003468, which authorizes discharge of cooling water (Outfall 001) and ash basin discharge (Outfall 002) to the Dan River in accordance with effluent limitations, monitoring requirements, and other conditions set forth in the permit. In addition to surface water monitoring, the NPDES permit requires groundwater monitoring to be conducted. Permit condition A(11), Attachment XX, Version 1.1, dated June 15, 2011, to the NPDES permit lists the groundwater monitoring wells to be sampled, the parameters to be analyzed, and the requirements for sampling frequency and reporting the results.
These
groundwater monitoring requirements are listed in Table 1. The groundwater monitoring wells, required by the NPDES permit, were installed by Duke Energy in 2010 and 2011.
The locations for the monitoring wells were approved by the
NCDENR DWQ APS. These monitoring wells are sampled three times a year and the analytical results are submitted to the DWQ. The compliance boundary for groundwater quality at the Dan River Steam Station ash basin site is defined in accordance with NCAC Title 15A Chapter 02L .0107(a) as being established at either 500 feet from the waste or at the property boundary, whichever is closest to the waste. The location of the monitoring wells, the waste boundary, and the compliance boundary are shown on Figure 2.
3
Section 5
Site Hydrogeology Dan River Steam Station and the ash basin are located within the Dan River Triassic Basin in the Piedmont physiographic province (Piedmont). The bedrock in Triassic Basin generally consists of conglomerate, sandstone, and mudstones with intrusive diabase dikes and sills. The following generalizations on the site hydrogeology are taken from A Master Conceptual Model for Hydrogeological Site Characterization in the Piedmont and Mountain Region of North Carolina (LeGrand 2004).
Piedmont bedrock primarily consists of igneous and metamorphic bedrock.
The fractured
bedrock is overlain by a mantle of unconsolidated material known as regolith. The regolith includes, where present, the soil zone, a zone of weathered, decomposed bedrock known as saprolite, and alluvium, where present. Saprolite, the product of chemical and mechanical weathering of the underlying bedrock, is typically composed of clay and coarser granular material up to boulder size, and may reflect the texture of the rock from which it was formed. The weathering product of granitic rocks may be quartz-rich and sandy-textured, whereas rocks poor in quartz and rich in feldspar and other soluble minerals form a more clayey saprolite. The regolith serves as the principal storage reservoir for the underlying bedrock (LeGrand 2004).
A transition zone may occur at the base of the regolith between the soil-saprolite and the unweathered bedrock. This transition zone of partially weathered rock is a zone of relatively high permeability compared to the overlying soil-saprolite and the underlying bedrock (LeGrand 2004).
Groundwater flow paths in the Piedmont are almost invariably restricted to the zone underlying the topographic slope extending from a topographic divide to an adjacent stream. LeGrand describes this as the local slope aquifer system. Under natural conditions the general direction of groundwater flow can be approximated from the surface topography (LeGrand 2004).
4
Section 5
Site Hydrogeology
Groundwater recharge in the Piedmont is derived entirely from infiltration of local precipitation. Groundwater recharge occurs in areas of higher topography (i.e., hilltops) and groundwater discharge occurs in lowland areas bordering surface water bodies, marshes, and floodplains (LeGrand 2004).
The site is bounded to the southeast by the Dan River, which flows from southwest to northeast along the ash basin dike. Two unnamed tributaries of the Dan River are located along the eastern and western sides of the site property.
A surface water divide is located generally along
Edgewood Road, with surface water on the east side of Edgewood Road draining towards the unnamed tributary located on the east side of the property and surface water on the west side of Edgewood Road draining towards the unnamed tributary located to the west of the property. The ground surface elevations at the site range from approximately 600 feet along Edgewood Road along the northern property line to approximately 482 feet along the Dan River.
5
Section 6
Description of Groundwater Monitoring System As discussed in Section 3, groundwater monitoring is performed in accordance with the requirements of the NPDES permit. The groundwater monitoring system for the ash basin system consists of the following monitoring wells: MW-20S, MW-20D, MW-21S, MW-21D, MW-22S, MW-22D, and MW-23D. These wells are sampled in January, May, and September. The locations for the monitoring wells were selected in consultation with the NCDENR DWQ APS. The location of the monitoring wells, waste boundary, and compliance boundary are shown on Figure 2. Monitoring wells MW-20S and MW-21S were installed to monitor the surficial aquifer. These wells were installed by rotary drilling methods using hollow stem augers, with the well screen installed above auger refusal to monitor the shallow aquifer within the saprolite layer. These wells were installed with screen lengths of 15 feet and 5 feet, respectively. The wells were installed with the screen interval for MW-20S from 4 feet to 19 feet below ground surface (bgs) and the screen interval for MW-21s from 3.5 feet to 8.5 feet bgs. Monitoring wells MW-20D and MW-21D were installed to monitor the transition zone of the surficial aquifer. These monitoring wells were installed by rotary drilling methods using hollow stem augers and by rock coring techniques (HQ diameter barrel) with the well screen installed in the uppermost region of the fractured rock transition zone. These wells were installed with 5foot-long screens. The wells were installed with the screen interval for MW-20D from 36.5 feet to 41.5 feet bgs and the screen interval for MW-21D from 13.6 feet to 18.6 feet bgs. Monitoring wells MW-22S and MW-22D are located at the toe of the earthen dike impounding the Primary Cell, where large diameter stone prevented installation by the drilling techniques used for the wells mentioned above. These wells were installed by using an air-powered ODEX drilling system. Well MW-22S was installed to monitor the surficial aquifer with a 10-foot-long screen from 12.35 feet to 22.35 feet bgs. MW-22D was installed to monitor the transition zone and was installed with a 5-foot-long screen from 31.95 to 36.95 feet bgs.
6
Section 6
Description of Groundwater Monitoring System
Monitoring well MW-23D is located approximately 3,100 feet northwest of the ash basin and is considered (by Duke Energy) to represent background water quality at the site. MW-23D was installed by rotary drilling methods using hollow stem augers and by rock coring techniques (HQ diameter barrel) with the well screen installed in the uppermost region of the fractured rock transition zone. This well was installed with a 10-foot-long screen from 6.7 to 16.7 feet bgs. Monitoring wells MW-20S and MW-20D are located north of the ash storage area. Monitoring wells MW-21S and MW-21D are located east of the Secondary Cell. Monitoring wells MW-22S and MW-22D are located south of the Primary Cell. Duke Energy installed monitoring wells MW-8, MW-9, MW-9D, MW-10, MW-10D, MW-11, and MW-11D prior to the installation of the compliance monitoring wells as part of a voluntary monitoring system. These wells are not shown on Figure 2. No samples are currently being collected from these wells.
7
Section 7
Groundwater Monitoring Results With the exception of MW-22S and MW-22D, the monitoring wells at the Dan River Steam Station have been sampled a total of seven times. These monitoring wells were sampled:
January 2011
May 2011
September 2011
January 2012
May 2012
September 2012
January 2013
Sampling at monitoring wells MW-22S and MW-22D began in January 2012. These wells have been sampled a total of four times.
With the exception of antimony, arsenic, boron, iron, manganese, total dissolved solids, sulfate, and pH, the results for all monitored parameters and constituents were less than the 2L Standards.
Table 2 lists the monitoring wells and the range of analytical results for the wells with exceedances of the 2L Standards.
8
Section 8
Groundwater Assessment Work Plan As presented in Table 2, exceedances of 2L Standards for antimony, arsenic, boron, iron, manganese, total dissolved solids, sulfate, and/or pH have been measured at the following monitoring wells: MW-20S, MW-20D, MW-21S, MW-21D, MW-22S, MW-22D, and MW-23D.
The proposed groundwater assessment work plan will evaluate the exceedances of the 2L Standards to determine if the exceedances are naturally occurring, if they are caused by particulate matter which is preserved in the sample as a result of well construction and/or sampling procedures, or if the exceedances can be attributed to impacts from the ash basin.
The groundwater assessment work plan report will include the following tasks: Task 1
Develop a Site Hydrogeologic Conceptual Model - Available reports and data on site geotechnical, geologic, and hydrologic conditions will be reviewed and used to develop a site hydrogeologic conceptual model.
The NCDENR document,
Hydrogeologic Investigation and Reporting Policy Memorandum, dated May 31, 2007, will be used as general guidance. Task 2
Discuss Site History and Land Uses – A discussion of the site history and land uses will be developed.
Task 3
Review Available Data on Ash Basin Water Quality- Available data on ash basin water quality will be reviewed to determine if a suitable “fingerprint” of ash basin water quality can be determined. If a suitable “fingerprint” of ash basin water quality can be determined, the parameters and constituents associated with the “fingerprint” will be used with the analytical results from the monitoring wells to determine if the exceedances in the monitoring wells can be attributed to impacts from the ash basin. This data will be provided by Duke Energy and will include NPDES-related monitoring data and additional data collected by Duke Energy from the ash basin during the May 2013 sampling event.
9
Section 8
Groundwater Assessment Work Plan
The ash basin data will be reviewed relative to groundwater sampling results for constituents included in the ash basin groundwater monitoring program and for major anion and cation data also collected during the May 2013 groundwater sampling event. The groundwater monitoring results at the monitoring wells with exceedances will be compared to the ash basin water quality data by utilizing water quality plots (i.e., Piper diagrams, Stiff diagrams, or others) to understand the possible influence of the ash basin on the groundwater quality at the monitoring wells with exceedances. Task 4
Review Available Ash Leaching Data – Existing results for leaching tests on ash will be reviewed to determine if the existing data can be used as input to the assessment or if additional leaching tests need to be performed. Additional leaching tests will be performed if needed and the results will be included in the assessment.
Task 5
Evaluate Well Construction Information – Well installation records will be reviewed to determine if well construction methods are contributing to the exceedances.
Task 6
Evaluate Exceedances Against Background Well Results – The analytical results from the wells with exceedances will be evaluated against results from the site background well to determine if the exceedances can be attributed to background water quality conditions.
Task 7
Evaluate Exceedances Against Turbidity Values – Exceedances will be evaluated against turbidity values measured during sampling to determine if the exceedances are a result of sediment or particulate matter which is preserved in the sample as a result of well construction or sampling methods.
Task 8
Evaluate Sampling Flow Rates – Sample collection flow rates will be evaluated to determine if the flow rates are affecting results. The use of low flow sampling techniques will be evaluated for selected wells.
10
Section 8
Task 9
Groundwater Assessment Work Plan
Collect and Analyze Filtered and Unfiltered Samples – Groundwater samples collected for compliance monitoring are not filtered in the field. In order to provide additional information for the assessment of exceedances, both unfiltered and filtered samples will be collected and analyzed for antimony, arsenic, iron, and manganese. The field filtration will be performed with an in-line, sealed, 0.45 micron filter.
Task 10
Collect Reduction/Oxidation Field Parameters – Reduction/oxidation (redox) processes can alternately mobilize or immobilize metals associated with naturally occurring aquifer materials. Iron and manganese are commonly associated with lakes and the associated sediments. The redox conditions associated with the aquifer/lake system may be a factor in the concentrations of iron and manganese observed at selected monitoring well locations.
Additional field parameters (i.e., dissolved
oxygen and redox potential) will be collected at selected wells to characterize the redox conditions at these locations. A discussion of the redox conditions at the wells will be provided in the assessment. Task 11
Collect Soil Samples - Analyze for Iron and Manganese Content - Soil samples will be collected from soil borings performed adjacent to monitoring wells MW-20S and MW-21S. One soil sample in each boring will be collected from above the observed water level in the adjacent monitoring well. Up to two soil samples in each boring will be collected from the depth of the screened interval in the adjacent well (within the shallow aquifer). The samples will be collected from different soil types where applicable. The borings will be logged for soil lithology by a Professional Geologist. The soil samples will be analyzed for total concentrations of iron and manganese, cation exchange capacity, redox potential, nitrate, sulfate, and pH. A discussion of the iron and manganese concentrations measured in the soils will be provided.
Task 12
Collect Surface Water Samples from the Dan River – Surface water samples will be collected from the Dan River and will be used in the evaluation of the exceedances in MW-22S and MW-22D. These samples will be collected from two locations; one
11
Section 8
Groundwater Assessment Work Plan
location will be upstream of MW-22S and MW-22D and the other location will be adjacent to the wells. Task 13
Collect Surface Water Samples and Sediment Samples from the Unnamed Tributary near MW-21S and MW-21D – Surface water and sediment samples will be collected from the unnamed tributary near MW-21S and MW-22D. The surface water and sediment samples will be used in the evaluation of the exceedances in MW21S and MW-21D. These samples will be collected from two locations; one location will be upstream of MW-21S and MW-21D and the other location will be adjacent to the wells.
Task 14
Perform Statistical Data Analyses of the Sampling Results – Statistical analyses of groundwater monitoring results will be performed to determine if the exceedances can be attributed to the ash basin water quality or if the exceedances can be attributed to naturally occurring background concentrations.
The NCDENR document,
Evaluating Metals in Groundwater at DWQ Permitted Facilities: A Technical Assistance Document for DWQ Staff, dated July 2012, will be used as general guidance. In addition to these tasks, HDR understands that Duke Energy will add total suspended solids to the list of analysis parameters for groundwater samples and will continue to analyze groundwater samples for total dissolved solids.
12
Section 9
Groundwater Schedule
Assessment
Report
and
Proposed
The groundwater assessment report will present results of the work proposed in Section 8.
After NCDENR has approved this proposed plan, the proposed schedule is to submit the groundwater assessment report approximately 120 days after the next scheduled groundwater sampling event at Dan River Steam Station.
The groundwater assessment report will be
submitted 150 days after the next scheduled groundwater sampling event if redevelopment of one or more of the monitoring wells is required. The next sampling event at Dan River Steam Station will occur in May 2013.
13
Section 9
References Harry E. LeGrand.
2004.
A Master Conceptual Model for Hydrogeological Site
Characterization in the Piedmont and Mountain Region of North Carolina, A Guidance Manual, North Carolina Department of Environment and Natural Resources Division of Water Quality, Groundwater Section.
14
FIGURES
Dr
600
60 0
600
600
Eden
S Edgewood Rd
um
600
E
i S ta d
0 60
60 0
600 600
60 0
50 0
500
0 60
Ash Basin 500
500 600
Dan River Steam Station
S Van Buren Rd
500
600
0 50
600
600
Ri
ve
r
600
600
an D 0 50
600
0
1,000
600
500
600
600
Notes: 1. Sources: US Topo; 2011, USGS National Map Aerial Imagery; 2010 North Carolina Statewide Orthoimagery, NC Geospatial & Technology Management Office SCALE (FEET)
600
600
500
500
600
600
50 0
0 60
14 U V
1,000
0 50
0 60
60 0
2,000 DATE
0 60
HDR Engineering, Inc. of the Carolinas License Number: F-0116 440 South Church Street, Charlotte, NC 28202
SITE LOCATION MAP DAN RIVER STEAM STATION DUKE ENERGY CAROLINAS, LLC ROCKINGHAM COUNTY, NORTH CAROLINA
1
February21, XX,2013 2013 February FIGURE
600
TABLES
TABLE 1 - GROUNDWATER SAMPLING REQUIREMENTS Well Nomenclature
Monitoring Wells: MW-20S, MW-20D, MW-21S, MW-21D, MW-22S, MW-22D, MW-23
Parameter Description
Frequency
Antimony
Chromium
Nickel
Thallium
Arsenic
Copper
Nitrate
Water Level
Barium
Iron
pH
Zinc
Boron
Lead
Selenium
Cadmium
Manganese
Sulfate
Chloride
Mercury
TDS
January, May, September
TABLE 2 - EXCEEDANCES OF 2L STANDARDS 2L Standard
Well ID
Antimony*
Arsenic
Boron
Iron
Manganese
TDS
Sulfate
pH
1 µg/L
10 µg/L
700 µg/L
300 µg/L
50 µg/L
500 mg/L
250 mg/L
6.5 - 8.5 SU
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
Range of Exceedances
µg/L
µg/L
µg/L
µg/L
µg/L
µg/L
µg/L
SU
MW-20S
1.04
No Exceedances
No Exceedances
2,350 - 3,190
864 - 945
No Exceedances
No Exceedances
5.9 - 6.2
MW-20D
No Exceedances
No Exceedances
No Exceedances
No Exceedances
489 - 519
No Exceedances
No Exceedances
No Exceedances
Comments Concerning Exceedances
Iron and Manganese concentrations have been generally consistent over the period of monitoring. Antimony has been below the 2L and MRL of 1.0 µg/L except during one (May 2012) sample event. pH has been generally consistent over the period of monitoring. Manganese concentrations have been generally consistent over the period of monitoring.
MW-21S
1.02 - 1.33
25.2 - 44.7
No Exceedances
No Exceedances
306 - 668
No Exceedances
No Exceedances
No Exceedances
Arsenic concentrations have been generally consistent. January 2013 sample event (25.2 µg/L) is the lowest arsenic concentration measured over period of monitoring. Manganese concentrations have generally increased from a low concentration in January 2011 (306 µg/L) to 668 µg/L in January 2013. Antimony has been >2L during four events and <MRL during three events including the last 2 sample events.
MW-21D
No Exceedances
No Exceedances
No Exceedances
No Exceedances
901 - 1,050
643 - 770
310 - 350
No Exceedances
Manganese, TDS, and sulfate concentrations have been generally consistent over the period of monitoring.
No Exceedances
Iron concentration in January 2013 sample event (13,900 µg/L) is the lowest concentration measured over period of monitoring. Manganese results have been generally increasing over the period of monitoring.
MW-22S
No Exceedances
No Exceedances
No Exceedances
13,900 - 19,400
701 - 806
No Exceedances
No Exceedances
MW-22D
1.06 - 1.60
No Exceedances
711 - 793
829 - 1,010
145 - 261
No Exceedances
No Exceedances
No Exceedances
MW-23D
No Exceedances
No Exceedances
No Exceedances
326 - 1,700
192 - 468
No Exceedances
No Exceedances
5.9 - 6.3
* Interim Maximum Allowable Concentration.
Boron concentrations have been generally consistent over the period of monitoring. Three out of the four sample results for Boron >2L. Iron and Manganese concentrations may be affected by turbidity. The two iron and manganese 2L exceedances are coincident with the high turbidity readings in January 2012 (80 NTU) and September 2012 (53.5). The two sampling events with turbidity
