Susan Thorneloe

1
Evaluating Life-Cycle Environmental Trade-Offs
from Use of FGD Gypsum

• Susan Thorneloe
• US EPA
• National Risk Management Research Laboratory
• Research Triangle Park, North Carolina
• September 13, 2006

2
Research Objective

• Evaluate impact of air pollution control on coal
  combustion residues (CCRs)
• Identify potential cross-media transfers of
  mercury and other metals from CCR management
  which includes FGD gypsum and fly ash
• Compare life-cycle environmental tradeoffs from
  use of CCR and non-CCR materials

3
Background

• In March 2005, EPA announced a multipollutant
  approach to reduce power plant air emissions
  through the Clean Air Interstate Rule (CAIR) and
  the Clean Air Mercury Rule (CAMR) through cap and
  trade approach.
• Air pollution control (APC) results in
  transferring metals from the flue gas to fly ash
  and other APC residues.
• Anticipate that wet scrubber usage and production
  of FGD gypsum will double or triple in response
  to CAIR.
• Primary focus on mercury but also interest in
  arsenic, selenium, and other constituents of
  concern.
• Key release route for land-managed CCRs is
  leaching to groundwater. Concern also for
  release to surface waters, re-emission of mercury
  (e.g., cement kilns), and bioaccumulation.

4
Importance of Coal - Electricity Production by
Fuel for 1980 2030 (Billion kilowatt hours)
Source DOE/EIA 2006
5
CCR Production and Utilization

• Production
• 122 million tons

• 40 Utilization
• 49 million tons

Source ACAA 2004 CCR Survey DOE, 2005
6
Calculating Hg Mass Balance in Response to CAIR
and CAMR Implementation
Source Thorneloe, 2006
7
Projection of Scrubber Use at Existing Units
8
FLUE GAS STACK
SORBENT
AMMONIA INJECTION
WET FLUE GAS DESULFURIZATION (FGD) SCRUBBER
SORBENT INJECTION
SUPERHEATER
SCR
COAL SUPPLY
BOILER
ESP OR FF
ASH SORBENT REMOVAL
FGD GYPSUM OR SCRUBBER SLUDGE REMOVAL
9
Tracking Fate of Hg and Other Metals Through
Life-Cycle Analysis

• In 2004, 31 million tons of wet scrubber residues
  were produced.
• 12 million tons (or 40) used to make gypsum.
• 90 of the 12 million tons used to make wall
  board.
• Expect increased interest in other uses of FGD
  gypsum such as use as soil amendment
  (collaboration with China).
• Comparing life-cycle environmental tradeoffs for
  production of wallboard with and without use of
  FGD gypsum. This is also being done for the
  production of cement and asphalt.
• Considering potential pathways of environmental
  release (includes used of leaching and thermal
  stability studies)
• Need to understand stability of Hg and track fate
  of Hg and other metals on a life-cycle basis.
• Information will help with ensuring if intended
  mercury reductions are achieved in mercury cap
  and trade program.

10
Series of 4 Reports Documenting Findings

• Enhanced sorbents for mercury capture (Jan, 2006)
• FGD gypsum and other scrubber residues (2007)
• Residues from other air pollution control
  strategies (2008).
• Probabilistic assessment of mass release rate for
  a range of management scenarios, including
  disposal and beneficial use (2008).

11
Leach Testing Protocol

• ORD adopted OSWs recommended approach to
  evaluating the leaching potential of coal
  combustion residues (CCRs) anticipated to be
  generated as a result of CAIR CAMR
• OSW recommended the use of a leach testing
  framework developed by Kosson et.al, from
  Vanderbilt University.
• The detailed protocol is published at Kosson,
  D.S., van der Sloot, H.A., Sanchez, F. and
  Garrabrants, A.C., 2002. An Integrated Framework
  for Evaluating Leaching in Waste management and
  Utilization of Secondary Materials. Environmental
  Engineering Science 19(3)159-204.
• An additional publication on using the data in
  probabalistic modeling is Sanchez, F., Kosson,
  D.S., 2005. Probabilistic approach for estimating
  the release of contaminants under field
  management scenarios. Waste Management, 25(5),
  643-472.
• OSWs recommendation was based on the fact that
  this approach
• Most fully considers the key conditions affecting
  leaching for a range of CCRs and their plausible
  management
• Is appropriate for evaluating a broader range of
  materials, beyond fly ash and
• Addresses previous concerns raised by Science
  Advisory Board.

12
Leach Testing Protocol

• Considers range of values for key parameters that
  both affect leaching and vary with disposal and
  reuse
• pH The solubility of constituents of concern
  vary with pH.
• Liquid to Solid ratio (L/S)
• Reflects rainfall infiltration
• Lower L/S ratio can result in different pH and
  contaminant concentration
• Waste form
• Fine particles (equilibrium test)
• Stabilized and solid materials (mass transfer
  effects)
• A single set of test results can be used to
  evaluate leaching potential for a range of
  management scenarios including disposal and
  reuse.

13
Data Can Support Environmental Assessment
Modelling for Different Scenarios..
Drinking water well
Drinking water pipes
Drinking water well
14
NAS Concern for Providing Full Characterization
of reuse materials .

• Historically, CCRs are given special
  consideration because of their wide range of
  beneficial use applications
• Since 1991, CCR utilization increased from 31 to
  40.
• RCC goal is to increase CCR utilization to 50 by
  2010.
• Recent National Academy of Science (NAS) report
  on CCR use in mine filling stated that full
  characterization should not be cut short in the
  name of beneficial use.

15
Arsenic Leaching as a Function of pH for Coal Fly
Ash
Facility L
Facility C
Brayton Point
16
Coal Fly Ash Results For Facilities Using
Sorbents for Enhanced Hg Capture

• Mercury Low totals and leach
• Total 0.1-1 mg/kg
• Leach Most 0.1 ug/L or lower
• MCL2 ug/L
• TC 200 ug/l
• Low leach variability relative to pH
• Results do not include modeling of transport from
  landfill site to drinking water well (i.e, no DAF
  applied)

17
Ranges of Hg Leachate Concentrations (From Report
1 on Use of Enhanced Sorbents)
18
Coal Fly Ash Results For Facilities Using
Sorbents for Enhanced Hg Capture

• Arsenic Totals and leach high/variable
• Total 20- 500 mg/kg
• Leach 1-1000 ug/L
• MCL10 ug/L
• TC5000 ug/L
• Leach variability is moderately to highly pH
  dependent
• Results will be used in modeling of transport
  from disposal or management site to drinking
  water well

19
Ranges of As Leachate Concentrations (From Report
1 on Use of Enhanced Sorbents)
20
Coal Fly Ash Results For Facilities Using
Sorbents for Enhanced Hg Capture

• Selenium Totals moderate leach high/variable
• Total 20- 500 mg/kg
• Leach 1-10,000 ug/L
• MCL50 ug/L
• TC1000 ug/L)
• Leach variability moderately pH dependent
• Results will be used in modeling of transport
  from disposal or management site to drinking
  water well

21
Ranges of Se Leachate Concentrations (From Report
1 on Use of Enhanced Sorbents)
22
What do the CCR Leach Test Results Mean for CCRs
Evaluated to Date?

• For CCRs evaluated in Report 1, found apparent
  low release potential for Hg from CCRs that are
  land applied or landfilled
• Current emphasis is on wet scrubber residues
  including FGD gypsum
• Arsenic and Selenium showed higher potential for
  release by leaching
• Highest As leach values at 20 of TC
• Highest Se leach value is 10 x TC
• Arsenic was identified as a concern in the 1999
  Report to Congress on coal combustion wastes
• Indicate importance of evaluating full range of
  CCRs and use of results in risk assessment
  modeling.

23
How Is This Information To be Used?

• Beneficial use programs to help clarify
  appropriate practices and quantify potential
  benefits
• RCC program for coal combustion products
• State, Federal (DOE, DOT, DOI), and industry
  programs that promote beneficial use
• Regulatory efforts including
• Effluent guidelines (OW),
• RCRA Subtitle D for coal combustion waste (OSW),
• Cap and trade programs through implementation of
  CAIR and CAMR (OAR)
• Identifying potential cross media transfers
• Helping to ensure that intended reductions are
  achieved
• Cement kilns (MACT) issue raised regarding use
  of CCRs (OAR)
• Helping to quantify life-cycle environmental
  tradeoffs

24
Development of a CCR Management Decision Support
Tool

• LeachXS is a set of integrated software tools
  under development to provide
• Guidance on the selection of test methods to
  answer specific management option questions
• Database of leaching characteristics, lysimeter
  and field data for wide range of materials for
  performance comparison
• Database of management scenarios (disposal,
  beneficial use), case studies and prior
  experience
• Data management, evaluation and presentation to
  communicate scenarios and results
• Geochemcial speciation and coupled reaction -
  mass transfer models to estimate long-term
  release for specific combinations of CCR material
  and use or disposal scenario
• Quality control for materials production and use
  tracking CCR material conformance with use
  criteria

25
FGD Gypsum is Under Evaluation for these Scrubber
Facilities
26
Conclusions

• Working to develop information that will provide
  understanding of impact of air pollution control
  on FGD gypsum and coal fly ash current emphasis
  is on FGD gypsum
• Conducting life-cycle analysis that allows
  comparison of environmental tradeoffs from use of
  CCR and non-CCR materials
• Providing information to help determine if
  intended reductions of CAMR cap and trade
  programs are being achieved
• Developing leach testing protocol into official
  EPA method in SW846
• Identifying potential CCR management practices of
  concern resulting from application of new air
  pollution control technology at coal-fired power
  plants