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Air Toxics Program

IDEM Air Toxics > Risk Assessment > Air Toxics Studies > SW Indy Air Toxics Study > Scope of the SW Indy Air Toxics Study Scope of the SW Indy Air Toxics Study

October 2007

Table of Contents

The goal of the Southwest Indianapolis Neighborhood Air Toxics Study is to conduct a community scale analysis of Hazardous Air Pollutants (more commonly known as "air toxics" or "HAPs") in southwestern Indianapolis, Indiana. In its 1999 National Air Toxics Assessment (NATA), U.S. EPA identified this neighborhood as being an area of potential concern for exposure to HAPs. In addition, there is considerable concern within the neighborhoods of that part of the city, as documented by articles in the Indianapolis Star (February 22-23, 2004). This study is composed of three components; with the parameters of the second and third components will be refined based on the results of the first component.

In the first component of the project, IDEM will conduct monitoring in two residential neighborhoods in the primary study area. The monitored concentrations will be evaluated and compared to a U.S. EPA based pre-determined threshold (see Table 4) for each pollutant, other Indiana ToxWatch sites, and the National Air Toxics Assessment. In addition, IDEM will collect speciated chromium data and a ratio of chromium VI to total chromium will be established.

In the second component, IDEM will develop a refined emissions inventory of sources and categories of sources likely to be contributing to the identified air toxic concentrations of interest at the monitors. The location and type of these sources will better define the secondary study area. IDEM will then conduct dispersion modeling of these identified sources to evaluate their relative contributions to monitored concentrations. Industrial sources, mobile sources (on-road and off-road) and background sources will be monitored.

In the third component, IDEM will conduct dispersion modeling of sources over a larger grid of receptors in order to estimate air toxic concentrations in the secondary study area. IDEM will use the estimated air toxic concentrations to calculate the inhalation health risk.

The results of the above analyses will be used to characterize the potential (not actual) excess cancer risk and non-cancer hazard posed by the air toxics in the study area. The resulting risk characterization can be used to inform citizens of potential health risks from air toxic emissions and to identify areas where in the future, IDEM, in cooperation with the City of Indianapolis, can work with local sources (point, area, and on-road) to reduce emissions and their potential health risks, if necessary.

Study Area

The study area for the project, defined using 1996 and 1999 National Air Toxics Assessment (NATA) results was identified in NATA as having potentially higher risk due to HAPs exposure than most other areas in Indiana. In addition, a neighborhood located in the middle of the study area was the focus of local media attention due to the perception that HAP concentrations are much higher than in other areas of Indianapolis.

The primary study area (See Map of Study Area [PDF]) is defined roughly by the boundaries of Washington Street to the north, Harding Street to the east, Troy Avenue to the south, and Lynhurst Avenue to the west. The primary study area represents the area where locations for monitor placement were considered. The secondary study area will be roughly bound by 10th Street to the north side, Bluff Road on the east side, Hanna Avenue to the south, and High School Road to the west. The study area represents the area in which modeling results will be evaluated for exposure. A list of sources, primarily located within the study area, will be compiled. However, there is the possibility of including sources that impact air quality within the study area that are located outside the defined boundary.


IDEM has the following goals for the project:

  • Determine measured levels of air toxics in ambient air in the neighborhood
  • Use monitored levels of air toxics, modeling data and the detailed emissions inventory to evaluate 1996 and 1999 NATA results
  • Develop a detailed emissions inventory for the area for certain air toxics
  • Establish a Chromium VI to total Chromium ratio for air quality in this neighborhood and add to the national knowledge base
  • Calculate the inhalation risk for air toxics in the neighborhood
    • Cumulative cancer risk estimate
    • Cumulative respiratory hazard
    • Cumulative neurological hazard
  • Communicate results derived from the study.

Project Outputs and Outcomes

This project will provide a detailed characterization of hazardous air pollutants in southwest Indianapolis. The project will also attempt to identify likely sources of the air toxics found in the community and the estimated contribution of each identified source.

IDEM will use the information to develop a risk characterization for the neighborhood. This risk characterization will include the calculated risk values and the assumptions associated with any calculations of the probabilistic risk and hazard estimations. The data, assumptions and calculation methodology used to calculate risk estimates will be coupled with the estimates.

IDEM will compare the results of this study to the results obtained in the 1996 and 1999 National Air Toxics Assessment. Even though the methodology, inventories, and goals for the NATA modeling exercises differ than those established for this study, comparing the NATA predictions to refined modeling exercises will help the public and IDEM evaluate the NATA information.

IDEM will work with the City of Indianapolis and community leaders to communicate the results of the study to the residents and treat the release of the as an opportunity to enhance public awareness on risk reduction opportunities available in the community. The characterization results will be used to identify whether there are emission and risk reduction opportunities for the study area. IDEM may also use the information gathered from this study to pursue pollution prevention opportunities that may be identified during the study.

In addition to the deliverables contained in the final report, IDEM will increase the understanding of the origin of air toxics and the associated estimated risk/hazard posed in the community. IDEM believes that a more detailed evaluation of the area along with a cooperative partnership with sources will produce economical and innovative pollution prevention opportunities that can be duplicated in other areas of Indiana. Through the course of this project, IDEM will enhance its technical abilities to perform similar work in the future.

Community Involvement

Community involvement and participation are essential to the successful completion of this project. It is important that the public's concerns and issues be addressed to the extent possible and that the results of the study (monitoring, modeling, risk characterization) are clearly and accurately communicated throughout the study. IDEM will work with residents, local industry, and the news media throughout the study.

IDEM had identified four major stakeholder groups with unique interests that have different needs for interaction, planning, and feedback.

  • The general public, especially those people who live in the study area.
  • Local industries in the study area that may have interest in the study.
  • Technical experts from a variety of areas to discuss specific technical issues and advise IDEM.
  • The news media.

Risk Characterization

The term "risk characterization" has many different meanings and can include projects of wide variability in depth and scope. The tools and resources available to IDEM limit the scale and scope of the risk characterization that IDEM can produce. This risk characterization will be designed to answer questions about the types, amounts, and potential health risks posed by air toxics in the study area. This risk characterization will focus on two toxic endpoints for each pollutant, cancer health effects and non-cancer health effects from inhalation exposure over a lifetime (70 years). In addition, in consultation with the technical experts, the characterization will calculate the maximum cumulative health effects of all the identified air toxics for three toxic endpoints: cancer, respiratory and neurological health effects.

IDEM will compare canister samples taken over a 24 hour period to acute (24 hour exposure values) to determine if there is the possibility of short term health effects due to exposure of air toxics in the area. The primary function of the risk characterization is to put into context the concentration of each of the pollutants to which the public is exposed taking into account the toxicity of the different pollutants. This characterization can then be used to make decisions about whether additional resources should be dedicated to reduce emissions and risk.

The risk characterization, while a useful tool, is not a statement of "actual risk" that the population faces but rather an estimate of upper bound potential risk. It is not the goal of the agency to identify the cause of any observed health effects in the area through this study. The "actual risk" that individuals face for the three identified endpoints is a complex combination of many factors, including genetic predisposition, diet, lifestyle choices, and environmental contribution. It is outside the scope of this study to determine what this complex combination of factors is for every person who lives in the study area. IDEM will make certain assumptions that will result in an estimate of upper bound potential risk posed by the pollutants in the ambient air. The assumptions made will be presented with the risk characterization results and covered in detail in the discussion of uncertainty in the final risk characterization report.

Any risk value produced will be the result of the assumptions and inputs used to derive the value. This is an important fact in that the "risk" for a single location can be calculated with a multitude of different assumptions. A risk estimate can be calculated assuming all worst case conditions, assumptions of average conditions, or the assumption of best case conditions (lower bound). The agency will examine possibilities ranging from an upper bound estimate of reasonable worst-case conditions to an estimate using a central tendency for factors such as exposure and toxicity when making assumptions. Examining a number of different combinations of factors will provide an understanding as to which factors are the most important in contributing to risk in the community. Calculated risk values will be combined with the assumptions used to derive those values when the values are presented.

IDEM will use risk characterization methodology based on U.S. EPA approved methodologies. Specifically, U.S. EPA's Air Toxics Risk Assessment Reference Library Volumes 1, 2, and 3, will be used.

Dose-response assessment involves describing the quantitative relationship between the amount of exposure to a substance and the extent of toxic injury. Data is derived from animal studies or, less frequently, from studies in exposed human populations. There may be many different dose-response relationships for a substance if it produces different toxic effects under different conditions of exposure. The risks of a substance cannot be ascertained with any degree of confidence unless dose-response relations are quantified, even if the substance is known to be toxic. U.S. EPA's Integrated Risk information System (IRIS) was developed as a tool to provide hazard identification and dose-response assessment information. Dose-response values will be used from the following databases and as recommended by the Technical Advisory Group:

  • Integrated Risk Information System (IRIS)
  • Agency for Toxic Substances and Disease Registry (ATSDR)
  • Health Effects Assessment Summary Tables (HEAST)
  • California Environmental Protection Agency Air Resource Board (CARB)
  • International Agency for Research on Cancer (IARC)
  • U.S. EPA Regions 3, 6, 9

The dose-response toxicity values from these databases are based upon health protective assumptions.

Ambient air monitoring

Additional ambient air monitoring equipment will be located at sites that IDEM currently operates within the study area that meet the EPA standards for ambient air monitoring placement. The monitors will provide a real world measurement of air toxics and trace metals in the ambient air.

Uses of Monitoring Data:
  • Evaluate ambient levels of air toxics for use in exposure assessment.
  • Aid in the development of a refined emissions inventory of sources and categories of sources likely to be contributing to air toxics concentrations in the study area.
  • A tool to compare results of the 1999 and future National Air Toxics Assessment (NATA) modeling projects.
  • Compare air toxic concentrations to those measured in other parts of Indiana.

IDEM will operate two identical monitoring sites in neighborhoods within the primary study area with one site having an additional chromium speciation monitor. One monitoring location will be at 1321 South Harding Street. The other monitor will be located at Stout Field National Guard Armory at 1802 South Holt Road. The sites meet U.S. EPA citing requirements for ambient air monitoring and already have operating monitors at the locations. Monitoring locations selection conforms to EPA standards for ambient air monitoring locations as detailed in the Quality Assurance Handbook for Air Pollution Measurement Systems - Ambient Air Quality Monitoring Program Quality System Development EPA-454/R-98-004. Each will be strategically located based on an evaluation of the EPA's 1996 and 1999 NATA, proximity to major sources for HAP emissions, and in locations where the general public lives and congregates. Each site will operate on a one in six-day frequency collecting 24-hour composite samples.

Currently there are two locations with existing monitors set up in the study area that conform to these requirements. The existing monitoring locations will be used in this study.

The U.S. EPA's National Air Toxics Assessments (NATA) of 1996 and 1999 identified a number of HAPs that could be present in the study area at potentially elevated concentrations. Chromium VI, benzene, arsenic, 1,2-dibromoethane, and carbon tetrachloride are pollutants identified as being drivers of risk in southwest Indianapolis. Monitoring methods selected are designed to analyze for those pollutants identified in NATA as well as a number of other air toxics known to be emitted in the study area.

IDEM routinely measures the levels of criteria pollutants in the air in the study area. However, IDEM will not conduct a risk assessment for these air pollutants. There are federal health-based standards for criteria air pollutants and compliance with the standards is ensured through the Clean Air Act. Measured air concentrations in the study area currently meet the eight-hour standard for ozone. Measured PM 2.5 air quality levels exceed the current annual federal standard; however, the area is on track to comply with this health-based standard by, if not prior to, the deadline established by the Clean Air Act.

U.S. EPA approved PM-10 samplers will be used to collect samples that will be analyzed for trace metals. The seven metals, listed in Table 1, will be analyzed using ICP-MS analysis. The method code for analysis is EPA compendium method IO-3.2.

Table 1: Method IO-3.2 Compounds
  • Arsenic Compounds
  • Beryllium Compounds
  • Cadmium Compounds
  • Chromium Compounds
  • Lead Compounds
  • Manganese Compounds
  • Nickel Compounds

Carbonyl samples will be collected using Atec 2-channel DNPH tube samplers, which allow for duplicate sample runs for quality assurance/quality control purposes. Carbonyl compounds listed in Table 2 are analyzed using U.S. EPA method TO-11 using DNPH (2,4-dinitrophenylhydrazine) cartridges. The cartridges are extracted and analyzed using HPLC (high performance liquid chromatography) equipment.

Table 2: Method TO-11A Compounds
  • 2,5-dimethylbenzaldehyde
  • Acetaldehyde
  • Acetone
  • Benzaldehyde
  • Butyr/Isobutyraldehyde
  • Crotonaldehyde
  • Formaldehyde
  • Hexaldehyde
  • Isovaleraldehyde
  • Propionaldehyde
  • Tolualdehydes
  • Valeraldehyde

Volatile Organic Compounds (VOC) will be collected in 6-liter stainless steel Summa-polished canisters using Meriter air toxic samplers, also capable of duplicate runs for QA/QC. All canister VOC samples will be analyzed for the constituents listed in Table 3 by IDEM using EPA method TO-15A.

Table 3: Compounds monitored using method TO-15A
  • 1,1,1-Trichloroethane
  • 1,1,2,2-Tetrachloroethane
  • 1,1,2-Trichloroethane
  • 1,1-Dichloroethane
  • 1,2,4-Trichlorobenzene
  • 1,2,4-Trimethylbenzene
  • 1,2-Dibromoethane
  • 1,2-Dichloroethane
  • 1,2-Dichloropropane
  • 1,3,5-Trimethylbenzene
  • 1,3-Butadiene
  • 1,4-dioxane
  • Acetone
  • Benzene
  • Benzyl Chloride
  • bromodichloromethane
  • Bromoform
  • Bromomethane
  • c-1,2-Dichloroethene
  • c-1,3-Dichloropropene
  • Carbon Disulfide
  • Carbon Tetrachloride
  • Chlorobenzene
  • Chloroethane
  • Chloroform
  • Chloromethane
  • Cyclohexane
  • Dibromochloromethane
  • Dichloromethane
  • Ethanol
  • Ethyl Acetate
  • Ethylbenzene
  • Freon-11
  • Freon-113
  • Freon-114
  • Freon-12
  • Heptane
  • Hexachloro-1,3-butadiene
  • Hexane
  • Isopropanol
  • m+p-Xylenes
  • MBK
  • m-Dichlorobenzene
  • MEK
  • MIBK
  • MTBE
  • o-Dichlorobenzene
  • o-Xylene
  • p-Dichlorobenzene
  • p-Ethyltoluene
  • Propylene
  • Styrene
  • t-1,2-Dichloroethene
  • t-1,3-Dichloropropene
  • Tetrachloroethene
  • THF
  • Toluene
  • Trichloroethene
  • Vinyl Acetate
  • Vinyl Chloride
  • Vinylidene Chloride

U.S. EPA will use a qualified contractor to analyze chromium speciation monitoring samples, metal samples, and carbonyl samples. Criteria and non-criteria pollutant monitoring conducted in the Southwest Indianapolis sector, as well as the whole of Marion County, will also be analyzed to aid in the characterization of the air toxic source/receptor relationship, if possible. For example, it may be possible to analyze PM 2.5 monitor filters for metals if needed. All monitors will operate following U.S. EPA approved protocols and quality assurance plans.

There are a number of different forms (valence levels) of chromium emitted to the ambient air. P.M.-10 and Total Suspended Particulate (TSP) monitors collect a total volume of chromium but do not differentiate between the different valence levels. Hexavalent chromium (chromium VI) is the most toxics form of chromium identified by the Integrated Risk Information System database (IRIS). The U.S. EPA, using a qualified contractor, will operate one co-located specialized monitor (RMESI Model 924-Cr+6 Sampler or equivalent) to collect hexavalent chromium data. Data will be collected at the site for one year. This activity will include sixty samples (1 every 6 days), ten-percent duplicates (additional 6), and twelve field blanks, for a total of seventy-eight samples. Data collected will enable IDEM and the U.S. EPA to determine what portion (fraction) of the total measured chromium is hexavalent (Cr+6).

Exposure and potential risk can be estimated from any valid monitoring data. However, the confidence in the characterization depends on a number of factors.
  • How representative is the monitored exposure concentration of actual exposure at that location?
  • How representative is the monitor location of exposure to those in the residential areas?
  • Does the monitoring data represent the maximum, average, or minimum exposure that the community will experience?
  • Quantity of data? Greater confidence in exposure concentration with more monitoring data.

Ambient air monitoring data most accurately represents a limited area near the monitor location. Therefore, two monitoring locations by themselves will not be sufficient to accurately characterize air toxic concentrations throughout the entire study area, however, results from the monitors will provide exposure concentrations with a great deal of confidence at the monitoring locations. Additionally, dispersion modeling will be used to supplement the monitoring data to perform a risk characterization for the entire study area. The combination of monitoring and modeling will increase the confidence that the risk characterization is representative of the entire area. 

Emissions Inventory

IDEM, in cooperation with the City of Indianapolis, will develop a detailed emissions inventory for HAPs in the study area for modeling purposes. The inventory will focus on those pollutants monitored at levels above U.S. EPA based pre-determined screening thresholds (see Table 4). Existing emission inventory databases will be used and enhanced. Available inventories that will be used are Indiana's i-Steps database, National Toxics Inventory, Toxics Release Inventory, and permit applications. IDEM will also work with industries that may impact the air quality in the study area to develop accurate emission estimates specific to the facilities. Currently, IDEM has identified 178 industrial and commercial sources within and nearby the study area. Mobile sources of air toxics will also be considered. 

Table 4: Monitored Compound Screening Levels
Monitored Compounds CAS Screening Level
Metals   µg/m3
Arsenic   0.00023
Beryllium   0.00042
Cadmium   0.00056
Chromium VI   8.3E-05
Lead   1.5
Manganese   0.05
Nickel   0.0042
2,5-dimethylbenzaldehyde 97-51-8 *
Acetaldehyde 75-07-0 0.45
Acetone 67-64-1 31000
Benzaldehyde 100-52-7 35
Butyr/Isobutyraldehyde 78-84-2 35
Crotonaldehyde 4170-30-3 0.0018
Formaldehyde 50-00-0 0.077
Hexaldehyde 123-05-7 *
Isovaleraldehyde 590-86-3 *
Propionaldehyde 123-38-6 *
Tolualdehydes   *
Valeraldehyde 110-62-3 *
1,1,1-Trichloroethane 71-55-6 1000
1,1,2,2-Tetrachloroethane 79-34-5 0.017
1,1,2-Trichloroethane 79-00-5 0.063
1,1-Dichloroethane 75-34-3 0.63
1,2,4-Trichlorobenzene 120-82-1 1
1,2,4-Trimethylbenzene 95-63-6 6
1,2-Dibromoethane 106-93-4 0.0045
1,2-Dichloroethane 107-06-2 0.038
1,2-Dichloropropane 78-87-5 0.052
1,3,5-Trimethylbenzene 108-67-8 6
1,3-Butadiene 106-99-0 0.033
1,4-dioxane 123-91-1 0.32
Acetone 67-64-1 31000
Acrolein 107-02-8 0.02
Benzene 71-43-2 0.13
Benzyl Chloride 100-44-7 0.020
bromodichloromethane 75-27-4 0.056
Bromoform 75-25-2 0.91
Bromomethane 74-83-9 5
c-1,2-Dichloroethene 156-59-2 0.357
c-1,3-Dichloropropene 10061-01-5 0.02
Carbon Disulfide 75-15-0 700
Carbon Tetrachloride 56-23-5 0.067
Chlorobenzene 108-90-7 1000
Chloroethane 75-00-3 7.52
Chloroform 67-66-3 0.043
Chloromethane 74-87-3 0.56
Cyclohexane 110-82-7 6000
Dibromochloromethane 124-48-1 0.042
Dichloromethane 75-09-2 2.13
Ethanol 64-17-5 2200
Ethyl Acetate 141-78-6 315
Ethylbenzene 100-41-4 1000
Freon-11 75-69-4 700
Freon-113 76-13-1 30000
Freon-114 124-73-2 *
Freon-12 75-71-8 200
Heptane 142-82-5 1900
Hexachloro-1,3-butadiene 87-68-3 0.045
Hexane 110-54-3 200
Isopropanol 67-63-0 7000
m+p-Xylenes 108-38-3 200
MBK 591-78-6 *
m-Dichlorobenzene 541-73-1 200
MEK 78-93-3 5000
MIBK 108-10-1 3000
MTBE 1634-04-4 3000
o-Dichlorobenzene 95-50-1 200
o-Xylene 95-47-6 200
p-Dichlorobenzene 106-46-7 0.15
p-Ethyltoluene 622-96-8 *
Propylene 115-07-1 3000
Styrene 100-42-5 1000
t-1,2-Dichloroethene 156-60-5 0.7
t-1,3-Dichloropropene 10061-02-6 0.027
Tetrachloroethene 127-18-4 0.067
Tetrahydrofuran 109-99-9 0.238
Toluene 108-88-3 400
Trichloroethene 79-01-6 0.32
Vinyl Acetate 108-05-4 200
Vinyl Chloride 75-01-4 0.11
Vinylidene Chloride 75-35-4 0.0029

* No current screening level developed. IDEM will work with the technical advisory group to develop a screening level for this pollutant.

Monitoring results will be evaluated to determine if there are pollutants that are not accounted for in the initial modeling emissions inventories. In addition, the results from U.S. EPA's 1999 National Air Toxics Assessment will be used to ascertain if there are possible sources that greatly impact the study area that were not initially included in the inventory. Sources that are identified as contributing significantly to the exposure of individuals in the study area will be included in the modeling. Possible sources include mobile sources, industrial sources, and background.

The information required for modeling will include emission rates, stack heights and locations, flow rates and exit temperatures. If this data cannot be found in an available database, individual sources may be contacted to determine emissions information.


IDEM will use the Regional Air Impact Modeling Initiative (RAIMI) to conduct the modeling for the Southwest Indianapolis project. RAIMI will evaluate the potential for health impacts resulting from exposure to multiple contaminants emitted from multiple sources, at a community level of resolution. RAIMI involves different tools to focus on the risk characterization process. The first tool is the Data Miner that allows data from different sources to be compiled and queried to obtain the necessary modeling inputs. The next step uses the Air Modeling Preprocessor. The preprocessor can process meteorological and terrain data and automatically input them into the model.

The processor also will create four separate input files for each source and phase, generate a receptor grid node for each source out to 10 kilometers, extract terrain elevations from Digital Elevation Mapping (DEM) data, and prepare output files based on chronic or acute averaging periods. It also creates source specific meteorological files for each year of data and merges the multiple years into a single file. The present version of RAIMI contains the ISC3ST model. A version containing AERMOD, the preferred U.S. EPA model, is being developed. After running the model, the next tool for RAIMI is Risk Management and Analysis Platform (Risk-MAP). Using a GIS platform, Risk-MAP has the ability to calculate exposure pathway-specific values, provide custom visual displays in table or mapped formats, and link results to source attributes. Air2GIS, another RAIMI tool, inputs the models output file directly into Risk-MAP.

IDEM will research the best way to incorporate roadway emissions into the results. One recommendation is to model the roadway traffic counts as point sources with a theoretical stack located at the center of the roadway at a specified spacing.

For potential emissions from the Indianapolis International Airport, a previous study used the Federal Aviation Administration's Emissions and Dispersion Modeling System (EDMS). EDMS is designed to assess the air quality impacts of aircraft, auxiliary power units, ground support equipment, stationary sources, fueling operations, motor vehicles and training fires. This is the required model for civil airports.

When performing a community risk analysis, it is advantageous to take a broad approach, as opposed to the traditional source-by-source, program-by-program evaluation. Developing the capability to conduct localized assessments in a timely manner will be useful when seeking voluntary emission reductions in areas with higher estimated risk, and provide better information to stakeholders. The modeling results will be used in the exposure/risk characterization phase of the assessment.


IDEM anticipates that the duration of the project will be approximately two years after ambient air monitoring commences in the study area. Assuming monitoring starts in September of 2006 IDEM will follow the schedule detailed below:

Table 5: Southwest Indianapolis Risk Characterization Project Schedule
  • Community Involvement: June 2006-January 2009
  • First year monitoring begins: October 2006
  • Technical Advisory group: November 2006
  • Request for emissions data from sources: October 2007
  • Emissions inventories refined: December 2007
  • Air toxics Modeling: January 2008
  • Model to monitoring comparison: March 2008
  • Meet with technical advisory group on risk characterization: March 2008
  • Risk characterization: April 2008
  • Communication of results to stakeholders: April 2008
  • Interim report issued: June 2008
  • Second year monitoring complete: September 2008
  • Technical advisory group review interim report: September 2008
  • Final report issued: January 2009

Meetings with the public, the regulated community, and the technical advisory group will be held throughout the course of the project. The stakeholders in the project will be involved in determining the number and frequency of those meeting and IDEM will schedule them appropriately during the course of the project.