## Review of Surface Impoundment Emissions Modeling Performed by New York State Department of Environmental Conservation Draft Supplemental Generic Environmental

Impact Statement On The Oil, Gas and Solution Mining Regulatory Program

Prepared for Halliburton Energy Services, Inc. P.O. Box 42806 Houston, TX 77242-2806



## December 31,2009



# Grad=ent

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## Table of Contents

1 2 3 Introduction .............................................................................................................. 1

4 NYSDEC Air Modeling Scenario ............................................................................ 2 Flaws in NYSDEC Air Modeling ............................................................................ 4 3.1 Air Modeling Mass Balance Flaws ..................................................................................... 4 3.2 Inappropriate Air Guideline Concentrations For Several Chemicals ................................. 6 

### Conclusion ................................................................................................................ 9 References ......................................................................................................................... 11

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## List of Tables

Table 1 Table 2 Surface Impoundment Air Emissions Mass Balance

Summary of Corrected Comparisons to NYSDEC Air Guideline Values



## List of Abbreviations AGC CA dSGEIS EC HESI HF IUR NYSDEC RED RfC RSL SGC SRBC US EPA VOC Air Guideline Concentration

Contaminant Concentration in Air Draft Supplemental Genetic Environmental Impact Statement Exposure Concentration Halliburton Energy Services, Inc. Hydraulic Fracturing Inhalation Unit Risk New York State Department of Environmental Conservation Reregistration Eligibility Decision Reference Concentration Residential Screening Level Short-term Guideline Concentration Susquehanna River Basin Commission United States Environmental Protection Agency Volatile Organic Compound

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## 1 Introduction

The New York State Department of Environmental Conservation (NYSDEC) published a Draft Supplemental Generic Environmental Impact Statement (dSGEIS), dated September 2009, which contains generic permit requirements for the development of natural gas production wells in the Marcellus Shale formation using horizontal drilling and high volume hydraulic fracturing techniques. One component of the NYSDEC evaluation included an assessment of potential volatile organic compound (VOC) emissions from surface impoundments storing the hydraulic fracturing (HF) flowback fluids. This report contains Gradient’s review of the NYSDEC air modeling analysis. Gradient has prepared this report on behalf of Halliburton Energy Services, Inc. (HESI).

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## 2 NYSDEC Air Modeling Scenario

The NYSDEC air emissions modeling procedures are described in Section 6.5 of the dSGEIS. As noted in the dSGEIS, "the Department has relied upon a United States Environmental Protection Agency (US EPA) document 44 on emissions from water treatment facilities which provide [sic] such methods for surface impoundments" (dSGEIS, p. 6-77). 1 The NYSDEC identified chemicals to model based on chemical additives used in the HF fluids, selecting those that had the more stringent air quality guidelines among the additive ingredients used in the HF fluids (see dSGEIS, p. 6-76). NYSDEC made a number of conservative assumptions when modeling chemical emissions that result in overstating air concentrations and human health risks:



### Estimated the constituent concentration in the flowback fluids in the impoundments to be equal to the maximum constituent content in the HF additives, as mixed for use during injection and fracturing (i.e., 100% flowback of the constituents, assuming no attenuation of concentrations due to mixing with liquids in the Marcellus Shale or due to removal of additives during the fracturing process); Did not consider the potential dilution effects of precipitation on the impoundments, or other weather conditions such as freezing conditions during the winter months, both of which would tend to reduce chemical emissions; and Did not consider attenuation mechanisms, such as photolysis, which could reduce concentrations for certain compounds.
Thus, the conservative assumptions adopted by NYSDEC yield high end estimates of chemical emissions.
NYSDEC evaluated emissions for two impoundment scenarios. One scenario is a centralized impoundment designed to serve multiple well pads. The centralized impoundment was assumed to have a surface area of 150m × 150m. The second scenario modeled was a smaller, on-site, impoundment meant to serve a single well pad with a surface area of 15m × 45m (dSGEIS, p. 6-62). Although recognizing that current NYSDEC regulations call for flowback water to be removed within 45 days of well completion, if flowback from multiple wells is managed in centralized impoundments, such impoundments could manage flowback water over the course of a full year. Thus, for the NYSDEC air emissions modeling, the HF constituent emissions were calculated for a full year, with the assumption that the impoundments would contain flowback water continuously for at least a year (dSGEIS, p. 6-63). For the centralized impoundment scenario, NYSDEC assumed that each centralized impoundment

1 The US EPA document is not cited in the dSGEIS, however it appears to be US EPA (1994).

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### handled the flowback water from 10 wells constructed and developed during a year (dSGEIS, p. 6-62).

Each well was assumed to employ 5,000,000 gallons of HF fluid of which 25% was assumed to be recovered as flowback fluid (dSGEIS, p. 6-57). Based on these parameters, each well would yield 1,250,000 gallons of flowback fluid, or 12,500,000 gallons per year for a centralized impoundment serving the needs of 10 wells per year (according to the NYSDEC analysis).

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## 3 Flaws in NYSDEC Air Modeling

Although the chemical emission and air dispersion models used by NYSDEC are generally accepted models, there are at least two significant technical flaws with the implementation of the models rendering the results and conclusions unreliable:

Based on a chemical mass balance analysis, the NYSDEC emissions are implausible for many of the chemicals modeled, and demonstrate a flawed modeling scenario. The annual air guideline concentrations (AGCs) for several chemicals used by NYSDEC in the analysis are based on a lifetime of exposure, yet the modeling scenario is a one (1) year exposure duration. The modeled one-year concentrations should not be compared to AGCs derived on the basis of a long term (e.g., 70-year) exposure without adjusting for the different exposure durations. These flaws are described in more detail in the following two sections.



### 3.1 Air Modeling Mass Balance Flaws
We conducted a mass balance to assess the appropriateness of the NYSDEC air emissions modeling results. Using the NYSDEC stated emission rates for the impoundments, and their modeled duration (one year), we calculated the total mass of the HF constituents that were modeled to be emitted from the surface impoundments. The mass emitted over the course of a year is simply the emission rate reported by NYSDEC (in grams/second) multiplied by the modeled duration (one year). In Table 1, we summarize the modeled total mass emitted (in kg/yr) for the HF constituents, several of which NYSDEC indicates exceed their respective guideline concentrations or AGCs. Based on the total mass emitted, we then calculated the volume of flowback fluid needed to release the chemical mass in one year as shown in the equation below and summarized in Table 1.2



### Volume (9al/yr) = ) .sec.



### Emissions ~ x 3.15 x 107 

### (-~--) Concentration x 9a~ x 10.3

~

2 The calculated volumes assume 100% loss of chemical from the impoundment. If less than 100% of the chemical is emitted, then an even greater volume of fluid would be required to generate the calculated emissions.

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## HESI302177The results of this mass balance calculation are striking. For the majority of the chemicals

evaluated, the volume of fluid necessary to yield the NYSDEC modeled emissions is significantly inflated compared to anticipated HF operational conditions. For example, it would take 454 million gallons of flowback fluid in a centralized impoundment to yield the stated emissions for "heavy naphtha" claimed by NYSDEC. Similarly implausible fluid volumes would be necessary to yield the stated emissions for benzene, xylene, and methanol: 508 million, 538 million, and 202 million gallons, respectively. 

### A centralized impoundment, serving 10 wells per year (dSGEIS p. 6-63), could not possibly generate these enormous flowback fluid volumes. As stated in the dSGEIS, the upper bound HF injection volume is expected to be approximately 5 million gallons per well, of which flowback volume was estimated to be approximately 25% of this amount, giving 1.25 million gallons of flowback per well.3 For 10 wells managed through a centralized impoundment this yields an upper bound estimate of 12.5 million gallons of flowback fluid per year. A single impoundment serving one well would generate 1.25 million gallons of flowback water.
For both xylene and benzene, the annual emission rates calculated by NSYDEC would require the flowback fluid from over 400 wells per year at the stated respective xylene and benzene concentrations in flowback fluid to yield the reported annual emission rates. Similarly, the NYSDEC calculated emission rates for heavy naphtha and methanol would require flowback fluid from over 350 and over 150 wells per year, respectively. As shown in Table 1, the mass balance error ratios (the ratio of the implied fluid volume divided by the annual maximum flowback volume) for two constituents exceed 40-fold, and several others have mass balance error ratios greater than an order of magnitude.
Based on these unrealistic results, the NYSDEC air emissions modeling results are technically unreliable.
Correction Of Mass Balance Errors 

### Because the air dispersion modeling performed by NYSDEC was based on "unit" emission rates which were scaled to the calculated emission rates for each constituent,4 it is a straightforward matter to adjust the calculated chemical concentrations in air to correct for the mass balance errors in the emission
3 Note, NYSDEC’s assumption of 25% flowback is conservative since the Susquehanna River Basin Commission (SRBC) has concluded that the average flowback rate in New-York is expected to be 18% (SRBC, 2009). 4 This is a commonly adopted approach when modeling air dispersion of multiple chemicals from the same source.

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## HESI302178rates. In Table 2, we summarize the NYSDEC modeled maximum annual and maximum 1-hour airborne

chemical concentrations, as well the NYSDEC comparisons to the Short-term Guideline Concentrations (SGCs) and AGCs. For methanol and heavy naphtha, the NYSDEC air emissions estimates predict both of these constituents to exceed annual AGCs and short term SGCs, with ratios ranging from 25.6-fold to 1.7-fold (see Table 2). However, as shown in Table 1, the emissions for heavy naphtha exceed mass balance by factors of 36-fold and 11-fold for the centralized and onsite impoundments, respectively. When the respective NYSDEC modeled heavy naphtha concentrations are adjusted by these factors, the predicted airborne concentrations are less than the AGC and SGC values for the maximum annual and maximum 1 hour scenarios. Similarly, when the NYSDEC modeled methanol concentrations are adjusted downward by 16-fold (centralized) and fivefold, the calculated concentrations in air fall below the AGC and SGC values. As a further note, although benzene, xylene and several other constituents had mass balance errors, the NYSDEC modeled concentrations in air did not exceed AGCs or SGCs. 

### While we have corrected these mass balance errors in the NYSDEC analysis, we have not made any changes to the remaining conservative assumptions in the NYSDEC emissions analysis, identified in Section 2.

3.2 Inappropriate Air Guideline Concentrations For Several Chemicals 

### Not only are the air modeling results themselves flawed, for several chemicals the approach used by NYSDEC to assess potential risks to human health is also inappropriate and results in a significant overestimation of risks. NYSDEC compared modeled chemical concentrations in air due to emissions from impoundments in operation for one year against air guideline concentrations derived on the basis of a lifetime exposure. In addition, the AGCs used by NYSDEC differ from their respective human health based values reported by US EPA.
Acrylamide and formaldehyde are two HF additives that are regulated as potential human carcinogens. In the dSGEIS, the maximum annual concentrations of acrylamide and formaldehyde modeled by NYSDEC are reported to be 5.7-fold (acrylamide) and 6.2-fold (formaldehyde) greater than their respective AGC values.
As we discuss below, the comparison of a one-year exposure (e.g., emissions calculated to occur over one year) to air guidelines that presume a lifetime of exposure, inappropriately inflates the implication of risk associated with such exposures. In addition, the NYSDEC AGC values for these

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## HESI302179compounds differ systematically from published US EPA risk-based guidelines, yet NYSDEC guidance

documents containing the AGC values purport to adopt US EPA toxicity values.
US EPA has derived risk-based concentrations ("Residential Screening Levels" or RSLs) for these chemicals based on a one in a million cancer risk assuming daily inhalation for 30 years and averaged over a 70-year lifetime. As summarized below, the US EPA RSLs are 2.5 to 3.2 times higher than their respective NYSDEC AGCs. Note that we include benzene in the comparison because the US EPA RSL again is 2.4-fold higher than the NYSDEC AGC, indicating a systematic difference between the USEPA and NYSDEC values for chemicals regulated as carcinogens.5 The NYSDEC modeled benzene concentrations do not exceed its AGC. 

### It appears that the main reason for this systematic difference between the RSL and AGC values is that NYSDEC assumes a 70-year exposure duration in its guidelines.6 Thus, the AGC values against which NYSDEC compared its one year emissions modeling results are guidelines that presume a lifetime (70 years) of exposure, not one year.

Chemical NYSDEC AGCIal U.S. EPA RSL[b] Ratio (~tg/m3) (~tg/m3) RSL/AGC Acrylamide 0.00077 0.0019 2.5 Benzene 0.13 0.31 2.4 Formaldehyde 0.06 0.19 3.2 Notes: [4 NYSDEC "DAR-1 AGC/SGC Tables," dated September 10, 2007 (http://www.dec.ny. gov/docs/air~df/agcsgcOZpdJ). [b] http://www.epa.gov/reg3hwmcYrisk/human/rb-concentration table/Generic Tables/pdf/resair sl table run APRIL2OO9.pdf

Comparing modeled maximum annual (e.g., one year) concentrations against these benchmarks is misleading and inappropriate. The US EPA RSL values are derived based on the presumption of continual long-term exposure over a lifetime (e.g., daily exposure over 30 years averaged over a 70-year lifetime), whereas the NYSDEC AGCs are derived based on 70-year exposure averaged over a 70-year lifetime. Thus, the implication in the dSGEIS that acrylamide and formaldehyde emissions would exceed 5 In addition, the NYSDEC Division of Air Resources "DAR-1 AGC/SGC Tables," dated September 10, 2007, state: "When a contaminant has both an RfC and Unit Risk Estimate value published on the IRIS website, NYSDEC will choose the more conservative of both limits as the AGC." In all cases the Unit Risk Estimates are lower than the RfC (non-cancer Reference Concentrations), thus the stated NYSDEC policy effectively indicates the selection of the Unit Risk Estimate for the AGC. 6 NYSDEC, 1997, Appendix C, p. C-5

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## HESI302180health based concentrations at the edge of the surface impoundments is based on a flawed scenario. That

conclusion would only hold if an individual were to stand at the edge of an impoundment 24 hours per day, daily for 70 years. Clearly, that is an unreasonable presumption and contradicts the very scenario modeled by NYSDEC which was one year of emissions from surface impoundments.
As described in US EPA’s, "Risk Assessment Guidance for Superfund, Part F: Supplemental Guidance for Inhalation Risk Assessment" (US EPA, 2009), when evaluating health risks over a particular exposure duration, the chemical concentrations used in the exposure calculation should be calculated as time-weighted concentrations:
The estimation of an EC [exposure concentration] when assessing cancer risks characterized by an IUR [inhalation unit risk] involves the CA [contaminant concentration in air] measured at an exposure point at a site as well as scenario-specific parameters, such as the exposure duration and frequency. The EC typically takes the form of a CA that is time-weighted over the duration of exposure [added emphasis] and incorporates information on activity patterns for the specific site or the use of professional judgment. If the modeled acrylamide and formaldehyde concentrations are correctly applied as their time-weighted "effective concentrations" of exposure for one year, that is averaged over a lifetime (70 years), this reduces the modeled concentrations by 1/70. When this adjustment is made, neither of these constituents would exceed their respective AGC values which are derived on the basis of a lifetime averaging period. This result is shown in Table 2, where the corrected maximum annual AGC ratios (the modeled concentration in air divided by the AGC) are in both instances < 1, indicating that neither compound would exceed its respective risk-based concentration guideline.7 It should be noted further, that this same conclusion holds if the emissions from the impoundments are assumed to last three years (i.e., in this case the modeled concentrations would be adjusted by 3/70). 8 For an assumed exposure duration of three years, the ratio of the maximum annual chemical concentration (adjusted for three years exposure) to the AGC is 0.25 and 0.27 for acrylamide and formaldehyde, respectively (e.g., three times the values shown in Table 2).

7 Note that the adjustment for the "effective" concentration does not affect the short-term scenario; however, neither compound exceeds its respective SGC value. 8 If the emissions are assumed to occur over three years, the annual emissions (e.g., grams/year) are the same, and the modeledconcentrations in air would also be unchanged (the air model results are based on a unit emission rate). The only thing a threeyear scenario changes is the exposure duration.

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## 4 Conclusion

As described in this report, the NYSDEC emissions modeling of HF additives from flowback water managed in surface impoundments is technically flawed and is not reliable. The calculated emission rates for many compounds represent releases that demonstrate severe mass balance errors, and cannot be relied upon. Furthermore, the health-based benchmarks for several chemicals, which are based on a lifetime of daily exposure, are inappropriately compared to a one-year exposure scenario.
When the mass balance errors are corrected, and the "effective concentration" correctly calculated for acrylamide and formaldehyde, the HF additive emissions from the impoundments based on the NYSDEC model all fall below their respective NYSDEC risk-based short-term (SGC) and annual (AGC) benchmarks, with the exception of glutaraldehyde. If glutaraldehyde were excluded from this analysis, then the corrected NYSDEC air modeling results presented here indicate that none of the modeled HF chemical emissions from the impoundments would exceed health-based air guidelines even in the absence of setback requirements (e.g., these guidelines are met at the maximum point of modeled impact which was set to 10 meters from the edge of an impoundment by NYSDEC).9 Consequently, based on the corrected emissions analysis, no additional setback requirements are needed on the basis of air emissions to comply with NYSDEC air guidelines - air guidelines are met at the edge of the impoundments with the possible exception of glutaraldehyde (for which, as discussed below, emissions have not yet been adequately assessed). The NYSDEC analysis was based on its assessment of the list of HF additives disclosed by the industry for use in New York State (discussed in Section 5 of the dSGEIS) and NYSDEC’s assessment of those additives deemed to present the greatest potential concern for air emissions. It also bears noting that NYSDEC’s consultant (ICF), who evaluated air emissions from equipment and operations during the HF well development process, indicated that the chemical emissions from the impoundments handling flowback water would be negligible (dSGEIS, p. 6-62). Although the modeled glutaraldehyde concentration exceeds its air guideline value, based on these modeling results it cannot be concluded that emissions of glutaraldehyde from open surface impoundments would present a significant risk to human health. As noted above, NYSDEC adopted several conservative assumptions in its analysis, which are expected to overestimate chemical emissions from surface impoundments. Furthermore, a detailed analysis of several key factors that affect the fate of glutaraldehyde in HF fluid would need to be undertaken before any conclusion could be reached that 9 NYSDEC indicated that the only requirement for the impoundment was that it be fenced, and that the closest practical distance that a fence could be placed was approximately 10 meters from an impoundment (dSGEIS, p. 6-67).

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### emissions of glutaraldehyde from open surface impoundments would pose any threat to human health.

These factors include: the degree to which glutaraldehyde could be retained (adsorbed) in the Marcellus formation, its relative concentration in flowback fluid, its actual emission rate, and its fate in air (e.g., half-life). All of these considerations would need to be evaluated to determine whether the emissions of glutaraldehyde calculated by NYSDEC are actually achieved or whether the actual emissions of glutaraldehyde are actually much lower, as is likely to be the case in light of the numerous conservative assumptions. For example, the US EPA Office of Pesticides Reregistration Eligibility Decision (RED) for glutaraldehyde indicates a half-life of three hours in the atmosphere.l° Such a short half-life would lead to far lower glutaraldehyde concentrations in air than those modeled by NYSDEC. Thus, the fate of glutaraldehyde, and attenuation by mechanisms as noted above, would need to be evaluated, in order to adequately address potential health effects of glutaraldehyde used in HF additives.

10 US EPA, 2007

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## References

New York State, Dept. of Environmental Conservation (NYSDEC). 2009. "Well Permit Issuance for Horizontal Drilling and High-Volume Hydraulic Fracturing to Develop the Marcellus Shale and other Low-Permeability Gas Reservoirs (Draft)." Division of Mineral Resources, Bureau of Oil & Gas Regulation / Supplemental Generic Environmental Impact Statement on the Oil, Gas and Solution Mining Regulatory Program. September. NYSDEC. 1997. "The DEC Policy System: Guidelines for the Control of Toxic Ambient Air Contaminants" Accessed at http://www.dec.ny.gov/docs/air~df/darl .pdf. DAR- 1. November 12. Susquehanna River Basin Commission (SRBC). 2009. "Susquehanna River Basin Commission - Natural Gas Development." Presented to the Independent Oil and Gas Association of New York, November 4. Accessed on December 28, 2009 at http://www.srbc.net/programs/docs/69796_l.pdf. United States Environmental Protection Agency (US EPA). 1994. "Air Emissions Models for Waste and Wastewater." Office of Air Quality Planning and Standards. EPA-453/R-94-08A. 

### US EPA. 2007. "Reregistration Eligibility Decision for Glutaraldehyde." EPA 739-R-07-006. US EPA. 2009. "Risk Assessment Guidance for Superfund, Part F: Supplemental Guidance for Inhalation Risk Assessment."

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