[Federal Register: July 8, 2010 (Volume 75, Number 130)]
[Rules and Regulations]
[Page 39365-39390]
[DOCID:fr08jy10-20]

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Part III

Environmental Protection Agency

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40 CFR Part 52

Revisions to the California State Implementation Plan, Imperial County
Air Pollution Control District; Final Rule

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2010-0120; FRL-9169-2]

Revisions to the California State Implementation Plan, Imperial
County Air Pollution Control District

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: EPA is finalizing a limited approval and limited disapproval
of revisions to the Imperial County Air Pollution Control District
(ICAPCD or the District) portion of the California State Implementation
Plan (SIP) under the Clean Air Act as amended in 1990 (CAA or the Act).
This action was proposed in the Federal Register on February 23, 2010
and concerns local rules that regulate coarse particulate matter
(PM10) emissions from sources of fugitive dust such as
construction sites, unpaved roads, and disturbed soils in open and
agricultural areas in Imperial County.

DATES: Effective Date: This rule is effective on August 9, 2010.

ADDRESSES: EPA has established docket number EPA-R09-OAR-2010-0120 for
this action. The index to the docket is available electronically at
http://www.regulations.gov and in hard copy at EPA Region IX, 75
Hawthorne Street, San Francisco, California. While all documents in the
docket are listed in the index, some information may be publicly
available only at the hard copy location (e.g., copyrighted material),
and some may not be publicly available in either location (e.g., CBI).
To inspect the hard copy materials, please schedule an appointment
during normal business hours with the contact listed in the FOR FURTHER
INFORMATION CONTACT section.

FOR FURTHER INFORMATION CONTACT: Andrew Steckel, EPA Region IX, (415)
947-4115<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us'' and
``our'' refer to EPA.

Table of Contents

I. Summary of Proposed Action
II. Public Comments and EPA Responses
III. EPA Action
IV. Statutory and Executive Order Reviews

I. Summary of Proposed Action

    On February 23, 2010 (75 FR 8008), EPA proposed a limited approval
and limited disapproval of the following rules listed in Table 1, known
collectively as Regulation VIII, that were adopted by ICAPCD and
submitted by the California Air Resources Board (ARB) for incorporation
into the California SIP for the Imperial County serious PM10
nonattainment area.

                                 Table 1
------------------------------------------------------------------------
  Local agency      Rule No.      Rule title      Adopted     Submitted
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ICAPCD..........          800  General             11/08/05     06/16/06
                                Requirements
                                for Control of
                                Fine
                                Particulate
                                Matter.
                          801  Construction &      11/08/05     06/16/06
                                Earthmoving
                                Activities.
                          802  Bulk Materials.     11/08/05     06/16/06
                          803  Carry Out &         11/08/05     06/16/06
                                Track Out.
                          804  Open Areas.....     11/08/05     06/16/06
                          805  Paved & Unpaved     11/08/05     06/16/06
                                Roads.
                          806  Conservation        11/08/05     06/16/06
                                Management
                                Practices.
------------------------------------------------------------------------

    We proposed a limited approval because we determined that these
rules improve the SIP and are largely consistent with the relevant CAA
requirements. We simultaneously proposed a limited disapproval because
some provisions of the rules conflict with the CAA section 110(a)
requirement that SIP rules must be enforceable and the requirement in
section 189(b)(1)(B) for implementation of best available control
measures (BACM) in serious PM10 nonattainment areas such as
Imperial County. We discuss these statutory requirements and the
Regulation VIII deficiencies in detail in the proposed rule and in the
Technical Support Document for that proposal (proposal TSD).\1\ In the
proposed rule and proposal TSD we also discuss our determination of
which fugitive dust source categories addressed by Regulation VIII are
significant and consequently require BACM pursuant to EPA guidance.
This determination was based in part on our 2009 decision \2\ to not
concur with the State's request pursuant to EPA's exceptional events
rule \3\ (EER) to exclude certain exceedances of the PM10
National Ambient Air Quality Standard (NAAQS) in Imperial County from
consideration in regulatory actions under the CAA.\4\
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    \1\ Our proposed rule and proposal TSD also describe additional
improvements that we recommend for future ICAPCD modifications of
the rules. This final action is not based on those recommendations.
As a result, we do not respond here to all comments we received on
them.
    \2\ Letter with enclosure from Laura Yoshii (EPA), to James
Goldstene (ARB), Re: exceptional events requests regarding
exceedances of the PM10 NAAQS in Imperial County, CA,
December 22, 2009.
    \3\ 40 CFR 50.1(j) and 50.14.
    \4\ Issues related to the Regulation VIII deficiencies,
significant source categories and our decision not to concur with
the State's exceptional events requests are addressed further below
in our responses to comments we received on the proposed rule.
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    We summarize the Regulation VIII deficiencies addressed in our
proposed rule below. These deficiencies concern Regulation VIII
provisions relating to open areas, unpaved roads and agricultural
lands.

A. BACM-Related Deficiencies for Open Areas

1. Recreational Off-Highway Vehicle Activity
    While recreational off-highway vehicle (OHV) \5\ activity causes
much of the PM10 emissions from open areas in Imperial
County, Rule 804 regulates only a small portion of these emissions,
including those from OHV activity on State lands on which the rule is
not being implemented. The vast majority of the OHV emissions in
Imperial County are addressed only by requirements in Rule 800 section
F.5 for dust control plans (DCPs) for sources under the control of the
Bureau of Land Management (BLM). While BLM is required to describe in
the DCPs the dust control measures that it intends to implement, BLM is
not required to implement any specific BACM-level controls for OHV use.
Moreover, ICAPCD has not provided an analysis of BACM for OHV activity,
including

potential OHV activity in open areas and on unpaved roads and paths
that are exempt from the specific requirements and measures in Rules
804 and 805. The proposed rule and proposal TSD address how ICAPCD can
correct these deficiencies.\6\
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    \5\ As used here and in the proposal TSD, the term ``off-highway
vehicle'' or OHV includes all vehicles subject to the exemption in
Rule 800 section E.6 for recreational use of public lands in
Imperial County.
    \6\ 75 FR 8008, 8010-8011 and our proposal TSD, section III.B.1.
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2. Definition of ``Disturbed Surface''
    The term ``disturbed surface area'' is used in several Regulation
VIII rules but is never defined. For example, Rule 804 applies to a
source category for which BACM is required and relies on the undefined
term to describe rule applicability in Rule 804 section B. A definition
of this term is necessary in order to ensure that these rules are
enforceable at a BACM level.

B. BACM-Related Deficiencies for Unpaved Roads

1. Unpaved Non-Farm Roads
    While CAA section 189(b)(1)(B) requires ICAPCD to implement BACM by
2008 (i.e., four years after reclassification to serious),\7\ Rule 805
section E.7 allows the County until 2015 to stabilize heavily-travelled
unpaved roads. This schedule is inconsistent with the statutory
requirement and ICAPCD has not provided adequate evidence that this
schedule is as expeditious as practicable, based upon economic
feasibility or any other appropriate consideration. In addition, Rule
805 section E.7's requirement to stabilize all non-exempt unpaved
County roads is not adequately enforceable as currently structured
because it is not clear that the County is required to implement (and
not just submit) a stabilization plan; stabilize different unpaved
roads each year; and maintain all stabilized roads. The proposed rule
and proposal TSD address how ICAPCD can correct these deficiencies.\8\
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    \7\ On August 11, 2004, EPA reclassified Imperial County as
serious nonattainment for PM10. 69 FR 48835. Since 2008
has passed, BACM is now required to be implemented as expeditiously
as practicable. Delaney v. EPA, 898 F.2d 687 (9th Cir. 1990).
    \8\ 75 FR 8008, 8011 and our proposal TSD, section III.B.3.
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2. Unpaved Farm Roads and Traffic Areas
    Rule 805 section D.2 exempts agricultural roads and traffic areas
from the opacity and stabilization requirements applicable to non-
agricultural operation sites. Farm roads and traffic areas are only
required to implement a conservation management practice (CMP) from the
menus for unpaved roads and traffic areas in Rule 806 in contrast to
analogous rules in other geographical areas.
    Rule 806 sections E.3 and E.4 list CMPs intended to control
emissions from agricultural unpaved roads and traffic areas but these
measures are broadly defined and there is no other mechanism in the
rule to ensure specificity. The absence of sufficiently defined
requirements makes it difficult for regulated parties to understand and
comply with the requirements, and makes it difficult for ICAPCD or
others to verify compliance and to enforce the requirements if
necessary. The lack of specificity similarly renders it difficult to
assess whether the measures constitute BACM level controls. The
proposed rule and proposal TSD address how ICAPCD can correct these
deficiencies.\9\
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    \9\ 75 FR 8008, 8011 and our proposal TSD, section III.B.4.
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3. Border Patrol Roads
    Rule 800 section F.6.c exempts roads owned or operated by the U.S.
Border Patrol (BP) from Rule 805 requirements that are ``inconsistent
with BP authority and/or mission.'' It is not clear what this exemption
is intended to address, or how it would be implemented and enforced in
order to meet BACM requirements. The proposed rule addresses how ICAPCD
can correct these deficiencies.\10\
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    \10\ 75 FR 8008, 8011.
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C. BACM-Related Deficiencies for Agricultural Lands

1. Tilling and Harvesting
    Rule 806 sections E.1 and E.2 list CMPs intended to control
emissions from agricultural land preparation and cultivation (including
tilling), and harvest activities, but these measures are broadly
defined and there is no other mechanism in the rule to ensure
specificity. The absence of sufficiently defined requirements makes it
difficult for regulated parties to understand and comply with the
requirements, and makes it difficult for ICAPCD or others to verify
compliance and to enforce the requirements if necessary. The lack of
specificity similarly renders it difficult to assess whether the
measures constitute BACM level controls.
    In addition, Rule 806 section E requires one CMP from the ``land
preparation and cultivation'' category and one CMP from the
``harvesting'' category, while rules in other geographic areas have
more stringent requirements.
    The proposed rule and proposal TSD address how ICAPCD can correct
these deficiencies.\11\
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    \11\ 75 FR 8008, 8011-8012 and our proposal TSD, section
III.B.4.
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2. Windblown Dust
    Windblown dust from non-pasture agricultural lands is also a
significant source of PM10 that requires BACM independent of
agricultural tilling. The CMPs in Rule 806 section E, however, mainly
control emissions by reducing the number of vehicle passes across
fields, and sources are not required to select BACM level practices for
controlling windblown dust from active or fallow agricultural fields.
The proposed rule and proposal TSD address how ICAPCD can correct these
deficiencies.\12\
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    \12\ 75 FR 8008, 8012 and our proposal TSD, section III.B.4.
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D. Non-BACM Deficiency

    Rule 802 section D.1 allows the Air Pollution Control Officer
(APCO) to set aside controls that might be used instead of water to
stabilize surfaces of bulk materials. This discretion allows ICAPCD to
approve alternatives to the applicable SIP without following the SIP
revision process described in CAA section 110. Moreover, ICAPCD has not
demonstrated why such discretion is needed for measures such as
covering, enclosing or sheltering material piles. The proposed rule
addresses how ICAPCD can correct these deficiencies.\13\
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    \13\ 75 FR 8008, 8012.
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II. Public Comments and EPA Responses

    EPA's proposed action provided a 30-day public comment period.
During this period, we received nine unique comment letters from public
agencies and broad-based organizations.
     Brad Poiriez, Air Pollution Control Officer, Imperial
County Air Pollution Control District, March 25, 2010 (ICAPCD).
     Daniel Steward, Acting Field Manager, United States
Department of the Interior, Bureau of Land Management, El Centro
Resource Area, March 24, 2010 (BLM).
     Kathleen Dolinar, District Superintendent, Ocotillo Wells
District, California State Parks, Off-Highway Motor Vehicle Recreation
Division, by e-mail dated March 24, 2010 (OWD).
     Gail Sevrens, Acting District Superintendent, Colorado
Desert District, California State Parks, by e-mail dated March 25, 2010
(CDD).
     David P. Hubbard, Gatzke Dillon & Balance LLP, on behalf
of EcoLogic

Partners, Inc., March 25, 2010 (EcoLogic).
     Lisa T. Belenky, Senior Attorney, Center for Biological
Diversity, March 25, 2010, representing several listed parties (CBD).
     Jose Luis Olmedo, Executive Director, Comite Civico Del
Valle, Inc., March 25, 2010, submitted and joined by other parties
(Comite).
     Ayron Moiola, Executive Director, Coalition of Labor,
Agriculture & Business, March 24, 2010 (COLAB).
     Mark McBroom, President, Imperial County Farm Bureau,
March 24, 2010 (Farm Bureau).
    We also received over 100 comment letters from individuals and
organizations associated with recreational OHV activities. We reference
these comments below by their identification in the Federal docket
management system (FDMS) found at regulations.gov. For example, the
comment listed in FDMS as document number ``EPA-R09-OAR-2010-0120-
0219'' is referenced below as ``0219.''
    We summarize the comments and provide our responses below. In our
responses we identify specific commenters in some cases but not in
others, particularly where many commenters made similar points.

A. General

    These overarching comments largely provide general support or
opposition to our proposal.
    General #1: CBD and Comite support EPA's proposal to find that the
Regulation VIII submittal does not fully implement BACM level controls
for all significant source categories in Imperial County, and support
EPA's nonconcurrence with associated exceptional event requests. They
ask EPA to finalize the proposed limited disapproval of Regulation VIII
and to require additional PM10 emissions restrictions. Many
other commenters disagree with EPA's proposed limited disapproval,
especially with EPA's identification of deficiencies for BACM
requirements and EPA's nonconcurrence with exceptional events. ICAPCD,
for example, believes that EPA's proposal is arbitrary and capricious,
and that California has demonstrated that all required BACM are being
implemented in Imperial County.
    Response: No response is necessary for the overarching statements
of support or opposition. Responses are provided below to the specific
comments that support these general statements.
    General #2: Several commenters believe that EPA's proposal lacks
adequate scientific support. One (0144), for example, states that
passing sweeping air quality regulations in an area with unique terrain
and climate with only generalities to prove the sources of pollution is
unethical and appears anti-development, anti-OHV and anti-agriculture.
    Response: The scientific support for EPA's action is documented in
our proposal and the associated proposal TSD and discussed further in
response to specific comments below. See, for example, response to
comment EI 3 below. The serious health impacts of exposure to
elevated levels of PM10 are well known and well documented
and need not be reiterated here.
    General #3: ICAPCD objects to EPA taking over four years to act on
its submittals of Regulation VIII for approval and claims that EPA is
only now raising basic issues that ICAPCD believes should have been
resolved before rule adoption. For example, ICAPCD objects to EPA
disapproving a definition that it claims is clear and understood by all
affected parties. ICAPCD and others (e.g., COLAB) comment that EPA
never raised this and other concerns despite ICAPCD's extensive public
process and communication with EPA before rule adoption. ICAPCD also
cites EPA's testimony before the District Board in which the Agency
supported Regulation VIII as BACM. As a result, ICAPCD concludes that
EPA's proposal undermines ICAPCD's ability to rely on EPA comments in
the future.
    Response: EPA reviews and comments on many draft State and local
agency rules during their development prior to submittal to EPA for
formal approval. It is generally more efficient for all parties to
identify and resolve issues early in the process, rather than after
rules are adopted and submitted to EPA for inclusion into the SIP.
EPA's formal action on local rules, however, can only occur through
notice and comment rulemaking after rules have been officially
submitted to EPA by the State. If EPA determines during that process
that a submittal does not fulfill relevant CAA requirements, we cannot
approve the submittal. Given time and resource constraints, it is not
always possible for the Agency to identify or analyze fully all issues
before State or local rule adoption. Moreover, EPA must carefully
consider all public comments submitted on proposed EPA actions on State
and local rules. Such comments often identify issues and concerns that
may not have arisen during the prior evaluation of drafts of a rule. We
continue to believe, however, that communication between EPA and State
and local agencies at the rule development stage is productive.
    General #4: OWD asks EPA to extend the comment period because it
was informed of EPA's proposal only nine days before the close of the
comment period. Several commenters also state that EPA did not provide
adequate notification time (0218.1 and 0098) or consultation with State
Park personnel (0218.1 and OWD).
    Response: EPA denied OWD's request to extend the comment period
because EPA is under a court order \14\ to finalize action by June 15,
2010, and needs time to analyze all comments submitted on the
proposal.\15\ While more time and outreach before EPA action is always
desirable, nothing in the comments suggests that EPA failed to follow
relevant public notification requirements found in the Administrative
Procedures Act.\16\ EPA notes that OWD did comment on the proposal and
EPA has taken those comments into consideration in the final action.
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    \14\ Comite Civico Del Valle, Inc., v. Jackson, No. 09-cv-04095
PJH (N.D. Cal.).
    \15\ E-mail from Andrew Steckel, EPA, to Kathleen Dolinar,
California State Parks, March 29, 2010.
    \16\ See 5 U.S.C. 553.
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B. State Implementation Plan (SIP)

    These comments generally address broad SIP issues rather than
specific Regulation VIII provisions.
    SIP #1: OWD believes the PM10 standard is nearly
impossible to attain given Imperial's climate, natural desert
condition, the cost of inappropriate BACM, and other local conditions.
In contrast, Comite asks EPA to find that California has failed to
submit a PM10 plan as required by 72 FR 70222 (December 11,
2007), and to consider imposing associated CAA section 179 sanctions
and a section 110(c) Federal implementation plan (FIP) in this area.
    Response: Our proposed action addresses the CAA section
189(b)(1)(B) requirement for BACM for certain PM10 sources
in Imperial County. The submittal at issue, Regulation VIII, is but one
portion of the complete SIP that ICAPCD must develop in order to meet
additional CAA requirements. These comments address the separate and
broader statutory obligations for the State to submit a PM10
plan that, among other things, demonstrates expeditious attainment of
the PM10 NAAQS. Those other obligations are not the subject
of this action.
    SIP #2: ICAPCD does not believe that any additional controls such
as those that may need to be implemented if EPA partially disapproves
Regulation VIII

will prevent PM10 exceedances during high winds or otherwise
materially benefit air quality on days unaffected by high winds. ICAPCD
further believes that such additional controls will waste limited
resources that should be used in other ways to improve local air
quality in the area.
    Response: CAA section 189(b)(1)(B) and EPA guidance \17\ require
that BACM be implemented for all significant source categories \18\ in
serious PM10 nonattainment areas such as Imperial County. As
explained in our proposal,\19\ we determined that each of the
subcategories under open areas, unpaved roads and agricultural lands
below meet or exceed the 5 [micro]g/m\3\ de minimis level in our
guidance and are therefore significant source categories in Imperial
County:
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    \17\ ``State Implementation Plans for Serious PM-10
Nonattainment Areas, and Attainment Date Waivers for PM-10
Nonattainment Areas Generally; Addendum to the General Preamble for
the Implementation of Title I of the Clean Air Act Amendments of
1990;'' 59 FR 41998 (August 16, 1994) (General Preamble Addendum).
    \18\ Under the General Preamble Addendum, a source category
``will be presumed to contribute significantly to a violation of the
24-hour NAAQS if its PM10 impact at the location of the
expected violation would exceed 5 [micro]g/m\3\.'' This is also
referred to as the de minimis level. Id. at 42011.
    \19\ 75 FR 8008, 8010, and proposal TSD, pp. 5-7.
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    Open areas:

--Windblown Dust, Other Open Area.

    Unpaved roads:

--Entrained Unpaved Road Dust, City/County.
--Entrained Unpaved Road Dust, Canal.
--Windblown Dust, Unpaved City/County Road.
--Windblown Dust, Unpaved Canal Road.
--Windblown Dust, Unpaved Farm Road.

    Agricultural lands:
--Tilling.
--Windblown Dust, Non-Pasture Agricultural Lands.

    As EPA stated in the guidance, the structural scheme throughout
title I of the CAA, including its provisions for the PM10
NAAQS, requires the implementation of increasingly stringent control
measures in areas with more serious pollution problems. EPA further
stated ``that the more serious the air quality problem, the more
reasonable it is to require States to implement control measures of
greater stringency despite the greater burdens such measures are likely
to cause.'' \20\ Imperial County continues to violate the
PM10 standard \21\ and our proposed action identifies
several components of the State's Regulation VIII submittal relating to
open areas, agricultural lands and unpaved roads that do not fulfill
the CAA BACM requirement and the enforceability requirements of CAA
section 110(a).
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    \20\ General Preamble Addendum at 42010.
    \21\ EPA's Air Quality System Preliminary Design Value Report
(May 18, 2010) shows 17 exceedances of the 24-hour PM10
NAAQS in Imperial County between 2007 and 2009.
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    We further address ICAPCD's contention that additional Regulation
VIII controls will not prevent PM10 exceedances during high
winds in our response to comment EE 1 below.
    SIP #3: Many commenters emphasize the importance of OHV areas in
Imperial County for recreation, and believe that enjoyment of the
desert should not be restricted. Commenters note that many
organizations help keep the desert clean, and one commenter (0175.1)
believes such efforts would be reduced if OHV areas are closed.
    Response: Recreation, enjoyment of the desert and clean deserts are
certainly desirable, whether for OHV use or otherwise. However, except
as implicit in our response to comment OHV 5 below, they are
not germane to the evaluation in our proposal and in this final rule of
Regulation VIII and its compliance with the applicable CAA
requirements.
    SIP #4: Two commenters (OWD and 0218.1) question whether EPA's
proposal is based on statistically significant data since there were
only three PM10 exceedances within a three year period.
    Response: ICAPCD's obligation to implement BACM for Regulation VIII
fugitive dust sources derives from the Imperial County's designation as
nonattainment and classification as serious. On November 15, 1990, the
date of enactment of the 1990 Clean Air Act Amendments, Imperial County
was designated nonattainment and classified as moderate.\22\ On August
11, 2004, EPA reclassified the area as serious in compliance with a
mandate of the U.S. Court of Appeals for the Ninth Circuit.\23\ The
reclassification, pursuant to CAA section 188(b)(2), was based on a
finding that the area failed to attain the PM10 NAAQS by the
statutory deadline of December 31, 1994. Once reclassified to serious,
the area was required to comply with CAA section 189(b)(1)(B), which
required that BACM be implemented for the area four years after its
reclassification to serious.
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    \22\ 56 FR 56694 (November 6, 1991).
    \23\ 69 FR 48792; Sierra Club v. United States Environmental
Protection Agency, et al., 346 F.3d 995 (9th Cir. 2003); cert.
denied, 542 U.S. 919 (2004).
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    The three exceedances to which OWD refers occurred during 2006 and
2007. The State requested that these exceedances be excluded from use
in regulatory actions pursuant to EPA's EER.\24\ Because we did not
concur with the State's request, BACM is required to be implemented for
certain windblown dust source categories, including open areas, for
which such controls would not have been required if we had agreed with
the State.\25\ See our responses to Exceptional Events comments below.
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    \24\ See section II.D.1 below.
    \25\ 75 FR 8008, 8010 and proposal TSD pp. 5-7.
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    We also note that California has chosen to sample PM10
in Imperial County only one out of every six days. As a result, by
regulation, each monitored exceedance is estimated to represent
approximately six exceedances rather than one.\26\ For example, in
2009, ICAPCD reported three monitored exceedances at the Ethel Street
monitoring site, which are estimated to represent 18.3 exceedances.
Exceedances were also monitored at Brawley, El Centro, Westmorland and
Niland in 2009.\27\
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    \26\ 40 CFR part 50, appendix K.
    \27\ EPA's Air Quality System Preliminary Design Value Report
(May 18, 2010).
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    SIP #5: Comite believes PM10 should be further
controlled in Imperial County by adoption of local fugitive dust
ordinances like those in Coachella's Cathedral City, and by
strengthening open burning regulations to be similar to those in the
South Coast Air Quality Management District (SCAQMD) and the San
Joaquin Valley Unified Air Pollution Control District (SJVUAPCD).
    Response: We assume the commenter refers to title 8, chapter 8.54
of Cathedral City's municipal code which describes requirements for
construction, unpaved roads and other local dust sources.\28\ These
requirements are generally similar to the type of controls adopted by
SCAQMD (e.g., Rule 403), SJVUAPCD (e.g., Regulation VIII) and ICAPCD
(Regulation VIII). The commenter does not identify any specific
Cathedral City controls that it believes are needed in ICAPCD
Regulation VIII to constitute BACM. Except where identified in our
proposal, we believe ICAPCD's BACM analyses include adequate evaluation
of analogous fugitive dust controls in other areas.\29\ It is possible
that the commenter is recommending duplicative city ordinances that
overlap County-wide Regulation VIII. While such redundancy could
improve compliance, it is generally not necessary

to meet CAA section 110(a) enforceability requirements.
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    \28\ Cathedral City Municipal Code, title 8, chapter 8.54,
Fugitive Dust Control; http://qcode.us/codes/cathedralcity/.
    \29\ 2009 PM10 SIP table 4.2 and 2005 BACM analysis
table 4.2.
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    Finally, our proposed action only addresses the ICAPCD controls for
certain PM10 source categories encompassed by Regulation
VIII, and therefore does not address control of open burning or many
other air pollution sources in Imperial County. See also responses to
comments SIP 1 and EI 1.
    SIP #6: Comite cites Vigil v. Leavitt, 381 F.3d 826, 834 (9th Cir.
2004) and Hall v. EPA, 273 F.3d 1146 (9th Cir. 2001), in commenting
that measures in other areas can be considered BACM for Imperial County
and are per se feasible. Comite further argues that what constitutes
BACM can strengthen over time. In contrast, OWD does not believe that
Imperial County should apply mitigation measures from other geographic
areas (e.g., SJVUAPCD and Maricopa) that have different geologic and
other local conditions. Similarly, COLAB believes that different
cultural practices prevent ICAPCD from blindly implementing controls
imposed in other areas, although the ICAPCD and SJVUAPCD CMP rules are
very similar. Still another commenter (0119) claims that similar
restrictions on construction, OHVs, farmers, etc., in Las Vegas and
elsewhere have not been effective, and there is no need for such
draconian and ineffective bureaucratic rules.
    Response: EPA believes that it is appropriate, when evaluating what
constitutes BACM for a given source category, to consider controls that
have been adopted and implemented in other geographical areas. EPA
agrees that the facts and circumstances in a given area can affect what
constitute BACM for that area, but that this determination must be
based upon appropriate consideration of relevant information specific
to that area.
    Comite does not explain how the cited cases support its position.
Nonetheless, we agree that in evaluating BACM for Imperial County,
ICAPCD should analyze analogous measures in other areas and that BACM
may strengthen over time.\30\ Our proposal identifies several
significant deficiencies in ICAPCD's analysis to date.\31\ While BACM
is determined on a case-by-case basis \32\ and, as such, the analysis
can include evaluation of local conditions that might make specific
controls economically and/or technologically feasible in one area but
not another,\33\ neither the 2009 PM10 SIP \34\ nor the
comment provides sufficient detail to adequately address the
deficiencies identified in our proposal.
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    \30\ General Preamble Addendum at 42013-42014.
    \31\ E.g., OHV controls in Arizona Revised Statute Sec.  49-
457.03 and Clark County Air Quality Regulations, section 90 (75 FR
8011, February 23, 2010).
    \32\ General Preamble Addendum at 42010 and 42012.
    \33\ In this respect, we do not agree with Comite that measures
adopted in other areas are automatically transferable to Imperial
County.
    \34\ ``2009 Imperial County State Implementation Plan for
Particulate Matter Less Than 10 Microns in Aerodynamic Diameter,
Final,'' adopted by ICAPCD Governing Board on August 11, 2009. (2009
PM10 SIP).
---------------------------------------------------------------------------

    OWD does not explain how Imperial County differs so markedly from
the San Joaquin Valley and the Maricopa area that it would be
inappropriate to consider BACM approved in those areas as part of the
evaluation of controls for the same source categories in Imperial
County. Similarly, COLAB does not elaborate on what ``cultural
practices'' in Imperial County would justify disregarding approved BACM
in the San Joaquin Valley and the Maricopa area as part of the
evaluation of what controls would be appropriate for comparable source
categories in Imperial County.

C. Emissions Inventory (EI)

    EI #1: Many commenters oppose further OHV controls because they
believe OHVs contribute little to Imperial County's PM10
pollution problem compared to other sources. Commenters identify
various sources they believe are more significant and/or should be
further addressed instead, including fallow fields, fireplaces, feed
lots, agricultural burning, pesticides, dirt roads, inefficient street
lights, insufficient public transportation, insufficient speed limit
enforcement, Interstate 8, the New River, the Salton Sea, Arizona to
the east, San Diego to the west, Mexican roads, fires and factories to
the south, rain, wind, erosion, dust storms and other natural
occurrences. These commenters include OWD, 0096, 0097, 0150, 0139,
0152, 0180, 0192, 0194 and 0219.1.
    Response: Our proposal explains that BACM is required for all
significant PM10 source categories in Imperial County, that
windblown dust from open areas is a significant PM10 source
category, and that OHVs greatly increase emissions from open areas in
Imperial County.\35\ Our proposal further explains that ICAPCD has not
demonstrated implementation of BACM for open areas with respect to
OHVs.\36\ These conclusions are based on inventory information prepared
by ICAPCD and ARB and used during development of Regulation VIII and
the 2009 PM10 SIP.\37\
---------------------------------------------------------------------------

    \35\ Proposal TSD, pp. 5-8.
    \36\ Id. at p. 8.
    \37\ Id. at pp. 5-8.
---------------------------------------------------------------------------

    The inventory in the 2009 PM10 SIP represents the most
comprehensive information currently available on OHV emissions in
Imperial County.\38\ ICAPCD's analysis in the 2009 PM10 SIP
concluded that windblown dust from open areas was not a significant
source category, but this conclusion was premised upon many exceedences
of the NAAQS being deemed to be the result of exceptional events.
However, EPA's own conclusion regarding those exceedences is that they
were not caused by exceptional events and, as a result, we consider
windblown dust from open areas to be a significant source category that
is subject to the CAA's BACM requirement. See response to comment SIP
4 and responses to Exceptional Events comments in section II.D
below. Therefore ICAPCD has failed to meet the BACM requirement for
windblown dust from open areas, in part because ICAPCD has not
evaluated what controls might be appropriate for OHV activities in such
areas.
---------------------------------------------------------------------------

    \38\ 2009 PM10 SIP, Chapter 3; Appendix III.
---------------------------------------------------------------------------

    EPA's action on the Regulation VIII submittal does not address or
depend on whether additional controls may also be appropriate for the
various other sources identified in the comments.
    EI #2: One commenter (0188) had driven past many farms in El Centro
during tilling and observes that the dust was very minimal. Another
(0201) thinks more attention should be paid to agriculture which the
commenter believes is exempt from many of the environmental
regulations.
    Response: See response to comment EI 1. Similar to
emissions from open areas, EPA has concluded that emissions associated
with tilling on and windblown dust from agricultural lands are
significant source categories in Imperial County and, as such, ICAPCD
needs to meet the BACM requirement for such sources.\39\
---------------------------------------------------------------------------

    \39\ Proposal TSD, pp. 5-8 and 9-11.
---------------------------------------------------------------------------

    The commenter (0201) concerned about exemptions for agriculture did
not specify which regulations exempt agriculture. As explained in our
proposal, however, because certain agricultural-related activities
constitute a significant source category for PM10 in
Imperial County, ICAPCD is required to meet the CAA's BACM requirements
for such sources. Any ``exemptions'' for any such sources would need to
be justified and explained in the context of meeting the BACM
requirements.
    EI #3: Several commenters claim that EPA has not proved the impact
of OHVs

on PM10 levels sufficient to require additional OHV
regulations. OWD notes, for example, that: (1) EPA did not analyze
extreme terrain, thermal stability and other effects on winds in the
desert; (2) most emissions from open lands come from undisturbed shrub/
grassland which are not anthropogenic sources; and (3) ICAPCD's 2009
PM10 SIP, on which EPA relies, uses worst-case assumptions
rather than actual soil condition information to estimate that OHVs
represent less than 5% of the County's total PM10 emissions
(13.9 of 282 tpd). OWD states that 99% of these total emissions relate
to OHVs subject to Federal and State stewardship. Therefore OWD
concludes that actual OHV emissions are small compared to worst-case
estimates. OWD also questions EPA's reference for the estimate of 22
tpd of windblown PM10 from OHVs.
    EcoLogic believes that EPA needs monitoring in the Ocotillo Wells
State Vehicle Recreation Area (SVRA) and other areas to show how
specific OHV activity affects sensitive receptors and for EPA to
identify OHV activity as a major contributor to the County's
PM10 problem. Another commenter believes EPA lacks data
tying PM to specific OHV activities (0218.1), and several commenters
believe that any pollution from OHVs is virtually immeasurable. Several
commenters believe additional inventory analysis is particularly
important because OHV areas are far from population centers and
monitors with PM10 exceedances. One commenter (0131)
requests an unbiased third-party study of OHV impacts. CDD explains
that PM10 emissions from several specific parks in Imperial
County should be low, partly because OHV activity is prohibited. In
contrast, CBD supports EPA's claim that OHVs on BLM land cause
considerable PM10 in Imperial County, and notes that BLM
previously estimated PM10 impacts from OHV activities at the
Aldodones Dunes alone as high as 11 tpd on holiday weekends.
    Response: It is extremely difficult to quantify and speciate
accurately the myriad sources of PM10 emissions and
PM10 precursor emissions spatially and temporally for
purposes of modeling air pollution impacts and developing cost
effective control programs. As a result, emission inventories are
constantly being refined as more and better science and data become
available. However, EPA, State and local air pollution agencies must
make policy and regulatory decisions based on the best information
available to comply with the CAA. As discussed in response to comment
EI 1, the inventory and other information underlying our
proposal regarding the emissions from OHV activity and the impacts of
such activity represent the most comprehensive information currently
available.
    Regarding specific concerns in this comment:
    (1) EPA's conclusion that BACM is required for OHV activity relies
on emissions inventory estimates that ICAPCD developed. If appropriate,
ICAPCD could choose to refine those estimates to take into
consideration factors such as terrain, thermal stability and other
effects on winds in the desert, as well as distances between OHV areas
and population centers and additional third party analysis. Such
refinements are beyond the level of detail normally used in inventories
required by CAA section 172(c)(3).\40\
---------------------------------------------------------------------------

    \40\ See, e.g., AP-42, Fifth Edition, Volume I, Chapter 13:
Miscellaneous Sources, 13.2.2--Unpaved Roads, Final Section, EPA,
November 2006. This document provides EPA guidance on estimating
emissions on unpaved roads and does not, for example, account for
road terrain. http://www.epa.gov/ttn/chief/ap42/ch13/index.html.
---------------------------------------------------------------------------

    (2) ICAPCD in its 2009 PM10 SIP quantifies the impact of
soil type and land cover (e.g., shrub/grassland) and degree of OHV
disturbance in OHV emission estimates relied on by our proposal.\41\
---------------------------------------------------------------------------

    \41\ 2009 PM10 SIP, appendix III.B.
---------------------------------------------------------------------------

    (3) ICAPCD used the best available information regarding soil types
in open areas and determined that the remaining uncertainty does not
affect the results of the technical analyses.\42\
---------------------------------------------------------------------------

    \42\ 2009 PM10 SIP, p. 3-2.
---------------------------------------------------------------------------

    (4) Even OWD's 13.9 tpd OHV emission estimate, which we believe is
too low,\43\ exceeds the presumptive 5 [micro]g/m\3\ de minimis level
for source categories requiring BACM.\44\
---------------------------------------------------------------------------

    \43\ In comparison to ICAPCD's 22 tpd estimate. Proposal TSD,
footnote 32.
    \44\ As discussed on pp. 5-8 of the proposal TSD, depending on
the specific monitor, 2-3% of Imperial County's annual inventory is
calculated to result in a 5 [micro]g/m\3\ contribution, which
equates to about 6-8 tpd emissions.
---------------------------------------------------------------------------

    (5) The reference for 22 tpd of windblown OHV emissions is
accurately explained in our proposal.\45\
---------------------------------------------------------------------------

    \45\ Id.
---------------------------------------------------------------------------

    The comment that monitoring is necessary in the Ocotillo Wells SVRA
and other areas before EPA should require controls for OHV activities
is incorrect. As stated previously, under CAA section 189(b) and EPA
guidance, BACM is required for all significant source categories in the
nonattainment area, including windblown dust in open areas caused by
OHV activity.\46\ Thus monitoring, which could provide valuable
information, is nevertheless not necessary to determine which source
categories require BACM.
---------------------------------------------------------------------------

    \46\ See, e.g., proposal TSD, p. 5.
---------------------------------------------------------------------------

D. Exceptional Events (EE)

1. Background
    On March 22, 2007, EPA adopted a final rule to govern the review
and handling of certain air quality monitoring data for which the
normal planning and regulatory processes are not appropriate.\47\ Under
the rule, EPA may exclude data from use in determinations of NAAQS
exceedances and violations if a State demonstrates that an
``exceptional event'' caused the exceedances. Before EPA can exclude
data from these regulatory determinations, the State must flag the data
in EPA's Air Quality System database and, after notice and opportunity
for public comment, submit a demonstration to EPA to justify the
exclusion. After considering the weight of evidence provided in the
demonstration, EPA decides whether or not to concur with each flag.
---------------------------------------------------------------------------

    \47\ ``Treatment of Data Influenced by Exceptional Events,'' 72
FR 13560 (March 22, 2007) (EER).
---------------------------------------------------------------------------

    On May 21, 2009, ARB submitted demonstrations for ``high wind''
events that allegedly caused ten exceedances of the 24-hour
PM10 standard at various monitors in Imperial County in 2006
and 2007. The demonstrations consisted of the following support
documents (listed in Table 2) prepared by ARB, ICAPCD, and ICAPCD's
contractor, ENVIRON:

                                                     Table 2
----------------------------------------------------------------------------------------------------------------
                   Description                           Document date                Abbreviated title
----------------------------------------------------------------------------------------------------------------
Natural Event Documentation: Calexico and          January 30, 2009........  September NED.\48\
 Westmorland, California--September 2, 2006.
Natural Event Documentation: Brawley and           April 15, 2008..........  Original April NED.
 Westmorland, California--April 12, 2007
 [enclosed with June 13, 2008 letter to Sean
 Hogan].

Natural Event Documentation: Brawley, Calexico,    April 15, 2008..........  Original June NED.
 El Centro, Niland, and Westmorland, California--
 June 5, 2007, Imperial County Air Pollution
 Control District [enclosed with June 13, 2008
 letter to Sean Hogan].
Natural Event Documentation: Brawley and           March 12, 2009..........  April NED.
 Westmorland, California--April 12, 2007
 [addendum to June 13, 2008 submittal].
Natural Event Documentation: Imperial County,      March 12, 2009..........  June NED.
 California--June 5, 2007 [addendum to June 13,
 2008 submittal].
----------------------------------------------------------------------------------------------------------------

    As stated above in section I, on December 22, 2009, EPA denied
ARB's request to exclude all of the exceedances as exceptional events.
The basis for our decision is specified in an enclosure which
accompanied the December 22, 2009 letter.\49\ By letter, including
Attachment A and Appendix A1, dated March 3, 2010, ICAPCD asked EPA to
reconsider this decision.\50\
---------------------------------------------------------------------------

    \48\ We refer to the natural event documentation in these five
documents, collectively, as the NEDs.
    \49\ See footnote 2. We refer to our December 22, 2009 letter
and the enclosure hereafter as ``2009 EE decision.''
    \50\ Letter from Brad Poiriez (ICAPCD) to Jared Blumenfeld
(EPA), March 3, 2010 with Attachment A and Appendix A1.
---------------------------------------------------------------------------

    Our proposal on Regulation VIII explained that our 2009 EE decision
led to an adjustment of ICAPCD's significant source analysis which in
turn led us to modify the list of significant sources for which BACM
must be implemented in Imperial County under CAA section
189(b)(1)(B).\51\ As a result, our 2009 EE decision was the subject of
public comments on our proposed action. ICAPCD resubmitted its March 3,
2010 letter, including Attachment A and Appendix A1, regarding our 2009
EE decision as Appendix C to its March 25, 2010 comment letter on our
Regulation VIII proposed action.\52\ EPA also received comments
pertaining to our exceptional events decision from Comite and CBD. A
summary of these comments and our responses follow.
---------------------------------------------------------------------------

    \51\ See 75 FR 8010 and the proposal TSD, pp. 5-7.
    \52\ We refer to ICAPCD's March 10, 2010 letter with its
Attachment A and Appendix A1, collectively, throughout our responses
to the exceptional events comments in section II.D as
``Attachment.''
---------------------------------------------------------------------------

2. Events Not Reasonably Controllable or Preventable
    EE #1: ICAPCD (Attachment) disagrees with EPA's interpretation of
the requirement in the EER at 40 CFR 50.1(j) that in order for an event
to meet the regulatory definition of exceptional event, such event must
be ``not reasonably controllable or preventable.'' Specifically ICAPCD
takes issue with EPA's statement in our 2009 EE decision that this
criterion inherently implies ``a requirement that the State demonstrate
that anthropogenic sources contributing to the exceedance caused by the
event were reasonably well controlled.'' ICAPCD believes that under the
plain regulatory language it is irrelevant whether ``reasonable and
appropriate'' controls are in place on the day of an otherwise
qualifying event when it can be shown that such controls would not
reduce emissions and impact at the monitor sufficiently to prevent the
exceedance. ICAPCD believes that it is inconsistent with the intent of
the CAA for EPA to refuse to concur with an exceptional event claim
solely due to EPA's dissatisfaction with the stringency of certain
controls when such controls could not have prevented the exceedance.
    Response: ICAPCD mischaracterizes both the plain language and the
regulatory intent of 40 CFR 50.1(j) by reading the words ``reasonably
controllable or'' out of that section. The regulation clearly requires
a showing that the event is not either reasonably controllable or
preventable, not as ICAPCD would have it, that the event cannot be
controlled to the extent that no exceedance would have occurred.
Furthermore, ``control'' as generally used in the CAA and EPA guidance
(e.g., RACT and BACM \53\), and as defined in the dictionary means to
regulate or to reduce the incidence or severity.\54\ Thus the meaning
of the word ``control'' undeniably differs from the words ``eliminate''
or ``prevent.'' Therefore, to meet the ``not reasonably controllable or
preventable'' criterion in 40 CFR 50.1(j), states must demonstrate that
reasonable controls were implemented to regulate or reduce emissions
regardless of whether the controls would have prevented
exceedances.\55\ Finally we note that the relevance of dust controls is
inherent in the District's own characterization of the ``event'' as the
combination of wind and dust entrainment from anthropogenic and
nonanthropogenic sources.\56\
---------------------------------------------------------------------------

    \53\ ``BACM is the maximum degree of emissions reduction of
PM10 and PM-10 precursors from a source * * * which is
determined on a case-by-case basis, taking into account energy,
environmental, and economic impacts and other costs, to be
achievable for such source through application of production
processes and available methods, systems, and techniques for control
of each such pollutant.'' General Preamble Addendum at 42010.
    \54\ Merriam-Webster's Ninth New Collegiate Dictionary.
    \55\ Similarly, EPA explained in the preamble to the EER that
analysis of exceptional events includes consideration of whether
anthropogenic activities have been controlled to the extent possible
through use of all reasonably available reasonable and appropriate
measures. 72 FR 13560, 13566, footnote 11.
    \56\ E.g., September NED, p. 9.
---------------------------------------------------------------------------

    As discussed in our 2009 EE decision, the State failed to
demonstrate that reasonable controls were implemented for anthropogenic
sources contributing to the exceedances, including recreational OHVs
and fallow agricultural fields.\57\ Nor does ARB or ICAPCD provide
convincing evidence in the NEDs or elsewhere to support the claim that
controls on these sources could not have either prevented the
exceedances or reduced emissions.
---------------------------------------------------------------------------

    \57\ 2009 EE decision, section 4.2.
---------------------------------------------------------------------------

    EE #2: ICAPCD (Attachment) further argues that the consequence of
EPA's action would be to require control measures beyond the area's
practical abilities--a result the EER is specifically designed to
avoid. ICAPCD claims that other specific provisions are in place to
prevent such difficulties, and ICAPCD quotes from EPA guidance: ``If
emissions from anthropogenic sources are reduced to the point that it
is no longer technologically or economically feasible to reduce those
emissions further, and the area still cannot attain the NAAQS, the EPA
may consider waiving the serious area attainment date and appropriate
serious area requirements.'' \58\
---------------------------------------------------------------------------

    \58\ General Preamble Addendum at 42008.
---------------------------------------------------------------------------

    Response: The provisions to which ICAPCD refers are contained in
CAA section 188(f) which authorizes EPA to waive subpart 4 requirements
applicable to serious PM10 nonattainment areas, including
BACM, where EPA determines that anthropogenic sources of
PM10 do not contribute significantly to the violation of the
standard in the area. Under section 188(f), EPA may

also waive a specific date for attainment of the PM10
standard if the Administrator determines that nonanthropogenic sources
contribute significantly to a violation of the standard.
    In guidance, EPA has established the same test for determining what
constitutes a significant contribution for section 188(f) as is used
for determining the sources for which BACM must be implemented under
CAA section 189(b)(1)(B).\59\ The passage in the guidance, quoted in
isolation by ICAPCD, is preceded by a lengthy discussion regarding the
circumstances under which a serious area such as Imperial County could
qualify for section 188(f) waivers. That discussion makes clear that
before EPA will consider waiving a serious area attainment date and
requirements for a serious area that failed to attain the standard by
the serious area deadline, the State must demonstrate that BACMs for
significant anthropogenic sources have been implemented and that the
area cannot attain the NAAQS with the implementation of additional
control measures to achieve at least 5% annual emission reductions
pursuant to CAA section 189(d). As discussed above and in the
proposal,\60\ ICAPCD has not shown that BACM has been implemented as
required by CAA section 189(b)(1)(B) for all significant source
categories in Imperial County.\61\ Thus it would be difficult to show
that additional controls are ``beyond the area's practical abilities''
or ``no longer technologically or economically feasible'' without a
more thorough BACM analysis.
---------------------------------------------------------------------------

    \59\ Id. at 42004.
    \60\ 75 FR 8008, 8010-8012 and proposal TSD, pp. 7-11.
    \61\ The 2009 PM10 SIP for Imperial County that is
intended to address the 5% requirement in CAA section 189(d) was
adopted by ICAPCD in August 2009 but has not been submitted to EPA
by ARB. The plan concludes that the area would have attained the
PM10 standard by the end of 2008 but for transported
emissions from Mexico and with the ``exclusion of PM10
measurements affected by high-wind exceptional events.'' As a result
of the claimed exceptional events, with which we did not concur in
our 2009 EE decision, the plan also concludes that ``[t]he 5% yearly
emission reductions requirement does not apply to future years.''
2009 PM10 SIP, section 5.3.
---------------------------------------------------------------------------

    EE #3: ICAPCD (Attachment) believes, citing the preamble to the
EER, that the rule only requires reasonable controls for anthropogenic
sources within the State.
    Response: While Imperial County air quality may be affected by
emission sources from areas outside California, such as Arizona and
Mexico, our 2009 EE decision relies on the lack of demonstrated
controls for anthropogenic sources within California.
    EE #4: ICAPCD (Attachment) believes that EPA has not specified
criteria for defining de minimis anthropogenic sources in the EER
context, explained how the EER justifies such criteria, or described
feasible analyses to implement such criteria.
    Response: As noted above, our 2009 EE decision stated that inherent
in the ``not reasonably controllable or preventable'' criterion of the
definition of ``exceptional event'' in 40 CFR 50.1(j) ``is a
requirement that the State demonstrate that anthropogenic sources
contributing to the exceedance caused by the event were reasonably
controlled.'' We also suggested that this requirement be limited to
``all non-de minimis anthropogenic sources.'' \62\ In this case,
however, rather than further interpreting the EER, we relied on
statements in the NEDs acknowledging anthropogenic contributions in
order to determine which anthropogenic sources were contributing to the
2006 and 2007 exceedances.\63\
---------------------------------------------------------------------------

    \62\ 2009 EE decision, section 4.2.
    \63\ See id., section 4.2.1.
---------------------------------------------------------------------------

    EE #5: ICAPCD (Attachment) opposes the statement in EPA's 2009 EE
decision that ``because implementation of BACM is required in serious
PM10 areas such as Imperial County under section 189(b) of
the CAA, it is appropriate to consider that level of control in
evaluating whether reasonable controls are in place for purposes of the
Exceptional Events Rule.'' Specifically, ICAPCD argues that (1) such a
standard would create a new standard for exceptional event showings
that is inconsistent with the language and intent of the EER which
entails only ``reasonable'' and not ``best'' control of anthropogenic
sources; (2) the purpose of the EER is to protect states from
consequences of reclassification as a result of exceptional events; (3)
by definition, exceptional events fall outside the normal planning
process and their analysis should not depend on elements of the normal
planning process including designation status; and (4) the meaning of
``reasonable controls'' for the EER should not vary by an area's
nonattainment status and should not be as stringent as BACM.
    Response: As stated in our 2009 EE decision and in the preamble to
the EER, EPA addresses the EER criteria, including that the event must
be ``not reasonably controllable or preventable,'' on a case-by-case
basis considering the weight of available evidence.\64\ Thus it is
appropriate to consider the totality of circumstances in Imperial
County in determining what constitutes ``reasonable'' controls. We note
again that the County has been designated nonattainment and classified
as moderate or serious since 1990. The area was reclassified to serious
in 2004.
---------------------------------------------------------------------------

    \64\ 2009 EE decision, pp. 4 and 7; 72 FR 13560, 13569.
---------------------------------------------------------------------------

    In evaluating rules as RACM or BACM, EPA has long considered it
appropriate to consider local conditions since what is technologically
and economically feasible in one area may not be in another.\65\
Moreover, EPA's 2009 EE decision did not define reasonable control as
BACM in all cases or suggest that the EER mandates such an outcome.
Rather, we stated that ``[b]ecause implementation of BACM is required
in serious PM10 nonattainment areas such as Imperial County
under CAA section 189(b), it is appropriate to consider that level of
control in evaluating whether reasonable controls are in place for
purposes of the Exceptional Events Rule.'' 66 67 While
ICAPCD states that this is inappropriate reliance on the normal
planning process, an area's nonattainment designation and
classification are inherently part of the local conditions that are
appropriately factored into what controls are reasonable for purposes
of the EER. We also noted that ARB had failed to demonstrate any
meaningful analysis of BACM or any other level of control for either
OHVs or fallow fields, despite apparent significant emissions and
available controls imposed elsewhere.\68\
---------------------------------------------------------------------------

    \65\ See 57 FR 13498, 13540-13541 (April 16, 1992) and the
General Preamble Addendum at 42010.
    \66\ 2009 EE decision, section 4.2.2; 72 FR 70222.
    \67\ We note that in EPA's Natural Events Policy which applied
prior to the EER, we stated that ``BACM must be implemented at
contributing anthropogenic sources of dust in order for PM-10 NAAQS
exceedances to be treated as due to uncontrollable natural events
under this policy.'' This requirement applied to moderate areas
which otherwise would not have been required to implement BACM at
all as well as to serious areas. Thus, while the EER does not
include such a mandate, it is entirely appropriate and consistent
with the Agency's past practice to consider a BACM level of control
in assessing whether reasonable controls are in place. Memorandum
from Mary D. Nichols, EPA, ``Areas Affected by PM-10 Natural
Events,'' May 30, 1996, p. 5.
    \68\ 2009 EE decision, pp. 9-10.
---------------------------------------------------------------------------

    EE #6: ICAPCD (Attachment) comments that OHV emissions were
quantified in the 2009 PM10 SIP at EPA's request, but EPA
ignored this information in its analysis of the exceptional event
requests.
    Response: It is the responsibility of the State to submit
demonstrations addressing the EER criteria \69\ to support its
exceptional event requests and it is generally not appropriate or
feasible for

us to correct NED deficiencies by searching for additional information.
Nonetheless, we did review the 2009 PM10 SIP before
preparing the 2009 EE decision and did not ignore ICAPCD's efforts to
quantify OHV emissions in the 2009 PM10 SIP. In fact, the
2009 EE decision references these efforts which undermine the
assumption in the NEDs \70\ that windblown dust from desert areas is
entirely from non-anthropogenic sources.\71\
---------------------------------------------------------------------------

    \69\ 40 CFR 50.14(c)(3).
    \70\ E.g., June NED, p. 2.
    \71\ E.g., 2009 EE decision, footnotes 12, 15 and 16.
---------------------------------------------------------------------------

    EE #7: ICAPCD (Attachment) believes it is not clear whether OHV
sources should be considered de minimis, what controls EPA expects for
illegal OHV use, and why current regulations do not constitute
reasonable controls.
    Response: As stated previously, the State must demonstrate
implementation of reasonable controls in documentation supporting
exceptional events requests. It is possible that ICAPCD/ARB may be able
to demonstrate in support of future exceptional events requests that
OHV sources are de minimis, that there are no reasonable controls for
OHVs under certain circumstances (e.g., certain illegal uses), and/or
that existing regulations constitute reasonable controls. The 2009 EE
decision, however, explains that the NEDs did not provide meaningful
analysis of any level of control for OHVs, and that such analysis
should include as a starting point evaluation of EPA's RACM guidance
\72\ and regulations adopted elsewhere under similar conditions.\73\
---------------------------------------------------------------------------

    \72\ 57 FR 18070, 18072 (April 28, 1992).
    \73\ 2009 EE decision, pp. 8-9.
---------------------------------------------------------------------------

    EE #8: ICAPCD (Attachment) comments that sand dunes are naturally
fully disturbed and that the 2009 PM10 SIP conservatively
projects that OHVs contribute only 0.9 tpd (10%) to the total windblown
emissions from them. Other commenters similarly question EPA's
assumption that OHVs disturb desert crust. OWD, for example, notes that
dune laminae are often mistaken for a crust but are broken by wildlife,
foot traffic and high winds.
    Response: We agree that effective control of fugitive dust is more
difficult for the sand dunes than for other parts of Imperial County
with different soil types. As a result, the State may be able to
demonstrate in support of future exceptional events requests, or for
other CAA purposes such as section 189(b)(1)(B) BACM, that dust control
for dunes should be different from and/or less stringent than controls
required for other areas with different soil types. However, the
September NED failed to provide meaningful analysis of reasonable OHV
controls for the sand dunes or any other areas. This comment has no
bearing on the April and June NEDs because the sand dunes were not
implicated by those events.
    EE #9: ICAPCD (Attachment) comments that OHV activity and related
direct PM10 entrainment should have been negligible because
of the high winds during the April 12 and June 5, 2007 events and
thunderstorms on September 2, 2006. OWD notes that two of the
exceedance events occurred during the OHV off-season and the third
occurred in April, when OHV use is also low. Similarly, BLM comments
that OHV use is lowest when dust potential is highest (June through
September).
    Response: Our 2009 EE decision appropriately relies on OHV emission
information from the NEDs and the 2009 PM10 SIP which
estimate large windblown dust emissions and significantly smaller
directly entrained emissions.\74\ Thus, even if no OHVs operate and
entrain dust on any exceedance days, previous \75\ OHV activity still
contributes to PM10 emissions by disturbing surfaces that
subsequently emit windblown dust. As a result, documentation supporting
future Imperial County exceptional events requests for events with
significant emissions from OHV areas should include analysis of
reasonable controls for OHVs even if there is no OHV activity during
the exceedances.
---------------------------------------------------------------------------

    \74\ E.g., 22 tpd windblown and 1.34 tpd entrained emissions,
2009 EE decision, p. 9.
    \75\ Particularly recent activity where there has not been time
or conditions to repair surface crusts.
---------------------------------------------------------------------------

    EE #10: ICAPCD (Attachment) comments that Regulation VIII
agricultural controls are well beyond the reasonableness level required
in the EER. ICAPCD further states that it and ARB have discussed
agricultural controls with EPA for many years, worked with EPA during
development of the 2005 BACM analysis, closely modeled Rule 806 on
SJVUAPCD Rule 4550 which EPA approved in 2004, and received EPA
testimony in 2005 that Regulation VIII, including Rule 806, fulfilled
BACM. ICAPCD also points out that the emission inventory in the plan
shows that agricultural lands are significantly less emissive than most
of the non-populated areas in Imperial County.
    Response: Our 2009 EE decision explains that neither Regulation
VIII nor any other programs require any level of emissions control of
certain fallow fields in Imperial County.\76\ Though ICAPCD comments
that emissions from agricultural fields are smaller than emissions from
other sources in the County, the NEDs for the exceptional events
requests do not identify any anthropogenic sources as being de minimis.
Rather, there are summary explanations that anthropogenic sources are
reasonably controlled through Regulation VIII and other local
programs.\77\ The only anthropogenic source discussed in any detail is
agriculture in the April and June NEDs. These NEDs rely on the Imperial
Irrigation District's (IID) fallowing program as the basis for claiming
that reasonable measures were in place for fallow fields which are not
subject to ICAPCD's Conservation Management Practices (CMP) Rule
806.\78\ However, there were approximately 32,000 fallow acres in
Imperial County in 2007 that were not subject to either Rule 806 or
IID's program which is more than the approximately 18,000 acres that
were a part of IID's program in 2007.\79\ As explained in our response
to comment EE 5, we stated in our 2009 EE decision that it is
appropriate to consider a BACM level of control in evaluating whether
reasonable controls are in place for purposes of the EER in Imperial
County. However, EPA found no meaningful analysis of BACM or any other
level of control for fallow land outside of IID's program referenced or
provided in the NEDs.
---------------------------------------------------------------------------

    \76\ 2009 EE decision, section 4.2.3.
    \77\ April and June NEDs, pp. 13-14, and September NED, p. 18.
    \78\ April and June NEDs, p. 13.
    \79\ 2009 EE decision, p. 9.
---------------------------------------------------------------------------

    EE #11: ICAPCD (Attachment) comments that EPA's 2009 EE decision
fails to mention Rule 806 in the discussion of controls for
agricultural lands. ICAPCD notes that fallowed land issues were
included in the 2005 BACM analysis \80\ and concludes that failure to
address Rule 806 makes EPA's conclusions regarding agricultural areas
suspect.
---------------------------------------------------------------------------

    \80\ ``Draft Final Technical memorandum: Regulation VIII BACM
Analysis,'' October 2005 (2005 BACM Analysis).
---------------------------------------------------------------------------

    Response: EPA did consider and reference Rule 806 in our 2009 EE
decision.\81\ Although the 2005 BACM analysis includes incidental
references to fallow lands, neither it nor the NEDs attempts to
quantify the fallow acreage in Imperial County. Nor has the State
demonstrated how any existing windblown dust controls might constitute
BACM for fallow fields outside of IID's program.
---------------------------------------------------------------------------

    \81\ 2009 EE decision, p. 9.
---------------------------------------------------------------------------

3. High/Unusual Wind Events
    EE #12: Comite agrees with EPA's disapproval of ARB's request to
exclude the monitored exceedances as

exceptional events. In support of our disapproval the commenter makes
several arguments: (1) That there is no statutory or regulatory
authority which allows windblown dust from land that has been disturbed
by human activity to be considered ``natural;'' (2) that while the
final rule includes specific language regarding the treatment of
anthropogenic emissions associated with fireworks and prescribed burns,
it does not include special provisions for anthropogenic sources
affected by the wind; (3) that the portion of the preamble which
suggests dust from anthropogenic sources may be treated as natural
events in certain circumstances was a drafting error and is legally
null; (4) where the Act does allow for consideration of human activity,
it is limited to activity that is unlikely to recur at a particular
location and agriculture does not meet that definition; and (5)
regardless of whether a high wind event is classified as ``natural'' or
``human activity,'' such an event exists only where the wind is
objectively a ``high wind'' and sufficiently high to cause a monitored
violation even in light of the implementation of whatever measures are
``necessary'' to protect public health under CAA section
319(b)(3)(A)(iv).
    Response: Comite's support for our decision not to concur with the
State's exceptional events claims is noted. We agree with Comite that
the events in question are not due to human activity that is unlikely
to recur and that the State failed to demonstrate that the events
qualify as natural events. However our conclusions with respect to
natural events are not based on all of the legal arguments proffered by
the commenter. We also are not relying on that portion of the preamble
that the commenter correctly points out is a legal nullity \82\ and
instead, where appropriate, we rely on and cite to other parts of the
preamble regarding natural events and high winds that remain
applicable. While EPA's views of the statute and the EER differ from
Comite's, we need not address Comite's arguments in detail because its
intent was clearly to support the outcome we have reached regarding the
exceptional events claims.
---------------------------------------------------------------------------

    \82\ NRDC v. EPA, 559 F.3d 561, 565 (DC Cir. 2009).
---------------------------------------------------------------------------

    EE #13: Comite cites additional support for nonconcurrence with the
State's 2007 exceptional events requests beyond what was relied upon by
EPA, namely that wind speeds were not shown to be ``exceptional'' for
the area or ``unusual'' since the State relied on flawed comparisons to
average wind speeds.
    Response: For the 2006 events, the State did not assert that the
winds were unusually high. For both sets of 2007 events, the evidence
provided by the State did lead EPA to conclude that winds were
unusually high.\83\ However, EPA's 2009 EE decision did not rely on the
State's conclusions about unusual winds for any of the exceedances and
we note that this commenter does not disagree with EPA's conclusions on
the exceptional events, or with EPA's proposed limited disapproval of
Regulation VIII.
---------------------------------------------------------------------------

    \83\ 2009 EE decision, pp. 19-20.
---------------------------------------------------------------------------

4. Clear Causal Relationship
    EE #14: Comite agrees with EPA that the State did not demonstrate
there was a clear causal relationship between the exceedances and the
events that are claimed to have occurred, as required under the EER.
With regard to the 2007 exceedances, the commenter cites the lack of
sufficiently detailed source attribution data. With regard to the 2006
exceedances, the commenter concludes that the proximity and nature of
the thunderstorms that occurred in northwest Mexico made them
``unlikely'' to be the cause of the winds at Calexico. This commenter
also believes that the possibility of any winds associated with
thunderstorm activity north of the County being the cause of the
Westmorland exceedance is ``problematical at best.''
    Response: Comite's agreement with EPA's 2009 EE decision regarding
the 2006 and 2007 exceedances is noted.
    EE #15: ICAPCD (Attachment) objects to EPA's analysis of a section
of the ARB documentation that compares September 2, 2006 to other days
with similar meteorological conditions in order to establish a causal
relationship between the claimed high wind event and the Calexico
exceedances on September 2, 2006. ICAPCD also rejects EPA's concerns
regarding the effect of emissions from OHVs and fallow fields on the
September 2, 2006 Calexico exceedances. ICAPCD concludes that EPA's
lack of sound technical understanding regarding the meteorological
evidence and OHV and agricultural emissions led EPA to erroneously
reject the State's finding of a ``clear causal relationship'' for the
September 2, 2006 Calexico exceedances.
    Response: In its documentation supporting its exceptional events
request, the State compared PM10 concentrations on September
2, 2006 to those on fifteen other days that had similar meteorology at
Calexico.\84\ The PM10 concentrations on most of the days
were low, but on August 18, 2002, August 19, 2003 and September 2, 2006
the PM10 concentrations were high. The concentrations on
these days in 2002 and 2003 are described in attachments to the State's
Natural Events Documentation \85\ as being due to transport from Mexico
under high wind conditions, and these conditions are stated to be
meteorologically different than the other days at locations other than
Calexico itself. Thus winds at Calexico were similar for all sixteen
days, but on these specific days the wind elsewhere and the Calexico
concentrations are higher. The State considered this to be evidence of
an association or causal relationship between high wind elsewhere and
high Calexico concentrations.
---------------------------------------------------------------------------

    \84\ September NED, pp. 12-14.
    \85\ September NED, p. 12, and Attachment G, ``179B(d) `But For'
Analyses--High-Wind Events from Mexico'', excerpt from Technical
Support Document: Exclusion of PM10 Measurements in Excess of the
24-Hour PM10 NAAQS for Imperial County from 2001 through 2003 Due to
Natural Events and Emissions from Mexico, Volume I of II, ENVIRON
International Corporation, November 2004.
---------------------------------------------------------------------------

    While we acknowledge that we misinterpreted the above portion of
the State's argument in our initial analysis, our ultimate conclusion
remains unchanged. As we discussed in our 2009 EE decision,\86\ the
State's argument is flawed because there were in fact no high wind
measurements on September 2, 2006; instead, the State merely assumed
that wind speeds increased to the east. As a result, the association
between the winds and concentrations that was seen for the events in
2002 and 2003 may not reflect what occurred on September 2, 2006. Thus
our original conclusion is still valid because the fact remains that
ARB's argument is founded on speculation. As we explained in our 2009
EE decision,\87\ such speculation is not adequate to establish a clear
causal relationship.
---------------------------------------------------------------------------

    \86\ 2009 EE decision, pp. 11 and 15.
    \87\ Id. at p. 11.
---------------------------------------------------------------------------

    Furthermore, as also discussed in our 2009 EE decision,\88\
significantly lower PM10 measurements in neighboring
Mexicali contradict ARB's assertion that the September 2, 2006 Calexico
exceedances were caused by windblown dust from a large-scale, regional
event that originated to the south or southeast of Calexico. Such an
event would have affected both Calexico and Mexicali. ICAPCD itself
concedes that its explanation for the Calexico exceedances does not
account for the difference in the PM10 concentrations

measured at the Calexico and Mexicali stations.\89\
---------------------------------------------------------------------------

    \88\ Id. at p. 12.
    \89\ ICAPCD Attachment A, Appendix A-1.
---------------------------------------------------------------------------

    ICAPCD further offers what it characterizes as the only three
possible explanations for the Calexico exceedances, and suggests that
EPA should accept the long range transport argument because it is the
most plausible one.\90\ To do so would be to make a decision based on a
predetermined outcome rather than reliable scientific data that
establish a clear causal relationship as required by the EER.
---------------------------------------------------------------------------

    \90\ Id.
---------------------------------------------------------------------------

    ICAPCD's next objection to our analysis of ARB's exceptional event
request with respect to the September 2, 2006 Calexico exceedances is
that EPA's concern regarding OHV and agricultural emissions \91\ is not
relevant because there are no OHV or domestic agricultural lands south,
southeast or south-southeast of the Calexico monitors. EPA disagrees.
The September NED states that the ``source of the PM10 that
impacted the Calexico stations corresponds to lands east and southeast
of the Mexicali stations * * *'' \92\ In fact, as shown in the TSD for
this final action,\93\ there is agricultural land immediately east of
Calexico.\94\ As also shown in the final TSD,\95\ the southern end of
the Imperial Sand Dunes OHV area is also directly east of Calexico,
though it is admittedly farther away. Thus consideration of these
sources was not inappropriate.
---------------------------------------------------------------------------

    \91\ 2009 EE decision, p. 14.
    \92\ September NED, p. 15.
    \93\ ``Technical Support Document for EPA's Notice of Final
Rulemaking on Revisions to the California State Implementation Plan,
Imperial County Air Pollution Control District Regulation VIII--
Fugitive Dust Rules 800-806'' EPA Region IX, June 2010 (final TSD),
Figure 1.
    \94\ Similar land use maps were provided in Figure 3 of both the
April and June NEDs.
    \95\ Final TSD, Figure 1.
---------------------------------------------------------------------------

    In summary, we are not persuaded by the above comments and we
reject the allegation that we did not have a sound technical
understanding of the claims ARB made as to the cause of the
exceedances. We therefore reaffirm our conclusion that ARB not only
failed to demonstrate that a high wind event occurred, but also that
there was a clear causal relationship between the alleged event and the
September 2, 2006 exceedances at the Calexico monitoring stations.
    EE #16: ICAPCD (Attachment) states that EPA mischaracterized some
evidence and inappropriately dismissed other evidence provided by the
State regarding a causal relationship between the claimed high wind
event and the Westmorland exceedance on September 2, 2006, and that
this led EPA to erroneously reject the State's finding of a clear
causal relationship. The comment has three parts, relating to alleged
EPA mischaracterizations of the timing of high winds, direction of
thunderstorm travel, and wind trajectories.
    Response: In response to this comment, we have again reviewed the
wind data provided in the September NED and, as explained further
below, we believe our original conclusion in our 2009 EE decision
remains correct, i.e., that the data presented by ARB did not
demonstrate a clear causal relationship between the claimed high wind
event and the Westmorland exceedance on September 2, 2006.
    The first part of ICAPCD's comment focuses on a statement made by
EPA that the increased wind at Oasis toward Westmorland was
simultaneous with the concentration spike that occurred at Westmorland
during the 19th hour rather than an hour or two before, as would be
necessary based on the distance between the two locations.\96\ We agree
with the comment that the increased wind at Oasis did in fact occur the
hour before the concentration spike. In addition, we stated that this
wind was directed toward Westmorland when in fact it was directed
toward the east-northeast.
---------------------------------------------------------------------------

    \96\ 2009 EE decision, p. 16.
---------------------------------------------------------------------------

    ARB presented the wind speed and direction data in a tabular format
that is difficult to interpret.\97\ To more clearly articulate why we
do not believe these data show a clear causal relationship between the
event and the exceedance, we have presented the data in the final TSD
in a visual form that is more readily understood.\98\ The arrows
represent the wind directions at Indio, Oasis, Salton Sea West, and
Westmorland during each of the four color-coded hours (e.g., all of the
yellow arrows represent the wind direction during hour 17, etc.). The
numbers above each arrow represent the wind speed for that hour, and
the numbers below the Westmorland arrows represent the PM10
concentration. The data show that the PM10 concentration
spike occurred during hour 19.
---------------------------------------------------------------------------

    \97\ September NED, Tables 1 and 2, and Figure 19.
    \98\ Final TSD, figure 2.
---------------------------------------------------------------------------

    ARB claimed that thunderstorm outflows on September 2, 2006 led to
high wind locally to the northwest and northeast of Imperial County,
and that dust generated there was carried to Westmorland. More
specifically, ARB stated the following:

    Very high winds were observed at the 17th and 18th hours north
of Imperial County, both to the west (in particular at the Oasis
CIMIS station, see Table 1) and to the east (see measurements at the
Blythe, Ripley, and Palo Verde stations, Table 1). These strong
winds were of very short duration and of changing direction * * *,
consistent with the collapse of one or several thunderstorm cells
north of Imperial County * * *. Very sharp peaks in PM10
concentrations were also observed at the 19th hour at the Brawley
and Westmorland stations (and to a lesser extent at the Niland
station), and appear to be long-range effects of the same events
(i.e. collapsing thunderstorm to the north of Imperial County) * *
*. [A]n analysis of wind direction at select stations between the
18th and 20th hours indicates that northwest winds (e.g. 6 p.m. at
the SSW and Indio stations, 7 p.m. at Oasis and Indio, and 8 p.m. at
Indio) and east-northeast winds (e.g. 7 p.m. at the Niland and SSE
stations) likely carried air containing elevated PM10
concentrations from areas northwest and northeast of Imperial County
stations toward the stations.(Emphasis added).\99\
---------------------------------------------------------------------------

    \99\ September NED, pp. 10-11.

    ARB's explanation first points to the ``very high'' winds (of 23.2
mph) recorded at the Oasis station and the northwest winds at Salton
Sea West during the 18th hour as factors that contributed to the
exceedance. As a preliminary matter, we note \100\ that no particular
wind speed has been established as ``high'' for Imperial County.
Further, winds with an average speed of 23.2 mph are not what we would
consider ``very high'' in the generally accepted meaning of the term.
With the exception of this value, the data in Figure 2 of our final TSD
show that the winds in this area were not very elevated.\101\ We also
note that the winds at Oasis during the 18th hour had a northerly
component rather than a southerly one, and while it is true that the
winds at Salton Sea West were blowing toward Westmorland at this time
and that these winds could have contained some of the dust that may
have been generated in the Oasis area, the winds at Westmorland were
blowing in almost the opposite direction. It is thus unclear how much,
if any, dust generated at Oasis during the 18th hour was actually
transported to Westmorland.
---------------------------------------------------------------------------

    \100\ As we did in our 2009 EE decision, pp. 15 and 19.
    \101\ EPA received comments on its proposed EER which stated
that we should replace the term ``high winds'' with the term ``wind-
generated dust.'' In response to those comments, EPA explained in
the final EER that the Agency chose to retain the original language
because it accurately connotes the type of natural event that should
be excluded under this rule and it serves as an indicator concerning
the level of wind that caused the exceedance. See 72 FR 13560,
13566.
---------------------------------------------------------------------------

    ARB also points to the 7 p.m. winds at Oasis (hour 19) as a
contributing factor. While these winds were directed

toward Westmorland, the winds at Salton Sea West had a distinct
westerly component so it is not clear that the winds at Oasis continued
on this path past Salton Sea West. In addition, as for the previous
hour, the winds at Westmorland were blowing counter to the wind at
Oasis and it is again not clear that any dust generated north of
Imperial County was transported to Westmorland during this hour as ARB
claims.
    The State finally points to the 8 p.m. winds at Indio as a
contributing factor. We find it unlikely that these winds made a
significant contribution to the exceedance at Westmorland given that
they were recorded after the concentration spike occurred and that the
winds at Oasis, Salton Sea West, and Westmorland all had northerly
components that ran counter to the winds at Indio.
    As stated in our 2009 EE decision,\102\ and as ARB stated in the
paragraph quoted above, the winds northwest of Imperial County
(particularly around the Oasis and Salton Sea West areas) were variable
in speed and direction. This variability is inconsistent with ARB's
hypothesis that the winds remained at an elevated speed and along a
straight line over the 45 mile distance between Oasis and Westmorland
for an hour or more. Thus it is anything but clear that dust generated
northwest of Imperial County caused the exceedance at Westmorland. As a
result, EPA's minor errors regarding the timing and direction of the
winds at Oasis do not undermine the Agency's conclusion that the
contradictory evidence does not support a finding of a clear causal
relationship.
---------------------------------------------------------------------------

    \102\ 2009 EE decision, p. 16.
---------------------------------------------------------------------------

    The second part of ICAPCD's comment on the causal relationship
regarding the Westmorland exceedance argues that the speed and
direction of the increased winds (27.0 mph) recorded at the Palo Verde
station during hour 17 are consistent with transport to Westmorland and
that the uncertainty of the precise location of the thunderstorms in
time is not relevant to a cause and effect analysis. The commenter
further states that EPA does not appear to argue that the wind speed or
direction is inconsistent with transport of dust from Palo Verde to
Westmorland.
    While we agree with the commenter that the winds at Palo Verde
(which is separated from Westmorland by a north-south distance of about
24 miles) were directed toward Westmorland during the 17th hour, the
winds at Westmorland were consistently from the south-southeast,
southeast, and east-southeast directions beginning at the 6th hour and
lasting until the end of the day. While it is remotely possible that
the winds that occurred at Palo Verde during the 17th hour led to the
transport of dust to Westmorland, the EER requires a demonstration of a
clear causal relationship and the limited data available do not rise to
that level.
    We also disagree with the commenter that the location of the
thunderstorms over time is not relevant to a cause and effect analysis.
The EER explicitly mentions the use of data that show the relationship
in time between the event, transport of emissions, and recorded
concentrations in exceptional event demonstrations.\103\ Furthermore,
in this case, ARB's basic premise is that ``thunderstorm activity
caused strong outflow winds over areas in close proximity to Imperial
County monitors * * * [which contributed] to the elevated
PM10 concentrations that were recorded in Imperial County on
that day.'' \104\ ARB could have attempted to provide more support for
its case by, for example, considering whether historical radar data
showed thunderstorms were at various locations around the time the high
winds occurred.
---------------------------------------------------------------------------

    \103\ 72 FR 13560, 13573.
    \104\ September NED, p. 2.
---------------------------------------------------------------------------

    Given the level of uncertainty as to the cause of the concentration
spike at Westmorland during the 19th hour and the statutory requirement
that EPA's exceptional events regulations be based on the principle
that protection of public health is the highest priority,\105\ we are
again led to the conclusion that the data before the Agency does not
establish a clear causal relationship between the exceedance and the
event that is claimed to have occurred.
---------------------------------------------------------------------------

    \105\ See CAA section 319(b)(3)(A)(i).
---------------------------------------------------------------------------

    The third part of ICAPCD's comment regarding causal relationship
for the Westmorland exceedance criticizes EPA's use of wind
trajectories from the HYSPLIT model since it is expected to capture the
underlying flow pattern but may not be able to capture the direction of
short-lived high winds that could transport dust from the north to
Westmorland.
    EPA acknowledges that the HYSPLIT model uses meteorological data
with relatively coarse resolution, e.g., a 40 km grid, and that there
may be short-lived or local deviations from the overall wind flow.
However, it remains true that the HYSPLIT back-trajectories are
inconsistent with transport from northern stations since they show
winds from the south.\106\ The HYSPLIT data simply add to the list of
inconsistencies in the State's explanation. In addition, ICAPCD's
suggestion that the high winds were ``short-lived'' is inconsistent
with ARB's hypothesis of straight line transport from the Oasis or Palo
Verde stations for an hour or more over the 45-55 mile distance to
Westmorland. Thus EPA disagrees with this comment.
---------------------------------------------------------------------------

    \106\ 2009 EE decision, p. 17.
---------------------------------------------------------------------------

    EE #17: ICAPCD (Attachment) makes an additional two-part comment
about the causal relationship claim for the September 2, 2006
exceedances at both the Calexico and Westmorland monitoring stations.
In order to buttress its argument that these exceedances were not the
result of recurring anthropogenic sources within Imperial Valley,
ICAPCD first states that it is extremely unlikely that all monitors in
the County would simultaneously have had unusually high PM10
concentrations if the causes were local to the monitors. The second
part of the additional comment states that since there were no high
winds throughout Imperial Valley on September 2, 2006, the cause of the
exceedances could not have been unpaved roads or agricultural or OHV
land within the Valley.
    Response: With respect to the first part of ICAPCD's comment, EPA
acknowledged the elevation of PM10 at all monitors, but did
not take a position on whether the causes were local or regional.\107\
Rather, we concluded that a clear causal relationship had not been
demonstrated since the regional sources alleged by ARB to be the cause
were not identified. Related to this lack of identification of the
contributing sources, EPA found that the State did not demonstrate that
the event was not reasonably controllable or preventable as there was
no attempt to analyze controls on the non-local sources. Thus this
comment does not affect our decision to not concur with the State's
exceptional event claims.
---------------------------------------------------------------------------

    \107\ 2009 EE decision, p. 14.
---------------------------------------------------------------------------

    With respect to the second part of ICAPCD's comment, as discussed
above, the State argued that high winds associated with thunderstorm
activity led to the generation of dust north of the County, which was
then transported to the Westmorland monitor. Even though agricultural
land and other anthropogenic sources do exist in areas north of the
County including Oasis,\108\ where the State claimed winds were high,
the State made no attempt to analyze controls on contributing sources
outside the County in order to address the EER requirement that the
event must be ``not reasonably controllable or preventable.'' Thus,
this requirement

was not met even if the commenter's arguments regarding transport were
correct. With respect to the Calexico exceedances, the State speculated
that high winds occurred east and southeast of Calexico based on
extrapolation of a west to east trend of increasing wind speed. The
same argument could have been used to conclude that there was high wind
east of Calexico within Imperial County, including over agricultural
and OHV lands. Therefore the commenter's claim that there were no high
winds throughout the Imperial County is not completely supported by the
State's own arguments that a high wind event occurred.
---------------------------------------------------------------------------

    \108\ See Figure 1 in the final TSD.
---------------------------------------------------------------------------

5. Concentrations in Excess of Normal Historical Fluctuations
    EE #18: Comite cites additional support for nonconcurrence beyond
what was relied upon by EPA. Specifically, the commenter states that
numerous monitored exceedances comparable to those that Imperial County
seeks to exclude from the data have been measured in the County from
2003-2007. Therefore, the commenter claims, the concentrations are not
``in excess of normal historical fluctuations'' as required by the rule
and are not exceptional events.
    Response: EPA's conclusions about the requirement that the events
be associated with measured concentrations in excess of normal
historical fluctuations mainly relied on the concentrations' rarity
relative to past measurements. For example, the September NED states
that the 167 [mu]g/m3 measurement at the Westmorland station was in the
98th percentile of all PM10 recordings at that station in
the 2001-2007 time period. As explained in our 2009 EE decision,\109\
we found similar evidence that the exceedances measured on the other
days in question also exceeded normal historical fluctuations. However,
we do agree with the commenter that the monitoring data for Imperial
County continue to show violations of the 24-hour PM10
standard. We believe that improvements to the ICAPCD's rules will lead
to improvements in air quality and we note that this commenter does not
disagree with EPA's conclusions regarding the State's exceptional
events requests, or with EPA's proposal to disapprove Regulation VIII.
---------------------------------------------------------------------------

    \109\ pp. 25-27.
---------------------------------------------------------------------------

6. Level of Documentation Required for EER
    EE #19: ICAPCD (Attachment) takes issue with EPA's suggestions that
additional data and analysis would have helped establish causality for
the 2006 Westmorland and the 2007 events. Specifically, ICAPCD states:

    Although EPA suggests that higher levels of documentation for
source attribution, thunderstorm activity, or investigation of other
potential causes would be preferred, EPA does not suggest
reasonable, technically implementable analyses to achieve these
higher levels of documentation. We would question what technical
analyses EPA suggests should be conducted. We would also question
whether these analyses and the required level of data are achievable
or realistic now or in the future for similar events in Imperial
County and in other areas (particularly those surrounded by remote,
non-populated, non-monitored source areas), and whether these
analyses exceed the requirements for SIP planning itself. EPA has
not (and, we believe, cannot) propose reasonable, technically
achievable investigations and analyses superior to those produced by
the District and ARB that would address EPA's stated concerns. Thus,
we find that both EPA's conclusions on causality and EPA's position
on the level of analysis required to demonstrate causality are
incorrect and inconsistent with the purpose of the EER * * *. Such a
narrow application of the EER will preclude states from excluding
from regulatory consideration exceptional PM data that are
completely inappropriate for inclusion in the normal planning
process.

    ICAPCD also includes a table on page A-8 which cites specific
passages of EPA's 2009 EE decision pertaining to source apportionment,
satellite imagery, and consideration of other causes.
    Response: Regarding the need for better source apportionment data,
it is important to identify contributing sources when evaluating
exceptional event claims involving windblown dust because it must be
demonstrated that anthropogenic sources contributing to the exceedances
at issue were reasonably controlled.\110\ Better source identification
is especially important in situations where we do not have confidence
that all potential anthropogenic sources are reasonably controlled and
where there are exceedances just above the NAAQS (such as the April 12,
2007 exceedance at Westmorland) which may have been preventable with
additional controls. In addition, the inability to identify the source
of the PM emissions associated with a wind event (i.e., the ``cause''
of the dust that led to the exceedance) hinders our ability to make
affirmative findings that the ``clear causal relationship'' and ``but
for'' provisions of the EER have been satisfied. A County-wide monthly
average emission inventory such as the one used by ARB that omits some
source types (e.g., OHVs) is insufficient for these purposes.
---------------------------------------------------------------------------

    \110\ See, e.g., 2009 EE decision, p. 7 and our responses to
comments EE s 1 and 4. See also 72 FR 49046, 49051 (August
27, 2007) and 72 FR 13560, 13566, footnote 11, explaining that the
weight of evidence approach to our analysis may consider winds that
produce emissions contributed to by anthropogenic activities that
have been controlled to the extent possible through use of all
reasonably available reasonable and appropriate measures.
---------------------------------------------------------------------------

    While perhaps not required for all demonstrations, our suggestion
for a wind field and a more highly resolved inventory are not
unreasonable given ARB's failure in the present case to demonstrate
that reasonable controls were in place for contributing sources.
Moreover, a more highly resolved inventory would provide better support
for any future exceptional events claims involving Imperial County.
Another method ARB could have potentially considered for identifying
the source of the emissions and supporting its claim of a causal
relationship is to collect and examine pollutant species-specific
information. As discussed in the EER preamble,\111\ such information
may be available through routine speciation, monitoring networks, or
from selective laboratory analysis of archived particulate matter
filters for the day thought to be impacted by an event. In this case,
such an analysis might have helped ascertain how much of the
PM10 that impacted certain monitors was from agricultural
sources versus natural desert sources.
---------------------------------------------------------------------------

    \111\ 72 FR 13560, 13573.
---------------------------------------------------------------------------

    Regarding ICAPCD's objection to our statement that the satellite
imagery provided was not frequent enough to compare the images with the
timing of the concentration spike at Westmorland during the 19th
hour,\112\ we note that ARB could have provided additional information
to supplement the satellite imagery. Such information could include,
but may not be limited to radar data and weather observations that note
the presence of blowing dust in areas around the monitors.
---------------------------------------------------------------------------

    \112\ 2009 EPA decision, pp 17-18.
---------------------------------------------------------------------------

    Finally, ICAPCD takes exception to our desire for better
documentation regarding the investigation of other potential causes. In
this regard, ARB made the following statement: \113\
---------------------------------------------------------------------------

    \113\ September NED, p. 2.

    (ICAPCD) investigated emission generating activities during this
episode, and found that PM10 emissions for BACM
controlled sources were approximately constant before, during and
after the event. The District determined that the * * *
concentrations of PM10 * * * were instead primarily the
result of wind-entrained dust * * * associated with a mesoscale
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convective system * * *.

    Although the preceding passage suggests that ICAPCD conducted an

active investigation of other emission generating activities on the day
of the event, this claim is largely unsupported except for an
interoffice memo included in Attachment H to the September NED. The
memo states that various records were inspected in 2008 but that no
inspections were conducted on the day of the event. We were thus left
wondering how a file review conducted two years after the fact
qualifies as an investigation of emission generating activities
``during [the] episode'' and how ICAPCD came to the somewhat
substantial conclusion that emissions from BACM controlled sources were
constant before, during, and after the event.

E. OHV Controls

    OHV #1: ICAPCD believes that EPA should have concurred with all of
the exceptional event requests associated with high winds as discussed
in the Exceptional Events comments summarized in section II.D above. As
a result, ICAPCD believes that windblown dust from open areas is not a
significant source category in Imperial County, and therefore is not
subject to the BACM requirement as part of the SIP.
    Response: In our proposed action on Regulation VIII, we explained
why windblown dust from open areas is treated as a significant source
category subject to BACM.\114\ We have not received information in the
comments or elsewhere that changes this conclusion or the related
decision to not concur with the State's exceptional event requests for
Imperial County. See also responses to Exceptional Events comments in
section II.D above.
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    \114\ Proposal TSD, pp. 5-7.
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    OHV #2: CBD comments that BLM land is the largest PM10
source in Imperial County and should be subject to the same controls as
adjacent land. CBD believes the Dust Control Plan (DCP) requirement for
BLM land in Rule 800 section F.5 is unenforceable, in conflict with the
CAA, while other areas are subject to more stringent Regulation VIII
requirements.
    In contrast, ICAPCD believes that Rule 800's DCP implements BACM,
and that Rule 800's exemption for BLM does not relax other Regulation
VIII requirements. For example, Rule 800 section F.5.c requires BLM's
DCP to be consistent with Rules 804 and 805 except where otherwise
prohibited, in which case section F.5.e requires all feasible control
measures during off-road events. ICAPCD also notes that where there are
such prohibitions, section F.5.d requires the DCP to discuss and
implement ``other possible control measures'' and that Rule 800 section
D.3 requires the DCP to be submitted to ICAPCD, ARB and EPA for review
and comment and to be updated every two years.
    ICAPCD believes BLM should be treated separately in Regulation VIII
because there are many restrictions imposed by a variety of laws other
than the CAA that apply to actions on Federal lands and that the
District's involvement in these issues would delay implementation of
the PM control program on BLM lands. ICAPCD also believes that BLM
should be treated separately because some Federal land uses preclude
traditional dust controls and because BLM's OHV areas are far from
Imperial County populations. ICAPCD argues that even if Rule 800
section F.5.c corresponds to requirements that are less effective than
those of Rules 804 and 805, such lower stringency is both necessary and
appropriate given the special nature of BLM lands.
    BLM agrees that many traditional BACM are not possible on Federal
land because of the large expanses of desert ecosystems. BLM continues
evaluating the DCP, however, which has led to closing areas and routes
to vehicle use, restoring closed surfaces to natural conditions,
hardening high traffic areas, posting and enforcing speed limits,
educating desert users, and controlling dust from non-OHV activities.
    Response: BACM is required but has not been demonstrated for OHV
activity on BLM land in Imperial County.\115\ EPA guidance explains
that this demonstration should include evaluation and documentation of
the technological and economic feasibility of potential control
measures, including implementation of measures on a limited basis if
full implementation is not feasible. As stated in our guidance, ``the
documentation should compare the control efficiency of technologically-
feasible measures, their energy and environmental impacts and the costs
of implementation.'' \116\ ICAPCD's demonstration should include
careful consideration of analogous controls implemented on private
lands in Imperial County and on public lands in Maricopa and Clark
Counties and elsewhere, as well as controls recommended in EPA's RACM
guidance,\117\ and suggestions provided in our proposal \118\ and
comments on the proposal.\119\
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    \115\ Proposal TSD, pp. 7-8.
    \116\ General Preamble Addendum at 42012-42014.
    \117\ 57 FR 18070, 18072.
    \118\ See proposal TSD, pp. 8 and 14-15.
    \119\ Moreover, as stated in the General Preamble Addendum at
42013, ``any control measures that a commenter indicates during the
public comment period is available for a given area should be
reviewed by the planning agency.''
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    The evaluation of technological feasibility may appropriately
consider the alleged ``special nature'' of BLM lands. Such an
evaluation, if conducted appropriately, may be sufficient to
demonstrate that what constitutes BACM for BLM land in Imperial County
is different from what constitutes BACM in other geographical areas and
for private land in Imperial County. The information provided in the
comments and Regulation VIII submittal, however, is not sufficient to
support such a distinction. For example, ICAPCD and other commenters
have not demonstrated how existing BLM controls implement BACM in the
Plaster City areas, which are open to OHV activity at all times, and,
if such controls do constitute BACM, why they cannot be incorporated
into Regulation VIII and the SIP.
    Furthermore, with regard to CBD's comment concerning the
enforceability of DCPs, State and local requirements that implement
BACM are subject to the enforceability requirement of CAA section
110(a). As we stated in our proposal, BACM has not been demonstrated
for OHV sources because, among other things, none of the OHV
restrictions are in regulatory form and submitted for inclusion in the
SIP.\120\
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    \120\ Proposal TSD, p. 14.
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    OHV #3: OWD notes that California State Parks (CSP) manages OHV
recreational activity in Imperial County at Heber Dunes State Vehicular
Recreation Area, Ocotillo Wells SVRA, and in an interdepartmental joint
management agreement at the Freeman Properties immediately north of
Ocotillo Wells SVRA and east of Anza Borrego Desert State Park. OWD
also notes that Ocotillo Wells SVRA alone represents approximately
85,000 acres of managed OHV recreational activity within Imperial
County. While much of this land is designated trail riding only and is
primarily defined by terrain constraints, OWD states that the majority
of the area is designated open riding, where OHVs are not limited to
defined trails. Rather than implement generalized BACM for OHV activity
in Ocotillo Wells SVRA and other State Parks, OWD explains that it has
adopted State mandated soil standards, a habitat monitoring system and
other policies tailored for the case-by-case conditions found in each
park unit. OWD believes

that fencing, and then maintaining, a vast amount of land is neither
economically nor environmentally feasible. OWD also believes that
watering, laying gravel, or applying a chemical solution to the miles
of trails that would be encompassed is neither economically nor
environmentally feasible. In contrast, CBD argues that further
implementation of Rule 804 and additional OHV controls may be needed
for State lands including the Ocotillo Wells SVRA in order to attain
air quality standards.
    Response: Rule 804 requires all persons, including public entities
such as CSP, with jurisdiction over open areas in Imperial County with
over 1,000 square feet of disturbed surface area to maintain a
stabilized surface, limit opacity to 20% and comply with at least one
of the following: (a) Apply and maintain water or dust suppressant to
all unvegetated areas; (b) establish vegetation on all previously
disturbed areas; or (c) pave, gravel or chemically stabilize.\121\
OWD's comment acknowledges that CSP has jurisdiction over open areas
with over 1,000 square feet of disturbed surface area within Imperial
County. Because these areas are not addressed by exemptions in Rule 800
section E or Rule 804 section D,\122\ these areas must comply with the
above requirements. However, from OWD's comment, CSP is clearly not
currently complying with these requirements. As a result of the
inclusion of Rule 804 into the SIP, these requirements will become
federally enforceable upon the effective date of this final action, and
such noncompliance could result in civil action under CAA section 113
and/or 304.
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    \121\ ICAPCD Rule 804, sections B, C.29, E and F.
    \122\ See also ``Fugitive Dust Control Plan,'' Bureau of Land
Management El Centro Field Office, June 29, 2006; ``Fugitive Dust
Control Plan,'' Bureau of Land Management El Centro Field Office,
January 25, 2010 Draft; e-mail from Andrew Trouette (BLM) to Andrew
Steckel (EPA), May 24, 2010.
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    OHV #4: Various commenters argue that controls suggested in our
proposal as part of the BACM analysis that ICAPCD still needs to
conduct would not reduce PM10 impacts from OHVs in Imperial
County.
     Many commenters oppose further restrictions during the
summer, claiming that OHV activity and emissions are very low in
Imperial County due to high temperatures and existing red sticker
regulations that restrict certain vehicles during the summer. BLM
concurs that OHV use is already lowest in the summer, and ICAPCD also
concurs and argues that OHV restrictions during the summer would burden
public resources without reducing emissions. However, one commenter
(0100) states that OHV use during summer nights is a great activity
which creates minimal dust because travel is at low speeds on
established trails. Another commenter (0204) indicates that many
promoters run OHV races at night that allow for fun recreational
activity in cooler temperatures. This commenter believes night races
decrease risks to spectators which is more important than reducing dust
emissions. Some commenters also observe that wind events can occur in
the summer and cause severe dust days. By contrast, another commenter
(0146) believes that the desert is mainly dry and free of wind in the
summer.
     ICAPCD believes that restrictions like those in place in
Arizona, during pollution advisory days, would be unproductive because
high-PM forecasts in Imperial County only occur on high-wind days when
OHVs are not used.
     Many commenters (e.g., 0094) observe that OHVs are already
restricted to certain areas, causing crowding and injuries. ICAPCD
notes that OHVs are restricted to 11% of local BLM land, and additional
closure would probably shift OHV activity and emissions to other areas
nearby. OWD also believes EPA's action could force OHV users to other
areas, causing environmental effects outside Imperial County.
     ICAPCD comments that EPA cannot demonstrate that OHV
restrictions would reduce windblown dust emissions because there is no
basis for EPA's contention that surfaces impacted by OHVs would form
any appreciable crust given Imperial's low level of rain. OWD similarly
comments that crust repair would be difficult due to the limited rain
in Imperial County. Another commenter (0120) believes that restricting
OHV areas could increase PM10 emissions because more
vehicles in smaller areas would disturb more soil that cannot crust
over. See also comment EE 8.
     OWD comments that fencing, watering, gravelling or
chemically stabilizing miles of OHV areas is not feasible. For example,
water resources are scarce and modification of existing OHV trails
could alter natural drainage patterns and increase erosion.
    Response: EPA believes that some of the information provided in
these comments could be relevant considerations in the comprehensive
BACM analysis that ICAPCD needs to undertake in order to determine what
controls constitute BACM for OHV activity in Imperial County. However,
in general, the comments are conclusory and not supported by data,
detailed information, or other evidence that would be required for an
adequate BACM demonstration under our guidance.\123\ As summarized in
the guidance:
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    \123\ General Preamble Addendum at 42010-42014.

    In summary, the State must document its selection of BACM by
showing what control measures applicable to each source category
(not shown to be de minimis) were considered. The control measures
selected should preferably be measures that will prevent PM-10
emissions rather than temporarily reduce them. The documentation
should compare the control efficiency of technologically-feasible
measures, their energy and environmental impacts and the costs of
implementation.\124\
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    \124\ Id. at 42014.

    Furthermore, contradictions in the comments also serve to
illustrate that there are fundamental factual questions that need to be
addressed about the amount of OHV activity during different seasons and
different times of the day, and the best ways to mitigate emissions
from such activities. At this juncture, ICAPCD has not conducted an
adequate analysis.
    OHV #5: Many commenters (e.g., 0108 and OWD) state that further OHV
restrictions would hurt the already depressed local economy, and cite
potential effects on local business owners, farmers, land owners, OHV
users, race car owners, construction companies, ranchers, the Imperial
Irrigation District and others. Commenters observe that recreational
activities generate substantial revenue (0196), and one (0156.1) claims
that OHVs have contributed several hundred million dollars to the local
economy. ICAPCD believes that the economic cost of OHV activity
restrictions is far more than appropriate for BACM. For example, ICAPCD
estimates that closing the Imperial Sand Dunes Recreational Area would
cost $370,000 to $640,000 per ton of PM10 reductions. ICAPCD
provides specific references to support its cost/benefit analysis.
Another commenter (0219) similarly believes that additional OHV
restrictions, such as closing land in the summer, would provide few
benefits given the relatively small emissions from OHVs, but would have
significant economic impacts.
    Response: We appreciate the value of OHV tourism to the local
economy, and agree that ICAPCD must consider economic feasibility in
BACM analyses evaluating potential controls for emissions from OHV
activities. However, the relevant inquiry in the economic feasibility
analysis required in BACM determinations is ``the cost of reducing
emissions from a particular source category and costs incurred by

similar sources that have implemented emission reductions.'' \125\ In
this case, the cost of OHV restrictions on OHV area owners (i.e., the
State and Federal governments) and users would appear to be minimal,
and the secondary economic impacts on businesses supporting OHV tourism
are not relevant to the required BACM analysis. In any event, ICAPCD
needs to evaluate the economic feasibility of potential controls,
including those adopted in other areas, in determining what controls
constitute BACM in this area.
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    \125\ General Preamble Addendum at 42013.
---------------------------------------------------------------------------

    OHV #6: EcoLogic asks EPA to clarify whether and where OHV
restrictions are being contemplated in the Imperial Sand Dunes
Recreation Area and elsewhere and to what extent OHV activity on
Federal land is subject to the proposed rule or ICAPCD jurisdiction.
EcoLogic and another commenter (0141) also request clarification on
which of the 250 square miles of OHV areas EPA is asking ICAPCD to
evaluate for closure and what the basis is for claiming that these
areas are likely to impact populations.
    Response: State and Federal agencies are subject to many local
requirements including Regulation VIII and other air quality related
ICAPCD rules.\126\ Our proposal explains why ICAPCD must analyze
whether additional controls (potentially including closure) are
appropriate for public land in Imperial County open to OHVs, which
ICAPCD estimates at over 250 square miles.\127\ We did not identify any
specific geographic areas needing more or less analysis or control or
having more or less impact on populations. Rather, in the analysis
ICAPCD should consider all potential available OHV controls in all OHV
areas in Imperial County and, where feasible, should consider whether
different areas within the County have different impacts on populations
or areas with exceedances of the NAAQS.
---------------------------------------------------------------------------

    \126\ See CAA section 116.
    \127\ See, e.g., proposal TSD, pp. 8 and 13-15.
---------------------------------------------------------------------------

    OHV #7: Several commenters believe additional OHV restrictions
should be analyzed and/or incorporated into Regulation VIII. CBD
believes that OHV requirements in Rule 804 are too vague to be
enforceable as required by CAA section 110(a), particularly regarding
BLM and State managed land. CBD believes Regulation VIII should require
specific BACM measures, such as restrictions on the number of OHV
vehicles operating each day, to improve emission quantification and
control. CBD believes such carrying capacity caps or other restrictions
should also address weather conditions when they exacerbate
PM10 emissions, such as during windy weather and the summer.
Comite comments that ICAPCD should analyze whether OHV permit
requirements, such as those that are required in San Bernardino County,
should be required in Imperial County. Comite also believes that ICAPCD
should analyze controls described in the California State Parks Off-
Highway Motor Vehicle Recreation Division's 2008 Soil Conservation
Standard and Guidelines.\128\ Lastly, instead of decreasing the size of
OHV areas, one commenter (0120) suggested rotating OHV areas to help
surface crust formation.
---------------------------------------------------------------------------

    \128\ Submitted as Exhibit D to Comite comment letter.
---------------------------------------------------------------------------

    Response: The commenters as a group make constructive suggestions
that would be appropriate for consideration in a comprehensive
evaluation of BACM for this source category. We believe ICAPCD should
analyze all potential available OHV controls to meet the CAA's BACM
requirement, including those mentioned in the comments and those
adopted in other areas, pursuant to EPA guidance.\129\
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    \129\ See, e.g., General Preamble Addendum at 42012-42013.
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F. Definition of Disturbed Surface (DS)

    DS #1: ICAPCD believes the term ``disturbed surface'' is self-
evident and that no questions have been raised about it since rule
adoption. ICAPCD believes Rule 804 is clear that an area is deemed