LLC

 

October 2, 2008 

Kimberly D. Bose 

Secretary 

Federal Energy Regulatory Commission 

888 First Street, N.E. 

Room 1A 

Washington, DC 20426 

RE: Docket No. CP07-208-000 

 Rockies Express Pipeline LLC, REX-East Project 

Request to Proceed for Construction in Exclusion Zones – Spread A-1, Missouri and 

Spreads D, E, and F, Indiana 

Ms. Bose: 

Rockies Express hereby files with the Commission a request for a Notice to Proceed 

(“NTP”) for previously identified Exclusion Zones surrounding sensitive resources in Spreads A1, D, E, and F of the REX-East Project.1

 The Federal Energy Regulatory Commission (“FERC” 

or “Commission”) granted the NTP for Spread A-1 on July 22, 2008, Spread D on August 1, 

2008, Spread E on September 11, 2008, and Spread F on September 26, 2008, identifying 

exclusion zones in all areas. 

For the NTP requests submitted by this filing, Rockies Express has obtained landowner 

easements, completed the outstanding cultural surveys, and has received State Historic 

Preservation Office (“SHPO”) clearance. Revised alignment drawings for the NTP requests for 

Spreads A-1 and Spread D are provided in attachment A. These alignment sheets will replace 

those previously submitted. To facilitate review of the revised alignment sheets, “bubble” lining 

has been drawn around the area where a modification is proposed. 

Copies of the approval letters from the state-specific SHPO cultural survey 

documentation to support each NTP request are provided in Attachment B. Copies of the 

easement agreements for two NTP requests in Spread A-1 and F are found in Attachment C. 

Rockies Express includes as Attachment D a table listing all the clearance areas for this request, 

as well as previously submitted requests that are outstanding for the REX East Project. Due to 

 

1

 The REX-East project was granted a certificate of public convenience and necessity pursuant to Section 7(c) of the 

Natural Gas Act by the Federal Energy Regulatory Commission on May 30, 2008 in this docket. Rockies Express 

Pipeline LLC, 123 FERC ¶ 61,234 (2008). On June 2, 2008, Rockies Express, pursuant to Section 157.20(a) of the 

Commission’s Regulations, 18 C.F.R. § 157.20(a), notified the Commission that it accepted the Commission’s 

Order. 

 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
2

the information provided in the table, Attachment D is privileged and confidential. Attachment 

E provides drawings depicting the requested clearance areas. Attachment F provides a 

supplemental noise analysis for the Illinois River and the 200th Avenue horizontal directional 

drills (“HDDs”). 

Spread A-1

 In Spread A-1, the Commission identified an exclusion zone between MPs 38.4 to 40.2 

that was established to protect sensitive resources requiring avoidance and/or mitigation (See 

Commission July 22, 2008, NTP Order for Spread A-1). 

a. Start Construction Between MPs 38.4 and 40.2

Between MPs 38.4 to 40.2, Rockies Express proposes a line change that avoids three 

sensitive resource sites as shown in the Missouri Treatment Plan No. 2 (REX-EAST-MO-14). 

For this proposed line change, no additional environmental surveys are required as the line 

modification is within the previously surveyed corridor. Additionally, landowner easements 

have been obtained and are appended in Attachment C. The Missouri State Historic Preservation 

Office (SHPO) concurrence is appended in Attachment B. The proposed route is shown on 

alignment sheet No. 1280-D-105-015 [REV 2, revised 9/26/08], submitted as part of Attachment 

A and further described in the table provided in attachment D. 

Rockies Express has completed the mitigation efforts at two other sensitive resource sites 

within MPs 38.4 to 40.2. The Missouri SHPO has concurred with all mitigation work at these 

two sites (See Attachment B). 

 

b. Use Travel Lane at MP 39.6

The only sensitive resource site that remains between MPs 38.4 to 40.2 is site SRMO006. 

To avoid this site, Rockies Express requests the use of a travel lane on tract MO-PI-087.000 as 

shown in the Missouri Treatment Plan No. 2 (REX-EAST-MO-14). An alignment sheet, sheet 

no.1280-D-105-015 [REV 2, revised 9/26/08], and a site-specific drawing of the travel lane, 

Drawing No. 1280-A-SR-006, are appended in Attachment A. 

Between MPs 38.4 to 40.2, Rockies Express requests authorization to commence 

construction for the entire exclusion area except for the area which is to be fenced and crossed 

using a travel lane (e.g., sensitive resource SRMO006) on tract MO-PI-087.000 as shown in the 

Missouri Treatment Plan No. 2 (REX-EAST-MO-14). Rockies Express agrees to implement 

Environmental Condition 130 during construction between MPs 38.4 to 40.2. 

c. Supplemental Information on the Illinois and 200th Avenue HDD 

As discussed in the September 24, 2008 request for Notice to Proceed, Rockies Express 

completed an acoustical assessment of the Illinois River HDD. Since the issuance of the Final 

Environmental Impact Statement, Rockies Express modified the Illinois River HDD crossing by 

reducing the length of the Illinois River HDD and adding the 200th Avenue HDD. The Illinois 

River HDD and the 200th Avenue HDDs share a common drill entry workspace. 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
3

Attached is Rockies Express’ acoustical assessment of the Illinois River HDD and 200th

Avenue HDDs (Attachment F). Based on the results of the analysis, the noise attributable to the 

drilling operations could exceed the sound criteria for HDD operations at the HDD entry 

workspace for the two drills if noise mitigation measures are not employed. Rockies Express 

intends to implement the appropriate noise mitigation measures at the drill entry site. The nearest 

NSA to the 200th Avenue HDD drill exit side is an unoccupied residence approximately 250 feet 

southwest. If this residence is occupied during HDD operations, Rockies Express will install 

additional noise mitigation measures or provide temporary housing during drilling operations. 

Spread D 

In Spread D, the Commission identified one exclusion zone between the east side of the 

Wabash River (MP 242.9 + 4.0) and the west edge of the workspace for the horizontal 

directional drill of the Wabash River (MP 242.9 + 4.0) (See Commission August 1, 2008, NTP 

Order for Spread D). Rockies Express proposes to move the additional temporary workspace 

(ATWS) for the Wabash River horizontal directional drill (HDD) water intake to the north side 

of the centerline. For this proposed ATWS change, no additional environmental surveys are 

required as the modification is within the previously surveyed corridor. Rockies Express will 

comply with Environmental Condition 74. This adjustment to the ATWS is shown on revised 

alignment sheet no. 1280-D-105-091 [REV 2, revised 9/25/08] and HDD site-specific drawing 

no. 1280-D-SX-SK-011 [REV 4, revised 9/30/08]. The revised alignment sheet and site specific 

drawing is appended in Attachment A. 

Spread E 

In Spread E, the Commission identified an exclusion zone between MPs 355.6 to 355.9 

requiring additional cultural resources survey (See Commission September 11, 2008, NTP Order 

for Spread E). Cultural resources surveys have been completed and are appended in Attachment 

B. The Indiana SHPO has concurred with all proposed work in this exclusion zone (Attachment 

B). 

Spread F 

In Spread F, the Commission identified three exclusion zones requiring additional 

cultural resources surveys, landowner easements, or agency clearances (See Commission’s 

September 26, 2008, NTP Order for Spread F). 

a. Between MPs 386.9 to 387.5

Rockies Express identified an exclusion zone between MPs 386.9 to 387.5 requiring 

additional cultural resources survey for line change 2035. Cultural resources surveys have been 

completed for line change 2035 and are appended in Attachment B. The Indiana SHPO has 

concurred with all proposed work in this exclusion zone (Attachment B). 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
4

b. Between MPs 392.2 to 393.6, including the Whitewater River HDD

The NTP identified an exclusion zone between MPs 392.2 to 394.5, which includes the 

Whitewater River HDD due to cultural resource concerns. A portion of the original exclusion 

zone, between MPs 392.2 and 393.6, were pending agency concurrences on report REX-EASTIN-48 and Indiana Treatment Plan No. 2 (REX-EAST-IN-44). The Indiana SHPO has concurred 

with all work in this area; supporting documentation is included in Attachment B. 

c. Between MPs 401.8 to 402.1

In accordance with Certificate Condition No. 33, Rockies Express is providing additional 

documentation of consultation with Mr. and Mrs. Stirn, landowners of tract IN-FR-181.S02, 

crossed by the project between mileposts (MPs) 401.8 and 402.1. As indicated in the attached 

notes and easement agreement, filed as Privileged and Confidential in attachment C, Mr. and 

Mrs. Stirn expressly have been offered the FERC route presented in the Final Environmental 

Impact Statement. Mr. and Mrs. Stirn are reluctant to provide signed documentation indicating 

their preferred route. Rockies Express subsequently has reached easement agreement with the 

landowner for the route as shown on the alignment sheet (1280-D-105-148) [REV 0, revised 

5/29/08] provided to the FERC as part of Rockies Express’ Notice to Proceed request with 

Spread F. 

Based on this additional documentation and clarification for FERC staff, Rockies Express 

is requesting Notice to Proceed with construction authorization between mileposts (MPs) 401.8 

and 402.1 (western boundary of tract IN-FR-168.00 at Johnson Fork Road and the western 

boundary of tract IN-FR-182.000). 

Conclusion

Based on the explanation provided above, and the data appended hereto, Rockies Express 

requests notice to proceed with construction across the following areas: 

 Spread A-1

1. between the western boundary of tract MO-PI-083.000 (MP 38.4) and the eastern 

boundary of tract MO-PI-089.000 (MP 40.2), as set forth on Alignment Sheet 1280-D105-015 [REV 2, revised 9/26/08], excluding the area to be fenced and crossed using a 

travel lane at MP 39.6; and 

2. the use of a travel lane from MPs 39.6 to 39.6 across sensitive resource SRMO006 on 

tract MO-PI-087.000, as set forth in site-specific drawing 1280-A-SR-006 and alignment 

sheet 1280-D-105-015 [REV 2, revised 9/26/08]. 

Spread D

1. between the east side of the Wabash River (MP 242.9 +4.0) and the west edge of the 

workspace for the horizontal direction drill of the Wabash River (MP 242.9 +4.0), as 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
5

shown on alignment sheet No. 1280-D-105-091 [REV 2, revised 9/25/08] and HDD sitespecific drawing No. 1280-D-SX-SK-011 [REV 4, revised 9/30/08]. 

Spread E

1. between the eastern side of County Road S. 500E (MP 355.6) to the western side of tract 

IN-SB-140.000 (MP 355.9) (see attached drawings 1280-D-105-131 [REV 0 revised 

5/29/08]; Letter Agreement with Indiana SHPO, received 7/2/08). 

Spread F

1. between the western boundary of WB-IN-375-D on tract IN-FR-065.000 (MP 386.9) and 

the western boundary of tract IN-FR-068.000 (MP 387.5) as shown on alignment sheet 

No. 1280-D-105- 142 [REV 0 revised 5/29/08] (Letter Agreement with Indiana SHPO, 

received 7/2/08); 

2. Southern boundary of tract IN-FR-105.001 (MP 392.2) and the western boundary of tract 

IN-FR-115.001 (393.6) (see attached drawings 1280-D-105-144 and – 145 ; SHPO 

concurrence on reports REX-EAST-IN-44 and REX-EAST-IN-48, received 8/21/08 and 

9/25/08, respectively); and 

3. Western boundary of tract IN-FR-168.000 at Johnson Fork Road (MP 401.8) and the 

western boundary of tract IN-FR-182.000 (MP 402.1) as shown on drawing 1280-D-105-

148 [REV 0 revised 5/29/08] (Landowner easement agreement appended to attachment 

C). 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
6

Rockies Express requests approval of these areas as soon as possible due to construction 

activities which would require a move around if timely approval is not granted. Please direct any 

questions with respect to this request for authorization to proceed to Ryan Childs at (307) 760-

5635. 

 

Respectfully submitted, 

 /s/ Shippen Howe 

 Shippen Howe 

 Van Ness Feldman, P.C. 

1050 Thomas Jefferson Street, NW 

Washington, DC 20007 

202-298-1800 

Attorney for 

Rockies Express Pipeline LLC 

Attachments 

 

cc: Laura Turner, FERC 

 John Peconom, FERC 

 Ellen Saint Onge, FERC 

 All Parties 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
Document Accession #: 20081003-5012 Filed Date: 10/03/2008
No vehicles allowed in this area

MO-PI-087.000

145’

46’

50’

25’

25’

25’

25’

39.6

M:\Clients\J-L\KMI\REX\_ArcGIS\2008\06\Phase3_Plans\Construction\_CP_006.mxd DATE: 06/26/08 REVISED: 06/26/08 DRAWN BY: RSMcGregor

This information is for environmental review purposes only.

1:1,000

Proposed CL

Permanent Easement

Temporary Easement

PEPL CL

Sensitive Resource

Property Line

Topsoil Storage Workspace

Travel Lane on PEPL Easement

Exclusion Fence

(remains until restoration)

Exclusion Fence

(remove after data recovery)

Rockies Express Pipeline - East Project

Pike County, Missouri

Drawing No. 1280-A-SR-006

Construction Note:

-restrict construction corridor to 100 ft; topsoil stripping will be limited to 75 ft, including 8 ft of overlap with PEPL easement

-a visual barrier of straw must be installed above the topsoil along the 25 ft topsoil storage area along the northern edge of the construction corridor. 

No excavation may occur in this area and any vehicular traffic is prohibited from this topsoil storage area. 

-install exclusion fencing along the perimeter of construction corridor, across the construction corridor, along outer edge of ATWS, and along edge of PEPL easement

-during data recovery, use 25 ft of PEPL easement as travel lane 

-after data recovery, remove exclusion fencing from across the 100 ft construction corridor and along northern edge of the travel lane

-fencing along northern boundary of construction corridor and along the ATWS outer edge to remain in place until final restoration is complete

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File [1280-d-105-131_MP355.6 to 355.9.PDF] cannot be converted to PDF. (Error: File not found)
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HOOVER & KEITH INC. 

ACOUSTICS & 

NOISE CONTROL 

ENGINEERING 

11391 MEADOWGLEN, SUITE D HOUSTON, TEXAS 77082 

(281)496-9876 FAX: (281)496-0016 

Date of Transmittal: 09/30/08 H&K Job No. 3913 

-Page 1- 

MEMORANDUM (Total of 6 Pages) 

Subject: Acoustical Assessment of the Modified HDD Crossing at the IL River for the 

Gas Pipeline associated with the REX-East Project 

Submitted to: Natural Resource Group, Inc. (NRG) 

Project Applicant: Rockies Express Pipeline, LLC (REX Pipeline)

Submitted by: Paul D. Kiteck, P.E., Hoover & Keith Inc. (H&K) 

1.0 INTRODUCTION

The following memo provides the results of an acoustical assessment of a recently-modified 

horizontal directional drilling (HDD) site for the natural gas pipeline associated with the Rockies 

Express Pipeline–East (i.e., REX-East Pipeline) Project. The purpose of the acoustical 

assessment is to estimate the sound contribution at nearby noise-sensitive areas (NSAs) 

resulting from drilling operations at the modified HDD site for NSAs within 1⁄2 mile and present 

noise mitigations measures to minimize the noise impact of HDD activities if the assessment 

indicates that the noise of HDD operations could exceed an equivalent day-night sound level 

(Ldn) of 55 dBA and/or could cause an increase of 9 dB or more above the ambient noise at the 

closest NSAs (i.e., defined as the sound criteria for project HDD operations). 

2.0 BRIEF DESCRIPTION OF HDD SITES AND HDD EQUIPMENT

In summary, the IL River HDD crossing (Pike County, IL) will be modified as follows: (1) location 

of HDD entry point for IL River HDD crossing will be somewhat different, and (2) a new HDD 

crossing of 200th Ave. East will be required in which the entry point for the new 200th Ave. HDD 

crossing will be the same entry point as the revised IL River HDD entry point. The HDD sites for 

the modified IL River HDD crossing and the 200th Ave. HDD crossing have NSAs within 1⁄2 mile of 

the entry side or exit side of the HDD. For reference, Figure 1 (p. 4) provides an area layout 

around the subject HDD sites showing the NSAs within 1⁄2 mile of the HDD entry or exit point. 

The following Table A summarizes the modified HDD sites for the project in which there are 

NSAs within 1⁄2 mile of either the HDD entry side or HDD exit side. Table A also includes the 

observed nearby NSA to the HDD entry/exit point along with the distance/direction of the nearby 

NSAs and observed land contour/obstructions, such as foliage/trees, between the HDD site and 

the nearby NSAs. Verification of NSAs (i.e., distance/direction) and ambient sound levels around 

these new HDD sites were determined by H&K via ambient sound surveys on 5/5/08. 

Subject HDD 

Construction Site 

Entry or 

Exit Point 

Approx. 

 Milepost 

Type of NSA Distance & Direction 

of Closest NSA 

Land Contour & Obstructions 

Between NSA & HDD Site 

IL River or 200th Ave. HDD Entry MP 71.0 Residence 600 feet (NNW) Some foliage/trees 

200th Ave. HDD Exit MP 70.1 Residence 250 feet (SW) Some foliage/trees 

Table A: Summary of Modified IL River HDD Sites with NSAs within 1⁄2 Mile and Distance/Direction of NSAs 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
Hoover & Keith Inc.

REX-East Project H&K Job No. 3913 

Acoustical Assessment of Modified HDD Crossing at the IL River for the Project Pipeline Date of Memo: 09/30/08 

-Page 2- 

3.0 ACOUSTICAL ASSESSMENT AND NOISE MITIGATION

3.1 Sound Contribution due to the Modified IL River HDD Sites 

The spreadsheet analyses (calculations) of the estimated A-wt. sound level contributed by HDD 

operations associated with the modified IL River HDD at the closest NSA are provided in Tables 

1 & 2 (p. 5). For the HDD sites (i.e., entry or exit location) in which the sound criteria could be 

exceeded, the acoustical assessment predicts the noise contribution of HDD operations if 

additional noise mitigation measures are employed to minimize the noise impact at the NSAs. 

For reference, a description of the acoustical analysis methodology and the source of sound data 

are provided at the end of the memo (p. 6). 

 The following sound sources (i.e., equipment) at the HDD entry side were considered significant: 

3⁄4 Drilling rig & associated engine-driven power unit; 

3⁄4 Engine-driven mud pump(s) and engine-driven generator sets; 

3⁄4 Mud mixing & mud cleaning equipment; 

3⁄4 Crane, sideboom & backhoe, frontloader, forklift and/or trucks; 

3⁄4 Engine-driven light plants (used for nighttime operation). 

The following sound sources at the HDD exit side were considered significant, and the noise 

generated at the HDD exit side is significantly lower than the noise generated at the entry side: 

3⁄4 Backhoe, sideboom, and possibly one (1) engine-driven generator set; 

3⁄4 Engine-driven light plants (used for nighttime operation). 

The following Table B summarizes the estimated Ldn (as calculated from estimated A-wt. sound 

level of drilling operations) at the closest NSA(s). For those sites in which the sound criterion 

could be exceeded, Table B denotes which sites that additional noise mitigation measures are 

required to meet the sound criteria and provides the predicted noise contribution of the HDD 

operations at the respective HDD sites if additional noise mitigation measures are employed.

Planned 

HDD Site 

Entry 

or Exit 

Point 

Distance & 

Direction of 

Closest NSA 

Added 

Mitigation to 

meet Criteria 

Calc’d Ldn 

due to HDD 

(via A-Wt.) 

Ambient 

Ldn 

Ldn of 

HDD plus 

Ambient 

Increase 

Above 

Ambient 

IL River HDD or 

200th Ave. HDD 

Entry 600 feet (NNW) Required 54.6 dBA 47.0 dBA 55.3 dBA 8.3 dB 

200th Ave. HDD Exit 250 feet (SW) Required 52.6 dBA 47.0 dBA 53.7 dBA 6.7 dB 

Table B: Summary of Est’d Sound Level Contribution and Calc’d Ldn of the Planned HDD Sites and 

assumes Added NC Measures if the Benchmark Sound Criteria is Exceeded. 

In summary, the assessment indicates that the noise generated by HDD operations at the HDD 

entry location for the modified IL River HDD crossing & new 200th Ave. HDD crossing and at the 

HDD exit location for the new 200th Ave. HDD crossing could exceed the sound criteria if no 

additional noise mitigation measures are employed. 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
Hoover & Keith Inc.

REX-East Project H&K Job No. 3913 

Acoustical Assessment of Modified HDD Crossing at the IL River for the Project Pipeline Date of Memo: 09/30/08 

-Page 3- 

3.2 Summary of Noise Mitigation Measures 

For the HDD operations at the modified IL River HDD sites in which 55 dBA (Ldn) could be 

exceeded if no additional noise mitigation measures are employed (i.e., HDD entry at the IL River 

HDD, which is same entry point as the new 200th Ave. HDD crossing, and the HDD exit site for 

the 200th Ave. HDD crossing), an adequate temporary noise barrier will have to be installed prior 

to commencement of drilling operations. Such a temporary noise barrier would be installed 

around 2 or 3 sides of the HDD equipment area, depending on the location of the nearby NSAs, 

which is constructed of 3⁄4-in. thick plywood panels. Also, prior to installation and operation of 

HDD activities at these 2 new HDD sites, temporary housing or equivalent monetary 

compensation should be discussed and/or offered to the nearby land owner(s), since some 

potential noise mitigation measures may not be a cost-effective option. 

4.0 FINAL COMMENT

The acoustical assessment indicates that if additional noise mitigation measures are not 

employed, the noise attributable to the drilling operations at the modified IL River HDD sites could 

be greater than the benchmark sound requirement (i.e., Ldn of 55 dBA and/or could cause an 

increase of 9 dBA or more above the ambient noise at the closest NSAs). As a result, feasible 

and cost-effective noise mitigation measures are discussed to reduce the noise associated with 

HDD operations to below the sound criteria for HDD operations. The results of the noise 

assessment indicates that if adequate additional noise mitigation measures are employed, the 

noise due to HDD drilling operations at these HDD entry site and/or HDD exit site should be 

below 55 dBA (Ldn) and/or should cause less than a 9 dB increase at the nearest NSAs. 

file: \ProjWord\NRG\REX-East Project\HDD Sites\Memo - Analysis of Modified HDD Crossing at IL River.doc 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
Hoover & Keith Inc.

REX-East Project H&K Job No. 3913 

Acoustical Assessment of Modified HDD Crossing at the IL River for the Project Pipeline Date of Memo: 09/30/08 

-Page 4- 

Figure 1: Modified IL River HDD Crossing for REX-East Project: Area Layout Showing the location 

of the Modified IL River HDD Crossing (Entry Side) and new 200th Ave. East HDD 

Crossing (Entry/Exit Sides) along with nearby NSAs around HDD Entry/Exit Sites. 

N

APPROXIMATE SCALE IN FEET

0 1200

(1 IN = 1200 FT)

600 2400

- HOUSE OR MOBILE HOME

NSA - NOISE SENSITIVE AREA

LEGEND

 - MEASUREMENT POSITION

- NON RESIDENTIAL BUILDING

NEW ILLINOIS

RIVER HDD

ENTRY POINT

ILLINOIS RIVER

HDD EXIT POINT

POS.1 600'

3200'

NSA#1

ILLINOIS RIVER

1000 N

200TH AVE. EAST

BEDFORD RD.

CR 4152 WILSON LN.

NEW 200TH AVE.

HDD ENTRY

POINT

NEW 200TH AVE.

HDD EXIT POINT

250'

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
Document Accession #: 20081003-5012 Filed Date: 10/03/2008
Hoover & Keith Inc.

REX-East Project H&K Job No. 3913 

Acoustical Assessment of Modified HDD Crossing at the IL River for the Project Pipeline Date of Memo: 09/30/08 

-Page 6- 

Description of Acoustical Assessment Methodology and Source of Sound Data

In general, the predicted sound level contributed by drilling operations at a HDD site was calculated as a 

function of frequency from estimated unweighted octave-band (O.B.) sound power levels (PWLs) and Awt. PWL of the respective equipment operations at either the HDD entry site or HDD exit site. The 

following summarizes the acoustical analysis procedure: 

3⁄4 Initially, unweighted O.B. PWLs of the HDD operations were determined from actual sound level 

measurements by H&K on similar type of HDD operations/equipment expected for this project. 

Estimated PWL values of the HDD operations were calculated from sound measurements at different 

distances/directions from HDD operations (e.g., sound measurements at 100 feet, 200 feet and 400 

feet from HDD equipment during operation). 

3⁄4 Then, expected attenuation in dB per O.B. frequency due to hemispherical sound propagation 

(discussed in more detail below*), atmospheric sound absorption (discussed in more detail below**) 

and other factors (e.g., attenuation due to foliage and land contour**) were subtracted from the 

unweighted O.B. PWLs to obtain unweighted O.B. sound pressure levels (SPLs) of HDD operations. 

3⁄4 Finally, the resulting estimated total unweighted O.B. SPLs for the HDD operations, including sound 

attenuation effects, were logarithmically summed and corrected for A-weighting to provide the 

estimated overall A-wt. sound level contributed by the drilling operations at the specified distance(s). 

*Attenuation due to hemispherical sound propagation: Sound propagates outwards in all directions (i.e., 

length, width, height) from a point source, and the sound energy of a noise source decreases with 

increasing distance from the source. In the case of hemispherical sound propagation, the source is 

located on a flat continuous plane/surface (e.g., ground), and the sound radiates hemispherically (i.e., 

outward, over and above the surface) from the source. The following equation is the theoretical decrease 

of sound energy when determining the resulting O.B. SPLs of a noise source at a specific distance (“r”) of 

a receiver from a source O.B. PWL values: 

Decrease in SPL (“hemispherical propagation”) from a noise source = 20*log(r) – 2.3 dB

where “r” is distance of the receiver from the noise source. 

**Attenuation due to air absorption, foliage & land contour: Air absorbs sound energy, and the amount of 

absorption (“attenuation”) is dependent on the temperature and relative humidity (R.H.) of air and 

frequency of sound. For example, the attenuation due to air absorption for 1000 Hz O.B. SPL is 

approximately 1.5 dB per 1,000 feet for standard day conditions. Potential attenuation of foliage, based 

on our experience and an ISO Standard1, the “medium-frequency” attenuation (i.e., 1000 Hz) due to 

forest/trees greater than 500 feet thick is approximately 10 dB. Also, forested areas with plantings more 

than 100 feet deep can provide some attenuation of ground level noise sources. 

End of Memo 

 

1 ISO Standard 9613-1: 1993 (E), entitled “Acoustics – Attenuation of sound during propagation outdoors – Part 1: 

Calculation of the absorption of sound by the atmosphere, and Part 2: General method of calculation” 

Document Accession #: 20081003-5012 Filed Date: 10/03/2008
Document Content(s)

Cover Letter.PDF..........................................................1

1280-d-sx-sk-011-WABASH RIVER.PDF.........................................7

1280-A-SR-006_MP 39.6 to 39.6.PDF.........................................8

1280-d-105-015_r3-1280-D-105-015.PDF .....................................9

1280-d-105-091_r3-1280-D-105-091.PDF ....................................10

1280-d-sx-sk-011-MP 242.9+4.0.PDF........................................11

1280-d-105-091_r2-MP 242.9+4.0.PDF.......................................12

1280-d-105-131_MP355.6 to 355.9.PDF......................................13

1280-d-105-142_MP 386.9 to 387.5.PDF ....................................14

1280-d-105-144_MP 392.2 to 393.6.PDF ....................................15

1280-d-105-145_MP 392.2 to 393.6.PDF ....................................16

1280-d-105-148_MP 401.8 to 402.1.PDF ....................................17

Attach F_Analysis Re HDDat IL River.PDF..................................18

Document Accession #: 20081003-5012 Filed Date: 10/03/2008