303 Wyman Street, Suite 295 | Waltham, MA 02451 | Phone: 781-890-2220 | Web: www.techenv.com

March 20, 2018

Mr. Corey Juhl

Juhl Energy Development Inc.

1502 17th Street SE

Pipestone, MN 56164

Re: Acoustic and Shadow Flicker Studies – Davison County Wind, LLC

Dear Corey:

Tech Environmental, Inc. (TE) has completed sound and flicker modeling of the proposed 20 MW

Davison County Wind Project in Beulah Township, South Dakota. These studies assumed nine GE 2.3-

116 wind turbines with an 80-meter hub height (T1 through T9).

Project Sound Levels

While there are no State or local regulations with decibel limits applicable to the Project, we recommend

using a goal of 45 A-weighted decibels (dBA) as a residential goal for non-participating (NP)

residences, to prevent annoyance. Acoustic modeling was performed assuming the 9 wind turbines

operating at maximum sound power, as measured by International Standard IEC 61400-11, plus a 2-

dBA uncertainty factor. Acoustic predictions used the Cadna/A model, which conforms to International

Standard ISO 9613, and simulates maximum sound levels. These calculations are conservative because

these assumed weather conditions most favorable for sound propagation, namely a ground-based

temperature inversion, along with winter ground conditions, and no attenuation from trees or other

vegetation.

Figure 1 displays the location of the 9 wind turbines plus 12 occupied dwellings. The 45 dBA contour

line is shown in Figure 1, which reveals that the 10 NP residences (R2, R3, R4, R6 through R12) are

outside of the contour line, meaning predicted maximum sound levels at those non-participating

dwellings are below 45 dBA. A table providing the predicted sound levels for each residence follows

Figure 1. All predicted sound levels at NP residences are within the proposed acoustic goal for Davison

County Wind.

Davison County Wind March 20, 2018

2

Project Shadow Flicker

There are no State or local shadow flicker limits. The guideline commonly used in our industry, to

minimize flicker effects, is a limit of 30 hours per year at a non-participating residence. Flicker

modeling was performed assuming operation of the 9 wind turbines and using the WindPro SHADOW

model. Data regarding local average sunshine probability and turbine operation by wind direction were

included in the calculations. These calculations are conservative because no adjustment was made for

visual shielding by trees or other vegetation, and the rotor plane of the turbines was assumed to always

be perpendicular to the line from the turbine to the sun, giving the largest shadow effect.

Figure 2 displays the location of the nine wind turbines plus 12 occupied dwellings. The 30-hour per

year contour line is shown in Figure 2, which reveals that the 10 NP residences (R2, R3, R4, R6 through

R12) are outside of the contour line, meaning predicted shadow flicker at those non-participating

dwellings are below 30 hours per hour. Shadow flicker is predicted to be zero hours per year at R12 north-northeast of the Project, and at R6 northeast of the Project. A table providing the predicted shadow flicker times per year for each residence follows Figure 2. All predicted flicker levels at NP

residences are within the proposed flicker goal for Davison County Wind.

Please call if you have any questions.

Sincerely,

TECH ENVIRONMENTAL, INC.

Peter H. Guldberg, INCE, CCM Senior Consultant 4074/Letter Report March 20 2018

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45 dBA

0 0.5 10.25 Miles

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0 0.5 10.25 MilesFigure 1Maximum Sound Levels from theDavison County Wind ProjectBeulah Township, SD

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Legend"/ Participating Residences"J Non-Participating Residences!? TurbinesExpected Shadow Flicker

30 hrs/year

0 0.5 10.25 Miles

±

0 0.5 10.25 MilesFigure 2Expected Shadow FlickerDavison County Wind ProjectBeulah Township, SD

Cadna Sound Modeling Results Davison County, SD

Sound HeightReceptor ID Status Level X Y Z

(dBA) (m) (m) (m) (m)R1 P 49.4 1.52 565450.5 4843449 409.72R2 NP 38.9 1.52 564012.4 4843490 414.89R3 NP 39.0 1.52 563985.5 4844166 414.28R4 NP 37.9 1.52 563914.6 4844491 410.59R5 P 44.7 1.52 567121.3 4843307 407.1R6 NP 27.7 1.52 568779.6 4845018 403.56R7 NP 29.9 1.52 568743.1 4844592 409.75R8 NP 32.8 1.52 568749.5 4843912 410.85R9 NP 33.4 1.52 568678.4 4843752 408.95

Coordinates

Expected HeightReceptor ID Status Shadow Flicker X Y Z

(hrs:min/year) (m) (m) (m) (m)R1 P 33:52 1.52 565,450.51 4,843,448.55 409.3R2 NP 9:23 1.52 564,012.42 4,843,489.79 414R3 NP 5:05 1.52 563,985.54 4,844,166.23 414.4R4 NP 9:39 1.52 563,914.60 4,844,490.59 411.5R5 P 15:30 1.52 567,121.31 4,843,306.93 406.6R6 NP 0:00 1.52 568,779.60 4,845,017.77 409.2R7 NP 0:57 1.52 568,743.10 4,844,591.89 405R8 NP 1:28 1.52 568,749.45 4,843,911.54 408R9 NP 2:17 1.52 568,678.40 4,843,752.33 405.5R10 NP 0:44 1.52 567,021.29 4,842,176.72 414.7R11 NP 0:03 1.52 565,382.27 4,842,703.31 410.7R12 NP 0:00 1.52 567,763.35 4,845,798.12 401.2

Coordinates

Cadna Results 2018.pdfPrintable

WindPro Results 2018.pdfSheet1