Item 10 - Noise Study
SAUNDERS & ASSOCIATES
1601 Elm Street, Floor 33
Dallas, TX 75201
Ph: 1-877-709-1400
Fax: 1-877-309-7268
www.saundersassoc.com
To: John Rose – P.E.
From: Melvin L. Saunders IV, MASA, INCE
CC:
Date: July 20, 2020
Re: HEB - 1425 East Southlake Blvd Southlake Generator Noise Study
At your request, we have conducted analysis of the property line noise levels for the proposed
natural gas generators at the HEB Grocery Store Located at 1425 East Southlake Blvd in
Southlake Texas. The following report highlights our findings and recommendations.
City of Southlake Local Noise Ordinance
It is our understanding that the generator noise levels at the property line must meet the
current maximum permissible sound pressure levels as found in Chapter 11 - Offenses and
Miscallaneous Provisions of the Ordinance. Section 11-60, subsection C, paragraph 12 states
the following:
(12) Conducting or permitting any activity that produces a dBA level beyond the immediate
vicinity that exceeds the dBA levels specified in Table 1 hereinbelow.
Product Information
We understand that three natural gas generators are proposed to be installed on the south side
of the HEB building. Each generator enclosure is rated to achieve an overall noise level of 68
dBA at a distance of 7 meters (23 feet) from the enclosure. The closest generator is
understood to be approximately 148 feet away from the nearest residential property line. Our
understanding of the site layout is shown below.
SAUNDERS & ASSOCIATES
1601 Elm Street, Floor 33
Dallas, TX 75201
Ph: 1-877-709-1400
Fax: 1-877-309-7268
www.saundersassoc.com
As currently designed, we estimate that the noise level at the property line with 3 generators
operating simultaneously is 61-62 dBA and just above the allowable daytime noise limit. This
assumes that there is a clear line of sight to the generator enclosures from the property line. If
it is desired to operate the generators overnight or on Sundays, an acoustical screenwall will be
required. Generally, the screenwall will need to be at least 3 ft taller than the tallest point on
the generator enclosure and ideally no more that 6 ft from the generator enclosure. With this
approach the resultant noise level will be approximately 50 dBA at the residential property line
and will meet the City or Southlake noise ordinance.
Barrier Height and Design
To evaluate the effectiveness of the screen wall, we examined the distance of the generator
from both the screen wall and the receiver location. The attenuation provided by a barrier is a
function of the relationship between the source and receiver and the extra distance sound has
to travel to the receiver due to the height of the barrier. The barrier provides a reduction of
sound pressure level in its shadow zone. Figure 1.0 shows the relationships between typical
source, receive, and barrier heights. For the HEB Southlake study, the receiver location was
SAUNDERS & ASSOCIATES
1601 Elm Street, Floor 33
Dallas, TX 75201
Ph: 1-877-709-1400
Fax: 1-877-309-7268
www.saundersassoc.com
taken to be a standing person at the
adjacent residential property line. In
most instances, the grading height of
the residential properties are higher
than the loading dock and this was
considered in the barrier calculation.
For most barrier considerations, any
sound transmitted through the barrier
can be neglected because it will be at
such low level relative to the sound
that travels over the barrier. The sound that comes through the barrier will typically be at least
20 dB(A) below the sound that comes over the barrier. As a rule of thumb, any material that
weighs approximately 2.5-4lbs/ sq. ft. has a transmission loss of at least 20 db(A) and will meet
this requirement. For your use and consideration, the table below lists some common barrier
material and the associated transmission loss values. It should be noted that the use of wood
should consider treatments to minimize gaps due to warping or shrinking.
Approximate sound transmission loss values for common materials.
Material
Thickness Weight Transmission
Loss (dB(A)) mm
(inches) kg/m2 (lbs/ft2)
Concrete Block, 200mm x
200mm x 405 (8" x 8" x 16")
light weight
200mm (8") 151 (31) 34
Steel, 18 ga 1.27mm
(0.050") 10 (2.00) 25
Steel, 20 ga 0.95mm
(0.0375") 7.3 (1.50) 22
Steel, 22 ga 0.79mm
(0.0312") 6.1 (1.25) 20
Wood, Fir 12mm (0.5") 8.3 (1.7) 18
Wood, Fir 25mm (1.0") 16.1(3.3) 21
Wood, Fir 50mm (2.0") 32.7 (6.7) 24
SAUNDERS & ASSOCIATES
1601 Elm Street, Floor 33
Dallas, TX 75201
Ph: 1-877-709-1400
Fax: 1-877-309-7268
www.saundersassoc.com
This concludes the review of the generator noise for the HEB Southlake project located in
Southlake, TX. If there are any comments or questions, please don’t hesitate to contact me.
Melvin L. Saunders IV, MASA, INCE
Principal Consultant
Saunders & Associates