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204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 1 of 2
Sand/Oil Separator Design Report
ENTERPRISE SITE PLAN
150 Automotive Way
Bozeman, Montana
February 2023
Prepared By:
Genesis Engineering, Inc.
GEI Project #: 1134.008
Prepared For:
J & D Family Limited Partnership
270 Automotive Drive
Bozeman, MT 59718
204 N. 11th Ave., Bozeman, MT 59715 Cell: (406) 581-3319 www.g-e-i.net Page 2 of 2
Enterprise Rental Car Expansion ‐ Design Methods
The proposed expansion of the existing Enterprise building includes adding one more wash‐
bay for trucks. The design of a sand‐oil separator for a manual power sprayer car wash
requires several steps, including determining the flow rate of water, selecting the
appropriate separator size, and calculating the capacity of the separator. Genesis has
proceeded with the following re‐design of the separator to evaluate if the existing separator
is adequate.
1. First, we determined the anticipated flow rate of water anticipated to be passing through
the separator. This can be done by measuring the water flow rate in gallons per minute
(GPM). The proposed project could possibly have two power washers operating at the same
time and the current power washer utilizes a flow of approximately 4 gpm. This double bay
scenario will likely produce a flow rate of 8‐10 gpm entering the separator.
2. Next, we verified that the appropriate separator structure had been selected. The existing
separator on site is a two compartment 1,500 gallon tank and is traffic rated and currently
operational.
3. Separator Capacity: To ensure that the existing separator can handle the volume of car
wash water produced, we have calculated the necessary capacity by multiplying the flow
rate into the separator by the retention time required for the separator to effectively
remove contaminants and sediment from the car wash water. According to our research
and standard practice, the typical retention times needed to settle out particles between
0.10 mm and 0.01 mm in size is 30 to 60 minutes. Using the inflow of 10 gpm and
multiplying by the retention time of 60 minutes yields a total settlement volume of 600
gallons. The existing separator tank is 1,500 gallons which exceeds the required volume by a
factor of 2.5 times.
4. Ensure proper maintenance: Genesis interviewed the current owner and operator of the
existing separator and determined that it is regularly maintained and pumped
approximately 3 times a year and has continued to function properly. We encourage the
owners to check the separator on a monthly basis to make sure any changes in use are
addressed accordingly.
A copy of the Anderson Precast cut sheet for the existing separator is attached and the location of
the existing separator is shown on the siteplan.
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