HomeMy WebLinkAboutSystem Design 10.26.2016October 26, 2016
Mr. Andy Schwaller, Building Official
Garfield County Building Department
108 8th Street
Glenwood Springs, CO 81601
RE: Tovar Residence
1860 CR 319, Rifle, Colorado
OWTS Design
Dear Andy,
The purpose of this letter is to transmit the installation design regarding the onsite waste water
treatment system (OWTS) for the Tovar Residence located at 1860 CR 319 in Rifle, Colorado. The
specific location of the property in question is located in Figure 1. .
Tovar Residence
Septic System
Location
The installation design accommodates a 4 bedroom single family home use. The new system consists of
a 1250 gallon concrete septic tank and a soil treatment area of standard depth and design for
infiltrators. An area located in the NE portion of the property, at the toe of the hill side, is where soil
testing was performed under our direction to determine the percolation rates of soils. Percolation
testing resulted in perc rates ranges from 17 mpi to 60 mpi. The location of the site is some 1,240 feet
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east from CR 319. The overburden soils were consistent and appeared to be a silty clayey material
consistent with the Soil Type 3 identified in the Garfield County OSWTS Regulations Table 10-1.
Along with the percolation testing and profile hole observations, research was performed to gain insight
on the specific soils parameters utilizing the NRCS WebSoil survey. The percolation test yielded a
percolation rate of 17 to 60 minutes per inch. With the high variability in the percolation rate, this has
given us cause to rely on on-site soil observations coupled with the data obtained from the NRCS
WebSoil Survey. The average percolation rates are consistent with our observations of the on-site soils
being an "Arvada loam" soil. The exhibits attached to this letter identify the information that was
researched in addition to the testing performed to help determine the LTAR (Long Term Acceptance
Rate) for the STA (Soil Treatment Area) for the design of the new disposal field/trench design. These
Exhibits are listed as follows:
1. Exhibit A:
2. Exhibit B:
3. Exhibit C:
4. Exhibit D:
NRCS Soil Map
NRCS Hydrologic Soil Group
NRCS Unified Soil Classification
NRCS Septic Tank Absorption Fields
Based upon the soils testing and the researched data, the LTAR for the on-site soils is 0.5 gallons per day
per square foot. With this data, the STA (Soil Treatment Area) is 1200 square feet. Because we will
incorporate the use of Infiltrators (chambers), we have employed the size adjustment factors and
reduced the bed size by the following:
For using chambers, a 0.7 factor is applied, thus resulting is an area of 840 sf. This results in four
infiltrator or chamber trenches of dimension 72' in length. The attached calculations identify the
thought process in the design of this system.
The design and layout of the system is shown on the attached drawing following this letter.
Upon your receipt and review, if you have any questions, please don't hesitate to call.
Respectfully,
SGM-Inc.
, CFM Principal
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Sizing of Absorption Field or Soil Treatment Area
5 Going with a soil type 3 and Treatment Level 2, LIAR = 0.5 g/sf/d
For a pressure dosed system, size adjustment factor is 1.0 for a bed configuration
For a gravity system, the size adjustment factor shall be 1.2 for a bed configuration
For a gravity trench system, adjustment factor = 1.0
For a pressure dosed trench system, adjustment factor = 0.9
For use of chambers: size adustment factor is 0.7
STA= Flow/LTAR 1200 square feet (unfactored)
For a chamber system, gravity flow, adjust size to 0.7*1200= 840 square feet
For a chamber system in a trench configuration, length= 280 feet
(this would equate to 4 runs of 70 feet each)
With the effective length of a Quick4 chamber at 4', use 17.5 (18) chambers per trench
Thus the net length of the runs will be 72' each.
If dousing tank and automatic siphon are used, the dosing tank would be a 250 gallon tank
with and automatic dosing siphon. The trench lengths would be reduced to 16 units per trench.
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OWTS Design Report and Calculations
Client: Tovar Residence
1860 CR 319
Rifle, Co 81650
Date: 25 -Oct -16
Flow Data for the OWTS Design
1 Home Use (4 Bedroom Home)
600
Total= 600
For Home Use, 2 persons per bedroom and 75 gallons per day per person, BOD5 = 0.06
#/person/day
Home Use
Totals:
Soil Data for the OWTS
600 gpd 0.48 #/day
600 gpd 0.48 #/day
2 Data from on-site soil observations: Appears to be a loamy soil of consistent
depth from surface to a depth of 10 feet.
At a depth of 10', neither bedrock or groundwater have been encountered.
Data from the web soil survey indicates an Arvada Loam exists.
Data from percolation testing indicated the following:
Average of 3 percolation holes: 41.0 mpi
Given the consideration of all data, the Long Term Acceptance Rate to use is 0.5 gallons/sf/day
Septic Tank Sizing
3 Flow calculated from above: 600 gpd
48 hour detention time for septic tank sizing;
Use a standard 1250 gallon precast concrete septic tank.
Volume= 1200 gpd