HomeMy WebLinkAboutAs-built Engineer's Report 07.12.2012wa-9-10G
July 12, 2012
Jeff Johnson
Johnson Carter Architccts,PC
136 East Third St., Suite U
Rifle, CO 81650
RE: As -Built On -Site Wastewater Treatment System ((AWTS), Bayou Well Services Building Expansion,
Parcel 2, (Green Subdivision, Rifle, Colorado
SE Job No. 11084.01
Dear Mr. Johnson:
Pursuant to County Regulations, this letter provides documentation that the new and expanded Onsite Wastewater
"Treatment System (OWTS) recently installed is in general compliance with the permitted design. Sopris
Engineering has performed site visits to measure, inspect, and document the as built conditions of the constructed
system. We have coordinated our efforts with the system installer. The systems were inspected prior to
backfilling and after component installations were complete. The as -built conditions and installation of the new
MIS components is in compliance with the permitted design specifications for the new and expanded system.
The OWTS systems were constructed in accordance with the design recommendations and specifications delineated
on the design plan, C-4, Utility and OWS Plan, by Sopris Engineering, dated 8-23-11.
The improved site includes a new East side facility addition with plumbed office space that is screed by a new
OWTS system. The original West side facility and plumbed office space is served by the existing expanded OWTS
system. The combined systems were designed based on an average flow of 1520 gpd and a peak sewage flow of
2280 gpd calculated by the per capital usage of employees and transient population.
Facility Usage
Existing
#
Max. 24 -hours
Proposed
#
Employees/transient
Total
#
daily
/capita
Usage
gpd/cap
Capita
Avg Rate
QA
gpd
-
Peaking
Factor
#
Design
QD
gpd
Facility description
Well Service
Truck
Maintenance
Job desription
Office, Shop,
Crew
Drivers,
Transient
WEST
EAST
Combined
Daily fulItime
office
7
14
21
15
315
L 1.5
472.5
Infrequent parttime
Temporary
8
0
8
5
40
1.5
60
Daily fulltime
shop
Crew & Drivers
13
20
13
94
26
114
20
5
520
570
1.5
1.5
780
855
Max. Daily
Transient
Infrequent
Guest visitor
Delivery
2
10
12
5
60
1.5
90
Infrequent
0
50
3
r 3
5 a
15 _
1520
1.5
1.5
22.5
2280
Existing +
Proposed
Design Calculations
The design flow is calculated for the subject facilities as shown in the table above based on usage descriptions and
per capita flow rates from the Stale 1. S. D. S. Regulations.
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313
SOPRIS ENGINEERING • LLC
civil consultants
Jeff Johnson, Bayou Well Services AB-OWTS
SE Job No. 11084.01
July 12, 2012
Page 2
The commercial building includes office, shop and maintenance Facilities. The Onsite Wastewater system has been
upgraded to include two distribution systems that serve the existing west side facilities and the proposed east side
facilities.
The total average flow (Regulatory Design Capacity) Qa = 1520 gpd.
The total Peak flow (Peak Daily Design Flow) Qd = 2280 gpd.
The combined system consists of the existing West side septic tank, distribution system and field and the new East
side septic tank, distribution system and field, The two separate collection and tank detention systems discharge
effluent to their respective secondary treatment absorption fields. The existing field has been expanded to
accommodate projcctcd increase in usage.
The West system has a projected peak design flow Qd 772.5 gpd
The East system has a projected peak design flow Qd = 1507.5 gpd
The total combined systems projcctcd peak design flow Qd = 2280 gpd.
Septic Tank Design
The volumetric capacity is based on 125% of peak design flow V = Q* 1.25
West Side: Qd = 772.5 gpd * 1.25 days = 966 gallons.
The existing 1,000 gallon concrete, dual compartment septic tank is adequate.
East Side: Qd = 1507.5 gpd * 1.25 days = 1884 gallons.
installed a 2,000 gallon concrete, dual compartment septic tank.
Sub Surface Conditions and Testing:
Percolation testing was performed by All Service Septic, LLC. A percolation rate of
32 minutes per inch has been reported in the location of the existing and proposed
treatment/absorption fields.
A soil investigation has been performed by CTL Thompson. The soil profile includes
approximately 1 foot of top soil overlaying nil to 5 feet of sandy clay underlain by clayey sand.
to a depth of 14 feet explored. Free ground water was measured at 8 to 14 feet.
Blgen In-Drain/Geotcxtilc Sand Filter (G.S.F.) Treatment System Design
The Commercial facility will have variable daily flows typically lower than the projected average,
The use of a single pass gravity Secondary treatment system is recommended due to the
Geotechnical conditions and the relatively high strength waste water from the facility.
Area required for a conventional pipe and gravel absorption system may be appropriately
reduced by using a secondary treatment GSF treatment bed system. The maximum reduction is
50% however are design allows for only a 40% reduction over a conventional system. No kitchen
facilities are included in the facilities.
Using a design percolation rate of 32 minutes per inch with a Design flow of 2280 gpd,
The standard absorption area equation yields:
A (sf) = Qd* t : where A = Area;
5 t = time in minutes per inch=32mpi
Qd = flow gpd = 2280 gpd Use 2300 gpd
A = = 2280 * 32 = 2580 S.F .
5
Apply sizing credit reduction of 40% for use of single pass secondary geotextile sand filter
(GSF) secondary treatment system. A(eredit reduction)= A*.G0 = ; 2580 * .6 = 1548 S.F.
Jeff Johnson, Bayou Well Services AB-OWTS
SE Job No, 11084.01
July 12, 2012
Page 3
Each In -drain unit area (Au) is 2 FT wide by 4 FT long (8 S.F. horizontal surface area)
with a loading rate (L.R.) of 2.5 gal. per S.F. of G.S.F.
Number of Eljen In -Drain units required equals Design Flow Qdr/L.R./Au— # units
2280 S.F. / 8 S.F./2.5 gsf = 114 units. Installed 116 total units including the 26 units in the
existing West side field. The total field Area is approximately 60% of a conventional field
size.
Standard Field requires 2580 S.F. with 40% reduction = 1548 S.F.
The total design area of the secondary treatment GSF field is 1595 S.F. that is
approximately 62% of the size of a conventional system.
Separate West and East collection pipes, septic tanks, individual distribution boxes
and treatment fields have been installed to treat the flow from each system.
The West system Qd = 772.5 gpd
In -Drain units Qd/L.R./Au= # units; 772.5 gpd / 8 S.F./2.5 gsf = 39 units. Use 40
26 units exists over a total sand basil area of 371 S.F. in two 3.5' wide x 53' long trenches.
An additional GSF Red on the terminal end of the System was installed. 'rhe installed Bed
contains 14 In -Drain units in two rows of 7 over a 30' long by 7' wide bed with 218 S.F.
of additional sand basil area. Therefore the total area is now 581 S.F.
The East system Qd = 1507.5 gpd
In -Drain units Qd/L.R./Au= # units; 1507.5 gpd / 8 S.F.l2.5 gsf 75 units. Use 76
A new GSF Bed System near the existing system was installed per the design plan. The Bed
contains 76 In -Drain units in four rows of 19 units each over a 78' long by 13' wide bed
with a total 1114 S.F. of sand basil area.
Therefore the combined total treatment field area is 581 S.F. + 1014 S.I. = 1595 S.F. as stated above_
The new septic tank was installed near off the Southeast corner of the building. The 2000 -gallon dual compartment
concrete septic tank was installed with an effluent filter installed in the outlet tee and with risers with lids to the
surface. The effluent line from the Building Addition and into the new tank is installed at a 2% slope. A two-way
cleanout was installed on the sewer lite between the exterior building wall and the tank.
A Geotextile Sand Filter (GSF) treatment/absorption systems were installing to provide single pass secondary
treatment of the effluent from the tank with ground infiltration of treated effluent into the ground. The GSF field
Eljen In -Drain units were installed as shown on the attached As -Built plan over a 12 -inch concrete sand filter Iayer
and backfilled with additional sand to approximately 12 -inches above the top of the distribution pipe. A
distribution box was installed next to the new field to equally distribute effluent to the trenches via individual 4"
distribution lines connected to individual perforated distribution pipes at the head of each row. A 4" perforated
distribution piping was placed on the center of each In -Drain row along the entire length of the row. Inspection
ports were installed on each end of the perforated distribution pipes. The individual beds were installed level with
suitable soil below the In -Drain units and sand filter layer with backfill over and around the In -Drain units. The
construction was completed utilizing specified materials installed according to design. The minimum setbaek
distances have been maintained.
Observations of the soils within the field were performed during construction indicating that the soils are consistent
with the descriptions in the geotechnical report. The soils consisted of uniform sandy clays to clayey sands. A
percolation test was performed by All Service Septic, LLC that resulted in an average percolation rate of 32 mpi.
Jeff Johnson, Bayou Well Services A13-OWTS
SE Job No. 11084.01
July 12, 2012
Page 4
OWS Operation and Nlaintenancc
The re establishment of vegetative cover over the field and responsibility for inspection and maintenance of the
system will remain with the Lot Owner or the owners representative. All components of the engineered OWS shall
be inspected on a regular basis and be properly maintained. The system and responsibility for repair and
maintenance of the system will remain with the Owner.
The OWS should require minimal maintenance. Several factors influencing the need for maintenance include:
actual wastewater flows versus design flows, the volume waste and amount of cleaning products, chemicals and
other toxic liquids. The tank, absorption field and other system components should be visually inspected bi-
annually for debris, damage, leaks, or other potential problems. In general, for a properly utilized system, septic
tanks should be pumped and inspected every 2 - 4 years. The effluent filter should be cleaned every six months and
at the time of pumping. Absorption fields should be maintained with suitable vegetative cover and kept free of root
inivaslve Omits. Positive surface drainage away from the absorption field should be maintained.
If you have any question or need any additional information, please call,
Sincerely,
SOPRIS ENGINEERING, LLC
Paul Rutledge
0
Ciea7M,.
•
Ora^l
9t0 f16A 3iOJ3a 11V)
�-`mear_'.7- .-
%k- • I -' �r1.A
.... • J. _ d f
- ,II
ti
,.4.,11..1..
o�
Unn111,1,114 111
wr Y1, wad. Vra
ON'931
vn. 0.7XMM \L-:--
5N011Y1fIONJ 30Vd5 ONINNYd
.rn.uw,ru.r.,.w.w.um nmw.i......a.uu..��ru �..rws. M•�i,q+'ra� w.
4
r
d
Nl • %.w
fIVO2 3111dY112
.�4 .� Miil«
.i..rPm!
l
r. In
L7 vr-C- • 0
,5310N N011011MISNO31Yd3N39
t
6101Y1f101VOV 30YN015M
�!I