HomeMy WebLinkAboutOWTS Installation Observation 03.31.2021March 31,
.lack Albright
RFLANDCO L.LC
402 Park Avenue, Unit A
Basalt Co 81621
".lack Albright" <j ack@albright-associates.comn>
RE: As-Constructed—Report—Onsite Wastewater Treatment System (OWTS)„ 17352 Highway 82 Professional Office, 17352
82 Hwy, Carbondale, CO, Section: 32 Township: 7 Range: 87 A Tr In Lot 18
SE Job No. 30201, Parcel No: 239t-321-00-043.
Dear .lack:
Pursuant to County requirements, this letter provides documentation that the Onsite Wastewater Treatment System (OWTS)
upgraded components recently installed at the above referenced site is in compliance with the permitted design. Sopris
Engineering inspected the excavations, soils, materials and the installation of the system components during construction, prior to
final backfil I and after all installations were completed. The replacement absorption field and tank installations were designed
and constructed to serve the proposed usage on the subject property.
Sopris Engineering performed site visits to inspect and document the as -constructed conditions of the OWTS. Inspections were
coordinated with the property owner and the Contractor, Timberline Excavation, that installed the system components. The as -
constructed conditions and installation of the new OWTS components is in compliance with Garfield County Regulations; the
recommendations and specifications delineated on the civil design plans, C2-OWTS Plan revision dated 1-06-2021, and the
OWTS design Report dated 1-6-202, by Sopris Engineering. The design criteria and system sizing information is summarized
below.
OWTS Design Criteria and Sizing
Based on our findings the design and installation of an engineered OWTS with enhanced treatment is feasible in accordance with
applicable County and the State of Colorado Regulation 43. The existing residential structure has 4 bedrooms and detached garage
structure that can be considered for use as a 1-bedroom ADU. In order to ensure adequate OWTS capacity for existing usage and
potential finure usage the new replacement system is designed for for the maximum design flow under anticipated re -development
scenarios. The residential facility design assumes a 4-bedroom single family residence plus a 1-bedroom detached ADU. The
system is designed based on the current County design criteria and the design criteria approved for the use of a pressure dosed
sand filter (SF) system The design is in compliance with the current County Regulation No. 43 with area calculations based on
the LTAR loading rate for ASTM-33 filter sand per a minimum equivalent 4-bedroom residential desi gn plus a 1 bedroom ADU
residential use flow capacity.
A a three -compartment t,500 gallon concrete septic tank that will be equipped with an Orenco Systems simplex high head pump in
a Biotube vault installed in the third 500-gallon volume chamber with associated piping and controls was installed. The total tank
volume is 2,000 gallons.
A fill pressure dosed Sand Filter (SF) single bed system installed to provide for equal pressure distribution of effluent across a
846 S.F. treatment/absorption SF field with 24-inches of filter sand below gravelless chamber spray shield units. The effluentis
dosed across the three distribution rows via an individual custom perforated pressure distribution pipe running the length of the
70.5 feet by 12 feet sand filter bed.
Design Calculations OWTS
Design Flow Criteria: Minimum population based on 2 person per bedroom for the first 3 bedrooms = 6 persons and 1 person per
bedroom for each additional bedrooms = 4 bedroom residence for a total of 7 persons. 75 gallpersonlday,
Max. Design flow (Qd)gallonslday = (# of people) x (avg. flow)gallpersonlday.
Design flow QdI Main house Residential: 7 persons @ 75 gpd = 7 x 75 = 525 gpd
Design flow Qd2 ADU a Residential: 2 persons @ 75 gpd = 2 x 75 = 150 gpd
Design flow Qd = QdI + Qd2 = 525 + 150 = 675 gpd
Sub Surface Conditions and Testier
502 Main Street ■ Suite A3 • Carbondale, CO 81623 ■ (970) 704-0311 • Fax (970) 704-D313
SGPRIS ENGINEERING* LLC civil consultants
OWTS AS-CONTRUCTED LEVER
RFLANDCO LLC
SE Job No. 13201.01
March 31, 2021
Page 2
Subsurface soil investigations and USDA soil texture method tests were performed by Sopris Engineering on November 27, 2020.
The soils below nil to 3 inches of topsoil consist of medium dense gravelly sandy loam to sandy silt loam with cobbles material to
0.3 to 5 feet below the surface. The soils become increasingly rocky with depth and appear to be consistent across the site.
The native soils sampled from 1-2 feet below the surface are characterized as a soil type 2 soil consisting of sandy gravelly silt
loam texture with moderate granular structure. This soil has an effective loading rate for conventional soil treatment of 0.6
Gal/S.F./day for a level 1 conventional treatment system Soils below 2 feet are increasingly rocky and are characterized as Type
Rl soils with rock content greater than 35% and less than 65% with 50% of the rock content size less than 314 inch. The rocky
soils at depth with 24 inches of filter sand replacement media have an effective loading rate of of 0.8 Gal/S.F./day for a level-3
treatment system. No free water was encouritered in excavations observed on site. Normal Groundwater levels are expected to be
below 10 feet from the existing surface grades. The soi is are suitable for the installation of a sand filter treatment bed system
consisting of a nuninnun 24" depth of secondary sand Media that is fiilly pressure dosed meeting the requirements under sections
(43.10.C,D,E,F & H and 43.11.C.).
Intermittent Sand Fitter Treatment Unit/ Absorption System De
The treatment/absorption field was desi pied based on utilizing the effective Long Term Acceptance Rate (LTAR) for an
intermittent sand filter treatment system utilizing pressure dosed distribution laterals and gravelless chamber units as spray shields.
Long Term Acceptance Rate (LTAR)
Receiving septic tank effluent; the treatment level for intermittent sand filters is considered TL3 for the rninimum 24" depth of
treatment media with the upper infiltrative surface being at least 4-feet above a limiting layer;
Maximum hydraulic loading rate for TL1 effluent applied to "Secondary Sand Media" in an unlined sand filter is 0.8
gal./sq.ft./day, or the long term acceptance rate of the receiving soil Type 2 R-1 for TL3 (1.1 gal./S.F./day) The maximum Loading
rate is therefore 0.8 gal.lsq.ft.lday
Loading factors; (Table 10-2, pressure dosed application bed = 1.0 )
A(sf) = dQ x LF1 = A = Area;
LTAR LTAR = 0.8 Gal/S.F./day for secondary sand, ASTM-33, " Concrete sand"
Qd = flow (gal/day) = 675gpd
LF 1=1.0 pressure dosing
A(sf) = 675 gpd x 1.0 = 843.75 S.F.
0.8 Gal/S.F./day
The standard Quick 4 chamber spray shields were installed over the top of the sand on 4 foot centers and backfil led with a
minimum 12-inch depth of cover. Filter fabric was placed over the chambers and the entire extents of the sand filter bed. The
chamber rows were completed with standard end caps installed at both ends. A piezometer monitoring well pipe riser with
threaded cap were installed at two corners of the field and be extended down to the excavated surface depth at the bottom of the
placed sand.
Effluent Distribution Svstem
The OWTS field is fully pressure dosed along the entire length of the distribution rows. An Orenco Systems $io Tube pump vault
system is installed with an effluent screen in the third compartment of the septic/dosing tank. The pump system has a single high
head pump with a 1.5" discharge assembly. The si mplex pump assembly demand doses effluent through a single 1.25-inch
diameter PVC transport pipe from the pump assembly and connect to manifold pipe that connects to the three custom perforated
pipes at the head of the bed. The perforated lateral pipes have 5132-inch orifices drilled every 3.0 feet oriented upward to spray
against the interior chamber. The first and last orifice was drilled and oriented downward with an orifice shield to allow drainage
of the line. Individual 1.25" ball valves were installed at the end of each perforated distribution lateral centered below the end
OWTS AS-CONTRUCTED LETITER
RFLANDCO LLC
SE Job No. 13201.01
March 31, 2021
Page 3
cap vertical inspection ports installed at the terrninal end of the field. Two vertical 4-inch inspection ports were installed at the
the head of the field. Piezometer inspection ports were installed at the corners of the field.
Pump operations shall be controlled by a remote post mounted control panel adjacent to the tank Automatic float switches for off,
redundant off, on and high water with alarm activation were installed on a dedicated PVC float tree. Two separate circuits from
the electrical circuit panel and/or junction box are routed to the control panel for separate power to the controls and pump.
OWTS Operation and Maintenance
All components of the engineered OWTS shall be inspected on a regular basis and be properly maintained. The responsibility for
repair and maintenance of the system will remain with the property Owner. The owner shall retain the services of qualified
personnel to inspect the 0WTS and to perform all maintenance and repairs necessary to ensure that the system is in good operating
condition and is in compliance with the manufacturer's performance requirements. The operating components of the OWTS shall
be inspected by the engineer within 30 days of being placed into operation and thereafter every six months by the owner or
qualified service provider. In general, for a properly utilized system, septic tanks should be pumped every 3 - 5 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 invasive plants. Positive surface drainage away from the absorption field should be
maintained.
If you have any question or need any additional information, please call.
Sincerely,
5OPR1S ENGINEERING, LLC
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37, 2027
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Paul E. Rutledge Yancy Nichol, PE
Design Engineer Principal