HomeMy WebLinkAboutOWTS Installation Observation Report 06.28.2024June 28, 2024
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313
S OPRIS E NGINEERING • LLC civil consultants
Caleb Waller
361 County Road 311
Silt CO 81652
"Caleb Waller" <rivernestllc@gmail.com>
RE: As-Constructed–Report, On-site Wastewater Treatment System (OWTS), 361 County Road 311
Silt, Garfield County, CO, Section: 10, Township: 6, Range: 92 A TR IN LOT 9 OF SEC 10.
SE Job No. 32128, Parcel No: 217910400516. OWTS Permit #SEPT-8313.
Dear Caleb:
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 and provides documentation that the Onsite Wastewater Treatment System (OWTS)
was successfully started up for continuous automatic operation. Sopris Engineering inspected the
excavations, soils, materials and the installation of the system components during construction, prior to
final backfill and after all installations were completed.
Sopris Engineering performed site visits to inspect and document the as-constructed conditions of the
OWTS. Inspections were coordinated with the property owner, electrician and the earthmoving contractor
(Great Lakes Construction) 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 plan, C1-OWTS Plan dated 09-12-2023,
by Sopris Engineering.
System Startup
Sopris Engineering was on site Novembr 4, 2023, to advise, inspect and coordinate, riser set, discharge
piping, control panel set, external splice box and component wiring for pump and floats. The Orenco
Systems S-1 control panel was energized and the pump and control wires were connected at the panel to
the external splice box by the electrician. It was reported that the system was started up and running.
Sopris Engineering adjusted float setting and performed a dry run system startup to test float and control
operations on June 07, 2024. The system floats were wired for correct functionality in compliance with
installation and design specifications. No water was in the tank at the time since the water system was not
active.
Sopris engineering performed a follow up inspection on June 28, 2024 to inspect system operations, to
check that system floats were wired for correct functionality in compliance with installation and design
specifications, perform a pressure test, test the pump and controls to verify that the system is functioning as
designed. Sopris Engineering checked water levels in tank dosing compartment, adjusted float settings and
performed manual float operational testing, observed system operation through two normal hydraulic pump
cycle with no issues and set panel for automatic normal operation with normal liquid level in the tank.
OWTS Upgrade OWTS As-Constructed
361 County Road 311
SE Job No. 32128.01
June 28, 2024
Page 2
The panel, floats and pump amperage and voltage was tested and found to be in compliance with
manufacturer’s specifications. The operational demand dose to the field is approximately 58 gallons per
dose cycle with an approximate end of lateral squirt height of 3.5 feet. The high level visual and audible
alarm is operational.
Current OWTS Conditions
OWTS Components:
The current OWTS system serves an existing plumbed structure that currently has a one-bedroom studio
apartment, a RV space with sewer hookup. The OWTS components consist of gravity service pipe, two
1,000-gallon septic tanks in series with a new installed dosing pump assembly in the second chamber of the
second tank installed in series. The installed OWTS components include a PVC pressure discharge
transport pipe connected to a manifold pipe installed at the head of the bed to deliver effluent to a mounded
sand filter bed consisting of 3 custom perforated distribution laterals installed with infiltrator chambers
over a minimum two foot depth of select filter media. The absorption field was originally installed in 2013;
under County ISDS Permit #SEPT-11-13-3052.
The repair/upgrade design specified an expansion of the existing bed to provide for a maximum 450 gallon
per day capacity based on current regulatory design criteria. An additional matching field may be
considered in the future to expand the capacity to 900 gpd.
OWTS System upgrade
The existing mounded treatment bed was expanded to increase design capacity to 450 gpd in order to serve
the current usage from an existing 1-bedroom apartment and single RV space and providing additional
capacity to manage and additional 200 gpd design flow for up to four no direct hook up campsites and 1
additional full bath. The system was constructed to provide for demand dosing of septic tank effluent
pursuant to Regulation 43 design criteria for Treatment Level-3 sand filters. The bed sizing is in
compliance with area calculations based on the design flow and LTAR loading rate for a 24-inch layer of
ASTM-33 secondary filter sand with respect to the underlying infiltrative capacity of the base and in-situ
soil materials.
The OWTS will maintain the existing gravity sewer service pipe from the existing dwelling/garage
structure to the two existing 1,000-gallon concrete 2-compartment septic tanks. The tank lids risers and lids
were extended to the finish surface. An Orenco Systems simplex high head pump (P300511) in a Biotube
vault (PVU57-1819-L) with associated piping and controls was installed in the second tank’s second
compartment to provide full pressure dosing of the expanded/refurbished treatment field. The pump
operation is controlled by an Orenco Systems S-1 control panel. The control panel and electrical supply
sub-panel is mounted on a strut frame set adjacent to the 2nd tank compartment access riser. The operation
demand dose to the field is approximately 58 gallons per dose cycle. The 47’ by 12’ sand filter bed system
consists of infiltrator chambers used as spray shields, 24” layer of filter sand and custom perforated
distribution laterals. The effluent discharge piping from the pump assembly connects to a common
manifold pipe with connections to each custom perforated distribution lateral. Each distribution lateral has
appropriate inspection ports and appurtenances.
OWTS Upgrade OWTS As-Constructed
361 County Road 311
SE Job No. 32128.01
June 28, 2024
Page 3
Design Calculations OWTS
The existing plumbed structure has a 1 bedroom apartment and a single RV space with sewer hookup. The
facility will likely include the addition of 1 additional full bath to serve guest occupying up to 4 campsites
without water/sewer hookups. Design capacity is equivalent to 3 bedroom residential usage.
Design Flow Criteria: Minimum population based on 2 people per 1 bedroom studio apartment, 1 existing
RV site with hookup and number of campsites without water or sewer hookups.
1 Bedroom apartment = 2 persons @ 75 gal/person/day,
RV space with sewer hookup = 1 @ 100 gal/space/day
4 campsites @ 50 gal/campsite/day
Alternative: 1 additional 1-bedroom studio apartment and 1 campsite without sewer or water hook up.
Design flow Qd = (2 x 75)+ (1 x 100) + (4 x 50) = 450 gpd
Septic Tank Design: 2-Day detention time = 450 x 2 = 900 gallons required.
There are two existing 1000 gallon concrete Copeland tanks in series. The second chamber of the second
tank will serve as a dosing basin to be equipped with a bio-tube simplex high head pump dosing assembly.
Sub Surface Conditions and Testing
Subsurface soil investigations and USDA soil texture method tests were performed by Sopris Engineering
in July of 2022. The soils in the area of the proposed absorption field were sampled and characterized by
application of the USDA soil texture method test. The soils below nil to 3 inches of topsoil consist of
medium dense gravelly silt loam material to 1 to 2 feet below the surface. The soils become increasingly
rocky with depth. The soil appears to be consistent across the designated field envelope.
The native soils observed 1.5 feet below the surface are characterized as a soil type 2 soil consisting of
sandy gravelly silt loam texture with fine 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 characterized as Type R1 soils with rock content greater than 35% and less than 65% with 50% of
the rock content size less than 3/4 inch. The rocky soils at depth have an effective loading rate of 0.8
Gal/S.F./day for a treatment level-1 system. To be consistent with the previous design criteria with respect
to limiting layers the expansion and refurbishment of the existing an intermittent sand filter is
recommended to provide for a treatment level TL3 mounded sand filter system. No free water was
encountered in shallow excavation on site at the time of exploration. Normal Groundwater levels are
expected to be below 3-4 feet below existing surface grades, seasonal high groundwater levels are expected
to be 2 foot below existing surface grades and the 100-year flood plain base flood elevation has previously
been determined to at elevation 5425+/- approximately 1 foot below the existing surface grade.
The underlying soils were found suitable for the installation of the sand filter treatment bed system
consisting of a minimum 24" depth of secondary sand Media placed at over class -3 base material
overlying the basal are consisting of R1 with Type 2 silt loam matrix soils.
OWTS Upgrade OWTS As-Constructed
361 County Road 311
SE Job No. 32128.01
June 28, 2024
Page 4
Sand Filter Treatment Unit/ Absorption System Design
The treatment/absorption field is designed based on utilizing the effective Long Term Acceptance Rate
(LTAR) for an intermittent sand filter treatment bed system utilizing pressure dosed distribution laterals
and gravelless chamber units as spray shields installed over a 24-inch layer of filter sand (ASTM-33,
"washed ASTM-33 Concrete sand").
Long Term Acceptance Rate (LTAR)
Considering the application of regulation 43 design criteria of unlined sand filters receiving septic tank
effluent, pressure dosed sand filter results in the applied effluent to be treated to Wastewater Treatment
Level 3 quality prior to infiltration into native soils:
The design basal area for a treatment level 3 STA is sized per the maximum LTAR of (1.1 gal./S.F./day)
for type 2 receiving soils or the maximum LTAR of 0.8 gal/S.F./day for the minimum 24" depth of
secondary sand treatment media whichever results in the larger area;
The maximum Loading rate for this design is therefore 0.8 gal./sq.ft./day The STA is designed utilizing a
loading factor of 1: (Table 10-2, pressure dosed application bed = 1.0)
A(sf) = Qd x L.F. A = Area;
LTAR LTAR = 0.8 Gal/S.F./day for secondary sand, ASTM-33, "
Concrete sand"
A(sf) = 450 gpd x 1.0 = 562.5 S.F. Qd = flow (gal/day) = 450 gpd
0.8 Gal/S.F./day L.F.1= 1.0 pressure dosed bed
Treatment Bed Design
The single 47' by 12' mounded sand filter bed with a minimum 24-inch depth of ASTM-33, concrete sand
over imported Class-3 pit run material placed over native soil to the specified depth at the bottom of sand.
The 12-feet width of sand media is contained on the mounded base material with extended sideslopes by
placement of an embankment consisting of native soil and/or imported Class-3 pit run material placed over
the native soil along the down gradient perimeter of the bed to the specified height of 12-inches above the
top of sand level. Installed 3 rows of custom perforated 1.5 inch distribution laterals on top of sand layer
and covered with 11 Quick-4 chambers per row for use as pressure dose spray shields, as delineated on the
plan. The chambers and top of sand were covered with filter fabric and entire bed was backfilled with
native soil, free of rocks, 8 to 12 inches above the top of chambers. The top of the sand filter absorptive
surface is set at a minimum 2.5 feet above the existing surface grades and a minimum 3-feet above the
limiting BFE.
Effluent Distribution System
The distribution system was installed to equally distributes effluent across the absorption surface via 1.5-
inch individual custom perforated full pressure distribution laterals connected to the distribution manifold
at the head of each perforated pipe installed on the sand filter surface along the entire length of the bed.