HomeMy WebLinkAboutEngineer's OWTS Design Planreffi1 COLORADO
Parks and Wildtife
Department of Natural Resources
Northwest Region Capital Development Office
7l I Independent Ave . Grand Junction, CO 81505
PH: (970) 2ss.6100
5/2912025
Garfield County Public Health
195 W. l4th Street
Rifle, CO 81650
On-Site Wastewater Treatment System Replacement - Rifle Gap State Park
Site Ovt,nership
This memo aims to provide background information and the basis of design for the proposed On-site
Wastewater Treatment System replacement at Rifle Gap State Park. The site is located at 5775 Co
Hwy 325, Rifle, Colorado 81650 on parcel # 212707100092. The parcel is owned by the U.S. Bureau
of Reclamation (USBR) and leased to Colorado Parks and Wildlife (CPW) for use as Rifle Gap State
Park. Contact information of parties associated with this site include:
U.S. Bureau of Reclamation
Carrie Sheata
970-248-0618
csheata@usbr.sov
Colorado Parks and Wildlife
Brian Palcer
Park Manager
970-625-1607
Brian.palcer@state.co.us
Colorado Parks and Wildlife
Eric Blake, P.E.
EngineerArlorthwest Region Proj ect Manager
970-640-2807
Eric.blake@state.co.us
.iel1'Davis. Director. C'olorado Parks and Wildlilb
Ilarks and Wildlil'e Cornnrissiorr: Dallas Mar,. Cha r- llir:harcl Reading. Vice-Charr' l(are:r Bailcy. Secretarv Jcssica Beaulicu
Marrellaskett.Tai Jacober.JackMurphv'Gabric'l Otero MurphvRobittsott-.lantes.lttvJLrtchton EdcrlVardl'
Site Investigation
A site investigation and soil classification was performed by Eric Blake, P.E., a licensed environmental
engineer in the State of Colorado. The site of the proposed OWTS is situated at the base of a valley
opening to Rifle Gap Reservoir. The site is approximately 500 feet north of the high water level of the
reservoir and 30 feet higher in elevation. Existing berms are in place surrounding the area of the
proposed leachfield that would prevent stormwater run-on from the adjacent dry gulch. Topography of
the site is relatively flat, except for existing berms. The berms were installed during initial
development of the area for future use as evaporative ponds for the park's water treatment plant,
should expansion be required. Current operations and future development plans have dictated that use
of this area for evaporation ponds will not be needed. Existing evaporation ponds used by the water
system are located approximately 1,000 feet east. Vegetation within the site consists primarily of
grasses and a few shrubs. A categorical exclusion was completed by USBR for the proposed
disturbance related to this activity. This report indicated there would be no significant impacts to high
quality vegetation or habitat. Additionally, the categorical exclusion documented no significant
impacts to endangered species or cultural sites as a result of the proposed OWTS installation.
Necessary setbacks to consider includes just a required 25 foot offset from a dry gulch.
Two test pits were excavated to a depth of 8 feet below ground surface in the area of the proposed
leachfield. A visual and tactile assessment of the soils was completed by Eric Blake, P.E. on October 2,
2024. No significant variations were observed between the two test pits, and no groundwater or
saturated soils were observed. No noticeable restricting layers were observed or encountered during
excavation with a mini-excavator.
Soil Test Pit #1
Depth (feet bes)Description
0-l Silt loam, tanllight brown, blocky/angular, very dry, few l" gravels, root layer
(topsoil)
l-8 Sandy loam, tanllight brown, blocky/angular, very dry, very few l" gravels,
very weakly cemented, soil structure 2 - moderate to weak
Soil Test Pit#z
Depth (feet bes)Description
0-l Silty clay loam, tanllight brown, blocky/angular, very dry, very few gravels,
root layer (topsoil), weak structure
1-8 Loam, tanllight brown, blocky/angular, very dry, very few gravels, very
weakly cemented, soil structure 2 - moderate to weak
.lelf Davis^ Di:ector'. ('olorado Pat'ks anrl Wildlilt
ParksandWildlili'Cornmission: DallasMa-v-.Chair'Rir:hirrdl{eading.Vicc-Cllrair"KarcrrBai1e1.Secrelarv.le'ssicalleaulieLt
Marie tlaskett . 'fai Jacober . .lack Murphv- Ciabriel Otero Murphv Rrlbirtson .latnc:s.[itv TutchLon l-rlett Vardi'
Site Background
An existing leachfield located approximately 150 feet northeast of the proposed leachfield is failing
and causing wastewater to back up in the septic tanks, requiring frequent pumping. The failing
leachfield was installed in 2016 and sized to accommodate 1,500 gallons per day. The existing system
utilizes three 1,000 gallon septic tanks. The existing OWTS serves a maintenance shop, RV dump
station, the Cottonwood Campground, and a day use restroom. A lift station is used to pump waste to
the OWTS septic tanks and then gravity flows to the leachfield. The Cottonwood Campground has two
full hookup RV spaces and six dry RV spaces that are served by a flush restroom.
Proposed Design
The proposed OWTS will serve the following:
o CottonwoodCampground
o 6 campsites without individual hookups (served by a flush restroom within the
campground)
o 2 campsites with individual water and sewerage hookups
o Maintenance Shop
o Restroom in shop that may serve up to 8 employees, including seasonal employees
. Day Use Restroom
o 2 flush restrooms with drinking fountains
o Park staff indicated minimal use of approximately I 0 people per day
o RV Dump Station
o Dump station may serve campers from Rifle Falls State Park or from within other
campgrounds at Rifle Gap State Park
o Staff observation indicated up to 24 RV dumps per day at peak visitation
The below table shows the anticipated peak daily wastewater flow for the proposed OWTS, calculated
using flow rates obtained from Table 6-2 of Garfield County On-Site Wastewater Treatment Systems
(OWTS) Regulations (Regulation 43, Mar ch 6, 2023).
Flnrrr obtair;d lrcm Table 6-2 af 6arlield Ccunly C*-Site Wartewater Treatment 5ys:em: {CWT9f *egulations {Regulafiar 43, March 6, 20e3}
.lejl'Davis- Dilector. C'olorado Parks anci Wildlit'e
Parks and Wildlilr Cornnrission: Dallas IVlar'. C.'hail liicharcl Rt'adirrg. Vicc.Clratr'' I(are;r Bailer'. Secrelar\' .lcssica lleairlieu
Mane I laskelt . 'l'ai .lacoher ' .lack Mrrrphv [iabrir'l Otero Mtrrphv Rotrittsor ' .lantes Jrx 'l utchtol'] ' [ldert Vardy
Un Unlt Flow QuudW Totrl flow (GPbl Not
Camtground uer campsite 50 6 io0
f otla*rvood restroom, :erving f ottonwood
canrpsit*g rvithout individual hookups
I:avel trailer park rvith individual water
and sewage hookuB per unit 100 2 200
Cott*nwood acce:sible:ite a*d camp host site
wit]: individual hookups
Travel !railer park rvithout individual
waler and selvage hookup per urit 50 24 120fl
Oumpstation, RV: from ather rompsites within
Rifle 6ap and Rifle Falls, bared on park stali
ob:ervati$n *f number *f userr per day al
peak visi:atio*
C{fie e }uildirgr per employee per €ig5!-
hour sfultt 15 I t2g
MaiRt€na:ree 3hop,8 ernployees al peak wi:h
reasonals
llay Use Reltroom {per urer}, custem
ll0wr,at€ assumptir*s 10 15 150
Fark staff ir:dieated average ol 1S pecple per
day {assu:ne 15}, tpA say! 3-1S gallper:an,
CXT sp€c$ s:y L6 gai/flush tailet, add ci*ks and
dri*king founlain
TOTAT L970
The soil test pits indicated Soil Type 2 is present within both test pits in the area of the proposed
infiltrative surface. From Table 10-1 of Garfield County On-Site Wastewater Treatment Systems
(OWTS) Regulations (Regulation 43, March6,2023) a Long Term Acceptance Rate (LTAR) of 0.60
gal/daylsf would apply. A percolation test conducted in the general area several years ago, resulted in a
rate of l6 minutes per inch, which is consistent with the soil types observed during the October 2024
soil investigation.
Soil Treatment Area : 1,970 gal (designflow) / 0.60 gal/day/sf &fAD : 3,283 sf
Table l0-2 and 10-3 of Garfield County On-Site Wastewater Treatment Systems (OWTS) Regulations
(Regulation 43, March 6,2023) state to use a Size Adjustment Factor of 1 .0 for trench treatment areas
applied by gravity and a size adjustment factor of 0.7 when using chambers.
Adjusted Soil Treatment Area: 3,283 sf * 1.0 * 0.7 : 2,298 sf
The Standard Quick4 Infiltrator chambers are proposed, which are 34" wide by 48" long. Per Section
43.13.E.1.d of the Regulation, the full width of the 36" excavated trench may be used. This results in
an effective area of 12 sf per infiltrator.
Number of Infiltrators Required: 2,298 sf / 12 : 192 infiltrator chambers
To be conservative, the number of infiltrator chambers could be rounded up to 200. Using the
maximum length of distribution laterals in gravity fed system of 100 feet, results in needing 8 rows of
25 infiltrator chambers. A 9-hole distribution box will be installed, with distribution to each lateral
being level. Chambers will be installed in 3 feet wide trenches, with 4 feet separation distance between
trenches. Chambers will be installed level on in-situ soils.
A septic tank capacity of 4,000 gallons will be required to provide 48 hours of detention time for the
average daily flow of 1,970 gallons/day. There are curently three 1,000 gallon, two-compartment
septic tanks installed in series. The final tank in series will be removed and replaced with a2,000
gallon tank in order to provide the necessary detention capacity.
Future Considerations
During installation of the new leachfield, a diverter valve will be installed to direct flows to the
existing leachfield during winter when wastewater flows are reduced drastically due to campground
closures, day use restroom closure, and fewer staff at the maintenance shop. Flows would be diverted
back to the new leachfield in the spring.
There are currently no expansion plans of the park, however recent trends have shown increases in
visitation. Increased visitation may potentially cause the design flow assumptions to be exceeded. Park
.lc.l'l Davrs. Dilector. f'olorado l)alks and WildIilb
I'alks arrd Wildlifi'Cornnrission: Dallas Ma1'. Chair'Ric:lrard Rcading. Vicc-Cltait Karcn Railcr,. Secre'tary .lcssica fleaulicLr
MalreIlasketl Tai Jacober'JackMtrrphy'Gabriel Otero MrrrphvRobinson'.larnesJ;rv Tutchton EdcrrVardy
staff will continue to monitor use of the RV dump station and day use restroom. If use becomes higher
than assumed in the above calculations, a new leachfield may be constructed in Cottonwood
Campground to accept wastewater from all Cottonwood Campground campsites and the flush
restrooms. The currently proposed OWTS would then only service the maintenance shop and RV
dump station in order to remain within its designed daily flows.
Sincerely,#ffi
Eric Blake, P.E.
Northwest Region Project Manager
.lefJ'Davis. Dilecbl o Parks and Wildliti'
!'arks and Wtldlif'e Cornnrission: Dallas Ma1'. Chair' Richarcl Readurg. Vicc-Clrair' l(arerr Bailev. Se'cretatv Jessica lleaulieu
Matre ['laskett.Tai Jacobcr..laek Murphy Gatrriel Otero Murphl,Robinson'.lanresJitv Tutchtorr' Eclen Vard1,
Project Address:
Project Locotion
5775 Highwoy J25
Rifle, C0 81650
Rifle Gop Stote Pork
Lotitude: 39'38'3.56"
Longitude: 1 07' 44' 4+.42"
PARKS & WILDLIFE PROJECT CONTACTS
RIFLE GAP STATE PARK 970-625-1607
REGIONAL ENGINEER/PROJECT MANAGER 970-640-2407
PROPERry TECH 970-625-1607
FOR BURIED UTILIry INFORMATION
CALL 81 1
TWO BUSINESS DAYS
BEFORE YOU DIG
UTILITY NOTIFICATION CENTER
oF coLoRADO (UNCC) OR
coMMoN GROUND ALLTANCE (CGA)
Rifle compl€x staie Parkt
COLORADO IF
I
w
Dl RECTI ON S ( Rifle G ap) :
:Take l-70 to Rifle (exit 90).
Go north on CO Highway 13 for three
miles,When the road comes to a y,
stay to the right on Highway 13. Turn
right onto CO325 and drive 6 miles to
the park entrance.
DTRECTIONS (Rifle Falls):
Take l-70 to the Rifle exit, then go north on
CO Highway 13 for three miles. This takes
you through the town of Rifle on Railroad Ave.
Turn right onto Highway 325 and
drive 9.8 miles to the park entrance.
Rifle Falls State Park
Rifle Gap State Park Harvey Gap State Park
PROJ ECT
LOCATION a
New Gastle
O
RcJ
DIRECTION S (Harvey Gap) :
From l-70 Silt Exit go 0.1 miles
east on Main. Turn nofth on 7th.7th will
become CR 214 (peach valley) Travel
1.2 miles. Turn west on CR233 (Silt Mesa),
Travel 1.1 miles. Turn north on CR 237
(Harvey Gap Rd) go 3.3 miles To the
park entrance.
Vega State Park
Glenwood Springs
r Cities/Towns
,$ State Parks
State Wildlife Area
@ earr Boundaries
! usrs
ndLege .,#,
Miles
o 375 75 15
t^',,LEGEND
Colorado State Parks
RITLE GAP STATE PARK Hh
Couniy R@d 219
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PROJECT LOCATION MAP
PROJECT VICINITY MAP
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DTSIGN PLANS
SITE LAYOUT
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RIFLT GAP STATE PARK
DUMP STATION LEACHFIELD REPLACEMENT
UE
PMtrrc.
SHEEI NO.
2
oF4
K;1#'C
;RId'{n:.
ru1,1c
BENCHMARK
(r-Posr)EXISTING
LEACHFIELD
:SOIL TEST PIT #2
ELEV = 5988.76'
9 HOLE
DISTRIBUTION
BOX EXISTING 1,OOO GAL
SEPTIC TANKS TO
REMAIN25'OFFSET
FROM DRY
GULCH
60
PIPE TO EXISTIN
71'LEACHFIELD AND INSTALL
DIVERTER VALVE FOR
TERNATING SEASONAL USE.SEWER
CLEANOUTS:ftgTTOM TRENCH
1S/trv = 5e85.75'\\./ (TYP)
'I 18'
&
lPv@
q,b
NEW 4" GRA VITY
REMOVE AND DISPOSE
OF 1,OOO GAL SEPTIC
TANK, REPLACE WITH
2,OOO GAL SEPTIC TANK
OUTLET
INVERT =
sggg.gt'SEWER
(?%o SLOPE)
&
SOIL TEST Pfi #1
ELEV = 5989.04'
PROPOSED
LEACHFIELD,2OO
QUICK 4 CHAMBERS
WITH END CAPS
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NATIVE
UNDISTURBED
SUBGRADE
NATIVE BACKFILL TOPSOIL
12" MlN
I
12"12"QUICK 4
INFILTRATOR
CHAMBERS, 8 ROWS
WITH 25 CHAMBERS
PER ROW
8'' INVERT
34"48"34"
1 00'(36" WIDE TRENCH)
QUICK 4 INFILTRATOR TRENCH DETAIL INSTALL CHAMBERS
LEVEL rN TRENCH @
O% SLOPE
NOT TO SCALE
DESIGN NOTES. Design per performonce test per ASTM
c1227
. Top surfoce oreo 87.75 ft'
r f'c @ 28 doys; concrete = 6,000 PSI
Min.
lnstollotion:
r Tonk to be set on 5" min. sond bed or
peo grovel
r Tonk to be bockfilled uniformly on oll
sides in lifts less thon 24" ond
mechonicolly compoctedr Excovoted moteriol moy be used for
bockfill, provided lorge stones ore
removed. Excovotion should be dewotered ond
tonk filled with woter prior to being put
in service for instollotion with woter
toble less thon 2' below grode
. lvleets C1644-06 for resilient connectorsr lnlet ond Outlet identified obove piper Delivered complete with internol piping
r 4' Moximum bury depth
INSPECTION PORTS
WITH CAP TO 4''
ABOVE GRADE
4'(rYP.)
4'(T/P.)
-l I
3'(r/P.)
Top View 52'
ABSORPTION FIELD I-AYOUT
Rlrcrs b Giad€NOT TO SCALE
Boot
SWEEP 90 ELBOW PRE-MANUFACTURED g-HOLE
POLY DISTRIBUTION BOX WITH
SPEED LEVELER AND FLOW
EQUILIZERS, INSTALL RISERS
TO GRADE
ALLOWABLE BURY
(Bosed on Woter Tcble)
WATER TABLE ALLOWABLL
EARTH FII I
0'-0"
1'-O"J'-0"
2'-O"4'-O"
3'-0"4'-O"
DRY 4'-O"
5l r
Section View 4" SOLTD PVC PIPE @
0% sLoPE (TYP)i ^. :Urgqrnq Specs:.::
15' Long x I' Wide
56" below inlei inveri.::::
I n vert
:L
Dimensions Net
Ccpocity
Net Weight
Tonk
:
I otol ii::ii 20,s60 rbs ::i: ..j
: Width r,7A"a
Lid CONNECT TO
INFILTRATION CHAMBER
PER MANUFACTURER'S
RECOMMENDATIONS
n et Outlet
53"
en I h H eigh t
68"1 62"2,142 gollons 5,420 lbs
2,OOO GAL SEPTIC TANK H EADER D ETAIL
i rrri ::roii..:
ClearAccees
-l
-
:-::=- '
'f"
Sealant
Rubber
56
NOT TO SCALE
15,140 lbs
NOT TO SCALE
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