HomeMy WebLinkAbout20101853.tiff •
PRELIMINARY DRAINAGE REPORT
CONQUEST OIL COMPAN7
C-7 FACILITY
Prepared for:
Conquest Oil Company
8207 W. 20th St., Suite B
• Greeley, Colorado 80634
Prepared by:
CGRS, Inc.
PO Box 1489
Fort Collins, CO
April 19, 2010
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2010-1853
• PRELIMINARY DRAINAGE REPORT
CONQUEST C-7
PRODUCED WATER TREATMENT FACILITY
I. General Location and Description
A. Location
Conquest Oil Company proposes to construct and operate a Produced Water Treatment
Facility in Weld County. The proposed site is located in the Southeast 1/4 of the
Southeast '/, Section 34, Township 7 North, Range 63 West. Weld County Road 74 is
adjacent to the property on the south and Weld County Road 69 is adjacent to the
property on the east. Colorado Highway 392 is adjacent to the southeast corner of the
property, running diagonally across the southeast corner in a southwest to northeast
direction. The nearest open water is Crow Creek, located approximately 1,500-feet
southeast of the property, flowing in a southwesterly direction. There is an unnamed
tributary to Crow Creek approximately 1,500-feet west of the property, flowing south
under WCR 74 to Crow Creek. There are no other major open channels, lakes,
streams, irrigation or other water resource facilities within or adjacent to the proposed
project site. The surrounding ground is agricultural in nature, and no other
• developments or municipalities are in the vicinity. Unincorporated Cornish, Colorado is
located east of the proposed project site, across WCR 69 and Colorado State Highway
392.
B. Description of Property
The proposed project site is approximately 11.09 acres in size configured as shown on
the Plot Plan. Native grasses cover the site, and site soils consist of Sandy Loam soils,
described as "well drained and somewhat excessively drained, moderately rapidly
permeable soils on smooth to dissected plains (Soil Survey of Weld County, Colorado,
Northern Part, United States Department of Agriculture Soil Conservation Service and
Forest Service, August, 1982). The proposed site is very flat, sloping gently to the
southeast at an average slope of approximately 0.4%. There are no major open
channels on the proposed project property. The property is owned by Mr. Rodney
Wilson (Weld County Parcel No. 071334000004).
The proposed project is generally described as a produced wastewater treatment facility
that will receive produced water from oil and gas well production facilities in Weld
County for treatment and disposal. Produced water will be delivered to the facility by
truck where the produced water will be collected from the truck and processed in the
• treatment facility. Following treatment to required discharge levels, the treatment
Conquest Oil C7 Site
Preliminary Drainage Report
Page 2
•
process effluent will be disposed of by deep well injection at an injection well to be
located on the project site.
Ownership information for the subject property and for properties within 200 feet of the
property is provided on the Vicinity Map. There are no irrigation facilities on or within
200 feet of the subject property.
Five (5) soil borings were advanced into the subsurface on March 18, 2010 to describe
both soils and groundwater characteristics at the property. Boring locations are
depicted on the Plot Plan provided with the USR Permit Application. As shown in the
boring logs (Appendix A), the soils are generally described as fine to very fine grained
sandy silt overlying fine to medium grained sand at depths of 8 to 10 feet below ground
surface (bgs). Groundwater was encountered in the borings at depths ranging from
17.8 feet to 19.5 feet bgs. Soil and groundwater quality samples were collected from
borings TH-3, TH-4, and TH-5 and delivered to Technology Laboratory in Fort Collins
for analysis. The soil samples were analyzed for benzene, toluene, ethylbenzene, total
xylenes (BTEX), gasoline range organics (GRO — also referred to as Total Volatile
Petroleum Hydrocarbons or TVPH), and diesel range organics (DRO — also referred to
•
as Total Extractable Petroleum Hydrocarbons or TEPH). Groundwater quality samples
were analyzed for BTEX. Analytical results show non-detectable levels for the soil
samples for all constituents sampled. Analytical results for the water samples show a
total xylenes concentration in the sample fromTH-3 of 0.002 mg/L (method detection
level is 0.001 mg/L); all other constituents are documented at less than detection levels.
Tables 1 and 2 present Soil Analytical Data and Groundwater Analytical Data,
respectively. Furthermore, geotechnical soil samples were obtained from soil borings
TH-1 through TH-3 to provide geotechnical information necessary for facility
engineering/design.
II. Drainage Basins and Sub-Basins
A. Major Basin Description
The Weld County Master Drainage Plan does not encompass the area of the proposed
project because no floodplain or floodway exists in this area. Additionally, a database
search for FEMA Flood Insurance Rate Maps (FIRM) in Weld County indicated that
there is an unpublished FIRM Map Panel (08026600525c) which covers the subject
property area. This is an unpublished map panel because there is no floodplain in this
•
Conquest Oil C7 Site
Preliminary Drainage Report
Page 3
•
area. Accordingly, no 100-year floodplain or floodway exists in this area that could
affect the subject property.
Surface topography on and around the subject property is extremely flat, gently sloping
to the southeast at an approximate slope of 0.4%. The Plot Plan provides on-site
contours at 1-foot vertical intervals, and shows both existing contours and proposed
contours as required to accomplish adequate site drainage, including the on-site storm
water detention pond. Major drainage basin characteristics are summarized in
Appendix B.
B. Sub-Basin Description
The subject property and adjacent properties historically drain to the south/southeast to
Crow Creek located approximately 1,500 feet to the southeast of the property. Crow
Creek flows in a southwesterly direction. The subject property slopes gently to a 15-
inch diameter culvert in the southeast corner of the property under Weld County Road
69, and thence across the abandoned Union Pacific Railroad right of way to a 24-inch
diameter culvert under Colorado State Highway 382, discharging to Crow Creek
approximately 1,500 feet to the southeast. Crow Creek flows to its confluence with the
•
South Platte River approximately 10 miles to the southwest.
Off-site drainage flow patterns include an unnamed intermitent tributary to Crow Creek
located approximately 1,500 feet west of the property that flows to the south. There is a
slightly-defined drainage divide approximately 350 feet west of the subject property.
Accordingly, drainage from the subject property and the ground directly to the west is to
the southeast to the aforementioned 15-inch diameter culvert under WCR 69. As
indicated above, the overall site is very flat and produced correspondingly slow runoff
patterns. This flat slope coupled with fairly permeable soils, generally consisting of "8 to
10-feet of silty sand over slightly silty to gravelly sands to the depths explored (CTL
Thompson, Geotechnical Investigation, Conquest Oil C7T, April 1, 2010)," result in
minimal runoff production in response to most precipitation events. Due to the soils that
are present in the area and the very flat slopes, both on-site and up-gradient of the
proposed site, off-site drainage flow onto the subject property are not expected. In fact,
there is a local high point in the northeast portion of the subject property from which on-
site drainage flows from the subject property off-site to the north.
•
Conquest Oil C7 Site
Preliminary Drainage Report
Page 4
•
III. Drainage Design Criteria
A. Development Criteria Reference and Constraints
As stated above, the Weld County Master Drainage Plan does not encompass the
subject property or adjacent properties because there are no mapped flood plains or
floodways in the vicinity. No other previous drainage study of the subject property has
been done. Accordingly, the proposed drainage design will not be influenced nor will it
have an influence on previous drainage studies for the area. Existing site constraints of
very flat sloping ground influence the drainage design by the requirement of importing a
modest amount of fill material in order to establish positive drainage of the site to the
aforementioned 15-inch culvert in the southeast corner of the property. No streets,
utilities, existing structures, or irrigation ditches are present on-site or in the immediate
area that would pose constraints on the proposed drainage plan.
B. Hydrologic Criteria
An on-site storm water detention basin is proposed based on the Urban Drainage and
Flood Control District (UDFCD) spreadsheets to calculate peak runoff using the Rational
Method. The detention pond is sized to contain runoff from the 100-year, 1-hour
• precipitation event. The detention pond must also provide for a release rate at the
historical 5-year, 1-hour precipitation event runoff rate for the site under undeveloped
conditions. The UDFCD spreadsheet using the Rational Method was also used to
predict the 5-year 1-hour runoff rate. Copies of the UDFCD spreadsheets for these
precipitation events are provided in Appendix B. UDFCD spreadsheets provided
include the following:
• Map of Colorado Hydrologic Zones showing the project site to be in Hydrologic
Zone 1;
• Intensity-Duration-Frequency (IDF) Table for Zone One in the State of Colorado;
• Area-Weighting for Runoff Coefficient Calculation;
• Calculation of Peak Runoff Using Rational Method for the 100-year, 1-hour
precipitation event; and
• Calculation of Peak Runoff Using Rational Method for the 5-year, 1-hour
precipitation event.
Rainfall data given on NOAA Atlas 2, Volume III for the 6-hour and 24-hour precipitation
events with 2-year, 5-year, 10-year, 25-year, 50-year, and 100-year return period were
entered on the UDFCD IDF Table for Zone One in the State of Colorado in order to
• develop the1-hour storm rainfall depth. The UDFCD IDF Table is provided in Appendix
Conquest Oil C7 Site
Preliminary Drainage Report
Page 5
•
B showing the 5-year and 100-year, 1-hour events rainfall depths of 1.49-inches and
2.86-inches, respectively. Hydrologic data used in the UDFCD model are based on a
drainage basin area of 11.09 acres, 45% impervious ground (post-development), Soil
Type A, and an area-weighted Runoff Coefficient of 0.27.
Model results indicate a 100-year, 1-hour precipitation event peak runoff flowrate of
19.79 cubic feet per second (cfs) and a regional time of concentration (Tc) of 14.44
minutes. The corresponding calculated peak storage volume required to detain the
100-year, 1-hour event is 17,146 cubic feet (cf). In accordance with Weld County
requirements, the detention pond must detain the total runoff volume produced by the
100-year, 1-hour precipitation event with a release rate not to exceed the historic 5-
year, 1-hour event discharge. Accordingly, the UDFCD spreadsheet was also run for
the 5-year event, with the results showing that discharge from this property does not
occur during the 5-year event. Accordingly, the detention pond for this project is
designed to completely detain a runoff volume of 17,146 cf.
C. Hydraulic Criteria
• On-site runoff to the proposed detention pond is via sheet flow, and as such no specific
channel or ditch exists to deliver surface runoff to the detention pond. Detention pond
requirements of Weld County are that an on-site detention pond must detain the total
runoff from the 100-year, 1-hour precipitation event while allowing a release rate not to
exceed the historic release from the 5-year, 1-hour precipitation event. As shown
below, there would be no discharge from the subject property in response to the 5-year
1-hour event. Accordingly, the proposed detention pond does not include outlet works,
nor will there be outlet water quality issues. Design flood calculations are based on
Urban Drainage and Flood Control District design spreadsheets.
IV. Drainage Facility Design
A. General Concept
The subject property is divided roughly in half, with the western (topographically higher)
portion to contain the Conquest C7 project development, and the eastern half to remain
open. It is in the eastern, topographically lower, portion of the site where the on-site
detention pond will be located. Structural fill material will be imported to the site in order
to slightly elevate the Conquest facility buildings and associated other structures and to
facilitate site drainage on this very flat property.
A detention pond capacity of 17,146 cubic feet will be required to detain runoff from the
• 100-year 1-hour event. Construction of the detention pond will require minor
Conquest Oil C7 Site
Preliminary Drainage Report
Page 6
•
excavation/earthwork to provide the required capacity. Typical on-site drainage patterns
will be split at the entrance road to the facility, with a small amount of on-site runoff
flowing off the entry drive to the west to a natural low area along the western property
line. The remainder of the property will drain to the on-site detention pond and drain
into the subsurface through the relatively porous soils that exist at this location.
There are no known off-site runoff considerations and constraints with respect to this
project with the exception of the detention pond release rate not to exceed the historic
release from the 5-year 1-hour precipitation event from the undeveloped site. Due to
existing topography of the site, including a natural "detention pond" in the southeast part
of the site, it is shown that there is no discharge from this site in response to the 5-year
1-hour event.
B. Specific Details
Maintenance of runoff control structures will be minimal. Once native grasses are
established within the detention pond, periodic mowing may be required to maintain
adequate detention pond volume.
• V. Conclusions
A. Compliance with the Weld County Code
The preliminary drainage design will meet applicable Weld County Code.
B. Drainage Concept
As proposed, the drainage plan is designed to prevent damage from storm runoff to
both the Conquest facility and to adjacent properties. The on-site detention pond will
mitigate runoff peaks in response to a 100-year, 1-hour precipitation event. Because
there is no Weld County Master Drainage Plan for this area, there are no related
recommendations that would influence or be influenced by the proposed project. There
will be no affect on irrigation companies or other property owners in the vicinity. The
drainage design is based on runoff calculations computed through the UDFCD
spreadsheets based on the Rational Method.
•
Table 1
• SOIL ANALYTICAL DATA
Proposed Conquest Oil C-7 Facility
WCR 69 and WCR 74
Briggsdale, Colorado
CGRS Project: 1-8019-12439aa
Depth Benzene Toluene Ethyl-Benzene Xylenes TVPH TEPH
Sample ID (ft.) Date (mg/Kg) (mg/Kg) (mg/Kg) (mg/Kg) (mg/Kg) (mg/Kg)
TH-3 15 03/18/10 <0.01 <0.01 <0.01 <0.01 <0.5 < 10.0
TH-4 15 03/18/10 <0.01 <0.01 <0.01 <0.01 <0.5 < 10.0
TH-5 15 03/18/10 <0.01 <0.01 <0.01 <0.01 <0.5 < 10.0
MDL 0.01 0.01 0.01 0.01 0.5 10.0
CDLE/OPS-RBSL/TPH Threshold 0.26 170 190 260 500 500
COGCC Allowable Concentration for 0.17 85 100 175 500 500
sensitive area
Notes:
Concentrations exceeding Tier 1 RBSLs,500 mg/Kg TPH threshold value or CGOCC allowable
• concettrations expressed in bold face
TVPH=Total Volatile Petroleum Hydrocarbons
TEPH=Total Extractable Petroleum Hydrocarbons
RBSL=CDLE/OPS-Tier 1 Risk Based Screening Level
TPH=total petroleum hydrocarbons
MDL=Method Detection Limit
• ,
1 of 1
TABLE 2
GROUNDWATER ANALYTICAL DATA
• Proposed Conquest Oil C-7 Facility
WCR 69 and WCR 74
Briggsdale, Colorado
CGRS Project: 1-8019-12439aa
Depth To Ethyl-
Sample ID Date Benzene Toluene Xylenes
Water Benzene
(ft) (mglL) (mill) (1112/14 (mg✓L)
TH-3 03/18/10 20.82 <0.001 <0.001 <0.001 0.002
TH-4 03/18/10 21.72 <0.001 <0.001 <0.001 <0.001
TH-5 03/18/10 22.55 <0.001 <0.001 <0.001 <0.001
COGCC Allowable - 0.005 0.56 0.7 1.4
Concentration for sensitive area
MDL - 0.001 0.001 0.001 0.001
Notes:
Depth to groundwater is measured from the top of the temporary monitoring well casing,which is
• approximately 3 feet above ground surface.
Values in bold face exceed MCLs
TVPH=Total Volatile Petroleum Hydrocarbons
TEPH=Total Extractable Petroleum Hydrocarbons
MTBE=Methyl Tertiary Butyl-Ether
MCL=Maximum Contaminant Level
MDL=Method Detection Limit
•
1 of 1
.
VI.Appendices
A. Soil Boring Logs
B. Hydrologic Computations
C. Hydraulic Computations
.
•
Appendix A
Soil Boring Logs
•
•
C G RS FIELD BOREHOLE LOG BOREHOLE NUMBER
TH-1
lirOJECT NUMBER: 1-8019-12439aa TOTAL DEPTH : 10'
ROJECT NAME: Conquest Oil C-7 TOP OF RISER:-
(wilh cap removed)
LOCATION : Briggsdale, CO _
DRILLING CO: Drilling Engineers, Inc. I STATIC WATER LEVELS (BGS)T
DRILLING METHOD: HSA Time
DRILLER: Sean Date
LOGGED BY: TJ Grisel Water Level
START: 3/18/2010 COMPLETED: 3/18/2010 Casing Depth
1
C
c
u a)
la Z o Notes LITHOLOGY
n a) DEPTH DESCRIPTION (PPm)
a) a) c a) a)
U
E a
o E E
cti (El
io. m ca
u)
—0 -- ...
SANDY SILT: Brown, fine to 7._-
very fine-grained, stiff, moist --
(SM) _.__41ill _CAL 1 15 18 18 0.0@2' bgs _ —
CAL 2 21 18 18 0.0@4' bgs - - -_
- 5 —. _
SAND: Brown, fine to medium-
CAL 3
grained, sub-angular, medium
dense, moist(SW) 0.0 @ 9' bgs
16 18 18
-- — 10
lip
End of Boring @ 10' bgs
I BOREHOLE NUMBER
CG RS FIELD BOREHOLE LOG --
TH-2
OJECT NUMBER: 1-8019-12439aa TOTAL DEPTH: 25'
ROJECT NAME: Conquest Oil C-7 TOP OF RISER:-
(with cap removed)
LOCATION: Briggsdale, CO I STATIC WATER LEVELS (BGS)
DRILLING CO: Drilling Engineers, Inc.
DRILLING METHOD: HSA Time
DRILLER: Sean Date
I
LOGGED BY: TJ Grisel Water Level
START: 3/18/2010 COMPLETED: 3/18/2010 Casing Depth
C
Q) tL v a)
a E z 0 Notes LITHOLOGY
Z j DEPTH DESCRIPTION cC (PPm)
a) a) O 0) W
U
E E o E E
U) cn m Cl) CO
—
SANDY SILT: Brown, fine to —-
very fine-grained, very stiff, -- -..
Ill --
moist(SM) - .,
CAL 1 30 18 18 . =
-�-5 .
0.0@5' bgs
CAL 2 36 18 18 .. _ __
— -10 •-v-
SAND: Brown, fine to medium- 0.0 @ 10' bgs
grained, sub-angular, very
dense, moist to wet @ 15' bgs
- to saturated @ 20' bgs; No
_ Recovery @ 20'bgs (SW)
CAL 3 45 18 18
-15 0.0@15' bgs
•1
CAL 4 50+ 18 0
- -20 NM @ 20' bgs Iiiiil I
CAL 5 50+ 18 4 ; 0.0 @ 25' bgs .. ...... . .....'1
- -- - -- -- -25
End of Boring @ 25' bgs '
C G RS FIELD BOREHOLE LOG BOREHOLE NUMBER
TH-3
"'PROJECT NUMBER:1-8019-12439aa TOTAL DEPTH : 30'
PROJECT NAME : Conquest Oil C-7 TOP OF RISER:-
LOCATION : Briggsdale, CO (with cap removed)
DRILLING CO : Drilling Engineers, Inc. STATIC WATER LEVELS(BGS)
DRILLING METHOD : HSA Time 0950 1050 1239
DRILLER: Sean Date 3/18/2010 3/18/2010 3/18/2010
LOGGED BY:TJ Grisel Water Level 20.90 20.84 20.82
START: 3/18/2010 COMPLETED : 3/18/2010 Casing Depth 32.25
c
NOTES O WELL WELL
Z m a DESCRIPTION (PPm) p DESIGN CONSTRUCTION
0a) g a) w I =
E Ea E E I-
a
LU
U) Cl) 0° co cn o
- Stick-Up(-3
- ft)
• -0 r7,77
r, , ,
SANDY SILT:Gray,fine-grained, -,
stiff,moist(SM) M
—-_ .`^ ��
CAL 1 18 24 9 --5 - •- - ''-' .
0.0@5'bgs ,.._ - `'. !"
4, -Ait
CAL 2 18 24 3 -
4.t.t 01F
—-1C P' 4741,
SAND:Brown,fine to medium- 0.0 @ 10'bgs '�""".�'
_ grained,sub-angular,medium- �5 . it
dense, moist to very moist @ 14' s
rr t
bgs : Natural , 4
-
CAL 3 15 24 7
Badcfill 'oi 1
'15 0.0@15'
_ SILTY CLAY:Wet, brown,rather
bgs;Sample
6=4-
`stiff,some fine sand(CL) ! *r''
/ Retained for
SAND:Brown,fine to medium- Analysis
CAL 4 50+ 24 0 grained,sub-angular,medium :'y:: ;
—-2C dense to very dense;wet to NM @ 20'bgs : 1"Sch.40
- saturated @ 20'bgs;No recovery : PVC Riser `' ..i:
- @ 20'bgs =,
10/20 Silica
Sand filter =
CAL 5 50+ 24 21 -.2F :•:.:•:•:•:-:-:•:. :-
SILTY SAND: Brown,fine-grained, 0.0 @ 25'bgs T T T T T w 1"Schedule T
g T.T,T.-1"T.� 40 PVC
• _ sub-angular,very dense, T T.r.T T-_ screen#10
T 17. T
saturated(SM) T.'T T T.T,: ,SIOt
7"77 T om..T.� :; '
.r T1-TT- r
CAL 6 50+ 24 24 0.0@30'bgs TTT.T.:.Tr.-
- 3C,
`End of Boring @ 30'bgs /
C G RS FIELD BOREHOLE LOG BOREHOLE NUMBER
TH-4
PROJECT NUMBER:1-8019-12439aa TOTAL DEPTH :20'
ROJECT NAME : Conquest Oil C-7 TOP OF RISER :
(with cap removed)
LOCATION : Briggsdale, CO —
Driilin Engineers, STATIC WATER LEVELS(BGS)
DRILLING CO: 9 Inc.
DRILLING METHOD : HSA Time 1149 1259
DRILLER : Sean Date 3/18/2010 3/18/2010
LOGGED BY:TJ Grisel Water Level 22.25 21.72
START: 3/18/2010 COMPLETED: 3/18/2010 Casing Depth 23.20
c �'
• }
E E LI:1 Z o NOTES O WELL WELL
E
? c DESCRIPTION (ppmj = DESIGN CONSTRUCTION
woo w w I H
I—
E E o E E w
cn cn 0, to ca O
Stick-Up(-3
_ ft)
• _0 r.
SANDY SILT:Brown,fine-grained, . .._,,,
medium-stiff,moist;Clay lense @ - - 4,
14'bgs(SM) -
_ "
Y_ '.
SB 1 7 18 12 - 'i-`
-5 __
0.0 5'bgs 7.7_77.•- Natural ' -•.
"— 7:7-- Backfill w , Y
SB 2 14 18 14 _ -._ 1"Sch.40
- -1C — 7-._ PVC Riser _
0A@10'bgs
SB 3 10 18 11 SAND:Brown,fine to medium- - "
—-le grained,sub-angular,loose,wet; 0.0 @ 15' • 10/20 Silica :i ::
Increasing fine-grained sand with bgs;Sample . Sand fitter
depth(SW) Retained for _
Analysis 1"Schedule =
-
40 PVC
• screen#10
SB 4 32 18 8
0.0 @ 20'bgs . slot
2
End of Boring @ 20'bgs
i
GRS FIELD BOREHOLE LOG BOREHOLE NUMBER
TH-5
"'PROJECT NUMBER:1-8019-124398a TOTAL DEPTH :20'
PROJECT NAME: Conquest Oil C-7 TOP OF RISER:
(with cap removed)
LOCATION : Briggsdale, CO
STATIC WATER LEVELS(BGS)
DRILLING CO: Drilling Engineers, Inc.
DRILLING METHOD : HSA Time 1228 1325
DRILLER: Sean Date 3/18/2010 3/18/2010
LOGGED BY:TJ Grisel Water Level 23.29 22.55
START: 3/18/2010 COMPLETED : 3/18/2010 Casing Depth 23.55
c >.
�i m > O WELL WELL
›- E a0i U DESCRIPTION NOTES r p DESIGN CONSTRUCTION
l� z' � � � (PP ) 2
a 8 a) a) I i-
0- i—
E E ° EE w
co kn m (i) O
- Stick-Up(-3
ft)
• —0
SAND:Brown,fine-grained, ' E
- medium dense to dense @ 15'bgs #.•:..':, 'fir
_ to very dense @ 20'bgs,moist toi.
::1 ` w r
wet @18'bgs to saturated @ 20'
T
bgs(SP) :,.• _.;,,
mac.. :.
:: 4:� ky
SB 1 9 18 9 ++�
— 5 0.0 •:•:-:•:•:•:•:•:•:
@ 5'bgs Natural backfill ` a ,
N..6�
.. M.
SB 2 9 18 18 - : 1"Sch.40 -
—-1C : PVC Riser
0.0@10'bgs
- ::j -
SB 3 22 18 10 - "j ]
-1f 0.0 @ 15 10/20 Silica :: ?
- bgs•Sample . Sand filter
Retained for -
- Analysis : 1"Schedule
40 PVC ` '``'
Wscreen#10
0.0 @ 20'bgs : slot
SB 4 40 18 12 _
- - 2 /
End of Boring @ 20'bgs
•
Appendix B
Hydrologic Computations
•
•
Hydrologic Computations
•
As required, hydrologic computations make basic assumptions regarding land use on
adjacent properties. The property is bordered on the south by Weld County Road 74,
on the east by Weld County Road 69, and by undeveloped pasture land on the north
and west sides. No developed land exists adjacent to the subject property, with the
exception of the area southeast of the subject property. In that direction is the
abandoned UP Railroad right-of-way and Colorado State Highway 392.
Storm runoff computations are based on the Rational Method as presented in UDFCD
spreadsheets. Design storms modeled include the 100-year, 1-hour and the 5-year, 1-
hour precipitation events. The site drainage plan is based on the requirement to detain
the 100-year, 1-hour precipitation event while maintaining off-site discharge at or below
historic discharge from the 5-year, 1-hour precipitation event. UDFCD spreadsheets
used include the following:
1. Map of Colorado Hydrologic Zones showing the project site to be in Hydrologic
Zone 1;
2. Intensity-Duration-Frequency (IDF) Table for Zone One in the State of Colorado;
3. Area-Weighting for Runoff Coefficient Calculation;
4. Calculation of Peak Runoff Using Rational Method for the 100-year, 1-hour
• precipitation event; and
5. Calculation of Peak Runoff Using Rational Method for the 5-year, 1-hour
precipitation event.
As shown on the UDFCD spreadsheet printouts, the 100-year 1-hour event will produce
a peak runoff flowrate of 19.79 cfs at a regional time of concentration (Tc) of 14.44
minutes. The corresponding runoff volume to be detained on-site is 17,146 cf. The 5-
year 1-hour precipitation event produces no storm water runoff from this site.
•
• HYDROLOGIC ZONES IN THE STATE OF COLORADO
Identify the hydrologic zone for your project site: Zone 1 , 2, 3 or 4.
Zone 1: South Platte, Republican, Arkansas, and Cimarron River Basins
Zone 2: San Juan, Upper Rio Grande, Upper Colorado, and Gunnison River Basins, and
Green River Basin below Confluence with the Yampa River
Zone 3: Yampa and Green River Basins above confluence of Green and Yampa Rivers
Zone 4: North Platte River Basins
Definition of these four zones:
109 tun 10/ 106 101 104 103 _ 102
1 1 I 1 T 1 _- 1 —
_
at 41
rN 1 i
I
I
I— I ,a
1
I II
I1
I
I r I
1
I
I 1 I
1 I I 39
• I 1
i 2 I
I
I i
I
I I
III -- I I
1&
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I I I
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I I
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100 roe 10/ 106 101 104 103 1O2
Design Parameters for Various Zones
Zone 1 - Hour 2 - hour 3 - Hour
a b c d e f m n r q
1 0.2180 0.7090 0.0000 1 .8970 0.4390 -0.0080 0.3420 0.6580 0.5970 0.4030
2 -0.0110 0.9420 p 0.0000 0.4940 0.7550 0.0000 0.3410 0.6590 0.5690 0.4310
3 0.0190 0.7110 0.0010 0.3380 0.6700 0.0010 0.2500 0.7500 0.4670 0.5330
4 0.0280 0.8900 0.0000 0.6710 0.7570 -0.0030 0.2500 0.7500 0.4670 0.5330
Duration in minutes 5.00 10.00 15.00 30.00
• Ratio to one-hr Depth 0.29 0.45 0.57 0.79
UD-RainZone v1 .01 a, ZONES 4/14/2010, 4:32 PM
IDF TABLE FOR ZONE ONE IN THE STATE OF COLORADO
• Zone 1: South Platte, Republican, Arkansas, and Cimarron River Basins
Project: Conquest Oil C7 Site
Enter the elevation at the center of the watershed: Elev = 4,713 (input)
1 . Rainfall Depth-Duration-Frequency Table
Enter the 6-hour and 24-hour rainfall depths from the NOAA Atlas 2 Volume III in rightmost blue columns
Return Rainfall Depth in Inches at Time Duration
Period 5-min 10-min 15-min 30-min 1-hr 2-hr 3-hr 6-hr 24-hr
(1 ) (2) (3) (4) (5) (6) (7) (8) (9) (10)
output output output output output output output input input
2-yr 0.30 0.47 0.59 0.82 1 .04 1 . 16 1 .25 1 .40 1 .70
5-yr 0.43 0.67 0.85 1 . 18 1 .49 1 .61 1 .70 1 .85 2.20
10-yr 0.52 0.80 1 .02 1 .41 1 .79 1 .93 2.03 2.20 2.60
25-yr 0.63 0.97 1 .23 1 .71 2. 17 2.33 2.46 2.65 3.00
50-yr 0.73 1 . 13 1 .44 1 .99 2.52 2.68 2.81 3.00 3.40
100-yr 0.83 1 .28 1 .63 2.26 2.86 3.04 3. 18 3.40 3.80
Note: Refer to NOAA Atlas 2 Volume III isopluvial maps for 6-hr and 24-hr rainfall depths.
2. Rainfall Intensity-Duration-Frequency Table
Return Rainfall Intensity in Inches Per Hour at Time Duration
Period 5-min 10-min 15-min 30-min 1-hr 2-hr 3-hr 6-hr 24-hr
( 1 ) (2) (3) (4) (5) (6) (7) (8) (9) (10)
output output output output output output output output output
• 2-yr 3.60 2.80 2.36 1 .64 1 .04 0.58 0.42 0.23 0.07
5-yr 5. 18 4.02 3.40 2.35 1 .49 0.81 0.57 0.31 0.09
10-yr 6.22 4.83 4.08 2.83 1 .79 0.96 0.68 0.37 0. 11
25-yr 7.54 5.85 4.94 3.42 2. 17 1 . 17 0.82 0.44 0. 13
50-yr 8.77 6.81 5.75 3.98 2.52 1 .34 0.94 0.50 0. 14
100-yr 9.94 7.71 6.51 4.51 2.86 1 .52 1 .06 0.57 0. 16
•
Copy of UD-RainZone v1 .01a, Z-1 4/14/2010, 4:53 PM
• One-Hour Rainfall Depth Design Chart
3.00 _. ---- ------. - -_._
2.86 ♦
2.50 - - ------. __ ...t 2.52-♦
2.17 •
2.00 - _- -
1.79 ♦
u
c
c
a 1.50 — 1A9 4-
• 1.00 1.04 •
i I
0.50
0.00
2-yr 5-yr 10-yr 25-yr 50-yr 100-yr
Return Period
•
Copy of UD-RainZone v1.01 a, Z-1 4/14/2010, 4:53 PM
• Area-Weighting for Runoff Coefficient Calculation
Project Title: Conquest C7
Catchment ID : 11 .09 Acre Project Site
Illustration
LEGEND:
Flow Direction
I:
t
s13 Cate in ens
Subarea 3 gam .
Instructions: For each catchment subarea, enter values for A and C.
Subarea Area Runoff Product
ID acres Coeff.
A C* CA
• input input input output
C7 Site 11 .09 0.27 2.99
sum: 11 .09 Sum: 2.99
Area-Weighted Runoff Coefficient (sum CA/sum A) = 0.27
*See sheet "Design Info" for inperviousness-based runoff coefficient values.
•
UD-Rational v1 .02a, Weighted C 4/14/2010, 5:02 PM
• CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
Project Title: Conquest C7 Site Drainage Report
• Catchment ID: 11 .09 Acre Projet Site
I. Catchment Hydrologic Data
Catchment ID = C7 Site
Area = 11 .09 Acres
Percent Imperviousness = 45.00
NRCS Soil Type = A A, B. C, or D
II. Rainfall Information I (inch/hr) = Cl * P1 /(C2 + Td)AC3
Design Storm Return Period, Tr = 100 years (input return period for design storm)
C1 = 28.50 (input the value of C1 )
C2= 10.00 (input the value of C2)
C3= 0.786 (input the value of C3)
P1 = 2.86 inches (input one-hr precipitation--see Sheet "Design Info")
III. Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C = 0.43
Overide Runoff Coefficient, C = 0.27 (enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 = 0.27
Overide 5-yr. Runoff Coefficient, C = (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
• __—�� , overland
Reach 1 flow
Reach 2 O Beginning
Flow Direction
Catchment
Reach 3 Boundary
NRCS Land Heavy Tillage/ Short Nearly Grassed Paved Areas &
Type Meadow Field Pasture/ Bare Swales/ Shallow Paved Swales
Lawns Ground Waterways (Sheet Flow)
Conveyance 2.5 5 7 10 15 20
Calculations: Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey- Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.0020 800 0.27 N/A 0.19 71 .87
1
2
3
4
5
Sum 800 Computed Tc = 71 .87
Regional Tc = 14.44
User-Entered Tc = 14.44
IV. Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I = 2.56 inch/hr Peak Flowrate, Qp = 7.65 cfs
Rainfall Intensity at Regional Tc, I = 6.61 inch/hr Peak Flowrate, Qp = 19.79 cfs
• Rainfall Intensity at User-Defined Tc, I = 6.61 inch/hr Peak Flowrate, Qp = 19.79 cfs
Calculated values for Tc & Qp are based on overide values entered for C & C-s
UD-Rational v1 .02a, Tc and PeakQ 4/14/2010, 5:08 PM
• CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
Project Title: Conquest C7 Site Drainage Report
Catchment ID: 11 .09 Acre Project Site - UNDEVELOPED CONDITION
I. Catchment Hydrologic Data
Catchment ID = C7 Site
Area = 11 .09 Acres
Percent Imperviousness = 0.00
NRCS Soil Type = A A, B, C, or D
II. Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)AC3
Design Storm Return Period, Tr = 5 years (input return period for design storm)
C1 = 28.50 (input the value of C1 )
C2= 10.00 (input the value of C2)
C3= 0.786 (input the value of C3)
P1 = 1 .49 inches (input one-hr precipitation--see Sheet "Design Info")
III. Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C = 0.00
Overide Runoff Coefficient, C = 0.27 (enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 = 0.00
Overide 5-yr. Runoff Coefficient, C = 0.27 (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
• overland
Reach I flow LEGEND
Reach 2 L) Beginning
flaw Direction
4—
Catchment
Reach 3 Boundary
id-
NRCS Land Heavy Tillage/ Short Nearly Grassed Paved Areas &
Type Meadow Field Pasture/ Bare Swales/ Shallow Paved Swales
Lawns Ground Waterways (Sheet Flow)
Conveyance 2.5 5 7 10 15 20
Calculations: Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey- Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.27 N/A 0.00 0.00
1
2
3
4
5
Sum 0 Computed Tc = 0.00
Regional Tc = 10.00
User-Entered Tc =
IV. Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I = inch/hr Peak Flowrate, Qp = #VALUE! cfs
Rainfall Intensity at Regional Tc, I = inch/hr Peak Flowrate, Qp = #VALUE! cfs
III Rainfall Intensity at User-Defined To, I = inch/hr Peak Flowrate, Qp = #VALUE! cfs
Calculated values for Tc & Qp are based on overide values entered for C & C-5.
Copy of UD-Rational v1 .02a_5-Yr 1-Hr Event, Tc and PeakQ 4/14/2010. 5:23 PM
•
Appendix C
Hydraulic Computations
•
•
• Hydraulic Computations
The detention pond for the proposed project is designed to detain the total runoff of
17,146 cf from the 100-year, 1-hour precipitation event. This is accomplished simply by
excavating a 100-foot by 100-foot detention basin within the existing on-site detention
area defined by the 4713 contour as shown on the Site Drainage Plan. The following
Area-Capacity table provides the calculations used to verify that a total runoff capacity
provided in the detention pond as designed is 18,511 cubic feet; well in excess of the
required storage volume of 17,146 cf for the100-year 1-hour event.
Detention Pond Area-Capacity Table (based on surveyed point elevations)
Elevation Elevation Surface Ave. Incremental Cumulative
(ft— MSL) Difference Area Surface Volume Volume
(ft) (ft2) Area (ft2) (ft3) (ft3)
4712 6,400 0
0.5 8,200 4,100
4712.5 10,000 4,100
0.5 28,822.5 14,411.25
4713 47,645 18,511.25
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