HomeMy WebLinkAboutWATERFIELD PUD - PRELIMINARY - 7-95B - SUBMITTAL DOCUMENTS - ROUND 2 - STORMWATER-RELATED DOCUMENTSi
1
1
1
1
1
i
1
1
1
1
1
1
1
i
1
1
1
-
4985.000
4980.000
Larimer and Weld Canal
,
-i
Looking East
4975.000
4970.000
4965.000
o
?'
Piezometer B4
m
Existing Ground Surface
d
4960.000
�
Piezometer Bi
w
4955.000
SLC ?
Ground Water Table
4950.000
SS _________
-- •- V 7
_______________
............
SLC
4945.000
_? —_— — — _ _ -----______
_
SS
.
SG __
4940.000
_.
0.000 200.000 400.000 600.000
800.000 1000.000
1200.006-:t 1400.000 1600.000
Distance (ft)
Legend
Riverside Technology, inc.
SLC - Sandy Lean Clay
SS - Silty Sand
Figure 6
Notes:
SG - Sand and Gravel
1. Boring lithology from Earth Engineering Consultants (Sept.1996).
p
E
2. Ground water table information is interpreted based on preliminary and limited information.
•-------- Interpreted Ground Water Table
Interpreted
Cross Section 4
4985.000
4980.000
HOYA POR
4970.000
4965.000
c
0
eo
4960.000
w
4955.000
4950.000
4945.000
4940.000
0.000
Larimer and Weld Canal :
. , Looking East
?
? Piezometer E35 Existing Ground Surface
Ground Water Table
?
SLC
200.000 400.000
Notes:
1. Boring lithology from Earth Engineering Consultants (Sept. 1996).
2. Ground water table information is interpreted based on preliminary and limited information.
800.000 1000.000 1200.000
Distance (ft)
Legend
SLC - Sandy Lean Clay
SG - Sand and Gravel
— 7 Interpreted Ground Water Table
1400.000
1600.000 1800.000
Riverside Technology, inc.
Figure 5
Interpreted
Cross Section 3
I
1
L7
F-
L
[1
1
IL 1
[1
4985.000
4980.000
4975.000
Looking East
4970.000
4965.000
? ?
Piezometer B6
c
4960.000
dGround
Water Table
Piezometer B9
w
4955.000
Existing Ground Surface
SLC , ?
Wetland Area
4950.000
SCS — — —•�._ _ _ _
SLC
_ ►. T.
4945.000
SG------------------------------------------SCS
SG
4940.000
4935.000
0.000 250.000 500.000 750.000 1000.000
1250.000 1500.000 1750.000
2000.000 2250.000 2500.000 2750.000
Distance (ft)
Legend
6,794Riverside Technology, inc.
SLC - Sandy Lean Clay
SCS- Sandy Clayey Silt
Notes:
SG - Sand and Gravel
Figure 4
1. Boring lithology from Earth Engineering Consultants (Sept. 1996).
r
2. Ground water table information is Interpreted based on preliminary and limited information.
7 --- Interpreted Ground Water Table
Interpreted
Cross Section 2
G••1
4980.000
4970.000
c
4960.000
m
w
4950.000
4940.000
4930.000
0.
Larimer and Weld Canal
Looking East
Piezometer B7
SLC Piezometer BS Existing Ground Surface
_tS_ _ _
? SLC
— .
V�Ground Water Table
SG
Inn nrn nnn -- •
- -•��� .,vv.vvv /DV.UVV IUUU.UUU
Notes:
1. Boring lithology from Earth Engineering Consultants (Sept. 1996).
2. Ground water table information is interpreted based on preliminary and limited information.
1250.000
Distance (ft)
Legend
1500.000 1750.000
SLC - Sandy Lean Clay
SS - Silty Sand
SG - Sand and Gravel
—V Interpreted Ground Water Table
2000.000
2250.000 2500.000
91,07"Riverside Technology, inc.
Figure 3
Interpreted
Cross Section 1
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
0
*A
* I
CN4 7A jpjwS n�36 PE.OH-kUnI66
N A,
CO
S I t' L
CO
Ui
0
z
C.0
0
LL
IT
C14
In
0 C
>
�2
Z P
>
N
LL1
'Cc
CC)
44-
CL
Ca
1.
0
tv
. . .. I. I. . .. .. . .............
-0
.0
EL
<
. .. ..
L)
C:
0
CD Cc$ 0
(.)
Z C
E 0
CO m OD
(D C3
�O
C
C
If
U)
to (2) CTJ
Cn , r
0 Cz :3
0
N
Cj) (5
cis
Co
:3
w
rL .2
rn U)
`;;
AQN3
A
`�
� l(� ; %' 1
�. o i
i
r� Riverside
Technology,
inc.
Figure
2
401
' `? `
;( :; ��/,'>%, / j ��—i'
�-�
��'� Lj 7
Potentiometric
Surface
1
C
C
C
C
C
0
O
O
N
of
C
C
C
y
7
O
CO
Cn
J
O
U
m
0
41
CO
m
Eo
m
a
m
(a
Ca
CO
a)D
Q
'0N
m
a)
hWel Riverside Technology, inc.
Figure 1
Water Field Site
Location Map
I
' APPENDIX A
Figures
1
1
F
1
1
1
RESOURCES
Earth Engineering Consultants, Inc. (1996). Preliminary Subsurface Exploration Report, Country
. Club Farms, Vine Drive and Summitview, Larimer County, Colorado.
Landstar Surveying. (1997). Map of Piezometers and Staff Gage Locations. Fort Collins, Colorado.
Riverside Technology, inc. (1996). Jurisdictional Wetlands Delineation Survey for the Country Club
Farms L.L.C. Fort Collins, Colorado.
Northern Engineering, Inc. (1997). Map of the site boundaries and topography. Fort Collins,
Colorado.
U.S. Department of Agriculture (USDA), Soil Conservation Service. (1993). Larimer County Area,
Colorado: Comprehensive Hydric Soils List.
------ (1963 and 1978). Aerial photographs of the Waterfield P.U.D. site.
USDA, Soil Conservation Service and Forest Service, in cooperation with the Colorado Agricultural
Experiment Station. (1980). Soil Survey of Larimer County Area, Colorado.
U.S. Department of the Interior, Geological Survey. (1960). 7.5-Minute Series Topographic Map for
Fort Collins, Colorado, Quadrangle.
U.S. Fish and Wildlife Service. (1975). National Wetlands Inventory Map for the Fort Collins,
Colorado, Quadrangle.
a42518weval.dac 04121197 5
function; however excessive amounts of sediment, oil and grease, or herbicides could be detrimental
to the wetlands vegetation and wildlife. If stormwater runoff is diverted into the wetlands area, Best
Management Practices (BMPs) should be implemented to reduce the amount of pollutants that reach
the wetlands. BMPs could include using a grass -vegetated swale or depression that would provide a
zone where the pollutants could adsorb onto the vegetation or settle out.
ADDITIONAL STUDIES
As project plans become more defined, it may be beneficial to obtain additional water level data and
hydrogeological information. There are no ground water elevation data near the south or north side
of the Larimer and Weld Canal. Additional piezometers and short-term aquifer tests (slug tests) in
the vicinity of the canal or immediately downgradient from the canal would provide information to
better define (1) interconnection between the canal and the water table and (2) the amount of seepage
- from the canal. Additional piezometers located north of the canal (upgradient) could be used to
obtain a better understanding of the regional ground water system. However this may not be
possible since this area is under a different ownership.
If additional information is collected to provide an understanding of (1) the existing
hydrostratigraphic conditions, (2) ground water level data, (3) hydraulic conductivity of defined
geologic units, and (4) construction design (utility trenches, subdrain and foundation layouts, etc.), it
would be possible to implement a ground water model, such as MODFLOW, to predict or estimate
how the water table will respond to site development plans. The model could also be used as a tool
to evaluate the efficiency of subdrains and to estimate discharge rates.
' As mentioned previously, there is a ground water discharge area on the north side of the wetlands
area with a flow of approximately 19 gallons per minute. This discharge may be an outlet for an
underdrain system; however, there are no data to support this. If a drain system is encountered in
' this area, additional studies may be necessary to determine the source of the water and if any impacts
to the wetlands area may occur by disturbing the drain system.
11
' a4751sw�w1.dvc 04121197 4
' Assu motions:
' • The ground water system below the project site is a component of the regional ground water
system and includes seepage from the Larimer and Weld Canal. There is no ground water
information available for the area near the canal or to the north (upgradient ) of the canal.
' • Ground water at borings B2 and B9 was encountered at a depth of 6 feet during drilling. No
piezometers were installed at these sites, so a depth to ground water was assigned an elevation
' that corresponded to the 6-foot depth recorded during the time of drilling.
• The potentiometric surface was based on average ground water elevations collected from
September, 1996, to April, 1997.
The wetlands pond is the result of a topographic low area that extends below the ground water
surface (Figure 4 - Appendix A). The existing data indicate that ground water flows to the southwest
' beneath the site (Figure 2 - Appendix A). The ground water gradient was determined to be
approximately 0.03 ft./ft. from piezometers B6 and B7 to the pond surface.
' The Larimer and Weld Canal, which borders the north boundary of the site, appears to have the
capacity to convey a considerable amount of water. During April, 1997, the water depth in the canal
was approximately 2 feet. The canal banks are composed of a silty clay covered with varying
' amounts of broken concrete. The canal width is approximately 100 feet at the top of bank and 50
feet at the bottom. If there is considerable seepage from the canal, the ground water gradient between
the canal and the wetlands pond may become steeper as flows increase in the canal
DISCUSSION
' The existing data indicate that the water level in the wetlands/pond area is maintained primarily by
ground water discharge. As indicated on the cross sections in Appendix A, the source of the ground
water may be from the regional ground water system, the Larimer and Weld Canal, or a combination
' of both sources.
Lowering the ground water table is an option that has been considered to allow for the construction
of basements. However, if the ground water table in the immediate vicinity of the pond is lowered
' below 4,949 feet, the wetlands area will most likely begin to dry up.
' If the ground water table is lowered but still retains a positive flow toward the wetlands pond, a
reduction in the wetland size may still occur due to the flattening of the ground water gradient. A
flatter gradient could reduce the rate of ground water discharge to the wetlands area.
' An option to maintain sufficient ground water flow to the wetlands area while still lowering the
ground water system would be to place the underdrain outfall in the wetlands area. Another option
' to consider is using canal or well water to supplement in flow to the wetlands area. The current
owner of the property has indicated that an adjudicated water right to canal water exists, as well as an
adjudicated well.
' In addition, it might be possible to direct stormwater runoff from the development into the wetlands
area to supplement the water source to the wetlands. Typically wetlands purify water by taking up
nutrients and filtering sediment. The wetlands at the Waterfield site would provide this purifying
' o+2518weml.da MUM 3 .
0
u
1
1
L
HYDROGEOLOGY
EEC observed the presence of and depth to ground water while drilling and after completing each of
the borings. Field piezometers were installed at six of the boring locations (B1,4,5,6,7, and 8) to
allow for longer term monitoring of ground water levels. The piezometers consisted of 2-inch
polyvinyl chloride pipe with slots in the bottom 5 feet. It does not appear that a gravel -pack back fill
or surface seal was used to construct the piezometers. The locations of the piezometers are shown in
Figures 1 and 2 in Appendix A. At the time of drilling, ground water depth was observed ranging
from 5 to 7 feet below the present ground surface.
Ground water levels were recorded at each of the piezometers during September, October, and
November, 1996, and March and April, 1997. These data are summarized in Table 1.
TABLE 1
Ground Water Elevations
(Waterfield P.U.D.)
Piezometer
Number
Ground
Surface
Elevation
(feet)
Ground Water Elevation (feet)
09/17/96
09/27/96
10/11/96
11/11/96
03/04/97
04/03/97
B 1
4957.19
4950.09
4949.66
4949.19
Dry
Dry
D*
B2
4961.00
4955.00
--
--
--
--
--
B4
4961.05
4956.87
4956.57
4956.17
4955.47
4955.07
4955.06
B5
4955.94
4951.34
4951.07
4950.67
4949.92
4950.87
4949.28
B6
4959.45
4956.20
4956.6
4956.5
4956.25
4956.0
4956.03
B7
1 4965.41
1 4960.57
1 4959.97
4959.77
4959.13
1 4959.68 1
4959.45
B8
4952.92
4947.78
4946.98
4946.18
Dry
Dry
Dry*
139
4947.00
4941.00
--
--
--
--
--
*Piezometers were silted in: Bl to 4947.75 feet; B8 to 4945.93 feet
Notes:
Borings B3 and B10 did not encounter any ground water. Boring depths extend approximately 15 feet below ground
surface.
Piezometers were not installed in borings B2 and B9. Water levels were only recorded at the time of drilling.
A staff gage was installed in the wetlands pond in April of 1997 to correlated the pond surface
elevation with the existing ground water elevation (Figure 2 - Appendix A). The pond surface
elevation was surveyed at 4,948 feet in April of 1997.
Ground water seepage was observed flowing into a ditch that extends along the north and east side of
the wetlands and then into the ponded area (Figure 1 - Appendix A). A flow measurement was taken
in the ditch on April 14, 1997, using a portable flume. The flow was estimated at 0.04 cubic foot per
second (cfs) or approximately 19 gallons per minute.
' The water level data, along with the assumptions listed below, were used to develop a potentiometric
surface map and cross sections for the site (Figures 2-6 - Appendix A) and to analyze potential
impacts to the wetlands area.
' u475/Rweml.doc 04121197 2
' INTRODUCTION
' This report presents the results of Riverside Technology inc.'s (RTi's) preliminary evaluation of the
ground water system at the Waterfield P.U.D. site located in the City of Fort Collins northwest of the
intersection of Summit View and East Vine Drive. RTi understands that the site is under
' consideration for single and multi -family residential development.
The purpose of this review is to evaluate the ground water system and determine if development
activities may impact the wetlands area or require corrective measures. RTi s scope of work was
limited to (1) compiling and analyzing existing data on the site, along with preliminary development
plans provided by Northern Engineering Inc.; (2) installing a staff gage in the wetland pond to allow
for a correlation between ground water elevations, flow in the canal, and pond surface elevation; and
(3) presenting a summary of the ground water system at the site and any potential impacts that the
project plans may have on the system, including the wetlands.
' SITE DESCRIPTION
The majority of the Waterfield site consists of upland agricultural development: The terrain slopes
' gently to the south, with elevations ranging from approximately 4,950 to 4,980 feet. The Larimer and
Weld Canal traverses the northern boundary of the property. A naturally occurring topographic low
area has developed into a cattail marsh with ponded water that is 1 foot deep on average (Figure 1 -
' Appendix A).
Excavations on the south side of the wetlands area appear to be in locations that, at one time,
' contained a tile drain system. Broken remnants of the tile drains were evident in the excavated areas.
Mr. Bob Rudolf, who is currently farming the site, was contacted to obtain information on any drain
systems that may have been installed. He was not aware of any existing drain systems, but felt that
' there was a high probability that some subsurface drains had been previously installed because of the
shallow ground water system and the property's proximity to the Larimer and Weld Canal.
' SOILS AND SUBSURFACE CONDITIONS
Ten soil borings extending to depths of 15 feet below present site grade were advanced by Earth
Engineering Consultants Inc. (EEC). The subsurface exploration results are presented in the report
entitled Preliminary Subsurface Exploration Report, Country Club Farms, Vine Drive and
Summitview, Larimer County, Colorado (1996). A summary of EEC's observations of the
' subsurface conditions is provided below:
Four to 6 inches of vegetation and/or topsoil was encountered at the surface of the boring locations.
' The topsoil/vegetation was underlain by brown and light brown sandy lean clay with varying
amounts of silt. These soils extended to depths ranging from approximately 4 to 14 feet. The sandy
lean clay was underlain by predominantly silt soils containing varying amounts of sand and clay or
' silty fine sands and ranged in depth from 9 to 14 feet. The fine grained sands and silts were
underlain by granular soils, including varying amounts of sand and gravel. The granular soils
extended to the bottom of the borings at depths of approximately 15 feet. The lithology of each
' boring is presented in Figures 3 through 7 - Appendix A.
' a425/Swewi.dac 0421N7
TABLE OF CONTENTS
Section PRO
Introduction..............................................................................................................................................1
SiteDescription.......................................................................................................................................1
Soilsand Subsurface Conditions............................................................................................................1
Hydrogeology..........................................................................................................................................2
Discussion...............................................................................................................................................3
AdditionalStudies....................................................................................................................................4
Resources...............................................................................................................................................5
APPENDIX A - Figures
Figure 1
Water Field Site Location Map
Figure 2
Potentiometric Surface
Figure 3
Interpreted Cross Section 1
Figure 4
Interpreted Cross Section 2
Figure 5
Interpreted Cross Section 3
Figure 6
Interpreted Cross Section 4
List of Tables
Table Page
1 Ground Water Elevations...........................................................................................................2
Ifl
Preliminary Evaluation
of the Ground Water System
at the Waterfield P.U.D. Site
submitted to
City of Fort Collins
and
Northern Engineering Inc.
by
Riverside Technology, inc.
2290 East Prospect Road, Suite 1
Fort Collins, Colorado
April 1997