HomeMy WebLinkAboutDesign ReportDESIGN REPORT FOR PROPOSED
SANITARY SEWER LINE IMPROVEMENTS
LAKESIDE VILLAGE SUBDIVISION
Longmire Drive near Eagle Avenue
College Station, Texas
Prepared for
MM&R Development, LLP
c/o Lagrone Construction Company
4603 Caddie Court
College Station, TX 77845
Submitted to
City of College Station
Development Services
1101 Texas A venue
Prepared by
CSC Engineering & Envirorunental Consultants, Inc.
3407 Tabor Road
Bryan, Texas 77808
(979) 778-2810
August 31 , 2006
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M. Frederick Conlin, Jr., P.E., J.D.
CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Sanitary Sewer Design Report Lakeside Village Subdivision; College Station, Texas
I. INTRODUCTION
A. General
This report describes the design procedure that was used for the sizing of the sanitary sewer
system that will service the proposed Lakeside Village Subdivision development (hereinafter Lakeside
Village) located northwest of the intersection of Longmire Drive and Eagle Avenue in the southern
portion of College Station, Texas. A general vicinity map illustrating the location of Lakeside Village
within the City of College Station is presented on Figure 1 -Project Vicinity Map in Attachment A ofthis
report (all report figures are contained in Attachment A).
This report presents flow capacity and velocity computations used to determine the required
design size of the new gravity sanitary sewer lines that will be constructed within the subdivision to
support the proposed development. The criteria used in the design of the proposed sanitary sewer lines are
discussed in this report.
B. Project Description
1. Proposed Residential Development. The proposed development extends over an area of
approximately 13 .79 acres and consists of approximately 55 residential lots that may be developed in two
separate phases as illustrated in Figure 2 -Proposed Subdivision Development Scheme and Sanitary
Sewer Layout. Phase I will involve approximately 27 residences located between Longmire Drive to the
northeast and the extension of Eagle Avenue to the southwest. Phase II will involve approximately 28
residences between Eagle Avenue and the western tributary stream to the South Fork of Lick Creek. This
report documents activities in both phases of the proposed development.
The residential lots all front proposed new roadways within the subdivision as indicated in Figure
2. Each of the proposed lots will be the site of a residential structure with approximate "footprint" areas
that range from 2,000 square feet (sq ft) to 3,000 sq ft. Each residence is expected to have between 3 and
4 bedrooms and 1 to 2 baths. The structural framing system for the proposed single-and two-story
residences will consist of conventional wood frame/bearing wall systems with a combination of brick,
stone, Hardi-plank and/or stucco exteriors. The residences are expected to have shallow foundation
systems consisting of subgrade-supported slabs-on-grade.
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CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Sanitary Sewer Design Report Lakeside Village Subdivision; College Station, Texas
2. Proposed and Existing Utilities -Water and Sanitary Sewer Lines. The public utilities
planned for the proposed development will consist of water and sewer lines as illustrated in Figure 2. The
design of the water lines is discussed in a separate report. This report only addresses the design of the
proposed sanitary sewer lines that will service the fully developed Lakeside Village Subdivision
development.
Proposed Sanitary Sewer Collector and Lateral Lines. The proposed sanitary sewer line within
the subdivision will consist of both lateral lines and a major collector line as illustrated on Figure 2. There
are a total of six proposed sanitary sewer lines and each line has been given a letter designation of A
through Fas indicated on Figure 2.
The proposed collector line from the subdivision was designated as Line A and will tie into an
existing 12-inch-diameter sanitary sewer trunk line that is present in an easement which parallels the
southwestern boundary of the proposed development. Proposed collector Line A will have a diameter of
10 inches with a length of approximately 1,306 linear feet and a minimum slope of 0.3 percent. There are
three proposed manholes and one clean-out on Line A.
The remaining sanitary sewer lines, which have been designated as Lines B through F, are lateral
lines . All of the lateral lines are planned to have a minimum diameter of 8 inches, a minimum slope of 0.4
percent. Lateral lines B through E are all connected to collector Line A but lateral Line F discharges
directly into the existing 12-inch truck line near the western corner of the Phase II portion of the proposed
development. The lengths of lateral Lines B through E which discharge into collector Line A vary from
approximately 359 linear feet to approximately 474 linear feet and all end in clean-outs. Some of the lines
have proposed intermittent manholes. Lateral Line E which discharges directly into the existing 12-inch-
diameter truck line is approximately 492 linear feet in length and has one manhole.
More specific information concerning the design of the proposed sewer lines and the analysis of
the existing lines is discussed in the following section of this report.
Proposed Sanitary Sewer Service Lines. The service lines for the proposed 55 residences of the
subdivision will tie into either the proposed lateral or collector lines or directly into the existing truck line .
A listing of each of the proposed sanitary sewer lines and the number of residences expected to tie into
each line is presented in Table 1.
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CSC ENGINEERING cl ENVIRONMENTAL CONSULTANTS, INC.
Sanitary Sewer Design Report Lakeside Village Subdivision; College Station, Texas
Table 1. Summary of Proposed SS Lateral and Collector Lines and Associated Service Line
Connections
SS NUMBER OF SS SERVICE LINES CUMULATIVE NUMBER O F
LINE TYING DIRECTLY TO SS SERVICE LINES TYING TO
DESIGNATION DESIGNATED SS LINE 1 DESIGNATED SS LINE
A 17 42
B 6 6
c 8 8
D 2 11
E 9 9
F 9 9
Notes:
1. Four (4) proposed service lines will tie directly into the existing 12-inch trunk line.
II. DESIGN CRITERIA AND OVERVIEW
A. Design Criteria
The design and analysis of the proposed sanitary sewer system for the subdivision was performed
in accordance with the criteria outlined in the sewer section of the Bryan/College Station Unified Design
Guideline Manual, Effective August 4, 2000 and Revised 2006 (hereinafter referenced as the BICS Design
Manual). The construction of the proposed improvements will conform to the current requirements of the
BICS Unified Technical Specifications; Water, Sewer, Street and Generals, 2006.
B. Design Overview
The design flows for the proposed laterals and collector lines were calculated on a per residence
or living unit basis as permitted in the referenced BICS Design Manual. The number of residences was
determined within the "service areas" for each of the proposed laterals and the proposed collector line and
is listed in the previously referenced Table 1. The average and adjusted average daily wastewater flows
and the peak hourly flows on which the design or evaluation of the lines was based were calculated by
multiplying the number of residences within the service area of each line times the unit sanitary sewer
flow for a single residence. The various segments of sewer line were then analyzed to determine if the
capacities of the lines exceeded the flows required to be carried by the lines.
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CSC ENGINEERING cl ENVIRONMENTAL CONSULTANTS, INC.
Sanitary Sewer Design Report Lakeside Village Subdivision; College Station, Texas
The lateral and collector lines with the most number of residences within the service area were
analyzed to establish the maximum line size and steepest slope required for the "most heavily loaded"
line. The line sizes and slope determined for the "most heavily loaded" line could also be conservatively
employed for the other "less heavily loaded" laterals and collaterals. As can be seen from a review of
Table 1, the collector Line A is planned to carry the cumulative flows from 42 residences and the lower
portion of lateral line D is the most "heavily loaded" lateral line with cumulative flows for 11 residences.
The determination of the unit design flows for each residence that would be serviced by the
proposed lateral and collector lines is explained in the following section of this report. The subsequent
section of the report will describe how the proposed sanitary sewer lines were sized to handle the
anticipated flows .
III. DETERMINATION OF DESIGN FLOWS IN PROPOSED SANITARY SEWER LINES
The first part of this section indicates how the unit flows per residence were determined and the
second part indicates the magnitude of flows that will have to be carried by the collector line and the most
"heavily loaded" sanitary sewer lateral line segments.
A. Computation of Unit Average Daily Wastewater Flow and Peak Hourly Flow Per Residence
The peak design flow for each residence that will be serviced by the proposed and existing
sanitary sewer lines was determined as previously indicated on an "individual residence" basis.
The sanitary sewer flows from each residence were computed based upon Method 2 -Land Use
Determination Method as outlined in the Sanitary Sewer Section of the Design Manual. The Land Use
Determination permits the use of a "population factor of 2.67 persons per unit, which is then applied to
the maximum number of units per acre, if known ... " The number of residential units for the proposed
development is known and the number of residential units or equivalent residential units within the
service area of the existing trunk line were computed as previously explained. The Design Manual states
that an average of 2.67 occupants per residence with an average flow per capita of 100 gallons per day
(Table III of Design Manual) can be assumed in computing the Average Daily Wastewater flows .
Based upon Table III and assuming that each residence will have a total of 2.67 occupants, the
average daily wastewater flow for each residence was calculated as follows :
Average Daily Wastewater Flow =Number of occupants *
unit flow of wastewater generated per occupant
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CSC ENGINEERING cl ENVIRONMENTAL CONSULTANTS, INC.
Sanitary Sewer Design Report Lakeside Village Subdivision; College Station, Texas
Average Daily Wastewater Flow= 2.67 occupants* 100 gpcd = 267 gallons per day
or (dividing by 1,440 minutes per day, i.e.,
[1 day I 24 hrs * 1 hour I 60 min])
= 0 .185 gallons per minute
or converting to cubic feet per second (cfs) ...
= 0.185 gpm * 0.1337 cubic foot I 1 gallon* 1 minute I 60
seconds
= 0.000412 cubic ft/sec
The Adjusted Daily Flow and the Peak Hourly Flow can be calculated from the Design Manual,
which states that ...
Adjusted Daily Flow =Average Daily Flow * 1.5
and ...
Peak Hourly Flow= Adjusted Daily Flow* 3.0
Therefore, substituting the equation for Adjusted Daily Flow into the Peak Hourly Flow equation
yields ...
Peak Hourly Flow= Average Daily Flow* 1.5 * 3.0 or Average Daily Flow* 4 .5
Substituting the previously calculated Average Daily Flow per residence into the above equation
yields the peak hourly flow for each residence ...
Peak Hourly Flow= 267 gpd * 1.5 * 3.0
= 1,202 gpd or 0.83 gpm
In addition, smce the peak hourly flow typically includes some consideration of
inflow/infiltration (III), we have conservatively added an III rate equal to 5% of the calculated flows
which yields ...
Peak Hourly Flow with Ill= 1,202 gpd + 5% Infiltration of 1,202 gpd (or 60 gpd)
= 1,262 gpd or 0.88 gpm
Converting the flow to cubic feet per second ( cfs) yields the following Peak Hourly Flow with
Inflow/Infiltration on an individual residence basis ...
Peak Hourly Flow with Ill= 0.88 gpm * 0.1337 cubic foot I 1 gallon *
1 minute I 60 seconds
= 0.00196 cfs
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CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Sanitary Sewer Design Report Lakeside Village Subdivision; College Station, Texas
B. Flows for Most "Heavily Loaded" Pipe Segments
As previously indicated, the peak design flows for each of the most "heavily loaded" sanitary
sewer line pipe segments (i.e., collector Line A and lateral Line D) were first determined based upon the
cumulative number of residences tying into each pipe segment and then multiplying the number of
residences by the unit flows for a single residence. In summary, the number of residences and the
corresponding design flows are presented in Table 2 for the two most "heavily loaded" pipe segments
(i.e., collector Lines A and lateral Line D) being designed.
Table 2. Summary of Computed Contributory Flows and Pipeline Sizes for Most "Heavily Loaded"
Segments of Proposed Sanitary Sewer Lines
Number Cumulative Computed
of Residences Number of Cumulative Computed
Pipe for this Residences Average Daily Cumulative Peak
Line Dia-Segment for this Wastewater Flow Hourly Flow
Se2ment 1 meter Alone 2 Se2ment 2 per Se2ment 3 per Se2ment 4
Inches Number Number cfs cfs
Collector Line A 10" 17 42 0.0173 0.0823
Lateral Line D 8" 2 11 0.0045 0.0216
Notes:
1. See Figure 2 for line segment designations and service areas.
2. Value determined from Table 1.
3. Based upon a per residence flow of0.185 gallons per minute or 0.000412 cfs.
4. Based upon a per residence flow of0.88 gallons per minute or 0.00196 cfs.
As can be seen from a review of Table 2, the current development plans call for approximately 42
resiµential units to generate wastewater flows to the proposed 10-inch collector Line A as previously
<ljsc¥ssed. The flows associated with the proposed residential structures were calculated as follows :
Peak Hourly Flow with Ill= 42 residential units* 0.00196 cfs per unit
Peak Hourly Flow with Ill= 0.0823 cfs as indicated in the right hand column of Table 2
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CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Sanitary Sewer Design Report Lakeside Village Subdivision; College Station, Texas
IV. PIPE SIZE, SLOPE, CAPACITY, AND VELOCITY DETERMINATIONS FOR EACH OF
THE SANITARY SEWER LINE SEGMENTS
The proposed size of the pipe required to carry the designed flows from the previously described
segments of the sanitary sewer line servicing the proposed development was determined from the
Manning Equation:
Where
Q =AV= A* (1.486/n)(R213 * S112)
Q = flow capacity of pipe in cubic feet per second ( cfs)
A = area of pipe in square feet (ft:2)
V =velocity in feet per second (fps)
n = roughness factor, dimensionless
R = hydraulic radius, feet
S =slope, dimensionless (feet/feet, i.e., slope in percent divided by 100)
A. Pipe Size Determination for Proposed Lines and Evaluation for Existing Lines
Using the Manning Equation with a roughness factor of 0.013, the flow capacity of the pipes in
each of the line segments can be determined based upon the assumption that the slope of the pipe is equal
to the slope of the hydraulic grade line. For example, the capacity of the proposed 10-inch trunk line with
a design slope of 0 .4 percent, can be calculated as follows:
to be ...
The Area of the 10-inch-diameter pipe is ...
A = (1/4) * n * D/\2 = 0.545 ft:2
The hydraulic radius (assuming full flow) is:
R =DI 4 = (0.83 ft) I 4 = 0.208 ft
Therefore, substituting into the general Manning Equation, the flow capacity is determined
Q = 0.545 ft2 * (1.486 I 0.013) * (0.208213 * 0.003 112)
Q -1.2001 cfs
The capacity of the proposed 8-inch-diameter lateral lines was similarly determined. The
summary of the calculations for the two most "heavily loaded" lines are presented in Table 3.
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CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Sanitary Sewer Design Report Lakeside Village Subdivision; College Station, Texas
Table 3. Summary of Computed Flows and Capacities for Each Segment of Sanitary Sewer Line
Design Flow
Maximum as% of
Pipe Slope Flow Computed Maximum Velocity at
Line Dia-of Capacity of Peak Design Flow Maximum
Se2ment1 meter Pipe Pipe Flow Caoacitv Flow (Full)
Inches Percent cfs cfs Percent fps
Prop Collector A 10" 0.30 1.200 0.0823 6.9% 2.2
Prop Lateral D 8" 0.40 0.7643 0.0216 2.8% 2.2
Notes:
1. See Figure 2 for designation of various sanitary sewer lines.
The previously computed design flows that are required to be handled by each line are also
presented in Table 3. Also, the percentage of each of those design flows as compared to the flow capacity
of each line is presented in Table 3. For example, the computed capacity of the 10-inch collector Line A
is 1.2000 cfs, and the computed peak hourly design flow to be handled by the referenced line segment as
outlined in Table 2 is approximately 0.0823 cfs. Consequently, the maximum design flow is
approximately 6.9 percent (0.0823 cfs I 1.2000 cfs) of the maximum capacity of the proposed line. Based
upon the flow capacity determined by the Manning Equation, the proposed pipe size of 10-inch-diarneter
would be sufficient to handle the sanitary sewer flows generated by the proposed development of
Lakeside Village. As can be seen from the proposed construction plans for Lakeside Village, the proposed
sanitary sewer lines were also sized to be able to tie-into the existing 12-inch trunk line.
In summary, the capacities of the proposed sanitary sewer line segments for the lateral and
collector lines which are summarized in Table 3 indicate that the proposed pipe line sizes of 8 inches for
the lateral lines and 10 inches for the proposed collector line provide sufficient capacities to handle the
design flows from the proposed development.
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CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Sanitary Sewer Design Report Lakeside Village Subdivision; College Station, Texas
B. Pipe Velocity
The flow velocity was also determined for each segment of sewer line flowing at maximum
possible flow, i.e., at capacity flow. The previously defined Manning Equation and the following general
flow equation were used to solve for the flow velocities:
Q=AV
and
V=Q/A
... where all of the terms are as previously defined.:.
Substituting the assumed n value of 0.013 into the Manning Equation, the known values of R for
the different design conditions, and the design grade or hydraulic grade line slopes of 0.30 and 0.40
percent for the collector and lateral line segments, respectively, we calculated the velocity values for each
segment of pipe and have presented those values in the previously referenced Table 3.
As illustrated in Table 3, the calculated flow velocities for each segment of sanitary sewer line
when flowing full will lie within the typically specified minimum and maximum flow velocities of
approximately 2 to 2.5 fps for minimum velocity and 10.0 fps for maximum velocity.
V. CONCLUSIONS
Based on our computations and the referenced design criteria, the proposed public sewer lines
planned to be constructed for the Lakeside Village Subdivision development will provide sufficient
capacity for the anticipated wastewater flows generated by the development and can carry the flows
within acceptable velocity limits.
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. . CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
ATTACHMENT A
Figures
Figure 1 -Vicinity Map
Figure 2 -Proposed Subdivision Development Scheme and Sanitary Sewer Layout
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VICINITY MAP OF PROPOSED
LAKESIDE VILLAGE SUBDIVISION
COLLEGE STATION, TEXAS
PROJECT: LAKESIDE VILLAGE SUBDIVSION
LOCATION: COLLEGE STATION TEXAS
APPR: MFC REV. DATE:
DRAWN BY: MOK SCALE: AS SHOWN
DATE: 09/01/06 FIGURE NO.: 1