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HomeMy WebLinkAboutSewer AnalysisSEWER ANALYSIS FOR SHENANDOAH SUBDIVISION PHASES 10 - 17 MAY 2004 r1s SUBMITTED BY: MCCLURE & BROWNE ENGINEERING/SURVEYING, INC. 1008 Woodcreek Drive, Suite 103 • College Station, Texas 77845 - /--Iv r SEWER ANALYSIS FOR SHENANDOAH SUBDIVISION, PHASES 10-17 General Information Shenandoah Subdivision, Phases 10-17 encompasses approximately 147 acres of land in southern College Station. It is located on the south side of Barron Road near its intersection with Newport Lane. There are 260 single-family residential lots planned for the eight phases. The area surrounding the site is rapidly developing with Alexandria subdivisions on the north, older phases of Shenandoah to the east, Reatta Meadows subdivision being constructed on the west, and undeveloped phases of the Castlegate Subdivision on the south. Sewer System Analysis Subdivision Collection System The primary sewer outfall for Shenandoah Subdivision, Phases 10-17 is a 21" line that was constructed with the Reatta Meadows Subdivision immediately west of the site. That line is an extension of the Spring Creek Sewer Trunk Line that was built by the City of College Station approximately 3 years ago. A secondary outfall is the 8" line along Alexandria Boulevard that was installed with Phase 7. It also flows to the Spring Creek Sewer Trunk Line. The sewer system in the subdivision is divided into three sections, two of which flow into the 21" line and the third into the 8" line. Exhibit A is a sketch of the proposed sewer system for Phases 10-17 of Shenandoah Subdivision. Using this layout, the spreadsheets in Exhibits B, C and D were prepared to compute the minimum slope of the lines needed to carry water at 2 feet per second or faster. The sewer demands were estimated assuming 267 gpd per residential lot and peaking factors were set at 4.0 as required by the Design Guidelines for the City of College Station. If the computed slope was less than the minimum slope required by TCEQ, the value appears in red and indicates that the line has adequate capacity even when laid on the minimum allowable slope. All of the lines in the spreadsheets on Exhibits B, C and D have computed slopes shown in red that are less than the minimum required by TCEQ. Therefore, we conclude that the lines are adequately sized and will easily carry the sewage flows that are expected to pass through them. Trunk Line Analysis As part of the sewer system analysis for the future phases of Shenandoah Subdivision, an analysis of the 21" sewer trunk line was also made to determine its capacity for this additional flow. A previous study associated with the development of Reatta Meadows indicated that a section of this line should be oversized to a 24" pipe to accommodate anticipated flows. The final decision was to leave it as a 21" line, which brought into question its ability to carry addition flows from Shenandoah. Pagel of 2 The original Reatta Meadows study makes assumptions regarding future development in the sewer drainage basin. These assumptions include fully developed conditions with a mixture of commercial and residential development. Residential development is anticipated at a density of 6 housing units per acre. This density assumption does not match the type of residential development that is occurring in the area. Development in nearby subdivisions such as Shenandoah, Castlegate, Westfield Village, and Alexandria are between 3 to 4 units per acre when land for parks, greenways, detention facilities, and other common areas are included in the computation. Therefore, it is reasonable to reduce the anticipated residential density to 4 units per acre for purposes of the sewer analysis. Another factor not included in the Reatta Meadows study is the 65 acre tract owned by College Station ISD that is planned for a future high school. Estimates of sewage flow from such a facility is significantly less than the flows from the residential development in the Reatta Meadows study. When these factors are incorporated into the analysis, the anticipated flow through the line is reduced to a rate that can be carried by the 21" line. Even when additional flows from the Shenandoah Subdivision are added to the trunk line as proposed, the line is still capable of serving the basin. This is demonstrated in Exhibit E where all segments of the 21" line have computed slopes shown in red, which means they are capable of carrying the anticipated flows if laid at the minimum slope required by TCEQ. Therefore, we conclude that the line is adequately sized and has capacity to carry the sewage flows that are expected to pass through it. Page 2 of 2 `j bdi~lsionr°~ nondoO g 6r 9 r I She phos ! I f i i , 1 1 o~~` ; t o o I !E ~l s' ~vV 6' Its' p A"" m c ~}F Z,I f ~ s _ 1 6' I I 1 1 h Subdi~sion ,,,non( . g do / I 1 e 0 1,~6 l f ~p i~ t' ~ E I I ~ O v I;rs" " 60 i U Newport Lane BBB DDD FFF HHH Al Y .r =-e 57c~~ -a SA - Ave A/exondna nue f' 'O 1 G DDI 16 8m 1 0 0 V ;t x ! f j! I i. 3_ i EEE I B 135 CCG r o _I M yl t + Qu~~ Lambsburg Lane Hi j FF 6. 1 X o___ - 6• E__ sr'I s II I -T _ p I ,I s ; I ; i y ~ AA' t B ; EE` W / I" lV I ,c s" - 21 S/1 - - 21+5/L - - 21 S/L - - 21 SA - - 21 SA 21 S/L - JJ1 p. SEWER LINE SCHEAM77C SHENANDOAH SUBDIVISION i PHASES 10-17 0204-SL-DNI8 DWG _16 sr- e S,L e s/~r-~ B /L- s/ ;e s/~_ - s sJ t' - E lodoyrs I ! ' I d Ws Red© eota~se) I f ho iR reI P I _.A _L I S 1 G.~ { ~ ~ ~ I f 6 6 I~ 0 i iN i