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Lift Station StudyLift Station Study FOR Creek Meadows Subdivision Section 7, Phase One & Two College Station, Brazos County, Texas March 27, 2015 Prepared For: Creek Meadow Partners, L.P. c/o Oldham Goodwin Group, LLC 2800 South Texas Avenue, Suite 401 Bryan, TX 77802 Prepared By: RME Consulting Engineers Texas Firm Registration No. F-4695 P.O. Box 9253 College Station, TX 77845 RME No. 260-0551 Lift Station Study FOR Creek Meadows Subdivision Section 7, Phase One & Two College Station, Brazos County, Texas March 27, 2015 Prepared For: Creek Meadow Partners, L.P. c/o Oldham Goodwin Group, LLC 2800 South Texas Avenue, Suite 401 Bryan, TX 77802 Prepared By: RME Consulting Engineers Texas Firm Registration No. F-4695 P.O. Box 9253 College Station, TX 77845 RME No. 260-0551 Lift Station Study Creek Meadows Subdivision Section 7, Phase One & Two College Station, Brazos County, Texas TABLE OF CONTENTS: PAGE 1.0 General Information ...................................................................................................................................... 1 1.1 Scope of Report ....................................................................................................................................... 1 1.2 Site and General Location ....................................................................................................................... 1 1.3 Description of Existing Sanitary Sewer Conditions ................................................................................ 2 2.0 Sanitary Sewer Flow ...................................................................................................................................... 2 2.1 Sanitary Sewer Demands ......................................................................................................................... 2 2.2 Outfall Capacity ....................................................................................................................................... 3 3.0 Lift Station Design .......................................................................................................................................... 3 3.1 General Information, Methodology & Design Criteria ............................................................................ 3 3.2 General Site Conditions ........................................................................................................................... 5 3.3 Wet Well & Storage Capacity ................................................................................................................. 5 3.4 Pumping Requirements ............................................................................................................................ 7 3.5 Force Main Evaluation ............................................................................................................................ 8 ATTACHMENTS: Section 1.0 Schematic Phase Layout Creek Meadows Subdivision -Preliminary Plan Vicinity Map Section 2.0 CMSSLS -Service Area Map Section 3.0 LS-01: Lift Station Site Plan Geotechnical Investigation LS-02: Lift Station Details Lift Station Design Worksheet Tank Floatation Worksheet Bearing Capacity Worksheet System & Performance Curves 260-0551 Lift Station Study.docx Page -i Lift Station Study Creek Meadows Subdivision Section 7, Phase One & Two College Station, Brazos County, Texas 1.0 GENERAL INFORMATION 1.1 Scope of Report: This report addresses the lift station system improvements, for the Creek Meadows Subdivision, Phase One & Two. The purpose of this study is to evaluate (1) outfall capacities and expected sanitary sewer demands (lift station flows being received by the 8" sanitary sewer collection line located in Creek Meadows Subdivision, Section 5, Phase 3), and (2) evaluate the proposed design of the lift station pumping, wet well storage, and forcemain piping. The ultimate desire, illustrated in this design report, is generally as follows: (1) Provide adequate service capacity for Creek Meadows Subdivision-Section 7, Phase One & Two, and other phases discharging to this lift station; (2) Verification that the outfall capacity of the existing collections systems is not overwhelmed. The proposed Creek Meadows Southside Lift Station (CMSSLS) improvements are generally described as follows and are in further detailed within the body of this report. Schematic Phase Layout, illustrates graphically these improvements is contained within the "Attachment -Section 1.0" portion of the report. Also reflected in this report, and the before mentioned schematic drawing, is information from the Creek Meadows Lift Station (CMLS) study (dated 9/11/13) and the Castlegate 2 Lift Station (CG2LS) study (dated 2/4/15). The proposed development's sanitary sewer improvements are analyzed in accordance with the criteria outlined in the "B/CS Unified Technical Specifications and Design Guidelines" (UTSDS) manual of the City of College Station (CoCS) and Chapter 217 of the Texas Commission on Environmental Quality (TCEQ) Rules & Regulations. 1.2 Site and General Location: The Creek Meadows Subdivision has access to Greens Prairie Road West, near its north property line, and is bisected by Greens Prairie Trail through its southern third. Adjacent existing developments generally consist of the Estates of Royder Ridge to the west, Turnberry Place and Benjamin Graham subdivisions to the north, Woodlake to the southeast, and Wellborn Oaks to the east. Originally all of these subdivisions were located in the College Station E.T.}. However, since the time of the original report much of these developments have been annexed by the CoCS. Currently sewer services, for these ETJ subdivisions, are still being provided by on-site sewerage facilities (OSSF's) on an individual bases. The Creek Meadows subdivision is further illustrated on the attached 260-0551 Lift Station Study.docx Page - 1 Creek Meadows, Section 7, Phase One & Two Lift Station Study RME Consulting Engineers March 27, 2015 Creek Meadow Preliminary Plan, which is contained within the "Attachment -Section 1.0" portion of the report. Also a Vicinity Map, for this project site, is provided and is located in the "Attachment" portion ofthis manual. This map is being provided as an aid in locating the site. Drawings describing the work and its specific locations are contained in the Construction Drawings prepared by RME Consulting Engineers, College Station, Brazos County, TX. These Construction Drawings are included as part of this Lift Station Study by reference. 1.3 Description of Existing Sanitary Sewer Conditions: The Creek Meadows Subdivision is currently partially developed. An existing 8" sanitary sewer collection line, which will be the discharge point for CMSSLS, was installed with Section 5, Phase Three. This collection line discharges to the Creek Meadows Subdivision Lift Station. 2.0 SANITARY SEWER FLOW 2.1 Sanitary Sewer Demands: The sanitary sewer requirements, for all contributing phaeses, were derived by implementation of Method 2 -"Land Use Determination" from the UTSDS. Lot totals, for the Creek Meadows Subdivision, are based on the latest approved Preliminary Plan (see "Attachment -Section 1.0" portion of report) and the CMSSLS Service Area Map (see "Attachment -Section 2.0" portion of report) Average daily sanitary sewer flow values were calculated and the results are summarized in Table #1 -"Sanitary Sewer Flows" shown below. Assumptions for these calculated sanitary sewer flow values are reported following Table #1. TABLE #1 -SANITARY SEWER FLOWS Average Average L-ttour Daily Flow Dwelling Daily Flow Peak Flow Peak Flow Section/Phase (gpd/cap) Units (gpd) (gph) (cfs) Section 6, Phase I 100 33 8,811 1,469 0.05 Section 6, Phase 2A 100 9 2,403 401 0.01 Section 6, Phase 3 100 28 7,476 1,246 0.05 Section 7, PhaseTwo 100 48 12,816 2,136 0.08 Section 7, Phase Three 100 14 3,738 623 0.02 Section 7, Phase Four 100 32 8,544 1,424 0.05 TOTAL EXPECTED FLOWS= 164 43,788 7,298 0.27 Flow Determination Assumptions: I) Residential density is at 2.67 capita/Dwelling Unit (D.U.); 2) Average Daily flows, for each use, were assigned per Table III-"Average Wastewater Generations" per the UTSDS; 3) A Peaking Factor of 4.0 will be utilized; Utilizing the flow data in Table #1 the minimum required Firm Pumping Capacity of the CMSSLS will be 121 gpm. The actual Firm Pumping Capacity is expected to be 133 gpm. 260-0551 Lift Station Study.docx Page -2 Creek Meadows, Section 7, Phase One & Two Lift Station Study 2.2 Outfall Capacity: RME Consulting Engineers March 27, 2015 As discussed in Section 1.3 of this report the proposed outfall for the CMSSLS is the existing 8" sanitary sewer collection line (located in Section 5, Phase 3 -Identification of MH #22). The existing 8" sanitary sewer collection line has been laid at a slope of 0.40% slope. This equates to a capacity of approximately 350 gpm (0.78 cfs) for the 8" line (n=0.013). The before mentioned 8" sanitary sewer line discharges directly into the CMLS. Prior to discharging sanitary sewer into the lift station the sanitary sewer line will collect an additional 81 gpm (0.18 cfs). Thus the total flow intercepted by this 8" sanitary sewer line will be as follows. As illustrated there is a surplus of 136 gpm (0.30 cfs) capacity in this collection line. 8" Sanitary Sewer Collection Line (Capacity = 350 gpm) Downstream areas of CMLS Firm Pumping Capacity CMSSLS TOT AL EXPECTED FLOW TO 8" SS: 3.0 LIFT ST A TI ON DESIGN 3.1 General Information, Methodology & Design Criteria: 81 gpm 133 gpm 214GPM Utilizing the proposed lift station layout, design conditions, expected flows from Table #1, the Creek Meadows Southside Lift Station (CMSSLS) was designed for compliance with proposed anticipated improvements. The applicable design criteria, from the TCEQ - Chapter 217, are briefly listed below: 1. §217 .59 -Lift Station Site Requirements; 2. §217.60-Lift Station, Wet Well, and Dry Well Designs: (b )(7) -Minimum pump cycle time· based on peak flow and pump horsepower requirements; ( d) -Lift Station Ventilation; 3. §217.61 -Lift Station Pumps: ( c) -Lift Station Pumping Capacity; ( d)(3) -Friction Coefficient; (d)(4)-System Curves; (e)(2)-Total number of pumps; 4. §217.63(d)(l)-Retention Capacity (Emergency Provision); 5. §217.64(b)-Material for Force Main Pipes; 6. §217.67 -Force Main Design: (a) -Velocities; ( c) -Water Hammer; ( d) -Connection to Gravity Main; (h) -Valves; 260-0551 Lift Station Study.docx Page -3 Creek Meadows, Section 7, Phase One & Two Lift Station Study 3.2 General Site Conditions: ROADWAY ACCESS: RME Consulting Engineers March 27, 2015 The CMSSLS will take access via the pubic street Crooked Creek Path. This public street is located in a 50' right-of-way with a 27' street section (laydown curb/gutter, 6" lime stablished subgrade, 6" limestone base & 2" HMAC surface) that has finished grades above the 100-year flood elevations. The adjacent nearby flooding source would be Peach Creek Tributary 16.4.3 with a maximum flood elevation of 288.18' during the 100-year rainfall event (per Limited Flood Study prepared by RME and dated 3/27/15). SECURITY FENCE & GATE: The CMSSLS is secured by means of an 8' high solid wood privacy fence. The site will be accessed by a 16' wide, 2-panel, swing gate. Also, the site will be 30'x 35' in size which will allow a minimum of 1 O' separation between the security fence and any portion of the wet well or vault box. SUBSURFACE EXPLORATION & GEOTECHNICAL STUDY: Gessner Engineering was retained and prepared a Geo technical Investigation (dated 1121/15) (see "Attachment -Section 3.0" portion of report) and will be utilized to assist in design of the wet well. Generally speaking the recommendations are based from a single bore (approximately located at the center of the proposed wet well) and extended 30' below existing grade (bottom of bore at an elevation of ~255'). Generally speaking it is estimated that the CMSSLS wet well foundation will be founded on stiff and moderate fat clays and that the water table is below the bottom elevation. 3.3 Wet Well & Storage Capacity: RETENTION STORAGE: The CMSSLS wet well is proposed to be a 6-foot in diameter with a minimum storage elevation of 272.00' and a maximum storage elevation of 287.00'. Further details of the CMSSLS wet well, and operation system, are illustrated on both the LS-02: Lift Station Details sheet and the Lift Station Design Worksheet contained in the "Attachment-Section 3.0" portion of this report. Emergency storage capacity was accounted for in the design of the wet well and is in accordance with TCEQ §217.63(d)(l). This information is as follows and is based on Peak Flow (PF) conditions. );>-Wet Well= 3,171 gallons; );>-Available line storage ~ 3,480 gallons; The CMSSLS collection system has a maximum storage elevation of 287. 00 ' before wastewater backs-up into any residential service line; );>-Available Retention Storage = 6,651 gallons (accommodates PF=229 gpm); );>-Required Retention Storage = 3,527 gallons (calculated PF=122 gpm); The longest power outage, provide by Bryan Texas Utilities (James Tanneberger - emailed 1120115), within the past 24 months is 29 minutes. 260-0551 Lift Station Study.docx Page -4 Creek Meadows, Section 7, Phase One & Two Lift Station Study RME Consulting Engineers March 27, 2015 Additional volume checks were performed utilizing Equation C.5, per TCEQ §217.60(b)(8), which utilized the reported Pump Cycle times below in Table #4 of Section 3.3 during the Ultimate Design Conditions. As illustrated below in Table #2 the combined wet well and available line storage will be adequate for this project. TABLE#2 MIN. EFFECTIVE VOLUME Firm Peak Flow Storage Volume Pumping Cycle Capacity Time Storage Storage m min (cu.ft.) (gal.) 133 40.7 180.9 1,353 WET WELL DESIGN DATA: Flood Protection: Per TCEQ §217.59(c) the design of the lift station shall provide flood protection during the 100-year flood event. However, the CoCS Lift Station Design Guidelines exceeds this requirement by requiring the top of the lift station to be equal to or greater than 3' above BFE. Thus the lift station flood protection is as follows: ~ 288.18' = 100-year pool elevation of adjacent detention facility (maximum pool elevation of Pond #8); ~ 291.25' =Top of Wet Well (required 291.18'); ~ 290.75' = Finish grade elevation (Top of lift station vault shall be set 6" above finish grade); Wet Well Piping & Mechanical: Addition data outlined in TCEQ §217 .60 or the CoCS Lift Station Design Guidelines are highlighted below. ~ Minimum of 6" clearance with flanges and wet well wall; ~ 15% bottom slope and grout doesn't extend up into "All Pumps Off'' (Top of grout is 9" above FFE and "All Pumps Off' is 18" above FFE); Passive Venting: Per TCEQ §217.60(d)(l) and the CoCS Lift Station Design Guidelines an 8" diameter vent pipe, with stainless steel screen, will provide up to 600 :tpm at the lift stations firm pumping capacity. STRUCTURAL DETERMINATIONS: Information and calculations shown in this subsection are based upon data provided in the Geotechnical Report (prepared by Gessner Engineering-dated 1/21/15). Buoyancy Calculations: The wet well shall be designed to resist the effects of buoyancy assuming full saturation of the surrounding soils to the finish grade of the wet well. No surface friction was provided in the attached Geotechnical Investigation therefore this measure of "resistance" to buoyancy will not be included in the calculations. Details of this information is contained on the Tank Floatation Worksheet contained in the "Attachment -Section 3.0" portion ofthis report. A brief summary is as follows. Please note this approach and resulting Factor of Safety (FOS) are conservative calculations (i.e. 260-0551 Lift Station Study.docx Page -5 Creek Meadows, Section 7, Phase One & Two Lift Station Study RME Consulting Engineers March 27, 2015 analyzed with an empty wet well, "anchoring" created by yard piping, no considerations for attached vault box, wet well lid, etc ... ). ~ 12" truck concrete bottom; ~ Buoyancy Resistance no Skin Friction -FOS = 1.53 The CoCS Lift Station Design Guidelines requires a FOS of 1.1 with surface friction not considered. Bearing Capacity: Calculation shown below consider 100% buoyant soils (less the 6" of lift station elevated above the finish grade). This is a conservative approach since no groundwater was present during the drilling operations and will thus result in smaller contribution with the "compensated foundation" system. Calculations are detailed on the Bearing Capacity Worksheet which is contained in "Attachment -Section 3.0" of the report. ~ Maximum allowable Bearing Capacity = 3,000 psf (FOS = 3) ~ Applied Stress = 1, 192 psf Predicted Settlements: Per the Geotechnical Report the total expected settlement is predicted to be minimal using the above Maximum Allowable Bearing Capacities. Lateral Earth Pressures: The following equation was utilized to calculate the maximum exerted Lateral Earth Pressure on the side wall of the wet well. This data will be reported on the construction drawings and verified by the wet well manufacture that the structural strength of the wet well will be sufficient. P1 = (100 pct) x d where, P1 =lateral earth pressure (pst); 100 = equivalent fluid unit weight; d =depth below ground surface (ft); therefore, P1 = (100 pct) x 21.25 ft = 1,850 pounds per foot of width of wall Utilizing a FOS = 3 then P1 = 6,375 pounds per foot of width of wall LEVEL CONTROL SETTINGS: The CMSSLS wet well will be equipped with PVC ball-type floats with mercury switch for each pump "on'', "off", and alarm elevations. Spacing of the level control points have been established to provide adequate pump cycle times, pumps "off' is no closer than twelve-inches (12") from the finished floor, and such that no level setting is closer than six inches (6") apart. Also the "high level" alarm has been set at an elevation two-feet (2') above the lag pump "on" elevation. These control settings are summarized below in Table #3. 260-0551 Lift Station Study.docx Page -6 Creek Meadows, Section 7, Phase One & Two Lift Station Study RME Consulting Engineers March 27, 2015 TABLE#3 LEVEL SETTINGS Elevation Condition (ft) FFE 270.50 ALI Pumps "Off' 272.00 Lead Pump "On" 274.00 Lag Pump "On" 274.95 Influent Pipe 274.95 High Level Alarm 276.95 Conditions Satisfied: l. Minimum sump required of 12" (18" provided); 2. Lead Pump "On" setting below influent tlowline (l l" difference provided); 3. Minimum float separation of6" (11" provided); 3.4 Pumping Requirements: PUMP INFORMATION: As discussed in Section 2.1 the required minimum Firm Pumping Capacity of the CMSSLS will be 121 gpm (133 gpm provided). In order to accommodate this required pumping capacity system curves where develop. System Curves utilized a friction coefficient of C=130 & C=150. These System & Performance Curves are contained within the "Attachment -Section 3.0" portion of the report. PROPOSED PUMPS: ~ Two Flygt Pumps (CP-3085 MT 3---434); ~ Duty Point -133 gpm at 30.3' TDH; ~ Pump efficiency at approximately 61 %; ~ Rated 3 hp with 460V (3 phase) 25 Amp starter service; Below in Table #4 are the Cycle Times during Average Daily Flows (ADF) and Peak Flow (PF) for CMSSLS improvements. Per Table C.4 of §217.60(b)(7) the minimum pump cycle time of 6 minutes is required for this system. This cycle time is analyzed between the "pump-on" and "pump-off' elevations report earlier in Table #3. The pump "on" elevation may need minor adjustments to obtain a more desirable pump cycle time. TABLE #4 -PUMP CYCLE TIMES CM:S:SL:S Firm Pump Cycle Time Pumping Capacity ADF Peak Flow PHASE (gpm) (min) (min) Ultimate Design 133 18.0 40.7 260-0551 Lift Station Study.docx Page -7 Creek Meadows, Section 7, Phase One & Two Lift Station Study 3.5 Force Main Evaluation: VELOCITIES: RME Consulting Engineers March 27, 2015 TCEQ §217.67(a) (2) requires that a minimum velocity of 3.0 fps be met in a duplex pump system with one (1) pump in operation. Therefore utilizing the Hazen-Williams equation the 4" forcemain will experience a velocity ofV=3.4 fps during pumping of 133 gpm. WATER HAMMER & PRESSURE: TCEQ §217 .67( c) requires that a forcemain with a velocity greater than 6.0 fps be designed to manage pressure and that the working strength of the forcemain not be exceeded due to water hammer. As reported above the 6.0 fps threshold will not be surpassed. As required in the UTSDS the pressure in a force main shall not exceed 1/2 of the maximum working pressure of the piping. The minimum working pressure of any type of force main is 160 psi. Therefore the maximum allowable pressure is 80 psi (185' TDH). As noted previously in Section 3.4 the "duty point" for the pumping capacity will not exceed this allowable pressure (maximum design = 30.3 ' TDH when C=130). CONNECTION TO GRAVITY MAIN: As previously mentioned the 4" forcemain will discharge into Manhole #22 which was installed with the development of Section 5, Phase 3. 260-0551 Lift Station Study.docx Page -8 SECTION 1.0 GENERAL INFORMATION CREEK MEADOWS: SECTION 7, PH . 1 VICINITY MAP NOT TO SCALE N NOTTO SCALE SECTION 2.0 SANITARY SEWER FLOW SECTION 3.0 LIFT STATION DESIGN