Section 3 Modeling and Capacity Analysis

Transcription

1 Section 3 Modeling and Capacity Analysis The capacity of the existing DSRSD wastewater collection system and the future capacity requirements of the system were determined through hydraulic modeling. This section describes how the model was constructed and presents the capacity analysis results. More detailed discussion of the model and modeling results are presented in TM 5 Hydraulic Model Results, included in the separately bound appendices to this report. MODEL DEVELOPMENT For the Master Plan Update, the DSRSD collection system was modeled using the hydraulic modeling program, H2OMAP Sewer/Pro, which was selected and purchased by the District following an evaluation of potential modeling software conducted at the beginning of the study (see TM 1 Hydraulic Model Evaluation, included in the separately bound appendices to this report). The 2000 Master Plan Update utilized a different modeling program, called Hydra. Figure 3-1 shows the modeled trunk sewer system for DSRSD. For this Master Plan Update, the trunk system was defined as all sewers 10 inches in diameter and larger, plus any 8-inch lines that were included and loaded with flow in the Hydra model used in the 2000 Master Plan Update or that otherwise effectively function as trunk sewers (i.e., convey flow from one or more entire model subbasins). The basic components of model data and the process of developing the model for use in the master plan capacity evaluation are described below. Model Network Data The primary components of the model network are nodes and links. Nodes are primarily manholes, but also include pump station wet wells. Links are primarily pipes (both gravity sewers and force mains), but also include the pumps connecting a wet well to a node that represents the upstream end of the pump station force main. Each model must also have one or more outlets, which represent the manholes or other structures to which the modeled system discharges. In the case of DSRSD, the single outlet of the modeled network is the headworks of the wastewater treatment plant (WWTP). Basic model input data associated with a node are its ID, diameter, and ground (rim) elevation, along with wastewater loads and infiltration/inflow parameters that represent the flows discharging from unmodeled sewers into the modeled network at that location. Basic model data associated with a pipe are its ID, the ID of its upstream and downstream nodes, pipe diameter, length, upstream and downstream invert elevations, and friction coefficient (Manning s n in the case of gravity sewers or Hazen-Williams C in the case of force mains). Some other optional data fields that can be included are manhole and pipe descriptions, pipe material, installation date, and subbasin. In addition, special data are needed for pump stations, including wet well elevations, pump on and off levels, pump capacities, and pump curves. The data for the model was derived primarily from DSRSD s sewer system AutoCAD MAP GIS files and GBA Sewer Master inventory database. For the Camp Park area, data were provided by Whitley, Burchett and Associates, Inc. (WBA). The data from GIS and GBA include manhole MWH Page 3-1

2 ³ 0 2,000 4,000 Legend Feet Modeled Manholes X WWTP + Modeled Trunk Sewer Other Sewer Mains Wastewater Treatment Plant Parcels Pine Valley Rd. X WWTP + FEDERAL CORRECTIONS SANTA RITA JAIL INSTALLATION CAMP PARKS I-580 San Ramon Rd. I-680 Alcosta Blvd. Dublin Blvd. Village Parkway South San Ramon Creek Amador Valley Blvd. Dougherty Rd. Arnold Rd. Gleason Dr. PARKS RESERVE FORCES TRAINING AREA Tassajara Rd. Central Parkway Fallon Rd. Dublin Blvd. Dublin San Ramon Services District Wastewater Collection System Master Plan Update 2005 MODELED TRUNK SEWER SYSTEM FIGURE 3-1

3 Section 3 Modeling and Capacity Analysis and pipe GIS IDs (used as the model node and link IDs), manhole numbers based on District s grid mapping system (used as the manhole and pipe descriptions in the model), manhole rim elevations, and pipe diameters, lengths, and invert elevations. Other data needed in the model were populated by default, e.g., all manhole diameters were assumed to be 4 feet, and Manning s n was set to for all gravity sewers. In addition to the sewers included in the GIS network, some recently constructed sewers in Eastern Dublin that were not yet incorporated into the District s GIS were added to the model manually based on sewer plans provided by the District. One pump station, the Dublin Boulevard Lift Station, is also included in the modeled system. Model Loading Data Loads (flow inputs) to the model were developed based on the land use and design flow criteria presented in Section 2 of this report. Loads were assigned to specific loading manholes, each associated with one or more sewer subbasins, which were delineated based on the configuration of unmodeled sewer lines (in the case of the existing system) or future development plans and topography (in the case of future growth areas). ID numbers were assigned to each subbasin, as defined in Table 3-1, and the appropriate model load point for each subbasin was determined. The sewer subbasins used for the DSRSD model were previously shown in Figure 2-4. TABLE 3-1 SEWER SUBBASIN NUMBERING CONVENTION Subbasin Prefix Area Description DE Central Dublin, east of I-680 DW Central Dublin, west of I-680 SE San Ramon, east of I-680 SW San Ramon, west of I-680 (Westside San Ramon) ED Eastern Dublin CP Parks Reserve Forces Training Area (Camp Parks) Santa Rita Alameda County Santa Rita Jail S_Ranch Schaefer Ranch PL Pleasanton Commerce Circle area The computation of subbasin flow inputs ( loads ) was described in Section 2. In H2OMAP Sewer, each loading manhole can receive up to 10 different types of loads, each with a specific diurnal pattern. For the DSRSD model, four load types were used. Load type 1 was equated to residential flow, load type 2 to non-residential flow (commercial/office/public facilities), load type 3 to specific point sources (Santa Rita Jail, the Federal Corrections Installation on Camp Parks, existing Camp Parks development, the future Schaefer Ranch development, and the area of the City of Pleasanton that loads to the Dublin trunk), and load type 10 to groundwater infiltration (GWI). Rainfall-dependent infiltration/inflow (RDI/I) flows are computed in H2OMAP Sewer based on a rainfall pattern and unit hydrograph shape. In the model, each subbasin and associated loading MWH Page 3-2

4 Section 3 Modeling and Capacity Analysis manhole was associated with a specific rain gauge and flow meter to compute its RDI/I hydrograph. Model Calibration Model calibration involves comparison of model-simulated flows to monitored flows in order to adjust model parameters to achieve the best fit to observed data. The DSRSD model was calibrated for both existing dry and wet weather conditions. The dry weather calibration process was used to confirm the overall validity of the BWF factors and diurnal curves, and the wet weather calibration process was used to refine GWI and RDI/I parameters. Once the model was calibrated, it was ready to be applied for simulations of design scenarios, as described below. Design Flow Scenarios The design scenarios defined for this Master Plan Update are: Existing dry weather flow (DWF) Existing design storm wet weather flow (WWF) Future DWF Future design storm WWF The design storm is a 6-hour duration, 20-year frequency rainfall event for the DSRSD service area, as described in Section 2. Existing conditions represent the year 2004; future conditions represent buildout of the service area based on the master plan land use map. Based on discussions with staff of the Cities of Dublin and San Ramon and DSRSD, buildout is expected to occur by about the year Model scenarios (represented by different sets of manhole loadings) were created for each of the above design flow scenarios. For each scenario, the model was run for a three-day weekday simulation, with the design storm event (in the case of the WWF scenarios) occurring on the second day. The resulting peak flows for each scenario at key locations in the system were previously presented in Table 2-7. Model Boundary Conditions Downstream hydraulic boundary conditions for the model are established by the hydraulic gradeline (HGL) at the model outlet. Information from the DSRSD Stage 4 WWTP Improvements design were used for this purpose. The downstream HGL was established at the point where the 48-inch influent line discharges into the headworks upstream of the bar screens. The Stage 4 Improvements plans provide HGLs representing the following three conditions: HGL = at Stage 4 Average Dry Weather Flow of 17.0 mgd HGL = at Stage 4 Equalized Peak Wet Weather Flow of 37.7 mgd (equivalent to an unequalized flow of 60.7 mgd) HGL = at Ultimate Unequalized Peak Wet Weather Flow of 74.0 mgd MWH Page 3-3

5 Section 3 Modeling and Capacity Analysis Note that these flows represent total flows to the DSRSD WWTP, including flows from the City of Pleasanton, so they cannot be directly related to the design flow scenarios for the DSRSD collection system service area. However, for purposes of modeling, the following assumptions were made with respect to the outlet HGL: HGL = for DWF scenarios HGL = for existing WWF scenario HGL = for future WWF scenario CAPACITY ANALYSIS RESULTS The model computes the flows in each pipe in the system at discrete intervals (e.g., every 15 minutes) as the flow is routed through the system. The primary parameter used to evaluate whether a specific pipe has sufficient capacity to handle the predicted flows is the ratio of the flow in the pipe to its full pipe capacity (q/q) at the time that the highest flow occurs. In the case of the WWF scenarios, the highest flow is termed the peak wet weather flow (PWWF). The PWWF may occur at slightly different times for different pipes due to the effect of hydraulic routing in the system. For example, in the three-day (72-hour) WWF simulation with the peak flow from the design storm occurring on the second day coincident with the diurnal peak flow, the PWWF typically occurs at about hour 31 (7 a.m. on the second day) of the model simulation for upstream pipes and about 1 to 1-1/2 hours later for more downstream pipes. Figures 3-2 and 3-3 present maps of the modeled system showing q/q at PWWF under the existing and future WWF scenarios, respectively. Pipes that are colored red (q/q > 1.2) represent significant capacity deficiencies, and pipes that are colored green (q/q > 1.0 but < 1.2) are considered minor (marginal) deficiencies. In some cases, the model indicates capacity deficiencies due to short reaches (one or two manhole-to-manhole pipe segments) of very flat or negative slope. In almost all of these cases, the potential surcharge that might result is very minor; and in many cases, it is likely that there may be an error in pipe invert data in GIS that results in an incorrect calculation of slope and pipe capacity. Table 3-2 summarizes the primary areas of capacity deficiencies in the DSRSD trunk sewer system under WWF conditions. Table 3-3 tabulates the minor deficiencies that are due to one or two pipe segments with flat or negative slopes, as noted above. Note that there are no deficiencies predicted in the system under DWF conditions, other than those caused by pipes with negative slope. Tabular printouts of model results for existing and future conditions are included in Appendix A. The impact of any specific capacity deficiency can be seen by viewing the hydraulic gradeline of the system upstream of that location. If a specific capacity deficiency results in only minor surcharge (e.g., the height of the HGL above the pipe crown is less than about a foot) and/or if the pipe is very deep and therefore not in any significant danger of overflowing, then the capacity deficiency may be considered acceptable. If the deficiency results in significant surcharge, or if the surcharged sewer is relatively shallow (e.g., less than 5 feet deep), then the deficiency is more critical and should be corrected. MWH Page 3-4

6 Dublin Blvd. ³ 0 2,000 4,000 Feet Pine Valley Rd. Alcosta Blvd. PARKS RESERVE FORCES TRAINING AREA I-680 San Ramon Rd. Village Parkway South San Ramon Creek Amador Valley Blvd. Dougherty Rd. CAMP PARKS FEDERAL CORRECTIONS INSTALLATION Arnold Rd. SANTA RITA JAIL Gleason Dr. Tassajara Rd. Central Parkway Fallon Rd. Dublin Blvd. I-580 Legend X WWTP + PWWF > 120% of full pipe capacity PWWF > 100% of full pipe capacity Pipes with zero or negative slope Trunk Sewer Other Sewer Mains Wastewater Treatment Plant Parcels X WWTP + Dublin San Ramon Services District Wastewater Collection System Master Plan Update 2005 PREDICTED CAPACITY DEFICIENCIES UNDER EXISTING PWWF FIGURE 3-2

7 Dublin Blvd. ³ 0 2,000 4,000 Feet Pine Valley Rd. Alcosta Blvd. PARKS RESERVE FORCES TRAINING AREA I-680 San Ramon Rd. 4a 4b Village Parkway South San Ramon Creek Amador Valley Blvd. 2 3 Dougherty Rd. CAMP PARKS FEDERAL CORRECTIONS INSTALLATION Arnold Rd. SANTA RITA JAIL Gleason Dr. Tassajara Rd. Central Parkway Fallon Rd. Dublin Blvd. I-580 Legend PWWF > 120% of full pipe capacity 1 5a X WWTP + PWWF > 100% of full pipe capacity Pipes with zero or negative slope Trunk Sewer Other Sewer Mains Wastewater Treatment Plant Parcels 1 Deficiency No. (See Table 3-2) 5b X WWTP + Dublin San Ramon Services District Wastewater Collection System Master Plan Update 2005 PREDICTED CAPACITY DEFICIENCIES UNDER FUTURE PWWF FIGURE 3-3

8 Section 3 Modeling and Capacity Analysis TABLE 3-2 PREDICTED TRUNK SEWER SYSTEM CAPACITY DEFICIENCIES No. Description US MH DS MH Location 1 Dublin Boulevard West T20D1-1 U20D1-15 Hansen Dr., Dublin Blvd. west of Golden Gate Dr. 2 Dublin Boulevard East V20A2-2 V20A1-3 Dublin Blvd. east of Clark Ave. 3 Dublin Lift Station V20A2-8 V20A2-6 Dublin Blvd. LS and influent sewer 4a Donahue Road/ U19C6-15 U19C4-15 Vomac Rd., Landale Ave., Vomac Road Donahue Dr. Dia. Maxium Surcharge PWWF (mgd) (a) q/q at PWWF (in.) above Crown (ft.) Exist. Future Exist. Future Exist. Future Overflow Comments <1 <1 PWWF exceeds LS firm capacity Overflow Overflow 4b Irving Way U19C4-15 U19C4-6 Irving Way a Dublin Trunk Sewer V21A2-14 V21A2-10 Dublin Trunk Sewer (Commerce Circle area) 5b Dublin Trunk Sewer V21A3-1 TP01 Dubin Trunk Sewer (Johnson Dr./WWTP access road) <1 2 HGL elevated due to WWTP influent water surface level HGL elevated due to WWTP influent water surface level (a) Range from upstream to downstream manhole MWH Page 3-5

9 Section 3 Modeling and Capacity Analysis TABLE 3-3 PIPE SEGMENTS WITH FLAT OR NEGATIVE SLOPE US MH DS MH Location Dia. Length Max. Surcharge at Slope (in.) (ft.) Future PWWF (ft.) Above Crown Below Ground U17D1-8 U17D U18B4-1 U18C U18D1-2 U18D V17A1-1 V17C V19B1-17 V19B V19A2-20 V19A V19A2-2 V19A2-1 Amador Valley Blvd T20B2-12 T20B U19C2-38 U19C U20A1-1 U20B1-28 Amador Valley Blvd U19D2-1 U19C1-13 Amador Valley Blvd U20B1-7 U20B1-4 Village Parkway U20D2-1 V20A1-1 Village Parkway V20A1-1 U20B2-3 Village Parkway V20A1-12 V20A1-8 Clark Avenue V20A2-18 V20A2-14 Sierra Court V19D2-7 V19D2-5 Camp Parks W19C1-11 W19C1-9 Camp Parks V19D2-3 V19D2-2 Camp Parks V20B3-2 V20B3-1 Camp Parks W20C1-23 W20C1-22 Camp Parks V20D2-14 V20D2-12 Camp Parks Trunk V20D2-3 V20D202 Camp Parks Trunk W19D2-2 W19D W20B4-1 W20C1-14 East Dublin Trunk X20A4-2 X2-A4-1 East Dublin Trunk X19C2-1 X19C3-2 Tassajara Road X18D1-20 X18D1-19 Tassajara Road New MH X20B2-10 East Dublin Trunk MWH Page 3-6

10 Section 3 Modeling and Capacity Analysis H2OMAP Sewer profile plots of the primary deficient sewer reaches (those listed in Table 3-2) were reviewed to determine the extent of surcharge caused by each capacity deficiency under future PWWF. Brief discussions of each of these areas and plots showing the model-predicted HGL under future PWWF conditions are presented below. 1. Dublin Boulevard west of I-680 (Figure 3-4). The model indicates that the 8-inch sewer in Dublin Boulevard and Hansen Drive from Golden Gate Drive to upstream to Betlen Drive is capacity deficient under both existing and future PWWF conditions. The model predicts a potential overflow condition in this pipe under future PWWF. This deficiency was also predicted in the 2000 Master Plan Update. However, in the current model, only minor surcharge is predicted in the downstream 10-inch sewer in Dublin Boulevard between I-680 and Golden Gate Drive. 2. Dublin Boulevard east of I-680 (Figure 3-5). The model indicates that the 10-inch sewer in Dublin Boulevard between Clark Avenue and Sierra Court is capacity deficient under both existing and future PWWF conditions. (Note: This segment also includes the 4- and 8-inch double-barrel siphon under the Alamo Canal; however, hydraulic analysis of the siphon pipes indicates that they have adequate capacity for PWWF conditions.) At future PWWF, the maximum predicted surcharge would be 2 to 3 feet above the crown of the pipe and about 5 feet below ground, and extend upstream to the Dublin Boulevard Lift Station. This deficiency was also predicted in the 2000 Master Plan Update. 3. Dublin Lift Station. The model-predicted future PWWF to the lift station is 0.38 mgd under existing conditions and 0.44 mgd in the future. The capacity of the lift station is rated at 0.36 mgd with one pump operating, indicating that the station would not have adequate firm capacity to handle the predicted flows. The 6-inch influent sewer to the lift station is also slightly capacity deficient. (Note that in the model, the lift station was modeled to pass all flow downstream so that the capacity of the downstream system could be accurately evaluated.) The Dublin Lift Station capacity deficiency was also predicted in the 2000 Master Plan Update; however, the projected flows were higher due to the inclusion in the lift station tributary area of the Arroyo Vista development, which has since been diverted to the Camp Parks system. 4. Donahue Drive/Vomac Road/Irving Way (Figure 3-6). The model predicts a significant capacity deficiency and severe surcharge condition (with potential overflows) in the 8-inch sewer in Donahue Drive, Landale Avenue, and Vomac Road from Irving Way upstream to north of Shannon Avenue under both existing and future PWWF. This segment was not predicted to be capacity deficient in the 2000 Master Plan Update. However, this sewer serves the area tributary to flow meter 10, which indicated a higher RDI/I contribution than most other areas of the DSRSD system. The model also predicts a capacity deficiency in the 10-inch sewer in Irving Way from Donahue Drive to Ironwood Drive. 5. Dublin Trunk Sewer (Figure 3-7). Several sections of the 36- through 42-inch main Dublin Trunk from the end of Village Parkway downstream to the entrance to the WWTP are predicted to be capacity deficient under future PWWF conditions (under existing PWWF, the surcharge would be minimal). This section of the trunk is impacted by the HGL at the MWH Page 3-7

11 FIGURE 3-4 DUBLIN BOULEVARD WEST SEWER (VILLAGE PARKWAY TO SILVERGATE DRIVE) HYDRAULIC GRADELINE AT FUTURE PWWF Hansen Drive Betlen Drive " Elevation (ft.) Golden Gate Drive Village Pkwy. 8" " 18" ,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 Distance (ft.) Ground HGL Pipe Crown Pipe Invert

12 FIGURE 3-5 DUBLIN BOULEVARD EAST SEWER (CLARK AVENUE AT VILLAGE PARKWAY TO DUBLIN BOULEVARD AT SCARLETT COURT) HYDRAULIC GRADELINE AT FUTURE PWWF Dublin Blvd. at Clark Ave. Sierra Ct. Village Pkwy. Dublin Blvd. Lift Station Scarlett Ct. 330 Elevation (ft.) " 15" 10" 4" & 8" siphons under Alamo Canal 4" force main 315 6" 10" ,000 1,500 2,000 2,500 3,000 Distance (ft.) Ground HGL Pipe Crown Pipe Invert

13 FIGURE 3-6 DONAHUE DRIVE/VOMAC ROAD SEWER (I-680 EASEMENT AT DUBLIN BOULEVARD TO VOMAC ROAD AT SAN RAMON ROAD) HYDRAULIC GRADELINE AT FUTURE PWWF San Ramon Rd. 380 Elevation (ft.) Amador Valley Blvd. Dublin Blvd. Irving Way Vomac Road Donahue Drive 8" " 12" 18" ,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000 Distance (ft.) Ground HGL Pipe Crown Pipe Invert

14 FIGURE 3-7 DUBLIN TRUNK SEWER (WWTP TO VILLAGE PARKWAY AT DUBLIN BOULEVARD) HYDRAULIC GRADELINE AT FUTURE PWWF Dublin Blvd. 330 Elevation (ft.) WWTP HGL ' Camp Parks Trunk Connection 33" Alamo Creek Crossing 36" " " 42" ,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000 7,500 Distance (ft.) Ground HGL Pipe Crown Pipe Invert

15 Section 3 Modeling and Capacity Analysis WWTP headworks, as shown on the hydraulic profile. The more significant deficiency is in the 42-inch sewer downstream of the Camp Parks trunk connection; the deficiency is less critical upstream, where the HGL is roughly parallel to the pipe. However, if the WWTP influent HGL were lower, the surcharge in the trunk, even in the downstream segments, would be fairly minimal. It should be noted that the model indicates that the 33-inch exposed crossing of Alamo Creek just north of I-580, which the District has planned to replace with a triple-barrel inverted siphon in a new alignment, is not predicted to be a capacity problem. PRELIMINARY SOLUTIONS FOR CAPACITY DEFICIENCIES Preliminary solutions to the predicted capacity deficiencies are described below. These solutions were incorporated into the hydraulic model to verify the size and extent of required relief pipes. The next section of the Master Plan Update report provides more detailed discussion of proposed capacity relief projects. 1. Dublin Boulevard west of I-680. Upsizing the existing 8-inch sewer is the obvious solution to this capacity deficiency. A 10-inch pipe would be adequate to handle the predicted PWWF. An alternative to upsizing the portion of the deficient reach in Hansen Drive would be to divert all or a portion of the flow at Silvergate Drive into a new 8-inch sewer in Dublin Boulevard, connecting into the upsized line at Hansen Drive. This alternative was recommended in the 2000 Master Plan Update. 2. Dublin Boulevard east of I-680. Upsizing the existing 10-inch to a 12-inch pipe would address this capacity deficiency. 3. Dublin Lift Station. A pump station capacity expansion would be needed to provide the required 0.44 mgd firm capacity for ultimate PWWF. 4. Donahue Drive/Vomac Road. Since the existing alignment is all in street rights-of-way, the obvious solution is to upsize the existing sewers. A 10-inch pipe would be adequate to handle the predicted PWWF. 5. Dublin Trunk Sewer. A parallel 36-inch pipe from the Camp Parks trunk connection to the 48-inch WWTP influent sewer would provide capacity relief for the 42-inch trunk. The relief pipe would be sized to divert all of the flow from the Camp Parks trunk. The remaining minor surcharge in the upstream portions of the main Dublin trunk (between Village Parkway and the Camp Parks trunk connection) was determined to be acceptable. MWH Page 3-8