section 2 land use projections and design flows

Section 2Land Use Projections and Design Flows

MWH Page 2-1

This section of the Master Plan Update report presents the basis of the land use and design flowsfor the DSRSD wastewater service area. The flows were used in the hydraulic model to evaluatethe capacity requirements of the trunk sewer system. More detailed discussion of the land useand design flow criteria used for this Master Plan Update are presented in TM 2 – Land UsePlanning Criteria, TM 3 – Design Flow and Hydraulic Criteria, and TM 4 – Wastewater FlowProjections, included in the separately bound appendices to this report.

LAND USE PROJECTIONS

Land use data form the basis for estimating wastewater flows in the sewer system. Land use datawithin the District’s study area are based on a number of planning documents, including theGeneral Plans of the Cities of Dublin and San Ramon; development plans for the Schaefer Ranchdevelopment in western Dublin and the East Dublin Property Owners (EDPO) development, nowknown as Fallon Village, in eastern Dublin; the redevelopment plan for the Parks Reserve ForcesTraining Area (Parks RFTA or Camp Parks); and the Alameda County East County Area Plan,which includes the Santa Rita Jail and adjacent County properties.

In coordination with the District’s Water System Master Plan Update, a digital land use mapwhich incorporates the land use mapping from all relevant planing documents was developed forthis study. For purposes of the digital land use mapping, land use categories for the variousjurisdictions within the District’s service area were grouped into 20 land use categories. Thesecategories were intended for use for both the wastewater collection system and water distributionsystem master plans (a few of the categories do not occur in the wastewater service area). Forthe wastewater service area, the digital land use map, shown in Figure 2-1, depicts the land usesrepresented in the General Plans of the Cities of Dublin and San Ramon (including the latestEastern Dublin and Westside San Ramon Specific Plans), the latest development plans forSchaefer Ranch and the EDPO area available at the time of this study, and the Camp ParksProposed Future Development Plan (FDP) map dated May 2004. Note that except for SchaeferRanch, no proposed development in western Dublin is included in this Master Plan Update.

For the wastewater collection system, the land use categories were combined into 10consolidated categories for purposes of developing wastewater flow estimates. Each land usecategory is categorized by a typical density or range of densities, expressed as a dwelling unit(DU) density (DUs per acre) for residential land uses or a floor area ratio (FAR) for non-residential uses, based on gross area. Each category has also been assigned a “design” densityfor purposes of calculating future wastewater flows. For residential categories, the typicalexisting net density (based on existing parcel sizes) is also shown. The consolidated land usecategories and densities are listed in Table 2-1. Use of these density values in computing basewastewater flows is discussed later in this section.

Discussions were held with city and District staff to identify the expected timing of developmentfor various portions of the study area, and specifically to identify areas anticipated to bedeveloped within the next 5- and 10-year periods. This information was used to develop

³

Dublin San Ramon Services DistrictWastewater Collection System

Master Plan Update 2005

PLANNED LAND USES

0 4,0002,000Feet

FIGURE 2-1

CAMPPARKS

FEDERALCORRECTIONSINSTALLATION

SANTA RITA JAIL

PARKS RESERVE FORCESTRAINING AREA

Dublin Blvd.

San Ram

on Rd.

I-680

Pine Valley Rd.

Alc

osta

Blv

d.

Amador Valley Blvd.

South San Ramon Creek

Villa

ge P

arkw

ay

I-580

Dou

gher

ty R

d.

Dublin Blvd.

Arn

old

Rd.

Tass

ajar

a R

d.

Fallon Rd.Gleason Dr.

Central Parkway

LegendStudy Area Boundary

County Line

Residential - Low (2.1 to 5.9 du/acre)

Residential - Medium (8.0 to 12.0 du/acre)

Residential - Medium High (13.0 to 27.0 du/acre)

Residential - High (> 27.0 du/acre)

Mixed Use (FAR: 0.75)

Commercial - Retail (FAR: 0.35)

Commercial - Office (FAR: 0.35)

Industrial - Business Park (FAR: 0.30)

Public - Public/Semi-Public (FAR: 0.25)

Public - Elementary School

Public - Middle School

Public - High School

Public - Jail

Open Space - City Park/Community Center

Open Space - Neighborhood Park

Open Space - Golf Course

Open Space - Open Space

City Boundary Lines

Jails

Parcels

Section 2 – Land Use Projections and Design Flows

MWH Page 2-2

estimates of projected wastewater flows and dwelling unit equivalents (DUEs) for 2010, 2015,and 2020, as presented later in this section. For this Master Plan Update, buildout is assumed tooccur by the year 2020.

TABLE 2-1CONSOLIDATED LAND USE CATEGORIES AND DENSITIES

Density (a)Category Range (b) Existing (c) Design (d)

LDR Low density residential 2.1 - 5.9 5 4LMDR (e) Low-medium density residential 6 - 7.9 -- 7MDR Medium density residential 8 – 12 9 10MHDR Medium-high density residential 13 - 27 20 (f) 20HDR High density residential >27 35 (f) 35MIXED Mixed use 0.75 0.75COM_OFF Commercial, retail and offices 0.35 0.35IND_BUS Industrial, business parks 0.30 0.30PUBLIC Schools, churches, public buildings 0.25 0.25OPEN Parks, open space 0 0

OTHER (g) Parks RFTA (existing development),FCI, and Santa Rita -- -- --

(a) Dwelling units per acre for residential categories; floor area ratio for non-residential categories.(b) Range based on the General Plans of Cities of Dublin and San Ramon (see Table 2-1)(c) Typical existing densities in service area, based on net parcel area.(d) Average of proposed densities in service area, based on gross area; to be applied to large parcels

(greater than 2 acres in size).(e) No LMDR land use is shown on the land use map in the DSRSD wastewater service area.(f) Could not be determined; assumed same as design values.(g) Large institutional customers; wastewater flows based on actual water usage.

WASTEWATER FLOW COMPONENTS

Wastewater flows are composed of several components, termed base wastewater flow (BWF),groundwater infiltration (GWI), and rainfall-dependent infiltration/inflow (RDI/I). The lattertwo components are collectively referred to as infiltration/inflow (I/I). Figure 2-2 illustrates atypical 24-hour hydrograph (graph of flow over time) showing the wastewater flow components.

Base wastewater flow is the sanitary flow contribution from residential, commercial, industrial,and institutional users. BWF is determined by type of land use and is affected by service areagrowth and development. BWF may also be impacted by water use practices such as waterconservation. Base wastewater flows vary in magnitude throughout the day but generally followpredictable diurnal patterns.


MWH Page 2-3

FIGURE 2-2WASTEWATER HYDROGRAPH COMPONENTS

Flow

Rainfall

Time(24 Hours)

RDI/I

BWF

GWI

Infiltration/inflow consists of groundwater and storm water runoff that enter the collectionsystem through defects in sewer pipelines, manholes, and service laterals, or in some casesthrough direct connections. GWI is groundwater that enters the sewer system through cracks anddefective joints in pipes and manhole walls. The magnitude of GWI depends on the condition ofthe sewers as well as on the depth of the groundwater table with respect to the local sewersystem. Therefore, GWI is highly dependent on location and topography, with sewers in low-lying areas typically exhibiting higher GWI rates. GWI varies seasonally (lowest in summer andearly fall, highest in late winter and spring), as well as from year to year depending on rainfallpatterns, but may not vary significantly on a day-to-day basis. For purposes of defining designflows for wastewater system planning, GWI is considered to be infiltration that occurs duringnon-rainfall periods to distinguish it from RDI/I. However, rainfall clearly has long-termimpacts on GWI rates, as evidenced by measurable increases in dry weather GWI afterprolonged periods of rainfall.

RDI/I is infiltration and inflow that is directly related to rainfall events. RDI/I may enter thesewer system through pipe and manhole defects, as well as through direct surface drainageconnections such as illegally connected roof and yard drains or storm drain cross connections.The magnitude of RDI/I flows is related to the intensity and duration of the rainfall, the relativesoil moisture at the time of the rainfall event, the condition of the sewers, and other factors. Inmost areas, peak flows during rainfall events are the highest flow rates that occur in thecollection system.


MWH Page 2-4

DEVELOPMENT OF DESIGN WASTEWATER FLOWS

For developing design flows for wastewater collection system planning, criteria must bespecified for each component of wastewater flows. Wastewater flow and water use data wereused to develop design flow criteria for the Master Plan Update. The wastewater flow data wereobtained from the flow monitoring program conducted as part of this study from mid-Januarythrough mid-March 2004, in which 23 flow meters and 4 rain gauges were placed throughout theDSRSD collection system. Figure 2-3 shows the location of the flow meters and the incrementalarea tributary to each meter. (A flow monitoring report prepared by E2 Consulting Engineers,flow monitoring subconsultant to MWH, has been provided to the District as a separatedeliverable. The report includes plots and summary tables of all of the flow and rainfall datacollected during the flow monitoring program.) The flow monitoring data collected in 2004were supplemented by limited flow data from several other meters previously placed by theDistrict at strategic locations, specifically to measure flows from Camp Parks, Santa Rita Jail,and on the main Dublin Trunk Sewer to the wastewater treatment plant.

For purposes of developing flow inputs to the hydraulic model, the DSRSD wastewater servicearea was divided into approximately 150 sewer subbasins, each representing a “load point” to themodeled trunk sewer network. Design wastewater flows were aggregated by subbasin forloading into the model. The sewer subbasin are shown in Figure 2-4. Note that a small area ofthe City of Pleasanton in the vicinity of Commerce Circle is tributary to the lower Dublin TrunkSewer and was therefore included as a sewer subbasin (PL) for purposes of loading flows to thehydraulic model. The concepts, methodologies, and information used to develop BWF, GWI, and RDI/I flows forthis Master Plan Update and the use of the flow monitoring data to verify design flows arediscussed in the paragraphs below.

Base Wastewater Flow

Base wastewater flow (BWF) consists of residential, commercial, industrial, and institutionalflow contributions. Theoretically, BWF excludes extraneous flow from groundwater orstormwater runoff. However, from a practical standpoint, it is difficult to separate BWF fromgroundwater infiltration during dry weather; therefore, BWF estimates generally include someamount of dry weather GWI.

BWF criteria are based on type of land use, since different land uses contribute wastewater flowsat different rates. BWF can be computed for different areas of the collection system byquantifying the land use areas (in acres) and then applying unit flow factors (in gallons per dayper acre) that represent the characteristic wastewater contribution from each land use type.Alternately, BWF can be calculated by tabulating actual numbers of dwelling units (DUs) orpopulation and applying unit flow factors expressed as gallons per day (gpd) per DU or percapita, with non-residential BWF calculated on the basis of flow per square foot of buildingspace. If water consumption data are available, BWF can also be calculated based on winterwater use, when outside irrigation is minimal.

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FLOW MONITOR LOCATIONSAND METER AREAS

0 3,9001,950Feet

FIGURE 2-3

CAMPPARKS

FEDERALCORRECTIONSINSTALLATION SANTA RITA JAIL

PARKS RESERVE FORCESTRAINING AREA

Dublin Blvd.

San Ram

on Rd.

I-680

Pine Valley Rd.

Alc

osta

Blv

d.

Amador Valley Blvd.


Villa

ge P

arkw

ay

I-580

Dou

gher

ty R

d.

Dublin Blvd.

Arn

old

Rd.

Tass

ajar

a R

d.


Central Parkway

Legend#* Flow Meters

Flow Meter Area

Modeled Sewer

Parcels

M01

M02

M03

M04

M05

M06

M07M08

M09

M10

M11 M12

M13M14

M15

M16

M17

M18

M19

M20

M21

M22

M23

CP21

CP-FT CP20

ED9B

S RANCH

SE20

ED9A

SW4

DE12

PL

SE15

ED10-1

CP-1

SE24

ED6P

DE3

ED6W

ED3C

SE16B

ED6Z

SE14

DW21B ED8B

ED6M

ED6X2

SW2

ED6N

DE23

DE18

SE13SW5

CP-6

ED2A

DE4

SE18A

SE23

SE8

DW14

SE18B

SE10

DW24

SE21

DE6

ED10-2D

SE19

DW31

ED10-2A

SE17A

ED10-2E

ED6Q

DW1

ED10-2B

ED6R ED8DDE2

DW13

SE12

DE11

SE6A

DE9

ED6X1

ED8C

DW30

SE7

CP-8

ED6S

ED6C

ED2D

SE5

DE22

DW2

DE1

DW21A

DE20

SANTA RITA

ED2B

DE13

CP-9

CP-5

DE19

DE15

DE17

ED10-2H

ED6A

DE8

DW5

SE3

DW10

SW6

ED6F

ED3A

SW1

ED5A

DW28

DW3

DE10

ED8E

DE14

ED6I

SE2

ED10-2G

DE21

DW25

ED6L

ED6U

SE6B

ED8AED2N1

DE7

DW17ED2KED2L

DW23ED3B

ED7

DE5

DW9

SE9B

ED10-2F

SE9A

CP-2

DW11

DW22

DW15 ED2G

ED2I

ED6G

SE17B

ED2H

SE22

ED2F

DW29

ED6J

DW16

DE16

CP-7

ED2M

ED6HDW26

SE4

ED6T

DW4

ED2N2

DW12

DW20

DW6

ED2J

DW7

SW3

SE1

CP-13

CP-14

DW18

CP-12

DW27

ED6E

ED2C

ED6D

CP-10

ED10-2C

ED2Q

ED6K

DW19

DW8

CP-11

SE16A

³



SEWER SUBBASINS

0 4,0002,000Feet

FIGURE 2-4

Dublin Blvd.

San Ram

on Rd.

I-680

Pine Valley Rd.

Alc

osta

Blv

d.

Amador Valley Blvd.


Villa

ge P

arkw

ay

I-580

Dou

gher

ty R

d.

Dublin Blvd.

Arn

old

Rd.

Tass

ajar

a R

d.


Central Parkway

LegendSubbasins

Parcels


MWH Page 2-5

For this study, water consumption data for the year 2003 were obtained from DSRSD forcustomers located within the City of Dublin, and for the year 2002 from the East Bay MunicipalUtility District (EBMUD) for customers located within the City of San Ramon. The DSRSDdata included a database of bi-monthly water consumption by customer account; the EBMUDdata included monthly total consumption by user category for major categories of users and alisting of customer accounts for the portion of San Ramon included in the DSRSD wastewatersystem. Water use data were also obtained from DSRSD for large users, specifically the ParksRFTA, the Federal Corrections Installation (FCI) located on Camp Parks, and Santa Rita Jail.

Because water meters are read bimonthly on an on-going basis, the consumption and customercounts for each month may represent different groups of users and different periods of time.However, an average of the per-customer consumption for the winter months can be used toapproximate the average winter water usage in the system.

As discussed previously, 10 consolidated categories were used for purposes of developing BWFestimates for this Master Plan Update. The water accounts in the DSRSD and EBMUDdatabases were linked to actual parcels in GIS to determine parcel acreage and associated landuse category. Using this information in conjunction with the winter water use data, typical BWFunit factors were computed for the various land use categories, as summarized in Table 2-2.

TABLE 2-2BASE WASTEWATER FLOW UNIT FACTORS

BWF Factor(gpd/unit)

Land Use Category Unit Existing (a) Design (b)LDR Low density residential DU 220 220LMDR Low-medium density residential DU 220 220MDR Medium density residential DU 190 190MHDR Medium-high density residential DU 140 140HDR High density residential DU 140 140MIXED Mixed use acres 900 1,500COM_OFF Commercial, retail and offices acres 900 1,500IND_BUS Industrial, business parks acres 900 1,300PUBLIC Schools, churches, public buildings acres 200 1,000OPEN Parks, open space acres 0 0OTHER Parks RFTA (existing development),

FCI, and Santa Rita-- (c) (c)

(a) Based on analysis of existing DSRSD water use data; existing factors provide reasonable overall fitto total dry day wastewater flows as measured during 2004 flow monitoring period.

(b) Proposed design BWF factors for non-residential land uses are based on design FAR and assumedunit flow rate of 0.1 gpd/square feet.

(c) For large institutional customers, BWF estimates were based on actual water usage (see Table 2-3for these values).


MWH Page 2-6

The BWF unit factors required to achieve a reasonable fit between the calculated and measuredflows in the system differ somewhat from the proposed design values. In particular, the existingnon-residential unit flows shown in Table 2-2 are considerably lower than the proposed designvalues. For planning purposes, use of the higher values for projecting future wastewater flow wasused to account for the potential for additional infill and densification in developedcommercial/industrial areas and potentially higher intensity uses in new development. Theproposed design values are very similar to those used for the 2000 Wastewater Collection SystemMaster Plan. For large institutional users, specifically existing development on Camp Parks (including the FCI)and Santa Rita Jail, BWF was estimated based on actual measured winter water use. For thebuildout scenario, however, BWF estimates for Camp Parks (excluding the FCI) were based onthe design unit flow factors applied to the land uses shown on the Parks RFTA Proposed FutureDevelopment Plan. The BWF factors were applied to each parcel in the wastewater service area based on its existingand projected land use. The parcel flows were then aggregated by sewer subbasin. Table 2-3lists the average BWF for each sewer subbasin for existing and buildout conditions, along with abreakdown of residential and non-residential flows and total sewered (developed) area. Diurnal Flow Variations. In domestic wastewater systems, BWF varies throughout the day in atypical way, generally peaking early in the morning in upstream sewers and later and less sharplyin larger downstream sewers. Typical hourly flow peaks from residential areas tend to be 1-1/2to 2 times the average flow. BWF patterns in commercial and industrial areas are determined bythe type of uses but are typically characterized by more gradual elevated flows over extendedperiods of time during the middle of the day. For both residential and non-residential areas, thereare also differences between typical weekday and weekend diurnal flow patterns.

When a “dynamic” analysis of the collection system is conducted, the peak flows are determinedby routing the diurnal BWF hydrographs through the collection system using a computer model(the computer modeling conducted for this Master Plan Update is discussed in Section 3 of thereport). Therefore, it is only necessary to define the daily flow relationships, or “diurnal curves”,for each area contributing flow to the collection system. Diurnal curves are generally defined fortypical residential and commercial/industrial areas and, if necessary, for any special or atypicalusers such as industries or major institutions. For example, the Camp Parks, FCI, and Santa RitaJail are areas that may have unique diurnal flow patterns that would need to be definedspecifically for collection system modeling. Diurnal curves are typically defined by 24 values,each representing the ratio of the hourly to average daily BWF.

For this study, diurnal curves were developed based on the flow monitoring data. The diurnalcurves used for the Master Plan Update are shown in Figure 2-5.


MWH Page 2-7

TABLE 2-3

PROJECTED BASE WASTEWATER FLOWS BY SEWER SUBBASIN

Developed

Subbasin Resid. Non-Resid. Total Resid. Non-

Resid. Total Area at Buidout (ac.) Notes

DE1 0.031 0.031 0.047 0.047 34.1DE2 0.012 0.012 0.018 0.018 24.0DE3 0.048 0.061 0.109 0.048 0.089 0.137 85.1DE4 0.031 0.035 0.066 0.031 0.055 0.085 49.7DE5 0.051 0.051 0.051 0.051 26.9DE6 0.036 0.036 0.056 0.056 39.5DE7 0.024 0.024 0.035 0.035 26.2DE8 0.037 0.001 0.038 0.037 0.001 0.038 30.2DE9 0.047 0.001 0.048 0.047 0.001 0.048 36.5

DE10 0.022 0.020 0.042 0.022 0.033 0.056 37.6DE11 0.071 0.071 0.071 0.071 46.1DE12 0.082 0.082 0.082 0.082 52.9DE13 0.046 0.001 0.047 0.046 0.001 0.047 26.9DE14 0.051 0.051 0.051 0.051 26.8DE15 0.069 0.069 0.069 0.069 25.8DE16 0.046 0.046 0.046 0.046 11.9DE17 0.035 0.005 0.040 0.035 0.008 0.043 34.6DE18 0.087 0.002 0.090 0.087 0.002 0.090 75.6DE19 0.049 0.049 0.049 0.049 38.2DE20 0.053 0.053 0.053 0.053 40.2DE21 0.009 0.009 0.009 0.009 44.6DE22 0.066 0.001 0.067 0.066 0.002 0.068 43.9DE23 0.082 0.003 0.085 0.082 0.003 0.085 74.2DW1 0.047 0.047 0.078 0.078 52.3DW2 0.040 0.040 0.066 0.066 46.0DW3 0.033 0.033 0.054 0.054 36.2DW4 0.015 0.015 0.025 0.025 16.9DW5 0.069 0.005 0.075 0.069 0.009 0.078 30.8DW6 0.013 0.013 0.019 0.019 14.1DW7 0.016 0.001 0.016 0.016 0.001 0.017 13.6DW8 0.014 0.014 0.014 0.014 12.9DW9 0.028 0.028 0.028 0.028 25.2

DW10 0.007 0.007 0.007 0.007 35.4DW11 0.035 0.035 0.037 0.037 1.9DW12 0.024 0.024 0.024 0.024 20.2DW13 0.042 0.042 0.042 0.042 35.8DW14 0.028 0.060 0.088 0.028 0.100 0.128 77.8DW15 0.042 0.042 0.042 0.042 32.6DW16 0.033 0.033 0.033 0.033 25.5DW17 0.061 0.061 0.061 0.061 32.1DW18 0.034 0.034 0.034 0.034 27.6DW19 0.011 0.002 0.013 0.011 0.002 0.013 19.0DW20 0.055 0.055 0.055 0.055 23.0

DW21A 0.015 0.015 0.015 0.015 12.9DW21B 0.010 0.010 0.010 0.010 9.0

Existing Average BWF (mgd) Future Average BWF (mgd)


MWH Page 2-8

TABLE 2-3 (continued)


Developed



DW22 0.034 0.034 0.034 0.034 29.8DW23 0.038 0.038 0.038 0.038 32.7DW24 0.062 0.062 0.062 0.062 54.4DW25 0.029 0.003 0.033 0.029 0.003 0.033 38.4DW26 0.010 0.002 0.012 0.010 0.002 0.012 17.3DW27 0.022 0.022 0.022 0.022 18.8DW28 0.044 0.005 0.049 0.044 0.008 0.052 39.2DW29 0.028 0.028 0.028 0.028 25.4DW30 0.064 0.064 0.064 0.064 57.1DW31 0.034 0.013 0.046 0.034 0.021 0.055 44.9

SE1 0.031 0.031 0.031 0.031 24.6SE2 0.033 0.033 0.033 0.033 27.3SE3 0.044 0.044 0.044 0.044 18.3SE4 0.029 0.029 0.029 0.029 11.4SE5 0.048 0.011 0.059 0.048 0.018 0.066 36.3

SE6A 0.052 0.002 0.055 0.052 0.002 0.055 55.0SE6B 0.040 0.040 0.040 0.040 34.5SE7 0.027 0.027 0.027 0.027 15.6SE8 0.058 0.058 0.058 0.058 50.8

SE9A 0.040 0.040 0.040 0.040 33.6SE9B 0.025 0.003 0.028 0.025 0.003 0.028 35.6SE10 0.043 0.005 0.048 0.043 0.005 0.048 59.8SE12 0.063 0.063 0.063 0.063 51.6SE13 0.072 0.002 0.074 0.072 0.002 0.074 70.0SE14 0.065 0.008 0.073 0.065 0.008 0.073 94.1SE15 0.108 0.005 0.112 0.108 0.008 0.115 54.5

SE16A 0.008 0.008 0.008 0.008 6.8SE16B 0.044 0.044 0.044 0.044 39.6SE17A 0.041 0.041 0.041 0.041 36.1SE17B 0.033 0.033 0.033 0.033 25.8SE18A 0.021 0.009 0.030 0.021 0.009 0.030 61.4SE18B 0.011 0.011 0.011 0.011 10.0SE19 0.070 0.070 0.070 0.070 57.8SE20 0.083 0.083 0.083 0.083 75.2SE21 0.021 0.021 0.021 0.021 19.0SE22 0.027 0.027 0.027 0.027 15.4SE23 0.051 0.051 0.051 0.051 38.8SE24 0.061 0.061 0.061 0.061 54.1SW1 0.030 0.030 0.030 0.030 26.5SW2 0.000 0.000 0.0SW3 0.002 0.002 0.002 0.002 8.1SW4 0.062 0.001 0.063 0.062 0.001 0.063 51.4SW5 0.052 0.000 0.052 0.052 0.000 0.052 37.4SW6 0.054 0.054 0.054 0.054 25.6



MWH Page 2-9



Developed



ED2A 0.000 0.121 0.121 80.6ED2B 0.048 0.048 0.080 0.080 53.4ED2C 0.024 0.024 0.040 0.040 26.6ED2D 0.042 0.042 0.070 0.070 46.8ED2F 0.030 0.030 0.043 0.043 32.8ED2G 0.015 0.021 0.036 0.015 0.030 0.045 30.4ED2H 0.056 0.013 0.069 0.056 0.026 0.081 29.7ED2I 0.060 0.060 0.060 0.060 19.0ED2J 0.024 0.024 0.024 0.024 9.0ED2K 0.036 0.002 0.038 0.036 0.002 0.038 33.6ED2L 0.025 0.025 0.025 0.025 0.3ED2M 0.035 0.035 0.035 0.035 17.8ED2N1 0.019 0.019 0.019 0.019 7.7ED2N2 0.000 0.000 0.0ED2Q 0.016 0.016 0.027 0.027 17.8ED3A 0.000 0.043 0.043 43.1ED3B 0.000 0.038 0.038 38.3ED3C 0.000 0.229 0.229 120.6ED5A 0.005 0.005 0.167 0.008 0.175 40.3ED6A 0.055 0.055 0.063 0.063 29.6ED6C 0.045 0.045 0.045 0.045 30.6ED6D 0.021 0.021 0.021 0.021 14.9ED6E 0.024 0.024 0.024 0.024 9.7ED6F 0.044 0.002 0.046 0.044 0.002 0.046 36.0ED6G 0.030 0.030 0.030 0.030 19.8ED6H 0.026 0.000 0.026 0.030 0.021 0.051 33.9ED6I 0.000 0.029 0.029 29.2ED6J 0.003 0.003 0.041 0.041 31.2ED6K 0.000 0.025 0.017 0.043 19.3ED6L 0.000 0.054 0.001 0.055 29.2ED6M 0.000 0.137 0.008 0.145 80.8ED6N 0.000 0.025 0.025 8.9ED6P 0.000 0.061 0.123 0.184 97.4ED6Q 0.000 0.048 0.068 0.116 58.1ED6R 0.000 0.101 0.057 0.158 65.5ED6S 0.000 0.014 0.045 0.059 37.4ED6T 0.000 0.000 0.0ED6U 0.046 0.046 0.047 0.047 27.9ED6W 0.058 0.058 0.058 0.006 0.064 49.4ED6X1 0.000 0.026 0.026 13.6ED6X2 0.035 0.035 0.035 0.035 30.7ED6Z 0.000 0.000 0.0ED7 0.018 0.018 0.048 0.048 25.2



MWH Page 2-10



Developed



ED8A 0.000 0.038 0.020 0.058 30.0 1ED8B 0.000 0.063 0.050 0.113 60.7 1ED8C 0.000 0.081 0.081 56.3 1ED8D 0.000 0.080 0.080 53.4 1ED8E 0.000 0.059 0.059 45.5 1ED9A 0.007 0.007 0.188 0.014 0.202 98.6ED9B 0.000 0.066 0.066 32.3

ED10-1 0.000 0.040 0.040 44.5ED10-2A 0.000 0.000 0.0 1ED10-2B 0.000 0.084 0.084 95.1 1ED10-2C 0.000 0.009 0.009 9.8 1ED10-2D 0.000 0.032 0.032 35.1 1ED10-2E 0.000 0.101 0.101 102.6 1ED10-2F 0.000 0.027 0.027 30.4 1ED10-2G 0.000 0.051 0.051 58.3 1ED10-2H 0.000 0.067 0.002 0.069 78.1 1

CP-1 0.004 0.004 0.190 0.190 126.5 2CP-2 0.005 0.005 0.054 0.054 51.5 2CP-5 0.034 0.034 0.050 0.050 51.1 2CP-6 0.207 0.207 0.000 0.207 0.207 81.3 3CP-7 0.012 0.012 0.029 0.029 29.1 2CP-8 0.042 0.042 0.040 0.034 0.074 53.8 2CP-9 0.003 0.003 0.081 0.081 55.5 2

CP-10 0.003 0.003 0.049 0.003 0.052 28.9 2CP-11 0.001 0.001 0.000 0.030 0.030 27.3 2CP-12 0.013 0.013 0.023 0.010 0.034 22.6 2CP-13 0.005 0.005 0.002 0.038 0.040 38.8 2CP-14 0.009 0.009 0.023 0.010 0.032 21.6 2CP20 0.000 0.000 0.0CP21 0.000 0.000 0.0CP-FT 0.000 0.000 0.0

SANTA RITA 0.511 0.511 0.511 0.511 134.5 4S RANCH 0.000 0.064 0.064 70.0 5

PL 0.100 0.100 0.100 0.100 90.0 6

Total 0.01 0.95 0.96 0.97 1.65 2.62 1,713

4. Santa Rita Jail. Existing BWF based on winter water use; no increase projected for future.5. Schaefer Ranch. Future BWF based on current development plans (292 single family residential units).6. Area of Pleasanton (Commerce Circle) tributary to Dublin Trunk Sewer south of I-580. BWF based on typical industrial flow factors.

1. EDPO (Fallon Village) area. Flows are based on preliminary land use mapping. Updated projections as of early 2005 are slightly higher.2. Existing BWF based on current Camp Parks winter water use allocated to subbasins based on distribution used in 2000 Master Plan Update. Future BWF based on future development plan land use mapping.3. Federal Corrections Installation. Existing BWF based on winter water use; no increase projected for future.


FIGURE 2-5DSRSD DESIGN DIURNAL CURVES

0.0

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Residential Weekday Residential Weekend Commercial/Industrial Santa Rita Camp Parks/FCI


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Typical weekday and weekend residential BWF diurnal curves were developed based on datafrom upstream flow meters in residential portions of the collection system (Meters 2, 4, 5, 9, 10,11, and 15). These curves illustrate a very typical residential diurnal flow pattern, with aweekday peak hour flow of almost two times the average daily BWF occurring around 7 a.m. inthe morning and a second lower peak occurring around 7 p.m. in the evening. The weekenddiurnal curve shows a similar pattern, but the morning peak occurs later and is not as high as theweekday peak. Because there was only limited meter data representing a predominantly non-residential area(Meter 16), a single diurnal curve was used, as shown in the figure. Diurnal flow patterns werealso developed for Santa Rita Jail and Camp Parks/FCI based, respectively, on flow meter datafrom 2004 for Meter 20 and from 2003 data from the previous meter (D2) installed by theDistrict at Camp Parks.

Groundwater Infiltration

Groundwater infiltration criteria are generally based on actual flow monitoring data, since it isdifficult to predict GWI rates based on physical system data alone. In the context of design flowcriteria, GWI represents the incremental groundwater infiltration that occurs during the wetweather season above the “baseline” dry weather infiltration level during the driest months of theyear. The baseline dry weather groundwater infiltration is assumed to be included in the BWFfactors (see previous discussion of Base Wastewater Flow).

GWI can be estimated based on minimum flows during non-rainfall periods during a wet weatherflow monitoring period. Minimum flows typically occur during the nighttime or early morninghours when base wastewater flows are at a low. Alternately, GWI can be estimated as thedifference between average metered flow during non-rainfall periods and computed average BWFbased on applying BWF unit flow factors to the land uses in the meter tributary area. In eithercase, the resulting GWI is expressed on a unit basis (gpd/acre or gpad) by dividing by the seweredacreage of the monitored area. Typical GWI rates may range from 100 to 1,000 gpad.

GWI flows were estimated through the model calibration process by comparing model-simulatedbase wastewater flows to actual flow measurements from the temporary flow monitoringprogram conducted in January through March 2004. Cases where model-predicted basewastewater flows were noticeably lower than monitored flows indicated the possible occurrenceof GWI. Two areas of the system, tributary to flow Meters 1 and 4 (areas M01 and M04 inFigure 2-3) in San Ramon, respectively, were identified as having GWI based on the modelcalibration. For these areas, estimates were made for “low GWI” (based on calibration to flowsduring the dry period in late January 2004) and “high GWI” (based on calibration to mid-February flows). In this case, “low GWI” is intended to represent a typical winter seasoncondition not impacted by recent antecedent rainfall, whereas “high GWI” is intended torepresent more saturated soil conditions. While winter season GWI likely does occur in otherparts of the system, the model calibration indicated that the BWF factors are sufficient to accountfor the smaller GWI flows in these areas. The GWI unit factors applied to the subbasins in theMeters 1 and 4 tributary areas are listed in Table 2-4.


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TABLE 2-4GROUNDWATER INFILTRATION RATES

Meter Area Subbasins Low GWI High GWI(mgd) (gpd/ac) (mgd) (gpd/ac)

M01 SE-13,14, SW-5,6 0.091 400 0.181 800M04 SE-5, 6A,6B 0.018 150 0.037 300Total 0.11 0.22

Rainfall-Dependent I/I

RDI/I flows result from rainfall events that produce infiltration and inflow of storm water runoffinto the sewer system. RDI/I represents the difference between the total flow during andimmediately following a storm event and the non-rainfall “base flow” (BWF plus GWI) that isestimated to have occurred during the storm flow period. The magnitude of the resulting RDI/Iresponse is typically described by the percentage of the rainfall volume (called the “R value”)represented by the volume of the RDI/I hydrograph. The R value can vary from storm to storm,depending on such factors as the degree of soil saturation (due to antecedent rainfall) prior to thestorm event.

The shape of the RDI/I hydrograph is also important in determining the peak RDI/I response.The RDI/I hydrograph shape is often defined by separating the total RDI/I hydrograph volumeinto components, each identified by a percentage of the total RDI/I volume and specific time topeak (T) and recession coefficient (K), as illustrated in Figure 2-6. The R componentpercentages and T and K values can be applied to each hour of rainfall to generate a “synthetichydrograph” that approximates the volume and shape of the hydrograph from the actual observedevent. These parameters, when applied to a different rainfall pattern, can then be used toestimate the RDI/I response to that particular rainfall event. This methodology is used tosynthesize RDI/I hydrographs for a “design storm” for collection system modeling. Often thecomputations are incorporated into the model program itself, and the user only needs to providethe appropriate “R, T, and K” values or equivalent hydrologic routing coefficients.

Design criteria for RDI/I includes design R values and hydrograph shape parameters and thehourly rainfall for the selected design storm event. R values and hydrograph parameters aredetermined through the process of model calibration, in which actual observed rainfall events aresimulated in the hydraulic model, and the resulting model hydrographs are compared to themeasured flows at flow meter locations. The RDI/I parameters are adjusted as needed to achievethe best match of modeled to monitored flows. Once calibrated, the model RDI/I parameters canbe applied to a design storm (see discussion below) to simulate wet weather flows for a designevent.


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FIGURE 2-6 SYNTHETIC RDI/I HYDROGRAPH COMPONENTS

RDI/I flows are computed in the model by applying synthetic hydrograph parameters (R, T, andK values) to the sewered area (acreage) of each subbasin. The RDI/I flows are added to theBWF and GWI flows, and the model-predicted flows are then compared to actual flow meterdata during monitored storm events during the flow monitoring period. Three storm events inFebruary 2004 were used for wet weather calibration for the DSRSD model. The latest andlargest event (February 25-27) produced approximately 2 inches of rain over two days with apeak 6-hour rainfall of about 0.9 inches and a peak hour intensity ranging from about 0.3 to 0.4inches (roughly half the size of the 20-year design storm described later in this section). TheFebruary 25-27 storm, which was assumed to represent an event occurring under relativelysaturated soil conditions, was used as the primary calibration event, and the RDI/I parameterscomputed based on this event were then verified and refined based on model comparison to the

T1 T1K1

T2T2 K2

T3 T3K3

RDI/I

R1R2

R3

R = R1 + R2 + R3

PP is rainfall intensity over 1 hour

Total Rainfall Volume = P x Drainage Area

1 hour

Triangular Synthetic Hydrograph 1



Total Synthetic Hydrograph

Time


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other monitored storm events. The final RDI/I parameters by meter area are listed in Table 2-5.In general, the parameters are similar to those used for the 2000 Master Plan Update.

TABLE 2-5RAINFALL-DEPENDENT INFILTRATION/INFLOW

HYDROGRAPH PARAMETERS

MeterArea (a)

Rt(%)

R1(%)

R2(%)

R3(%)

T1(hrs)

K1 T2(hrs)

K2 T3(hrs)

K3

M01 4 1 1 2 1 3 4 2 12 5M02 2.5 0.5 1 1 1 3 4 2 12 5M03 2.5 0.5 1 1 1 3 4 2 12 5M04 2.5 0.5 1 1 1 2 3 2 10 2M05 5 1 2 2 1 2 3 2 10 2M06 2.5 0.5 1 1 1 3 4 2 12 5M07 2.5 0.5 1 1 1 3 4 2 12 5M08 2.5 0.5 1 1 1 3 4 2 12 5M09 2.5 0.5 1 1 1 3 4 2 12 5M10 5 1 2 2 1 3 4 2 12 5M11 2.5 0.5 1 1 1 3 4 2 12 5M12 2.5 0.5 1 1 1 3 4 2 12 5M13 2.5 0.5 1 1 1 3 4 2 12 5M14 2.5 0.5 1 1 1 3 4 2 12 5M15 2.5 0.5 1 1 1 3 4 2 12 5M16 2.5 0.5 1 1 1 3 4 2 12 5M17 2.5 0.5 1 1 1 3 4 2 12 5M18 4 1 1.4 1.6 1 1 3 1 10 2M19 4 1 1.4 1.6 1 2 3 2 10 2M20 2.5 0.5 1 1 1 3 4 2 12 5M21 1.5 0.5 0.5 0.5 1 3 4 2 12 5M22 1.5 0.5 0.5 0.5 1 3 4 2 12 5M23 1.5 0.5 0.5 0.5 1 3 4 2 12 5

(a) Applied to incremental area tributary to flow meter (see Figure 2-4).

The RDI/I percentages determined for the DSRSD system indicate that, overall, the sewers arerelatively “tight” and do not exhibit excessive I/I. A few areas with higher than typical RDI/Irates were observed (e.g., areas tributary to Meters 1, 5, and 10, as well as the Camp Parks areatributary to Meters 18 and 19). The flow response to rainfall at the Eastern Dublin meters(Meters 21, 22, and 23) was very small, as would be expected in this relatively new area of thecollection system, and difficult to quantify. Therefore, a low design RDI/I was assigned to theseareas. Note that the Master Plan does not assume any increase in I/I rates in the future, whichassumes that the District will continue to be proactive in regularly inspecting the sewer systemand repairing significant sewer defects when they are discovered.


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Design Flow Condition

Wastewater collection systems are typically sized for a specific “design” condition, oftenrepresented by a wet weather event in combination with a designated system performancecriterion.

Generally, the performance criterion is defined by the maximum allowable water level in thesystem, which may be at the ground surface (i.e., “no overflows”), a specified distance below theground (say, 3 to 5 feet below the manhole rims), or more conservatively, by a maximumallowable flow depth to pipe diameter (d/D) ratio. The maximum d/D may vary by pipe size. Amaximum allowable d/D of 1.0 (i.e., “no surcharge”) is commonly used, although a smallervalue (e.g., 0.75) may be used for smaller diameter (typically 6- and 8-inch) sewers to accountfor the greater potential for reduced capacity due to possible obstructions in the pipe.

The “design event” establishes the maximum recurrence frequency under which the designperformance criterion can be exceeded. Thus, if the performance criterion is “no overflows” andthe recurrence frequency is 20 years, then the system must be designed such that overflowswould occur no more frequently than once every 20 years.

In practice, the design event is often equated to a specified recurrence frequency rainfall event.Thus, the “design flow” is equated to the flow that would occur for a x-year frequency rainfallevent, and the system would be sized such that the design performance criterion is not exceededfor the x-year rainfall event flows. It is important to note that this is not necessarily the same assaying that the flows in the system would violate the performance criterion only once in every xyears, because the magnitude of wet weather flows are governed by other factors in addition tothe intensity and duration of the rainfall. However, using rainfall recurrence frequency as adesign flow criterion is generally considered to be a reasonable approach to establishing designflows in wastewater collection systems.

For DSRSD, a “no surcharge” performance criteria under a 20-year design rainfall event wasestablished as the criteria for evaluating the capacity of the trunk sewer system under design flowconditions. The selection of a 20-year storm is based on the District’s interpretation of the SanFrancisco Bay Region Basin Plan, which requires that DSRSD wastewater facilities be designedto accommodate a 20-year recurrence frequency flow event without overflows of untreatedwastewater to receiving waters, and to maintain consistency with the design of the DSRSDtreatment and LAVWMA disposal facilities.

Design Storm. The 2000 DSRSD Wastewater Collection System Master Plan Update utilized asynthetic 6-hour, 20-year frequency design rainfall event as the basis for wet weather capacityassessment. A relatively short duration storm (e.g., 6 hours) is typically used for collectionsystem planning because short-duration peak flows are generally more critical for determiningrequired sewer pipeline capacity. The storm duration is selected to reflect the approximate traveltime (“time of concentration”) of flows from the upstream to the downstream ends of the system.The 6-hour duration was selected as the approximate time of concentration of flows in DSRSD’swastewater collection system and is a typical design rainfall duration used for modeling ofmedium sized wastewater collection systems such as DSRSD’s.


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Design of downstream treatment and disposal facilities (particularly wastewater equalization andstorage basins) are generally based on longer duration events (24 hours and longer). For thisreason, a 24-hour event was also developed for the 2000 Collection System Master Plan forcomparison purposes and for use in estimating the volume of flow reaching the treatment plantfrom a 20-year, 24-hour design storm. The Wet Weather Operations Model used by LAVWMAfor sizing of its facilities focused primarily on rainfall events of 24 hours and longer because theprimary concern was related to equalization storage capacity. The design rainfall events were developed based on rainfall intensity-duration-frequency (IDF)statistics for Alameda and Contra Costa Counties. The IDF statistics are typically presented inthe form of curves, which give the long-term average rainfall intensity for various rainfalldurations and recurrence frequencies. The magnitude of rainfall is also related to location, asreflected by variations in mean annual rainfall by area. Based on the IDF curves, the total rainfallamounts for 20-year frequency, 6- and 24-hour duration design storms were developed for theDSRSD service area, as shown in Table 2-6. Because average annual rainfall varies throughoutthe service area, generally decreasing from west to east, a distinction in design rainfall amountswas made between the western portion of the service area (San Ramon and central Dublin) andEastern Dublin.

TABLE 2-6DESIGN STORM RAINFALL FOR DSRSD

20-Year Design Storm Rainfall (inches)6-Hour Duration 24-Hour Duration

Area Total Peak Hr. Total Peak Hr.Central Dublin and San Ramon 2.2 0.71 4.1 0.71Eastern Dublin 2.0 0.65 3.7 0.65

Note: Total rainfall amounts based on IDF statistics; peak hour intensity based on ContraCosta County rainfall distribution coefficients.

To construct the actual hourly rainfall pattern of the design storm (see Figure 2-7), rainfalldistribution coefficients used by Contra Costa County were utilized. These coefficients define thepercentage of the total rainfall amount allocated to each time interval for storms of varyingdurations. Typical hourly rainfall patterns may vary based on the type of storm events that occurin any given area. The rainfall distribution used by Contra Costa County reflects the typicallower-intensity winter storms generally experienced in the San Francisco Bay Area (as opposed tohigher intensity, thunderstorm-type events which may be more typical in valley areas furthereast).


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FIGURE 2-7 DESIGN STORM FOR DSRSD COLLECTION SYSTEM MASTER PLANNING

For the hydraulic modeling, the design storm was assumed to occur at a time such that the peakRDI/I flow generated by the design storm would coincide with the peak hour BWF diurnal pattern(for residential flow input points to the model). This assumption increases the conservatism ofthe peak wet weather flows, i.e., the actual flow recurrence frequency could be greater than 20years. It should be noted that many agencies in the Bay Area use other design storm criteria forevaluating their systems (e.g., 5- or 10-year recurrence frequencies, shorter or longer durationdesign storms, and different rainfall distributions). In the absence of definitive guidance fromregulatory agencies, these differences will likely continue to exist. DSRSD may want toencourage greater collaboration among the wastewater agencies in the Amador Valley area tofacilitate consistent planning for wastewater facilities.

0.280.30 0.31

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WASTEWATER FLOW PROJECTIONS

Table 2-7 presents the existing and future projected average dry weather flow (ADWF), peak dryweather flow (PDWF), and 20-year design storm peak wet weather flow (PWWF) at key locationsin the DSRSD trunk sewer system based on the model runs. The dry weather flows represent atypical weekday condition with “low GWI.” The wet weather flows represent a 20-year, 6-hourdesign storm occurring on a weekday under “high GWI” conditions, with the peak RDI/I responseoccurring at roughly the same time as the peak diurnal BWF. It should also be noted that averageflows on weekdays in residential areas are slightly lower than weekend days, but peak flows onweekdays are higher (see diurnal curves in Figure 2-5). Therefore, weekday flows wereconsidered to be appropriate (i.e., more conservative) for use as a design condition for evaluatingcollection system capacity requirements.

TABLE 2-7WASTEWATER FLOW PROJECTIONS

Area Location ADWF (mgd) PDWF (mgd) PWWF (mgd)Pipe Manhole Exist. Fut. Exist. Fut. Exist. Fut.

Total (a) 48" WWTP 6.0 9.6 9.0 14.2 17.2 24.9Central Dublin and San Ramon 39" U20B2-2 3.8 4.1 6.3 6.8 12.2 12.8Eastern Dublin/Camp Parks 36" V20D2-15 1.8 5.0 2.3 7.3 4.8 11.8Eastern Dublin (b) 36" W20C1-2 1.4 3.9 1.8 5.7 2.6 8.3Camp Parks (c) 24" W20C1-15 0.4 0.9 0.5 1.3 2.2 3.3

(a) Includes flows from Pleasanton Commerce Circle area and 0.36 mgd discharge from FacultativeSludge Lagoon (FSL).

(b) Includes Santa Rita Jail.(c) Includes flows from Arroyo Vista (Subbasin DE5).

Comparison to Previous Flow Projections

Table 2-8 compares the 2000 and 2005 Master Plan Update flow projections. As indicated by thetable, the 2005 Master Plan Update ADWF projections are slightly lower than previousestimates. The projected PDWF is similar to that projected in the 2000 Master Plan Update, butthe projected PWWF is lower. Most of the differences in flow projections can be accounted forby changes in planning assumptions, as described below, and the more detailed analyses of I/Iflows based on the 2004 flow monitoring data.

▪ The 2000 Master Plan Update projections included an allowance for “densification” in thedowntown Dublin area (subbasins DW-1, 2, 3, and 14). In the 2000 study, a FAR of 1.11was assumed for downtown Dublin, compared to the standard commercial FAR of 0.35 usedfor the 2005 Master Plan Update. Discussions with DSRSD and City of Dublin planningstaff earlier in the project indicated that this higher densification was no longer beingplanned.


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TABLE 2-8COMPARISON OF BUILDOUT WASTEWATER FLOW PROJECTIONS

2000 VS. 2005 COLLECTION SYSTEM MASTER PLANS

Area ADWF (mgd) PDWF (mgd) PWWF (mgd)2000MP

2005MP

2000MP

2005MP

2000MP (a)

2005MP

Total (b) 10.2 9.6 14.2 14.2 33.3 24.9Central Dublin and San Ramon 4.8 4.1 6.9 6.8 15.8 12.8Eastern Dublin plus Camp Parks 5.3 5.0 7.2 7.3 17.4 11.8Eastern Dublin 4.5 3.9 6.2 5.7 12.1 8.3Camp Parks 0.7 0.9 1.0 1.3 5.3 3.3

(a) Assumes rehabilitation of Camp Parks sewer system.(b) 2005 MP flows include 0.36 mgd FSL discharge.

▪ The 2000 Master Plan Update was based on previous land use mapping for the EasternDublin area. At that time, the land use planning for the most eastern portions of EasternDublin (subbasin groups ED-8, 9, 10-1, and 10-2) was not well defined, and it appears thatmore area was projected for development in the earlier plan than is currently projected. Inthe earlier plan, a substantial portion of the area was indicated to be very low density (rural)residential, which generated relatively small flows but occupied substantial area (acreage);thus, previous RDI/I projections, which are based on sewered area, were likely overestimatedin proportion to the amount of projected development.

▪ Current flow projections for Schaefer Ranch, based on the latest development plans, arelower than previous estimates.

▪ Current flow projections for Westside San Ramon are lower than previous estimates becausethe most western areas (e.g., subbasins SW7 through SW10) are now identified as beingpreserved as open space, whereas the 2000 Master Plan Update assumed similar developmentas in the eastern portions of Westside San Ramon.

▪ The current flow projections for Camp Parks are based on the latest future development plan,which appears to generate more flow than the values used in the 2000 Master Plan Update.The 2000 Master Plan Update projections were based on information from the 1998 CampParks Privatization Study prepared by Whitley, Burchett and Associates.

▪ The 2000 Master Plan Update assigned GWI to all parts of the system, whereas the 2005Master Plan Update applies GWI to only selected areas (Meters 1 and 4) based on modelcalibration to 2004 flow monitoring data.

▪ Based on information provided by the District, the current model includes a continuousdischarge of 250 gpm (0.36 mgd) to the Camp Parks trunk sewer from the facultative sludgelagoons (FSL). This discharge was not included in the 2000 Master Plan Update.


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Potential Impact of Water Conservation

Future water conservation has the potential to decrease wastewater flows. To assess the potentialimpact of water conservation on wastewater flows, an analysis was conducted to estimate thepotential reduction in BWF that could be achieved through residential water conservation. Sincethe DSRSD wastewater collection system service area is primarily residential in nature (80percent of the service area water usage is attributed to residential accounts), it was consideredappropriate to focus the water conservation analysis on residential users.

Estimates of potential water conservation were developed from published documents, specificallythe “Residential End Uses of Water,” developed by the American Water Works AssociationResearch Foundation. This document is referenced by the California Urban Water ConservationCouncil, as well as other agencies concerned with promoting water conservation. Based on theinformation contained in this document, toilets and washing machines provide the greatestopportunity for water conservation. It is estimated that approximately 17 gallons per capita perday (gpd/capita) or approximately 44 gpd per household could be saved with water conservation.Therefore, the single-family residential wastewater generation rate used for this Master PlanUpdate (220 gpd/DU) could potentially be reduced by approximately 20 percent with waterconservation. This is a conservative assumption, since it assumes that existing units are largelynon-conserving, whereas it is likely that at least some residences in the service area are alreadyequipped with low flow toilets, washing machines, or other conserving fixtures.

To assess the potential impact of water conservation on flows in the wastewater collection system,and specifically on the peak flows for which capacity must be provided, the residential loads inthe hydraulic model were reduced by 20 percent under the future scenario. The results of themodel runs for the 20 percent residential water conservation scenario are summarized in Table2-9 and compared to the model results for the non-conservation, base-case scenario for buildoutconditions.

As indicated in the table, water conservation has the potential to reduce overall dry weatherflows by about 10 to 15 percent, but the potential impact on peak wet weather flows would beless (7 to 8 percent). Based on model results, this small reduction in peak flows would have noimpact in terms of eliminating or significantly reducing predicted capacity deficiencies in thecollection system under PWWF conditions.

Future Connections

Table 2-10 presents the estimated future connections to the DSRSD wastewater (local sewer)service area for existing, 2010, 2015, and 2020 development, in terms of average basewastewater flows and dwelling unit equivalents (DUEs). A DUE is considered to be theequivalent to the average BWF from one single family dwelling unit, or 220 gallons per day.Non-residential flows, existing flows from the Parks RFTA, and existing and projected flows forthe FCI and Santa Rita Jail were converted to DUEs based on this factor.


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TABLE 2-9COMPARISON OF BUILDOUT WASTEWATER FLOWS

WITH AND WITHOUT WATER CONSERVATION

Area ADWF (mgd) PDWF (mgd) PWWF (mgd)Non-

Conserv.Conserv. Non-

Conserv.Conserv. Non-

Conserv.Conserv.

Total 9.6 8.5 14.2 12.3 24.9 23.0Central Dublin and San Ramon 4.1 3.5 6.8 5.7 12.8 11.8Eastern Dublin plus Camp Parks 5.0 4.5 7.3 6.4 11.8 10.9Eastern Dublin 3.9 3.5 5.7 5.0 8.3 7.6Camp Parks 0.9 0.9 1.3 1.3 3.3 3.2

TABLE 2-10ESTIMATED FLOWS AND EQUIVALENT CONNECTIONS IN

DSRSD LOCAL SEWER SERVICE AREA

Estimated Flows/ConnectionsExisting 2010 2015 2020

Average Base Wastewater Flow (mgd) Residential 3.98 5.91

6.11 (a) 7.73 (a) Non-Residential 0.87 2.55 FCI and Santa Rita Jail 0.72 0.72 0.72 0.72 Total 5.57 6.83 8.45 9.18

Dwelling Unit Equivalents (DUEs) (b) 25,308 31,046 38,401 41,742

(a) Breakdown between residential and non-residential flows not computed for 5- and 10-year growthscenarios.

(b) One DUE is equivalent to 220 gallons per day average flow.

section 2 land use projections and design flows

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