TECHNICAL MEMORANDUM (FINAL VERSION)

Date: October 8, 2019

To: Robert Armijo, City Engineer

From: Jim Nelson

Subject: Supplement No. 3 to Citywide Storm Drainage Master Plan Lammers and Mountain House Watersheds

SWC File: 2014-96CC

This Technical Memorandum and its supporting exhibits and tables present Supplement No. 3 to the Citywide Storm Drainage Master Plan (SDMP) that was adopted by the Tracy City Council on April 16, 2013 by Resolution No. 2013-056. This supplement has been prepared to revise and update components of the storm drainage infrastructure plan for the Lammers and Mountain House Watersheds in the City’s Sphere of Influence. The primary reasons for preparing this Supplement No. 3 to the Citywide SDMP at this time include the following:

• The alignment of selected segments of the Lammers Outfall Storm Drain system is proposed to be altered. Alterations will include a northerly shift of some storm drain segments to follow the south side of Eleventh Street to more efficiently follow existing topography and allow certain storm drain and sanitary sewer trunk lines to align parallel and contiguous to each other to improve efficiency of construction and maintenance.

• Extensive development has occurred in this area since the current Citywide SDMP was adopted, and an update is needed to allow for official adoption of minor changes in Sub-basin boundaries and Supplement No. 3 to Citywide Storm Drainage Master Plan (FINAL VERSION) Lammers and Mountain House Watersheds To: Robert Armijo, City Engineer October 8, 2019 Page 2

detention basin sizes and locations associated with proposed storm drainage infrastructure.

• The revisions herein may improve opportunities to accelerate the construction of the Lammers Outfall Storm Drain System, facilitating the conversion of several existing temporary retention basins serving existing development to detention basins having a positive drainage outflow.

Proposed revisions and updates to the Citywide SDMP presented herein have been supported by additional hydrologic and hydraulic calculations, additional investigation of physical conditions and input from City staff. Exhibit A is a portion of Figure 5-1A from the Citywide SDMP that depicts the existing adopted storm drainage plan for the broader portion of the City where changes and updates are being proposed with this Supplement No. 3. The area to be served includes Cordes Ranch, various International Park of Commerce existing and proposed development areas, the property formerly known as the Gateway property, and other properties in the area.

Proposed updates to program storm drainage infrastructure and minor adjustments to Sub-basins and Watershed boundaries proposed per this Supplement No. 3 to the Citywide SDMP are depicted and listed on Exhibit B and include the following:

• Changes to the alignment of selected segments of the Lammers Outfall Storm Drain system.

• Minor Sub-basin changes (L17A/L17B, transfer 22 acres of the Mountain House Watershed into the Lammers Watershed, L20/L14).

• DET MWH3a/3b/3c storage volume is reduced from 37 acre- feet (AF) to 33 AF due to a 22 acre reduction in the contributing drainage area per the watershed adjustment cited above.

Supplement No. 3 to Citywide Storm Drainage Master Plan (FINAL VERSION) Lammers and Mountain House Watersheds To: Robert Armijo, City Engineer October 8, 2019 Page 3

• DET LW6 storage volume is increased from 101 AF to 103 AF due to minor sub-basin changes (L20/L14).

• DET LW9a storage volume is increased from 89 AF to 94 AF due to minor sub-basin changes (L17A/L17B) and watershed adjustments.

• DET LW8 is no longer depicted as a linear basin.

• DET LW10A, LW10B, LW9a and LW6 have minor location or configuration changes.

• DET LW3 is shown as an aggregate basin not located as of yet and will become three (3) or so smaller basins to be determined by the Specific Plan process for the property formerly known as Gateway.

• DET LW4 and LW5 will drain to the existing Lammers Road street storm drain system and/or future onsite storm drainage facilities serving the property formerly known as Gateway that will be directed to DET LW3; DET LW4 and LW5 (1 cfs outflow, total) will be “pass through” drainage in DET LW3 and will not affect the DET LW3 storage volume. Also, the following statement contained at the top of page 5.22 in the Citywide SDMP relevant to new development within the Mountain House Watershed is proposed to be changed from:

New development within the Mountain House Watershed will not be allowed by the City prior to the execution of said agreement. (“Said agreement” refers to a future drainage agreement with Mountain House CSD). to:

New development within the Mountain House Watershed will not be allowed to discharge to downstream facilities operated by the Mountain House CSD Supplement No. 3 to Citywide Storm Drainage Master Plan (FINAL VERSION) Lammers and Mountain House Watersheds To: Robert Armijo, City Engineer October 8, 2019 Page 4 unless an agreement that authorizes said discharge is executed between the City and the Mountain House CSD.

Supplement No. 3 does not alter the following relevant components of the Citywide SDMP as it pertains to the subject area:

• The 2010 Drainage Agreement Between the City of Tracy and The West Side Irrigation District • Outflow rates from detention basins proposed to serve this area (except for a DET LW3 outflow increase from 4 cfs to 5 cfs for “pass through” of storm water already stored and detained in DET LW4 and LW5).

This Supplement No. 3 to the Citywide Storm Drainage Master Plan also includes updated Opinions of Probable Cost (OPCs) for program storm drainage infrastructure that will serve the Lammers and Mountain House Watersheds. Separate OPCs have been prepared each watershed. These OPCs will be incorporated into an updated impact fee analysis performed by Harris & Associates for these watersheds.

Exhibits:

Exhibit A – Portion of Figure 5-1A from Existing Citywide Storm Drainage Master Plan Showing Existing and Proposed Storm Drainage Facilities in the City’s Lammers and Mountain House Watersheds Exhibit B – Proposed Revisions to the Existing Citywide Storm Drainage Master Plan per Supplement No. 3

Tables:

Table 1 – Opinion of Probable Cost for Program Storm Drainage Infrastructure, Supplement No. 3 to the Citywide SDMP (Lammers Watershed) Table 2 – Opinion of Probable Cost for Program Storm Drainage Infrastructure, Supplement No. 3 to the Citywide SDMP (Mountain House Watershed)

Supplement No. 3 to Citywide Storm Drainage Master Plan (FINAL VERSION) Lammers and Mountain House Watersheds To: Robert Armijo, City Engineer October 8, 2019 Page 5

Cc: Andrew Malik, City of Tracy Bill Dean, City of Tracy Al Gali, City of Tracy Ilene Macintire, City of Tracy Nanda Gottiparthy, SNG Associates Mike O’Connor, SNG Associates Alison Bouley, Harris & Associates Sarah McIlroy, Stantec

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Provisions that are not changing: List of proposed changes:

V Supplement No. 3 Changes to the Citywide SDMP

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LAMMERS WATERSHED Construction of Major Facilities DET LW1 (90 AF, plus 32 AF add'l excavation) 122 AF $ 16,000 $ 1,952,000 DET LW2 (27 AF, plus 10 AF add'l excavation) 37 AF $ 16,000 $ 592,000 DET LW3 (87AF, plus 30 AF add'l excavation) 117 AF $ 16,000 $ 1,872,000 DET LW5 (Non-Program) DET LW6 (103 AF, plus 50 AF add'l excavation) 153 AF $ 16,000 $ 2,448,000 DET LW7 (Non-Program) DET LW8 (34 AF, plus 5 AF add'l excavation) 39 AF $ 16,000 $ 624,000 DET LW9a (94 AF, plus 38 AF add'l excavation) 132 AF $ 16,000 $ 2,112,000 DET LW9b (18 AF, plus 6 AF add'l excavation) 24 AF $ 16,000 $ 384,000 DET LW10a/10b (20 AF, plus 7 AF add'l excavation) 27 AF $ 16,000 $ 432,000 DET LW11 (30 AF, plus 11 AF add'l excavation) 41 AF $ 16,000 $ 656,000 DET LW12 (13 AF, plus 4 AF add'l excavation) 17 AF $ 16,000 $ 272,000 DET LW4 Pump Station (0.5 cfs capacity) 1 LS $ 350,000 $ 350,000 DET LW5 Pump Station (0.5 cfs capacity, Non-Program) DET LW12 Pump Station (0.5 cfs capacity) 1 LS $ 350,000 $ 350,000 Greenbelt Parkway 11,200 LF $ 340 $ 3,808,000 Construction of Storm Drains 12" SD & SDFM 13,400 LF $ 75 $ 1,005,000 18" SD 4,100 LF $ 100 $ 410,000 24" SD 7,900 LF $ 150 $ 1,185,000 30" SD 6,185 LF $ 200 $ 1,237,000 36" SD 3,590 LF $ 300 $ 1,077,000 36" SD (Crossing of Eleventh Street) 102 LF $ 500 $ 51,000 42" SD (Von Sosten Road, WSID Sub-Main Drain) 150 LF $ 500 $ 75,000 Other Items Dewatering 1 LS $ 2,500,000 $ 2,500,000 WSID Crossing Agreement 2 EA $ 5,000 $ 10,000 Interflow Structure at WSID Connection (Lammers Road) 1 LS $ 30,000 $ 30,000 WSID Discharge Agreement (First 30 Years) 1 EA $ 2,040,000 $ 2,040,000 Subtotal of Construction $ 25,472,000 Design & Planning @ 10% of Construction Subtotal $ 2,547,200 Construction Management @ 10% of Construction Subtotal $ 2,547,200 General Contingency @ 15% of Construction Subtotal $ 3,820,800 Program Administration @ 5% of Construction Subtotal $ 1,273,600 Land Acquisition DET LW1 35.0 AC $ 150,000 $ 5,250,000 DET LW2 11.0 AC $ 150,000 $ 1,650,000 DET LW3 48.0 AC $ 150,000 $ 7,200,000 DET LW5 (Non-Program) DET LW6 21.0 AC $ 150,000 $ 3,150,000 DET LW7 (Non-Program) DET LW8 5.0 AC $ 150,000 $ 750,000 DET LW9a 25.0 AC $ 150,000 $ 3,750,000 DET LW9b 7.0 AC $ 150,000 $ 1,050,000 DET LW10a/10b 9.0 AC $ 150,000 $ 1,350,000 DET LW11 12.0 AC $ 150,000 $ 1,800,000 DET LW12 6.0 AC $ 150,000 $ 900,000 Greenbelt Parkway 51.4 AC $ 150,000 $ 7,710,000 12" SD Easement 2.2 AC $ 50,000 $ 110,000 Subtotal of Land Acquisition $ 34,670,000 TOTAL ESTIMATED COST $ 70,330,800

Table 1_Lammers_OPC_May2019 City of Tracy Table 2 Opinion of Probable Cost for Program Storm Drainage Infrastructure Supplement No. 3 to the Citywide SDMP (Mountain House Watershed)

UNIT TOTAL DESCRIPTION QTY UNIT COST COST

MOUNTAIN HOUSE WATERSHED Construction of Major Facilities DET MHW3a/3b/3c (33 AF, plus 14 AF add'l excavation) 47 AF $ 16,000 $ 752,000 DET MHW 3a Pump Station (3.0 cfs capacity) 1 LS $ 350,000 $ 350,000 Construction of Storm Drains 18" SDFM 3,300 LF $ 100 $ 330,000 Other Items Dewatering 1 LS $ 150,000 $ 150,000 Mountain House Discharge Agreement 1 LS TBD TBD Subtotal of Construction $ 1,582,000 Design & Planning @ 10% of Construction Subtotal $ 158,200 Construction Management @ 10% of Construction Subtotal $ 158,200 General Contingency @ 15% of Construction Subtotal $ 237,300 Program Administration @ 5% of Construction Subtotal $ 79,100 Land Acquisition DET MHW3a/3b/3c 10.0 AC $ 150,000 $ 1,500,000 18" SDFM Easement 1.5 AC $ 50,000 $ 75,000 Subtotal of Land Acquisition $ 1,575,000 TOTAL ESTIMATED COST $ 3,789,800 Note: TBD = To Be Determined and Added to Costs at a Later Date

Table 2_Mountain House_OPC_May2019 City of Tracy