ams associates, inc. • 801 Ygnacio Valley Rd., Suite 220 • Walnut Creek, CA, 94596 • Phone 925.943.2777 • Fax 925.943.2778
STORMWATER CONTROL PLAN
for
Mixed-use Building
Humboldt Street & Jefferson Street
Yountville, CA 94559
APNs: 036-054-022 & 036-054-023
ams Project No. 06-1972-01
Prepared: January 25
th, 2024
prepared for:
Yountville Pacific, LLC
P.O. Box 2176
Chico, CA 95927
Phone: (530) 898-0640
prepared by:
ams associates, inc.
Mr. Farhad Iranitalab, RCE No. 33142
801 Ygnacio Valley Road, Suite 220
Walnut Creek, CA 94596
Phone: (925) 943 - 2777
i
TABLE OF CONTENTS
I. Project Data (Table 1)............................................................................................1 II. Setting ....................................................................................................................1 A. Project Location and Description................................................................................. 1 B. Existing Site Features and Conditions ......................................................................... 1 C. Opportunities and Constraints for Stormwater Control ........................................... 1 Figure 1 – Vicinity Map.................................................................................................. 1 III. Low Impact Development Design Strategies....................................................... 2 A. Optimization of Site Layout .......................................................................................... 2 B. Use of Permeable Pavements........................................................................................ 2 C. Dispersal of Runoff to Pervious Areas........................................................................ 2 D. Stormwater Control Measures....................................................................................... 2 IV. Documentation of Drainage Design..................................................................... 3 A. Descriptions of Each Drainage Management Area.................................................... 3
1. Table 2- Drainage Management Areas............................................................ 3
2. Drainage Management Area Descriptions..................................................... 4 B. Tabulation and Sizing Calculations............................................................................... 4
1. Table 3 - Information Summary for Bioretention Facility Design................ 4
2. Table 4 - Self-Treating Areas.............................................................................. 4
3. Table 5 - Self-Retaining Areas ............................................................................ 4
4. Table 6 - Areas Draining to Self-Retaining Areas............................................ 5
5. Table 7 - Areas Draining to Bioretention Facilities......................................... 5 V. Source Control Measures ...................................................................................... 5 A. Site activities and potential sources of pollutants....................................................... 5 B. Table 8 - Source Control Table........................................................................................ 5 VI. Stormwater Facility Maintenance......................................................................... 6 A. Ownership and Responsibility for Maintenance in Perpetuity ................................. 6 B. Summary of Maintenance Requirements for Each Stormwater Facility ................. 6 VII.Construction Checklist.......................................................................................... 6 VIII.Certification ......................................................................................................... 6 Attachments
• Exhibit ‘A’ - Topographic Survey
• Exhibit ‘B’ - Grading & Drainage Plan
• Exhibit ‘C’ - Stormwater Control Plan
This Stormwater Control Plan was prepared using the template dated October 2018.
Mixed Use Building January 25
th, 2024
Humboldt St. & Jefferson St. Page | 1 ams Project No. 22-2620 Yountville, CA 94599
I. Project Data
Table 1. Project Data Form
Project Name/Number Mixed-use Building
Application Submittal Date January 25, 2024
Project Location APNs: 036-054-022 and 036-054-023
Project Phase No. N/A
Project Type and Description Mixed-use Building
Total Project Site Area (acres) 0.249
Total New and Replaced Impervious
Surface Area
0.249 acres/ 10,843 sf
Total Pre-Project Impervious Surface
Area
0 sf
Total Post-Project Impervious Surface
Area
0.226 acres/ 9,842 sf
II. Setting
A. Project Location and Description
The project consists of one Mixed-Use Building, Parking Lot and Sidewalk. Sidewalk will be constructed along Jefferson Street and Humboldt Street.
B. Existing Site Features and Conditions
The 0.249 ± acre undeveloped Parcel slopes 1.3% from West to East towards Humboldt St. There is no Stormwater Drainage Structure or Municipal Storm Drain on Site. Soils is Coombs Gravelly Loam, Hydrologic Soil Group “C”.
C. Opportunities and Constraints for Stormwater Control Soils are relatively impermeable, disposal of runoff to infiltration is not feasible on site. There is no City Storm Drain System for the Site.
The proposed development includes Bio-Retention Facility to mitigate impacts from increased runoff.
Mixed Use Building January 25
th, 2024
Humboldt St. & Jefferson St. Page | 2 ams Project No. 22-2620 Yountville, CA 94599
Figure 1 Vicinity Map
III. Low Impact Development Design Strategies
A. Optimization of Site Layout
The Site is infill within the urbanized area. Existing trees around the Property are to be preserved.
B. Use of Permeable Pavements
Conventional Concrete and Asphalt are to be used to construct Sidewalks, Driveway and Parking Lot.
C. Dispersal of Runoff to Pervious Areas
D. Stormwater Control Measures
Runoff from Roof and Parking Lot will be routed to a rectangular Bio-Retention facility on the East side of the Property. The Facility will be designed and Mixed Use Building January 25
th, 2024
Humboldt St. & Jefferson St. Page | 3 ams Project No. 22-2620 Yountville, CA 94599
constructed to the criteria in the BASMAA Post-Construction Manual (July 2014), including the following features:
• Surrounded by a Concrete Curb. Where adjacent to Pavement and Curb will be thickened and an impermeable vertical cutoff wall will be included. • Each layer built flat, level, and to the elevations specified in the plans:
▪ Bottom of Gravel Layer (BGL)
▪ Top of Gravel Layer (TGL)
▪ Top of Soil Layer (TSL)
▪ Overflow Grate
▪ Facility Rim
▪ 12 inches of Class 2 permeable, Caltrans specification 68-2.02F(3) • 18 inches sand/compost mix meeting BASMAA specifications. • 4 in. dia. PVC SDR 35 perforated pipe underdrain, installed with the invert at the top of the Class 2 permeable layer with holes facing down, and connected to the overflow structure at that same elevation.
• 6-inch-deep reservoir between top of soil elevation and overflow grate elevation • Concrete drop inlet with frame overflow structure, with grate set to specified elevation, drains to the gutter on Humboldt St.
• Plantings selected for water conservation.
• Irrigation system on a separate zone, with drip emitters and “smart” irrigation controllers.
• Sign identifying the facility as a stormwater treatment facility.
IV. Documentation of Drainage Design
A. Descriptions of Each Drainage Management Area
1. Table 2 - Drainage Management Areas
DMA
Name Surface Type Area (square feet)
DMA-1 Roof 5,112
DMA-2 Paving 4,730
DMA-3 Landscaped 605
Mixed Use Building January 25
th, 2024
Humboldt St. & Jefferson St. Page | 4 ams Project No. 22-2620 Yountville, CA 94599
2. Drainage Management Area Descriptions
• DMA-1: Totals 5,112 square feet, drains the East Parking Area. Runoff will enter the bio-retention facility through curb cuts.
• DMA-2: Totals 4,730 square feet, drains to the Bio-Retention Facility through Curb Cuts.
• DMA-3: Totals 605 square feet that is a Landscaped Area, self-treating area.
B. Tabulation and Sizing Calculations
1. Table 3 - Information Summary for Bioretention Facility Design Total Project Area
(Square Feet) 10,843
DMA-1 5,112
DMA-2 4,730
DMA-3 605
IMP-1 396
2. Table 4 - Self-Treating Areas
DMA Name Area
(square feet)
DMA-3 605
3. Table 5 - Self-Retaining Areas
DMA
Name
Area
(square feet)
N/A N/A
Mixed Use Building January 25
th, 2024
Humboldt St. & Jefferson St. Page | 5 ams Project No. 22-2620 Yountville, CA 94599
4. Table 6 - Areas Draining to Self-Retaining Areas
5. Table 7 - Areas Draining to Bioretention Facilities
V. Source Control Measures
A. Site activities and potential sources of pollutants
Landscape/ Outdoor Pesticide Use/Building and Grounds Maintenance B. Table 8 - Source Control Table
Potential source of
runoff pollutants
Permanent
source control BMPs
Operational
source control BMPs
D2. Landscape/
Outdoor Pesticide
Use/Building and
Grounds
Maintenance
Existing mature trees to be retained.
Landscaping will minimize irrigation
and runoff and be selected for pest
resistance and will minimize the need
for fertilizers and pesticides.
Plants will be selected appropriate to
site soils, slopes, climate, sun, wind rain,
land use, air movement, ecological
consistency, and plant interactions.
Landscaping will be
maintained using
minimum or no
pesticides.
IPM information will
be provided to new
owners, lessees, and
operators.
DMA
Name
Area
(square
feet)
Postproject
surface
type
Runoff
factor
Product
(Area x
runoff
factor)[A]
Receiving
selfretaining
DMA
Receiving
selfretaining
DMA Area
(square
feet) [B]
Ratio
[A]/[B]
DMA Name
DMA
Area
(square
feet)
Postproject
surface
type
DMA
Runoff
factor
DMA
Area
runoff
factor
Facility Name
IMP-1
DMA-1 5,112 Roof 1 5,112
Sizing
factor
Minimum
Facility
Size
Proposed
Facility
Size
DMA-2 4,730 Paving 1 4,730
DMA-3 605
Total> 9,842 0.04 393.68 396
Mixed Use Building January 25
th, 2024
Humboldt St. & Jefferson St. Page | 6 ams Project No. 22-2620 Yountville, CA 94599
VI. Stormwater Facility Maintenance
A. Ownership and Responsibility for Maintenance in Perpetuity As required by the Municipal Regional Permit (MRP), the Owner will be responsible for Operations and Maintenance of the Stormwater Treatment Facility. The Owner agrees to give the Municipality a right of access for inspections.
The Owner is also required to conduct maintenance inspection annually and address any issues to the Treatment Facility accordingly.
B. Summary of Maintenance Requirements for Each Stormwater Facility • Daily: Trash removal.
• After significant rain: Inlets will be inspected and trash/debris will be removed.
VII. Construction Checklist
VIII. Certification
The preliminary design of stormwater treatment facilities and other stormwater pollution control measures in this plan are in accordance with the current edition of the BASMAA Post-Construction Manual.
Stormwater Control Plan
Page #
Source Control or Treatment Control
Measure See Plan Sheet #s
Storm Drain Inlets Mark All Inlets with the words “No
Dumping, Drains to Bay”. Exhibit ‘B’
Drainage Management
Area DMAs 1 through 3. Exhibit ‘C’
Hazardous Materials
Hazardous Material will not be
stored outside and will be handled
properly.
N/A
Mixed Use Building January 25th, 2024
Humboldt St. & Jefferson St. ams Project No. 22-2620
Yountville, CA 94599
Attachments
• Exhibit ‘A’ – Topographic Survey
• Exhibit ‘B’ – Grading & Drainage Plan
• Exhibit ‘C’ - Stormwater Control Plan
Mixed Use Building January 25th, 2024
Humboldt St. & Jefferson St. ams Project No. 22-2620
Yountville, CA 94599
Exhibit ‘A’
Topographic Survey
N 60°31'53" E 107.65'
N 29°29'44" W 100.60' N 60°30'16" E 107.76'
N 29°25'50" W 100.69' 50.00' 57.65' 57.76' 50.00' LOT 1 [14 M 75] LOT 2 [14 M 75] LOT 3 [14 M 75] LOT 4 [14 M 75] PARCEL 3 [19 PM 77] PARCEL 2 [19 PM 77] PARCEL 1 [19 PM 77] HUMBOLT STREET
JEFFERSON STREET
S 28°47'03" E 345.59' 23.76'
23.45' N 60°30'16" E 370.11' 0.133± ACRES 0.116± ACRES DRAINAGE EASEMENT [14 M 75]
NON-ACCESS
[14 M 75]
WASHINGTON STREET FND REBAR/CAP "LS 4510" FND REBAR/CAP "LS 4510" N 29°29'44" W 100.63' FND BD MON IN MON WELLWEBBER STREET NOTES BACK FLOW PREVENTER CATCH BASIN / DROP INLET WATER METER FENCE PROPERTY LINE LEGEND RECORD INFORMATION W/ REFERENCE GAS SANITARY SEWER RETAINING WALL SIGN VALVE FIRE HYDRANT FOUND MONUMENT AS NOTED CENTERLINE EASEMENT BOLLARD LIGHT SANITARY SEWER MANHOLE UNDERGROUND ELECTRIC STORM DRAIN WATER ADJACENT PROPERTY LINE STORM DRAIN MANHOLE GAS METER BUILDING LINE W/ DOOR TRANSFORMER ABBREVIATIONS CLEAN OUT TRAFFIC SIGNAL POLE (100.00') EDGE OF PAVEMENT BUILDING OVERHANG FOUND IRON PIPE OR AS NOTED UTILITY BOX (SIZE VARIES) STREET LIGHT NON-ACCESS LIGHT 1. All distances shown hereon are in U.S. Survey feet and decimals thereof. 2. This boundary and easements shown on this survey was based solely on the following recorded documents: Final Map of Whitton Place filed for record on August 20th, 1985 in Book 14 of Maps at Pages 74-76, Napa County Records. No liability is assumed for matters of record not shown on said document that may affect the boundary lines, exceptions, or easements affecting the property. 3. The types, locations, sizes and/or depths of existing underground utilities as shown on this topographic survey were obtained from sources of varying reliability. The contractor is cautioned that only actual excavation will reveal the types, extent, sizes, locations and depths of such underground utilities. (A reasonable effort has been made to locate and delineate all unknown underground utilities.) However, the surveyor can assume no responsibility for the completeness or accuracy of its delineation of such underground utilities which may be encountered, but which are not shown on these drawings. 4. A.P.N.: 036-054-022 and 036-054-023 5. Basis of Bearings: The bearing of North 60°34'50" East taken on the centerline of Webber Street as shown on that certain Final Map of Whitton Place filed for record on August 20th, 1985 in Book 14 of Maps at Pages 74-76, Napa County Records was taken as the Basis of all Bearings shown hereon. 6. Benchmark: NGS Monument "E 468 Reset": Elevation: 106.4 feet (GPS Observed) (Datum) NAVD 1988 7. Flood Zone Note: The subject property is shown on the Federal Emergency Management Agency Flood Insurance Rate Map, Community Panel Number 060205 0413 E, dated September 26, 2008, as being located in Flood Zone "X"; Areas of determined to be outside the 0.2% annual chance flood. Information was obtained from the FEMA website (www.fema.gov) on July 11, 2022.
NORTH
[email protected] R. BARBER, L.S. 9097 DATE PREPARED BY OR UNDER THE SUPERVISION OF CONCRETE INDEX CONTOUR CONTOUR CURB TREE W/ SIZE AND ELEVATION CURB & GUTTER SPOT ELEVATION 0 Scale 1" = ft 10 10 20 30 BL BUILDING BRC BACK OF ROLLED CURB DI DROP INLET EB ELECTRIC BOX EP EDGE OF PAVEMENT EV ELECTRIC VAULT FL FLOW LINE FNC FENCE GV GAS VALVE LIP LIP OF GUTTER MB MAIL BOX IE INVERT ELEVATION RE RIM ELEVATION SLB STREET LIGHT BOX SSCO SANITARY SEWER CLEAN OUT SSMH SANITARY SEWER MANHOLE TC TOP OF CURB 12 JULY 2022 Mixed Use Building January 25th, 2024
Humboldt St. & Jefferson St. ams Project No. 22-2620
Yountville, CA 94599
Exhibit ‘B’
Grading & Drainage Plan
T
SHED
SSCO
GRAVEL DRIVEWAY
EB EV
LOT 1
[14 M 75]
LOT 2
[14 M 75]
LOT 3
[14 M 75]
[19 PM 77]
HUMBOLDT STREET
JEFFERSON STREET
0.133± ACRES 0.116± ACRES
DRAINAGE EASEMENT
[14 M 75] NON-ACCESS [14 M 75]
WASHINGTON STREET
BIKE
USPS
EV
ART
11 10
9 8
7 6
5 4
3 2
1 EV
BIKE
USPS
EV
DWTR
DWTR
ART
Know what'sbelow. Callbefore you dig.
R
’
’
’
’
’
’
’
Mixed Use Building January 25th, 2024
Humboldt St. & Jefferson St. ams Project No. 22-2620
Yountville, CA 94599
Exhibit ‘C’
Stormwater Control Plan
T
SHED
STOP
SSCO
GRAVEL DRIVEWAY
EB EV EB
LOT 3
[14 M 75]
PARCEL 3
[19 PM 77]
HUMBOLDT STREET
JEFFERSON STREET
DRAINAGE EASEMENT
[14 M 75] NON-ACCESS [14 M 75]
WASHINGTON STREET VAN
BIKE
USPS
EV
ART
11 10
9 8
7 6
5 4
3 2
1 EV
BIKE
USPS
EV
DWTR
DWTR
ART
Know what'sbelow. Callbefore you dig.
R