COUNTYof NAPA
ROBERT J. PETERSON, P.E.
District Engineer
March 16, 2005
To whom it may concern:
This letter is to inform you that Napa County has drafted a policy to establish new regulations to
control polluted runoff from new structures, roads, driveways, and mass grading (nonagricultural) projects and would like your comments before the final draft is prepared. The Napa
County Construction Site Runoff Control requirements were developed to comply with the State
Water Resource Control Board’s (SWRCB) Phase II NPDES Municipal Stormwater General
Permit (Phase II General Permit). A copy of the proposed policy is enclosed for your review and
comment. Please submit your comments to the following address by April 15, 2005:
Napa County Flood Control and Water Conservation District
Attn: Todd Adams
804 First Street
Napa, CA 94559-2623
NPDES LEGAL REQUIREMENTS
According to the Phase II General Permit issued to Napa County on May 20, 2004, the County
must develop, implement, and enforce a program to reduce pollutants in stormwater runoff from
construction activities that result in a land disturbance of greater than or equal to one acre. The
program must include the development and implementation of, at a minimum:
1. An ordinance or other regulatory mechanism to require erosion and sediment controls, as
well as sanctions, or other effective mechanisms, to ensure compliance, to the extent
allowable under State, or local law;
2. Requirements for construction site operators to implement appropriate erosion and sediment
control BMPs;
3. Requirements for construction site operators to control waste such as discarded building
materials, concrete truck washout, chemicals, litter, and sanitary waste at the construction site
that may cause adverse impacts to water quality;
4. Procedures for site plan review which incorporate consideration of potential water quality
impacts;
5. Procedures for receipt and consideration of information submitted by the public; and
6. Procedures for site inspection and enforcement of control measures.
As required by the Phase II General Permit, Napa County adopted Ordinance No. 1240 (Chapter
16.28) to prohibit illicit discharges to the stormwater conveyance system (e.g. creeks, ditches,
NAPA COUNTY FLOOD CONTROL AND WATER CONSERVATION DISTRICT
804 First Street Napa, CA 94559-2623  (707) 259-8600  FAX (707) 259-8619
www.co.napa.ca.us/departments/publicworks
www.napaflooddistrict.org
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culverts) and to establish authority to adopt requirements for construction site operators to
implement Best Management Practices (BMPs) to control polluted runoff.
PROPOSED CONSTRUCTION SITE RUNOFF CONTROL REQUIREMENTS
The proposed Construction Site Runoff Control requirements were developed to meet the
requirements of the General Permit and to eliminate illicit discharges from construction sites.
Under the proposed requirements structural, road, driveway, and mass grading (non-agricultural)
projects that meet one or more of the following criteria must prepare and submit a BMP
implementation plan with any building or grading permit:
1. Projects on slopes 5% or greater,
2. Soil disturbance of 10,000 sq ft or greater,
3. Earthmoving of 50 cu yds or greater,
4. Soil disturbance within 100 feet of a stormwater conveyance system.
The purpose of adding these additional categories of development projects are: 1) to simplify and
strengthen the County’s existing requirements for structural erosion control plans under the
Conservation Regulations and 2) to ensure that projects with a high potential to pollute
waterways have an adequate plan to prevent all potential illicit discharges.
1. Proposed changes to existing Conservation Regulations
The proposed Construction Site Runoff Control policy will simplify the County’s Conservation
Regulations by eliminating the need to apply for a separate Erosion Control Plan Permit. Under
the proposed Construction Site Runoff Control requirements, a Stormwater Quality Management
Plan (SQMP) or Stormwater Pollution Prevention Plan (SWPPP) will be submitted with a
building or grading permit application. These plans will be reviewed by the Department of
Public Works for completeness and will be approved as a ministerial action. The plan review fee
will be based upon time and materials and is expected to cost significantly less than the fees
currently charged for an Erosion Control Plan permit.
The proposed policy also makes changes to the grading deadlines for structural projects on
slopes greater than 5% to better reflect Napa County’s rainy season. The figure below shows the
average monthly precipitation in the City of Napa and Angwin.
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Average Monthly Rainfall
10
9
Napa Fire Department (NSH)
8
Angwin Pac Union College (APU)
Precipitation (Inches)
7
6
5
4
3
2
1
0
October
November
December
January
February
March
April
May
June
July
August
September
Under the existing Conservation Regulations, projects within Sensitive Domestic Water Supply
Watersheds (SDWSWs) and on slopes 5% or greater are required to cease all grading by
September 1st of each year. Extensions of this deadline cannot be granted by the Conservation,
Development, and Planning Department. Under the proposed requirements, earthwork and
grading is prohibited from October 15th though April 15th for ALL projects on slopes 5% or
greater, regardless of watershed type. This proposed change to the Conservation Regulations will
extend the grading season for projects in SDWSWs by four weeks and shorten the grading
window for projects in non-SDWSWs by two weeks. Grading on slopes under 5% will continue
to be allowed throughout the year.
The extension of the grading season within SDWSWs is not likely to negatively impact Napa
County’s water supply and other beneficial uses for the following reasons.
1. Under most circumstances the average rainfall generated during the months of September
and October does not generate significant runoff. Most of this rainfall is absorbed by the
soil and it is not until late October or November that soils become saturated to the point
where surface runoff is generated.
2. The grading restrictions in the SDWSWs were adopted as a result of failed vineyard
erosion control plans that contaminated municipal water supplies with sediment. The
grading restriction for vineyards development may be appropriate in SDWSWs due to the
fact that most of these projects disturb a large area of land, however, structural, road,
driveway, and non-agricultural mass grading projects generally disturb a smaller area and
therefore are easier to manage in terms of erosion and sediment control.
3. The proposed policy requires all structural projects to implement a weather-triggered
BMP implementation plan whenever there is a 40% or greater chance of precipitation
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regardless of the time of year. These BMPs must be fully implemented to eliminate all
pollutants (sediment, nutrients, pathogens, oils, pesticides, etc) from stormwater runoff.
4. The County’s construction site runoff control program will be more inspection intensive
than the existing Conservation Regulations. In addition to conducting inspections at the
onset of the wet season and upon completion of construction, the new program will
conduct inspections during each rain event greater than 0.25 inches to ensure that illicit
discharges eliminated. The frequency of inspection at a particular site will depend on the
projects inspection priority and past compliance.
2. Proposed additional project categories required to prepare a SQMP/SWPPP.
While the Phase II General Permit only requires Napa County to establish requirements for
projects over one acre, projects that disturb more than 10,000 sq ft, move 50 or more cubic feet
of soil, or are located within 100 feet of a stormwater conveyance system will be subject to the
proposed Construction Site Runoff Control requirements. These additional project categories
were included because they are likely to generate illicit discharges and violate Local, State, and
Federal laws if effective BMPs are not implemented. By requiring these projects to prepare a
SQMP or SWPPP, the County will reduce the number of illicit discharges and associated
enforcement actions against project applicants and contractors.
After comments are reviewed and discussed, it is anticipated that staff will proceed to introduce
the policy for Board of Supervisor’s action in May 2005. Your input and review of the draft
policy is valued. Please give me a call if you have any questions regarding these proposed
regulations to protect stormwater runoff from pollution.
Sincerely,
Todd Adams
Stormwater Program Specialist
707-253-4823
Enclosure