Stormwater

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Program Description

The purpose of Monterey County Code Chapter 16.14 is to enhance watercourses within the unincorporated Urbanized Areas by, among other methods, controlling the entry of urban pollutants into stormwater runoff that may enter the County storm drain system. Other goals of this chapter include, but are not limited to, benefit the people and the environment of the County by protecting water quality in the waters within its jurisdiction, reduce the presence of pollutants in stormwater to the maximum extent practicable, and effectively prohibit non-stormwater discharges into the County storm drain system. For all projects across the County of Monterey, regardless of the total land disturbance, the peak offsite drainage of a parcel can’t increase post-development.

The federal Clean Water Act mandates that any municipal, industrial, or commercial facility that discharges storm water runoff must first obtain coverage under a National Pollutant Discharge Elimination System (NPDES) permit. In California, the State Water Regional Control Board (SWRCB) and the nine Regional Water Quality Control Boards have been given regulatory authority by the federal government to manage NPDES programs. In July 2013, the Central Coast Water Board adopted Order R3-2013-0032 with more stringent Post Construction Requirements (PCRs).

What is Stormwater and why is it important to manage?

Stormwater can be defined as rain, snowmelt or any other precipitation event that flows over the land or any other surface (MCCO 16.14.030). This runoff water will percolate into the ground, be absorbed by vegetation, evaporate or flow over the land into rivers, lakes and storm drains.

As urban development and expansion becomes more prevalent, the amount of impermeable ground surfaces increase. Impermeable ground surfaces such as parking lots, sidewalks, roofs and compacted soils increases the amount of runoff into waterways and decreases the amount of water that slowly infiltrates back into the ground. The water runoff that flows over the impermeable ground surfaces can accumulate sediment, fertilizers, pesticides, gasoline, heavy metals, animal waste, litter, etc., which, if left untreated can diminish the quality of local waterways.

What Projects must comply with the Post Construction Requirements?

Only projects located within the NPDES Municipal General Permit Boundary that create or replace a Net Impervious Area of over 2,500 square feet (SF) are generally subject to the state adopted Post Construction Requirements (PCRs). See the “NPDES Urbanized Area Post Construction Requirements” section below for more information and how to determine what PCRs are applicable to your project.

Net Impervious Area = (Total New and Replaced Impervious Area) – (Total Reduced Impervious Area)

Projects outside the NPDES Municipal General Permit Boundary that create or replace a Net Impervious Area of over 2,500 SF don’t require adherence to the PCRs.

NPDES Urbanized Area Post Construction Requirements

The Post-Construction Requirements (PCRs), adopted by the Central Coast Water Board in July 2013, will require projects located within the NPDES General Permit Boundary Urbanized Areas to implement a range of low impact development (LID) techniques. The goal of LID techniques is to better enable water to infiltrate into the soil before it becomes runoff. The PCRs emphasize protection and restoration of watersheds to promote sustainable relationships required for a watershed to be considered healthy.

The PCRs required for a project are generally dependent on a projects net impervious area, whether it is a detached single-family residence, and what Watershed Management Zone (WMZ) it is within. The Stormwater Technical Guide, developed by the Monterey Regional Stormwater Management Program, can be used to determine which PCRs are applicable to your project.

In general, the PCRs begin once a project has a net impervious area over 2,500 square feet. The PCRs become increasingly in depth depending on what range the net impervious area falls into above the 2,500 SF minimum.

Watershed Management Zones

The urbanized area of the Central Coast Region is categorized into 10 Watershed Management Zones (WMZs), based on common key watershed processes and receiving water type (creek, marine nearshore waters, lake, etc.). Identifying the WMZ that your project is in will be necessary for projects that must implement Post Construction Requirement No. 3 Runoff Retention and Post Construction Requirement No. 4 Peak Management.

Groundwater Basins underlie some of the Watershed Management Zones (WMZs) in the urbanized area, but not all. Identifying the Groundwater Basin, if present, and Watershed Management Zone that your project is in will be key in implementing applicable Post Construction Requirements (PCRs).

To determine your projects WMZ use the County of Monterey GIS Parcel Viewer Map to view the Watershed Management Zones layer under the Stormwater Layer dropdown.

What Projects must obtain a Construction General Permit through the State?

Construction projects within the County of Monterey that disturb a total area of one (1) acre or more, or are a part of a larger project disturbing one or more acre, are required to apply for a Construction General Permit as per the California State Water Resources Control Board NPDES General Permit for Stormwater Discharges Associated with Construction and Land Disturbance Activities (Order WQ 2022-0057-DWQ NPDES No.CAS000002).

Land disturbance activities include, but are not limited to, the following that temporarily or permanently disturb earth materials:

Clearing, Grading, Excavation, Stockpiling, Demolition
Construction activity related to residential, commercial, or industrial development on lands currently used for agriculture

Land disturbance activities that are exempt from the State Construction General Permit include, but are not limited to, the following:

Routine maintenance of road and highway projects where the underlying soil and erodible subgrade (road surface and base aren’t apart of the subgrade) aren’t exposed
Disturbance to land surfaces solely related to growing crops or agricultural operations, such as disking, harrowing, terracing, etc.

Construction General Permit Application Process

Once a project’s total disturbed acreage triggers the state requirement, construction activities can’t begin until Environmental Services (ES) Staff receive confirmation of a valid Construction General Permit in the form of a Notice of Intent (NOI), Stormwater Pollution Prevention Plan (SWPPP), and a Waste Discharge Identification (WDID) number. By providing these documents it also shows that the State has approved for construction to begin.

If your project triggers the disturbance requirements, the general steps with the County and State requirements to obtain your County permit are as follows:

Setting up a Legally Responsible Person (LRP) account within the State’s Stormwater Multiple Application and Report Tracking System (SMARTS) and submitting all plans, calculations, and supporting docs needed to complete the NOI
Submitting a project-specific SWPPP made by a qualified individual
Obtaining a WDID from the State
Send Monterey County ES Staff the final NOI, SWPPP, and WDID

Stormwater Control Plan Requirements

For projects that create or replace a Net Impervious Surface area of over 15,000 square feet, a Stormwater Control Plan must be submitted to ES Staff. This plan shall include at minimum the following:

Project type and description
Total new impervious area
Total replaced impervious area
Total pre-project impervious area
Total post-project impervious area
Net impervious area
Watershed Management Zone
Groundwater Basin (if applicable)

Watershed Management Zones and Groundwater Basins

The urbanized area of the Central Coast Region is categorized into 10 Watershed Management Zones (WMZs), based on common key watershed processes and receiving water type (creek, marine nearshore waters, lake, etc.). Identifying the WMZ that your project is located in will be necessary for projects that must implement Post Construction Requirement No. 3 Runoff Retention and Post Construction Requirement No. 4 Peak Management.

Groundwater Basins underlie some of the Watershed Management Zones (WMZs) in the urbanized area, but not all. Identifying the Groundwater Basin, if present, and Watershed Management Zone that your project is located in will be key in implementing applicable Post Construction Requirements (PCRs).

View the GIS Map.

Best Management Practice Guidance Series - Pre-Construction

Stormwater Management Resources (Links)

NOTICE – ARCHIVED DOCUMENT SECTION

The electronic files below are exempt from compliance with ADA web accessibility requirements pursuant to 28 C.F.R. 35.201(a) and (b). These files are considered preexisting conventional electronic documents, retained exclusively for reference, research, or recordkeeping. No updates of or changes to the documents in this section will occur. If you need assistance accessing any of the documents in this section, please contact us at 831-755-5025.

Stormwater Management

Structural Stormwater Control
- Site Design and Runoff Reduction Checklist

Maps

1441 Schilling Place

South 2nd Floor

Salinas, CA 93901

831-755-5025

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