Last Updated 07/21/2026
Modesto Stormwater Laws & Regulations
The City of Modesto has enacted a Stormwater Ordinance in order to establish minimum stormwater management requirements and controls to protect and safeguard the general health, safety, and welfare of the public residing in watersheds within this jurisdiction. The City of Modesto is the permitting authority for all land disturbing activities and requires the land owner to maintain all on-site stormwater control facilities and all open space areas (e.g. parks or “green” areas) required by the approved stormwater control plan. The City of Modesto will only provide construction permits to projects that establish a plan to manage stormwater runoff occurring during the construction process. The City of Modesto, under the NPDES program, also has the authority to inspect properties for noncompliance and can issue a notice of violation (NOV) for any deficiency or infraction onsite. Property owners are responsible for the maintenance of any stormwater facilities or practices located on the property. The City of Modesto has the authority to inspect stormwater facilities and practices in order to ascertain that they are properly maintained and functioning.
EXCERPT-City of Modesto Stormwater Management Program
2011 Guidance Manual for Development Stormwater Quality Control Measures
‘The control measures, often termed Best Management Practices (BMPs), described in the 2011 Guidance Manual were selected to optimize post-construction, on-site stormwater pollution control. All Priority Projects must apply all four categories of stormwater pollution control measures: Site Design Control Measures (Section 4); Source Control Measures (Section 5); Low Impact Development Control Measures (Section 7); and Treatment Control Measures (Section 8).”
9.1. Maintenance Plan
A post-construction Maintenance Plan shall be prepared and submitted to the City as part of the Project Stormwater Quality Control Measures Plan submittal. The Maintenance Plan should address items such as: Operation plan and schedule, including a site map; Maintenance and cleaning activities and schedule; Equipment and resource requirements necessary to operate and maintain facility; and Responsible party for operation and maintenance.
This section identifies basic information that shall be included in a Maintenance Plan.
Refer to Fact Sheets for individual control measures regarding device-specific maintenance requirements. Site Map Provide a site map showing boundaries of the site, acreage, and drainage patterns/contour lines. Show each discharge location from the site and any drainage flowing onto the site. Distinguish between soft and hard surfaces on the map. Identify locations of existing and proposed storm drain facilities, private sanitary sewer systems, and grade breaks for purposes of pollution prevention. With a legend, identify locations of expected sources of pollution generation (e.g., outdoor work and storage areas, heavy traffic areas, delivery areas, trash enclosures, fueling areas, industrial clarifiers, and wash-racks). Identify any areas having contaminated soil or where toxins are stored or have been stored/disposed of in the past. With a legend, indicate types and locations of stormwater control measures that will be built to permanently control stormwater pollution. Distinguish between pollution prevention, treatment, sewer diversion, and containment devices.
Baseline Descriptions List property owners and persons responsible for operation and maintenance of the stormwater control measures on-site. Include phone numbers and addresses. Identify intended method of funding (i.e., homeowners association fees) for operation, inspection, routine maintenance, and upkeep of stormwater control measures. List all permanent stormwater control measures. Provide a brief description of stormwatercontrol measure selected and, if appropriate, fact sheets or additional information.
As appropriate for each stormwater control measure, provide:
- A written description and checklist of all maintenance and waste disposal activities that will be performed. Distinguish between the maintenance appropriate for a 2-year establishment period and expected long-term maintenance. For example, maintenance requirements for vegetation in a constructed wetland may be more intensive during the first few years until thevegetation is established. The post-establishment maintenance plan shall address maintenance needs (e.g., pruning, irrigation, weeding) for a larger, more stable system. Include maintenance performance procedures for facility components that require relatively unique maintenance knowledge, such as specific plant removal/replacement, landscape features, or constructed wetland maintenance. These procedures shall provide enough detail for a person unfamiliar with maintenance to perform the activity or identify the specific skills or knowledge to perform and document the maintenance.
- A description of site inspection procedures and documentation system, including recordkeeping and retention requirements.
- An inspection and maintenance schedule, preferably in the form of a table or matrix, for each activity for all facility components. The schedule shall demonstrate how it will satisfy the specified level of performance, and how the maintenance/inspection activities relate to storm events and seasonal issues.
- Identification of equipment and materials required to perform maintenance. As appropriate, list all housekeeping procedures for prohibiting illicit discharges or potential illicit discharges to the storm drain system. Identify housekeeping BMPs that reduce maintenance of treatment control measures.Spill Plan Provide emergency notification procedures (phone and agency/persons to contact). As appropriate for site, provide emergency containment and cleaning procedures. Note downstream receiving waters, wetlands, or ESAs that may be affected by spills or chronic untreated discharges. As appropriate, create an emergency sampling procedure for spills. Emergency sampling can protect the property owner from erroneous liability for downstream receiving area cleanups.
Facility Changes
“Operational or facility conditions or changes that significantly affect the character or quantity of pollutants discharging into the stormwater control measures may require modifications to the Maintenance Plan and/or additional stormwater controls.”
Basic Inspection and Maintenance Activities
“Create and maintain on-site, a log for inspector names, dates, and stormwater control measure devices to be inspected and maintained. Provide a checklist for each inspection and maintenance category. Perform and document annual testing of any mechanical or electrical devices prior to wet weather. Report any significant changes in stormwater control measures to the site management. As appropriate, assure mechanical devices are working properly and/or landscaped BMP plantings are irrigated and nurtured to promote thick growth. Note any significant maintenance requirements due to spills or unexpected discharges. As appropriate, perform maintenance and replacement as scheduled and as needed in a timely manner to assure stormwater control measures are performing as designed and approved. Assure unauthorized low-flow discharges from the property do not bypass stormwater control measures. Perform an annual assessment of each pollution-generating operation and its associated stormwater control measures to determine if any part of the pollution reduction train can be improved. Annual assessment reports must be submitted to the City.”
9.2. Maintenance Agreement
Verification of maintenance provisions is required for all stormwater control measures specified in the2011 Guidance Manual, whether Site Design Control Measures (Section 4), Source Control Measures (Section 5), LID Control Measures (Section 7), or Treatment Control Measures (Section 8). Verification, at a minimum, shall include: The owner/developer’s signed statement accepting responsibility for inspection and maintenance until the responsibility is legally transferred. A sample Owners Certification statement is provided in Appendix D; and either. A signed statement from the public entity assuming responsibility for stormwatercontrol measure inspection and maintenance and certifying that it meets all City design standards; or Written conditions in the sales or lease agreement that require the recipient to assume responsibility for inspection and maintenance activities and to conduct a maintenance inspection at least once a year; or written text in project conditions, covenants, and restrictions for residential properties that assign maintenance responsibilities to the Home Owners Association for inspection and maintenance of stormwater control measures; or a legally enforceable maintenance agreement that assigns responsibility for inspection and maintenance of post-construction control measures to the owner/operator. A Maintenance Agreement with the City must be executed by the owner/operator before occupancy of the project is approved. Example Maintenance Agreement forms are provided in Appendix D.
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Frequently Asked Questions
What is a post-construction Maintenance Plan, and does my Modesto property need one?
Yes, if your project is designated a Priority Project. The plan has to be prepared and submitted to the city as part of your Project Stormwater Quality Control Measures Plan, and it needs to cover the operation schedule, cleaning activities, required equipment and resources, and who’s responsible for ongoing operation and maintenance.
What has to be included on the site map in my Modesto Maintenance Plan?
More detail than a typical site plan. It needs property boundaries, acreage, drainage patterns, every discharge location, and a distinction between soft and hard surfaces. You also have to mark expected pollution sources like outdoor storage, delivery areas, and wash racks, along with any areas with contaminated soil or a history of toxin storage, and show exactly where your permanent stormwater controls sit relative to all of that.
Do I need to identify who pays for stormwater maintenance in Modesto?
Yes. Your Maintenance Plan has to name the property owners and responsible parties, including contact information, and identify the intended funding method, whether that’s homeowners association fees or another mechanism, for ongoing operation, inspection, and upkeep.
How often do I need to test mechanical stormwater equipment in Modesto?
At least annually, and specifically before wet weather season. The city’s guidance requires performing and documenting that testing ahead of the rainy season so mechanical or electrical stormwater devices are confirmed to be working before they’re actually needed.
Do I have to submit anything to the city every year after my stormwater controls are approved in Modesto?
Yes. An annual assessment of each pollution-generating operation and its associated control measures is required, evaluating whether any part of the site’s pollution reduction approach can be improved, and that assessment report has to be submitted to the city.
Can I modify my stormwater controls in Modesto without city approval?
No. Any future correction or modification to existing stormwater control measures or procedures requires city approval before work begins, and whatever changes you make can’t cause discharges to bypass or otherwise impede the controls already in place.
What are my options for formally assigning stormwater maintenance responsibility in Modesto?
A few paths, depending on your property type. You can use a signed owner or developer statement accepting responsibility, a public entity’s signed statement assuming responsibility, written conditions in a sales or lease agreement requiring at least one maintenance inspection a year, CC&Rs assigning responsibility to a homeowners association, or a standalone legally enforceable maintenance agreement. Whichever path you choose, a Maintenance Agreement with the city has to be executed before your project can be occupied.
Does a change in how my Modesto property operates affect my stormwater obligations?
It can. Any operational or facility change that significantly affects the type or amount of pollutants discharging into your stormwater controls may require updating your Maintenance Plan or adding further control measures, so a change in use or tenant activity is worth reviewing against your existing plan.
How can AQUALIS help my property stay compliant with Modesto's stormwater requirements?
AQUALIS helps Modesto property owners prepare the detailed Maintenance Plan the city requires for Priority Projects, conduct the annual mechanical testing and pollution-source assessments the guidance manual calls for, and put a legally enforceable maintenance agreement in place before occupancy approval.
The information on this page is provided for general informational purposes only and is not legal advice. Regulations change frequently — AQUALIS makes no warranty as to the accuracy or completeness of this content, and any reliance on it is at your own risk. Consult a qualified professional or your local regulatory authority to confirm requirements applicable to your specific property.
