Stormwater Compliance

Stormwater Compliance
It’s Up to Us to Prevent Stormwater Pollution
The City of San Dimas has two drainage systems, (1) the sewers and (2) the storm drains. The storm drain system was designed to prevent flooding by carrying excess rainwater away from city streets out to the San Gabriel River and finally, out to the ocean. During storms in urban areas, rainwater runoff carries pollutants generated from commercial businesses, residential areas, streets, and sidewalks, directly to the ocean, creating stormwater pollution. Materials such as sediment, paint, plaster, yard waste, used motor oil, animal waste, and trash contain chemicals, nutrients, and bacteria that are harmful to aquatic life and humans.

Tips to Prevent Stormwater Pollution
To prevent stormwater pollution, follow these simple tips:
  • Never pour household hazardous waste materials down the drain, onto sidewalks or into catch basins. Take these materials to a hazardous waste materials collection center or round-up event. For the next Household Hazardous Waste Round-up, visit the
  • Use pesticides, herbicides, and fertilizers according to the label instructions. Remember not to apply them before rain and avoid overwatering your plants or lawn.
  • When walking your pets, remember to pick up your animal's waste and dispose of it in a trashcan.
  • Never put motor oil in the trash or pour it on the ground or down a storm drain. For more information on used motor oil or filter, recycling click on the following link Used Oil & Filter Recycling.
  • If you're using latex-water-based paints, you can wash your paintbrushes directly in your kitchen or bathroom sink. Don't rinse your brushes into the street.
  • If you use oil-based paints, clean them by rinsing brushes with solvent in a container. Take the unused liquid and residue to an HHW collection event. For the next Household Hazardous Waste Round-up, visit the Los Angeles County Public Works website.
Illegal disposal of any material other than stormwater in the storm drain system is a violation of the National Pollutant Discharge Elimination System (NPDES) Permit (Section 402 of the Federal Clean Water Act). Violators and cities can be subject to serious financial penalties in excess of $10,000 per day.  Call the City of San Dimas Public Works Department at (909) 394-6240 or Los Angeles County Department of Public Works at 888-CLEAN LA (888-253-2652) for more information on stormwater pollution prevention or to report illegal dumping.

Annual Stormwater Reports

The City tracks the implementation of stormwater compliance measures through the Annual Report process. Data is collected by the city throughout the year and reported to the Los Angeles Regional Quality Control Board each December. Annual Reports are available for review at the Los Angeles Regional Water Quality Control Board office in downtown LA or online on the California Water Boards website.

Stormwater Quality and Regulations
Water quality is a growing concern in communities throughout the country and municipalities including San Dimas are focusing on storm-water runoff as one approach to address this concern. Storm-water runoff results from rain or melting snow in some areas that are not absorbed into the ground. Runoff is also generated outside of the “rainy season” by nuisance water resulting from activities such as over-watering lawns, vehicle washing, or draining of swimming pools and other water features. This excess water carries trash, motor oil, fertilizers, pet waste, and other contaminants directly to our lakes, streams, and beaches untreated. Excess contaminants dumped into our environment and the depletion of our valuable water resources negatively affect the entire community. Many cities like San Dimas will be at risk of serious fiscal impacts, including fines (could be up to $10,000 per day per violation), costly retrofit projects, and repairs if the storm-water quality is not properly addressed. Federal regulations such as the National Pollutant Discharge Elimination System (NPDES) Permit are a catalyst for San Dimas to create storm-water quality programs.

For additional information regarding the new and previous NPDES Permit requirements, as well as program updates, please call 909. 394.6242.

Watershed Control Measure Milestone Progress
Below is a summary on Watershed Control Measure requirements and dates for these milestones as identified in the East San Gabriel Valley Watershed Management Program for the period beginning July 1, 2021, through June 30, 2022.  The document submittals related to the East San Gabriel Valley Watershed Management Group are available on the California Water Board website:

In 2015, the Cities of Claremont, La Verne, Pomona, and San Dimas, collectively referred to as the East San Gabriel Valley Watershed Management Group (the Group), developed a Watershed Management Program (WMP) to fulfill the requirements of the National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) Permit No. R4-2012-0175 (2012 Permit). The original WMP established the scheduling of Best Management Practices (BMPs) by applying percent milestones from the San Gabriel River and Impaired Tributaries Metals and Selenium TMDL (Metals TMDL) to the runoff volume from the 85th-percentile storm. For example, the Metals TMDL requires 35% compliance in 2020 for lead in wet weather and the 2015 WMP proposed capturing 35% of runoff from the 85th-percentile storm by 2020. While the compliance pathway chosen in the 2015 WMP was to capture runoff from the 85th percentile storm, the actual required reductions and volume of stormwater capture were uncertain due to the limited availability of water quality data within the Group’s WMP area. The Group acknowledged that monitoring data collected through implementing the Coordinated Integrated Monitoring Program would allow a more refined assessment of the receiving water quality in the Group’s WMP area. Therefore, the assessment to track progress on Watershed Control Measure requirements was evaluated by measuring the percent compliance of water quality samples compared to the water quality objectives. For example, in 2020, 35% of wet weather data collected for a given constituent (except E. coli) were to be in compliance with water quality objectives. (E. coli was analyzed differently, as it has an established Total Maximum Daily Load (TMDL) with final deadlines of 6/30/2026 for dry weather and 6/30/2036 for wet weather.)

Progress toward achieving these milestones is documented yearly in the Group’s Watershed Annual Report Forms. Table A documents the Group’s progress reported in the Reporting Year 2021-2022 Annual Report. The constituents included in Table A are E. coli, dissolved copper, dissolved zinc, dissolved lead, selenium, and nutrients. The 2015 WMP identified the limiting pollutant for dry weather as E. coli and the limiting pollutant for wet weather as zinc. Dissolved lead and selenium are the applicable constituents for the Group from the Metals TMDL. Similarly, nutrients are noted in the Los Angeles Area Lakes TMDLs for Puddingstone Reservoir. Table A shows that the Group is generally successful in respect to the 2020 compliance objectives. The first of two dry weather sampling events revealed exceedances for dissolved copper at San Jose Creek and San Dimas Wash. Low hardness is suspected to be the cause of exceedances, and these data points are presumed to be an outlier. The second dry weather sampling revealed that concentrations returned to compliance levels. No other exceedances in respect to 2020 objectives were noted.

Table A – Percent Compliance of Collected Water Quality Data versus Water Quality Objectives

Section 1.1

It should be noted that the Group submitted an update to the WMP in 2021 with a resubmittal in 2022, which is pending approval. The compliance milestones for metals and nutrients in the 2022 WMP are extended based on the analysis of monitoring data, modeling results, and available Safe, Clean Water Program funding for capital projects to address issues. The compliance milestones for bacteria continue to be set forth by the TMDLs for Indicator Bacteria in San Gabriel River, Estuary, and Tributaries.

The Group has collaborated with others to work toward achievement of the WMP milestones. As part of WMP implementation the Group has been implementing the Public Information and Participation Program Minimum Control Measures. Informational flyers and a short video educating the community about the stormwater program were developed for distribution in City Halls, during community events, and posted online to solicit community input. Additional presentations were provided at City Council meetings and on city websites that are televised to distribute information regarding 2012 Permit compliance to interested parties. More recently, the Group has provided opportunity for input and public comment during project development for regional projects submitted to the Safe, Clean Water (SCW) Program for funding, including conversations with the Bonita Unified School District, La Verne Little League, San Dimas Little League, and the Los Angeles County Fair Association. The Group has also coordinated with the Six Basins Watermaster to perform a site selection prioritization process. The goal of the project was to coordinate the benefits associated with stormwater treatment projects to drive additional groundwater supply and production during the historic California drought. The project successfully produced the document titled Reconnaissance-Level Recharge Study in the Six Basins (February 2020). Conceptual project designs were produced for eight potential projects, six of which are in the WMP area: Brackett Field, LA County Fairplex, Las Flores Park, Lutheran High School, Pedley Spreading Grounds, and La Puerta Sports Park. Conceptual project development included coordination with landowners and identification of potential multi-benefits for inclusion in the projects. The Group has initiated contact with CALTRANS to coordinate stormwater programs and identify collaborative projects for potential cost sharing. The major CALTRANS right-of-ways within the WMP area include the 210, 10, 57, 60, and 71 Freeways and Foothill Blvd (Route 66). The outreach effort has resulted in a decision to evaluate the potential for collaboration on a project-by-project basis. As a potential cost sharing partner, Caltrans has identified two routes of potential funding options, the Cooperative Implementation Agreement and the Financial Contribution Only. Finally, the Group has met with the Regional Board several times throughout the past few years to explain challenges, seek clarity, and ask questions, while collaborating to develop feasible solutions. The Group will continue to solicit input of interested parties as part of the Capital Improvement Project Planning process associated with regional projects. In addition, these projects will be featured at respective city council meetings attended by the public. Participation from interested parties will continue to occur as WMP implementation and detailed designs of projects progresses.

To-date, the Group has received funding from the SCW Program for stormwater capture projects at the Pedley Spreading Grounds for design and construction, as well as at Fairplex, Lone Hill Park, Pelota Park, and Marchant Park for design only. Once constructed, these projects will provide multi-benefits to the community, such as increasing the native plant palette, improving recreational opportunities within the project area, providing educational opportunities, and increasing water supply. In 2020, the City of Claremont completed a 2-mile Green-Streets project along Foothill Boulevard, from Towne Avenue to Monte Vista Avenue. The project serves a 151-acre tributary area, incorporating stormwater infiltration and groundwater recharge sustainability practices. The project creates and/or restores 65,000 square feet of green habitat and replaces over 37,000 square feet of impermeable asphalt with bio-swales that capture both stormwater and dry-weather flows, redirect drainage away from the existing storm drain system, and prevent polluted water from discharging to local creeks and rivers (San Gabriel and Middle Santa Ana rivers). In addition, the project features educational kiosks throughout its length. The project is designed with a total retention capacity of 3.66 acre-feet; additional infiltration testing will be conducted to more accurately reflect the capacity of the system.