Update on City of Torrance Stormwater Quality Projects
This presentation summarizes some of the lessons learned in performing stormwater monitoring and reporting for stormwater projects in the City of Torrance (“the City”). The goal of this presentation will be to provide data and experience regarding monitoring activities, sample collection methodologies, health and safety concerns, and the implementation of multi-benefit projects utilizing stormwater to assist in future stormwater design and field management strategies. The content of this proposed presentation follows the conference theme of “Stormwater Evolution: Source to Resource” as the project work discussed will highlight pollutant source recognition, groundwater recharge, and habitat management through the City’s multi-benefit stormwater basins project that retains, treats, and infiltrates runoff.
The City is a permittee under the Los Angeles County Municipal Separate Storm Sewer System (MS4) permit, and discharges stormwater accordingly. Northgate Environmental Management, Inc. (Northgate), provides monitoring and reporting services to the City to quantify changes in stormwater runoff volumes and pollutant loading for compliance with the Machado Lake Nutrient and Toxics Total Maximum Daily Loads (TMDL) regulations. The monitoring shows that the City has been significantly below both interim and final waste load allocations for total nitrate and total phosphorous in stormwater discharge. Nitrogen as nitrate, nitrite, ammonia, total Kjehdal nitrogen, total phosphorous, orthophosphate, total suspended solids, total organic carbon, pesticides, PCBs, and field water quality parameters were measured in stormwater or sediment extracted from the stormwater. Samples are collected in underground conveyances, surface culverts, and reservoirs. Flow measurement is accomplished using a combination of field portable equipment and dedicated electronic flow sensors installed within the conveyances. Challenges with sampling surface runoff, and issues created with laboratory data QA/QC in non-homogeneous sample streams will be discussed.
The City implemented a multi-benefit project that reconstructed the Amie, Henrietta, and Entradero Stormwater Basins to retain, treat, and infiltrate runoff (Stormwater Basins Enhancement Project or “the Project”). The Project provides passive wetlands treatment, stormwater retention and infiltration, enhanced groundwater recharge, improved public trails and recreational opportunities, and habitat restoration. Runoff from the Project enters the Herondo Drain, eventually draining to the Santa Monica Bay. Fecal indicator bacteria, total suspended solids, total oil and grease, and field water quality parameters were measured in the stormwater samples. Initial indications show that after the Project was completed, bacterial exceedances in the receiving waters of the Santa Monica Bay Beaches have declined.
Northgate will also present some of the unique worker health and safety considerations related to water sampling and flow measurement in underground conveyances and artificial structures. Routine sampling is performed without workers entering the underground conveyance by utilizing specialized sampling and flow monitoring equipment designed to be operated at the surface. When entry into the underground conveyance is required, Northgate implements confined space entry and manhole safety protocols and utilizes specialized safety equipment to ensure worker safety.
Through the combined efforts of the TMDL, toxics, and bacteria monitoring with the multi benefit stormwater basins project to retain, treat, and infiltrate runoff, the City maintains a strong commitment to stormwater management and utilizing stormwater as a resource. Audience members will learn the overall goals, methodologies, and current status of the various aspects of the stormwater program for the City.