Water Quality Monitoring has been an integral component of the Ventura Countywide National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) permit (Permit) since the first Permit was issued in 1994. Previous permits have focused on Mass Emission, Receiving Water, and Land Use water quality monitoring. The current Permit (adopted in 2010) focuses on Mass Emission and Major Outfall water quality monitoring.
Mass Emission Monitoring
The purpose of mass emission monitoring is to identify pollutant loads to the ocean and identify long- term trends in pollutant concentrations in the receiving waters. Mass Emission sites are located in the lower reaches of the three major Ventura County watersheds: Calleguas Creek (ME-CC), Ventura River (ME-VR2), and Santa Clara River (ME-SCR). Mass Emission drainage areas are large and include multiple sources of discharge, including natural sources, wastewater treatment plants, municipal and agricultural sources, and groundwater discharges. Monitoring at these sites allows the Program to measure water quality parameter concentrations resulting from discharges throughout an entire watershed and evaluate the cumulative effects of stormwater and other surface water discharges on beneficial uses in the watershed prior to discharge to the ocean.
In accordance with the current NPDES permit, water quality samples are collected for chemistry, and bacteriological analysis from each Mass Emission site during three wet weather events including the first significant (>0.25”) storm during the wet season (October 1 – April 15) and one dry weather event during each monitoring year (July 1 – June 30). Aquatic toxicity samples are collected during the first significant storm of the season.
Major Outfall Monitoring
Major Outfall stations, a component of the Permit since 2009, are located in subwatersheds representative of each Co-Permittee’s jurisdiction, and are used to determine their contribution to downstream waters. Stations are located in the Cities of Camarillo (MO-CAM), Fillmore (MO-FIL), Moorpark (MO-MPK), Ojai (MO-OJA), Oxnard (MO-OXN), Port Hueneme (MO-HUE), Santa Paula (MO-SPA), Simi Valley (MO-SIM), Thousand Oaks (MO-THO), and Ventura (MO-VEN), and the County unincorporated area (MO-MEI in Meiners Oaks).
Receiving Water (Tributaries) Monitoring
Land Use Site (Discharge Characterization) Monitoring