TMDL for Chlorpyrifos and Diazinon in Lower Salinas River Watershed, Monterey County, California
This page is a a summary of the Regional Water Quality Control Board Central Coast Region report on Total Maximum Daily Load for chlorpyrifos and diazinon for the Lower Salinas River Watershed, Monterey County, California (Rose et al. 2011). The summary was prepared by the Spring '11 ENVS 560/L Watershed Systems class at CSUMB.
Project DefinitionCCRWQCB), the State Water Resources Control Board and the Environmental Protection Agency (EPA) approved the Total Maximum Daily Load (TMDL) report for the pesticides, chlorpyrifos and diazinon for the Lower Salinas River Watershed in Monterey County, California. The TMDL report evaluated: current concentrations of both pesticides in the watershed area waterbodies, source identification, contaminant reduction, implementation actions, and monitoring requirements.
The water bodies of the Lower Salinas River Watershed are used for a variety of purposes including, but not limited to: groundwater recharge, wildlife habitat, industrial and agricultural supply, commercial and recreational fishing, and other recreational activities. When a water body fails to meet the minimum quality standards required for its beneficial uses (assigned purposes), a TMDL is established.
In 2001 the EPA reviewed the registration for both chlorpyrifos and diazinon. The EPA mandated the restriction of both pesticides including the phase out and elimination of all residential and non-agricultural uses. These restrictions were expected to facilitate concentration reductions within the impaired waters of the Lower Salinas River Watershed. However, widespread agricultural use of these two pesticides continues to influence water quality.
The TMDL for Chlopyrifos and Diazinon addresses the following impaired waterbodies:
|Water Body||Chlorpyrifos||Diazinon||Unknown Toxicity||Pesticides|
|Moss Landing Harbor||2008 5A||2008 5A||2008 5A||1990 5A|
|Old Salinas River Estuary||1990 5A|
|Old Salinas River||2008 5A||2008 5A||2008 5A|
|Salinas River Lagoon (North)||1992 5A|
|Tembladero Slough||2008 5A||2008 5A||2008 5A||1996 5A|
|Alisal Slough||2008 5A|
|Blanco Drain||2008 5A||2008 5A||1998 5A|
|Salinas Reclamation Canal||2008 5A||2008 5A||2008 5A||1992 5A|
|Salinas River||2008 5A||2008 5A||2008 5A||1994 5A|
|Espinosa Slough||2008 5A||2008 5A||1996 5A|
|Espinosa Lake||2008 5A||2008 5A|
|Natividad Creek||2008 5A|
|Quail Creek||2008 5A||2008 5A||2008 5A|
|Chualar Creek||2008 5A||2008 5A||2008 5A|
- The number represents the first year the water body was listed for the given impairment | Class 5 describes a water body where the TMDL water quality standards are not met and a TMDL is required but not complete.
The project area consists of the Salinas River valley floor north of Gonzalez, out to the dunes along the Monterey Bay. The TMDL study is defined by the lower 400 square miles (195,000 acres) of the Lower Salinas River Watershed and includes two major drainage ways leading to Moss Landing Harbor and Salinas River Lagoon (North).
Surface water sources include precipitation, releases from reservoirs, groundwater, and return flows from agricultural irrigation. Mean annual precipitation in the project area ranges from approximately 13 to 16 inches per year with the majority of precipitation occurring between November and April.
Land use in the project area includes intensive agriculture as well as the urban centers of Salinas, Castroville and Prunedale.
The project area is characterized by both ephemeral and perennial stream reaches, as the Lower Salinas River runs dry during the summer months, and in comparison the lower Reclamation Ditch flows year-round.
Within the Lower Salinas River Watershed fifteen waterbodies are impaired as a result of pesticides (chlorpyrifos or diazinon) or unknown toxic contamination and only eleven are listed as impaired according to the Clean Water Act 303(d) list. All Beneficial uses (BUs) of the waterbodies impaired by high concentrations of chlorpyrifos and/or diazinon are shown in the table below where "P" denotes a BU directly affected by increased diazinon and chlorpyrifos, "X" denotes all other BUs of the waterbody, "E" denotes an existing BU, and "a" denotes a BU occurring in the North Harbor.
BUs for Inland Waters
|Old Salinas River Estuary||X||X||P||P||P||P||P||X||P||P||X||X|
|Salinas River Lagoon (North)||X||X||P||P||P||P||P||X||P||P||X||X|
|Salinas Reclamation Canal||X||X||P||P||X|
|Salinas River, dnstr of Spreckels Gage||X||X||X||P||P||P||P||X||X|
|Salinas River, Spreckels Gage-Chualar||X||X||X||X||X||X||X||P||P||P||P||X|
|Old Salinas River*||X||X||X||P||P|
|Moss Landing Harbor||E||E||E||E||E||E||E||Ea||E||E|
BUs for Natividad Creek, Quail Creek, Chualar Creek, Old Salinas River, and Alisal Slough are not specifically assigned. However, MUN and recreational and aquatic habitat uses are assigned to characterize the waterbodies.
Data Analysis & Sources
- Rose C, Harlan L, Osmolovsky P. 2011. Regional Water Quality Control Board Central Coast Region. Available from:Total Maximum Daily Loads for Chlorpyrifos and Diazinon in Lower Salinas River Watershed in Monterey County, California
- USEPA. 2011. Diazinon:Phase out of all residential uses [Internet]Available from: http://www.epa.gov/pesticides/factsheets/chemicals/diazinon-factsheet.htm
- USEPA. 2005. Pesticide News Story: Chlorpyrifos Pre-Construction Termiticide Products Phase Out on December 31, 2005.[Internet].Available from: http://www.epa.gov/oppfead1/cb/csb_page/updates/chlorpy-phasout.htm
- DPR. 2003. Diazinon and Chlorpyrifos Loads in Precipitation and Urban and Agricultural Storm Runoff during January and February 2001 in the San Joaquin River Basin, California http://www.cdpr.ca.gov/docs/emon/surfwtr/contracts/USGS_03-4091.pdf