Total Maximum Daily Loads for Chlorpyrifos and Diazinon in Lower Salinas River Watershed in Monterey County, California

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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)[1]. The summary was prepared by the Spring '11 ENVS 560/L Watershed Systems class at CSUMB.


Project Definition

In 2011, the Central Coast California Regional Water Quality Control Board (CCRWQCB), 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 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 mandated the cancellation and restriction of chlorpyrifos and diazinon, until reassessments could ensured that safety requirements were being met [1]. The phase out of chlorpyrifos and diazinon were expected to reduce the concentrations of these pesticides in the following impaired water bodies:


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

Watershed Description

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 Valley 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.

Problem Statement

Within the Lower Salinas River Watershed fourteen waterbodies are impaired as a result of pesticides (chlorpyrifos or diazinon) or unknown toxic contamination and are listed as impaired according to the Clean Water Act 303(d) list. Beneficial uses (BUs) affected by high concentrations of chlorpyrifos and/or diazinon are as follows:

  • Cold Freshwater Habitat (COLD)
  • Warm Freshwater Habitat (WARM)
  • Estuarine Habitat (EST)
  • Wildlife Habitat (WILD)
  • Rare, Threatened, or Endangered Species (RARE)
  • Migration of Aquatic Organisms (MIGR)
  • Spawning, Reproduction, and/or Early Development (SPWN)
Waterbody MUN AGR PROC IND GWR REC1 REC2 WILD COLD WARM MIGR SPWN BIOL RARE EST FRESH COMM SHELL
Old Salinas River Estuary X X P P P P P X P P X X
Salinas River Lagoon (North) X X X P P P P P X P X X
Tembladero Slough X X P P P P P X X
Espinosa Lake X X X P X
Espinosa Slough X X P P X
Salinas Reclamation Canal X X P P X
Alisal Creek X X X X X P P P P X
Blanco Drain 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

Data Analysis

Water quality data for Diazinon and Chlorpyrifos were collected under protocols specified by the California Dept of Fish and Game (CDFG). Although the CDFG protocol for Criterion Maximum Concentrations (CMC) called for hourly averaged data, instantaneously collected samples were treated as one hour average samples due to data collection limitations. Additionally, the CDFG published criterion for continuous concentrations (CCC), where a four day average would be collected. Water quality data collection staff have so far not been able to collect four day average samples, and therefore an assessment on chronic toxicology is not currently available. As stated in the 2010 draft report (**ADD LINK**), staff will incorporate a four day average sampling frequency during the TMDL implementation.

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The Salinas watershed was found to be impaired due to elevated concentrations of Fecal Indicator Bacteria (FIB). FIB indicate the general presence of fecal coliform and Escherichia coli (E. coli) O157:H7 bacteria, and are monitored because specific human pathogens are difficult and expensive to measure. There is some scientific uncertainty about the accuracy of FIB as a gauge for pathogen risk, but monitoring FIB is currently the most cost efficient and effective method.

The presence of FIB were determined through water sample analysis using various methodologies including The Multiple Tube Fermentation (MTF) method and the Colilert method, the polymerase chain reaction (PCR), culture, and Pathatrix methods. The combination of these various methods indicated the magnitude of the pathogen problem and the potential presence of other fecal pathogens. Analysis of the results from these various methods, indicated the presence of a pathogen problem, consistent with the listing of the The Lower Salinas Watershed as "impaired."

Spatial data were used to estimate the impact of various land uses on waterbodies. Spatial data analyzed included streams, watershed boundaries, roads, land use and elevation. FIB concentration and presence data were also analyzed temporally, with respect to the dry and wet seasons. USGS flow data were incorporated into the study to estimate current load and assimilative capacity, and to derive daily load expressions.

E. coli rain event data were collected from thirteen sites after two separate rain events, neither of which were first flush rain events. It was found that the median E.coli density was significantly higher during rain events (2,685 MPN/100mL) than non rain events (224 MPN/100mL). There were multiple identifications of E. coli O157:H7, mostly at the confluence of Gabilan Creek and Towne Creek in the northern part of the study area. E. coli O157:H7 identification coincided with pasture and shrubland areas with generally large amounts of ranch land and animal activity.

Other assessed waterbodies for which data did not indicate impairment, or for which data were insufficient were:

  • Blanco Drain- not impaired
  • El Toro Creek- insufficient data
  • Alisal Slough- insufficient data

Numeric Target

Numeric targets for Chlorpyrifos and Diazinon are established in the Basin Plan based on the designated beneficial uses of a given water body. In the impaired waterbodies of the Lower Salinas watershed, the numeric targets of Chlorpyrifos and Diazinon were created to uphold Aquatic Life and defined by a 2000 report by the CDFG. The goal is for all water bodies in the TMDL area to meet the numeric targets for both the water column and additive numeric targets that include the presence of both organophosphate pesticides.

Water Column Numeric Targets

The criterion maximum concentration (CMC) is the average concentration per 1-hour period. The criterion continuous concentration (CCC) is the 4-day concentration average. The table below contains the CMC and the CCC for water column numeric targets for each pesticide:[1][2].

Compound CMC (ppb) CCC (ppb)
Chlorpyrifos 0.025 0.015
Diazinon 0.16 0.10

Additive Toxicity Numeric Targets

The additive numeric targets is applied when both chlorpyrifos and diazinon are present in the water column. This additive target is calculated as follows:

<math> {Cdiazinon \over NTdiazinon} + {Cchlorpyrifos \over NTchlorpyrifos} = S ; S\le1.0 </math>

Where:

C= concentration of pesticide measured in water body.
NT= the numeric target for the water body.
S = sum. If the sum is greater than 1.0, the beneficial uses are impaired.

Linkage Analysis

Linkage Analysis is intended to link the numeric target concentration (amount per volume) to a daily load (amount per day) for the watershed. For Chlorpyrifos and Diazinon the load allocations are equal to the numeric targets. These are the same values that are used for the TMDL.

The CCRWQCB examined data regarding use of both chlorpyrifos and diazinon in the lower Salinas River watershed and concluded that agricultural lands were the primary source for both chlorpyrifos and diazinon.

TMDL Development

The official TMDL objective is expressed as a numeric target concentration that applies to all impaired waterbodies in the lower Salinas River watershed to protect aquatic life. The CCRWQCB gathered information from the Central Coast Ambient Monitoring Program, California Department of Pesticide Regulation, CDFG, Cooperative Monitoring Program for the Central Coast Agricultural Waiver Program, and California State University, Monterey Bay.

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Water column numeric target and the additive toxicity numeric target.

Staff also used discharger data and reports, land use data, field reconnaissance work, USEPA-recommended or recognized empirical load assessment methods, and conversations with staff from other agencies.


The maximum allowable loads for fecal coliform are based on a three-tiered flow regime, wherein each water body has different allowable loads established for high (top 5%), moderate (middle 25%), and low (bottom 60%) flows. For ungaged streams, flow was estimated from measurements on comparable streams and adjusted based on the Drainage Area Ratio (DAR). Allowable loads were calculated by multiplying the average flow within each flow regime (low, moderate, or high) by the target concentration [volume/time * mass/volume = mass/time] and then compared to existing loads derived from field data.

Margin of Safety

The margin of safety is a concentration based TMDL which is the same as the TMDL numeric targets developed for chlorpyrifos and diazinon. The TMDL assumes that there is no additional reduction of compounds resulting from degradation or sediment deposition. Since it is possible that there will be some small amount of reduction through these processes, this assumption contributes to the margin of safety TMDL in the proposed allocation methods. These numeric targets were developed by the California Department of Fish and Game (CDFG), using protocols created by the United States Environmental Protection Agency (USEPA).

Critical Conditions and Seasonal Variation

Critical conditions are defined as environmental factors that result in exceedance of the water quality standard expressed in terms of load. Because this TMDL is expressed as a concentration, which is equal to the desired water quality condition, there are no critical conditions reported. Water quality objectives may be exceeded during all seasons and therefore are not valid for the Chlorpyrifos and Diazinon TMDL.

TMDL Allocations

In TMDL documents, 'Wasteload' and 'Load Allocations' are the maximum load of a pollutant that each point-source discharger is allowed to release. In the Chlorpyrifos and Diazinon TMDLs for the Lower Salinas River Watershed allocations and maximum loads apply to owners and operators of irrigated agricultural lands who have discharges from their lands. Dischargers into an impaired waterbody may not release more diazinon (0.16 ppb) or chlorpyrifos (0.025 ppb) than the Criterion Maximum Concentration (CMC), an allowable concentration that does not exceed one hour. The Criterion Continuous Concentration (CCC) states that over a four hour diazinon and chlorpyrifos concentrations cannot exceed 0.10 ppb and 0.016 ppb, respectively. Where diazinon and chlorpyrifos are both discharged there is also an additive restriction such that the sum from the following equation must not exceed 1.0:


where Cd is the concentration of diazinon in a waterbody, LCd is the CCC or CMC of diazinon, Cc is the concentration of chlorpyrifos in a waterbody, and LCc is the CCC or CMC of chlorpyrifos.

Public Participation

In an effort to include the public in the development of TMDLs, the Central Coast Water Board (CCWB) solicited public participation in a 45-day public comment period preceding the Central Coast Water Board hearing. Public notice of the hearing was mailed to interested persons and to applicable government agencies, and were available on CCWB website. A series of meetings were conducted to form the current final report for the the Chlorpyrifos and Diazinon TMDL and included the following stakeholders:

A series of stakeholder meetings were conducted to form the current final TMDL report with stakeholder input[3].

Implementation and Monitoring

The Chlorpyrifos and Diazinon TMDLs are being implemented through the Conditional Waiver of Waste Discharge Requirements for Irrigated Lands(the Ag Waiver program), and the California Department of Pesticide Regulation (DPR). Suggestions for implementation, monitoring, and tracking TMDL progress is given in the TMDL report written for the Central Coast California Regional Water Quality Control Board (Rose et al. 2011)[1].

Implementation

Ag Waiver

The TMDL is implemented through the Ag Wavier program. Participants in the program are required to meet the stated reductions of Chlorpyrifos and Diazinon in discharged waters. Allocations, numeric targets, and TMDLs in the impaired Waterbodies are planned to be achieved by 2025. However, accelerated implementation should occur whenever feasible in order to reach targets as soon as possible. The 2004, and 2011 drafts of the Ag Waiver report include TMDL implementation. The Ag Waiver program is seen by the RWQCB as a sufficient regulatory mechanism to remedy impairments caused by chlorpyrifos and diazinon. The Ag Waiver is the regulatory tool used by the water board to enforce and evaluate the implementation of this TMDL.

The Ag Waiver states that if a contaminant discharger does not meet the timeline provided in the TMDL, enforcement actions may be made by the regional water board. Compliance with TMDL requirements is assessed by regional board staff, through inspections and monitoring. The Final Project report recommends the Agricultural Waiver should establish timeframes for individual dischargers to reach set water quality standards, giving the shortest timeframes to dischargers who pose the greatest risk to water quality. Impairments caused by chlorpyrifos and diazinon will be reevaluated Water Board staff when monitoring data is received and during renewals of the Agricultural Order. The conditions of the agricultural waiver will be modified to address remaining surface water impairments. The order states that if the discharger does not meet the timeline provided in the TMDL, enforcement actions will be made by the regional water board.

California Department of Pesticide Regulations

In addition to the Ag Waiver, the California Department of Pesticide Regulations (DPR) is another regulatory mechanism that may reduce the amount of chlopyrifos and diazinon entering waterways. DPR is required to reevaluate registration of pesticides. If adverse effects to surface waters caused by chlorpyrifos and diazinon cannot be mitigated, DPR can cancel or suspend the registration of the pesticides

TMDL Final Project Report Recommendations

The TMDL Final Project Report provides the following suggestions for implementation:

  • hold agricultural runoff for 72 hours after pesticides are applied
  • improve granular application methods to prevent spills
  • use enzymes to degrade the chemicals before they enter waterways
  • incorporate drip irrigation to reduce agricultural runoff
  • rotate crops which do not harbor pests requiring pesticides

Monitoring

These TMDLs are implemented, monitored, and enforced through the Conditional Waiver of Waste Discharge Requirements for Discharges from Irrigated Lands (Ag Waiver).(reference) Participants in current or future versions of the Ag Waiver are required to either perform individual water quality monitoring or participate in cooperative water quality monitoring (e.g. The Cooperative Monitoring Program managed by Central Coast Water Quality Preservation Inc.). Land owners must also complete annual implementation and management progress reports RWQCB. These TMDLs rely on the Region 3 RWQCB to implement and enforce monitoring of this TMDL. (reference) To reach RWQCB objectives, the new monitoring and reporting strategies are proposed to be included in the next version of Ag waiver to assess progress towards reaching Cholpyrifos and Diazinon TMDL limits. (ref -Final report)

Recommended Monitoring Strategy

The following recommendations have been made by Cal EPA and Region 3 RWQCB for monitoring and reporting strategy in the next Ag Waiver. Monitoring and reporting for Chlorpyrifos and Diazinon should (reference):

  • Span a variety of flow regimes, with sampling occuring four times per water year; twice between May 15th and October 15th, and twice between Oct 15th and March 15, aproximately. One of these sampling events between October 15 and March 15th should include a 7-day continuous sampling event during and/or following a storm event.
  • Encourage high-resolution source analysis near farming operations using chlorpyrifos or diazinon that discharge to waterbodies impaired by chlorpyrifos, or diazinon, or toxicity
  • Use laboratory and analytical methods that enable data comparison with numeric targets
  • Include toxicity identification evaluation (TIE) for waterbodies listed as impaired for toxicity, or unknown toxicity. Implementing suggested monitoring and reporting requirements if TIEs help determine chlorpyrifos or diazinon are contributing to toxicity in a waterbody.
  • Be located in the lower portions of the watershed, whenever feasible, giving preference to previously established monitoring sites to facilitate trend detection.

Proposed Impaired Waterbody Monitoring Sites

Impaired Waterbody Proposed Monitoring Site
Tembladero Slough 309TEH
Alisal Slough 309SSB
Blanco Drain 309BLA
Salinas Reclamation Canal (Upper) 309ALG
Salinas Reclamation Canal (Lower) 309JON
Salinas River 309SSP
Espinosa Slough EPL-EPL
Espinosa Lake EPL-EPL
Natividad Creek 309NAD
Quail Creek 309QUA
Chular Creek 309CRR

References

  1. 1.0 1.1 1.2 1.3 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
  2. Siepmann S, Finlayson B. 2000. California Department of Fish and Game. Available from:Water Quality Criteria for Diazinon and Chlorpyrifos
  3. Resolution (No. R3-2011-0005). 2011. Regional Water Quality Control Board Central Coast Region. Available from:Resolution (No. R3-2011-0005)

Links

Disclaimer

This page may contain student work completed as part of assigned coursework. It may not be accurate. It does not necessary reflect the opinion or policy of CSUMB, its staff, or students.