Difference between revisions of "Total Maximum Daily Loads for Chlorpyrifos and Diazinon in Lower Salinas River Watershed in Monterey County, California"

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* Central Coast Water Quality Preservation, Inc.
 
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Revision as of 17:19, 31 March 2011

This page is a a summary of the Regional Water Quality Control Board Central Coast Region report on Total Maximum Daily Load for Fecal Coliform 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

The California Regional Water Quality Control Board for the Central Coast Region (CCRWQCB), in collaboration with the Environmental Protection Agency (EPA), established a Total Maximum Daily Load (TMDL) for Fecal Coliform for the Lower Salinas River Watershed in Monterey County, California. The final TMDL report was available as of March 18, 2010.

The TMDL report addresses the impairment of the Lower Salinas River and several of its tributaries as a result of increased fecal coliform concentrations. The fecal coliform group of bacteria (otherwise known as 'fecal indicator bacteria' (FIB)) are readily used to help identify water body contamination as a result of pathogens. If fecal coliform concentrations exceed certain criteria, the water body may be listed as impaired pursuant to Section 303(d) of the Clean Water Act. The project area includes the following impaired water bodies:

  • Lower Salinas River (from Gonzales downstream to the Salinas River Lagoon)
  • Old Salinas River
  • Tembladero Slough
  • Salinas Reclamation Canal
  • Gabilan Creek
  • Alisal Creek
  • Natividad Creek
  • Santa Rita Creek
  • Quail Creek
  • Chualar Creek
  • Towne Creek

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.

Watershed Description

The project area is bounded by the Gabilan Range to the east, the Sierra de Salinas range to the west, and the Monterey Bay to the northwest.
TMDL Project Area
The TMDL study is defined by the lower 400 square miles of the Lower Salinas Valley and includes two major watersheds, the The Gabilan / Reclamation Ditch Watershed and The Lower Salinas Watershed.

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 fifteen waterbodies are impaired as a result of pesticide (chlorpyrifos or diazinon) or unknown toxic contamination. Of the fifteen bodies, eleven are listed as impaired according to the Clean Water Act 303(d) list. Beneficial uses affected by high concentrations of chlorpyrifos and/or diazinon are as follows:

  • cold freshwater habitat,
  • warm freshwater habitat,
  • estuarine habitat,
  • wildlife habitat,
  • rare, threatened, or endangered species,
  • migration of aquatic organisms, and
  • spawning, reproduction, and/or early development.

Data Analysis

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 FIB 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 FIB for Water Contact Recreation, Non-Contact Recreation, and Shellfish Harvesting were noted as being exceeded. As shellfish harvesting is likely to be eliminated as a beneficial use, the numeric target adopted by the TMDL is the water quality standard for Water Contact Recreation (which is the next most protective beneficial use).

The goal is for all water bodies in the TMDL area to meet this numeric target:

  • The total coliform concentration for a minimum of five samples in any 30 day period should not exceed a log mean (i.e. geometric mean) of 200 per 100 ml, or 400 per 100 ml for 10% of total samples in any 30 day period.

Linkage Analysis

In a TMDL document, the Linkage Analysis is intended to link the numeric target concentration (amount per volume) to a daily load (amount per day) for the watershed. No explicit linkage analysis was given in the TMDL report because the CCRWQCB expressed the intent to implement the TMDL based on a target concentration of fecal coliform rather than a load. However, under the 'TMDL Development' section of the TMDL report, methods are described to link target concentrations to loading capacity.

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. In the TMDL report, the target concentration is also converted to maximum allowable loads (MPN/per day) for each individual waterbody as mandated by Friends of the Earth, Inc. v. EPA, et al..

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.

For example, at Gabilan Creek, during an average high flow event of 26 cfs, the Total Maximum Daily Load of FIB that can be absorbed without exceeding the target concentration is <math> 2.8 \times 10^{11} </math> (orgs/day). This goal represents an 89% reduction from the current estimated load of <math>2.62 \times 10^{12}</math> (orgs/day).

Margin of Safety

TMDLs are required to include a margin of safety that accounts for uncertainty in the linkage between loading capacity of the watershed and pollutant concentration in the receiving water body. In the case of fecal coliform, the goal specified in the TMDL report is for all controllable water sources to meet the target concentration. As a load-based approach was not adopted in the TMDL, no margin of safety was given.

Critical Conditions and Seasonal Variation

The TMDL report does not identify any "critical" environmental factors, in which a slight change could lead to exceedence of water quality objectives. However, it was noted that pollutant concentration is dependent on flow volume, which is often irregular in Monterey County. Also, localized areas of stagnant water with fine sediments foster bacterial growth and may increase concentrations of Fecal Indicator Bacteria.

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 TMDL report summarized here, they are equal to the TMDLs (which are actually concentrations; see above), and are thus expressed as receiving water concentrations. For non-human fecal indicator bacteria, allocations are the numeric target for fecal coliform and equal to the concentration-based TMDL. The allocation assigned for human FIB is zero because of the increased pathogenic risk related to human waste.

Wasteload and load allocations for responsible parties associated as sources of fecal coliform for waterbodies are shown in Table 10-1 of the TMDL report.

Public Participation

Stakeholders involved with the development of and affected by the Chlorpyrifos and Diazinon TMDL.are as followed:

Implementation and Monitoring

The Chlorpyrifos and Diazinon TMDLs are being implemented through the agricultural order titled: Conditional waiver of waste discharge requirements for irrigated lands. The requirements of implementation are described in the agricultural order. 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

  • Implementation Actions: 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. The TMDL does not state that polluters of Chlorpyrifos and Diazinon are required to participate in the Ag waiver program. The 2004, and 2011 draft of the Ag waiver report include TMDL implementation. The report states that all dischargers must comply with applicable TMDLs and meet the requirements within the given compliance date.

The TMDl document provides some suggestions for implementation. The suggested implementation actions are:

    • Holding runnoff for 72 hours after pesticides are applied.
    • Using technology that degrades the chemicals before allowing waters to runoff into the environment
    • Use of drip irrigation to limit runoff
    • Improvement of application methods to eliminate spills
    • Use of treatment enzymes to break down the pesticides
    • Use rotation crop methods to reduce the need for pesticides
  • Evaluation of Implementation Progress: The agricultural order is the regulatory tool used by the water board to enforce and evaluate the implementation of this TMDL. 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. Compliance with TMDL requirements is assessed by regional board staff, through inspections and monitoring.

Monitoring

  • Monitoring Sites: Because this TMDL is implemented through the Conditional Waiver of Waste Discharge Requirements for Discharges from Irrigated Lands; it is also enforced and monitored according to the ag order regulations. The ag order requires that all participants perform individual water quality monitoring or participate in cooperative water quality monitoring. Land owners must also complete annual implementation and management progress reports to the regional water board. The TMDL relies on the regional water board to implement and enforce monitoring of this TMDL, but there are some suggestions given in the TMDL document.
    • The Ag order should prioritize efforts in waterbodies impaired by Chlorpyrifos and Diazinon.
    • The Ag order should prioritize efforts towards minimizing runoff from areas where Chlopyrifos and Diazinon are applied.
    • Monitoring should include a frequency that includes a range of hydrologic conditions.
    • Lab methods that are accurate enough to compare data with numeric goals.

References

  1. ↑ 1.0 1.1 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

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.

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