TMDL for Nutrients in Lower Salinas River Watershed, Monterey County, California

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This summary page is based on the Regional Water Quality Control Board Central Coast Region progress report on Total Maximum Daily Load for Nutrients and other TMDL projects for the Lower Salinas River Watershed, in Monterey County, California. This summary was prepared by the Spring 2011 ENVS 560/L Watershed Systems class at CSUMB.
Map Of The Lower Salinas River Watershed (Map by Gabriela Alberola 2011)

Project Definition

The California Regional Water Quality Control Board for the Central Coast Region (CCRWQCB) is currently developing a TMDL project for nutrients in the Lower Salinas River Watershed in Monterey County. The CCRWQCB presented a progress report in June 2010 that contains background information, provisional nutrient targets, and a compilation of water quality data for water bodies in the region. Although the progress report identifies potential sources of nutrient loads, the source analysis portion of the TMDL project is still pending.

This TMDL project will address the nutrient-related impairments in the Lower Salinas River watershed water bodies listed under the 303(d) section of the Clean Water Act. The 2006 303(d) List of Impaired Waterbodies is the current and active list for the California Central Coast. In 2010, the CCRWQCB presented an updated list in its' 2010 Integrated Report, but this report is still waiting for approval by the USEPA. The following table contains the water bodies and the nutrient-related reason for their listing in both the 2006 active list and in the 2010 list:


Water Body 2006 Listed Impairment 2010 Listed Impairment (Proposed)
Alisal Creek Nutrient Chlorophyll-a, Nitrate
Alisal Slough Not Listed Low Dissolved Oxygen, Nitrate
Blanco Drain Not Listed Low Dissolved Oxygen, Nitrate
Chualar Creek Not Listed Ammonia (Unionized), Nitrate
Esperanza Creek Not Listed Nitrate
Espinosa Slough Not Listed Ammonia (Unionized), Nitrate
Gabilan Creek Nitrate Ammonia (Unionized), Nitrate
Merrit Ditch Not Listed Ammonia (Unionized), Low Dissolved Oxygen, Nitrate
Moro Cojo Slough Ammonia (Unionized),Low Dissolved Oxygen Ammonia (Unionized), Low Dissolved Oxygen
Natividad Creek Nitrate Ammonia (Unionized), Low Dissolved Oxygen
Old Salinas River Not Listed Chlorophyll-a, Low Dissolved Oxygen, Nitrate
Old Salinas River Estuary Ammonia (Unionized), Low Dissolved Oxygen, Nutrients Nutrients
Quail Creek Nutrients Ammonia (Unionized), Low Dissolved Oxygen, Nitrate
Salinas Reclamation Canal Ammonia (Unionized), Low Dissolved Oxygen Ammonia (Unionized), Low Dissolved Oxygen, Nitrate
Salinas River (lower, estuary to near Gonzales Rd

Crossing)

Nitrate, Nutrients Nitrate
Salinas River Lagoon (North) Nutrients Nutrients
Santa Rita Creek Nitrate Ammonia (Unionized), Low Dissolved Oxygen, Nitrate
Tembladero Slough Ammonia (Unionized), Nutrients Chlorophyll-a, Nitrate, Nutrients

Problem Statement

Nitrogen and phosphorus are naturally limiting nutrients in many ecosystems. Eutrophication of waterways occurs when excess nurtients are present. Water quality issues associated with eutrophication include: increased algal biomass (including potentially toxic species), increased turbidity, alterations in dissolved oxygen concentrations, decreased biodiversity, and decreased aesthetic value of the waterway due to foul smells and change in color. Severe eutrophication can create anoxic areas also known as dead zones. Sources contributing to the issue of nutrients in the Lower Salinas Watershed have not yet been identified. In general, sources of nutrients in watersheds include: urban runoff, the application of fertilizers, groundwater, livestock, wastewater treatment plants, and septic systems. Specifically for the lower Salinas Watershed Anderson et al. identified .... Beneficial uses of waterways and water quality objectives are considered when determining water quality standards.

Beneficial Uses (BUs) Associated with Waterways Listed for Nutrient Impairments

  • Municipal and Domestic supply (MUN)
  • Agriculture (AGR)
  • Industrial Process (PRO)
  • Industrial Service (IND)
  • Ground Water Recharge (GWR)
  • Water Contact Recreation (REC1)
  • Non-Contact Water Recreation (REC2)
  • 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)
  • Biological Habitats of Special Significance (BIOL)
  • Shellfish Harvesting (SHELL)
  • Commercial and Sport Fishing (COMM)
  • Freshwater replenishment (FRESH)
Waterbody MUN AGR PRO IND GWR REC1 REC2 WILD COLD WARM MIGR SPWN BIOL RARE EST FRESH COMM SHELL
Old Salinas River Estuary X X X X X X X X X X X X
Salinas River Lagoon (North) X X X X X X X X X X X X
Tembladero Slough X X X X X X X X X
Espinosa Slough X X X X X
Salinas Reclamation Canal X X X X X
Alisal Creek X X X X X X X X X X
Blanco Drain X X X X X
Salinas River, down stream of Spreckels Gage X X X X X X X X X
Salinas River,Chualar to Spreckles X X X X X X X X X X X X
Quail Creek X X X X

A more complete table of beneficial uses will be available in the final project report.

Data Analysis

Within theJune 2010 California Regional Water Board Nutrient TMDL Progress Report it is acknowledged that the presence of excess nutrients does not directly impair waterways, rather it is the indirect impacts associated with the presence of excess nutrients that diminish beneficial uses of waterways. Secondary indicators of eutrophication such as nuisance algal blooms, drastic diel swings in dissolved oxygen concentrations, and loss of habitat must also be monitored and documented as they are more directly linked to the beneficial uses of waterways than nutrient concentrations alone.

Data analysis for the June 2010 California Regional Water Board Progress Report included:

  • A delineation of watershed boundaries
  • A list of subwatersheds
  • Stream classification, Which revealed in general low gradient streams on the valley floor were perennial, and many headwater streams tended to be ephemeral.
  • An assessment of groundwater as baseflow. For the TMDL project area baseflow index values for groundwater ranged from 38 to 26 percent.
  • An assessment of mean groundwater nitrate concentrations for the project area. Values reported ranged from 0.1-10.0 mg/l to 100.1-200.0 mg/l of nitrate.
  • An assessment of mean annual precipitation for the project area. For the project area values ranged between 11.1 inches to 33.5 inches on average annually.
  • An analysis of land use and land cover. In the project area land uses include approximately 34% farmland, 31% grazing land, 8% urban, and 26% undeveloped/forested/restricted.

Numeric Target

Numeric targets are concentrations of specified nutrients that would not impair designated beneficial uses of a given water body. Water quality objectives given in the Basin Plan are attempts to quantify the allowable nutrient concentrations. The objectives listed in the Basin Plan are used as a starting point during TMDL development and adoption. The water quality objective for nitrogen for the beneficial use MUN (defined above) is 10 mg/L. Currently, the numeric targets for nitrogen in the Lower Salinas River watershed are being developed. CCRWQCB staff prepared a progress report that summarized the development of provisional and preliminary numeric targets for total nitrogen.

The progress report described that one uniform nutrient target may not be sufficient in light of the large variability of stream morphology and hydraulics in the waterbodies contributing to the Lower Salinas River. The report explored a variety of ways to define a range of numeric targets. Final nutrient targets can be developed based on either calculations or estimations. The percentile based approach calculates the numeric target by using either the 25th percentile of nutrient data from reference streams or the 75th percentile of all nutrient data for the project area streams. The nutrient numeric endpoints (NNE) approach estimates in-stream benthic algal response to ambient stream conditions. Based on these approaches, the provisional and preliminary numeric targets for total nitrogen listed in the progress report range from 1.4-2.2 mg/L depending on waterbody type. That range is consistent with established nutrient TMDLs on Malibu Creek and Rainbow Creek in Southern California.

Source Analysis

The source analysis for nutrients in the Lower Salinas River watershed has not been completed at this time. There is a preliminary source analysis prepared by Anderson, et al. in 2003 that identified irrigated agriculture as a dominant source of high nutrient concentrations in southern Monterey Bay watersheds.

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 summary report because the numeric target concentration is not finalized. Once a target has been established, the linkage analysis will be used to convert that target concentration to daily load.

TMDL Development

The nutrient TMDL for the Lower Salinas River watershed is still being developed. The CCRWQCB progress report summarized the process to date and established preliminary and provisional numeric targets to be included in the TMDL (see Numeric Targets above).

TMDLs establish the concentration or daily load of nutrients a body of water can contain while continuing to support its' defined beneficial uses. TMDLs can be defined in terms of a mass load or can be set as a unit of concentration. Defining a unit of concentration may be a useful approach for the Lower Salinas River Watershed. During TMDL development, it is necessary to consider secondary indicators, such as dissolved oxygen levels and algal biomass, that are linked to the beneficial uses for the water body. A modelling tool can be used to link secondary indicators to concentrations in the water column and predict levels of nutrients that would impair specific beneficial uses. Some approaches to nutrient TMDL development can be found in the following reports:

  • The Chorro Creek Nutrient TMDL report set a sodium concentration limit of 50 mg/L and total dissolved solids concentration of 500 mg/L in order to help achieve the water quality objective for nutrient concentations
  • The Pajaro River and Llagas Creek report sets the maximum concentration for nitrate within the water body at 10mg/L in order to protect beneficial uses. The report does not include seasonality because it the TMDL is equal to the water quality objectives of the region.
  • The San Diego Creek and Newport Bay Report set the nitrate TMDL according to different seasons. They allow 13 lbs/day of inorganic nitrogen for reach 2, 224lb/day from October 1 to March 31 total nitrogen and 175lb/day from April 1 to September 30.

Margin of Safety

The margin of safety for the Lower Salinas River Watershed is still being developed. A margin of safety is used to account for the uncertainty in the linkage between nutrient loads and nutrient pollutant concentrations in the receiving water body. There are two methods to approach the margin of safety in a TMDL report. One can either incorporate the uncertainties implicitely by making conservative estimates into the model or quantify a portion of the total TMDL, leaving the remainder as sources (allocations are important in this circumstance). It is important to not only make conservative assumptions about the parameters, but the thresholds as well. Uncertainties that would be useful to take into consideration in regards to the lower Salinas valley include:

  • there is a finite amount of data available
  • concentrations are discrete values that have been estimated based on a specific amount of parameters and do not necessarily account for the interactions of parameters
  • the model may not be representative of the actual environmental conditions
  • rain patterns vary from one year to the next so dilutions vary
  • what form nutrients become bioavailable to macrophytes

In order to develop a proper margin of safety it is useful to reference other TMDL reports. The Pajaro River and Llagas Creek TMDL report, Chorro Creek TMDL Report and San Diego Creek TMDL report are examples of nutrient TMDL reports that employed conservative estimates within their water quality objectives, thus implicitly accounting for the margin of safety. An important factor to consider when using conservative estimates in lieu of quantitaive margins is to explicitly address the individual assumptions that are being accounted for. An efficient way to make conservative assumptions on a in an efficient way is to assume low flow conditions.

San Louis Obispo Creek TMDL Report used the quantitative approach and estimated the margin of safety to be about 20% of the total nitrate-N mass load based on a number of uncertainties and limitations in their data. Malibu Report Malibu Creek watershed TMDL report also estimated a 20% margin of safety and implicitly included conservative assumptions into the TMDL analysis. However, it is important to note that this TMDL report has not yet been approved on the state or federal level.

The margin of safety to consider for the Lower Salinas River Watershed is dependent on the assumptions made in the INN benthic biomass modeler. If all of the sources of varibility have been accounted for in the model by incorporating conservative assumptions then that may be stated as the margin of safety. However, if there are any uncertainties that have not been incorporated in the model, then an explicit margin of safety should be identified. The typical margin of safety that has been accepted in California lies around 20 percent, but this can vary depending on land uses and other variables affecting nutrient loading into water bodies.

Critical Conditions and Seasonal Variation

The TMDL progress report did not addressed the “critical” environmental factor for nutrient loading in the Lower Salinas River Watershed, in which a slight change could lead to exceeding the water quality objectives. However, the progress report does specify some indicators that can impair the beneficial uses of the regional water bodies.

Previous TMDLs in the Monterey Bay Region of California have not included critical conditions, however critical conditions for a Nutrient TMDL may be advisable due to the high occurrence of nutrient loading for agriculture in the Salinas Valley. The 2003 Santa Clara River Nitrogen TMDL included critical conditions. Although the climate around the Santa Clara River is drier, that water body is similar to the Lower Salinas River in seasonal flow and the effects of the first big storm (first flush). Although not a perfect approach, the Santa Clara River TMDL makes an attempt to incorporate the increased impairment hazard presented by seasonal variation [1]. Specifically, critical condition were evaluated on the basis of those conditions that would cause an increase in inorganic nitrogen species due to either 1) low flow conditions, 2) the effects of the first big storm of the season (first flush), or 3) rising groundwater effects.

TMDL Allocations

TMDLs include the total concentration of nutrients allowed to be discharged into a water body by all possible sources. The allocations are typically comprised of Load Allocations (LAs) from nonpoint sources and Waste Load Allocations (WLAs) from point sources and also includes a Margin of Safety (MOS) to account for unexpected sources of a particular contaminant and Future Growth (FG):

 TMDL = LAs + WLAs + MOS + FG


The Lower Salinas River Watershed Nutrient TMDL Progress Report has summarized procedures to develop numeric targets for nutrient loading reductions (see above) in impaired water bodies, but did not provided recommended LAs. TMDLs in other parts of California provide examples of different approaches used to set TMDL allocations:

In establishing TMDL allocations in the Lower Salinas River Watershed for nutrients, the Regional Water Quality Control Board could approach the allocations in a similar fashion as that taken in the Pajaro River Nitrate TMDL. By setting the load allocations as a concentration at or below the numeric target for all sources, future growth and changes in land use will not lead to an exceedance of the TMDL. This will also eliminate the need for setting critical conditions based on changes in flow rate, which would absolutely be required if allocations were set as loads given in mass.

Public Participation

Image taken from California Regional Water Quality Control Board Development of total maximum daily loads for nutrients and nutrient-related impairments: lower salinas river watershed Factsheet

Public participation is a requirement [2] of the TMDL process and is vital to a TMDL’s success. The August 23, 1999, proposed regulation states that the public must be allowed at least 30 days to review and comment on a TMDL prior to its submission to the EPA for review and approval. In addition, with a TMDL submittal, the EPA must be provided with a summary of all public comments received regarding the TMDL and staff response to those comments, indicating how the comments were considered in the final decision. During the completion of past TMDLs the Central Coast Water Board presented TMDL project reports during different stages of the analysis process and to present preliminary findings of the report. The development of this TMDL will affect many stakeholders regulated by the California Environmental Quality Act (CEQA) documents that demonstrate any potential impacts on these stakeholders should be prepared ahead of time to present alternative schemes and implementation strategies to the public.

The Public Participation (Factsheet)

Implementation and Monitoring

Monitoring

The Environmental Protection Agency Nutrient TMDL development protocol document [2] suggested steps: identify key questions, evaluate monitoring options and implement the monitoring program. It is suggested that monitoring plans describe the timing, location, responsible parties, and quality assurance and control procedures. The level of rigor required for a monitoring plan is dependent on the confidence in the TMDL analysis. A greater level of uncertainty requires more rigorous monitoring actions and must allow more room for future revision. Since watershed process drivers are not identical before and after implementation, models are useful for evaluating results of monitoring. Models can be calibrated to pre or post implementation to better compare results of monitoring actions. Coordination with other existing or planned monitoring activities can be particularly helpful for long-term monitoring programs, large study areas, or if the water quality agency’s monitoring resources are limited. It is also important to choose the type of monitoring that will be most appropriate to yield desired goals and then develop a quality assurance plan to ensure the data can support future analysis. Overall a monitoring plan is created to evaluate the effectiveness of the implementation strategies and TMDL elements such as numeric targets and pollutant estimates.

Examples of key questions: Are the selected indicators capable of detecting designated use impacts of concern and responses to control actions? Have baseline or background conditions been adequately characterized? Are the numeric targets set at levels that reasonably represent the appropriate desired conditions for designated uses of concern? Have all important pollutant sources been identified? Have pollutant sources been accurately estimated?

Examples of approaches to monitoring found in similar Regional TMDL reports

  • Pajaro/Llagas Creek Nutrient TMDL [3]: Follow-up monitoring data on Nitrate will be provided by the Monitoring and Reporting Program in the Ag waiver. Water Board staff will review data every three years. Additional monitoring will assess causes of excessive algae and low dissolved oxygen conditions that lead to impairment of water bodies.
  • San Luis Obispo Creek Nutrient TMDL [4]:The City of San Luis Obispo required to monitor effluent from the Water Reclamation Facility (WRF)in accordance with the NPDES permit. Cropland monitoring is consistent with the Ag Waiver. Regional Water Board Staff will review the results every three years.
  • Santa Clara River Nutrient TMDL[5]: dry and wet weather discharges will be monitored from agricultural, urban and open space sources to determine if best management practices are effective at reducing nutrient loading, Publicly Owned Treatment Works (POTW) monitoring is outlined in Plans submitted by permitees in Los Angeles and Ventura Counties.

Sources contributing to the issue of nutrients in the Lower Salinas Watershed have not yet been identified. In general, sources of nutrients in watersheds include: urban runoff, the application of fertilizers, groundwater, livestock, wastewater treatment plants, and septic systems. The Monitoring plan for the Lower Salinas River Watershed mainly needs to quantify agricultural nutrient sources. Monitoring can likely follow the requirements outlined in the Ag Waiver and then staff can evaluate the results to ensure that agricultural best practices are adequate to reduce nutrient levels.

Implementation

On August 8, 1997, the Environmental Protection Agency (EPA) issued a memorandum [2] , “New Policies for Establishing and Implementing Total Maximum Daily Loads (TMDLs),” which directs EPA regions to work in partnership with states to achieve nonpoint source load allocations established for 303(d)-listed waters impaired solely or primarily by nonpoint sources. To this end, the memorandum asks that regions assist states in developing implementation plans that include reasonable assurances that the nonpoint source load allocations established in TMDLs for waters impaired solely or primarily by nonpoint sources will in fact be achieved; a public participation process; and recognition of other relevant watershed management processes. Although implementation plans are not approved by EPA, they help establish the basis for EPA’s approval of TMDLs.

The purpose of an Implementation Plan is to describe the steps necessary to reduce pollutant loads to achieve these TMDLs. Implementation Plans identify the following: 1) actions expected to reduce pollutant loading; 2) parties responsible for taking these actions; 3) regulatory mechanisms by which the Central Coast Water Board will assure these actions are taken; 4) reporting and evaluation requirements that will indicate progress toward completing the actions; 5) a timeline for completion of implementation actions. Implementation Plans also address economic considerations to achieve compliance. Several approaches to specifying a monitoring plan have been adopted in federally approved TMDLS in the Monterey Bay area

Examples of approaches to implementation found in similar Regional TMDL reports

  • Laguna de Santa Rosa [2] : the Waste Reduction Strategy includes: a grant program aimed at reducing waste inputs from confined animal operations, a stormwater runoff program, an NPDES permit program,and voluntary actions organized by the Laguna Watershed Coordinated Resource Management and Planning Task Force.
  • San Luis Obispo Creek [6]: the NPDES permit for the City of San Luis Obispo will incorporate an effluent limit for their NPDES permit, regulations for storm water through a small MS4 permit, cropland nitrate sources will be regulated and monitored through the Ag Waiver.
  • Santa Clara River [7]: Ammonia, nitrite, and nitrate reductions will be regulated through denitrification upgrades to Publicly Owned Treatment Works (POTW) and enforcement of effluent limits, NPDES permits, and agricultural Best Management Practices.

To develop the implementation plan for the Lower Salinas River Watershed sources will need to be identified in order to place appropriate effluent limiting permits and/or prohibitions. It will likely be necessary to control effluent from the City of Salinas' stormwater discharge, croplands, and lands containing livestock.

References

  1. Keller AA, Zheng Y, Robinson TH. 2004. Determining critical water quality conditions for inorganic nitrogen in dry, semi-urbanized watersheds. JAWRA 40(3): 721-735. Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1752-1688.2004.tb04455.x/abstract
  2. 2.0 2.1 2.2 2.3 [1]
  3. [2]
  4. [3]
  5. [4]
  6. [5]
  7. [6]

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.