Difference between revisions of "TMDL for Fecal Coliform for the Lower Salinas River Watershed, Monterey County, California"
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explicitly, that accounts for uncertainty in the relation between pollutant loads and | explicitly, that accounts for uncertainty in the relation between pollutant loads and | ||
the quality of the receiving water body. Conceptually, this definition is denoted | the quality of the receiving water body. Conceptually, this definition is denoted | ||
| − | by the equation: TMDL = SWLA + SLA + MOS "<ref>TMDL Report<http://www.waterboards.ca.gov/centralcoast/board_info/agendas/2010/mar/item_12/att_2.pdf>February 2010. Pg 159 <ref> | + | by the equation: TMDL = SWLA + SLA + MOS "<ref>TMDL Report<http://www.waterboards.ca.gov/centralcoast/board_info/agendas/2010/mar/item_12/att_2.pdf>February 2010. Pg 159 <ref>. |
==Margin of Safety== | ==Margin of Safety== | ||
Revision as of 11:51, 31 March 2010
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 (RWQCB, 2009)[1] by the Spring '10 ENVS 560/L Watershed Systems class at CSUMB.
Contents
Project Definition
The California Regional Water Quality Control Board for the Central Coast Region (CCRWQCB), in collaboration with the Environmental Protection Agency (EPA), established the Total Maximum Daily Load (TMDL) for Fecal Coliform for the Lower Salinas River Watershed in Monterey County, California. The final TMDL report was available 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 used to help identify water body contamination from 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
When a water body fails to meet the minimum quality standards required for its beneficial uses (assigned purposes), a TMDL must be established. 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.
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.
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 is dry in the summer months, but the lower Reclamation Ditch flows year-round.
Problem Statement
The Lower Salinas River and eleven of its tributary water bodies are listed as impaired under section 303(d) of the Clean Water Act due to elevated levels of fecal coliform. Observed levels of fecal coliform for some or all these water bodies do not meet the water quality objectives for the following beneficial uses (BUs) designated in the basin plan:
- Water contact recreation.
- Non-contact water recreation.
- Shellfish harvesting for human consumption. (This BU is under review, and may be eliminated)
Data Analysis
The Salinas watershed was found to be impaired because of elevated concentrations of Fecal Indicator Bacteria (FIB). FIBs indicate the presence of human pathogens. FIBs are monitored because specific human pathogens are difficult and expensive to measure. There is scientific uncertainty about the accuracy of FIBs as a gauge for pathogen risk, but monitoring FIBs is an efficient method to assess bacteria levels.
FIBs analyzed for this project were fecal coliform and Escherichia coli (E. coli). The presence of fecal coliform and E. coli was determined through water sample analysis. The Multiple Fermentation method (MFT) and the Colilert method were used to quantify the FIBs. Most E. coli strains are harmless and reside naturally in the intestines of humans and animals, but the E. coli O157:H7S strain can be a deadly human pathogen. Polymerase chain reaction (PCR), culture, and Pathatrix methods were used to identify E. coli O157:H7. A combination of these methods indicated the magnitude of the pathogen problem, the potential presence of other fecal pathogens and the impairment of the water body.
This study required a qualitative and quantitative approach and various types of data were used. Spatial data for streams, watershed boundaries, roads, land use and elevation were mapped with Geographic Information Systems (GIS) software. FIB concentration and presence data were collected from various sites within the study area during the dry and wet seasons. USGS flow data was used to estimate the load, assimilative capacity and to derive daily load expressions. Rain event data was collected from thirteen sites after two separate rain events, neither of which were first flush rain events. There was a general trend of higher FIB levels during the rainy season compared to the drier summer months. 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. The E. coli O157:H7 identification coincided with mostly pasture and shrubland use, areas with generally large amounts of ranch land with 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 are being exceeded. As shellfish harvesting is likely to be eliminated as a beneficial use, the numeric target for this TMDL is the water quality standard for Water Contact Recreation, which is the next most protective. 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 of 200 per 100 ml, or 400 per 100 ml for 10% of total samples in any 30 day period.
Linkage Analysis
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 is given because the CCRWQCB expresses the intent to implement the TMDL based on a target concentration of fecal coliform rather than load allocation. However, under 'TMDL Development' 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. However, additional analysis links the target concentration to maximum allowable loads for each individual waterbody, which meets the more traditional interpretation of the TMDL approach.
The TMDLs 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. 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]. The target loads were 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 2.8x10^11 (orgs/day). This goal represents an 89% reduction from the current estimated load of 2.62x10^12 (orgs/day).
The method described above is dependent on streamflow data. For ungaged streams, flow was estimated from measurements on comparable streams and adjusted based on the Drainage Area Ratio (DAR) of the two streams. Flow at coastal confluences also had to be estimated, as stage data from these areas is complicated by tidal fluctuation.
Although the intent is to implement the concentration-based allocations and TMDLs, due to a court decision in Friends of the Earth, Inc. v. EPA, et al., No. 05-5015 (D.C. Cir. 2006),and the resulting U.S. EPA guidance, the following MPN/per day interpretation is provided as well [2].
"A TMDL is allocated into waste load allocations (WLAs) for point sources
(NPDES permits; general permits), load allocations (LAs) for nonpoint sources
(including background loads), and the margin of safety (MOS). The TMDL is the
sum of the individual WLAs for point sources, and load allocations (LAs) for
nonpoint sources and natural background levels. In addition, the TMDL must
include a margin of safety (MOS), either implicitly within the WLA or LA, or
explicitly, that accounts for uncertainty in the relation between pollutant loads and
the quality of the receiving water body. Conceptually, this definition is denoted
by the equation: TMDL = SWLA + SLA + MOS "Cite error: Closing </ref> missing for <ref> tag
Cite error: <ref> tags exist, but no <references/> tag was found
