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NONPOINT SOIREE SICCESS STOIY
Implementing Agricultural Best Management Practices Reduces Nutrients
in 23 miles of Sonoma Creek
Waterbody Improved
Nonpoint source-related nutrient loading from onsite wastewater
treatment systems and agricultural lands contributed to high nutrient
levels in Sonoma Creek. As a result of these conditions, the main stem of Sonoma Creek was added
to the state's 1986 Clean Water Act (CWA) section 303(d) list due to excess nitrates and phosphorus
nutrients. Since that time, landowners, local watershed organizations and many federal, state and local
government agencies have collaborated to implement nonpoint and point source control measures to
reduce nutrient loading to the creek. Due to these efforts, nutrient levels have decreased, and the non-
tidal portion (23 miles) of Sonoma Creek has been recommended by the Regional Water Quality Control
Board 2 (RWQCB-2) for removal from the 2016 CWA section 303(d) list.
Problem
The Sonoma Creek watershed is in the California
Coast Ranges north of San Pablo Bay and San
Francisco Bay, and covers an area of approxi-
mately 165 square miles (Figure 1). The creek flows
approximately 30 miles in a southeasterly direction
though the Sonoma Valley before discharging to
San Pablo Bay. The watershed provides habitat for
several native threatened or endanger species of
concern, including steelhead trout, Chinook salmon,
and California freshwater shrimp.
Historical sources of nutrients dating back to the
1970s in the watershed included cattle grazing
(probably with direct access to streams and tributar-
ies), dairies and confined animal feeding operations,
and rudimentary public wastewater treatment. In
1986 the creek was identified on California's CWA
section 303(d) list as impaired by nutrients result-
ing in eutrophication. Excessive levels of nutrients
can alter dissolved oxygen levels and pH, and
impact beneficial uses including cold freshwater
habitat, warm freshwater habitat, agricultural sup-
ply, municipal and domestic supply, water contact
recreation and noncontact water recreation.
Sonoma Creek was also listed as impaired by
pathogens and sediment in 1998. RWQCB-2 devel-
oped total maximum daily loads (TMDLs) for these
parameters (pathogens in 2008 and sediment in
2010). Although the mechanisms by which nutrients,
pathogens and sediment are transported differ, they
share some common sources. Therefore, implement-
ing the two TMDLs was expected to help reduce
nutrient loadings concurrently.
Napa River
Watershed
Sonoma Creek
Watershed
— Nutrient Impairment Removed
— Remains Impaired for Nutrients
Figure 1. The Sonoma Creek and Napa River
watersheds are on the California coast. California
will recommend removal of the nutrient impairment
from the 23-mile-long non-tidal portion of Sonoma
Creek from its list of impaired waters in the
upcoming cycle.
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Project Highlights
Results
Major actions that contributed to reductions in nutri-
ent loading to the creek since the 1986 listing have
included National Pollutant Discharge Elimination
System (NPDES) permit restrictions on wastewater
discharges, changes in land use, and the implemen-
tation of improved dairy, cattle grazing and agricul-
tural best management practices (BMPs). Some
specific practices include:
• Prohibitions on the discharge from municipal
wastewater treatment during the "dry season,"
when the minimum 10:1 creek water to discharge
dilution ratio could not be achieved as dictated by
the 1982 Basin Plan.
• Implementation of RWQCB-2 pathogen and sedi-
ment TMDLs for the Sonoma Creek watershed,
which serve the dual purpose of reducing nutri-
ent loading.
• Issuance of the 2003 general Waste Discharge
Requirements (WDRs) (currently under revision).
• Issuance of the 2011 waiver of WDRs for grazing
operations in the watershed.
• Renewal of conditional waivers of WDRs for
existing dairies in 2015.
• Shifts in agricultural practices, including reduc-
tions in the amount of land available for grazing
and the number of confined animal facilities.
In addition, RWQCB-2 is developing permits and
regulations to ensure that confined animal facilities
and vineyards in the watershed do not cause future
nutrient impairments.
As a result of the above restoration work, data
collected between 2002 and 2012 show that
nutrient-related numeric and narrative Water Quality
Objectives are being met, and that impacted
beneficial uses are supported in this waterbody.
The eight lines of evidence did not show exceed-
ances beyond what is allowed in the Water Quality
Control Policy for Developing California's Clean
Water Act Section 303(d) List (Table 1). On the
basis of these data, it is anticipated that the State
Board will recommend removal of the non-tidal
portion (23 miles) of the creek from the state's list of
impaired waters for nutrients in the next listing cycle.
The original 30-mile-long segment is being split into
two segments: a 23-mile-long non-tidal segment and
a 7-mile-long tidally influenced segment.
Partners and Funding
Overall, increased water quality regulation, controls
on municipal wastewater discharges, changes in
land use and implementation of BMPs have contrib-
uted to reductions in nutrient inputs and improve-
ment in water quality. Guidance provided by the
U.S. Department of Agriculture National Resources
Conservation Service and by local resource con-
servation districts has led to the use of improved
agricultural BMPs for grazing animals and confined
animal facilities.
To date, California has invested at least $950,391 of
CWA section 319(h) funds in a total of five projects
to support watershed coordination and agricultural
BMPs in the watershed. California Nonpoint Source
Program San Francisco Regional Board staff mem-
bers responsible for program implementation were
also supported with CWA section 319 grant funding.
Table 1. Sonoma Creek, Summary of Line of Evidence and Exceedances of Evaluation Guidelines
Line of Evidence
1
2
4
5
6
7
8
Analyte
Benthic biomass chlorophyll a
Percent macroalgae cover
Water column chlorophyll a
Nitrate + Nitrite
Ammonia, un-ionized
Ammonia, total
PH
Numeric Evaluation
Guideline1
< 150 mg/m2
30%
15yg/L
10mg/L
0.025mg/L
0.1-2. 8 mg/L
6.5-8.5 units
Number of Exceedances Per
Total Samples
1 of 18
Oof 18
Oof 25
Oof 86
Oof 6
Oof 86
Oof 27
Evaluation Metric2
Evaluation Guideline (a)
Evaluation Guideline (a)
Evaluation Guideline (a)
Water Quality Objective (b)
Water Quality Objective (b)
U.S. EPA Criterion (b)
Water Quality Objective (b)
Notes:
1 mg/m2 = milligrams per square meter; /jg/L = micrograms per liter; mg/L = milligrams per liter
2 (a) = Listing Factor 4.11, weight of evidence (b) = Listing Factor 4.1, toxicant
(Listing Factor Source: http://www.waterboards.ca.gov/water _ issues/programs/tmdl/docs/ffed
303d _ Iistingpolicy093004.pdf)
UJ
o
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-15-001III
December 2015
For additional information contact:
Kevin Lunde, Environmental Scientist
San Francisco Bay Regional Water Quality Control Board
Kevin.Lunde@waterboards.ca.gov
510-622-2431
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