Appendices A-H

455 Pages·2012·7.74 MB·English

U.S. Environmental Protection Agency
Los Angeles Area Lakes TMDLs

March 2012

Appendices
Appendix A. Methodology for Nutrient TMDL Development March 2012
Appendix A. Methodology for Nutrient TMDL Development
�

A-1
Appendix A. Methodology for Nutrient TMDL Development March 2012
(This page left intentionally blank.)

A-2
Appendix A. Methodology for Nutrient TMDL Development March 2012
A.1 Introduction
�
USEPA Region IX is establishing TMDLs for impairments in nine lakes in the Los Angeles Region
(Figure A-1). USEPA was assisted in this effort by the Los Angeles Water Quality Control Board
(Regional Board). Impairments of these waterbodies include low dissolved oxygen/organic enrichment,
odor, ammonia, eutrophication, algae, pH, mercury, lead, copper, chlordane, DDT, dieldrin, PCBs, and
trash.

Figure A-1. Location of Impaired Lakes
Eight of these waterbodies have impairments that may be due to elevated nutrient levels: Peck Road Park
Lake, Echo Park Lake, Lincoln Park Lake, Lake Calabasas, the El Dorado Park lakes, Legg Lake,
Puddingstone Reservoir, and Santa Fe Dam Park Lake. These impairments include algae, ammonia,
eutrophication, low dissolved oxygen/organic enrichment, odor, and pH. A steady-state lake response
model has been set up for each impaired lake to determine whether or not eutrophication is the primary
cause of these impairments. This appendix discusses the problems associated with eutrophication,
sources of nutrient loading, and the approach used for determining loading capacities for nitrogen and
phosphorus based on observed and simulated levels of chlorophyll a.

A-3
Appendix A. Methodology for Nutrient TMDL Development March 2012
(This page left intentionally blank.)

A-4
Appendix A. Methodology for Nutrient TMDL Development March 2012
A.2 Conceptual Model: Nutrients, Algae, and
Eutrophication
Excessive algal growth in the urban lakes of the Los Angeles region has resulted in several waterbodies
not supporting their designated beneficial uses associated with aquatic life and recreation (LARWQCB,
1996). Unaesthetic amounts of algal biomass can directly impair swimming and wading recreational
uses. Algal growth in some instances has produced algal mats in the lakes (UC Riverside, 1994). Excess
growth of algae can also result in loss of invertebrate taxa through habitat alteration (Biggs, 2000). In
addition, ammonia, a nitrogen compound, has been measured at concentrations exceeding objectives
designed to protect aquatic life (LARWQCB, 1996).
Rates of algal growth depend on the availability of nutrients, light, and other factors. Stimulation of
excess algal growth by nutrient loading is referred to as eutrophication. There are many biological
responses to nutrients (nitrogen and phosphorus) in lakes. The biologically available nutrients and light
will stimulate phytoplankton and or macrophyte growth. As these plants grow, they provide food and
habitat for other organisms such as zooplankton and fish. When the aquatic plants die, they will release
nutrients (ammonia and phosphorus) back into the water through decomposition. The decomposition of
plant material consumes oxygen from the water column; in addition the recycled nutrients are available to
stimulate additional plant growth. Physical properties such as light, temperature, residence time, and
wind mixing also play integral roles throughout the pathways described.
These typical biological processes can become over-stimulated by the addition of excess nutrients to a
waterbody and create a situation in which water quality becomes degraded and beneficial uses are
impaired. The following flow chart (Figure A-2) outlines the responses within a lake to excessive
nutrient loading and how the beneficial uses will be impacted.
Excessive nutrient loading, from either external or internal processes, can cause excessive phytoplankton
and macrophyte growth. The resulting plant biomass may cause increased turbidity, altered planktonic
food chains, unaesthetic conditions, reduced dissolved oxygen concentrations, and increased nutrient
recycling (Figure A-2). These changes can lead to a cascade of biological responses culminating in
impaired beneficial uses.
Typically, excessive plant growth can quickly lead to an altered planktonic community; in many cases the
dominant phytoplankton species may become blue-green algae (cyanophytes) and algal blooms may
occur, especially in the summer months. These blooms cause fluctuations in dissolved oxygen
concentration and pH that can negatively affect aquatic life in the waterbody. Senescence and decay of
the biomass present in algal blooms may also cause problems with scum and odors that affect recreational
uses of the affected waterbody. Likewise, macrophyte growth may increase and become expansive
throughout the lake (Figure A-2). Particularly in shallow lakes, the combination of available nutrients
and greater light intensity throughout the water column provides the light that is needed for rapid plant
growth. In addition, light can penetrate to the bottom of shallow lakes, promoting macrophyte growth. In
comparison, in deep lakes a greater portion of the water column is not able to support photosynthesis as a
majority of the water column is below the light penetration depth. Thus, the impacts of nutrient loading
and the biological response of planktonic algae and macrophytes are often very apparent in shallow lakes.

A-5
Appendix A. Methodology for Nutrient TMDL Development March 2012

Figure A-2. Conceptual Model for Lakes

A-6
Appendix A. Methodology for Nutrient TMDL Development March 2012
As noted above, eutrophication can also lead to increased daytime pH in lakes due to rapid uptake of
carbon dioxide by photosynthesizing algae. The elevated pH creates a harmful environment for
organisms and can increase the concentration of un-ionized ammonia, potentially leading to direct toxicity
to fish and other organisms. Dense algal populations also cause diurnal swings in dissolved oxygen
concentrations, as oxygen is released during daytime photosynthesis and consumed during nighttime
respiration. Decomposition of algal biomass can consume oxygen and dramatically reduce the oxygen
levels found in the lake. Low dissolved oxygen levels can become very stressful for fish and other
organisms and may in fact lead to fish kills (Figure A-2). Moreover, as the plant material is decomposed,
the nutrients are released and will recycle through the system. Shallow lakes tend to have increased
biological productivity because it is likely that the photosynthetic zone and decomposition zone of the
water column overlap, creating the situation where as materials are decomposed and the nutrients
released, they are also immediately available for photosynthesis and plant growth continuing to drive
ongoing impairments.
Control of the deleterious effects of eutrophication in lakes typically requires reduction in nutrient loads.
Both external and internal (recycled) nutrient loads may need to be addressed.

A-7
Appendix A. Methodology for Nutrient TMDL Development March 2012
(This page left intentionally blank.)

A-8
Appendix A. Methodology for Nutrient TMDL Development March 2012
A.3 Source Assessment
�
Sources of nutrient loading to a lake may include both point and nonpoint sources. For the purposes of
allocating loads among nutrient sources, federal regulations distinguish between allocations for point
sources regulated under NPDES permits (for which wasteload allocations are established) and nonpoint
sources that are not regulated through NPDES permits (for which load allocations are established) (see 40
CFR 130.2). This section describes how the loading from point and nonpoint sources were estimated.
A.3.1 POINT SOURCES
Point sources are discharges that occur at a defined point, or points, such as a pipe or storm drain outlet.
Most point sources are regulated through the NPDES permitting process.
A.3.1.1 MS4 Permittees
In 1990 USEPA developed rules establishing Phase 1 of the NPDES stormwater program, designed to
prevent pollutants from being washed by stormwater runoff into the Municipal Separate Storm Sewer
Systems (MS4), or from being directly discharged into the MS4 and then discharged into local
waterbodies. Phase I of the program required operators of medium and large MS4s (those generally
serving populations of 100,000 or more) to implement a stormwater management program as a means to
control polluted discharges. Phase II of the program extends the requirements to operators of small MS4
systems, which must reduce pollutants in stormwater to the maximum extent practicable (MEP) to protect
water quality.
Nitrogen and phosphorus loads from urban stormwater runoff are estimated from event mean
concentration (EMC) data and flows predicted from calibrated watershed models (Appendix D, Wet
Weather Loading). Two flow-calibrated LSPC models were previously developed for the San Gabriel
and Los Angeles river basins (Tetra Tech, 2004; Tetra Tech, 2005). To estimate runoff volumes, average
monthly areal flow rates have been extracted for each land use and applied to the land use composition
that drains to an MS4 for each lake. The county of Los Angeles and the Southern California Coastal
Water Research Project (SCCWRP) have been collecting pollutant concentration data for storm events in
the county of Los Angeles for representative land use classes. These concentrations can be applied to the
flow volumes predicted by the LSPC models for each land use to estimate average wet weather nutrient
loading to each lake. Appendix D (Wet Weather Loading) describes the datasets, assumptions, and
loading results for this analysis.
These systems may also discharge during dry weather as a result of irrigation, car washing, etc.
Estimation of nutrient loading from MS4 systems in dry weather is based on SCCWRP regional studies
and is described in Appendix F (Dry Weather Loading).
A.3.1.2 Non-MS4 NPDES Discharges
In addition to MS4 stormwater dischargers, the NPDES program regulates stormwater discharges
associated with industrial and construction activities and non-stormwater discharges (individual and
general permits). To quantify nutrient loading from non-MS4 NPDES discharges, the permit databases
maintained by the Los Angeles Regional Board were downloaded for the Los Angeles River, San Gabriel
River, and Santa Monica Bay Basins. Geographic information listed for each permit was used to
determine which facilities are located in the watersheds of the eight nutrient-impaired lakes. Nutrient
loading from each facility was estimated based on the reported disturbed area. The facilities and
estimated loads are described in more detail in the lake specific sections of this report.

A-9