|
What
type of water quality is measured?
Runoff from creeks, rivers or storm drains is the largest
source of pollution to California beaches. Runoff may
contain toxic heavy metals, pesticides, petroleum hydrocarbons,
animal waste, trash and even human sewage. The Beach
Report Card includes an analysis of shoreline (ankle-deep)
water quality data collected by various county and city
public agencies for fecal indicator bacteria. At present,
the report card contains no information on toxins or
trash in the water.
Currently,
there are over 400 shoreline monitoring locations analyzed
in the California Beach Report Card from Del Norte County
south to San Diego County. Shoreline water samples are
analyzed for three indicator bacteria: total coliform,
fecal coliform (or E.coli) and enterococcus. Total coliform,
which contains coliform of all types, originates from
many sources, including soil, plants, animals and humans.
Fecal coliform and enterococcus bacteria are found in
the fecal matter of mammals and birds. This fecal matter
does not necessarily come from humans, although numerous
prior studies have demonstrated that there is a significant
possibility of human sewage contamination in storm drain
runoff at any given time.
The
amount of indicator bacteria present in runoff, and
consequently in the surfzone, is currently the best
indication of whether or not a beach is safe for recreational
contact. Indicator bacteria are not usually the microorganisms
that cause illness in swimmers. Instead, their presence
indicates the potential for water contamination with
other pathogenic microorganisms such as bacteria, viruses
and protozoa that do pose a health risk to humans. The
link between swimming in waters containing elevated
levels of bacteria indicators and health risk was confirmed
in the groundbreaking 1996 Epidemiological Study conducted
by USC, the Sanitation District of Orange County, the
City of Los Angeles, and Heal the Bay, under the auspices
of the Santa Monica Bay Restoration Project.
Most
sample locations are selected by monitoring, health,
and regulatory agencies to specifically target popular
beaches and/or those beaches frequently affected by
runoff. Water quality samples were collected by the
appropriate agency at a minimum of once a week from
April through October, as required under AB411. Many
agencies conducted year-round sampling, while others
scaled back their monitoring program from November through
March. All counties that have beach monitoring programs
and provide the data to the public were included in
the Beach Report Card.
Water
quality thresholds
Concentrations
of total coliform, fecal coliform and enterococcus bacteria
are typically measured in colony-forming units (cfu)
per 100 milliliters of ocean water. Colony-forming units
are the number of bacteria in a given volume of ocean
water that are capable of reproduction during the course
of sample analysis. The Beach Report Card methodology
utilizes four thresholds, or specific bacterial densities,
that are associated with increased health risks. These
thresholds were derived from California Department of
Health Services standards set forth in AB411 and findings
from the 1996 SMBRP Epidemiological Study on swimmers
at urban runoff polluted beaches. The four exceedance
thresholds for various indicator bacteria can be found
in Appendix
A.
Heal
the Bay's Grading System
Heal
the Bay's grading system takes into consideration the
magnitude and frequency of an exceedance above indicator
thresholds over the course of a year. Furthermore, those
beaches that exceed multiple indicator thresholds in
a given day received lower grades than those beaches
that exceeded just one indicator threshold.
The
grades are based on a 100-point scale. For each monitoring
location, points are subtracted from a perfect score
of 100 points depending upon where the data falls within
the designated thresholds. As the magnitude or frequency
of bacteria density threshold exceedance increases,
the number of points subtracted increases. The threshold
points and grading system can be found in Appendix
A.
Water
quality drops dramatically during and immediately after
a rainstorm, but often rebounds to its previous level
within a few days. For this reason, wet weather data
was analyzed separately in order to avoid artificially
lowering a location's grade. A wet weather data point
is any sample collected during or for three days following
the cessation of a rainstorm. Heal the Bay's annual
report card and weekly report cards utilized a definition
of a significant rainstorm as precipitation more than
or equal to one tenth of an inch (>=0.1"). Also, in
response to requests from health agency officials, the
BRC now analyzes dry weather water quality data for
two time periods, 1) April 2002 to October 2002 (AB411
time period), and 2) April 2002 to March 2003.
What
does this mean for the beach user?
Simply
put, the higher the grade a beach receives, the better
the water quality at that beach. The lower the grade,
the greater the health risk. Potential illnesses include
stomach flu, ear infection, upper respiratory infection
and major skin rash (full body). The known risks of
contracting illnesses associated with each threshold
are based on a one-time, single day of exposure (head
immersed while swimming) in polluted water. Increasing
frequency of exposure or the magnitude of bacteria densities
may significantly increase an ocean user's risk of contracting
any one of a number of these illnesses.
It
is important to note that the grades derived for the
California Beach Report Card represent the most current
available information to the public, but they do not
represent real-time water quality conditions. Currently,
laboratory analyses of beach water quality samples take
18 to 48 hours to complete, then the data must be entered
into a database before it is sent to Heal the Bay for
a grade calculation. However, the Report Card on the
Heal the Bay web site includes real-time information
on beach closures because most closures are due to sewage
spills and all health agencies close beaches immediately
after a spill. The Report Card is designed to give the
beachgoer historical information on the water quality
at a given beach. The public can then make informed
decisions about which beach to visit safely.
|
