2014 Water Report Card Executive Summary
Save the Harbor / Save the Bay’s annual Boston Harbor Region Beach Water Quality
Report Card is based on an in-depth analysis of thousands of samples taken by the DCR
and the Massachusetts Water Resources Authority (MWRA) in 2013. The samples were
collected at 34 testing sites on public beaches in 9 communities including Nahant, Lynn,
Revere, Winthrop, East Boston, South Boston, Dorchester, Quincy and Hull. The report
card is based on methodology developed by the Save the Harbor/Save the Bay’s
Beaches Advisory Committee (BSAC), Co-Chaired by Dr. Judy Pederson of MIT’s Sea
Grant Program and Dr. Jim Shine of the Harvard School of Public Health.
Water Quality
Save the Harbor uses quantitative metrics for assessing beach water quality and
management at the Boston Harbor region beaches. Enterococcus is the current
microbial indicator of GI illness used in marine waters, as established by the EPA. To
assess and compare the water quality and conditions on each beach, we looked at the
percentage of test samples exceeding the state swimming standard of 104 colony
forming units (cfu) of Enterococcus/100 ml of water. This metric is called “Beach
Safety,” and is a metric that is independent of the flagging program.
Another indicator of water quality is the geometric mean (GM). The GM indicates the
central tendency of a set of numbers from the product of their values. For our analysis,
we calculated the GM based on bacterial exceedance values from the previous five days
without rain. A GM of 35 cfu/100 ml or greater is considered statistically significant in
water quality analysis, and is included with bacterial exceedances when determining
Overall Beach Safety.
The total number of samples collected varies across these beaches, as some are
sampled weekly and others are sampled daily throughout the swimming season. Also,
beaches vary in the number of sampling locations; some have only one location whereas
others have as many as four.
The summer of 2013 was a relatively wet season, with 6 days exceeding 1 inch marker of
rain at Boston Logan Airport’s rain gauge. Rainfall measured at Logan during the
swimming season of 2013 was significantly higher than the rainfall amount of 2012, with
20.88 inches vs. 12.24 inches respectively.
Beach Flagging and Management
The metrics for assessing Beach Management with the Flagging Program include
Sensitivity, Positive Predictive Efficiency, Specificity, Negative Predictive Efficiency, and
Overall Predictive Efficiency.
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Sensitivity tells us when the beach is not safe for swimming, what fraction of the
time the beach is correctly labeled with a red flag. This is expressed as, “When
this beach is not safe for swimming, it is correctly labeled with a red flag x% of
the time.” 100% yields a perfect Sensitivity score.
Positive Predictive Efficiency measures what fraction of the time a posted red
flag is correct.
Specificity tells us when the beach is safe for swimming, what fraction of the
time the beach is correctly labeled with a blue flag. This is expressed as, “When
this beach is safe for swimming, it is correctly labeled with a blue flag x% of the
time.” 100% yields a perfect Specificity score.
Negative Predictive Efficiency measures what fraction of the time a posted blue
flag is correct.
Overall Predictive Efficiency measures what fraction of the time the flags are in
general correct. This metric can be expressed as, “The flags correctly indicate
that the beach is safe or unsafe for swimming x% of the time.”
Beach Flagging and Management metrics are only available for beaches that are tested
on a daily basis.
Overall Beach Safety
Beach
2013 Overall Beach Safety
Test Frequency
# of sampling
locations
Nantasket
City Point
Savin Hill
Carson Beach
M Street
Constitution Beach
Pleasure Bay
Short Beach
Winthrop Beach
Revere
Nahant
Wollaston*
King's Beach**
Malibu Beach
Tenean Beach
100%
100%
100%
98.73%
98.73%
97.05%
95.78%
94.12%
94.12%
93.75%
91.18%
88.27%
83.12%
76.47%
62.96%
weekly
daily
weekly
daily
daily
daily
daily
weekly
weekly
weekly
weekly
daily
daily
weekly
daily
4
1
1
2
1
3
3
1
1
4
4
4
3
1
1
*Wollaston Beach includes the Milton St, Channing St, Sachem St, and Rice Road sampling
locations.
**King’s Beach has 3 primary sampling locations, but is also tested at Stacey Brook outfall for
bacterial exceedances.
Overall Beach Safety (2011-2013)
Beach
2013
2012
2011
3-year Avg
Nantasket
City Point
Savin Hill
Carson Beach
M Street
Constitution Beach
Pleasure Bay
Short Beach
Winthrop Beach
Revere
Nahant
Wollaston*
King's Beach
Malibu Beach
Tenean Beach
All Beaches
100%
100%
100%
98.73%
98.73%
97.05%
95.78%
94.12%
94.12%
93.75%
91.18%
88.27%
83.12%
76.47%
62.96%
91.62%
98.33%
100.00%
88.24%
98.68%
98.68%
88.60%
93.86%
100.00%
100.00%
100.00%
89.29%
93.20%
86.40%
88.89%
81.82%
93.73%
100.00%
98.60%
91.70%
97.30%
98.60%
93.20%
94.50%
83.30%
84.60%
87.50%
88.50%
88.73%
73.20%
91.70%
79.50%
90.06%
99.44%
99.53%
93.31%
98.24%
98.67%
92.95%
94.71%
92.47%
92.91%
93.75%
89.66%
90.07%
80.91%
85.69%
74.76%
91.80%
*Wollaston Beach includes the Milton St, Channing St, Sachem St, and Rice Road sampling
locations.
Individual Beach Summaries
Nahant
Nahant Beach is located in Nahant, MA and has four sampling locations that were tested
weekly for bacterial counts in 2013. In 2013, Nahant received an Overall Beach Safety
score of 91.18%, which was higher than the previous year’s score of 89.29%. There were
6 bacterial exceedances in the 68 samples taken in 2013.
Nahant Beach Safety 2013
Total # Samples
# Exceedances
Test Frequency
Overall Beach Safety
68
6
weekly
91.18%
Nahant posts a red flag when there is a bacterial exceedance at 2 or more of its
sampling locations. In 2013, Nahant had one red flag posting. As previously stated, the
metrics on flagging accuracy cannot be computed for beaches with weekly bacterial
testing.
King’s
King’s Beach is located on the Lynn and Swampscott line. It has three sampling locations
that were tested daily for bacterial counts in 2013. In 2013, King’s received an Overall
Beach Safety score of 83.12%, which is lower than the previous year’s score of 86.40%.
There were 22 bacterial exceedances in the 237 total samples taken in 2013.
King's Beach Safety 2013
Total # Samples
237
# Bacterial Exceedances
22
Test Frequency
Overall Beach Safety
daily
83.12%
King’s Beach posts a red flag when there is a bacterial exceedance at 2 or more of its
sampling locations. In 2013, King’s had 13 red flag postings.
King's Flagging Metrics
Sensitivity
Positive Predictive Efficiency
Specificity
Negative Predictive Efficiency
Overall Predictive Efficiency
63.64%
50.00%
89.71%
93.85%
87.34%
Revere Beach
Revere Beach is located in Revere, MA and has four sampling locations that were tested
weekly for bacterial counts in 2013. In 2013, Revere received an Overall Beach Safety
score of 93.75%, which was lower than the previous year’s score of 100%. There was
one bacterial exceedance in the 64 samples taken in 2013.
Revere Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
64
1
weekly
93.75%
Revere posts a red flag when there is a bacterial exceedance at two or more of its
sampling locations. In 2013, Revere had one red flag posting. Since Revere Beach is
tested on a weekly basis, beach management metrics are not computed.
Short Beach
Short Beach is located in Revere, MA and has one sampling location that was tested
weekly for bacterial counts in 2013. In 2013, Short Beach received an Overall Beach
Safety score of 94.12%, which was lower than the previous year’s score of 100%. There
was one bacterial exceedance in the 17 samples taken in 2013.
Short Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
17
1
weekly
Overall Beach Safety
94.12%
Short Beach posts a red flag when there is a bacterial count greater than 104 cfu. In
2013, Short Beach had one red flag posting. Since Short Beach is tested on a weekly
basis, beach management metrics are not computed.
Winthrop
Winthrop Beach is located in Winthrop, MA and has one sampling location that was
tested weekly for bacterial counts in 2013. In 2013, Winthrop received an Overall Beach
Safety score of 94.12%, which was lower than the previous year’s score of 100%. There
was one bacterial exceedance in the 17 samples taken in 2013.
Winthrop Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
17
1
weekly
94.12%
Winthrop Beach posts a red flag when there is a bacterial count greater than 104 cfu. In
2013, Winthrop had one red flag posting. Since Winthrop is tested on a weekly basis,
beach management metrics are not computed.
Constitution
Constitution Beach is located in East Boston and has three sampling locations that were
tested daily for bacterial counts in 2013. In 2013, Constitution received an Overall Beach
Safety score of 97.05%, which was higher than the previous year’s score of 88.60%.
There were 4 bacterial exceedances in the 237 samples taken in 2013.
Constitution Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
237
4
daily
97.05%
Constitution posts a red flag when there is a bacterial exceedance at two or more of its
sampling locations. In 2013, there were 5 red flags posted on Constitution Beach.
Constitution Flagging Metrics
Sensitivity
50.00%
Positive Predictive Efficiency
20.00%
Specificity
94.81%
Negative Predictive Efficiency
98.65%
Overall Predictive Efficiency
93.67%
Pleasure Bay
Pleasure Bay is located in South Boston and has three sampling locations that were
tested daily for bacterial counts in 2013. In 2013, Pleasure Bay received an Overall
Beach Safety score of 95.78%, which was higher than the previous year’s score of
93.86%. There were 10 bacterial exceedances in the 228 samples taken in 2013.
Pleasure Bay Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
237
10
daily
95.78%
Pleasure Bay posts a red flag when there is a bacterial exceedance at two or more of its
sampling locations. In 2013, there were no red flags posted on Pleasure Bay Beach.
Pleasure Bay Flagging Metrics
Sensitivity
0.00%
Positive Predictive Efficiency
0.00%
Specificity
98.73%
Negative Predictive Efficiency 100.00%
Overall Predictive Efficiency
98.73%
M Street
M Street beach is located in South Boston and has one sampling location that was
tested daily for bacterial counts in 2013. In 2013, M Street received an Overall Beach
Safety score of 98.73%, which was higher than the previous year’s score of 98.68%.
There was one bacterial exceedance in the 79 samples taken in 2013.
M Street Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
79
1
daily
98.73%
M Street posts a red flag when there is a bacterial count greater than 104 cfu. In 2013,
M Street had one red flag posting.
M Street Flagging Metrics
Sensitivity
0.00%
Positive Predictive Efficiency
0.00%
Specificity
Negative Predictive Efficiency
Overall Predictive Efficiency
98.72%
100.00%
96.20%
Carson Beach
Carson Beach is located in South Boston and has two sampling locations that were
tested daily for bacterial counts in 2013. In 2013, Carson received an Overall Beach
Safety score of 98.73%, which was higher than the previous year’s score of 98.68%.
There were 2 bacterial exceedances in the 158 samples taken in 2013.
Carson Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
158
2
daily
98.73%
Carson posts a red flag when there is a bacterial exceedance at one or more of its
sampling locations. In 2013, there were 2 red flags posted on Carson Beach.
Carson Flagging Metrics
Sensitivity
Positive Predictive Efficiency
Specificity
Negative Predictive Efficiency
Overall Predictive Efficiency
0.00%
0.00%
96.10%
97.37%
93.67%
City Point
City Point is located in South Boston and has one sampling location that was tested daily
for bacterial counts in 2013. In 2013, City Point received an Overall Beach Safety score
of 100% as there were no bacterial exceedances on the days sampled. This score is the
same as the previous year’s score of 100%.
City Point Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
79
0
daily
100.00%
City Point posts a red flag when there is a bacterial count greater than 104 cfu. In 2013,
there were no red flag postings on City Point Beach.
City Point Flagging Metrics
Sensitivity
Positive Predictive Efficiency
Specificity
Negative Predictive Efficiency
Overall Predictive Efficiency
0.00%
0.00%
98.73%
100.00%
98.73%
Tenean
Tenean Beach is located in Dorchester and has one sampling location that was tested
daily for bacterial counts in 2013. In 2013, Tenean received an Overall Beach Safety
score of 62.20%, which was lower than the previous year’s score of 81.82%. There were
a total of 17 bacterial exceedances and 14 GM exceedances in the 82 samples taken in
2013.
Tenean Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
81
31
daily
62.96%
Tenean posts a red flag when there is a bacterial count greater than 104 cfu. In 2013,
Tenean Beach had 38 red flag postings.
Tenean Flagging Metrics
Sensitivity
Positive Predictive Efficiency
Specificity
Negative Predictive Efficiency
Overall Predictive Efficiency
61.29%
55.88%
70.00%
74.47%
66.67%
Malibu Beach
Malibu Beach is located in Dorchester and has one sampling location that was tested
weekly for bacterial counts in 2013. In 2013, Malibu received an Overall Beach Safety
score of 76.47%, which was lower than the previous year’s score of 88.89%. There were
a total of 4 bacterial exceedances in the 17 samples taken in 2013.
Malibu Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
17
4
weekly
76.47%
Malibu posts a red flag when there is a bacterial count greater than 104 cfu. In 2013,
Malibu had 3 red flag postings. Since Malibu Beach is tested on a weekly basis, beach
management metrics are not computed.
Savin Hill Beach
Savin Hill Beach is located in Dorchester and has one sampling location that was tested
weekly for bacterial counts in 2013. In 2013, Savin Hill received an Overall Beach Safety
score of 100% as there were no bacterial exceedances on the days sampled. This was
higher than the previous year’s score of 88.24%.
Savin Hill Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
17
0
weekly
100.00%
Savin Hill posts a red flag when there is a bacterial count greater than 104 cfu. In 2013,
there were no red flag postings on Savin Hill Beach. Since Savin Hill Beach is tested on a
weekly basis, beach management metrics are not computed.
Wollaston Beach at Milton Road
Milton Rd is one of four sampling locations on Wollaston Beach in Quincy, MA that was
tested daily for bacterial counts in 2013. In 2013, Milton received an Overall Beach
Safety score of 88.89%, which was lower than the previous year’s score of 96.05%.
There were a total of 9 bacterial exceedances in the 81 samples taken in 2013.
Milton Rd Beach Safety 2013
Total # Samples
# Exceedances
Test Frequency
Overall Beach Safety
81
9
daily
88.89%
Milton posts a red flag when there is a bacterial count greater than 104 cfu. Wollaston
Beach posts a red flag across the beach when there is a bacterial exceedance at two or
more sampling locations. In 2013, Milton Rd had 6 red flag postings.
Wollaston @ Milton Rd Flagging Metrics
Sensitivity
22.22%
Positive Predictive Efficiency
33.33%
Specificity
94.44%
Negative Predictive Efficiency
90.67%
Overall Predictive Efficiency
86.42%
Wollaston Beach at Channing Street
Channing St is one of four sampling locations at Wollaston Beach that was tested daily
for bacterial counts in 2013. In 2013, Channing received an Overall Beach Safety score of
80.25%, which was lower than the previous year’s score of 87.18%. There were a total of
16 bacterial exceedances in the 81 samples taken in 2013.
Channing St Beach Safety 2013
Total # Samples
# Exceedances
Test Frequency
Overall Beach Safety
81
16
daily
80.25%
Channing St posts a red flag when there is a bacterial count greater than 104 cfu.
Wollaston Beach posts a red flag across the beach when there is a bacterial exceedance
at two or more sampling locations. In 2013, Channing St had 10 red flag postings.
Wollaston @ Channing St Flagging
Metrics
Sensitivity
25.00%
Positive Predictive Efficiency
40.00%
Specificity
90.77%
Negative Predictive Efficiency
83.10%
Overall Predictive Efficiency
77.78%
Wollaston Beach at Sachem Street
Sachem St is one of four sampling locations on Wollaston Beach that was tested daily for
bacterial counts in 2013. In 2013, Sachem received an Overall Beach Safety score of
90.12%, which was lower than the previous year’s score of 94.81%. There were a total of
8 bacterial exceedances in the 81 samples taken in 2013.
Sachem St Beach Safety 2013
Total # Samples
# Exceedances
Test Frequency
Overall Beach Safety
81
8
daily
90.12%
Sachem St posts a red flag when there is a bacterial count greater than 104 cfu.
Wollaston Beach posts a red flag across the beach when there is a bacterial exceedance
at two or more sampling locations. In 2013, Sachem St had 6 red flag postings.
Wollaston @ Sachem St Flagging Metrics
Sensitivity
12.50%
Positive Predictive Efficiency
16.67%
Specificity
93.15%
Negative Predictive Efficiency
90.67%
Overall Predictive Efficiency
85.19%
Wollaston Beach at Rice Road
Rice Road is one of four sampling locations on Wollaston Beach that was tested daily for
bacterial counts in 2013. In 2013, Rice Road received an Overall Beach Safety score of
93.83%, which was lower than the previous year’s score of 94.74%. There were a total of
5 bacterial exceedances in the 81 samples taken in 2013.
Rice Road Beach Safety 2013
Total # Samples
# Exceedances
Test Frequency
Overall Beach Safety
81
5
daily
93.83%
Rice Road posts a red flag when there is a bacterial count greater than 104 cfu.
Wollaston Beach posts a red flag across the beach when there is a bacterial exceedance
at two or more sampling locations. In 2013, Rice Road had 2 red flag postings.
Wollaston @ Rice Road Flagging Metrics
Sensitivity
0.00%
Positive Predictive Efficiency
0.00%
Specificity
97.37%
Negative Predictive Efficiency
93.67%
Overall Predictive Efficiency
91.36%
Nantasket
Nantasket Beach is located in Hull, MA and has four sampling locations that were tested
weekly for bacterial counts in 2013. In 2013, Nantasket received an Overall Beach Safety
score of 100% as there were no bacterial exceedances on the days sampled. This was
higher than the previous year’s score of 98.33%.
Nantasket Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
56
0
weekly
100.00%
Nantasket posts a red flag when there is a bacterial exceedance at two or more of its
sampling locations. In 2013, there were no red flags posted on Nantasket Beach. Since
Nantasket is tested on a weekly basis, beach management metrics are not computed.
Aggregated Data for South Boston
The South Boston beaches at M Street Beach, Carson Beach, and City Point received an
aggregated Overall Beach Safety score of 99.15% in 2013, which was slightly higher than
the previous year’s score of 99.12%.
South Boston Beach Safety 2013
Total # Samples
# Exceedances
Test Frequency
Overall Beach Safety
316
3
daily
99.15%
The South Boston beaches post a red flag on the beach when there is a bacterial count
greater than 104 cfu at that sampling location. In 2013, South Boston had a total of 3
red flag postings.
South Boston Flagging Metrics
Sensitivity
0.00%
Positive Predictive Efficiency
0.00%
Specificity
97.44%
Negative Predictive Efficiency
98.70%
Overall Predictive Efficiency
96.20%
Aggregated Data for Wollaston Beach: All Sampling Locations
In 2013, Wollaston received an Overall Beach Safety score of 88.89%, which was lower
than the previous year’s score of 93.20%. There were a total of 21 bacterial exceedances
in the 81 samples days in 2013.
Wollaston Beach Safety 2013
Total # Samples
# Bacterial Exceedances
Test Frequency
Overall Beach Safety
324
21
daily
88.27%
Wollaston posts a red flag when there is a bacterial exceedance at two or more of its
sampling locations. In 2013, Wollaston Beach had 12 red flag postings.
Wollaston Flagging Metrics
Sensitivity
33.33%
Positive Predictive Efficiency
Specificity
Negative Predictive Efficiency
Overall Predictive Efficiency
25.00%
87.32%
91.18%
81.25%
Save the Harbor/Save the Bay would like to thank Dr. Jim Shine and Dr. Judy Pederson,
Co-Chairs of our Beaches Science Advisory Committee, Kelly Coughlin of the MWRA, Dr.
Andrea Rex, DCR’s Gary Briere, SH/SB’s Water Quality Analyst Jacqueline Sussman and
Policy Intern Yudan Jiang for their help with this report.
For more information on Save the Harbor/Save the Bay’s Beaches Report Card, contact
Bruce Berman on his cell at 617-293-6243 or email [email protected]
You can find data and learn more about the methodology on which the report card is
based at www.savetheharbor.org/beachesreportcard