2014Water 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 BostonHarbor 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 BostonLoganAirport’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.

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.

OverallBeach Safety

Beach / 2013 OverallBeach Safety / Test Frequency / # of sampling locations
Nantasket / 100% / weekly / 4
City Point / 100% / daily / 1
Savin Hill / 100% / weekly / 1
CarsonBeach / 98.73% / daily / 2
M Street / 98.73% / daily / 1
ConstitutionBeach / 97.05% / daily / 3
PleasureBay / 95.78% / daily / 3
ShortBeach / 94.12% / weekly / 1
WinthropBeach / 94.12% / weekly / 1
Revere / 93.75% / weekly / 4
Nahant / 91.18% / weekly / 4
Wollaston* / 88.27% / daily / 4
King's Beach** / 83.12% / daily / 3
MalibuBeach / 76.47% / weekly / 1
TeneanBeach / 62.96% / daily / 1

*WollastonBeach 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.

OverallBeach Safety (2011-2013)

Beach / 2013 / 2012 / 2011 / 3-year Avg
Nantasket / 100% / 98.33% / 100.00% / 99.44%
City Point / 100% / 100.00% / 98.60% / 99.53%
Savin Hill / 100% / 88.24% / 91.70% / 93.31%
CarsonBeach / 98.73% / 98.68% / 97.30% / 98.24%
M Street / 98.73% / 98.68% / 98.60% / 98.67%
ConstitutionBeach / 97.05% / 88.60% / 93.20% / 92.95%
PleasureBay / 95.78% / 93.86% / 94.50% / 94.71%
ShortBeach / 94.12% / 100.00% / 83.30% / 92.47%
WinthropBeach / 94.12% / 100.00% / 84.60% / 92.91%
Revere / 93.75% / 100.00% / 87.50% / 93.75%
Nahant / 91.18% / 89.29% / 88.50% / 89.66%
Wollaston* / 88.27% / 93.20% / 88.73% / 90.07%
King's Beach / 83.12% / 86.40% / 73.20% / 80.91%
MalibuBeach / 76.47% / 88.89% / 91.70% / 85.69%
TeneanBeach / 62.96% / 81.82% / 79.50% / 74.76%
All Beaches / 91.62% / 93.73% / 90.06% / 91.80%

*WollastonBeach includes the Milton St, Channing St, Sachem St, and Rice Road sampling locations.

IndividualBeach Summaries

Nahant

NahantBeach 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.

NahantBeach Safety 2013
Total # Samples / 68
# Exceedances / 6
Test Frequency / weekly
OverallBeach Safety / 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 / daily
OverallBeach Safety / 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 / 63.64%
Positive Predictive Efficiency / 50.00%
Specificity / 89.71%
Negative Predictive Efficiency / 93.85%
Overall Predictive Efficiency / 87.34%

RevereBeach

RevereBeach 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.

RevereBeach Safety 2013
Total # Samples / 64
# Bacterial Exceedances / 1
Test Frequency / weekly
OverallBeach Safety / 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 RevereBeach is tested on a weekly basis, beach management metrics are not computed.

ShortBeach

ShortBeach is located in Revere, MA and has one sampling location that was tested weekly for bacterial counts in 2013. In 2013, ShortBeach 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.

ShortBeach Safety 2013
Total # Samples / 17
# Bacterial Exceedances / 1
Test Frequency / weekly
OverallBeach Safety / 94.12%

ShortBeach posts a red flag when there is a bacterial count greater than 104 cfu. In 2013, ShortBeach had one red flag posting. Since ShortBeach is tested on a weekly basis, beach management metrics are not computed.

Winthrop

WinthropBeach 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.

WinthropBeach Safety 2013
Total # Samples / 17
# Bacterial Exceedances / 1
Test Frequency / weekly
OverallBeach Safety / 94.12%

WinthropBeach 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

ConstitutionBeach 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.

ConstitutionBeach Safety 2013
Total # Samples / 237
# Bacterial Exceedances / 4
Test Frequency / daily
OverallBeach Safety / 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 ConstitutionBeach.

Constitution Flagging Metrics
Sensitivity / 50.00%
Positive Predictive Efficiency / 20.00%
Specificity / 94.81%
Negative Predictive Efficiency / 98.65%
Overall Predictive Efficiency / 93.67%

PleasureBay

PleasureBay is located in South Boston and has three sampling locations that were tested daily for bacterial counts in 2013. In 2013, PleasureBay 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.

PleasureBayBeach Safety 2013
Total # Samples / 237
# Bacterial Exceedances / 10
Test Frequency / daily
OverallBeach Safety / 95.78%

PleasureBay 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 PleasureBayBeach.

PleasureBay 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 StreetBeach Safety 2013
Total # Samples / 79
# Bacterial Exceedances / 1
Test Frequency / daily
OverallBeach Safety / 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 / 98.72%
Negative Predictive Efficiency / 100.00%
Overall Predictive Efficiency / 96.20%

CarsonBeach

CarsonBeach 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.

CarsonBeach Safety 2013
Total # Samples / 158
# Bacterial Exceedances / 2
Test Frequency / daily
OverallBeach Safety / 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 CarsonBeach.

Carson Flagging Metrics
Sensitivity / 0.00%
Positive Predictive Efficiency / 0.00%
Specificity / 96.10%
Negative Predictive Efficiency / 97.37%
Overall Predictive Efficiency / 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%.

CityPointBeach Safety 2013
Total # Samples / 79
# Bacterial Exceedances / 0
Test Frequency / daily
OverallBeach Safety / 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 CityPointBeach.

City Point Flagging Metrics
Sensitivity / 0.00%
Positive Predictive Efficiency / 0.00%
Specificity / 98.73%
Negative Predictive Efficiency / 100.00%
Overall Predictive Efficiency / 98.73%

Tenean

TeneanBeach 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.

TeneanBeach Safety 2013
Total # Samples / 81
# Bacterial Exceedances / 31
Test Frequency / daily
OverallBeach Safety / 62.96%

Tenean posts a red flag when there is a bacterial count greater than 104 cfu. In 2013, TeneanBeach had 38 red flag postings.

Tenean Flagging Metrics
Sensitivity / 61.29%
Positive Predictive Efficiency / 55.88%
Specificity / 70.00%
Negative Predictive Efficiency / 74.47%
Overall Predictive Efficiency / 66.67%

MalibuBeach

MalibuBeach 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.

MalibuBeach Safety 2013
Total # Samples / 17
# Bacterial Exceedances / 4
Test Frequency / weekly
OverallBeach Safety / 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 MalibuBeach is tested on a weekly basis, beach management metrics are not computed.

SavinHillBeach

SavinHillBeach 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%.

SavinHillBeach Safety 2013
Total # Samples / 17
# Bacterial Exceedances / 0
Test Frequency / weekly
OverallBeach Safety / 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 SavinHillBeach. Since SavinHillBeach is tested on a weekly basis, beach management metrics are not computed.

WollastonBeach at Milton Road

Milton Rd is one of four sampling locations on WollastonBeach 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 / 81
# Exceedances / 9
Test Frequency / daily
OverallBeach Safety / 88.89%

Milton posts a red flag when there is a bacterial count greater than 104 cfu. WollastonBeach 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%

WollastonBeach at Channing Street

Channing St is one of four sampling locations at WollastonBeach 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 / 81
# Exceedances / 16
Test Frequency / daily
OverallBeach Safety / 80.25%

Channing St posts a red flag when there is a bacterial count greater than 104 cfu. WollastonBeach 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%

WollastonBeach at Sachem Street

Sachem St is one of four sampling locations on WollastonBeach 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 StBeach Safety 2013
Total # Samples / 81
# Exceedances / 8
Test Frequency / daily
OverallBeach Safety / 90.12%

Sachem St posts a red flag when there is a bacterial count greater than 104 cfu. WollastonBeach 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%

WollastonBeach at Rice Road

Rice Road is one of four sampling locations on WollastonBeach 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.

RiceRoadBeach Safety 2013
Total # Samples / 81
# Exceedances / 5
Test Frequency / daily
OverallBeach Safety / 93.83%

Rice Road posts a red flag when there is a bacterial count greater than 104 cfu. WollastonBeach 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

NantasketBeach 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%.

NantasketBeach Safety 2013
Total # Samples / 56
# Bacterial Exceedances / 0
Test Frequency / weekly
OverallBeach Safety / 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 NantasketBeach. 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, CarsonBeach, 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%.

SouthBostonBeach Safety 2013
Total # Samples / 316
# Exceedances / 3
Test Frequency / daily
OverallBeach Safety / 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 WollastonBeach: 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.

WollastonBeach Safety 2013
Total # Samples / 324
# Bacterial Exceedances / 21
Test Frequency / daily
OverallBeach Safety / 88.27%

Wollaston posts a red flag when there is a bacterial exceedance at two or more of its sampling locations. In 2013, WollastonBeach had 12 red flag postings.