Issues & Goals for Bridgewater WWTP

High phosphorus levels are the primary issue in regard to Bridgewater. Our goal should be to advocate for more stringent phosphorus limits in the next NPDES Permit.

WHY......? Because phosphorus is a nutrient which when present in excess causes eutrophication in the water. Eutrophication can reduce water oxygen levels and cause excessive weed and algae growth, both of which negatively impact the aquatic ecosystem.

HOW.....? By using available water quality data and nutrient guidelines established by EPA.

Learn more about nutrients HERE


The following is an excerpt from the Bridgewater NPDES Permit.

"EPA has released "Ecoregional Nutrient Criteria", established as part of an effort to reduce

problems associated with excess nutrients in water bodies in specific areas of the country. The published

criteria represent conditions in waters in that ecoregion minimally impacted by human activities, and thus

representative of water without cultural eutrophication. Bridgewater is within Ecoregion XIV, Eastern Coastal

Plains. The total phosphorus criteria for this ecoregion, found in Ambient Water Quality Criteria

Recommendations, Information Supporting the Development of State and Tribal Nutrient Criteria, Rivers and

Streams in Ecoregion XIV, published in the December, 2000 is 24 ug/l (0.024 mg/l)."

What does the excerpt above mean? It means when phosphorus levels in a stream in our region climb above 0.024 mg/l eutrophication begins.

Below is a chart used in the permit to demonstrate the impact of the plant on phosphorus levels downstream from the plant.

EPA, in the permit says the following about the above figures.

"These values exceed recommended phosphorus criteria published by EPA. In July 2003, EPA conducted

a site visit to observe water quality conditions at the point of discharge, and at the downstream of the

discharge. Based on observation, the Town River at this location did not appear to be highly eutrophied.

This may be due partly to the natural dark color of the river which prevents sunlight from contributing to algae

growth.

Consequently, the draft permit will not establish limits based on the EPA ecoregion guidance but, will instead

establish a monthly average total phosphorus limit of 1.0 mg/l to prevent eutrophication problems. This limit

will be in effect seasonally, from April 1 to October 31. The draft permit also contains total phosphorus

monitoring requirements from November 1 to March 31.

When, in the future MADEP adopts nutrient criteria, a TMDL is completed, or additional water quality

information shows that the phosphorus limit is not stringent enough to meet water quality standards, a more

stringent limit may be imposed."

 

Facility info and location

NAME AND ADDRESS OF FACILITY WHERE DISCHARGE OCCURS:

Bridgewater Wastewater Treatment Facility

Morris Avenue

Bridgewater, Massachusetts 02134

RECEIVING WATER: Town River

Taunton Watershed (62)

CLASSIFICATION: Class B

The Bridgewater Wastewater Treatment Plant was upgraded in 1987 and has an design flow of 1.44 MGD (million gallons per day)

sanitary sewage, which includes 20,000 GPD of septage. The unit processes are comminutor, aerated grit

chamber, two primary clarifiers, 14 rotating biological contractors (RBC), two secondary clarifiers,

chlorination and dechlorination. Sludge is dewatered on two belt filter presses then composted for

stabilization.

Receiving Stream - Town River

7 day 10 year low flow (7Q10) 1.713 MGD

Design flow of plant 1.44 MGD

As you can see by the above figures when Town River is at low 7Q10 flows the flow from the plant nearly equals the flow of the stream!

 

Total Phosphorus

The Massachusetts Surface Water Quality Standards (314 CMR 4.00) do not contain numerical criteria for

total phosphorus. The criteria for nutrients are found at 314 CMR 4.05(5)(c), which states that nutrients "shall

not exceed the site specific limits necessary to control accelerated or cultural eutrophication". The Water

Quality Standards also require that "any existing point source discharges containing nutrients in concentrations

which encourage eutrophication or growth of weeds or algae shall be provided with the highest and best

practicable treatment to remove such nutrients (314 CMR 4.04). MADEP has established that a monthly

average total phosphorus limit of 0.2 mg/l represents highest and best practical treatment for POTWs.

EPA has produced several guidance documents which contain recommended total phosphorus criteria for

receiving waters. The 1986 Quality Criteria of Water (Gold Book) recommends in-stream phosphorus

concentrations of 0.05 mg/l in any stream entering a lake or reservoir, 0.1 mg/l for any stream not discharging

directly to lakes or impoundments, and 0.025 mg/l within the lake or reservoir.

More recently, EPA has released "Ecoregional Nutrient Criteria", established as part of an effort to reduce

problems associated with excess nutrients in water bodies in specific areas of the country. The published

criteria represent conditions in waters in that ecoregion minimally impacted by human activities, and thus

representative of water without cultural eutrophication. Bridgewater is within Ecoregion XIV, Eastern Coastal

Plains. The total phosphorus criteria for this ecoregion, found in Ambient Water Quality Criteria

Recommendations, Information Supporting the Development of State and Tribal Nutrient Criteria, Rivers and

Streams in Ecoregion XIV, published in the December, 2000 is 24 ug/l (0.024 mg/l).

In February 2001, the Taunton River Watershed Association published, TRWA Water Quality Monitoring

Report 1999-2000. The report includes data on dissolved oxygen, total phosphorus, and nitrogen from

monitoring upstream and downstream of the Bridgewater Wastewater Treatment facility. Phosphorus data

recorded for the months of June, July, August, September and October show an increase in phosphorus levels

between the two monitoring sites. See table below.

These values exceed recommended phosphorus criteria published by EPA. In July 2003, EPA conducted

a site visit to observe water quality conditions at the point of discharge, and at the downstream of the

discharge. Based on observation, the Town River at this location did not appear to be highly eutrophied.

This may be due partly to the natural dark color of the river which prevents sunlight from contributing to algae

growth.

Consequently, the draft permit will not establish limits based on the EPA ecoregion guidance but, will instead

establish a monthly average total phosphorus limit of 1.0 mg/l to prevent eutrophication problems. This limit

will be in effect seasonally, from April 1 to October 31. The draft permit also contains total phosphorus

monitoring requirements from November 1 to March 31.

When, in the future MADEP adopts nutrient criteria, a TMDL is completed, or additional water quality

information shows that the phosphorus limit is not stringent enough to meet water quality standards, a more

stringent limit may be imposed.

 

Ammonia Nitrogen

Limits for total ammonia will remain the same in the draft permit as in the existing permit from the months

of May 1 through October 31. Ammonia can impact the receiving streamís dissolved oxygen concentration

and can be toxic at elevated levels. Ammonia limits during the warm weather season are necessary to maintain

the dissolved oxygen levels of 5 mg/l in the receiving stream as required by the Stateís Water Quality

Standards for Class B waters. Dissolved oxygen (D.O.) levels downstream of the discharge were below water

quality criteria in the months of July and August 2000, see Taunton River Watershed Association (TRWA)

2001 Water Quality Monitoring Report.

 

 

 

 

 

 

Bridgewater WWTP NPDES Permit............ HERE

After following link click on fact sheet for basic overview and location of plant.