CT DEP Developed an 

Interim Nutrient Management 

Strategy for Freshwater While 

Working to Develop Nutrient 

Criteria

CT DEP Went to Public 

Notice with Beacon Falls 

NPDES Permit

EPA Evaluated and Objected 

to the Permit Primarily Based 

on Concerns with Phosphorus 

Limits

CT DEP Analyzed 

Preliminary Data Collected in 

Efforts to Develop Nutrient 

Criteria and is Proposing a 

Shift Based on the Best 

Available Science to Address 

EPA Concerns

CT DEP Will Continue to 

Study Nutrient Dynamics in 

Streams and May Modify the 

Strategy Based on Future 

Findings (Adaptive 

Management) 

Addressing EPA 

Concerns: CT 

NPDES

Phosphorus 

Limits
Addressing EPA Concerns: CT NPDES

Phosphorus Limits

 “The Naugatuck River is listed as impaired for aquatic life, and municipal point 

source discharges are listed as one of the causes of impairment.”

 “No analyses of (aquatic life) data relative to general impairment status or 

eutrophication impacts was presented.”

 “CTDEP must conduct an appropriate analysis of the potential that phosphorus in 

the discharge will cause or contribute to a violation of water quality standard and, if 

so, must establish a WQBEL...”

EPA Concerns (Re: Beacon Fall CT NPDES Draft Permit Letter June 18, 2010)
Addressing EPA Concerns: CT NPDES

Phosphorus Limits

 Using best available science, we shifted the strategy to develop 

biologically based Phosphorus Limits for WWTPs that meet aquatic 

life designated uses

CT DEP Response (Re: Beacon Fall CT NPDES Draft Permit Letter June 18, 2010)
Anthropogenic 

Input of Nutrients:

 Sewage Treatment 

Plants

 Non-Point Sources

 Canopy Cover

 Temperature

 Flow

 Natural Nutrient 

Loading

Sources Habitat Conditions

Changes in Algal 

Community and 

Biomass

Response

Changes in Habitat 

Structure (Smothering 

Rocks, Reduction of food 

Sources)

Changes in Water 

Chemistry (pH, Dissolved 

Oxygen)

Changes in Other 

Biological 

Communities (i.e. 

Macroinvertebrate

and Fish) 

Physical /Chemical 

Changes

Secondary Response

Develop Criteria to Support Aquatic Life Uses in CT Fresh Waters by Linking Excess 

Nutrients with Direct Aquatic Life Responses

Capture Spatial and Temporal Variation

Account for Excess Nutrients Interactions with Habitat Conditions

Create Model to Establish Site-Specific Goals on a Statewide Scale that can be Continually 

Modified with Monitoring Data 

CT DEP Nutrient Management / Criteria Strategy

Currently Working on Project 

to Better Link Excess 

Nutrients to Aquatic Life 

Under an EPA 104(b)3 Grant. 

Additional funding for next 

year provided by EPA 604(b) 

Grant.
Anthropogenic 

Input of Nutrients:

 Sewage Treatment 

Plants

 Non-Point Sources

 Canopy Cover

 Temperature

 Flow

 Natural Nutrient 

Loading

Sources Habitat Conditions

Changes in Algal 

Community and 

Biomass

Response

Stream Benthic 

Algal Community: 

Epilithic Diatoms

CT DEP Nutrient Management / Criteria Strategy

Develop Criteria to Support Aquatic Life Uses in CT Fresh Waters by Linking Excess 

Nutrients with Direct Aquatic Life Responses

Capture Spatial and Temporal Variation

Account for Excess Nutrients Interactions with Habitat Conditions

Create Model to Establish Site-Specific Goals on a Statewide Scale that can be Continually 

Modified with Monitoring Data 
Anthropogenic 

Input of Nutrients:

 Sewage Treatment 

Plants

 Non-Point Sources

 Canopy Cover

 Temperature

 Flow

 Natural Nutrient 

Loading

Sources Habitat Conditions

Changes in Algal 

Community and 

Biomass

Response

Current In-Stream 

Phosphorus Load At Point 

of Discharge: 

Total Forested Condition 

Phosphorus Load

Current Load 

(lbs/day)

205.3

Forested Load 

(lbs/day)

4.80

Enrichment Factor 42.79

Enrichment Factor (EF)

Example:

CT DEP Nutrient Management / Criteria Strategy

Develop Criteria to Support Aquatic Life Uses in CT Fresh Waters by Linking Excess 

Nutrients with Direct Aquatic Life Responses

Capture Spatial and Temporal Variation

Account for Excess Nutrients Interactions with Habitat Conditions

Create Model to Establish Site-Specific Goals on a Statewide Scale that can be Continually 

Modified with Monitoring Data 
Exploratory Data Analysis: Existing Data

Diatom Species Data Collected From 

2002 – 2004

78 Sites

2002 – 2003 Probabilistic Sites

2004 Additional Sites at Established 

Reference and Known Highly Enriched 

Sites

Readily Available GIS Data and Tools

Diatom Images From : ANSP Algae Image Database from the Phycology Section, Patrick Center for Environmental Research, The Academy of 

Natural Sciences at http://diatom.acnatsci.org/AlgaeImage/
Community plot shows additive 

response of diatom species

 Curve height shows signal 

strength

 Evidence for community 

threshold comes from 

synchronous taxa response 

 Sharp peaks denote threshold 

changes in community

 Z- (black dots) are individual 

diatom (algae) species that 

decrease when the Enrichment 

Factor (EF) increases

 Z+ (red dots) are individual 

diatom (algae) species that 

increase when EF increases

Preliminary Work (Best Available Science): Making the Biological Connection to Phosphorus 

Threshold Indicator Taxa Analysis (TITAN)
Community plot shows additive 

response of diatom species

 This analysis indicates a 

community threshold in the EF

range of 4.5 – 8.4

 This means there is little 

change in the biological 

community after an EF of 8.4 

(reduction in biodiversity) and 

dominance by only a few 

„tolerant‟ species

Preliminary Work (Best Available Science): Making the Biological Connection to Phosphorus 

TITAN 

Analysis Observed Change Point Bootstrap Replicate Change Points At Quantiles

0.05 0.1 0.5 0.9 0.95

sumz- 1.9 1.9 1.9 2.305 4.1665 4.27

sumz+ 6.16 4.485 4.845 5.89 7.55 8.435

8.4 EF
TITAN Analysis - Macro-invertebrate Community and Phosphorus Concentration

 Very Weak Relationship Between Phosphorus and Macroinvertebrate Community

 Very Few Significant Species

 No Strong „Change‟ Signals

Preliminary Work (Best Available Science): Making the Biological Connection to Phosphorus 
Preliminary Work (Best Available Science): Making the Biological Connection to Phosphorus 

Beach Brook in Granby (Drainage Basin = 1.2 mi2)

 Small Drainage Basin

 Highly Forested Basin
Preliminary Work (Best Available Science): Making the Biological Connection to Phosphorus 

Farmington River in Canton (Drainage Basin = 354 mi2)

 Premier Trout Fishery

 Healthy Macro-Invertebrate 

Community

 Average Seasonal 

Phosphorus Concentration: 

0.02 mg/L
Preliminary Work (Best Available Science): Making the Biological Connection to Phosphorus 

Thoughts for Future Work...

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Preliminary Work (Best Available Science): Making the Biological Connection to Phosphorus 

Naugatuck River in Beacon Falls (Drainage Basin = 259 mi2)

8.4 EF
DEP Interim Strategy for Issuing NPDES Permits Until 

Full Nutrient Strategy Criteria is Developed

Best Available Science: The preliminary work presented in the 

previous slides along with other exploratory analyses suggeststhat the diatom community 

is indicative of enrichment conditions and that an 

enrichment factor of 8.4 may be an appropriate biological goal to maintain 

diatom community diversity
DEP Interim Strategy for Issuing NPDES Permits Until 

Full Nutrient Strategy Criteria is Developed

 Maintain an in-stream enrichment factor of 

8.4 throughout the drainage basin

Margin of Safety

 Conservatively Assumed No Reductions in 

Current Land Cover / Use Loadings 

 Assumed Worst Case Steady – State Land 

Cover / Use Loadings Based on Export 

During „First Flush‟ Storm (Much Higher 

than Normal) Conditions

 Assumed No Attenuation 

 WWTP Load Based on Current Flow Rate 

(Increases in Flow Rate Would Require 

WWTP to Lower Limits)

East Branch Naugatuck River in Torrington. 

July 2010.
Facility

Original 

Strategy 

(mg/L)

Modified

Strategy 

(mg/L)

Modified STP Load

At Current Flows 

(lbs/day)

Enrichment Factor* At 

Discharge 

TORRINGTON 

WPCF 0.7 0.4 17.29 7.94

THOMASTON 

WPCF 0.7 1 7.35 6.84

WATERBURY 

WPCF 0.7 0.2 34.26 7.96

NAUGATUCK 

WPCF 0.7 0.4 16.43 8.39

BEACON FALLS 

WPCF Cap 1 2.67 8.07

SEYMOUR 

WPCF Cap 0.7 7.54 7.90

ANSONIA WPCF Cap 0.7 11.92 8.36

* No Reduction in Land Cover/Use Loading

Maintain an EF of 8.4 or lower throughout the Naugatuck River 

Naugatuck River Modified Strategy