Still River Study 2004-2005Sponsored by Friends of the Lake

Presented by Curtis Read

November 17th, 2005

2

Background

• From its headwaters in the Housatonic River in New Milford, Lake Lillinonah extends 12 miles to the Shepaug Dam

• Lake covers 1900 acres to a maximum depth of 110 feet with 45 miles of shoreline.

• Connecticut Light and Power created Lake Lillinonah in 1955 as a source of hydroelectricity and flood control.

• The dam's 57,000-horsepower turbine drives a 43,000-kilowatt generator in what is Connecticut's newest and largest hydroelectric plant.

3

Determination of Influence by the Still River Tributary to the Water Quality &

Algae Blooms in Lake Lillinonah

• Lake Lillinonah suffers algae blooms due to infusion of nutrients (primarily phosphorus and nitrogen compounds) from both non-point stormwater and point source pollution.

• It was postulated that a significant loading of nutrients to the lake is the result of the Still River contribution directly into Lake Lillinonah.

• The Friends of the Lake contracted Hydro Technologies, Inc. to design and perform the comprehensive “Still River Study” to pinpoint the source(s) of nutrient loading in the urban watershed that includes Danbury and the narrow corridor flowing north along Route 7 through Brookfield and New Milford to enter the top of Lake Lillinonah at “Lover’s Leap”.

4

Upper Still – Site 1

Below STP –Site 4

Lover’s Leap

5

Water Sampling Sites

• Site 1 - Still River above Limekiln Brook• Site 2 - Limekiln Brook at Bennet Park above Sewage

Treatment Plant• Site 3 - Limekiln Brook below Sewage Treatment Plant• Site 4 - Confluence of Still River and Limekiln Brook• Site 5 - Harry Brook Park• Site 6 - Lover’s Leap Gorge• Site 7 - Housatonic River at Addis Park• Site 8 - Housatonic River at Boardman Bridge above New

Milford

6

7

8

Danbury SewageTreatment Plant (STP)

• DEP permit issued Feb, 2003, Valid for 5 years

• Design capacity = 15.5 mgd. Typical discharge = 10

• At 10 mgd = 15.5 cfs flow for 24 hours every day

• Permit allows STP to discharge daily avg of 1.0 mg/L T-Phos in “season” (April 1 – September 30), no limit other 6 months

• Nitrogen “credits” (fine) bought by Danbury (highest or 2nd most $ in CT) = $378,000 in 2003

9

10

Site 7 Addis ParkSite 8 – Boardman Bridge

Still River Inlet

Housatonic - New Milford

Site 6 - Lover’s Leap

11

GIS Mapping and AVI by Northwest Conservation District

12

USGS Gage in Brookfield records flows constantly. There appears to be a daily variance of discharge of approx. 10 cfs.

Note the spikes on this graph showing storm effects in urban watershed of Danbury. This is a result of a high % of impervious cover.

13

Flow in Cubic Ft/Sec

2004 2005 Average

79 52 66

1283 508 896

6.2 10.2 8.2

Still USGS Gage

Housatonic Gage

Still as % of Housatonic

Flow in Cubic Ft/Sec

Site 3 – Below STP Site 5 – Harrybrook Park

14

2004 Data

T-Phos Increase in Housatonic from Still

0.023

0.041

0.000

0.010

0.020

0.030

0.040

0.050

After Still Before Still

mg/L

Warning Level

15

2005 Data

Total Phosphorus

36243

413

832

3032

0100200300400500600700800900

Still River above Limekiln Brook Tributary

Limekiln Brook above Danbury STP

Limekiln Brook below Danbury STP

Still River below confluence with Limekiln

Still River at Harrybrook Park New Milford

Housatonic River at Lover's Leap below Still Riv..

ug/L

Total Phosphorus

1215

36

0

5

10

15

20

25

30

35

40

Lover's Leap --- Addis Park --- Boardman Bridge

ug/L

16

2005 Data used for 10-10-10 Fertilizer Equivalent

Avg. Conc.

NitrateEquivalent

lbs/dayFertilizer Tons/day

Influence % of Lake

Housatonic 225 615 3.1 27

Still River 688 1,668 8.3 73

Lake Lillinonah 2,283 11.4 100

Avg. Conc.

T-PhosEquivalent

lbs/dayFertilizer Tons/day

Influence % of Lake

Housatonic 12 32.8 0.49 28

Still River 36 83.4 1.25 72

Lake Lillinonah 116.2 1.74 100

17

Comparison of Data from 2004 & 2005

2004 2005 Average 2004 2005 Average

T-Phos in ppb 29 15 22 46 36 41

Nitrate in ppb 270 210 240 850 688 769

at Addis Park at Lover's Leap

Comparison of Data from 2004 & 2005

Data sets for four summer months only May - August

Lillinonah Before Still River Lillinonah After Still River

Data sets for four summer months only May - August

18

Recommendations

• Year round removal of phosphorus, not just seasonal.

• Lower the phosphorus level of 1.0 mg/L allowed by the Danbury STP discharge permit to a “Technology-Based Permit Limit achieved now by sewage treatment plants in other states (0.3 mg/L)

• Look at Lake Champlain, Chesapeake Bay and others where Sewage Treatment Plants have invested in infrastructure where mandated by regulating agencies.

19