Town-wide Lakes Management Plan for the Town of Lewisboro Mark - - PowerPoint PPT Presentation

Town-wide Lakes Management Plan for the Town of Lewisboro

Mark Arrigo

EcoLogic, LLC May 7, 2009

Scope

 Summarize the water quality and aquatic

habitat conditions of the Town’s Lakes

 Develop a unified document to

protect/improve water quality

 Recommend specific actions

Outline

 Lake Ecosystems  Lakes Impairment  Symptoms  Root causes & Sources  Reductions Needed  Management Options  Next Steps  Final Thoughts/Questions

Understanding Lake Ecosystems: The Importance of Nutrients

 Focus on Phosphorus



Limiting nutrient in most freshwater systems  Nutrients grow plants…  Algae– makes the water turbid  Rooted plants

Understanding Lake Ecosystems: The Importance of Nutrients

 Trophic State



Defines the status of lakes from nutrient-poor, clear water state to nutrient-rich, very high biological productivity

 Eutrophication



The process of moving from nutrient-poor to nutrient-rich conditions

• A natural process that can be greatly accelerated by

human activity

Lewisboro Lakes Impairment

Lakes Perception Summary

CSLAP Perception Survey 2006 Lakes Excellent to slightly impaired; Not quite crystal clear Waccabuc; Rippowam Slightly impaired, definite algal “greeness” Oscaleta Slightly to substantially impaired Timber; Truesdale No data Kitchawan; Katonah

Lewisboro Lakes Algal Blooms

 Algae in water measured by Chlorophyll-a  New York State Guidance  Chloro-a > 15 ug/L = Notable

Impairment

 Chloro-a >30 ug/L = Severe Impairment

N=21 N=12 N=2 N=50 N=26 N=26 N=27 0% 10% 20% 30% 40% 50% 60% 70% 80%

Lake Kitchawan* Lake Rippowam Lake Oscaleta Lake Waccabuc Timber Lake Truesdale Lake Lake Katonah

Percent

Percent of Chlorophyll-a Measurements Exceeding Thresholds During Summer Period Nuisance bloom (greater than 30 ug/l) Perceived Impairment (greater than 15 ug/l)

*Lake Kitchawan represents two samples, one collected July 2007 and one collected August 2008. Both results were less than 15 ug/l.

Pollutant of Concern

Algal blooms result from excessive phosphorus phosphorus

R² = 0.9442 10 20 30 40 50 20 40 60 80 100 Chlorophyll-a (ug/l) Total Phosphorus upper waters (ug/l)

Total Phosphorus vs Chlorophyll-a June 15 - September 15 Average

Lake Result Perceived Impairment (<15 ug/l) Nuisance Bloom (>30 ug/l) Linear (Lake Result)

Katonah (2006-2007) Truesdale (1999-2007) Timber (2005-2007) Kitchawan (2007) Oscaleta (2002-2007) Waccabuc (2002-2007) Rippowam (2002-2007)

Take Away Message to This Point

 Lakes are Impaired  Primary Impairment is from Algae



Poor water clarity



Pond scum

 Algal blooms caused by excessive

phosphorus

Where’s the Phosphorus Coming From: Primary External Sources?

 Sources:



Land use in the watersheds

 Develop natural areas = >P to lakes 

Septics

 Primarily from within 100m of waterways 

Point sources

 Upstream lakes

Sources of Phosphorus: Results



P from Land Use in Watershed +



P from Septics +



P from Point Sources = Total External Phosphorus Load

Sources of Phosphorus: Lewisboro Lakes (Average)

7% 9% 22% 62%

Point sources (upstream lakes) Development Natural land cover (forest, wetlands, etc) S eptic

External Sources of Phosphorus

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Rippowam Oscaleta* Waccabuc Truesdale* Kitchawan Katonah Timber Contribution (kg/yr)

Phosphorus Loading Estimate, Lewisboro Lakes Point Sources (upstream lakes) Estimated Septic - 100m buffer Land Cover - Human Activity Land Cover - Natural

*Septic contributions for Oscaleta and Truesdale Lakes do not include possible contributions from Connecticut, therefore these values may be underestimated.

Additional Take Away Message

 Septics are the primary source of

phosphorus

 Can’t restore/protect the lakes without

addressing septics issue

Lake Reduction needed to meet 20 ug/l Very aggressive controls in developed areas (ex. BMPs) Eliminate Septic Oscaleta 9% 6% 29% Rippowam 27% 4% 68% Waccabuc 28% 4% 27% Kitchawan 46% 9% 72% Timber 52% 10% 75% Truesdale 63% 13% 65% Katonah 82% 9% 84%

Phosphorus Reductions Needed

• Target concentration: 20 ug/l (currently: ~22 - 98 ug/L)
• NYSDEC guidance value
• selected based perceived water quality impairment for

recreational use to total phosphorus concentration.

Assumes no new sources…..

Conclusions

 Phosphorus is Primary Pollutant



Septics are the largest contributor to P load



Soils mostly not suitable for septics



High density of houses near waterbodies



Septic systems aging

 With no action eutrophication likely to

accelerate

 Significant reductions in phosphorus

loading required

Management Options

• 1. Do nothing
• 2. “Maintain” current conditions
• 3. Improve water quality

• 1. Do Nothing

 Rate of eutrophication will increase



Septics will continue to deteriorate



Nonpoint from development will increase



More septics with development



Sedimentation will increase  End Result: greener and shallower lakes

• 2. “Maintain” Current Conditions



Implement Code revisions

• Mandatory inspection/maintenance of septics
• Restriction on watershed development and landuse

near waterbodies 

BMPs



Focus on priority areas



Retention basins (stormwater)



Erosion controls



Public Education



End Result:



Short term “stabilization” (variable)



Probable long term decline

• 3. Improve Water Quality



Significantly reduce/eliminate septic contribution

• Install Sewers in watersheds (Peach Lake example- next slide)
• Holding tanks for more lightly populated areas



Code revisions

• Restriction on most watershed development and landuse
• Restrictions on fertilizers in watershed



Public Education



BMPs



End Result: Gradually improving water quality

• Timeframe for improvement variable
• Groundwater transport

Wastewater Treatment



1 Treatment plant : 120,000 gallons per day.



New York City Watershed :



requires advanced level of treatment including: ammonia removal, sand and membrane filtration, and ultraviolet disinfection. 

Estimated project costs:



Treatment plant: $10 million



Collection system: $14 million



Average cost per resident $1200 per year for 30 years



Compare to cost of maintaining septics…



Funding:



Putnam County: $2.5 million



Westchester County: $10 million



NYCDEP: TBD (reimburse for the tertiary level of treatment estimated to be $2.4 million)

Peach Lake Example

Recommended Next Steps



Convene a public educational forum(s) to discuss current water quality, and future goals for the lakes of Lewisboro.



Initiate Sewer Feasibility/Cost Study



Discuss creation of watershed tax districts to help fund efforts



Continue the expanded annual lakes monitoring program and create a Lewisboro Lakes Report Card

Final Thoughts

 It took over a century to get to this point

you’re not going to restore the lakes

• vernight

 This will not be easy or inexpensive  It will require long term planning and

commitment from the community

 With community support, it can be done!

Thank you, Questions?