The State of Webber PondUnderstanding the Factors

Affecting Water Quality in the Webber Pond Watershed

Colby Environmental Assessment TeamColby College Biology Dept.

December 5, 2002Vassalboro Town Office

PART 2

Presentation OverviewIntroduction

Water Quality Analysis

Land Use Analysis

- Intermission -

GIS Analysis and Models

Future Predictions

Remediation Measures

Recommendations

Geographic Information Systems Maps and Models of the Webber Pond

Watershed

Lauren Bliss

GIS and Modeling• Geographic Information System (GIS)

- Combines geographic data with thematic attributes

- Creates layers of maps with themes aligned in a common coordinate system (“georeferenced”)

• Modeling

- Representation of reality that helps to predict how natural systems will work

- Simplifies systems by assessing pertinent factors

- Uses ModelBuilder extension

Bathymetry MapImportant for identifying sub-basins and water sampling sites,

computing lake volume, and predicting the occurrence of

organisms in Webber Pond

ModelBuilder

Bathymetry MapPEARL Depth Map

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Bathymetry Map

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• Webber Pond is primarily shallow

• 61% less than 16 feet deep

• Basin in southern portion

• Deepest point is 41 feet

Soils• Organized into phases and grouped into series

• Classification depends on a number of factors:

• Important to consider soil type when developing in watershed

• Nutrients bind to soil particles and enter lake via runoff

• Erosion factors important

Georeferencing

Aligning Print Maps

Soil Map: An Overview

Digitizing the Print Map

Soil Map

Soil Map Theme Table with Multiple Attribute Fields

K value

- Erosion factor (0.00 to 0.49 for Webber Pond watershed soils)

- Based on a standard size plot tilled and plowed

- Value based on amount of water and sediments in runoff

Soil Map• 31 phases divided into 16 series

• Majority (82.3%) of watershed composed of five soil series

• Septic limitations severe for most Webber Pond watershed soils

• Majority of K values (erosion factor) range from 0.20 to 0.32

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Slope Map

Contour Map

ModelBuilder

Slope Map

Septic Suitability Model

• Open residential land increased from 0.7% of the watershed in 1956 to 7.1% in 1997

• Inadequate septic systems (leach fields) associated with residential or commercial land can contribute to non-point source nutrient loading into Webber Pond

• Beneficial to understand where septic system installment is suitable in the Webber Pond watershed

+

Slope Map Soil Map Septic Suitability

Septic Suitability ModelFactors that influence septic suitability:

Weighted Overlay

Septic Suitability Model

Unsuitable areas• Steep grade

• High septic rank

• Indicated by light purple shading

Highly suitable areas• Gentle slope

• Low septic rank

• Indicated by pale yellow shading

SepticLimitations

SepticRank Slope

SlightModerate

Severe

159

A range from 0-55percent and rankedon a scale from 1 to 9

Septic Suitability Model

• 99% of the watershed is highly unsuitable for septic system development (rank of 4 or above) without prior modifications

• Attributed to steep slopes and soil composition

• Area near Quaker Lane most suitable

• Recommend working with the Kennebec County Soil and Water Conservation Service

GIS, Phosphorus Model, and Future Predictions

Bill McCloy

Erosion Potential Model

Inputs

1. Soil Map

2. Land Use Map

3. Slope Map

Weighted Overlay

Soil Map

• K values represent a soil’s erodibility

• K values were reclassified to range from 1 to 9

• 9 represents the most erodible soil types and 1 represents the least

Land Use MapErosion Risk ValuesMature Forest - 1Wetlands - 1Transitional Forest - 3Reverting Land - 4Pasture - 7Golf Course - 7Cleared Residential Land - 8Cleared Land - 9Crop Land - 9Commercial / Municipal - 9Roads - 9

Slope Map

ModelBuilder

Contour Map Slope Map

Weighted Overlay• Combines 1-9 erosion risk

value for each input

• Factors in the percent importance of each input for the model

Slope - 50% Land Use - 25%

Soil Type - 25%

Erosion Model Inputs

+ + =

Final Erosion Potential Map

• 93.9% of Webber Pond watershed ranks 5 and below for erosion potential

• Only 6.1% of watershed ranks above 5

• No part of watershed ranks very high

Water Budget

Threemile Pond

Mud Pond

Threecornered Pond

Webber Pond

• A water budget measures a ponds inputs and output of water

• The water budget helps determine the flushing rate for a pond or lake

• The flushing rate is a measure of how many times the pond’s water is replaced per year

Data needed for calculation:1. Evaporation Rates2. Precipitation (10 year average)3. Runoff4. Watershed area5. Pond area6. Average pond depth

Areas calculated using ArcView® GIS

Calculation

Flushing Rate Calculation

constants

Inet

Phosphorus Loading Model• Predicts total phosphorus concentrations

• Predicts relative phosphorus loading from each input category

• Input categories:1. Land use patterns2. Atmosphere3. Septic systems4. Soil retention potential5. Sediment release

• Used to predict impact of future development in watershed

Creating the Model

• Area of input categories

• Export coefficients

• Surface area of lake

• Annual total water inflow

• Number of capita years

- Lower for seasonal residences

- Higher for year-round residences

Examples

Mature Forest0.10 kg/ha/yr 245.20 ha 24.52 kg/yr

Camp Roads3.45 kg/ha/yr 6.51 ha 22.46 kg/yr

Golf Course1.60 kg/ha/yr 52.40 ha 83.84 kg/yr

Sediment Release0.7 kg/ha/yr 550.0 ha 385.69 kg/yr

Coefficient Area Phosphorus Loading

Calculated Phosphorus Concentrations

CEAT/MDEP Sampling: 22.97 ppba

Phosphorus Loading Model: 23.35 ppbb

a Mean epicore concentration from Site 1

b Best estimate

Percent Contribution for Different External Loading Categories

3%

3%

7%

6%

4%

1% 6%

12%

10%

10%

28%4%

1%2%3%

Atmospheric Input

Mature Forest

Transitional Forest

Agricultural Land

Wetlands

Cleared Land

Commercial Land

Camp Roads

State/ Town Roads

Golf Course

Reverting Land

Shoreline Development

Non-shoreline Development

Shoreline Septic Systems

Non-shoreline Septic Systems

Institutional

Historical Population Trends and Future Population Predictions

• 1950 - 2000: 1.26% annual pop. growth

• 1990 - 2000: 10% growth in population

• Webber Pond watershed population growing at about same rate as Vassalboro population

• Projected growth: 0.7% annual increase for next 25 years

• Projected 2022 population: 4,698

Future Development Predictions for Webber Pond Watershed

Increased ResidentialDevelopment Scenario

1. Incorporates new shoreline and non-shorelineresidential land

2. Incorporates estimated population in 2022

3. Decrease in agriculture in watershed

No Increase in Residential DevelopmentScenario

1. Incorporates natural forestsuccession

2. No increase in residentialland

3. Decrease in agriculture in watershed

Predicted Land Use Changes with Increase in Residential Land

in 2022

• Mature Forest 602.54 acre increase• Shoreline Residential 10.50 acre increase• Non-Shoreline Residential 212.00 acre increase• Transitional Forest 610.60 acre decrease• Reverting Land 52.19 acre decrease• Agriculture 145.57 acre decrease• Cleared Land 10.00 acre decrease

Phosphorus Loading Model Predictions

Increased Residential Land

• 2002 phosphorus concentration: 23.35 ppb

• 2022 phosphorus concentration estimate: 23.52 ppb

• 0.17 ppb increase

No Increase in Residential Land

• 2002 phosphorus concentration: 23.35 ppb

• 2022 phosphorus concentration estimate: 22.82 ppb

• 0.53 ppb decrease

• Very small changes due to high level of internal phosphorus release, and also phosphorus input from Threemile Pond

Remediation Techniques and Recommendations

Melanie Newton

Remediation

Problem- Reducing phosphorus loadingDirect Control - Decreasing amount of phosphorus that

enters the watershed• Point source diversion• Erosion control

Nutrient Control - Reducing sediment release of phosphorus• Water Drawdown• Phosphorus inactivation• Hypolimnetic withdrawal

Point Source Diversion

Diverting tributaries or point sources high in nutrients

Seaward Mills Brook Tributary from Threemile Pond

Nutrient Interception

• Erosion carries sediment, nutrients, pesticides, and pathogens into the watershed

• Methods to control erosion:

• Maintenance of roads

• Control of shoreline erosion

• Construction of vegetated buffers

• Agriculture BMPs

Ideal Road

• Constructed of proper

materials

• Graded and Crowned

• Diversions, turnouts,

buffers, and ditches

Road Surface• Larger gravel for base, finer gravel on top• A crown should be 1/4 inch high for each foot of road

width• Grading uses a steel blade to level the soil material on the

road’s surface.• Grading should be done often and crowning should be

done annually

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Ditches

• Flat bottom and surface

• Gradually graded sides

• Trapezoidal or parabolic in

cross-section

• Stone-lined or vegetated

• Sufficiently wide and deep

Culverts

• Convey water under road surface• Discharge water into ditch or vegetated buffer area• Should be adequately sized and have a 2% slope• At least a foot of soil covering

Vegetated Buffers

• Remove sediments, nutrients from runoff water• Forests:

- Uneven surfaces obstruct flow- Roots promote absorption

• Seeding and mulching is beneficial where forests have been removed

Shoreline Erosion

• 914 m (6%) are high risk

shoreline

• Several residents have

taken action by constructing

• Concrete walls

• Log crib

• Riprap

RiprapPrevents erosion and allows nutrient-rich runoff to be

absorbed by shoreline first.

• Grade of slope should be reduced 2:1

• Base of bank should be stabilized with gravel blanket and rock riprap

• Slope covered by vegetation

Water Drawdowns

Purpose:Remove water high in nutrientsKills some nuisance macrophytes

Benefits:Low costFacilitate other remediation techniquesMay increase spawning areas for bass

Drawbacks:Could facilitate growth of some macrophytesInterferes with recreational activitiesCould kill planktivorous fishRemoves only water from surface

DEP Drawdown Management Plan

Presented in 1991 to Webber Pond Association

• Water Quality Manager, Dam ManagerWater Level Coordinator

• Bi-weekly transparency readings• Algal bloom before July, no drawdown• Algal bloom late August, drawdown

as soon as possible• Drawdown 1.5 ft. below spillway by

Labor Day• Drawdown no later then September 3rd

CompromiseResidents

Recreational use of Webber PondSwimming, Boating, Fishing, until Labor Day

Natanis Golf CourseDraws water from Webber Pond to

maintain holes

Best Biological PracticeDrawdown occur as soon as possible after algal

bloom, when nutrient levels are highest

Phosphorus Inactivation Process

• Al2(SO4)3 and sodium aluminate added to water, bind with phosphorus forming AlPO4

• Falls as floc onto sediment

• Aluminum best in anaerobic conditions

• pH must be between 6-8. pH below 6 forms toxic Al(III)

Phosphorus Inactivation as Remediation

PurposeTo reduce internal phosphorus

BenefitsVery effectivelong-term benefits

DrawbacksCostly. Estimates for Webber Pond

from $180,000-$890,000Potentially toxicIncrease in macrophyte growth

Hypolimnetic Withdrawal

Purpose

To remove nutrient-rich, deoxygenated

water from hypolimnion

Benefits

Cheap

Effective reduce from

200 mg/L to 91 mg/L

Drawbacks

Where will water go?

Pipes for hypolimnetic withdrawal

Possible Collaboration with Natanis Golf Course

• Golf Course uses approximately 1 million gallons of water from Webber Pond each year

• If golf course could extend pipe deeper than 6 m into hypolimnion, it could drain nutrient-rich water

• Golf course could use this in irrigation and possible fertilization

• Remove nutrients from Webber Pond

Recommendations

The primary problem at Webber Pond is cultural eutrophication

• Nutrient run-off from agriculture, roads, residential, and commercial land uses

• Historical cultural eutrophication created the problem in high internal phosphorus recycling levels

• Remediation must address both of these issues

Monitoring Suggestions

• Bi-weekly transparency readings from May through August

• Test surface and epicore samples for phosphorus yearlyDEP Site (Site 1)Green Valley Campground (Site 6), Natanis Golf Course (Site 9),Dam (Site 10).

• Transparency and Dissolved Oxygen profile at Site 1 monthly May-September

Regulatory Measures

AgricultureIncrease use of BMPs in agricultureBetter monitoring of these farms

ForestryRestrict future timber harvestingIf harvesting occurs follow a BMP

RoadsConduct road surveys frequently to identify trouble spotsRepair Trouble Spots

Residential Measures• Encourage addition and enhancement of vegetated buffers

and riprap

• Encourage road improvements and maintenance by residents

• Limit use of lawn fertilizers

• Reduce shoreline alteration

Nutrient Control Measures• Continue the yearly drawdown, investigate the possibility

of drawing water down from hypolimnion not just surface

• Investigate the possibility of using nutrient-rich hypolimnetic water in irrigating the Natanis golf course

• Investigate the possibility of phosphorus inactivation

Educational Measures• Encourage the availability of this report to the general

public

• Work closely with the China Region Lake Alliance

• Develop and distribute pamphlets to homeowners (road repair, riprap, vegetated buffers, detergents, and water level drawdown)

• Involve local schools in monitoring Webber Pond

AcknowledgementsPeter Abello Kelly KarterRoy Bouchard Jim LucasBob & Julie Brown Kevin MichaudRussell Cole Judy MoodyGene Field Peter MosierDale Finesth Rebecca MantheyDavid Firmage Edward NoelBetsy Fitzgerald Frank RichardsNate Gray Bruce RuegerDavid Halliwell Dan Tierney

Vassalboro Town Office StaffMaine Department of Environmental Protection Staff

Maine Department of Inland Fisheries and Wildlife StaffMaine Soil and Water Conservation Staff

Green Valley Campground

Questions