presentation to 19th annual nps...

Presentation to19th Annual NPS Conference

Funding provided by Rhode Island DEM through a USEPA section 319 grant

Narrow River Stormwater Abatement Narrow River Stormwater Abatement Jim Riordan, AICPMay 20, 2008

Jim Riordan, AICPMay 20, 2008

Narrow River Study Goals & ObjectivesNarrow River Study Goals & Objectives

GOAL: Reduce pathogens and nutrients; and return baseflow to predevelopment levels.

Assess watershed conditions.

Conduct conceptual planning study.

Select 4 subwatersheds and appropriate BMPs with Stakeholder Input.

Design BMPs to 75%.

GOAL: Reduce pathogens and nutrients; and return baseflow to predevelopment levels.

Assess watershed conditions.

Conduct conceptual planning study.

Select 4 subwatersheds and appropriate BMPs with Stakeholder Input.

Design BMPs to 75%.

Project Study AreaProject Study Area

PETTA LAKE SHORES 2PETTA LAKE SHORES 2WOODSIA TRAIL –NORTH

PETTA LAKE SHORES 3WOODSIA ROAD –SOUTH

METTATUXET 4METTATUXET 4WOODBRIDGE ROAD

CIRCUIT DRIVE 1WAMPUM ROAD

EDGEWATER 2EDGEWATER 2SOUTH FERRY ROAD

METTATUXET 3METTATUXET 3SHAGBARK ROAD

PETTA LAKE SHORES 1SHADBUSH TRAIL

PETTASQUAMSCUTT COMBINATION

PETTASQUAMSCUTT TERRACE 1 & 2

PETTAQUAMSCUTT AVENUE

METTATUXET 1METTATUXET 1OLD PINE ROAD

METTATUXET ROAD

METTATUXET 2METTATUXET BEACH

EDGEWATER 1EDGEWATER 1LAKESIDE DRIVE

INDIAN HEADINDIAN HEADINDIAN TRAIL

CIRCUIT DRIVE 2CONANICUS ROAD

Technical Memorandum Subwatersheds

Narragansett Subwatershed Names

TMDL Subwatershed Names

Hydrologic Data by SubwatershedHydrologic Data by Subwatershed

27.73.21.180.300.6050.862.37.219.5Mettatuxet 4

35.93.70.980.320.6454.865.37.620.1Mettatuxet 3

51.35.61.640.420.8554.868.610.226.8Mettatuxet 1

119.022.83.120.971.9464.774.923.289.2PettasquamscuttTerrace Combo

22.23.50.340.170.3567.575.24.213.5Edgewater 2

70.213.21.120.761.5170.278.018.147.2Edgewater 1

225.727.73.251.282.5767.077.030.8100.4Petta Lake Shores 2

52.16.51.480.420.8458.972.910.127.2Indian Head

cfsacre-ftacre-ftacre-ftacre-ftacresacres

Q25V25VGWRV1flushWQV CNnCN

AimpATotalOutfall

Key Points

• WQV = 9.3 ac/ft

• VGWR = 13.11 ac/ft

Available BMPsAvailable BMPs

•Roof leader disconnection

Impervious surface disconnection

•Vegetated strips

Engineered vegetative strips and conveyances

•Permeable Pavement

•Dry wells

••Disconnected catch basins and proprietary infiltration units

••Infiltration trenches

•••Bioretention

•••Sand filters

Filtration and infiltration

Source Reduction

UplandEnd-of-PipePractices and Strategies

Key Points

• Considered all BMPs in Table 3 (page 8).

• Analyzed only BMPs that produced quantifiable result.

Sand FilterSand Filter

Elevation

Typical Section

OPTIONAL IMPERMEABLE LINER

Plan View

Section View

BioretentionBioretention

Plan View

Elevation

Typical Section

Infiltration TrenchInfiltration Trench

Disconnected Catch BasinDisconnected Catch Basin

Dry WellsDry Wells

Permeable PavementPermeable Pavement

Vegetative StripVegetative Strip

Roof Leader DisconnectionRoof Leader Disconnection

On-Lot BMPsAssuming 20% ParticipationOn-Lot BMPsAssuming 20% Participation

68Study Area (weighted average)1

811Mettatuxet 4

910Mettatuxet 3

611Mettatuxet 1

611Pettasquamscutt Terrace 2

67Pettasquamscutt Terrace 1

77Edgewater 2

56Edgewater 1

49Petta Lake Shores 2

36Indian Head

VGWRWQV

Percent Treated (%)

Subwatershed

• Based on a recent survey conducted by the Town, actual willingness to participate is 10 – 18%.

Upland BMPsUpland BMPs

32% - 47%62% - 96%TOTAL

62%100%Mettatuxet 3

100%100%Mettatuxet 1

100%100%Pettasquamscutt Terrace 2

0% – 30%48% - 100%Pettasquamscutt Terrace 1

0%0%Edgewater 2

0% – 56%42% - 100%Edgewater 1

0% -23%29% - 100%Petta Lake Shores 2

58%100%Indian Head

VGWRWQV

Best Available Volumetric CapacitySubwatershed

End-of-Pipe BMPsEnd-of-Pipe BMPs

73%78% - 80%TOTAL





100%100%Edgewater 2

100%100%Edgewater 1

0% -9%11% - 29%Petta Lake Shores 2

97%100%Indian Head

VGWRWQV

Best Possible Level of Treatment Subwatershed

Conceptual DesignsConceptual Designs

Order-of-Magnitude Opinions of CostOrder-of-Magnitude Opinions of Cost

98139$3,000,000TOTAL

913$260,000Mettatuxet 4



2433$690,000Pettaquamiscutt Terrace Combo

34$80,000Edgewater 2

1216$340,000Edgewater 1

2028$710,000Petta Lake Shores 2

1116$330,000Indian Head

% GWR% WQVCOSTSUBWATERSHED

Key Points

• Cost are ESTIMATES for planning purposes only.

• Cost do not include, land, design and permitting.

• Actual costs may be 2x or greater.

Rating MatrixRating Matrix

Key Points

• Allows comparison of BMPs across subwatersheds.

• Does not rate on-lot BMPs as the decision to implement is primarily in the hands of property owners.


Criteria Rankings as Determined by TACCriteria Rankings as Determined by TAC

Types of BMPs Analyzed

Types of BMPs Analyzed


Calculated from Reference MaterialsCalculated from Reference Materials

Calculated Based on Hydrologic Data

Calculated Based on Hydrologic Data

Subjective Values—Based on BPJ

Subjective Values—Based on BPJ

Scoring RubricScoring Rubric

NA

NA

1

3

1

2

2

2

2

3

3

Assigned Weight

Fraction town-owned x 1Fraction in roadway, managed open space or stabilized x 0.5Fraction unmerged vacant land x 0.25Fraction merged vacant land x 0.13

Multiplier B – Type of Area Available

=( 0.75(Vtreatable1/WQVtotal) + 0.25(Vtreatable /VGWR-total))4 x 10Multiplier A – Treated

Volume

Project has few impediments to being implemented (permitting, engineering, other approvals)=10

Project has significant impediments to being implemented (permitting, engineering, other approvals)=0

Ability to Implement

Finished project has limited impacts to neighborhood (perceived or otherwise) = 10

Finished project has significant impacts to neighborhood (perceived or otherwise) = 10

Public Acceptance

High reliability to function during range of storm events = 10Little reliability to function during range of storm events = 0

Reliability

O&M cost/ability low = 10O&M cost/ability moderate = 5O&M cost/ability high = 0

Operation & Maintenance (O&M)

= 10 – unit cost (Table 153)Construction Cost

= 10 – VPA (Table 153)Space Requirement/Land

=VGWR1 x GWR factor

VGWR-SW2

Groundwater Recharge

= WQV x nitrogen reduction benefit factorWQVSW

2Nitrogen Reduction

= WQV1 x bacteria reduction benefit factorWQVSW

2Bacteria Load Reduction

Scoring RubricCriteria

BMP SelectionBMP Selection

Recommendations

• Scores provide a strong starting point for identifying locationsfor BMPs.

• Based on the scores (above) and additional information from the Town, we would recommend:

– Pettaquamscutt Terrace Combination (PTC).

– Edgewater 1 & 2 (E1 & 2).

75% Plans75% Plans

75% Plans—Pettaquamscutt Terrace75% Plans—Pettaquamscutt Terrace

75% Plans—Edgewater 1&275% Plans—Edgewater 1&2

Next StepsNext Steps

Grant of $1.1M from RIDEM

• Final design and permitting for Pettaquamscutt and Edgewater.

• Construction and monitoring of BMPs at Pettaquamscutt and Edgewater.

• Further design work for the other Narrow River Subbasins

presentation to 19th annual nps...

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