HomeMy WebLinkAboutEngineer's Report 2021-11-17 Final
TOWN OF DANBY
TOMPKINS COUNTY, NEW YORK
November 17, 2021
ENGINEER’S REPORT
Proposed Town of Danby
Drainage District #1:
CMC Development Subdivision
PREPARED BY:
T. G. Miller, P.C.
Engineers and Surveyors
Ithaca, New York
ENGINEER’S REPORT
PROPOSED TOWN OF DANBY
DRAINAGE DISTRICT #1: CMC DEVELOPMENT SUBDIVISION
TABLE OF CONTENTS
SECTIONS
Section 1 - Introduction
Section 2 - Service Area
Section 3 - Overview of Maintenance Responsibilities
Section 4 - Overview of Maintenance Activities
Section 5 - Maintenance Cost Estimates
Section 6 - Method of Financing
MAPS
Figure 1 - Vicinity Map
Figure 2 - CMC Development Plat Map
Engineer’s Report Drainage District #1
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SECTION 1 - INTRODUCTION
The CMC Development Subdivision (“Subdivision”), located in the Town of Danby, was granted final
subdivision approval by the Town in 2004. Consequently, the soil disturbance activity associated with
physical construction of the Subdivision was regulated under the New York State Department of
Conservation (DEC) State Pollutant Discharge Elimination System (SPDES) Permit GP-02-01, which
required temporary and permanent stormwater management controls and practices. In accordance with this
permit, the Danby CMC Development Co. (“Developer”) prepared a Stormwater Management Pollution
Prevention Plan (SWPPP) which proposed post-development stormwater facilities consisting of two
stormwater ponds and swales that convey stormwater to the ponds. The Developer filed for and obtained
coverage under the SPDES permit to discharge stormwater runoff from their construction activity.
The SPDES Permit required, and the SWPPP addressed, on-going maintenance of these facilities knowing
that maintenance responsibility “…shall be vested with a responsible authority by means of a legally
binding and enforceable maintenance agreement…”1. In order to ensure ongoing maintenance, the
Developer had requested that the stormwater management facilities within the Subdivision be dedicated to
the Town, and that the Town assume maintenance responsibility for these practices. In order to provide and
pay for the long-term maintenance, the Town is proposing to establish pursuant to Town Law a drainage
benefit district to be known as Drainage District #1 (“District”) which will encompass all of the lands within
the bounds of the original approved Subdivision.
SECTION 2 - SERVICE AREA
The Subdivision, located adjacent to the intersection of NYS Route 96B and Nelson Road as illustrated
on Figure 1, initially consisted of tax map parcels 2-1-9 and 2-1-17 totaling approximately 75.8 acres in
area. At present, this Subdivision includes 24 individual tax map parcels comprised of 22 residential
building lots and 2 stormwater management lots. As of May 2011, the ownership and parcel acreage
obtained from Tompkins County Assessment Department data is summarized below in Table 1.
Table 1. Tax Map Parcels in Proposed Drainage District #1
Tax Map
Parcel # Property Owner Acres
2.-1-9.1 Matzo Ball Properties, LLC 3.38
2.-1-9.2 Paulino, Heidi & Schreiner Carla & Dane 6.00
2.-1-9.3 Heaton, Andrew 4.26
2.-1-9.4 Matzo Ball Properties, LLC 4.91
2.-1-9.5 Ithaca College 3.97
2.-1-9.6 Burrow, Anthony L 1.82
2.-1-9.7 Harrington, Larry W & Junco-Larraguivel, Maria del Pilar 1.87
2.-1-9.8 Lazarenko, Roman 2.53
2.-1-9.9* N/F Tompkins County 1.12
2.-1-9.10 Kim, Harryette 5.03
2.-1-9.11 Lazarenko, Roman 5.05
2.-1-9.12 Browning, Jill G & Jason E 4.40
2.-1-9.13 Goggs, Robert & Elizabeth 1.40
2.-1-9.14* N/F Tompkins County 0.90
1 New York State Department of Environmental Conservation. 2003. New York State Stormwater Management Design Manual. Albany, NY.
p. 6-14
Engineer’s Report Drainage District #1
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2.-1-9.15 Tesi, Virginia & Magden, Hallie 1.98
2.-1-9.16 Bataille, Christine 1.35
2.-1-9.17 Davis, Andrew M 1.81
2.-1-9.18 Muenzen, Jason B & Christine 1.77
2.-1-9.19 Merryfield, Dennis 1.88
2.-1-9.20 Costa, Guilherme & Jennifer M 1.99
2.-1-9.21 Cove, Andrew B & Montgomery, Deborah 2.19
2.-1-9.22 Thompson, Jerry D 3.85
2.-1-9.23 Vakiner, John G & Monica S 5.68
2.-1-9.24 Lazarenko, Roman 3.37
Total Area of Buildable Lots = 70.49
*Parcel has been deeded to the Town and is not included in the total area
SECTION 3 – OVERVIEW OF MAINTENANCE RESPONSIBILITIES
The Developer obtained coverage under NYSDEC Permit GP-02-01 in March 2005 and was assigned ID#
NYR101583. Based on NYSDEC data that is publicly accessible through the Stormwater Interactive Map,
the Developer has not filed a Notice of Termination (NOT) and, therefore, continues to retain permit
coverage. The NOT cannot be filed until the site is completely stabilized and all construction is completed.
At the time of this Report, there are three vacant residential building lots all owned by Lazarenko that
remain to be developed. Concurrent with the establishment of the District, the Developer should confirm
with NYSDEC the appropriate process for terminating permit coverage.
Subject to the establishment of the District, the Town will be responsible for maintaining stormwater
practices within the Subdivision that are dedicated in fee or encumbered by permanent easements, as
outlined in this Report and shown on the Final Subdivision Plat. In addition, the Town will be responsible
for administration of the District, including tracking expenses, assessing fees, and collecting fees to fund
ongoing maintenance.
SECTION 4 - OVERVIEW OF MAINTENANCE ACTIVITIES
The Developer has constructed two stormwater management ponds, a series of swales and roadside ditches
that convey stormwater to these permanent practices. The two ponds, Stormwater Management Facility 1
(SWM 1) and Stormwater Management Facility 2 (SWM 2) receive drainage from the majority of the
Subdivision. Both pond sites were previously owned by Tompkins County and recently conveyed to the
Town through a quit-claim deed filed March 15, 2021. A 30-foot-wide permanent drainage easement
dedicated to the Town is located along the common boundary of parcels 2-1-9.5, -9.6, -9.7, -9.8, and -9.24
for the purpose of directing drainage from Loomis Court to SWM 2. There are a number of smaller drainage
easements located upon parcels 2-1-9.6, -9.11, -9.13, and -9.23 that adjoin the Town highway rights-of-
way for grading and erosion control purposes. All of the permanent drainage easements are identified on
the Developer’s Plat Map filed with the Tompkins County Clerk on March 9, 2005 (See Figure 2).
4.1 Current Maintenance Conditions
In anticipation of the District formation, the Town retained this firm to conduct an initial assessment of the
existing stormwater facilities to determine what, if any, maintenance would need to be performed
subsequent to the initial construction.
A site visit in July 2019 revealed the following list of maintenance activities within SWM 1 and SWM 2
that would restore the facilities to post-construction conditions:
Engineer’s Report Drainage District #1
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SWM 1
1. Remove fallen trees and limbs from within the pond.
2. Mow the embankments in-board of the pond twice per year.
3. Fill the void spaces between the HDPE outlet pipe and the concrete control structure with non-
shrink grout.
4. Replace stone fill (rip-rap) on the main channel leading into the permanent pool basin. It is
noticeable where the underlying filter fabric is exposed.
5. Additional earth fill may be needed behind the concrete outlet control structure in order to establish
the correct top elevation of the surrounding berm. This will become more apparent after mowing
has been completed.
SWM 2
1. Mow the embankments in-board of the pond twice per year including the removal of trees and
invasive shrubs.
2. Fill the void spaces between the HDPE outlet pipe and the concrete outlet control structure with
non-shrink grout.
A second site visit was conducted in December 2020 by this firm to assess the condition of the swale
connecting Loomis Court drainage to SWM 2. This assessment included the collection of topographic data
to ascertain the presence of a graded swale that ensures the drainage from Loomis Court is adequately
directed into SWM 2. From this site visit, the following conditions related to maintenance were noted:
Swale
1. Cut and remove trees and brush smaller than 3-inch diameter within the limits of the 30-foot-wide
easement the full length of the easement area. Trees larger than 3-inch diameter can remain unless
dead or known to be an invasive species.
2. Perform excavation and soil stabilization restoration from the northeast corner of parcel 2-1-9.7 to
SWM 2 to conform with the Developers original grading plan. The alignment of the swale can be
adjusted to avoid removing trees over 3-inch diameter that are determined desirable to remain.
4.2 Post-Construction Maintenance Activities
Maintenance activities for these permanent practices should include annual inspections and repairs to the
stormwater infrastructure based on those inspections. This section describes some of the typical activities
needed to maintain both the long-term pollutant removal and structural integrity of stormwater facilities.
These activities are encompassed within six general categories as described below. In addition, Table 2
outlines some of the detailed activities within these categories, together with an estimated frequency.
A. Inspections
An annual inspection is needed to monitor the stormwater ponds and swales. In the long term, these
inspections reduce expenses by allowing the Town to address small problems as they occur with relatively
low-cost solutions.
B. Sediment and Debris Removal
As sediment accumulates in stormwater practices, they lose their capacity to treat stormwater. In addition,
the sediment can clog outflow pipes and reduce the capacity of channels and swales. Some typical
maintenance activities include removing sediment and debris, and unclogging outlet pipes.
C. Vegetation Management
Vegetation can enhance pollutant removal in some stormwater management practices, but needs to be
managed. Mowing is necessary to maintain a safe pond embankment, and to retain the capacity of swales.
In addition, algae can create odor issues, and invasive plants such as cattails can create mosquito habitat.
Engineer’s Report Drainage District #1
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D. Animals and Nuisances
Some typical nuisance issues for stormwater ponds are mosquitoes and animal burrows. Mosquitoes can
sometimes breed in ponds, particularly if dense vegetation develops. Some non-toxic methods are available
to discourage mosquito breeding. Animal burrows damage pond embankments, and need to be filled
immediately.
E. Erosion
Over time, soil erosion can occur at some critical points in a stormwater management practice, particularly
when bare soil exists. When erosion occurs, the area needs to be stabilized to prevent further damage.
F. Structural Repairs
Although the stormwater ponds that treat this Subdivision have relatively few moving parts and structural
elements, some long-term repairs may be needed. These will include replacing or repairing cracked pipes,
concrete, and metal grates as needed.
TABLE 2. STORMWATER MAINTENANCE ACTIVITIES FOR DRAINAGE DISTRICT #1
Maintenance Item Frequency
(years)1,2
Practices Where Performed
Inspections
Inspection 1 SWM 1-2 and Swale
Sediment and Debris Removal
Unclog outlet pipes 2 SWM 1 and 2
Debris/Trash Removal 1 SWM 1 and 2 and Swale
Remove sediment from forebays 5 Both forebays to SWM 1 and 2.
Remove sediment from swales 5 Swale
Dredge ponds 20 Both SWM 1 and 2.
Remove accumulated sediment in riprap
conveyances.
5 Both SWM 1 and 2.
Vegetation Management
Mowing 1 SWM 1 and 2 Embankments and Swale
Tree removal from embankment 10 SWM 1 and 2 Embankments (should be limited by
mowing)
Cattail management 1 SWM 1 and 2
Animals/ Nuisances
Remove animal burrows from pond
embankment.
5 SWM 1 and 2
Mosquito treatment (only if needed) 4 months Not anticipated for SWM 1 and 2
Erosion
Repair areas of erosion 2-5 SWM 1 and 2 ‘shoreline’, outlets and Swale
Replace rip rap channels 20 SWM 1 and 2 inlet, outlets, and forebays
Structural repairs
Repair low spots on the embankment 5 SWM 1 and 2
Repair or replace manhole frames/grates 25 SWM 1 and 2
Repair cracks in concrete 10 SWM 1 and 2
Replace CMP Outfall Pipe 25 SWM 1 and 2
Replace outlet control structure 50 SWM 1 and 2
1: Maintenance Frequencies derived from the “New York State Stormwater Management Design Manual created by the New York State Department
of Environmental Conservation.
2: Frequency may vary, and the need for maintenance will be determined by annual inspections.
SECTION 5 – MAINTENANCE COST ESTIMATES
This Section estimates maintenance costs for the permanent practices in the current condition as well as the
regular activities in subsequent years, with the goal of deriving an initial charge for land owners of
Engineer’s Report Drainage District #1
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benefitted property within the District. Over time, these costs will vary, based on the occurrence of
relatively higher-cost items.
5.1 Current Condition Maintenance Costs
This cost estimate includes assumptions regarding the items that will occur within the first year upon
establishment of the District, the extent (e.g., area, volume, quantity) of these items, and the unit costs. The
maintenance items, along with a total estimated cost, is presented in Table 3.
The first-year maintenance items are derived from the maintenance frequencies presented in Table 2 in
addition to the items noted in Section 4.1, with the following assumptions:
1) Vegetation removal, grading and soil stabilization of the Swale occurs in the first year.
2) Items listed as annual or more frequent occur within the first year, at the frequency named.
3) Each inspection takes about four hours of a staff day, including a site visit by one Qualified
Professional, travel time, and report writing.
4) Although unclogging the outlet pipe is assumed to occur once every two years, it is assumed that this
will be required in the first year.
5) Mowing is needed on SWM 1 and 2 embankments, representing a total of approximately 2 acres.
6) Cattail management includes cutting or “weed whacking” cattails at their base in the late summer and
removing the cut vegetation.
7) Mosquito treatment is not required unless dictated by State or Local agencies.
8) Some erosion occurs within the Swale leading to SWM 2, and will need to be repaired.
9) As a contingency, it is assumed that two, five-year frequency items occur in the first year, including
repairing low spots on the SWM 1 and 2 embankments and removing animal burrows.
TABLE 3. COST OF FIRST-YEAR MAINTENANCE
Maintenance
Item Description Unit Cost Extent Cost
Swale (Loomis
Court to SWM 2)
Tree/brush removal and grading to SWM 2. $5,000 1 time $5,000
Inspection Inspect using forms derived from Appendix G of
the “New York Stormwater Management Design
Manual”
$155/hour 4 hours/year $620
Unclog outlet
pipes
Remove accumulated debris from the outlet
pipes, possibly by jet cleaning. $600 1 $600
Debris/Trash
Removal
Remove trash, coincident with site inspection or
other annual maintenance. $250 1 time $250
Mowing Mow the SWM 1 and 2 parcels and
embankments $450/acre 2.0 acres $900
Cattail
management
Weed Whack cattails in late summer $75/hour 4 hours $300
Fill animal
burrows in
embankment
Need to fill burrow with dirt and compact.
Requires importing some soil. $200 2 burrow/year $400
Repair areas of
erosion
Replace topsoil and reseed in two areas. $450/area 2 areas $900
Repair low spots
on the
embankment
Import soil and compact to achieve original
grade. $500 1 time $500
Repair connection
between pipe and
outlet control
structure
Install non-shrink grout between pipe and
concrete outlet control structure $500 1 time $500
TOTAL ESTIMATED FIRST-YEAR MAINTENANCE COST $9,970