THE KNOLLS OF DOVER
Town of Dover, New York
WATER TREATMENT
FACILITY REPORT
Prepared for:
BENJAMIN DEVELOPMENT CO., INC.
377 Oak Street, Suite 110
Garden City, New York 11530
Prepared By:
DELAWARE ENGINEERING, P.C.
8-12 Dietz Street, Suite 303
Oneonta, New York 13820
November 21, 2008
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THE KNOLLS OF DOVER
TOWN OF DOVER, NEW YORK
WATER TREATMENT FACILITY REPORT
TABLE OF CONTENTS
PAGE
NO.
INTRODUCTION ................................................................................................................. 6
A. Existing Conditions ........................................................................................................ 6
1. Plant Description ..................................................................................................... 7 - 8
1.1. Treatment Process Description......................................................................... 9
2. Process Flow Description ........................................................................................ 9
2.1. Aeration ............................................................................................................ 10
2.2. Rapid Mix, Coagulation, Flocculation ............................................................. 11
2.3 Sedimentation................................................................................................... 11
2.4. Rapid Rate Filtration ........................................................................................ 11-12
2.5. Disinfection ...................................................................................................... 13
2.6. Distribution System.......................................................................................... 13
3. Current Conditions & Regulatory Compliance ....................................................... 13-14
3.1. Reservoir & Swamp River Safe Yield Estimate .............................................. 14-15
3.2. Water Quality Concerns…………………………………………………….. ..15-16
3.3. Recommended Plant Improvements................................................................. 16-17
(3.3.1) Complete Upgrade of Existing WTF.................................................... 17-19
(3.3.2) Temporary Upgrade of Existing WTF……………………………….. 19
B. Potential Impacts ............................................................................................................ 20
1. Modifications Required to Meet Regulatory Compliance....................................... 20
2. Watershed Protection Requirements ....................................................................... 20
3. Phasing Impacts on Plant......................................................................................... 21
4. Potential Impacts Due to Treatment Plant Upgrades .............................................. 21
4.1. Land Area Requirements.................................................................................. 21
4.2. Effect on Recreational Uses in Reservoir ........................................................ 22
4.3. Increase in Chemical Usage and Storage ......................................................... 22
4.4. Increase in Energy Consumption ..................................................................... 22
5. Mitigation Measures ................................................................................................... 23
5.1. Treatment Plant Improvements Temp. Upgrades of Existing WTF. ............... 24
5.2Water Saving Fixtures ........................................................................................23-24
5.3. Use of On-Site Wells........................................................................................24-25
D. Conclusion ...................................................................................................................25-26
LIST OF TABLES
FIGURE
NO.
1
PAGE
NO.
Process Flow Schematic................................................................................. 9
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5
INTRODUCTION
Delaware Engineering was retained by the Benjamin Co. Inc. to prepare this water treatment
facility report of the former Harlem Valley Psychiatric Center (HVPC) site in connection with
the proposed Knolls of Dover project – a mixed use community which will include 1,376
dwelling units, approximately 245,800 square feet of commercial space, and approximately
77,000 square feet of community facility or recreation center space. The project site consists of
approximately 937 acres on the site of the former HVPC property and a neighboring parcel. The
site straddles the eastern and western sides of NYS Route 22 in the Wingdale Hamlet. The
purpose of this report is to assess the conditions and operations as well as the historical operating
data of the existing public water supply known as the Harlem Valley Water Treatment Facility.
This report will assess the potential impacts related to the planned improvements at the water
treatment facility as well as the mitigation measures necessary to meet the current and future
needs of the development project as well as meeting the requirements under the New York State
Sanitary Code.
A. Existing Conditions
1.
Plant Description
The Harlem Valley Psychiatric Center operated and maintained a public water supply since the
1930’s. Prior to that date a prison was located on the site and the upland reservoir was used to
provide water for the staff and inmates. Plans from 1919 show the design of the dam that is
currently in place, the original water facility from 1919 is an old foundation from the first water
treatment facility that was located on site prior to the 1934 construction of the existing treatment
facility. The plans for the current water filtration facility are dated 1934 when the conventional
water filtration facility was constructed, which [the facility] was designed to treat approximately
1.2 MGD. Both the reservoir and the treatment plant are located at the southeast part of the
project site. The existing water filtration facility is a conventional treatment process as discussed
herein, which we will explain in detail; Conventional water treatment is used to remove
impurities from water making it potable, safe to drink.
6
1.1. Treatment Process Description
The following is a general description of the current Water Treatment Facility (WTF).
The first step in the treatment process includes Preliminary Treatment of the surface water by
removing debris such as leaves, sticks and large particles which may interfere with downstream
processes. Following preliminary treatment is the use of an oxidizing process such as aeration
and or the introduction of an oxidizing chemical like chlorine, peroxide or potassium
permanganate. Oxidation is used to precipitate the naturally occurring Iron and Manganese and
to treat for taste and odor often found in surface water and also to prepare the water for the other
chemical processes. Together, coagulation and flocculation is a traditional purification method
which works by using active chemicals called coagulants that effectively "bond" small
suspended particles together which cause turbidity into a particle of greater density so that they
settle out of the water or stick to sand or other granules in a granular media filter. Coagulation
normally works by eliminating the natural electrical charge of the suspended particles so they
attract and cling to each other. The joining of the particles so that they will form larger settleable
particles is called flocculation. The larger formed particles are called flock. Many of the
suspended water particles have a negative charge. The charge keeps particles suspended because
they repel similar particles. Coagulation processing reduces the surface charge to encourage
attraction which forms flock which increases the particle density allowing it to settle.
7
The coagulants are added to a tank called the rapid mix tank, which typically has rotating
paddles. In most treatment plants, the mixture remains in the rapid mix tank for 10 to 30 seconds
to ensure full mixing; with the HV facility the design of the rapid mix tank is based on the size of
the tank and velocity and shape of the tank to create enough turbulence through the pumping
process to insure mixing, an actual mixer would be more effective. The amount of coagulant that
is added to the water varies widely due to the different source water quality. Testing varying
amounts of coagulants with samples of the source water to see which dosage creates the best
flock is a routine process control test. The chemicals also act as additional particles which the
suspended solids can bond to form flock. Flocculation is the clumping together of small particles
to form larger particles, called flock, which is more readily settled out of the water. To aid in the
flocculation, water is slowly mixed in a tank called the flocculation basin, the mixing is done by
using the water velocity through the basin. Water exiting the flocculation basin enters the
sedimentation basin, also called a clarifier or settling basin. The clarifier is a large tank where
water velocity is slowed allowing flock to settle to the bottom, the clarifiers are located outside
of the building and they are covered with a concrete cover and buried. As the floc particles settle
to the bottom of the basin, a layer of sludge is formed on the floor of the tank. This layer of
sludge must be removed and treated. The amount of sludge that is generated is significant, often
3%-5% of the total volume of water that is treated. Next the water is filtered as the final step to
remove remaining suspended particles and unsettled flock. The type of filter is a rapid rate sand
filter. Water moves vertically through sand which often has a layer of anthracite coal above the
sand. The space between sand particles is larger than the smallest suspended particles, so simple
filtration is not enough. Most particles pass through surface layers but are trapped in pore spaces
or adhere to sand particles. So not just the top layer of the filter cleans the water, but effective
filtration extends into the depth of the filter. To clean the filter, clean water is passed quickly
upward through the filter, opposite the normal direction (called backwashing) to remove
embedded particles. This contaminated water is disposed of, along with the sludge from the
sedimentation basin into the sludge hold tank where it is drained into the gravity sewer main and
disposed of at the wastewater treatment facility. The following schematic diagram illustrates the
treatment process that currently exists at the project site.
8
TREATMENT PROCESS FLOW SCHEMATIC
Note: The 2- 500,000 gallon tanks just prior to the distribution system hold the finished water.
2.
Process Flow Description, Design Capacity
2.1. Aeration
A 12” ductile iron intake main that lies behind the dam is connected to a 12” x 10” x 10” tee,
where the intake main splits into two 10” mains that direct reservoir water flow into the
spray aeration tank. The aeration tank is: 6 ft. deep X 40 ft. long X 25 ft. wide = 6,000
cubic feet yielding 44,880 gallons. of operating volume. With a minor change to the piping
elevation, the depth of storage could be increased to 8.5 ft. resulting in an increased volume
of 8,500 cubic feet or a total of 63,580 gallons. Aeration is an effective treatment for taste
and odor removal as well as the oxidation of soluble Iron and Manganese; aeration is also
used for the treatment of volatile organic chemicals. The aeration process was sized for the
design capacity of the facility, 1.2 MGD.
9
2.2. Rapid Mix, Coagulation, Flocculation
The design of the rapid mix process is based on the untreated water quality, water chemistry,
chemicals being used in the downstream processes, water temperature and other related
parameters. The current WTF facility uses a “mixing pot” that consists of a small round
tank, 5 feet in diameter. The flow enters the mixer and uses the velocity of the discharge to
create a swirling effect within the tank and the circulating energy provides the mixing.
Generally detention time recommendations are for <30 seconds. Based on the size of the
tank and a flow rate of 1,200,000 GPD, this would result in a <40 second contact time. The
historical data indicates that the rapid mixing process as designed was capable of providing
the necessary treatment for standards of the time. Flow from the reservoir or upstream
aeration tank enters the rapid mix tank and a number of treatment chemicals are added and
begin the treatment processes. Potassium permanganate is added to oxidize the Iron and
Manganese that was not oxidized in the aeration process including compounds that cause
taste and odor will also be oxidized. The coagulant Aluminum Sulfate (Alum) is also mixed
into the process to bring together smaller suspended solids and through the flocculation
process these particles grow in density and size into a more easily removed particle. Soda
Ash is added as a pH buffer and to increase the alkalinity, this optimizes the effectiveness of
the Alum as the coagulation is pH dependant since Alum can drop the pH below the optimal
range for coagulation. The chemical reactions are instantaneous with the proper mixing and
doses. Flocculation follows the rapid mix and
is where the various particles come together to form the larger dense particles that can be
removed in the downstream sedimentation process. The flocculation basins at the WTF
include a series of baffled tanks that are sized to maintain a set velocity through the process,
the movement or velocity of the water through the tanks prevents the dense particle from
settling; the velocity also provides the required energy that is necessary to build a flock
particle that is dense enough to settle in the downstream sedimentation basins. The flows
through velocities are adjusted by the operator to maintain the optimal conditions for
building a strong dense flock. The rapid mix was sized for the design capacity of the
facility, 1.2 MGD.
10
2.3. Sedimentation (Clarification)
As discussed, the sedimentation process allows dense flock particles settle to the bottom of
the clarifier by slowing the velocity within the basin so the heavy dense particles that were
created during the upstream processes is allowed to settle. Each clarifier is fitted with 3
hoppers on the drain end; the tank is sloped 1.74 ft. from the effluent end to the influent end
over the entire length of the basin which is 47 ft. Each of the 3 sludge hoppers has a drain
valve for wasting sludge. The design of the clarifier bottom impacts the way in which this
settled sludge is removed from the clarifier, to insure complete removal of settled solids the
operator will periodically take a clarifier out of service to drain the sludge out of the bottom
of the tank into the downstream sludge treatment process. The size of each clarifier is:
14.54 ft. deep X 17.5 ft. wide X 47 ft. long = 11,959.2 cu. ft. yielding 89,454.4 gallons.
At a flow rate of 1,200,000 GPD or 833.3 GPM, the detention times in the sedimentation
process with the 2 clarifiers on line would be 3.6 hrs. This is consistent with
recommendations outlined in the Recommended Standards for Waterworks.1 Detention
times are established to provide enough time for the solids to settle to the bottom; 3-4 hours
is an acceptable time to allow for settling (see chart above). The overflow rate is the
velocity and volume that water leaves the clarifier, the less flow in GPM per surface area the
better the settling characteristics of the basin; regulations state that an overflow rate of <0.5
GPM/sq.ft. would allow the detention time to be <4 hrs. The surface area of each clarifier
is: 822.5 sq. ft. ÷ 0.5 GPM = 411.25 GPM or a flow rate of 592,200 GPD per clarifier.
The total operating capacity of the clarifiers is _1,200,000 gpd.
2.4. Rapid Rate Filtration
Flow leaves the two clarifiers through a buried header made of 10 in. cast iron pipe and
enters the high rate sand filter header that is located in the basement of the treatment facility.
There is a series of valves located at the clarifier effluent which allow the operator to direct
the flow from either clarifier into the filters of which there are four. The rapid rate filters
1
Recommended Standards for Waterworks, 2003 Edition; Policies for the Review and Approval of Plans and
Specifications for Public Water Supplies.
11
use Greensand or oxidizing sand as a media, when oxidizing sand is used as a part of the
treatment process. There are advantages to using Greensand; the filter performs a dual role
of strainer and oxidizer, over the years when the facility was fully functional the use of
Greensand was an important part of the treatment process for the removal of Iron (Fe) and
Manganese (Mn). The historical preventative maintenance records indicate that each filter
bed was regenerated with a prescribed solution of Potassium Permanganate (KMnO4)
annually and the continuous use of KMnO4 was also a part of the O&M practices of the
NYS Operators that were employed at the site by NYS. The WTF is equipped with four
filters each 157.5 sq. ft., so the maximum filtration capacity is determined by multiplying
the total square ft. of filtration for three filter = (157.5 sq. ft. X 3 GPM/ sq. ft.) = 472.5 sq. ft. x
3 gpm = 1,417.5 GPM or 2,041,200 GPD [the flow rate for rapid rate filtration with oxidizing media
calls for a rate of 3 GPM/sq. ft.]
Based on the size of the filters and the use of Greensand media
for Fe & Mn treatment the filtration process provides for a flow in excess of 2 MGD at 3
GPM/sq. ft. of filter area. By using an oxidation/precipitation process Fe & Mn could be
removed through the clarification process, the WTF is capable of this process adjustment. At
a flow rate of 5 GPM/sq. ft., the facility is capable of treating 3.4 MGD with one filter out of
service; therefore, the capacity of the filtration process should be between 2.0 to 3.4 MGD.
There is a 100,000-gallon steel stand pipe that is located at a higher elevation overlooking
the water facility; historical records indicate the tank was built in 1934 which would make it
72 years old. According to the 1993 Gray, Railing & Heinsman, P.C. study2, this stand pipe
provides the necessary elevation and storage for backwashing the sand filters and, when
building #1 and #85 were built, records indicate that because of their elevation these new
building were connected directly to the steel stand pipe with a 6” and 10” cast iron water
main because the storage tank was at a high enough elevation to provide adequate pressure
for those buildings. The tank volume has sufficient capacity to properly backwash the sand
filters when the WTF is running at maximum flow of 1.2 MGD.
2.5. Disinfection
2
(Dutchess County Water and Wastewater Authority: Proposed Ownership & Operation of the Water &
Wastewater Facilities at the Harlem Valley Psychiatric Center, 1993 BY-Gray, Railing & Heinsman, P.C.
12
The WTF currently injects a 12% solution of sodium hypo-chlorite into the filter effluent
prior to filling the stand pipe and storage tank (clear well). After the filtration process and
disinfection the treated water enters one of two buried 500,000-gallon concrete storage
tanks, these tanks provide contact time for the disinfection process as well as storage for the
operation of the distribution system. The size of the storage facility provides operational
flexibility especially during construction of the upgrade because the operator will be able to
produce water in batch to provide the day to day needs when the initial demand is low. The
existing storage facility can
2.6. Distribution
The existing distribution system appears to be mostly cast iron pipe, and it is not known if
the conditions of the system are adequate to support the new development. There have been
a number of main breaks over the years which have been repaired. The project will include
the installation of new water mains for the development; however, some existing water main
may be used after the pipe conditions and needed restoration have been determined.
3.
Current Conditions and Regulatory Compliance
The conditions of the existing WTF will require some level of improvement if it is to be
used during the early phases of the development project. The timing and level of
improvements needed to support the project will be determined during the preparation of the
construction documents and permitting process. With a newly developed ground water
source designed with enough capacity for the projected average day needs, a new single
train filtration system to serve only as the water supply back up and to meet peak hour and
peak day requirements of the project may be provided once there are an adequate number of
customers connected. Most new water filtration systems are designed with 100%
redundancy built in; however, this would not be necessary with the development of the new
ground water supply. If necessary, the installation of a single train filtration process
installed over the existing clear well (1 MG storage tanks) could be much more cost
effective then rehabbing the existing.
13
Since the current usages are extremely low at 0.03 MGD, the facility is only operated for 2
days (16 hrs.) each week in order to maintain the necessary storage tank levels. Sludge is
removed from the clarifiers infrequently; for the most part the system is dormant 90% of the
time. Since the water demand projections for the proposed development are considerably
lower then past usage at the hospital center, the use of the Swamp River for additional water
supply is not anticipated. The hospital records indicate that the treatment system was
designed and approved to deliver 1.2 MGD of potable water. The historical records
observed indicate very few issues with maintaining compliance with Part-5 of the New York
State Sanitary Code regulations that govern public water supplies in NYS, over the years
compliance has become more stringent and the newest regulation may require additional
processes to be added to be in full compliance. Some modifications will include, but not be
limited to: On-line monitoring for chlorine residual and turbidity; Enhanced coagulation for
increased settling and solids removal; Organic Carbon removal for taste, odor and
disinfection byproducts treatment. These additional processes can be added to the existing
facility.
3.1. Reservoir & Swamp River Safe Yield Estimate
The reservoir’s watershed is approximately 250 acres and the reservoir water surface area is
approximately 10 acres with a maximum reservoir depth of 58 feet at the dam which is 64 ft.
at its highest point. The overall volume is approximately 150 acre feet (49,000,000 gallons).
The discharge pipe is elevated off the bottom which reduces the useable capacity by
13,000,000 gallons so the useable volume of the reservoir is 36,000,000 gallons. Hospital
records indicate that during dry weather and at full population and flows in excess of 0.6
MGD without Swamp River water, the reservoir water surface levels dropped, such that the
banks eroded and raw water quality deteriorated creating operational issues within the
filtration facility. The historical record also indicates that a drop in reservoir elevation of 10
ft. has been reason for concern. At historical usage under maximum occupancy, the Swamp
River pumping supply was an integral part of maintaining water volume and quality. While
the reservoir safe yield is not known from historical data, preliminary analysis using readily
14
available data indicates a safe yield of less than the WTF capacity of 1.2 MGD. The
assumptions used in this analysis include:.
•
Using an average annual rain fall of 50 inches
•
(50”/yr ÷12”/ft.) x 250 acres x 43,560 sq. ft. /acre x 7.48 gals. / Cu. ft. =
339,405,000 gallons ÷ 365 days/yr = 929,876.7 GPD [this assumes the
only source is rain and does not consider the potential of spring water
feeding the reservoir].
•
Water Treatment Facility design flow is estimated at 1.2 MGD, reservoir
safe yield of 0.93 MGD is considerably less then design.
The analysis of safe yield is a function of available volume and as the reservoir approaches
the theoretical safe yield, water quality issues would be expected to arise,raw water turbidity
will deteriorate and greater amounts of chemical treatment will be required, and a higher
level of operation and energy input will be necessary.
Historical data indicates that the Swamp River water use peaked as high as 124,000,000
gallons per year or 330,000 GPD, with annual averages running 40,000,000 gallons per year
or 110,000 GPD. These amounts must consider that most of the Swamp River usage was
during the summer months so peak day pumping had to be very high during the year that
124,000,000 gallons was pumped. There is no way of knowing if there was severe water
loss due to leaks and waste from the distribution system during that time. The desk top
analysis taken from the Gray, Railing & Heinsman, P.C. 1993 report for the Swamp River
indicates a safe yield of 250,000 GPD and determined the volume to be unreliable and
impacted by the same drought conditions that impact the reservoir.
3.2. Water Quality Concerns
Because the current water demand is relatively low, water quality entering the WTF is good.
If the WTF were to meet project demand of >500,000 GPD as a stand alone system, water
quality would be compromised; a secondary supply must be developed other then the
reservoir alone. Adding water to the reservoir from alternate sources appears to keep
reservoir raw water at a consistent level. This could be provided by adding ground water
sources currently being proposed for the project or identifying a better source of surface
15
water such as the 10 Mile River. In addition, a program for reservoir water quality
maintenance will be needed, which may include a method to disperse copper sulfate for the
control of algae and maintenance to the intake structure, valve building, and delivery piping
from reservoir to the first treatment process. The day to day operation and maintenance
should be performed with the understanding of the overall development plan and the
importance of maintaining a high level of water quality. Many of the current processes used
will require modernization to meet today’s standards and the level of improvement will be
determined during the preparation of the construction documents. Some of the anticipated
improvements may include:
Improved Rapid Mix and Chemical Injections
Enhanced Coagulation
Powdered Activated Carbon Additions for (TOC) Total Organic Carbon
Removal
Clarifier Rehabilitation with Improved Sludge Removal
Rapid Rate Filter Rehabilitation and New Filter Backwash with Air Scour
New Disinfection System
SCADA System (Supervisory Control And Data Acquisition) for Process
Management with On Line Turbidimeters and Chlorine Analysis
Building, HVAC, Lighting and Mechanical Systems
3.3. Recommended Plant Improvements
In determining what improvements will be necessary, the primary source of water for the
projected project must be first determined. A reliable ground water source to support the
project has been found and is available to meet the average day needs. The use of the
surface water supply is anticipated to be required to meet the peak day demands as defined
in Part-5 of the NYS Sanitary Code. It is also anticipated that the existing 1 MG water
storage tank will be used in any future system. The existing facility was built in the early
1930’s, over the years there have been a number of improvements made to the facility, the
16
last being in the mid 1980’s. During the time that the state employees operated the facilities,
a meticulous amount of detail went into the operation and maintenance of the facilities.
There are two potential plans for the WTF; the first is to upgrade the facility as it exists into
a state of the art water filtration plant using the major pieces of equipment with
modernization and replacement; the second option would be to replace equipment and repair
equipment to insure the facility will continue to be in compliance with the NYS Sanitary
Code. The replace and repair option would be a temporary improvement to the existing
facility to insure an adequate back up supply of high quality potable water was available for
the initial phases of construction of the development of the project. While the initial phases
of construction were occurring, a new facility could be designed and permitted by NYS.
Depending on the initial water demand, this new facility would be designed to provide
between 0.25 to 0.5 MGD of potable water. The new facility would be constructed as the
back up to the ground water facility that would be constructed simultaneously with the
project development. Because this would be a back up facility, it would not be required to
be sized to meet the instantaneous peak demand of the system and so it would not have to be
oversized as if it were the only source of supply. The new facility could be located in the
area of the existing 1 MG storage tank. It has not been determined if any of the existing
treatment process equipment would be used with this new facility. Below is a description of
the necessary improvements that will be required with both options:
3.3.1.
Complete Upgrade of Existing WTF
1. Restore existing dam structures where required as part of normal
maintenance.
2. Establish a reservoir maintenance program which would include chemical
treatment of the reservoir for algae removal, regular flushing of sediment
from the intake structures, and routine exercise of gates and valves.
3. Establish a watershed management program to protect surface water
quality that may include notification, signage, limited access and
installation of stormwater systems to cleanse the water before it enters the
reservoir.
17
4. Upgrade aeration basin to a fine bubble diffused air system for iron
oxidation and taste and odor treatment
5. Install new rapid mixing process for initial chemical introduction into the
process.
6. Replace existing chemical feed system with new chemical Feeders; this
includes the pre-oxidation process, pH adjustment, powdered activated
carbon feed, chemical coagulant feed which will include a polymer and a
metal salt injection.
7. Install a mechanical flocculator in coagulation/flocculation tank.
8. Remove cover from 2-sedimentation basins and build a structure over
sedimentation tanks to allow for process control adjustments.
9. Install mechanical sludge collectors in sedimentation basins to improve
sludge removal process and reduce the amount of water within the sludge.
10. Upgrade existing rapid rate sand filters, rebuild all automatic systems and
valves, core sample each filter, install an air scour system and rebed filters
with new media where necessary.
11. Install filter backwash pumps to eliminate the need for the 100,000-gallon
exterior steel water storage tank.
12. Upgrade sludge and backwash process to include the recycle of clean
supernatant back to the reservoir for water conservation.
13. Install new disinfection process with pH adjustment for corrosion control.
14. Install a SCADA system to control and monitor all of the processes within
the facility including storage tank levels, chemical feed, filter backwash
and data management.
15. Clean and resurface the existing 1 MG storage tank, repair any concrete,
install new valves and piping to new distribution system or replace with
new above ground tank.
16. Rebuild building structure updating electrical service, HVAC, internal
water distribution and process piping and lighting.
17. Clean both interior and exterior building systems and surfaces of any
contaminants.
18
3.3.2.
Temporary Upgrade of Existing WTF (New WTF & Ground Water Use)
1. Restore existing dam structures where required as part of normal
maintenance.
2. Establish a reservoir maintenance program which would include chemical
treatment of the reservoir for algae removal, regular flushing of sediment
from the intake structures, and routine exercise of gates and valves.
3. Establish a watershed management program to protect surface water
quality that may include notification, signage, limited access and
installation of stormwater systems to cleanse the water before it enters the
reservoir..
4. Install a diffused aeration system in aeration basin.
5. Install static mixers for initial chemical introduction into the process.
6. Replace existing chemical feed system with new chem. Feeders; this
includes the pre-oxidation process, pH adjustment, powdered activated
carbon feed, chemical coagulant feed which will include a polymer and a
metal salt injection. This new process would be reinstalled in new facility
and so most of the costs would reduce the construction cost of the new
facility.
7. Provide a safe access to the sedimentation basins and improve sludge
removal system.
8. Core rapid rate sand filter and add media as needed.
9. Install backwash pumps to eliminate the need for existing 100,000-gallon
exterior steel storage tank.
10. Install new disinfection process with pH adjustment for corrosion control,
this system will be transferred to new facility.
11. Clean and resurface the existing 1 MG storage tank, repair any concrete,
install new valves and piping to new distribution system or replace with
new above ground tank.
12. Build a new groundwater pumping and disinfection facility.
13. Build a new 0.25 to 0.5 MGD water filtration facility.
19
B. Potential Impacts
1.
Modifications required to meet regulatory compliance
The current plant, while it has aged and is in need of repair and requires frequent
maintenance, does provide potable water to its users. To provide a more efficient and
reliable WTF, both options will require improvements to meet current regulatory
compliance measures.
2.
Watershed protection requirements
The proposed project will include stormwater measures to capture and filter stormwater
runoff from the development that will drain into the reservoir. The measures have been
identified in the Stormwater Management Plan prepared for this project. Watershed
rules and regulations will be established so as to notify the property owners who
purchase land within the watershed of the importance of maintaining the land
around the watershed. The New York State Public Health Law allows local water
supply providers to initiate a process leading to enactment of watershed rules and
regulations by the Commissioner of the State Health Department. These rules were first
developed in the late 19th century to protect tributary streams and reservoirs used to
supply drinking water. They were later applied to public well fields and adjacent aquifer
areas. Most of the nearly 200 public supply systems that have adopted watershed
rules did so prior to 1940.
Watershed Rules specify minimum linear setbacks for different uses. For example,
many regulations prohibit the location of salt storage sites within 500 feet of public
supply wells, reservoirs or tributary streams to reservoirs. Since 1972, setback standards
have been promoted for activities involving synthetic organic chemicals; however, for
this class of contaminants, a minimum distance may not be effective because of their
persistence and ability to effect large areas over extended periods of time. Water supply
protection regulations should be customized to the particular hydrogeologic conditions
existing at the public supply well field or reservoir; and that the concept of minimum
20
acceptable distance does not address the differences between types of potential
contaminants such as pathogens and synthetic organic chemicals, nor the inherent
characteristics of groundwater transport found in different geologic and hydrologic
situations. Watershed rules and regulations are unique in being the only controls
specifically designed to protect public water supplies. These regulations are
prepared jointly by the water purveyor and the NYSDOH local public health
engineer. Enforcement responsibility rests with the water purveyor, the district and
the NYSDOH health officer.
3.
Phasing Impacts on Plant
The conditions at the existing water facility do not currently allow for production of the
volumes necessary to support the proposed project. A preliminary/interim improvement
plan has been developed to modernize the systems and processes so as to allow for the
production of enough water to meet the projected demand over the short term. The long
term plan would provide state of the art treatment for the required volumes necessary to
meet the ultimate demand of the facility.
4.
Potential Impacts Due to Treatment Plant Upgrades
4.1. Land Area Requirements
The land area required for the interim improvements to the treatment plant will be
limited to the existing water treatment facility. By contrast, the long term plan
would allow for a new facility to be built on top of the existing 1 MG ground
storage tank. Because the storage tank is below grade the new facility could easily
be built from the ground level up using the storage facility as the facility’s clear
well for filter back washing. The WTF is located in the southeast section of the
site.
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4.2. Effect on Recreational Uses in Reservoir
Watershed rules and regulations will be adopted to prevent any type of water
contaminants from entering the reservoir, the proposed project will be constructed
insuring the necessary watershed rules and regulation are followed and the water
supply is protected. Recreational uses including fishing, canoeing or kayaking with
hiking trails are expected to be permitted. The use of internal combustion motors
on the reservoir will be prohibited as will swimming because of possible
contamination of the water supply.
4.3. Increase in Chemical Usage and Storage
Chemical storage will be limited to the water treatment plant chemical rooms and
will include less than ten - 55 gallon drums of 12% sodium hypochlorite, less than
six 55-gallon drums of Poly-aluminum Chloride, several dozen bags of powdered
activated carbon and soda ash. The chemicals will all be stored with containment
as required by the regulations. The new facility will be much more efficient then
the old WTF in the use of chemicals and the production of residuals and waste; the
current facility’s entire top floor was dedicated for chemical storage, the new
facility will require about 25% of the original area for chemicals
4.4. Increase is Energy Consumption
Electrical usage will increase over current demand with the proposed treatment
plant upgrade as more water will be consumed. The electrical demand can be
estimated once the final designs of the system are completed. It should be noted
that the new facility will be designed with energy efficient motors with
consideration for time of day demand (off peak use). The new plant will most
likely use less energy than the existing plant did at full operating capacity.
Emergency standby power will need to be provided to the water pumping facilities.
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5.
Mitigation Measures
Treatment plant improvements to improve reliability: In the short term, the water
filtration facility will be improved with the following measures as previously discussed
herein. The upgrade plan will be completely covered in the design documents:
5.1. Temporary Upgrade of Existing WTF with New WTF & Ground Water Use
1. Restore existing dam structures where required as part of normal
maintenance.
2. Establish a reservoir maintenance program which would include
chemical treatment of the reservoir for algae removal, regular flushing
of sediment from the intake structures, and routine exercise of gates and
valves.
3. Establish a watershed management program to protect surface water
quality that may include notification, signage, limited access and
installation of stormwater systems to cleanse the water before it enters
to reservoir.
4. Install a diffused aeration system in aeration basin.
5. Install static mixers for initial chemical introduction into the process.
6. Replace existing chemical feed system with new chem. Feeders; this
includes the pre-oxidation process, pH adjustment, powdered activated
carbon feed, chemical coagulant feed which will include a polymer and
a metal salt injection. This new process would be reinstalled in new
facility and so most of the costs would reduce the construction cost of
the new facility.
7. Provide a safe access to the sedimentation basins and improve sludge
removal system.
8. Core rapid rate sand filter and add media as needed.
9. Install backwash pumps to eliminate the need for existing 100,000
gallon exterior steel storage tank.
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10. Install new disinfection process with pH adjustment for corrosion
control, this system will be transferred to new facility.
11. Clean and resurface the existing 1 MG storage tank, repair any concrete,
install new valves and piping to new distribution system or replace with
above ground tank.
12. Build a new groundwater pumping and disinfection facility.
13. Build a new 0.25 to 0.5 MGD water filtration facility.
The adoption of the above items goes hand in hand with the eventual construction of a
ground water supply. A small portion of the existing water distribution system may be
used until the project development extends in size to the east side of NYS Route 22
where the majority of the existing system lies. An evaluation will be performed on the
existing distribution system to determine which sections will be used at the initial stages
of development. Many sections not serving buildings and structures will be
abandoned.
5.2. Water Saving Fixtures:
The new building construction will be designed and built in accordance with the new
regulations which will include the use of water saving devices in all fixtures as is
required by law. The water saving fixtures will reduce water demand by approximately
20%.
5.3. Use of On-Site Wells to Reduce Demand on the Plant:
With the improvements outlined above, the ground water supply will be able to meet
the demand throughout the initial phases of the development project. The long term use
of the water filtration facility will be as a back up supply for the ground water system.
Both short term and long term plans for the WTF will allow the development project to
move forward. The existing storage facilities will provide greater than 1 day of storage
at full build out. Because the reservoir will not be stressed, the raw water quality will be
of very high quality which will allow for the WTF to economically produce the
necessary volumes of potable water. Even though the filtration process will only be
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needed as a back up source, it will still be operated on a fairly regular basis. Similar to
the operation of an additional well, this will insure the facility is always ready when
called to operate. The actual operating plan and schedule will be developed as a part of
the design process.
D. Conclusion
•
Rehabilitation of the entire 1.2 MGD facility needs to be further analyzed to determine
what the future benefits will be of having the excess capacity over and above the
demands of the Knolls at Dover current projected needs.
•
With development of a ground water source for the primary needs of the development
project the surface water facility will assume the role of backup supply. Under the
current regulations a ground water supply must have the available capacity to meet the
peak day demand with the largest well out of service. Actual peak day could be a much a
twice the projected average day demand of 514,360 GPD with peak days of close to 1
MGD, NYSDOH assumes peak day at twice the average day demand, the upgrade WTF
will provide the back up capacity as required under Part-5 of the NYS Sanitary Code.
•
A plan has been established for improving the water filtration facilities with the short
term upgrade of the existing water treatment facility as discussed in item “C” of this
report, the key elements of the upgrade are:
o Establishment of a ground water supply as the primary source.
o Repairs to the dam
o Demolition of existing steel storage tank and installation of new backwash
pumps to replace.
o Upgrade of chemical feed systems and rapid mix process.
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•
The existing facility will be repaired to meet the back up demands of the early phases
of the development project, during this time a replacement water filtration facility will
be designed and submitted for approval. It is expected that the facility will be
constructed on top of the existing 1,000,000 gallon water storage tank that is located
down gradient from the existing WTF. Construction of the new facility can occur while
the existing WTF is operational.
•
A water supply that draws from separate sources is a more reliable supply then one that
draws from only one source, the combined use of ground water and surface water will
make the Knolls at Dover water facility a very stable source of supply.
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