MILL POND RESTORATION PROJECT Phase II by fuf15836

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									   MILL POND RESTORATION PROJECT
                                    Phase II


                                     2002-2004




                                     Prepared by the



               NASHUA REGIONAL PLANNING COMMISSION



This project was funded in part by a New Hampshire Department of Environmental Services
   Nonpoint Source Program Local Initiative Grant with in-kind services provided by the
              City of Nashua, the Mine Falls Park Advisory Committee, and the
                                 NH DES Watershed Bureau
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                                                          Nashua Regional Planning Commission
                                                             Mill Pond Restoration Project
                                                                       2002-2004




                                                         TABLE OF CONTENTS


I.     INTRODUCTION .........................................................................................................................................1
II.    PROJECT SUMMARY AND GOALS ........................................................................................................1
III.   PROJECT TASKS..........................................................................................................................................1
       A. Task One - Quality Assurance Protection Plan...................................................................................2
       B. Task Two - Monitor flows from the Gatehouse into Mill Pond ......................................................2
       C. Task Three - Establish volunteer water quality monitoring program.............................................4
       D. Task Four - Calculate drainage area and catch basin information ...................................................5
            1.   Drainage to Outfalls 1-4 ....................................................................................................................5
            2.   Runoff Calculation .............................................................................................................................5
            3.   Construction of the Conway Ice Arena-Outfall 1 ..........................................................................7
            4.   Renovation of Nashua High School-South.....................................................................................7
            5.   Drainage to Outfall 5 .........................................................................................................................8
            6.   Drainage to Outfall 6 .........................................................................................................................8
            7.   Drainage to Outfall 7 and 8...............................................................................................................9
       E. Task Five - Develop GIS database and map for Task 4 ...................................................................11
       F. Task Six - Assess stormwater management measures.....................................................................12
       G. Task Seven - Research treatment systems that could be used ........................................................16
            1. Effectiveness of Swirl Separators in Stormwater Treatment......................................................16
       H. Task Eight - Water quality sampling..................................................................................................17
            1. In-Pond Sampling ............................................................................................................................18
                 a Transparency ................................................................................................................................19
                 b. Chorophyll-a.................................................................................................................................19
                 c. Total Phosphorous .......................................................................................................................20
                 d. pH ..................................................................................................................................................20
                 e. Acid Neutralizing Capacity (ANC) ...........................................................................................21
                 f. Conductivity.................................................................................................................................21
                 g. Gate House Sample on the Nashua River - August 16 ...........................................................21
            2. Stormwater Outfall Sampling.........................................................................................................21

       I. Task 9 - Mine Falls Park Master Plan Committee.............................................................................22
IV.    CONCLUSION............................................................................................................................................24
V.     GENERAL RECOMMENDATIONS ........................................................................................................24




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LIST OF TABLES
  Table III-1: Grass Treatment Swale......................................................................................................................8
  Table III-2: Detention Pond Infiltration Volume..............................................................................................10
  Table III-3: Summary of Drainage Calculations...............................................................................................11
  Table III-4: Stormwater Catch Basin (CB) Assessment – July 17, 2003 .........................................................13
  Table III-5: Stormwater Catch Basin Assessment – July 25, 2003 ..................................................................14
  Table III-6: Dissolved Oxygen/Temperature Profile ......................................................................................18
  Table III-7: Mill Pond Epilimnion Layer – 2 Meters .......................................................................................18
  Table III-8: Hypolimnion Layer – 4 Meters .....................................................................................................19

LIST OF MAPS
  Map III-1: Outfall Watershed Drainage Areas ................................................................................................11
  Map III-2: Catch Basin Locations ......................................................................................................................15
  Map III-3: Water Quality Sampling ..................................................................................................................17
  Map III-4: Mine Falls Park .................................................................................................................................23

LIST OF APPENDICES:
  Appendix A                        Task Two – Gatehouse Flows
  Appendix B                        Task Four - Drainage Calculations for Outfalls 1-4
                                    Prepared by the City of Nashua Engineering Department
  Appendix C                        Task Four - Drainage Calculations for Outfalls 1
                                    For the Conway Ice Arena
                                    Prepared by Hayner/Swanson, Inc
  Appendix D                        Task Four - Drainage Calculations for Outfalls 5-8
                                    For Nashua High School - South
                                    Prepared by Hayner/Swanson, Inc.
  Appendix E                        Task Seven - Vortechs Stormwater Treatment System
                                    NH Design and Operation Specifications
  Appendix F                        Task Eight – Laboratory ResultsAnd Field Observations for
                                    In-Pond Sampling
  Appendix G                        Task Eight – Laboratory Results for Outfall
                                    Stormwater Sampling
  Appendix H                        Task 9 – Public Outreach




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I.    INTRODUCTION
The Mill Pond Restoration Project Phase I in 200I assessed the water quality of the 20 acre Mill Pond as well
as nonpoint sources of pollution (NPS) impacting the water quality of the pond, and the Nashua River
Canal (Canal). Both Mill Pond and the Canal have seen increased growth of aquatic vegetation in the past few
years. In 1998, the New Hampshire Department of Environmental Services (NH DES) surveyed Mill Pond
as part of the Lake Monitoring for Trophic Classification Program. The survey, conducted on July 21, 1998,
                               documented extremely dense growths of Coontail (Ceratphyllum demersum) and
                               Milfoil (Myriophyllum heterophyllum), and indicated that algal mats covered 40% of
                               the pond. Water quality analysis indicated total phosphorous levels of .046
                                                                              and .098 milligrams per liter (mg/L), at
                                                                              2.5 and 4 meters respectively,
                                                                              substantially above the recommended
                                                                              level of concern of 0.05 mg/L. The NH
                                                                              DES survey also noted that Mill Pond
                                                                              receives massive urban runoff from
                                                                              parking lots and other impervious
                                                                              areas in the watershed.


                                                   Milfoil
            Coontail

The drainage area of Mill Pond and the Canal was determined to be approximately 515 acres, with an
estimated impervious surface coverage of 41% using Nashua Regional Planning Commission (NRPC)
Geographic Information System (GIS) data. Eight outfalls drain directly into Mill Pond from the Nashua
High School parking lots and athletic fields, Riverside Drive and approximately 20 businesses between
Riverside Drive and West Hollis Street (Route 111).

II.   PROJECT SUMMARY AND GOALS
The goal of the Mill Pond Restoration Project Phase II was to continue to assess drainage in the watershed
and establish baseline water quality data in Mill Pond and the Canal. Water quality analysis indicates
that conditions have not improved between 1999 and 2002. Untreated stormwater remained a problem
during the study period.

NRPC worked with many departments in the City of Nashua to ensure that five of the outfalls were
rerouted to secondary stormwater treatment devices during construction at Nashua High School – South,
and the new Conway Ice Arena. The remaining three outfalls are slated to be treated as part of the Army
Corps of Engineers, Section 206, Aquatic Ecosystem Restoration Project.

III. PROJECT TASKS
Task 1. Develop a Quality Assurance Protection Plan (QAPP) for the project to be reviewed and
approved by EPA prior to the start of water quality monitoring.

Task 2. Monitor flows from the Gatehouse on the Nashua River into Mill Pond and report flows under
the minimum 10 cubic feet second (cfs) level to the proper authorities.

Task 3. Establish a volunteer water quality monitoring program for in-pond and wet weather sampling
in the Mill Pond and Canal. Identify and train volunteers to collect samples throughout the spring,
summer and fall.


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Task 4. Calculate drainage area, drainage volumes, pipe width/type, flow, the number of catch basins on
site plans and impervious surface area coverage per outfall, and the anticipated change in impervious
surface area following renovation of the high school.

Task 5. Develop a GIS database and map for Task 4.

Task 6. Assess the condition and effectiveness of stormwater management measures in the watershed
and identify those in need of replacement or repair.

Task 7. Research the type and size treatment systems that could be used based on the flow calculations
in Task 4.

Task 8. Collect and analyze samples in-pond once a month from June to October. Storm event sampling
will be conducted five (5) times at the eight (8) outfall locations throughout the project period.

Task 9. Organize clean up days and develop public information materials to inform the general public of
the clean up efforts and activities that they can become involved in.

Task 10. Prepare a summary report with the analyzed results and make general recommendations.

A.       Task One
The New Hampshire Department of Environmental Services (NH DES) requires that a Quality Assurance
Protection Plan (QAPP) be developed and approved by; the Environmental Protection Agency (EPA);
NH DES; and all participating laboratories. This document details the methods of data collection, storage
and analysis. This project utilized the Nashua Wastewater Treatment Plant Laboratory, and the
Volunteer Lake Assessment Program (Limnology) and New Hampshire State Laboratories located in
Concord at NH DES. The purpose of the QAPP is to ensure credibility and representative data for all
users. The Army Corps of Engineers, U.S. Fish and Wildlife Service and Bio Engineering Group have
used data from both Phase I and II of this project for other studies for the Mill Pond Watershed.

The QAPP1 was completed in the early summer of 2002, and reviewed by
the following personnel, and their respective agencies:

     •    NRPC Project Manager – Betsy Hahn
     •    NH DES Lab Manager – Rachel Rainey
     •    NH DES Limnology Center Project QA Officer – Andy Capman
     •    Nashua Division of Public Works Wastewater Treatment Facility
          Lab - Nancy Lesieur
     •    Program QA Coordinator – Andrea Donlon
     •    NH DES QA Manager – Vince Perelli
     •    US EPA Project Manager – Warren Howard
B.       Task Two
The Federal Energy Regulatory Commission (FERC) license L.P. 3442-NH
was issued on January 31, 1989 for the 3.0 megawatt (MW) hydroelectric
generating system located on the Nashua River at Mine Falls. Article 32
of the FERC license stipulates that the licensee at Mine Falls is required to
discharge a minimum flow of 10 cubic feet per second (cfs) to Mill Pond
for “the maintenance of visual quality and recreational opportunities in
                                                                                     Measuring Gatehouse Flow
1Nashua Regional Planning Commission, Quality Assurance Protection Plan, 2002. The
approved QAPP and all appendices are on file with the NH DES Watershed Bureau.
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the Mill Pond and associated Canal.” During Phase I of the Mill Pond Restoration Project, the Nashua
River Watershed Association (project partners) investigated the flow rate during the summer of 2000. It
was discovered that the average flow from four sampling days was only 1.30 cfs. Bank seepage was
noted east of the outfall pipe. Since the sound of water could be heard in the Gatehouse, it was
concluded that the pipe must be obstructed or crushed between the Gatehouse and the pond. Energy
Resources Group, the former owners, filed a Minimum Flow Compliance Report with FERC the year before
stating that 10 cfs was flowing into Mill Pond.

In 2000, Algonquin Power Systems, Inc. (APS) purchased the generating station. Since the transfer of
                                                      ownership, APS, the City of Nashua and all the
                                                      Restoration Project Partners have searched for
                                                      solutions to increase the flow to the pond.
                                                      During Phase I of this project, the Nashua River
                                                      Watershed Association (project partners)
                                                      determined the average velocity in the culvert to
                                                      the Mill Pond to be 0.0616 feet per second,
                                                      resulting in a calculated flow of 1.586 cfs. By
                                                      cross-sectioning the inlet Canal and measuring
                                                      velocities, it was calculated that the total flow
                                                      entering the Mill Pond was 3.237 cfs. Engineers
                                                      from APS and the City of Nashua reviewed the
                                                      Gatehouse Water Diversion Plan, which
                                                      determined that to meet minimum flow, the
                                                      original openings of the historic Gatehouse had
                                                      to be sealed. One gate would be used to direct
                                                      flow through a 24-inch pipe into an 8-foot
                                                      culvert to the Mill Pond. The examination of the
                                                      Gatehouse revealed that the 24-inch pipe was
                                                      installed at gate #4 and the control valve on the
               Mine Falls Generating Station          pipe was inoperable.

A three person dive team was dispatched to further investigate the existing conditions and determine if,
or how, to de-water gate chamber #4 to gain access to repair or replace the drainpipe valve. It was
concluded that de-watering the gate chamber was not an option and a plan was developed to send in a
dive team to repair or replace the valve. Prior to sending in the dive team, the operator of the generating
station was able to open and operate the valve. The chamber was flushed and the water velocities were
permanently set using a portable flow meter.
The valve was then secured in position. (The
last Minimum Flow Compliance Report is
Appendix A.)

In 2001, the City of Nashua met with officials
from the U.S. Fish and Wildlife Service
(USFWS), Central New England Fisheries Office
(CNEFRO) and the Army Corps of Engineers to
discuss pursuing a Section 206 Aquatic
Ecosystem Restoration funding. A proposal
was developed to investigate and identify ways             Historic 1860 Gatehouse on the Nashua River




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 to improve water quality so that Mill Pond could be used as a nursery for anadromous river herring
(Alewife, Blue Back Herring). The historic 1860 Gatehouse and the Mine Falls hydropower dam control
flows to the Mill Pond and Canal system. The dam has a maximum operating capacity of approximately
1,600 cfs.

Appropriating any water in excess of the dam’s capacity of 1,600 cfs has the potential to increase flows
through the system. The USGS provisional flow data for East Pepperell, MA upstream on the Nashua
River indicates that flow on average only exceeds 1600 cfs only 6% of the time, mostly in the early spring.
It was determined that relying on excess flowage was not a viable solution and that other measures were
needed for optimal flow through the Gatehouse to help reduce anoxic conditions and excessive algae,
vegetation.

Part of the proposed project includes improving flow through the Gatehouse to the Mill Pond. A dye test
performed in July 2004 revealed that water is entering Mill Pond from a seep on the east side of the 8-foot
culvert pipe. Water was determined to be seeping from the Gatehouse water chamber through the coarse
soils. A site assessment and cost estimate is currently being undertaken by the Army Corps of Engineers
and their consultant The BioEngineering Group. The expected completion date for the report is spring
2005.
C.     Task Three
The New Hampshire Department of Environmental Services (NH DES) Watershed Bureau coordinates
the Volunteer Lake Assessment Program (VLAP). Each
year, biologists in the Limnology Department teach
volunteers collection techniques and handling and storage
of water samples. Water samples are typically sampled at
all streams and outfalls entering a lake or pond and the in-
lake deep spot.

The data collected by volunteers allows NH DES biologists
to determine the lake’s water quality and monitor its trends
over time. After ten consecutive years in the VLAP
Program, a statistically sound set of water quality baseline
data has been established, allowing determination of an
annual mean. This information is vital to calculate averages for the more than 800 lakes in New
Hampshire.

On June 30, 2002 Andrea Lamoreaux, VLAP Coordinator, conducted a training session for volunteers
Betsy Hahn, Ralph Andrews and Angie Rapp. Using a bathymetric map, Mill Pond’s deepest spot was
determined to be approximately 20 feet located
near the bridge going over weir #2 on the
northern side of the pond. Using triangulation
or three reference points from the shoreline,
monitors set a weighted buoy for sample
location consistency.

Monitors were taught how to use a Kemmerer
bottle to collect samples for phosphorus and
chlorophyll-a analysis. They were also
instructed on proper use of a Secchi disk and
calibrated chain to determine transparency.
Duplicates for all parameters were taken. This
was the only day that dissolved oxygen,
temperature and phytoplankton were sampled.
                                                             VLAP In-Pond Training Session 2002
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D.   Task Four
The City of Nashua Engineering Department (project partners) determined the watershed area for
Outfalls 1-4. The drainage volume, impervious surface area and peak flow was calculated for each
outfall pipe. The Nashua Regional Planning Commission researched the site plans and Stormwater
Management Plans for the Conway Ice Arena and Nashua High School South.
     1. Drainage to Outfalls 1-4
     The amount of runoff being discharged to the Mill Pond at Outfalls 1, 2, 3, and 4 needed to be
     determined. The Rational Method of determining peak runoff was used to calculate the flows
     being discharged at each outfall. The Rational Method is one of the simplest and best-known
     methods routinely applied in urban hydrology. The parameters used for the rational method are
     time of concentration to determine the rainfall intensity, basin size, and a runoff coefficient that is a
     function of the land use, cover and slope.

     Peak flows are computed from the simple empirical formula of Q = ciA where:

     Q = peak discharge, cubic feet per second (cfs)
     c = runoff coefficient
     i = rainfall intensity for a storm of a certain frequency and for a duration equal to the time of
         concentration, inches per hour
     A = area of the drainage basin, acres

     The rainfall intensity is determined from the longest time of concentration when multiple sub-
     drainage basins arrive at point of discharge. The time of concentration for the drainage area is
     dependent upon the distance from the furthest point in the drainage area and the difference in
     elevation from the highest point in the drainage basin to the point of discharge. Using Time of
     Concentration of Small Drainage Basins Calculation Method (Figure 2-2) published in the New
     Hampshire Department of Transportation Manual on Drainage Design for Highways, revised in April
     1998, the time of concentration was determined to be ten minutes for the entire drainage basin.
     Figure 2-2 is in Appendix B.

     Knowing the time of concentration, the rainfall intensity (i) is typically found from
     Intensity/Duration/Frequency curves (Figure 2-3) for rainfall events in the geographical region of
     interest. Figure 2-3 of the Manual on Drainage Design for Highways was used to determine that
     the rainfall intensity for a 10-year storm with a time of concentration of 10 minutes to be 4.6 inches
     per hour. Figure 2-3 is in Appendix B.

     The Rational Method runoff coefficient (c) is a function of the soil cover and ground slope. The table for
     Runoff Coefficients (Figure 2-1) in the Manual on Drainage Design for Highways was used to determine
     the runoff coefficients. Figure 2-1 is in Appendix B. The four drainage basins contributing to the four
     outfalls were each divided into sub-drainage basins. A combination of examining sewer plans for pipes
     in the street, site plans for building located in the drainage area and field inspection was used to
     determine the contributing sub-drainage area. Using the parameters as described above and inputting
     them in the formula used for the Rational Method, the peak discharge for each outlet was calculated.
     2. Runoff Calculations
     The Mill Pond Watershed consists of a 65 acre drainage area. Four outfalls discharge into the
     southern most edge of Mill Pond. The sub-drainage basins for the four outlets were delineated and
     depicted on Map III-1 Outfall Watershed Drainage Map in Task 5 of this report. Each sub-drainage
     area was accessed for its soil characteristics, land use and slope.



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•   Mill Pond Sub-drainage Watershed Number 1

Discharges into the 30-inch diameter reinforced concrete pipe at Outfall 1 as shown on
Watershed Drainage Map #1 (Figure 1) in Appendix B. The sub-drainage basin contains the
Division of Public Works garage, the Conway Ice Arena, an area of undeveloped land and the
New Hampshire Department of Transportation commuter parking lot. The total 14.75 acres
were determined to be 6.28 acres of impervious surface and 8.47 acres of pervious materials.
Slopes are generally flat for paved areas with a runoff coefficient of 0.85. Commercial roof
areas also have a runoff coefficient of 0.85. Slopes for non-paved areas range from 3-8% with
runoff coefficients of 0.12 or 0.20 depending on vegetation and slope. Peak discharge for a 10-
year storm was calculated to be 18.29 cfs.
•   Mill Pond Sub-drainage Watershed Number 2

Discharges into the 24-inch diameter transite pipe at Outfall 2 as shown on Watershed
Drainage Map #2 (Figure 2) in Appendix B. The sub-drainage area contains a residential area
along Pitarys Drive, the Nashua Police Department Headquarters, a professional office park
surrounded by Panther Drive, Riverside St. and West Hollis St. and the St. Philips Greek
Orthodox Church. The total 31.52 acres were determined to be 14.88 acres of impervious
materials and 16.64 acres of pervious materials. The detention basin on the St. Philips Greek
Orthodox Church site was determined to have sufficient capacity as to not overflow during the
10-year frequency design storm. Therefore, the area tributary to this detention basin was
removed from the study. Slopes for paved areas vary from 1-5% for the parking lot areas and
10% for Pitarys Drive and have an average runoff coefficient of 0.85. Commercial roof areas
also have a runoff coefficient of 0.85. Slopes for non-paved areas range from 3-5% with runoff
coefficients varying from 0.07 for lawns to 0.20 for wooded areas, depending on vegetation and
slope. Peak discharge for a 10-year storm was calculated to be 28.21 cfs.

•   Mill Pond Sub-drainage Watershed Number 3

Discharges into a 24-inch diameter transite pipe at Outfall 3 as shown on Watershed Drainage
Map #3 (Figure 3) in Appendix B. The total 8.92 acres are made up of 4.42 acres impervious
materials and 4.50 acres pervious materials. The sub-drainage basin contains predominantly
commercial properties along the south side of Riverside Drive, directly opposite Mill Pond.
These include Brookstone and Storage Computer. Slopes for paved areas vary from 1-5% for
the parking lot areas and have an average runoff coefficient of 0.85. Commercial roof areas also
have a runoff coefficient of 0.85. Slopes for non-paved areas range from 3-5% with runoff
coefficients varying from 0.07 for lawns to 0.20 for wooded areas, depending on vegetation and
slope. Peak discharge for a 10-year storm was calculated to be 9.78 cfs.

•   Mill Pond Watershed Number 4

Discharges into a 24-inch diameter reinforced concrete pipe at Outfall 4 as shown on
Watershed Drainage Map #4 (Figure 4) in Appendix B. The total 9.85 acres were determined to
be 2.75 acres of impervious materials and 7.10 acres of pervious materials. The sub-drainage
basin consists of a combination of residential, commercial and cemetery properties. These
include the commercial properties at Mercier and West Hollis Streets, residential properties
along both Mercier and West Hollis Streets, and the French Catholic and Beth Abraham
Cemeteries on West Hollis Street. The area is bounded on the southeast by the southbound off
ramp to Route 111 off the FE Everett Turnpike. Slopes are generally flat for paved areas with
runoff coefficients varying from 0.80 to 0.90 depending on pavement surface conditions.
Commercial roof areas also have a runoff coefficient of 0.85. Slopes for non-paved areas vary
from less than 1-23% with runoff coefficients varying from 0.07 to 0.13 depending on vegetation
and slope. Although apparently removed from Mill Pond, it is piped through the commercial
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      property to the north and discharges into the pond through the 24-inch diameter RCP drain
      pipe. Peak discharge for a 10-year storm was calculated to be 8.70 cfs.
 3. Construction of the Conway Ice Arena-Outfall 1
 In June 2002, Hayner/Swanson, Inc. presented a Stormwater Management Report to the City of
 Nashua for a new 37,000 square foot ice center with associated parking and site improvements on
 the existing east parking lot of the Division of Public Works (DPW) Garage. The site plan included
 additional parking spaces adjacent to Riverside Drive, Stellos Stadium and on the north side of
 DPW abutting Mill Pond. The report provided a qualitative measure to meet both State of NH DES
 Site Specific Regulations and the City of Nashua Stormwater Regulations. Options for stormwater
 management were limited due to the presence of an old landfill. Extended detention basins were
 determined to be infeasible resulting in the use of a Vortechs unit designed to treat stormwater
 prior to entering Outfall 1.

 Section 16-145(h) of the Nashua Zoning and Subdivision Ordinances requires that post
 development rates of discharge not exceed pre-development peak rates. Drainage calculations,
 located in Appendix C, indicate a small increase in peak rate. The volume of stormwater runoff
 during the 100-year, 24-hour storm event is 0.362 acre-foot. The volume of stormwater entering the
 22.5+/- acre Mill Pond would raise the water level by 0.016 feet or 0.19 inches. The City of Nashua
 Planning Board granted a waiver for the recharge component due to the landfill and the small
 increase rate of runoff in July 2002.




Drain Leading to Outfall 1 via Catch Basin #37                     Roof Drainage System Erosion


 During construction of the ice center NRPC photographed the land use changes for this final
 report. Several erosion control problems were observed and documented including runoff, and a
 clogged drain leading to Outfall 1. The problems were quickly corrected and the catch basins were
 cleaned.

 The new grading and installation of a picnic area/vegetation at the existing boat ramp also reduced
 overland flow of sediments to Mill Pond. The site improvements were completed in 2003.

 4. Renovation of Nashua High School South
 The project partners recognized a significant opportunity to improve water quality in the Mill Pond
 and the Canal system during the expansion of Nashua High School South. The City of Nashua
 worked with the School Board and Hayner/Swanson, Inc. to develop a comprehensive stormwater
 management design. Treatment measures within the system included water quality inlets (i.e.,
 catch basins), a detention pond and grass swale, and Vortechs units to reduce flow velocities,
 remove suspended solids and debris from runoff prior to being released into the ground and Mill

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Pond. The following sections will discuss the drainage areas, changes to the drainage system and a
comparison of existing conditions and post construction runoff data.
5. Drainage to Outfall 5

The drainage area for Outfall 5 is 12.4 acres including a segment of Riverside Drive, the school
entrance driveways, school parking areas and a portion of the school roof. Currently runoff flows
untreated, and discharges at a 24-inch
concrete outfall (flared end section) to the
Mill Pond. The Stormwater Management
Plan designed by Hayner/Swanson, Inc.
calculated runoff to be 19.94 cfs for a 10-year
and 34.06 cfs for a 50-year storm event. A
Vortechs Model 11000 and a 30-inch outfall
were installed in the winter of 2004. The post
construction runoff remains exactly the same
for a 10-year and 50-year storm. The net
annual total suspended solid removal
efficiency was calculated to be 83%. The
calculations and unit design parameters are                 Installation of the Vortechs Unit
located in Appendix D.
6. Drainage to Outfall 6=
The drainage area to Outfall 6 consists of 8.2
 acres including the driveway bordering Mill
Pond, new parking on the westerly and
northerly sides of the existing building and a
portion of the school roof. Part of this drainage
area flows to the 15-inch outfall on Mill Pond
and the remainder discharges to the 24-inch
headwall at Outfall 7 on the Canal. There is no
treatment of stormwater at either of these
outfalls. Hayner/Swanson, Inc. calculated
existing runoff velocities in the Stormwater
Management Plan. Pre-construction velocities
were 13.12 cfs for a 10-year and 22.39 cfs for a
                                                                Outfall from Swale and Vortechs
50-year storm event.

Outfall 6 was removed in 2003 and all of the runoff was combined to flow into a Vortechs unit
before entering a grass swale. The calculations and unit design parameters are located in Appendix
D. Water exits the swale through a 36-inch outlet in the headwall. Although post construction
velocities are higher at 15.64 cfs for a 10-year and 25.38 cfs for a 50-year storm, water quality is
projected to improve with the Vortechs unit.

                            Table III-1. Grass Treatment Swale
 Storm Event                Discharge                   Depth of Flow                  Velocity
    10 year                  8.56 cfs                      0.8 feet              0.85 feet per second
    50 year                  26.35 cfs                     1.5 feet              1.20 feet per second
               Source: Hayner/Swanson, Inc., Stormwater Management Report, 2002.




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          Swale Construction 2003                                 Post Swale Construction 2004


7. Drainage to Outfall 7 and 8
The remainder of the school property drains to
Outfalls 7 and 8. The drainage area includes
the new building roof, new/upgrades of
parking lots on the north and east sides of the
school, new tennis courts and a portion of the
existing school roof. The majority of the
runoff flows to Outfall 7. During both phases
of this project no flow was observed during
wet weather sampling. Indications are that
more water is taken out of the Canal for
irrigation than flows overland from the
athletic fields.

Hayner/Swanson, Inc. calculated existing
runoff velocities in the Stormwater
Management Plan. Calculations and drainage area                      Detention Pond Construction
delineations are in Appendix D. Pre-construction
velocities were 8.69 cfs for a 10-year and 17.99 cfs for a 50-year storm event. Post construction
velocities are higher at 31.18 cfs for a 10-year and 45.05 cfs for a 50-year storm. To accommodate
the calculated 5.31 acre increase in impervious surface area created by the new addition and
parking lot, a detention pond was designed to attenuate the increased rate of runoff. The detention
pond outlet holds water below the outlet invert to allow infiltration to compensate for the increased
impervious surface area.

Post construction drainage from the detention pond outlet was calculated to be 8.56 cfs for 10-year
and 26.35 cfs for a 50-year storm event. The outflow from the detention pond is further treated in
the grass swale before final discharge through the 36-inch pipe at the headwall.




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                            Table III-2. Detention Pond Infiltration Volume
     Increase in Impervious Area         Required Infiltration         Pond Storage Below Outlet Invert
                                               Volume
               5.31 acres                   0.18 acre-feet                       0.59 acre-feet
                      Source: Hayner/Swanson, Inc., Stormwater Management Report, 2002.

Hayner/Swanson, Inc. also conducted a
Point of Analysis calculation for pre-
construction and post development in the
Canal downstream of all drainage
discharges. Pre-construction velocities
were 40.95 cfs for 10-year and 73.40 cfs for a
50-year storm event. Post construction
velocities are lower at 40.64 cfs for a 10-year
and 69.89 cfs for a 50-year storm.

The net improvements to this site are
anticipated to improve water quality
without affecting the quantity of runoff
downstream. The project is in compliance
with Section 16-145(h) of the Nashua Zoning
and Subdivision Ordinances. The project is
expected to be completed in 2004.                                      Completed Detention Basin




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E.     Task Five
The City of Nashua Engineering Department prepared drainage calculations and computations of outfall
watershed areas. A summary of the drainage calculations is in Table III-3 and the outfall watershed areas
are depicted on Map III-1. The entire database is in Appendix B.

                              Table III-3. Summary of Drainage Calculations
     Outfall   Drainage Area        Impervious          Outfall Pipe        Drainage Volume   Catch Basins
     Number                         Surface Area         Diameter                  “Q”
                                                                               (C x I x A)
        1       14.75 acres           6.28 acres        30” concrete            18.29 cfs             12
        2       31.52 acres          14.88 acres        24” transite            28.21 cfs             25
        3       8.92 acres            4.42 acres        24” transite             9.78 cfs             18
        4       9.85 acres            2.75 acres        24” concrete            9.782 cfs              2
                               Source: City of Nashua Engineering Department, 2004.


                                 Map III-1. Outfall Watershed Drainage Areas




                              Source: City of Nashua Engineering Department, 2004.                =




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F.    Task Six
                                                        A field assessment was conducted on catch basins
                                                        (CB) and swales on July 17, 2003. Field observations
                                                        are in Table III-4 and CB locations are illustrated on
                                                        Map III-2. The weather on July 17th and the previous
                                                        two days was dry and in the 80’s. Catch basins were
                                                        found to be in good shape overall and the City of
                                                        Nashua has done a good job of street cleaning in the
                                                        study area. However, the two swales along Riverside
                                                        Drive illustrate two separate problems. The first is the
                                                        application of fertilizers, pesticides and herbicides in
                                                        the landscaped swale. The swale drains directly into
                                                        CB #15, which flows to Outfall #5 into Mill Pond.


         Landscaped Swale - Riverside Drive

The second swale located on the lot west of Brookstone has not
been maintained. There are large amounts of sediment present,
and saplings growing in the swale.

Nashua High School South was not inspected during the field
assessment because the majority of the drainage system was
being re-routed to a secondary stormwater system and believed
to be in compliance. Structures found to have maintenance
problems (indicated in bold in Tables III-4 and 5) were reported
to the Division of Public Works. Built up sediment was the main
                                                                                Non Maintained Swale - Brookstone Property
problem from construction at the High School.

The following roadways and City of Nashua properties were
examined:

     •    Pitarys Drive off West Hollis Street (NH 111)
     •    West Hollis Street to the FE Everett Turnpike
     •    Panther Drive
     •    Riverside Drive from Panther to the High School




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               Table III-4. Stormwater Catch Basin (CB) Assessment – July 17, 2003
  CB Number       Condition of CB/Area         Sediment Present         Trash Present         Water in CB
      1                   Good                    Moderate                   No                   Full
      2                   Good                       No                      No                   Full
      3                   Good                       No                      No                   Full
      4                   Good                       No                      No                   Full
      5                   Good                       No                      No                   Full
      6                   Good                       No                      No                   Half
      7                   Good                       No                      No                   Half
      8                   Good                       No                      No                   Dry
      9         Minimal pavement cracking            No                      No                   Half
      10                  Good                      Light                   Light               Quarter
      11                  Good                       No                      No                 Quarter
      12                  Good                       No                      No                 Quarter
      13        Minimal pavement cracking           Light                    No                   Half
      14        Minimal pavement cracking           Light                    No                 Quarter
      15                                             No                      No                   Dry
      16        Minimal pavement cracking            No                      No                   Dry
      17        Minimal pavement cracking           Light                    No                 Quarter
      18        Minimal pavement cracking            No                      No                 Quarter
      19                  Good                    Moderate                  Light               Quarter
      20                  Good                      Light                    No                 Quarter
      21        Minimal pavement cracking         Moderate                   No                 Quarter
      22                  Good                     Heavy*                    No                 Quarter
      23                  Good                     Heavy*                    No                 Quarter
      24                  Good                      Light                    No                   NA
      25                  Good                       No                      No                   Half
      26                  Good                      Light                    No              Three Quarters
      27                  Good                       No                      No                   Half
      28                  Good                       No                      No                   Half
      29                  Good                       No                      No                   Half
      30                  Good                       No                      No                   Half

                                           Source: NRPC, 2003.
                                  * Reported to Division of Public Works.


Another field assessment was conducted on catch basins
and swales on July 24, 2003. Field observations are in
Table III-5 and catch basins are depicted on Map III-2.
The weather on July 24th and the previous two days was
rainy and in the 80’s. The amount of water in the
drainage system was similar to the dry weather during
the July 17th field assessment. The following roadways
and City of Nashua properties were examined:

   •   Mercier Lane
   •   Division of Pubic Works
   •   Redmond Street
   •   Conway Ice Arena
   •   Ride-Share Commuter Parking Lot                                      Sediment Problems at CB #37




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The Mercier Lane catch basins were the oldest in the drainage area.
While showing signs of age, they appeared to be functioning
properly. The stormwater drainage for the Division of Public
Works was re-routed to the Nashua WasteWater Treatment Plant
subsequent to the findings in the first Mill Pond Study. Structures
found to have maintenance problems (indicated in bold in Table
III-5) were reported to the Division of Public Works. The
Treatment Plant Lab chemically analyzed samples from catch basin
31. Redmond Street does not have curbing allowing the
stormwater to flow into the vegetation along the road.
                                                                                      Problematic Color at #31

                                                     The ice arena was under construction during this field
                                                     investigation and several erosion and sedimentation
                                                     problems were documented. In the fall of 2003, a
                                                     Vortechs unit was installed near the entrance of the
                                                     commuter parking lot. All stormwater flowing from the
                                                     ice arena site flows through the unit prior to draining
                                                     into Mill Pond at Outfall 1.

                                                     An adjacent Ride-Share Commuter Parking Lot is
                                                     owned and maintained by the City of Nashua.
                                                     Currently stormwater flows into natural vegetation
                                                     (sheet flow) or into three catch basins at the entrance to
                                                     the lot.
             Vortechs Unit at Outfall 1


                 Table III-5. Stormwater Catch Basin Assessment – July 25, 2003
    CB Number          Condition of CB/Area         Sediment Present             Trash        Water in CB
                                                    Around Structure            Present
        31                    Good                        No                      No        Problematic Color
        32                    Good                       Light                    No         Dry - Sediment
        33                    Good                        No                      No              Half
        34                    Good                        No                      No               Dry
        35                    Good                        No                      No             Quarter
        36                    Poor                      Heavy*                   Light           Quarter
        37                    Good                      Heavy*                   Light           Quarter
        38                    Good                      Heavy*                    No             Quarter
        39                    Good                        No                      No             Quarter
        40                    Good                        No                      No             Quarter
        41                    Good                        No                      No             Quarter
        42                Under Repair                    No                      No             Quarter
        43                    Poor*                    Moderate                  Light           Quarter
        44              Minimal Cracking               Moderate                   No               Dry
        45                    Good                        No                      No               Dry
        46            Good (Needs Cleaning)*              No                      No               Dry
        47              Minimal Cracking                  No                      No               Dry
                                              Source: NRPC, 2003.
                                     * Reported to Division of Public Works.




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Map III-2. Catch Basin Locations




                                         =
        Source: NRPC, 2003.




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G.   Task Seven
The City of Nashua Engineering Department researched the type of treatment systems that could be used
based on the flow calculations in Task 4.

     1. Effectiveness of Swirl Separators in Stormwater Treatment
     The National Urban Runoff Program2 demonstrated that stormwater discharges from land surfaces
     contain various pollutants. Environmental concerns about nonpoint sources of pollution and the
     regulation of these discharges had led to a rapid increase in the number and types of products and
     systems that are marketed to reduce the impacts from urban areas on water quality. Most products
     target removal of sediment, hydrocarbons and debris for the stormwater runoff. Laboratory tests
     produced by product developers state that most products could remove up to 80% total suspended
     solids from the water. One of these products, the Vortechs system, uses swirl-concentrated flow
     movement and flow control measures to capture sediment, floating hydrocarbons (oil) and debris
     from surface runoff.

     A January 2001 document titled A Study of the Effectiveness of a Vortechs Stormwater Treatment System
     for the Removal Of Total Suspended Solids and Other Pollutants in the Marine Village Watershed, Village of
     Lake George, NY reported the results for field-testing of the stormwater pretreatment and post
     treatment. The study area was 3.78 hectares and 95% impervious. The New York State Department
     of Environmental Conservation, Division of Water completed the report.

     Thirteen storms were sampled over a continuous ten-month period. The sampled results indicated
     at least 50% removal in all of the storms and many of the storms had well over an 80% removal. As
     stated in the Conclusions and Recommendation section of the report:

       “The evaluation of the Vortechs System through the comparison of the inflow to the outflow
       shows that the System removes at least 60% of total suspended solids from stormwater for
       individual storms under most flow conditions. The TSS removal efficiency for the entire study
       period was calculated to be 88%, exceeding the manufacturer’s estimated annual removal
       efficiency (80%).”

     The conclusion continues to state that the Vortechs System removes some coarse particulates of
     nutrients (phosphorus and nitrogen), but that the bulk of the nutrients pass through the System.

     The City of Nashua recently installed a Vortechs unit when the drainage system serving the
     Conway Ice Arena was constructed. The location of this unit is upstream of Outfall 1, near node
     DMH 2 as shown on Watershed Drainage Map #1 (Figure 1) in Appendix B. Prior to a recent
     cleaning of the unit, floatables observed in the unit included Styrofoam cups, a tennis ball, a one-
     gallon plastic milk carton, and cigarette butts. A sheen of oil was also observed. Sediment in the
     basin was measured to be about 6 inches in depth. While no inlet or outlet sampling has been done
     on the stormwater runoff flowing through the Vortechs system, based on observed debris in the
     unit, it can be stated that the Vortechs unit has been effective in preventing some sediment and
     debris contained in stormwater from entering Mill Pond.

     Outfalls 2-4 have been identified to receive secondary stormwater treatment as part of the Army
     Corps of Engineers Section 206 Aquatic Ecosystem Restoration Project. A proposal was developed
     to investigate and identify ways to improve water quality so that Mill Pond could be used as a
     nursery for anadromous river herring (Alewife, Blue Back Herring). This project is currently under
     budget review and awaiting a Memorandum of Understanding between the City of Nashua and
     other project partners. Once the installation location is determined, types and sizes can be

       2   http://www.stormwater-resources.com/Library/011 BVortecs 2.PDF
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      researched based on the drainage calculations developed by the City of Nashua Engineering
      Department. Basic design and operation specifications for Vortechs Stormwater Treatment Systems
      are in Appendix E.

H.    Task Eight
In 2002, volunteers sampled Mill Pond and the stormwater flowing into Mill Pond. Similar to the
summer of 2001, the summer of 2002 was filled with many warm and sunny days and there was a lower
than normal amount of rainfall during the latter-half of the summer. The combination of these factors
resulted in relatively warm surface waters throughout the state. The lack of fresh water reduced the rate
of flushing which may have resulted in water stagnation. The BioEngineering Group estimated the
residence time to be 11 days based on an inflow of 12 cfs.

For both in-pond and stormwater testing, the project used both laboratories at Department of
Environmental Services (NH DES). The Volunteer Lake Assessment Program (VLAP) lab, a project
partner, analyzed pH, conductivity, turbidity, chlorophyll-a and alkalinity. The state lab was used only
for analysis of total phosphorus. The City of Nashua Wastewater Treatment Plant provided E. coli and
total suspended solids results.

When the application for the grant was prepared, there were eight operating outfalls in the project area.
Outfalls 7 and 8 were disconnected in the summer of 2002 for reconstruction of athletic fields and parking
lots at Nashua High School South. Instead, a sample was taken from the Nashua River at the Gatehouse
and duplicate samples were analyzed. It should also be noted that the lag time at Outfall 4 was far
greater due to detention in the watershed. The following section will discuss each of the parameters
tested and discuss the results. Annual trends can not be predicted based on only two sampling seasons.

                               Map III-3. Water Quality Sampling Sites




                                        Source: NRPC, 2002.

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    1. In-Pond Sampling
    The first sampling day, June 20, 2002 was a training day for the monitors and served as the annual
    visit by a NH DES biologist. Samples were taken at a depth of two meters (epilimnion layer) and
    four meters (hypolimnion layer). This was the only day that readings were taken for dissolved
    oxygen and temperature due to the lack of equipment. All field sheets and lab results are in
    Appendix F. Results from eight previous samplings in 2000 and one in 2002 indicate a severe
    oxygen deficit at 4 meters. This indicates that bacteria in the pond sediment are decomposing the
    dead organic matter (algae/vegetation). Mill Pond is considered an organic rich or productive
    water body. Levels of oxygen below 1 milligram per liter (mg/L) trigger the release of phosphorus
    that normally is bound chemically in the sediments. The release of phosphorus into the water
    column is referred to as internal loading. Temperature is also a factor in dissolved oxygen
    concentration. Cooler temperatures allow the water to hold more oxygen. The low oxygen levels
    and warm temperatures are tolerable to fish species such as bass which habitat the pond.

 Table III-6. Dissolved Oxygen/Temperature Profile
Depth (M)       Temperature       Dissolved Oxygen Mg/L
                  Deg C
   0–1             21.1                         8.93
    1              18.7                         7.63
    2              17.1                         5.48
    3              14.9                         0.25
    4              13.1                         0.33
                Source: NRPC, June 20, 2002.

                         Table III-7. Mill Pond Epilimnion Layer – 2 Meters
 Sampling             pH             Total             Conductivity   Turbidity   Alkalinity   Chlorophyll-a
   Dates                          Phosphorus             uS/cm          NTU         Mg/L         Mg/m3*
                                    Mg/L                                           CaCo3
   June 16            6.82           .057                      234       2.4         21.2           8.34
   July 17            6.99           .032                      331       3.85        32.8          11.63
 August 16            7.22           .019                      399       2.23        39.4            55
September 19           7.3           .021                      438       1.52        45.2           6.3
 October 10           7.17           .024                      446       2.22        43.9          10.23

 Site Range         6.82–7.3        .019-.057             234-446     1.52–3.85   21.2–45.2       6.33-55
 Site Mean             7.1             .03                  370          2.44       36.5            18.3

State Mean**          6.5            N/A                       59.4     N/A          6.6           7.16
     State            6.6            0.012                     56.8      1.0         4.8           4.58
  Median**
State Concern       5.5 – 6.0     .02-.04 High             > 100        >10.0       10-20          > 15
   Level**        Endangered     >.04 Excessive           Human         High      Sensitive      Nuisance
                                                          Impacts                                Impacts

                                          Source: NRPC, 2002.
                          Composite chlorophyll- a sample at 1, 2, 3, and 4 meters
                   ** NH DES Volunteer Lakes Assessment Program, Interpreting Data, 2001.




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                                Table III-8. Hypolimnion Layer – 4 Meters
    Date             pH            Total          Conductivity        Turbidity     Alkalinity       Chlorophyll-a
                                Phosphorus          uS/cm               NTU         Mg/L CaCo3          Mg/m3
                                  Mg/L
    June 16          6.34          .147                 611              38.7          N/A               8.34
field duplicate      6.29          N/A                  696              50.8
    July 17           6.9          .036                 345              3.88          N/A               11.63
   August 16         6.34          .065                 780              7.44          N/A                55
 September 19        6.86          .034                 534              5.88          N/A                6.3
  October 10         7.11          .023                 442              2.75          N/A               10.23

 Site Range       6.29 - 7.11    .023 - .147         345 - 780        2.75 - 50.8      N/A              6.3 -55
 Site Mean           6.64           .061               568               18.24         N/A               18.3

Concern Level      5.5 – 6.0       > 0.02              > 100            >10.0          10-20             > 15
                                             Source: NRPC, 2002.
        G Mg/L CaCo3 is calcium carbonate, US/cm is micro siemens per cubic meter, NTU is nephelometer
        turbidity
     a. Transparency

     Transparency, a measure of water clarity, can
     be affected by the amount of algae and
     sediment from erosion, as well as the natural
     colors of the water. Secchi disk readings
     indicate the transparency of the water. The
     Secchi-disk is a 20-centimeter (cm) disk with
     alternating black and white quadrants. The
     disk is lowered into the water on the shady
     side of the boat to measure how far a person
     can see into the water. The mean (average)
     summer transparency for New Hampshire’s
     lakes and ponds is 3.7 meters. The Mill Pond
     ranged from 1.7 (July) to 3.27 (August) meters
     compared to 2000 sampling range of 2.7 to 2.9                     Black and White secchi-disk
     meters all season. VLAP ranks 2-4.5 meters as “Good”.

    In late May and early June of 2002, numerous rainstorms occurred. Stormwater runoff associated
    with these rainstorms may have increased phosphorus loading, and the amount of soil particles
    washed into Mill Pond. Clarity did decrease slightly from June to July. Lower than average amount
    of rainfall and the warmer temperatures during the latter-half of the summer resulted in increased
    clarity. August and September had the best readings even though this is the time for increased algal
    growth. Overall, visual inspection of the limited historical data shows stable trend for in-lake
    transparency, meaning that the transparency has remained approximately the same since monitoring
    began.
    b. chlorophyll-a
    Phytoplankton or microscopic algae floating in the water column was collected using a plankton
    net and identified by species quantity within the collected sample. The type of phytoplankton
    present in a lake can be used as a general indicator of water quality not unlike the type/presence of
    benthic macroinvertebrates in riverine systems.


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Phytoplankton populations are cyclical through the warmer months of the year with dominant
species of algae declining as other species of algae increase and become dominant. Mill Pond was
dominated with Asterionalla (86.4%) which is a Pennate Diatom and Ceratium (8.7%) which is a
Dinoflagellate. Diatoms are the natural dominant species in the spring. Green algae is dominant in
the early summer, followed by blue-green algae in mid to late summer.

Chlorophyll-a, a pigment naturally found in plants, is an indicator of the algal abundance. Because
algae are usually microscopic plants that contain chlorophyll-a, and are naturally found in lake
ecosystems, the chlorophyll-a concentration measured in the water gives an estimation of the
concentration of algae or lake productivity. The mean (average) summer chlorophyll-a
concentration for New Hampshire’s lakes and ponds is 7.02 micrograms per liter.

Chlorophyll-a concentration increased slightly from June to July, increased greatly from July to
August, decreased greatly from August to September, and then increased slightly from September
to October. The chlorophyll-a concentration in August (55 mg/m3) greatly exceeded the state
mean, which suggests that a major algal bloom occurred in the pond on this sampling date. The
transparency reading on the August sampling date was not severely reduced, as one would expect
during a major algal bloom. It is possible that the elevated chlorophyll concentration in August
was due to sampling or laboratory error. Overall, the data suggest an increasing in-lake
chlorophyll-a trend, meaning that the concentration has worsened since monitoring began in 2000.
However, please keep in mind that this trend is based on only two sampling seasons.

c. Total Phosphorus
Phosphorus is the limiting nutrient for plant and algae growth in New Hampshire’s freshwater
lakes and ponds. Too much phosphorus in a lake/pond can lead to increases in plant and algal
growth over time. The median summer total phosphorus concentration in the epilimnion (upper
layer) of New Hampshire’s lakes and ponds is 11 micrograms per liter (ug/L) The median summer
phosphorus concentration in the hypolimnion (lower layer) is 14 ug/L.

Total phosphorus concentration decreased greatly from June to August, and then increased
gradually from August to October in the epilimnion. The total phosphorus concentration on each
sampling event was greater than the state median, and was greatly exceeded the state median in
June and July. The 2002 mean epiliminetic total phosphorus concentration is approximately two
and a half times greater than the state median. Overall, the data shows slightly increasing total
phosphorus trend, which means that the concentration has slightly worsened in the epilimnion since
monitoring began.

Data for the hypolimnion show that the total phosphorus concentration decreased greatly from
June to July, increased from July to August, and then decreased from August to October. The total
phosphorus concentration on each sampling event was greater than the state median, and was
greatly exceeded the state median in June and August. The 2002 mean hypolimnetic total
phosphorus concentration is approximately five times greater than the state median. The data for
the hypolimnion shows stable total phosphorus trend, which means that the concentration has
remained approximately the same in the hypolimnion since monitoring began.
d. pH
The pH of water is measured on a logarithmic scale of 0 (acidic) to 14 (basic). A balanced pH is
important to the survival and reproduction of fish and other aquatic life. A pH below 5.5 severely
limits the growth and reproduction of fish. A pH between 6.5 and 7.0 is ideal for fish. The mean
pH value for the epilimnion (upper layer) in New Hampshire’s lakes and ponds is 6.5, which
indicates that the surface waters in state are slightly acidic.

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The mean pH at the deep spot this season ranged from 6.60 in the hypolimnion to 7.06 in the
epilimnion, which means that the pH of the water column ranged from slightly acidic to neutral, in
line with the State average.

e. Acid Neutralizing Capacity (ANC)
Buffering capacity or Acid Neutralizing Capacity describes the ability to resist changes in pH by
neutralizing the acidic input. The higher the ANC the greater the ability of the water to neutralize
acids such sulfur oxides (acid precipitation) atmospherically transported from mid-west power
plants. The abundance of granite bedrock in the state makes the water low in ANC. The ANC of the
epilimnion is greater than the state mean of 6.7 mg/L. Specifically, this indicates that Mill Pond is
not vulnerable to acidic inputs and has a greater ability than most lakes and ponds in the state to
buffer against acidic inputs. While this may seem like a positive condition in the pond, according to
NH DES, the high ANC is likely due to higher concentrations of ions such as phosphorus, calcium,
and metals from watershed runoff into the pond.
f. Conductivity
Conductivity is the numerical expression of the ability of water to carry an electric current.
Typically conductivity levels greater than 100 micromhos per centimeter (umhos/cm) indicate the
presence of inorganic metals, landscape/agricultural runoff, and road runoff (which contains road
salt during the spring snowmelt). The in-pond conductivity has been very high since monitoring
began, ranging from 369 to 628 umhos/cm. This corresponds with the BioEngineering Group, Inc.
2002 report “Sediment Sampling, Sediment Profiling and Bathymetric Mapping of Mill Pond”. The grab
samples taken in the upper organic-rich soil horizons in the deep spot revealed high concentrations
of metals and a significantly higher concentration of arsenic.
g. Gate House Sample on the Nashua River - August 16
The Kemmerer bottle was lowered from the Gatehouse wall on the south bank of the Nashua River.
This is directly above the gates flowing through the Gatehouse and into Mill Pond. The bottle was
lowered to a depth of 3 meters. There was a large amount of algae present in this location. Total
phosphorus was 0.119 mg/L, conductivity was 360 uS/cm and the turbidity measured 2.72
nephelometer turbidity.

2. Stormwater Outfall Sampling
Summer rainfall proved to be very elusive this year. It always rained at hours which made it
difficult to catch the first flush or after the laboratories were closed in the afternoon. Determined to
get data in a drought summer, the first flush sampling was not always achieved. Field sheets and
laboratory results are in Appendix G.

The BioEngineering Group prepared a report entitled “Sediment Sampling, Sediment Profiling and
Bathymetric Mapping of Mill Pond”, May 2002 for the Army Corps of Engineers Aquatic Ecosytem
Restoration Project for Mine Falls Park. The quantity and quality near stormwater outfalls
determined that:

   •   Sediment thickness varies from 0 to 12.5 feet throughout the pond, with the greatest thickness
       near stormwater outfalls.
   •   Several semi-volatile organic compounds (SVOCs), one polychlorinated biphenyl (PCB) and
       a few metals exceed National Oceanic Atmospheric Administration safe levels for benthic
       organisms.




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      a. Conductivity
      The conductivity level for the majority of the stormwater outfall samples collected this season was
      relatively low. The VLAP program emphasizes that conductivity is directly related to the total
      dissolved (in solution, not in particulate form) inorganic chemicals (meaning chemical substances
      of mineral origin, not of basically carbon compounds) in the water. Therefore, the stormwater data
      for this season shows a relatively small amount of dissolved inorganic chemicals, such as chloride
      or metals, in the stormwater outfalls. This is “good” with respect to water quality. However, the
      “first flush” (the stormwater containing the high initial pollutant load) was not always captured
      due to the erratic timing of storm events and the differing rates of discharge at outfalls. Chlorine
      DES has a tendency to be tied up in the soils and/or quickly travel through the soils to the
      groundwater. According to NH DES, it is possible that a portion of the chlorine DES never reached
      it to the surface water that was sampled during the stormwater sampling events.

      b. Total Phosphorus
      The total phosphorus concentration was very high in the majority of the stormwater outfall samples
      that were collected this season. In addition, most of the stormwater samples were high in turbidity
      and were gray colored. According to NH DES, the data and field observations, combined with the
      low conductivity levels, suggest that two phenomena may be occurring. Most of the phosphorus in
      the stormwater runoff is organic (plant and animal residues, or substances made by living
      organisms, based upon carbon compounds). The second is that the phosphorus is particulate
      (meaning not dissolved) which is attached to aluminum silicates (clay particles) from soil erosion
      which is occurring in the watershed. However, the only way to be sure that this is the case is to
      test the stormwater runoff for orthophosphate (inorganic phosphate).

     c. Turbidity
      Turbidity in the water is caused by suspended matter, such as clay, silt, and algae. Water clarity is
      strongly influenced by turbidity. As discussed previously, the majority of the stormwater outfall
      samples were high in turbidity and gray in color. These data and observations suggest erosion of
      soils in the watershed is producing stormwater runoff high in aluminum silicates (clay particles)
      and is occurring in the watershed and causing aluminum silicates (clay particles) to be present in
      high amounts in stormwater runoff.

I.   Task 9
In January 2001, a group of volunteers formed the Mine Falls Park Master Plan Committee with the goal
of defining the vision for future development and maintenance of this multiple use park. The Committee
included members from the following departments and organizations:

•    Mine Falls Park Advisory Committee
•    City of Nashua Division of Public Works, Parks and Recreation Department
•    City of Nashua Community Development
•    City of Nashua Division of Public Works, Engineering Department
•    Nashua Regional Planning Commission
•    New Hampshire Audubon Society
•    Urban Trails Alliance
•    New Hampshire Mountain Biking Association
•    New Hampshire Department of Environmental Services

The park is approximately three miles long consisting of 325 acres of primarily woods and fields
geographically located in the center of the City of Nashua. The north/south bound FE Everett Turnpike
passes over the center of the park with the Nashua River forming the north boundary, the 1886
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Gatehouse and Mill Pond the west end and the Nashua River Power Canal the south boundary ending at
the Millyard in the east. Nashua High School South, Stellos Stadium and the Conway Ice Area abut the
park’s southwest entrance, the City Youth’s rectangular stadium borders the west entrance and Lincoln
Park is located at the bridge entrance on the north side of the Nashua River. In addition, the parks
northern and southern borders are densely developed residential and commercial districts.

                                       Map III-4. Mine Falls Park




                      ============




                          Source: BioEngineering Group, Inc. 2003.

Current uses in Mine Falls Park include passive recreation such as fishing, walking/running, bicycling,
birding, cross-country skiing, etc. as well as a section used for organized sports such as softball and
soccer. People canoe in the Mill Pond and Canal
and a motorboat ramp is located just above the
Gatehouse on the Nashua River. The park’s central
location and proximity to residential
neighborhoods is a magnet to residents and
visitors alike. The trails literally take a beating
from overuse by park enthusiasts. Continual
maintenance is required to keep trails from eroding
and hikers and bicyclists in the desired locations.
The City of Nashua aggressively pursued funding
to accomplish the goals outlined in the Mine Falls
Master Plan. To date the City has received over
$900,000. Many of the goals outlined in the 2001                Boat Ramp improvements to reduce erosion
Mine Falls Park Master Plan have been met.

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 They include:

 •     Interpretive sign at the 1886 Gatehouse to explain the history and uses of the National Register
       Historic District (Gatehouse, Mill Pond, Power Canal, Millyard).
 •     An interpretive sign above the Cove to describe its origination as an oxbow and environmental
       aspects on the park’s east side.
 •     Completion of the River Run Trail and Bridge.
 •     Improvements to the Boat Ramp area including picnic area and landscaping for wildlife.
 •     Two educational overlooks were constructed to provide information and scenic views of the Cove,
       Nashua River and Millyard, while preserving this nature area.
 •     Completion of an Arbor Walk along the Nashua River with signage identifying
       existing trees and shrubs.

One of the goals of the Mine Falls Park
Advisory Committee (MFPAC) is to
provide safe and interesting trails while
preserving the natural park environment.
In conjunction with the City of Nashua
Parks and Recreation Department, the
MFPAC organize yearly, cleanup and repair
days from April through October. The trail
flyer and MFPAC minutes concerning
public outreach are in Appendix G.

All of these accomplishments and
maintenance efforts on the part of officials -
and citizen volunteers have improved water
quality, reduced bank erosion and provided
educational outreach to the general public
to respect the environment, and enjoy the
recreational opportunities that the park
                                                                      Educational Overlook Deck
provides.

 IV.      CONCLUSION
 The Mill Pond Restoration Project Phase II revealed and developed important data that can be built upon
 and used by all the project partners. Water quality and drainage data have already been incorporated
 into other State, Federal and consulting companies’ projects concerning Mine Falls Park and the Mill
 Pond watershed. The continued commitment by the City of Nashua to improve environmental
 conditions and pursue funding and provide the necessary match is to be commended.

 The completion of the recommendations of the Mine Falls Park Master Plan and a Memorandum of
 Agreement (MOA) for the Aquatic Restoration Project will enhance the Park in the years to come.


 V.       GENERAL RECOMMENDATIONS=
 •     Streamlining the Quality Assurance Protection Plan (QAPP) for projects and lengthening the period
       of eligibility to 5 years would be helpful for establishing baseline data.
 •     Consider replacing the transite pipe at outfalls two and three when secondary stormwater measures
       are installed. Transite pipes contain asbestos that leaches into the water.
 •     Test the stormwater outfalls to assess conditions after the installation of secondary stormwater
       treatment systems.

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•   Continue to assess the condition and effectiveness of stormwater management measures in the
    watershed and identify those in need of replacement or repair.
•   The Volunteer Lake Assessment Program advocates ten years of water quality monitoring to
    establish annual trends for each lake or pond.
•   The long attenuation period in the Mill Pond may be contributing to stagnation. A site assessment
    and cost estimate is currently being undertaken by the Army Corps of Engineers and their consultant
    the BioEngineering Group to repair the gatehouse to increase flows. The City of Nashua should
    actively pursue the MOA for the Aquatic Restoration Project.




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        Appendix A

Task Two – Gatehouse Flows




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                   Appendix B

Task Four - Drainage Calculations for Outfalls 1-4

         Prepared by the City of Nashua
            Engineering Department




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                  Appendix C

Task Four - Drainage Calculations for Outfalls 1
           For the Conway Ice Arena

      Prepared by Hayner/Swanson, Inc.




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                   Appendix D

Task Four - Drainage Calculations for Outfalls 5-8
        For Nashua High School South

       Prepared by Hayner/Swanson, Inc.




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              Appendix E

   Task Seven - Vortechs Stormwater
          Treatment System

NH Design and Operation Specifications




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          Appendix F

Task Eight – Laboratory Results
  And Field Observations for
      In-Pond Sampling




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               Appendix G

Task Eight – Laboratory Results for Outfall
          Stormwater Sampling




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August 29, 2002

August 29 was a scattered, moderately heavy rain event that registered 0.05inches of precipitation at the
Pennichuck Water Works Treatment Plant in Nashua. The first flush occurred between 10:00-10:30 am
depending on the outfall. There is a water quality violation at sites 1 & 2 because the E.coli was greater
than 800. Total Phosphorus is considered excessive at all outfalls since rates exceed .02 Mg/L.


                                   G-1. Storm One Sampling Results
   Site           Location of Outfall                E.coli        TSS          Cond.    Turb.     TP       PH
                                                   Col/100ml       Mg/L         uS/cm    NTU      Mg/L
   WW1        Pipe under bush at boat ramp           >800           26           316      167     .155      6.49
   WW2          Second pipe at boat ramp             >800           41           89.4     77.1    .254      6.31
   WW3        Cement pipe down path from             >320           61          117.8     88.6    .207      6.2
            Riverside Dr. near wooden railing
   WW4        Cement pipe down path from             0 Flow          0          0 Flow   0 Flow   0 Flow   0 Flow
            Riverside Dr. near wooden railing                      Flow
   WW5      Drainage swale from cement pipe            90           23          34.55     41.8     .102     6.52
                   near school entrance
   WW6      Drainage swale from cement pipe          0 Flow          0          0 Flow   0 Flow   0 Flow   0 Flow
                halfway down parking lot                           Flow
   WW7      **Disconnected for Construction**         N/A          N/A          N/A       N/A     N/A      N/A
   WW8      **Disconnected for Construction**         N/A          N/A          N/A       N/A     N/A      N/A

                                                    Source: NRPC, 2002


September 23, 2002
Rainfall was .35 inches


                                   G-2. Storm Two Sampling Results
   Site           Location of Outfall              E.coli         TSS       Cond.        Turb.     TP       PH
                                                 Col/100ml       Mg/L       uS/cm        NTU      Mg/L
   WW1       Pipe under bush at boat ramp        No bottles       No         272          8.04    .057      6.38
                                                                 bottles
   WW2         Second pipe at boat ramp          No bottles       No        24.77         3.4      .06      6.34
                                                                 bottles
   WW3       Cement pipe down path from          No bottles       No        23.15         6.68     .148     6.35
              Riverside Dr. near wooden                          bottles
                        railing
   WW4       Cement pipe down path from            0 Flow        0 Flow     0 Flow       0 Flow   0 Flow   0 Flow
              Riverside Dr. near wooden
                        railing
   WW5       Drainage swale from cement          No bottles        No       22.82         3.02     .033     6.3
               pipe near school entrance                         bottles
   WW6       Drainage swale from cement            0 Flow        0 Flow     0 Flow       0 Flow   0 Flow   0 Flow
            pipe halfway down parking lot
   WW7            **Disconnected for                N/A          N/A        N/A          N/A      N/A      N/A
                    Construction**
   WW8            **Disconnected for                N/A          N/A        N/A          N/A      N/A      N/A
                    Construction**

                                                Source: NRPC, 2003




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September 27, 2002
Rainfall was .35 inches
                                    G-3. Storm Three Sampling Results
   Site            Location of Outfall               E.coli         TSS          Cond.       Turb.      TP      PH
                                                   Col/100ml        Mg/L         uS/cm       NTU       Mg/L
  WW1      Pipe under bush at boat ramp              >1600           54          100.7        56.2     .119     6.68
  WW2         Second pipe at boat ramp               >1600           21           17.13       27.1     .084     6.47
  WW3       Cement pipe down path from               >1600           19          13.95        28.8     .231     6.36
             Riverside Dr. near wooden
                       railing
  WW4       Cement pipe down path from               >1600           <1           7.27       3.22      .034     5.98
             Riverside Dr. near wooden
                       railing
  WW5       Drainage swale from cement             No sample          No         20.25       29.9      .053     6.53
              pipe near school entrance                             sample
  WW6       Drainage swale from cement             No sample          No         19.42       19.5      .083     6.06
           pipe halfway down parking lot                            sample
  WW7            **Disconnected for                   N/A            N/A         N/A         N/A       N/A      N/A
                   Construction**
  WW8            **Disconnected for                   N/A           N/A          N/A         N/A       N/A      N/A
                   Construction**

                                                  Source: NRPC, 2002
October 16, 2002

This rainstorm was steady and heavy at times although no precipitation was registered at the Pennichuck
Water Works Treatment Plant.

                                    G-4. Storm Four Sampling Results
    Site               Location of Outfall                 E.coli         TSS       Cond.      Turb.    TP      PH
                                                         Col/100ml        Mg/L      uS/cm      NTU     Mg/L
   WW1          Pipe under bush at boat ramp               >320            4        No Lab      36.4   .093     6.85
                                                                                     Data
   WW2            Second pipe at boat ramp                   >320          20        84.77      43.8    .0168    6.6
   WW3          Cement pipe down path from                   >320          10        45.05      18.4     .077   6.45
              Riverside Dr. near wooden railing
   WW4          Cement pipe down path from                No Flow          No         No        No       No      No
              Riverside Dr. near wooden railing                           Flow       Flow      Flow     Flow    Flow
   WW5        Drainage swale from cement pipe                 12           <1        33.63     11.5     .044    6.45
                     near school entrance
   WW6        Drainage swale from cement pipe             No Flow          No         No        No       No      No
                  halfway down parking lot                                Flow       Flow      Flow     Flow    Flow
   WW7        **Disconnected for Construction**              N/A          N/A        N/A       N/A      N/A     N/A
   WW8        **Disconnected for Construction**              N/A          N/A        N/A       N/A      N/A     N/A

                                                  Source: NRPC, 2002




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November 22, 2002

This was a cold and fairly steady rain. Rainfall amounts were not recorded at the Pennichuck
Water Works Treatment Plant.


                                   G-5. Storm Five Sampling Results
    Site            Location of Outfall                 E.coli      TSS         Cond.    Turb.     TP     PH
                                                      Col/100ml     Mg/L        uS/cm    NTU      Mg/L
    WW1         Pipe under bush at boat ramp           TNTC          67          7.38     125     .173    6.71
    WW2           Second pipe at boat ramp               < 10        19          221      21.5    .253    7.01
                                                      Dup < 10                                    Dup
                                                                                                  .249
    WW3         Cement pipe down path from              TNTC          24        41.40     54.9    .099    6.51
              Riverside Dr. near wooden railing
    WW4         Cement pipe down path from            No Flow        No         0 Flow   0 Flow     0    0 Flow
              Riverside Dr. near wooden railing                     Flow                          Flow
    WW5       Drainage swale from cement pipe             50         25         41.91     57.9    .086    6.44
                     near school entrance
    WW6       Drainage swale from cement pipe           TNTC          57        66.51     157     .51     6.47
                  halfway down parking lot
    WW7       **Disconnected for Construction**         N/A         N/A         N/A      N/A      N/A    N/A
    WW8       **Disconnected for Construction**         N/A         N/A         N/A      N/A      N/A    N/A

                                               Source: NRPC,2002




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      Appendix H

Task 9 – Public Outreach




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