HomeMy WebLinkAboutWATER REPORT -51AR 688 9542
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Oct- 14-99 02 : 17P North Andover Com. Dev _ 508 688 9542 P . 02
E T L A N O S
II ■, RESERVATION
INC.
Water Quality Evaluation
Lot #1, Dale Street
North Andover, Massachusetts
October 5, 1999
Prepared for
Peter Hatem
Hatem & Mahoney
127 Tumpike Street
North Andover, Massachusetts 01845
i
Prepared by
i
Wetlands Preservation, Inc.
47 Newton Road
Plaistow, New Hampshire 03865
WPI Job #2407A
475 Ipswich Road E-mail: wedandwpiCgreennet.net 47 Newton Road
r, I r,,. C__ rcnrDi oon ID/10"i Pimiatnw r\jw n.,gRf-,ii
Oct.- 14-99 02 : 17P North Andover Com. Dev . 508 688 9542
P _03
Water Quality Evaluation
Lot #1, Dale Street
North Andover Massachusetts
Introduction
The purpose of the following evaluation is to assess the potential impacts to the quality of water
le
discharging to Lake Cochichewick from the development of a proposed residential huse lot
of Bone
Street in North Andover, Massachusetts. The proposed project entail edevelopment
isting undeveloped parcel located on Dale Street. This study will focus
single-family home on an ex
on water quality issues of site development and the potential increases to nutrient levels, in particular
phosphorus and nitrogen, to water discharging from the site and possible effects to downstream Lake
Cochichewick.
For this evaluation, the Lake Cochichewick Watershed Plan dated August 1987 and th more recent
lake study, an Evaluation of Water Quality and Management Options in Lake Cochich wick and Its
Watershed dated February, 1999, were reviewed and used for existing water quali conditions
within the lake and to evaluate consistency of project impacts with the goals set forth s part of the
Watershed Protection District,
Watershed Setting and Background
The proposed site is located within the Lake Cochichewick Watershed Protect i0 Area. Lake
Cochichewick serves the Town of North Andover as the primary water supply sour e. Watershed
area to the lake is estimated at 2,732 acres (1,106 hectares) and the surface ar of the pond
approximates 564 acres (228 hectares) (IEP, 1987). The average flushing rate or the rate at which
the quantity of water within the lake is completely renewed in percent nnt volume the 1 Per Year
c is 0.57 (Ised
1987). Previous monitoring of in-lake and discharge points tributary
algal growth, occasional elevated levels of nutrients, turbidity, and bacteria were the principal
concerns for maintaining a high level of water quality in the lake (IEP, 1987). Th town of North
Andover has invested a substantial effort in following the recommendations of the 987 Watershed
Plan, but recent water quality sampling have shown these principle concerns are st 11 valid (ENSR,
1999).
The lake has seven tributaries which make up the primary contribution of flow o the lake. The
tributaries were assigned names in the Lake Cochichewick Watershed Plan w�hicA were originally
given by a North Andover Town water chemist while conducting a monitoring program. The project
site of this analysis is located in the subwatershed to the
is� hectares) w hick akeseupB 3 9%
Brook. Batell's Brook has a total watershed area of 3 4 acres
of the total tributary watershed to Lake Coe hich�e�vtcwithlth P rm remaining b inoamade Bp of
watershed is forested (43%), and residential (33%), upper reaches of this `�''atershed has
pasture, and open land (ENSR, 1999). The residential de��awl�en the11987 study was prepared (IEP, 1987).
increased from a total watershed percentage
The proposed project, assuming the entire lot area is developed would add less than 03p/o to the total
residential area in the Batell's Brook watershed.
i
Oct- 14-99 02 : 17P North Andover Com. Dev . 508 688 9542
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The project site is located within upper reaches of the Batell's Brook watershed. Existing land use is
primarily undisturbed wooded uplands and wetlands. Stormwater runoff under existing conditions
flows overland to wetlands on the east and west property boundaries. The wetlands to the east and
west of the property are tributary to the large wetland on the north side of Dale Street which forms
the headwaters to Batell's Brook. Batell's Brook from this point flows in an easterly and then
northerly direction through a system of wetlands and small ponds to Lake Cochichewick The
shortest now path from site boundaries to the lake is estimated at 1.34 miles (2,160 meters).
Proposed Project
The proposed project entails the development of a single family house lot adjacent to existing
roadway and necessary infrastructure. The proposed home is to be serviced by Town of North
Andover sewer and water lines and therefore no septic systems will be installed alleviating a major
potential source of nutrient loads. The proposed project has been designed to minimize land
disturbance and the associated water quality impacts by placing the actual home location as far away
from the wetlands as possible and limiting grading by blending the house lot into the existing
topography. Site plans limit the actual disturbance area to the one-acre site at 6,500 sf to
accommodate the structure (1,613 so and the driveway (1,200 sf). For the purpose of this analysis, a
more aggressive grading plan was assumed using a disturbed area more than triple what is proposed
maintaining the limit of the 25-foot wetland setback giving a total disturbance area of 20,000 sf.
This was assumed to be a reasonable maximum disturbed area for the lot. The proposed roof runoff
is directed to a rooftop leaching system located on the western side of the proposed structure. The
disturbed portion of the lot and the proposed driveway are graded to drain toward Dale Street to be
collected in the roadway storm system.
Phosphorus Loading
In-lake phosphorus concentrations are often the determinant of the trophic st to of a lake.
Phosphorus is generally the controlling nutrient for algal growth. The watershed plan prepared by
Phosph b
IEP (1987) documented monthly sampling during 19$� and 1986 to showy mean to-lake
concentration of phosphorus of 20 parts per billion (ppb). Data collected for the years 1994-1996 by
the North Andover Water Department showed the same in-lake co cen ati n lap all
at 1,x83
calculation of the average annual phosphorus load to Lake Cochiche
lbs/yr (ENSR, 1999). This suggests Lake Cochichewick falls into the category of a esotrophic lake
which typically ranges between 10.0 to 25.0 ppb (EPA, 1990). Average concept ations of total
phosphorus at the tributary discharge locations were elevated to high (25pp and 50 ppb
respectively) in the 1985-1986 period and consistently high during the 1993-1997 period. This may
suggest some increase in the watershed phosphorus contribution but the limits of the data (frequency
and conditions of sampling, detection limits) do not allow for a strong or substanti 1 comparison
(ENSR, 1999). From the data which are available it is evident that the loads into th lake may be
of
increasing and are not declining despite the attempts of watershed management by the town. One
the goals of the 1999 watershed study by ENSR was to detennine the potential ro e of internal
recycling as a threat to water quality. Although change in the
values wmere n1 ch highe ientthteo199of
phosphorus has been undetectable, maximum hy�p
1997 data set. Again the limits of the data limit the conclusions that can be made, 1 ut it appears
Oct- 14-99 02 : 18P North Andover Com. Dov _
508 688 9542 P . 05
d'ments has evident that the internal release of phosphorus from bottom hat he tributaries appear r
to still be the
Watershed Plan(ENSR, 1999). The ENSR study concluded
largest load of phosphorus to the lake but the potential load from ed e external inputs to one which is
g y governed y
ignored. The lake could be changing from a system g the process of
driven p ven by the internal process of recycling which commonly occurs during
eutrophication.
Phosphorus loading estimates are developed using the loading
the loading ssource d from methodology
p
provided in the Watershed Plan (IEP, 1987). This analysis her
's adjacent to and drains directly into the lake. In other wordsesta loadineIn coef is ent for forested
i ]
meters) of downstream drainage path does T11 relis no di Plan differentiation for loading between forest and
wetland of 0.18 lbs/ac/yr, (0.20 kgfha/yr).
forested wetland. Table 18 on page 67 of the Watershed Plan uses a "most likely t residential
f The original source for coefficients for use in
loading coefficient of 0.38 lbs/ac/yr (0.43 kg/ha/yr)• The 1.0 Ibs/ac/yr
the Plan (Reckow, 1980} uses a loading coef oleffi ient l and Sis cconsistent with ythe total residential
is used as a more conservative loading c
contribution estimate which is discussed on page 69 of the Plan.
Existing conditions on the 1.0 acre (0.4047 hectare) site is wooded wetlands and uplands. The
E g using the above
existing annual load of phosphorus from this site
retention and annuual0load reduction in the
assumptions. The mitigative properties of phosphorus
downstream wetlands and ponds between the site and the e mitigative ative propertie d°�vnst earn to
under existing or post development conditions. Were the g
considered, the annual load would be significantly reduced from that calculated abo4.
Under proposed conditions the site is represented by
0.46 acres (0.186 hectare) of residential
in a threefold increase to the area of disturbance as shotirna on the n undistu bed d plan, and 0.64
assum g
acres (0.256 hectare} of wooded wetland and upland which wtl re
Under proposed conditions the site is estimated to contrib account for sreducttionslto he proposed
U p p
increase of 0.4 lbs (0.1S kg). Again, these calculations do not
loadin s which would occur due to mitigative properties of downstream areas before discharging to
g
the lake.
e im act on Lake Cochichewick from the increase in phosphorus loading is analyzed using a
Th p
modified version of the input-output model developed by Vollen preferred method of1evaluati The and
o�ned
mod
widely used model has gained international acceptance as the pr
model is modified to analyze relative changes in phosphorus loading to determin trophic state
relationships and is expressed below. ,
,Tp = AL (1/(V 4p + P))
where: ATP =the change in in-lake total phosphorous concentration in ppb
AL
= the change in total phosphorous loading in kg/yr
V =Lake volume in in x 10° i
p =Lake flushing rate per year
Oct-14-99 02 : 19P North Andover Com. Dev . 508 688 9542
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Using a lake volume of 16.2 x 106 m' and a flushing rate of 0.57 per year, it is estimated that the
maximum impact of the proposed project would be an increase to in-lake phosphorus concentrations
an in-
of 0.01 ppb.. The total phosphorus data collected by verified h a Watershed Plan
in the emoreerecent
lake concentration of 20.0 ppb (1987), which was g
investigation (1999}. Therefore the estimated increase in phosphorus concentration would represent
less than 0.05% increase over mean annual levels. Given today's standard analytical techniques the
estimated increase in proposed levels is essentially immeasurable and well within the expected range
of natural variability.
The results of this phosphorus analysis are on the man nattural side and
mitigative structures downstream
be much less than has been estimated due to the y
This proposed residential house lot which is tributary to ,h l 25-foot, treated first be th natural
lter
wooded filter strip which will be maintained as required y t7). The extensive
strips can remove up to 60% of the total phosphorus etlandscwulll also rgduce the phosphorus lloads
which exist downstream of Dale Street and the site
The EPA (1983) reported that wetlands have been found to be greater than 80% efficient in
removing phosphorus except during winter months treat the runoff from dtl�e site before he ponds downstream of the wetlands will even further
to the lake. Wet ponds such as this are expected to remove 80% of phosphorous loads (Scheeler,
1987).
Nitrogen Loading
loading analysis was performed to determine if average annual concentranti�is of o i will be A nitrogen
would exceed the lOmg/l drinking water standard. All of the nitrogen loading o
in the form of stormwater runoff as no septic systems 'se be
systemsd and la vi hfertilizers.
coefficients for residential areas include contributions from p
Loading coefficients were not reduced because of eotos being gingulardCOntrib bons sewer m as is a
lack of information concern ing the weighted proportions
septic systems or fertilizer use alone. The empirical total nitrogen coefficients e for
ur si e tial and for
forested areas are 5.3 (5.9), and 2.5 lbs/ac/yr (2.8 kgfhaiyr), annual
Based on the above coefficients for loading and the existing and proposed site plans,ns, tl ons and 04
site export of total nitrogen is estimated as 2.5 lbs l
yr (1.13 g/yr) nder
Ibs/yr (1.82 kg/yr) under proposed conditions. The watershed plan presented a ual runoff at
approximately 20 inches (510 mm) for the Lake Cochichewick watershed. Therefo the one acre
0.4047 hectare) parcel has a total annual site runoff volume of 0.072 o 8 6 t' (l 0.2t X 10'1) and the existing and
average annual nitrogen concentration The nitroi estimated 1 d levels in runoflleaving the site will be well below
proposed conditions respectively. g
the 10 mg/l drinking water standard even when "using the conservative i loading coefficient which
assumes the use of septic systems which will in fact not be a p s project.
Oct-14-99 02 : 20P North Andover Com. Dev . 508 688 9542 P . 07
Suinmary and Conclusions
The nutrient loading analysis which has been based on conservative assumptions has shown minor
increases in both phosphorus and nitrogen export with the proposed plan. The minor increases will
have essentially no impact to the water quality of Lake Cochichewick. The downstream natural
BMPs including the wooded filter strip left undisturbed, extensive wetland systems and several
ponds along the course of the brook which will remove a considerable proportion of the nutrient load
from site runoff, but were not accounted for in this analysis, give further assurance that water quality
impacts from the proposed project will not be realized. In addition, the loading calculations
presented here assumed a site disturbance area of 20,000 sf when the present site plan calls for a
disturbed area of only 6500 sf. An actual disturbance area of less than 20,000 sf would further
decrease the expected negligible impacts to Lake Cochichewick.
Based on the results of the enclosed evaluation and analysis, it is our professional opinion that there
will be no significant degradation of the quality of water in or entering Lake Cochichewick as a
result of the proposed project.
References
ENSR. February 1999. An Evaluation of Water Quality and Management Options in Lake
Cochichewick and Its Watershed, North Andover, Massachusetts.
Environmental Protection Agency (EPA). 1990. The lake and reservoir restoration gui ance manual.
Second Edition EPA 440/4-90-006.
Environmental Protection Agency (EPA). 1983. Results of the Nationwide Urban Ruoff Program.
Volume 1. Final Report. Water Planning Division, Washington D.C.
IEP. 1987. Lake Cochichewick Watershed Plan. Final Report, August 1987.
Massachusetts Department of Environmental Protection and Office of Coastal Zone Management.
Stormwater Management. Volume One: Stormwater Policy Handbook. March 1997.
Reckow, K.H., M.N. Beaulac and JT Simpson. 1980. Modeling phosphorous loading and lake
response under uncertainty: A manual and compilation of export coefficients.
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and design urban
BMPs. Metropolitan Washington Council of Governments.
Vollenweider, R.A., 1976. Advances in defining critical loading levels for phosphorous loading in
lake eutrophication. Mem. Ist. Ital Idrobiol 33: 53-83.
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