Conservation Commission Meeting Agenda/Materials 109R and 131 Clark Lane Exhibit List (linked)

UL
FEB 06 2023
Attached —
2009 AND 2012
University Of New
Hampshire Reports
Bioretention Systems
PUBLIC HEARING
| (CSE y \//! ) |


009: UNH Report
Bioretention
Systems
About Bioretention Systems
Bioretention systems, also known as “rain
gardens,” are among the most common LID
stormwater approaches in use today. In general,
runoff flows into landscaped depressions, where
it ponds, filters through a soil mix, and infiltrates
into the ground, or is connected to storm drains.
The engineered soil mix and vegetation mimic
the water quality treatment and infiltration
similar to undeveloped areas. Soil mix design
is essential to the performance and longevity
of these systems. While the mix must contain
enough fines and organic matter to sustain
vegetation and slow down infiltration rates,
too much of these components may cause
systems to clog prematurely eliminating any
water quality benefits. There are soil mix
specifications available to support designers
in successfully implementing bioretention
systems in a wide range of site conditions.
UNHSC has evaluated many such systems;
this report looks at a design we call “Bio II.”
Implementation
Bioretention systems can be used throughout
the United States, and their acceptance and
implementation varies regionally. However,
an increasing number of states require a
level of water quality treatment and volume
reduction that only can be achieved through
CATEGORY /
Cece (Vegetative Uptake),
the incorporation of LID designs like bioreten-
tion. In some regions, local acceptance is
hindered by lack of performance data, unfamil-
jarity with the design, and suspicions about
seasonal functionality.
To achieve maximum volume reduction,
bioretention systems should be located in
soils that accommodate infiltration, such as
those in group “A” (sand, loamy sand, or sandy
loam with high infiltration rates) and “B” (silt
loam or loam with moderate infiltration rates).
Careful site analysis is required to design an
effective, integrated network of these systems
that allows infiltration throughout a site.
Bioretention systems can also be used to
great effect in areas with poor soils, where
pre-development infiltration would have
been minimal. These systems in poor soils
will require underdrains to ensure proper
drainage and treatment.
UNHSC research is showing that bioretention
systems are most effective when they serve as
local source control devices, intercepting and
managing relatively small areas of impervious
cover in a well-distributed network of runoff
control measures. They can be used as an
end-of-pipe system; however, such usage
requires a more sophisticated design for the
system to function properly, particularly when
Forebay: 14 ftlongX INSTALLATION CosT
HREESER AE ¢ Chemical (Some 8 ft wide $18,000 per acre
nfiltration, Low orption possible 5
i Impact Development with trated design) Total Area: 272 sf MAINTENANCE 0
-4 ‘ aa e i ¥
= Design BEeneuOsce SPECIFICATIONS Aaipteralce iy 8
UNIT OPERATIONS Low Impact Develop- Catchment Area: : yi AY
UNHSC research is showing that bioretention eC ESSES ment Center, Maryland Lacre Inspections: Low wm
systems are most effective when they serve as Hydrologic Z Water Quality Flow: Sediment Removal: i
local source control devices, intercepting and (Flow Alteration) BASIC DIMENSIONS icfs High i
managing relatively small areas of impervious Water Quality: Physical Filtration Basin: Water Quality
cover, in a well-distributed network of runoff (Sedimentation, 8 ft wide X 34 ft long Volume: 3,300 cf
control measures, Filtration), Biological X 2.5 ft deep
How the System Wi WATER QUALITY TREATMENT OCESS
1. Runoff flows into a sedimentation 3. Nutrients like nitrogen are taken up 4. The treated runoff can be allowed to
forebay or other pretreatment by the roots of the vegetation and infiltrate the native soils, or collected
chamber. From there, it is slowly metabolized by the system’s plants, in a perforated subdrain and returned
released into the filter basin through shrubs, and trees. to a storm drain system or discharged
a perforated standpipe. When forebay yi to the surface.
capacity is reached, the overflow
spills across a weir into the bioreten- “ ‘
tion basin. is Perforated standpipe Perforated riser
with 1” orifice plate (CPy overflow) 12” Qy Bypass
2. Biological treatment occurs through
the uptake of pollutants by vegetation
and soil microorganisms. Physical and
chemical unit operations and processes
that occur within the soil media
include sedimentation, filtration,
and sorption with organic matter
and mineral complexes.
Geotextile on walls
Of exc
6” Perforated
subdrain
Not drawn to scale,
20 vertical exaggeration

ATT. B2: 2009 UNH
NHSC Pollutant Removal Effi
ep
TPH-D
Treatment Unit Description Reference | total Meat feanes! in ‘titel rte Total nanan “peak Fom eo eerie
Sollds (% Removal) un lee se anny (He Removal) (Ch Removal) reacren (Minutes)
ConVentional Treatment Devices
Retention Pond UNH 68 82 33 68 NT 86 455
Stone (rip-rap) Swale UNH 50 33 NT 64 - 6 7
Vegetated Swale UNH 58 82 NT 88 NT 52 38
Berm Swale UNH 50 81 NT 50 8 24 58
Deep Sump Catch Basin UNH 9 14 NT NT NT NT NT
Manufactured Treatment Devices (MTDs) |
ADS Infiltration Unit UNH 99 99 NT 99 81 87 228
StormTech UNH 80 93 NT 56 49 76 274
Aquafilter UNH 62 26 NT 52 59 NT NT
Hydrodynamic Separators UNH 27 1 NT 24 42 NT NT
Low Impact Development (LID)
Surface Sand Filter UNH 51 98 NT 77 33 69 187
Bioretention
Bio I - 48” depth UNH 97 99 44 99 - 75 266
Bio II - 30” depth UNH 87 99 NT 68 34 79 309
Gravel Wetland UNH 99 99 98 99 56 87 251
Porous Asphalt UNH 99 99 NT 75 60 82 1,275
Pervious Concrete UNH 97 99 NT 99 NT 93 1,144
Tree Filter UNH 93 99 3 78 NT NT 62
Removal Efficiencies
TSS rotatetateum | NO3-N (DIN) TZn 1?
Treatment Unit Description Reference ane Heel ieee Ha Inorganic Hitrogen anon) ret pheariens
(ts Removal) (% Removal)
Sub Surface Detention/Infiltration EPA Fact Sheet: Infiltration Trenches = - - 60
Sand Filter EPA Fact Sheet: Sand Filters 70 - NT 45 33
Claytor & Schueler, 1996 85 - - 7A, 50
Bell, W., et al, 1995 61-70 - - >82 =
Winer, R., 2000 87 = NT 80 59
Retention Pond EPA Fact Sheet: Wet Detention Ponds 50-90 - - 40-50 30-90
EPA Fact Sheet: Wet Detention Ponds 80-90 - - - -
Bioretention Winer, R., 2000 79 - 36 65 49
EPA Fact Sheet: Bioretention 90 - - - 70-83
Bio - 12” depth Winogradoff, 2001 - - -97 87 NT
Bio - 24” depth Winogradoff, 2001 - - -194 98 73
Bio - 36” depth Winogradoff, 2001 - - 23 99 81
EPA website 84 - - - -
Hydrodynamic Separators various 52-84 - - = 30
Gravel Wetland Claytor & Schueler, 1996 80-93 - 75 55-90 80-89
Winer, R., 2000 83 - 81 55 64
Vegetated Swale EPA Fact Sheet: Vegetated Swales 81 - 38 71 9
Claytor & Schueler, 1996 30-90 - 0-80 71 10-65
Porous Pavement NAPA, undated 89-95 - = 62-99 65-71
EPA Fact Sheet: Porous Pavement 82-95 - - - 65
Winer, R., 2000 95 - = 99 65
11

treating one or more acres of impervious cover.
As with any infiltration or filtration system,
when used in pollution hotspots or poor
soils, they should be lined and outfitted
with subdrains that discharge to the surface.
System Performance
Cost & Maintenance
The cost to install Bio II to treat runoff from
a one-acre parking lot was $18,000. However,
UNHSC expects this cost to come down as
installers and designers gain familiarity with
the systems. The Center installed a third
bioretention system in 2007 at $14,000 per
acre for the total cost; labor and installation
were calculated to be $8,500 per acre, and
materials and plantings cost $5,500 per acre.
This indicates that for a municipality that has
both equipment and personnel, the cost for
retrofits is nearly $5,500 per acre of drainage.
Bioretention systems are designed to minimize
maintenance. Generally, the highest maintenance
burden is in the first three to four months, as
the vegetation grows and the system begins
to stabilize. Once vegetation is established,
the maintenance decreases and becomes similar
to that required for standard landscaping, such
as seasonal mowing, raking, and pruning of
vegetation. Systems with fine media may
require more frequent attention due to
clogging. However, since most clogging occurs
on the surface, servicing these systems is
simple. Long-term maintenance may involve
routine inspection and occasional scraping
and removal of surface fines.
Cold Climate
Bio II's ability to treat water quality and
control water quantity remained relatively
consistent in all seasons. UNHSC researchers
have observed that most LID stormwater
systems, when properly designed and installed,
are not negatively impacted by cold climate.
In fact, these systems showed fewer
seasonal variation than many conventional
approaches that depend on sedimentation
as the primary unit operation. While some
seasonal variation did occur in Bio II, 100
significant design alterations do not z A
appear to be necessary for cold weather ¢ 70
applications of this system. £ 60
DT)= 50
Water Quality Treatment g 40
Bio II has proven effective at removing & a
nearly all of the pollutants commonly 2 10
associated with stormwater treatment 0
performance assessment. It consistently
exceeded EPA’s recommended level of
removal for total suspended solids and
meets regional ambient water quality
criteria for petroleum hydrocarbons. This
system had lower removal of nitrogen and
phosphorous than the previous bioretention
system tested at the UNHSC. This may be
due to reduced contact time and/or less
dense root mat. These design variations
are being examined in Bio III and Bio IV
presently, Like the other systems monitored
at UNHSC, Bio II does not provide chloride
removal, although it does exhibit an ability
to dampen chloride peaks.
350
= 300
5 250
= 200
2 150
The chart at top right reflects the = 100
bioretention performance in removing
TSS
sediments
48
POLLUTANT REMOVAL: 2006-2008
Summer © Winter 1 Annual |
TPH-D DIN
total dissolved
petroleum | inorganic
hydrocarbons | nitrogen
754 ug/L | 24
Z
metalsn TP
total |
phosphorus
Median Annual Influent Event Mean Concentrations (EMC) in mg/L
043
09
HYDRAULIC PERFORMANCE
—=Influent —Effluent
total suspended solids, total petroleum 0
hydrocarbons, dissolved inorganic
nitrogen, total phosphorus, and zinc.
Water Quantity Control
100
Minutes
Average Peak Flow Reduction
Like other infiltration and filtration systems,
Bio II has a tremendous capacity to reduce
peak flows and runoff volume in appropri-
ate soils, i.e., those belonging to groups
Aand B. In the figure at bottom right, Bio II
demonstrates effective peak flow reduction and
large lag times regardless of season. Vegetation
contributes to stormwater volume reduction
through the process of evapotranspiration.
SYSTEM DESIGN
Bio II is comprised of a sedimentation forebay
and a bioretention filtration basin. The basin
is filled with a 30 inch bioretention soil mix
(BSM), consisting of 60 percent sand, 20 percent
woodchips, 10 percent compost, and 10 percent
native soil. The filtration basin is well vegetated.
Researchers selected vegetation for flood and
drought tolerance, the capacity for maximum
ground cover, and aesthetics.
The forebay holds 25 percent of the water quality
volume (WQ,), and drains through a stone level
spreader into the bioretention basin, which holds
75 percent of the WQ,. The basin allows eight
inches of ponding, and the BSM has an infiltration
rate of eight feet per day. Overflow contingencies
exist for channel protection volume (CP,) and
conveyance protection volume (Q10) events.
Typically Q2 events are conveyed over 24 to 48
hours, and Q10 events bypass to the surface.
The appropriate BSM design is important to ensure
adequate drainage, support plant growth, and
achieve water quality treatment objectives. It is
important for soils to slowly percolate enough to
achieve high quality treatment, yet fast enough
to filter sufficient volumes of water such that the
filter area not be inordinately large. Bio II's BSM
specifications were developed with input from the
Low Impact Development Center. The resulting
BSM had reduced silts and clays of about 6 percent
maintains an infiltration rate of approximately
8 feet per day, and had about 3 percent organic
matter. Results indicate that this BSM had reduced
removal performance for nitrogen and phosphorus,
in comparison to Bio I that had an infiltration rate
of 0.5 feet per day.
UNHSC is currently studying BSM for two other
designs with high infiltration rates that use outlet
controls to slowly release the WQ,. One with 8
percent fines and 10 percent organic matter, and
infiltration rate of 100 feet per day, and another
with 10 percent fines, 7 percent organic matter,
and an infiltration rate of 40 feet per day. Soil
chemistry is important, especially when target-
ing phosphorus reduction. BSMs must contain
relatively low levels of phosphorus to maintain
a sorption capacity that can remove phosphorous
from runoff. Studies from North Carolina State
University recommend BSMs with a Phosphorus
Index (P-Index) of 25 to 40.
Average Lag Time (minutes)
Winter
76%
376
150 200
Annual
Summer Average
82% 79%
254 309
21

2012 UNH REPORT
02
gt
Gd
aes
TLO'L
SLe'L
TL6E
19
gte
60€
992
L8L
iN
iN
iN
SEZ
822
iN
8S
T€
66
€6
2
26
56
98
6L
SL
69
AN
iN
iN
gL
Lg
IN
ot
es
£6
iN
%66
iN
%LS
8S
iN
VE
EE
iN
AN
he
2S
1B
iN
AN
iN
“poyzau 4seq B42 4o UWL] UO!IIaIIq Mojeg SI 3eY3 aNjen e SazeD1pUul Tag,
90°0
10g
s9°0
00
20°0
90°0
s0°0
50°0
90°0
s0°0
TL'0
50°0
€0°0
20°0
£0°0
60°0
oro
L400
€1'0
90°0
80°0
90°0
40°0
£0°0
80°0
210
S00
60°0
L0°0
L0°0
21-0
80°0
£0°0
80°0
ouny
be7
di
SL
%66
SL
SL
78
LO
SL
PEL
66
LL
ole
92
EY
%L9
%66
IN
0S
0%
679
%0S
89
100
10a
10°0
100
1070
100
100
20°0
10a
100
20°0
0°0
20°0
100
109
700
20°0
200
200
200
t0°0
700
s0°0
€0°0
70°0
70°0
€0°0
€0°0
90'0
L0°0
90°0
£0°0
s0°0
0°0
£0°0
S00
700
€0°0
400
L400
€0°0
s0"0
66 1a = 70
AN
sO
£0
iN
20
20
iN
70
70
iN
£0
0
iN
sO
£0
(feu)
uabos34y 2tieB10ur panjossia
(NIG)
N-€0N
66
$66
F066
66
66
%%S9
79
66
66
86
99
27
99
%T6
66
YL
18
28
WEE
VL
28
mlei:)
10a
aa
10a
10a
SOL
€9L
da
10a
av
08st
ey
9ST
sy
108
ory
19
Loz
ose
SOL
Oot
Te9
org
OLE
Teg
799
S67
osy
OSL
862
8g
ols
LL
€LS
os
992
ots
£69
OTL
08s
067
OLL
(i/bn)
sbuey
jpsera
ain
ur
16
66
S83
66
%96
WES
16
LB
%L6
1S
SL
62
29
ES
%66
6
60S
69S
0S
6L
$89
108
IL
108
TW
Te
62
tL
€L
108
ve
€2
OL
ST
oT
0€
Te
1s
TOL
Oz
8y
LE
sy
O2t
Ww
82
8
67
87
1S
87
0€
EL:
SS
(1/5)
spies
papusdsns
jrioy
Yy224 W035
u01}d119Seq tun JUueUjeeI)
11

2012 UNH REPORT
Bioretention
Systems
Bioretention systems are the workhorse of
LID approaches and offer flexible, adaptive
and reliable treatment of stormwater runoff.
Issues in Focus
About Bioretention Systems
Bioretention systems, also known as “rain
gardens,” are among the most common Low
Impact Development (LID) stormwater approaches
in use today. These systems consist of land-
scaped depressions which collect runoff that
subsequently ponds, filters through a soil mix,
and infiltrates into the ground, or discharges to
the surface. The UNHSC has evaluated many
different bioretention systems; this report
specifically examines four bioretention designs
(Bio 1, Bio 2, Bio 3, and Bio 4), two of which
are new, and two of which have been studied
and reported on previously. While structural
variations exist, the main differences between
these systems relate to the composition of
bioretention soil mix (BSM) - namely sand,
compost, wood chips, and loam.
Implementation
Bioretention systems are used throughout all
areas of the U.S., but their acceptance and
implementation varies regionally. An increasing
number of states are requiring higher levels of
water quality treatment and volume reduction
that only can be achieved through the
incorporation of filtration and infiltration
designs like bioretention systems. In some
regions, local acceptance is hindered by lack
of performance data, unfamiliarity with the
design, concerns over maintenance, and
suspicions in regards to seasonal functionality.
To maximize volume reduction of stormwater
runoff with bioretention systems, they should
be located in soils that accommodate infiltra-
tion, such as those classified as hydrologic soils
group “A” (sand, loamy sand, or sandy loam
with high infiltration rates) and group “B” (silt
loam or loam with moderate infiltration rates).
BIOR
Hydraulic Loading Ration
fem | com | s_| ein | Vegetation Cover Drainage Area: Filter Area —
NTION SOIL MIX COMPOSITION
System Performance
Cost
The installation costs associated with the
bioretention systems implemented by UNHSC
ranged from $14,000 to $25,000 per acre of
impervious cover “IC” treated. These costs will
moderate as installers and designers gain
familiarity with the systems. In 2007, UNHSC
installed Bio 4 in a vegetated parking lot median
strip as a retrofit at a total cost of $14,000 per
acre, including $8,500 per acre for labor and
installation, and $5,500 per acre for materials
and plantings. These findings indicate that for
municipalities with equipment and personnel,
the retrofit costs are nearly $5,500 per acre of
drainage. These costs do not include design,
permitting, or construction supervision costs.
Maintenance
Bioretention systems are designed for minimal
maintenance. As indicated by the graph in the
bottom right, the highest maintenance burden
occurs during the first two years of operation
as the vegetation grows and the system begins
to stabilize. Once vegetation is established,
maintenance decreases and becomes very
predictable, similar to what is required for
standard landscaping. Common maintenance
tasks include seasonal mowing, raking, and
pruning of vegetation, Beyond two years,
long-term maintenance tends to level off and
involve more routine and schedulable mainte-
nance activities. The average of all mainte-
nance costs and personnel hours required for
the bioretention systems studied at UNHSC
were $1,820 and 21 hours of labor per year
per acre of IC treated, respectively.
Infiltration rates (IR) are easily measured in
bioretention systems using standard methods
(ASTM D3385 - 09) or even more simply with
instruments like the Turf-Tec Infiltrometer. At
the UNHSC, IR was measured for all bioreten-
Bio-1 2004 45% 10% 45% 0% Vos an 5 2004 4.2 2%
Bio-2 2005 60% 10% 10% 20% eee 160:1 2005 2.9 7%
Bio-3 2009 60% 10% 10% 20% Eco-Lawn 160:1 2009 6.6 10%
Bio-4 2008 || 70% | 30% | (om | (om |) pralieMeadow 321 2008 9.9 8%
Perennial
The soil mix used in the bioretention systems is central for determining flow control and water quality treatment performance. Hydraulic conductivity of bioreten-
tion soil mixes is variable and usually trends toward higher infiltration rates than originally designed for. Infiltration rates of BSM mixes are strongly correlated to
the percent that passes the 200 sieve and guidance largely suggests that the fines should ideally be between 2-5%. Current research shows variable nitrogen and
phosphorus removals and that additional research is needed to optimize bioretention systems for nutrient treatment.
20

tion systems studied. The figure below
compares IR over the range of bioretention
systems. Of particular interest is the decline of
IR over time for 3 out of the 4 bioretention
systems. This can be predicted and is likely due
to the accumulation of fine materials on the
surface of the filter. The IR reduction rate can
be used to schedule cleanings and maintenance
of the filter.
In contrast to the other systems vegetated with
native perennial plants, the Bio 3 system was
different in that the basin was vegetated with
a conservation mix often used for detention
basins), and contained a continuous dense
vegetative cover, Previous studies have indicated
that plant roots generally experience a 30% die
back each year which aids in the development
of macropores that keep soil surface IC high
over time. The data from this study seems to
suggest that dense vegetative cover is more
important than plant type for maintaining IR
in vegetative systems. If aesthetics are not
a concern, then it is conceivable that grassed
bioretention systems could reduce overall
maintenance burdens in bioretetnion systems.
Cold Climate
The ability for bioretention systems to treat
water quality and control water quantity
remained relatively consistent in all seasons
over the range of systems monitored. UNHSC
researchers have observed that most LID
stormwater systems, when properly designed
and installed, are not negatively impacted
by cold climate,
Water Quality Treatment
All bioretention systems have proven effective
at removing sediment-bound pollutants
commonly associated with stormwater treat-
ment performance assessments. Additionally,
the systems consistently exceed EPA’s recom-
mended level of removal for
total suspended solids and
achieved requisite removal
WATER QUANTITY CONTROL
for petroleum hydrocarbons Systems Winter Summer Average
and metals (TZn). However, | |
the performance for nutrients | ifjgaciistay | | | |
is more variable. With the : a
exception of Bio 2, the range Average Peak Flow Reduction 77% 74% 75%
of systems consistently Average Lag Time (minutes) 408 108 266
removed dissolved inorganic j |
nitrogen (DIN). A consistent als Ee 1
trend with respect to percent — Average Peak Flow Reduction 74% 85% 79%
removals was apparent in . . 265 309
that a definite seasonality AvetegerLag Time (minutes) eg
and a virtual ceiling at Bioretention 3 | ee ee
40 ~ 45% removal were Average Peak Flow Reduction 84% 85% 84%
observed. Exceptions include
Bio 2 which had no real Average Lag Time (minutes) 215 217 216
DIN removal. This may be Bioretention 4 | | |
due to a less dense root mat
and a reduced filter area Average Peak Flow Reduction 94% 95% 95%
caused by shading and Average Lag Time (minutes) 52 67 61
pedestalling from woody
vegetation. Over time woody
vegetation can crowd and shade out
bioretention areas and may not be
BIORETENTION PERFORMANCE
suitable for this application, Total
Phosphorus (TP) treatment performance
was variable but trended toward
9
efficiencies of roughly 20-30%, and may 100%
be maximized by limiting phosphorus 80%
levels in the design BSM. The chart at the
right reflects bioretention performance 60%
in removing total suspended solids, total
petroleum hydrocarbons, total zinc, 40%
dissolved inorganic nitrogen, total
nitrogen, and total phosphorus. 20%
0%
MBio1 Bio2 MBio3 MBio4
| |
TSS -TPH-D Zn DIN TN TP
NA = pollutant not monitored
BIORETENTION
| Cost MM Hours
3,500 50
BSM INFILTRATION RATES y re
2,500
30
INFILTRATION RATES OVER TIME 1,500 5
Myr yr2 Ml yr3 500 10
70
0 0
yrd yr2 yr3 yr4
50
30
20
10
oo
Bio I Bio Bio II Bio IV
Cost $
Hours
Infiltration Rate (in/hr)
&
The accepted optimum infiltration rate for bioretention soil mixes ranges between
0.5 to 12 inches per hour. Sandy bioretention soil mixes should provide excellent
water quality performance with respect to most sediment associated pollutants.
Designs with safety factors >3 should consider orifice control in bioretention
underdrains in N and P sensitive watersheds, UNHSC research indicates that more
robust vegetative cover is higher in importance as compared to plant selection
or placement in maintaining long term surface infiltration rates. 21