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Appendix I
Best Management Practices (BMPs)
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BMP/Design
ExtendedDetcntion Pond
Design 1 ~
Design 2 .
Wet Pond Design 3 .
Design 4, ())
DesignS &
Design 6 .
Infùtnûon Trench
Design 7
Design 8
Design 9
Infùtration Basin
, Design 7
Design 8
Design 9
Porous Pavement
Design 7
Design 8
Design 9
w~ Quality Inlet
Design 10 0
Fùter Strip ,
Design 11 fð,
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Grassed Swale
Design 13 0 0 G 'ø
Design14 fð ø 0 'ø
Design 1:' FIlSt..flush nmoff volwne detained for '
6-11bours. '
Dulgn 2: Runofholume produced by 1.0 inch.
, ',', detained 24 bouts.
Design 3: As in Design 2. but with shallow manh in
bottom stage.
~sign4: ~ent pool equalto 0.5 inch storage
per imercious acre.
Design 5: Permanent pool equal to 2.5 (Vt); where
'it = mean stomí nmoff.
, Design 6: Permanent pool equal to 4.0 (Vt): approx.
1 weeks retention.
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Design 7: Facility cxfitratcsfust-flusb; 0.5 inch
nmoffJimpervious acre.
Dulgn 8: Facility exfùtrates one inch nmoff volwne per
, imperviouS acre.
Design 9: Facility exfùtratcs alhunotT. up to the 2 year
design storm.
, 1)esign 10: 400 cubiè feet wet sunge per impervious ICtC.
Design 11: 20 foot wide turf strip.
Design 12: 100, foot wide forested strip. with level spreader.
Design 13: mgh slope swales, with 110 check dams.
Design 14: Low gfadient swales with èheck dams.
F181JrC 16: Compuativc PoUutlnt llemovll OfUtbm BMPDesips
SO/ITU: Thocus 1. Scbuelcr. CDiVrollinf' UrlHJn RUM/!: A Practical Manaallor Pltwùng twl Dui,1ÛnI Urban SMPs. (MCIl'Opolitan
WlSbin¡t.on CounciIotGovemmcnts, July; 1987) p. 26.
Dev~loþinq Effective BMP Systems tor Urban Watersheds
FtCiuttE 7 ,
Urbali Siormw.1U IWrofi, Techniques
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STANDARD POND SYSTEM DESIGN
CROSS·SECTION VIEW
safety st=rm stQra~e'
ba.'\Ió.lIlflcoC: $ora;a (2yr.)
vari;ë)le :D S".oragi!
per::'\2.:"Ient pool s:o:ag.
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Copyright 1991, ~tropolitðr\ washi."\gt:on Coonc:il of Goverruœnts
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POND DESIGN NO. 1: DRY ED POND SYSTEM
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POND DESIGN NO.2: EO MICRO?OOL SYSïEM
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POND DESIGN NO.3: SHALLOW EO MARSH SYSTEM
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POND DESIGN NO. G: SHALLOW MARSH SYSTEM
Co~ight 1991, ~tropolitan \"ashington Council of Gov'erments
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"-- Tef11:lOraty storage
'----
, Pennanent:-J" ,
~~ . ~ ' ,
sec.ment OrifIce. pia PVCprlncipal/ ' ' .'~ .
storage ,. required, spiUway pipe, " ,~et protection ~ .
, if required
Figure 6.1-6: Slotted rIs~r with PVC pipe,
Prefabricated slotted rISer
"
10/89
'.. ;...~.., ::::,...... ~. .~......~:~.
6.1·9
f B I Slotted Inlet
~ Removable cap,
0 plug or sctgen ~! 2"
, DO' Embankment' ". D. Rows of 1- x 4-
vef1Jcal slots
°or Slotted inlet ,,- centered.
o D See detaU. m E. Degrees around
,,- the cln::uri1fer·
lnee. See '
;~~ ... notes 1 & 2.
See detail ,Orifice plate
"
to ' . . ~. ;J'
~EIbow MlninlJm thickness:
.10· for metal or fiberglaSS \
See note '5.
.25" ,for PlasticorPVC
Principat spillway pipe with slotted riser
Standard DimensionsTable
A
In.
BCD E SlotareaMinimum wan thickness
in. In.' rows ,degr. ft2/1t. corrugated, smooth steet PVC
min. metal base In. In.
~
150--3.50 '6
3.75-5.50 . 8
f;.7s.G.OO10
,'NotesandCommeris
1. SIotted'lnIets shall be fabricated from cori)Jgated
metal. smooth steel or PVCpIastic pipe. Materials
shall have at least ~. miniinum waI thickneì$ given in ,
'the standard dimensions table. ' .'
....
6 6
8 IS
90
60
45
.161
.250
.383
16
16
. 16
.10
.10
.13
.15
.20
.2S
'.
5. Fabricated or $tandard .bow. fabricated Of
standard t.. witt main tile Bne or plug in upstream
,end, Of ~ard t.. with one eod embedded in
concrete.
"i
2. Slots shall 1M. cut clØanly and deburred. Ends of
slots may ~ ~undorsq JIU..
3. Orifice plate, cap and .. fittings shall be snug 8nd
securely f.ned. Orif1ce plate shall be cleanly cut
andfr.. of bUrrs with ~. take,,U'IOt to round the
edgeS. It should be . minimum 01 2.Of..t below
g~e fqr properfùnc:tlonfng.
4. The portion 01 the Inlet below grade may be·perfo-,
rated with a gráYeUltter for additlonat dewatering of
~; ,
6. The height if Inlet Is above the sediment pool level
, shall be such that the Velocity of ftow through the. slots
Is less than 2.0 feet per second. '
7. Head on the Orif1C8, I placed as suggested, may
1M figured by adding 0.7 times the maximum depth of '
Impounded water plus the- depth of the orifICe IMlow
, grade. Has a relatively constant rate 01 change.
Figure 6.1-7:StottedÌlSe" standard dimensions
6.1-10
10/89
.. ..... ..4 .- -
paMnQ ~
[1J1I1IUIIIO" ".nch ..ft1uUrIaCIlnlel)
~\" . .... AIt!tr striP '
't..t~ .
I-·...'~.........,,,.:( ,.',I......~·
-,,-.
Filter fabriC
Ines trenCh
., ~ Washed stone
.., ~ 'orgcavel ,
~ 6"-12" sand 1i1\er
. \ u_r<JU1ICIuinch_oIIIødt~ \
, r paved surface
( I . '
if' - overfloW to ~onn ~er
( I
I.
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~nn-
t· ,
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1
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grit separator'
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or grave'
, ':Jl:..'..
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If
lit
sewer
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. " .
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. ,washed stone
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, 10'minimum - J
, '
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. " . 6"-12" sand1\tter
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FIgure 4.4-1: ,.yp\C81 'nU\trat\on trencb use
101ß9'
4.4--'3
CHAPTER 5: INFILTRATION TRENCHES
Infiltration trenches are an adaptable BMP that effectively remove both
soluble and particulate pollutanu. As with other infiltration systeass t
trenches are not intended to trap coarse sediments. Grass buffers (for
surface trenches) or special inlets (for underground trendhes) IIUSt be
installed to capture sediment before it enters the trench. Depending on the
degree of st;orage/exfiltration achieved, trenches can provide groundwater
recharge, low flow aus-entationand 10éalized streambank erosion control.
Individual trenches are' priaaarily an on-site control~ and an Seldoll
practical or econOllic41 on sites larger than 5 or 10 acres. Trenches are
only feasible when soils are permeable and the water table and bedrock Are
sitU4t~d well below the bottoaa of the trench. Aside frOal,reguh.r.inspections
and aaore rigorous sedim~t and erosion control, trenches have limited routine
alaintenance ' requirements. However ~ trenches' will pretDatùrely clog 'if
: sedilllent is not kept out before, during and afterconstruc:,tion of a site. If
a trench does becOllle severely clogged,- partial or coaaplete replacetDent of the
structure lIay be reqUired. .
f
,Figure 5.1: Schematic, of an Infiltration Trench
. '
{oJ',
Emetg.~ Overftow Berm
Ob$efvation Well
,/
'.',>.
,.,..~ .. .
;"";'.' .
5.4
ChapterS: Infiltration Trenches
DESIGN 1:
Median Strip Desi~ (Figure 5.2). This design is frequently used
for highway .edian strips and parking lot "islands" (depresSions
in between two lots or adjacent sides of one lot). Sheet flow is
accepted from both sides of the trench. and is filtered through a
20 foot wide grassed buffe'r strip. The strip is an integral part
of the trench, and should b. graded to have a unifona slope not
greater than S%, and should directly abut the contributing
impervious, area. Benaslocated on each side of the strip form a
shallow depression that temporarily storeS runoff before it enters
the trench. An overflow pipe is used to pass eXcess runoff., .
Figure 5.2: Medi~n Strip Trench Design
,Top View
Sid~. View
Inflow
20·G..... Alter Strip
. Sc:mned ove,ftow....
~
Outflow
.-'
. Chaptu 5: Infil1::ration Trencbes
5.S
DESIGN 2.:
Parkinx Lot Perimeter (Figura 5.3). This design accepts sheet flow
frOll! the lower end of a parking lot. ,Slotted curb spacers are used
as level spreaders to route sheet flow from the parking lot over
the 2.0 foot wide filter strip (and also keep C&r$ froGl damaging tbe
strip). After being filtered over the grass strip, runoff enters
the surface of the trench. A shallow berm is installed at the fÀr
end of the trench to ensure that runoff does not escape. The
,tren~should ha~e an overflow to pass large design stormS, such as
a PVC pipe with holes drilled on its underside, set near the top of
the trench (Figure S. 3) . .
Figure 5.3: 'P~rking LotPerimete,r Trench Design
'\
Dripline of 1ieeShould
, Not Extend Ovet 1i'enC:h
Top View'
Side View
----...
,~'
.
I
I
~CutbsAct ' : f -
h.~Spfeadet ~.J \~~
~... .""~)w. ~ J.=
- """'" (=. .s4I~~\~,_,~
....'.., Trench '
FiIfet SCri . ~ .oI!i
. Difeeùy ~ ' :J.:1 "~oi;",: ~,....,
. Pavement . \ NfòjQ Cloth Layer ,
.í)~..~.
·":ó:·:~~~:..~
..:...~:'t''',~
~,~~!;!i~ Sand Filter
~
.
~
5.6
Chapter S: Infiltration Trenches
DESIGN 3:
Swale DesiRns (Figure 5.4). Low density residential runoff (S-lSt
impervious) can be tre.tedthrou~ a series of surface trenches
located in swale drainage systetaS., The lIajor design requirement is
that the longitudinal slope of the swale collection system should
never exceed st. Otherwise, concentrated flows will develop that
lIight erode the swales and cQntaiainate the trench. In addition,
concentrated flows .ay pass around or over the surface of the
trench and never infiltrate. An earthen check d.. or, railroad tie
placed perpendicularly to the floW path. on the dóWnstream side of
the trench, can prevent "short-circuiting" and increase the volume
of runoff exfiltrated by .the trench. The slope of the trench
should be as close to zero.s feasible, and should have ~ides1opes
()f S: 1 (h:v) or less. "
,Figure 5.4: SwalelTrench ,Design
"
Top View
"'-
Side View
."
t
CHAPTER 6: INFILTRATION BASINS
InfUtntion basins are effective in recaoving both soluble and fine
par1:iculate pollutants borne in urban runoff. Coarse-grained' pollutants
,shouldCenerally be rèlDoved before they enter a basin. Unlike other
'in(iltration systems, basins can be eas11y adapted tp provide full control of
peak discharges for large desi¡n storms. Also, ,basins can serve relatively
large drainage areas (up to SO acres). Depending on the degree of
,stong./eX-filtration açh1eved, , in the basin, significant groundwater
, recharge..lowflow aupentatiOn and localized streaøabank erosion control ,can
be achieve.d. '
Figure 6 .1: Schèmatic' ôf an Infiltration Basin
. j
, '
Top YIeW
...,
...- - -
-
/ - -
- --. -- -..;......
/ "
\
\,
I
I
/
I
/, /
/
-"
--
-
-
- -
'- -
'- - -
,.
\
',.......--..
. .............",,- . ..
Side View
6.6
Chapter 6: Infiltration B6Jins
Figure 6.4: Off-line Infiltration Basin Design
Top View
FIrII...1f
Inch of
RunofI
Diwfted
'""" CMnMf
Side View
=, E/ntIIfIII"*". 4 .,'... ~ ~~... .
"..... . <-::, ",«-,j:,::~i~~ ,
fIuitoI -'>; '-';;'~"" -")":.'ll/'~'~~
,r ' ::::~:':".. ~ j: "/{; ::·,'~:>.<::<Š~}f,;~.;2J:·~,ifEY:f~2'~~
~~. ~i-~~~:_~-~~~;~!..
.~. . ", - :~~;};,'i:.:':; ~,if.l"·~;':;;::SS;,:·;,;;;,:
~"JtT~¡V"';-" ~,~~ 5~ ~<:~ _ . ,;~/~~:,,1/_~ ~.:·?·t·~,,(::/: <,-: ..
~ _ _ ..; - - "'!Þ -. ".-t - :'; '.,.~,,'. :"'{ ::<.',:_:. /:~:.~(it:·~;,. ~~",:'~': t;_~;. ';)/;::.~'~~.
.. c: I '1. , '. .,. ....,...',"......,...,. ",.."j,' d.
~; I 1:-' ':-1--; - - ~.~ ·,;·;:·~·:·'::':.?·,';,'.:;::~~~·~:;;~?·,~6::~:~:'::·,:-~,!;:.~:-:~.;1:(~.:·~
· .. .;.."j "'··N "."IW
'=. ,." '·<;.{F:;~I
LMdto "'-.J'" . . _'S-' ,'/'
Iuift ' ".I.e. -/
, Vefocfty
DiS~
fL.-LT
..---~..._-_.......
-.- .~-..........~-;:¡- - .-
Grawe ," ..... oi II . ~-:r.:
. al 11.11I11\1I "P'''''''
Perforated
,~
6.12
Chapter 6: Inf 1.1 tration Basins
. Depth to'Seasonally High Water Table
A minimWl of two to four feet of clearance is needed between the floor of
the basin and the seasonallybigh water table. This deptb can be readily
deteruained from soil borings taken during wet weatber. High water tables
often present a IQAjoJ:o obstacle to tbe use of ,infiltration basins, since
basins an usually located in depressions at tbe low end of a watershed where
local water tables are l",catad' near the the ground sUJ;'face.
Proximity to Wells and Foundations
Basins sbould be located at least 100 feet away from drinking water wells
to muiøaiu ~he possibility of groundwater '. contamination, and should be
situated at least 10,£..t down-gradient and 100 feet up-gradient from
building foundatiôus to avoid potential seepage problems.
Maximum Depth of Reservoir
'-
, '
Tc) insure that the basin 'completely drains within 72 hours, it may be,
necessary to' limit the depth of the basin if underlying soils have relatively
low exfiltrat.i:on rates. 'ReCOllllDended depth limits for basins are sbown for
vµious soil textures in Table 6.2.
Watershed Size
. lid WRA Ú983b)suggest:s that basin$ can be applied to sites ranging from 5
,to 50 acres, in size. Other BHPs, such as extended detention ponds and wet
ponds, are better cmdidates on larger sites as they are more capable of
handling sustained baseflow. '
'Table 6.2: Soil Limitations For Infiltration Basins
.. MINIMUM 1NFIL- SCS SOIL~ MAXIMUM DEPTH OF%
SOIL TRATION RAn GROUP STORAGE (inches)
TYPE (fcninches/hr) 48 brs 72 brs ~
Sand 8.27 A 397 S9S
,.
Loamy ,Sand 2.41 A 116 174
Sandy Lo,8111 1.02 B 49 73
Loam 0.52 B 25 37
Silt Loam 0.27 C 13 19
1 Sandy Clay Lo8ms, Clay Lo8llls, Silty Clay Loams. Sandy Clay, Silty
Clay,an~ Clay Soils are not included as these soil types are all
NOT FEASIBLE for infiltration basins.
'2 Maximum Depth in ,the Basin that can ,drain completely~within 48 or
72 hours after a storm, given the soil infiltration rate.
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