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SENT BY:DPRA St.Paul, MN ; 4-12-83 ; 9:32AM ; 612 227 5522 612 407 4191;#
<br />CHES'TER L. ARNOLD, JR. AND C. JAMeLs CiiBBONS
<br />commercial development tops the chart at around
<br />95% coverage, with other business areas and industrial
<br />development lagging slightly behind. In residencial
<br />areas, there is a wide range of imperviousness that var-
<br />ies predictably with lot size, going from about 20% in
<br />one -acre zoning to as high as 65% in one -eighth -acre
<br />zoning.
<br />The CitW of Olympia, Washington, recently con-
<br />dueteci a thorough study of impervious coverage in
<br />their area. For 11 sites measured, they found coverage
<br />values similar to the SCS values, finding four high -
<br />density residential developments (3-7 units/acre) to
<br />average 40% impervious, four multifamily develop-
<br />ments (7-30 units/acre) to average 48% impervious,
<br />and three commercial/industrial sicrs to average 86%
<br />impervious coverage (City of Olympia 1995) (table 1).
<br />In addition to the relationship between land use
<br />and the total amount of impervious coverage, studies
<br />show char all land uses are not equal with regard to
<br />the levels of contaminants present in the runoff. As
<br />noted, pollutant or land -use -specific studies are rela-
<br />cively new ro the scientific community, buc exischit! it
<br />formation supports the common-sense assumla t, .
<br />that some land uses are more contaminating than i ,i I
<br />ers; for instance, runoff from gasoline stations
<br />tains extremely high levels of hydrocarbons and
<br />metals (Schueler 1994b).
<br />Recent research from Wisconsin goes one nt,il
<br />step further, actually determining the pollutant ,.••
<br />cenrrations from specific categories of imperviott:,
<br />Fares. Using micro -monitoring samplers that cnI1NI 1.
<br />the runoff from 12 different types of surfaces (r
<br />roofs, streets, parking lots, lawns, driveways) iu i,
<br />dential, commercial, and industrial areas, Bannrrn.
<br />et al. (1993) were able to show distinct different,". .
<br />the types and amounts of certain pollutants. .I.
<br />pending on the source of the runoff. The study tir.n.
<br />identified streets as the impervious surfaces ha, it
<br />the highest pollutant loads for most land -use raw ,
<br />ties (table 2). Roofs, with the exception of r1w . ,
<br />from industrial roofs, were generally low in pollui.,
<br />loads, while parking lots had surprisingly mod. t..
<br />TABLE 1. Ste coverage for three land uses in Olympia, Washington
<br />Average Approximate Site Coverage, %
<br />High Density Multifamily
<br />Res;dendal (7-30 units/
<br />Surface Coverage Type (3-7 uoits/acre) acre) Comn�� i
<br />1. Streets
<br />16
<br />11 u .
<br />2. Sidewalks
<br />03
<br />05
<br />3. Parking/driveways
<br />06
<br />15
<br />4. Roofs
<br />is
<br />17
<br />S. Lawns/landscaping
<br />54
<br />19
<br />6. open space
<br />n/a
<br />34
<br />Total impervious surface (1-4)
<br />40
<br />48 .,
<br />-Road-related impervious surface (1-3)
<br />25
<br />31 ,d
<br />(Road -related al a percentage of total
<br />,
<br />Impervious coverage)
<br />(63%)
<br />(65%) (/tr•
<br />Adtpod fimrr GryofolbmJna 1995
<br />TABLE 2. Surfaces exhibiting highest levels of runof66orne pollutants, out of twelve surface types sampled in selected it. I ,.
<br />ertsas in Wisconsin
<br />POLLUTANT SURFACE
<br />Highest levels Second highest levels Third highest I, „ I
<br />-• e. tali (pathogens)
<br />solids (sediment)
<br />total phosphorous
<br />zinc
<br />cadmium
<br />..:'_copper
<br />Adyud fiv $65 1994d
<br />�� �,; , 248 APA JnURNAL•SPRING 199fi
<br />residential feeder streets
<br />industrial collector streets
<br />residential lawns
<br />industrial roofs
<br />industrial eollect:orstreem
<br />industrial collector streets
<br />residential collector streets
<br />industrial arterial streets
<br />industrial collector streets
<br />industrial arterial streets
<br />industrial arterial streets
<br />industrial arterial streets
<br />residential lawns
<br />residential feeder ,n '.,
<br />residential Feeder sin•• ,
<br />commercial arterial •.I„ .
<br />commercial arterial •a..
<br />residential collecnui J,-
<br />
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