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<br />. <br /> -~W1 CONSULTING ENGINEERS <br />. Maier Stewart & Associates Inc. <br /> November 8, 1990 <br /> File No: 520-000-00 (7) <br /> Mr. Gary Berger <br /> City Administrator <br /> City of Arden Hills <br /> 1450 W. Hwy. 96 <br /> Arden Hills, M~J 55112 <br /> RE: KEITHSON ADDITION DRAINAGE <br /> Dear Mr. Berger: <br /> As directed by the Ci ':y of Arden H:lls, Maier Stewart Cinu As'.oci,:ces, Inc. <br /> has prepared a report that analyzes the Grairage into the area known as t~e <br /> Keithson Pond. Kei.,~hson Pond is a. drtl~;1cQ2 '2(~senll;nt encor:.;pa.ssi~i;l IJclf'Lion of <br /> lots 3,4,5 and 6 in 810ck I of the Keithson Addition. <br />. The drainage from the area trioutar'Y to che KeiHlson PGnd 116S JEfl' cc.]cul~I2.j <br /> for a variety of rainfall events. The following table illustrates the type of <br /> storm, rainfall amount and the volume of runoff. <br /> Storm Ra i nf.9l~__UJ:l_cJ:!es) yo I um~jAcre_feet) <br /> 5 year 24 hour 3.5 0.87 <br /> 10 year 24 rlour 4. l l.15 <br /> 25 year 24 hour .1 c 1.46 <br /> ,,/ <br /> 50 year 24 hour ~ : 1.77 <br /> ., . ~, <br /> 100 YPijf 24 h.Jur ~J, S 2.10 <br /> Typically to deslgn a runoff detention basin (no outlft), a 100 year 24 hOLr <br /> rainfall is used to calcL:le.te the sto~~age 'iolu;r.e ~equired.. An .irnport~ln~. <br /> faccor in the design of a detention basin is t.he ~:el'meabi'ity 'Jf the soils <br /> beneath the pend. The permeability ~ill determine how Quickly tne w~[er <br /> elevation wi i 1 decrease to a: low cdd'; ,iona~ rW1Gf'f to be co!!~cced. <br /> We have cont.act.ed Braun Engineering Testing te perform d 50il bc'r'irl~ wi ':flin <br /> Lot 5, Block 1, Keithson Addition t.o det.ermine the permeability of the soils <br /> beneath the pond bottom and to determine the groundwater level. The soi 1 <br /> report. which has been included with this report. indicates that. t.he mat.erial <br /> beneath the pond bottom is silty and clayey sands, and sandy clays, which <br /> have a very low permeability and the ground water level is at dCDroximately <br /> the elevation of the pond bottom. Therefore, these soils are not suitable <br />. for a detention basin, regardless of the volume. <br /> 1959 SLOAN PLAOE. ST, PAUL, MINNESOTA 55117 612,774-6021 Equal Opportunity Employer <br />