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show the Ksat-;n;c�oi rate converging to about 2 inches per hour. The PIT conducted in TP-17 (Figure 8) show <br /> the Ksat-in�tia� rate converging to about 4 inches per hour and then decreasing until the final reading of <br /> r <br /> 1.7 inches per hour. The.decreasin� rate in TIP-1�is li� caused b__y mounding of water within the <br /> weathered glacial till and on top of the very denseglacial tilL F` J �,, <br /> Recommended Design Infiltration Rates <br /> The measured hydraulic conductivity (KSac-m;c;a�) of the weathered glacial soils should be adjusted for site <br /> variability, test method, and siltation and bio-buildup potential. We recommend correction factors be <br /> used consistent with Table 3.3.1 of the 2012 Washington DOE stormwater manual. The partial correction <br /> factors listed in Table 4 were used to determine the design hydraulic conductivity values based on the PIT <br /> resu Its. <br /> ��� <br /> �TABLE 4. RECOMMENDED INFILTRATION RATE CORRECTION FACTORS <br /> Factor Description Partial Correction Factor,CF <br /> Site variability and number of locations tested 0.5 <br /> Test method, Large-scale PIT 0.75 <br /> Degree of influent control to prevent siltation and bio-buildup 0.9 - -.-._ <br /> Total Correction Factor,CFT 0.33 -��� <br /> / <br /> We recommend the following design hydraulic conductivity (KSat-aes���) rates for each of the geologic units <br /> encountered at the site. <br /> � ��� <br /> ■ Fill. Directing stormwater to infiltrate i�a:to existing loose fill soi�s�ay induce ground settlement, <br /> especially in the area of the 115kV yard where deeper fills exas#!Therefore, we do not recom.mend <br /> directing stormwater infiltration wher�structures are planned on the existing fill. Incidental (passive) <br /> -------._---__. __-- ----- --- - - _____--- <br /> infiltration from rainfall is acceptable within the fill soi�s when conducting stormwater evaluations for <br /> the site. We recommend a passive design infiltration rate of no more than 0.25 inches per hour <br /> within the fili soils. <br /> ■ Weathered Glacial Till. Based on the results of the PIT and sieve analyses, we recommend a design <br /> infiltration rate of no. m�r�e��an 0:�-inches.�per. h� ai r within the weathered_glacial till_soils at the site <br /> -------- --- -- - ...p.;= <br /> for active or engineered infiltration s�ystem�._„ <br /> ■ Relatively Una�veathered Glacial Till. The results of the sieve analyses indicated that the fines <br /> content (material passing the US No. 200 sieve) ranges from 15 to 27 percent. Due to the density <br /> .._.._��.__ .-------_ <br /> and relative impermeability of the relatively_unweathered �cial_till, design infiltration ahould be <br /> �... -- -4._______.—__..__._� ...__ : _ __.__. �_._.__._.-_..._.�-- <br /> assumed to be_.l.ess than 0.1 inches per.l�our when_designin.gthe infiltration facilities._ <br /> Based on the subsurFace conditions observed in the explorations, we anticipate that the northern portions <br /> of the proposed 115kV and 230kV yards will be underlain with fill and weathered till soils, while the <br /> southern portions of the proposed yards will be underlain by very dense glacial till at shallow depths. <br /> We recommend that a passive infiltration rate of not more than 0.25 inches per hour be assumed for the <br /> northern portions of the yards where thicker deposits of weathered till or fill is assumed, and a passive <br /> .�..�_._..�._. .._ __..___. <br /> rate of_less than 0.1 inches_per hour should__be assumed for the southern portions of the yards where <br /> ,--- --.-- -_. _ _._,_...___ - ------ _ -- <br /> dense glacial till is expected at shallow depths,as shown on the Site PIan1 Fi,ure 2. We recommend that <br /> - -- .-...� �__.__.e_ �. �..f_ <br /> __. ��G o.J ���-�� � � �1"�'�c�I �'..i� l;�� � S �� � �L' ��lX_�-v;-m� 1 �� � � � <br /> GEOENGINEERS� October24,2014 Page20 <br /> Flle No.0482-027-02 <br />