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k`� ; Correction factors higher than those provided in Table 3.7 should be <br />considered for situations wbere long-term maintenance will be difficult to <br />implement, where ]ittle or no pretreatrnent is anticipated, or where site <br />conditions are highly vaziable or uncertain. These situations require the <br />use of best professional judgment by the site engineer and the approval of <br />the local jurisdiction. .An Operation and Maintenance plan and a fmancial <br />bonding plan may be required by the locat jurisdiction. <br />2. ASTM Gradation Testing at Full Scale Infiltration Pacilities <br />As an alternative to `I'able 3.7, recent studies by Massmann and Butchart <br />(2000) were used to develop the correJation provided in Table 3.8. These <br />studies compare infiltration measurements from full-scale infiltration <br />facilities to soil gradation da#a deve]oped using the ASTM procedure <br />(ASTM d�422). The primary source of the data used by Massmann and <br />Butchart was from �ltsie (1998), who included limited infiltration <br />studies only on Thurston County sites. Howev�r, Massmann and Butchart <br />also included limited data from King and Clark County sites in their <br />analysis_ This table provides recommended long-term infiltration ra#es <br />that have been correlated to soil gradation parameters using the ASTM <br />soil gradation procedure. <br />`!'able 3.`� ca�,. b,� „s<,� �;, �t;ma�n i�,��_,� � �-. �'^,.; . .:;�rt'�_�ticri ~s�.t�s <br />directly from soil gra�aYior� data, subj�ct to the appro�al o$�the local <br />jurisdiction. As is true of Table 3.7, the long-term rates provided in Table <br />3.8 represent average conditions regarding site variability, the degree of <br />long-term maintenance and pretreatment for TSS control. The long-term <br />infiltration rates in Table 3.8 may need to be decreased ifthe site is highly <br />variable, or if maintenance and influent characteristics are not well <br />controlled. The data that forms the basis for Table 3.8 was from soils that <br />would be classified as sands or sandy gravels. No data was available for <br />finer soils at the time the table was developed. Therefore, Table 3.8 should <br />not be used for soils with a d�o size (10% passing the size listed) less than <br />0.05 mm (U.S. Standard Sieve). <br />Table 3.8 — Alternative Recommenu'ed In�l#ration <br />Rates based on ASTM Gredation Testin . <br />Dla Size from AS�'IVI D422 Soil Estimated T.ong-Term (Design) <br />Gradation Test (mm) Infiltration Y2ate (inJhr) <br />> 0_4 9• <br />0.3 6.5* <br />0.2 3 g� <br />0.1 2.0*# <br />o.os � o.s <br />• Not recommended for veatment <br />' Refer tn SSC-4 and SSC-6 for treatrnent acceptability criteria <br />February 2005 Volume Ul — Hydrologic Analysis and Flow Contr�! BMPS 3-77 <br />� l�r�T� �A� <br />