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� Correction factors higher than those provided in Table 3.7 should be considered for situations where long-term maintenance will be difficult to implement,where little or no pretreafinent is anticipated,or where site conditions are highly variable or uncertain. 'I'hese situations require the use of best professional judgment by the site engineer ar�d the approval of the local jurisdiction. An Operation and Maintenance plan and a fmancial bonding plan may be required by the local jurisdiction. 2.ASTM Gradation Testin�at FtilI Scale Infiltration Facilities As an alternative to Table 3.7, recent studies by Massmann and Butchart (2000) were used to develop the correlation provided in Tablc 3.8. These studies compare infiltration measurements from full-scale infiltration facilities to soi] gradation data developed using ihe ASTM procedure (ASTM D422). The primary source ofthe data used by Massmann and Butchart was from Wiltsie(1998),who included limited infiltration studies only on Thurston Couniy sites. However,Massmann and Butchart also included limited data from King and Clark County sites in their analysis. This table provides recommended long-term infiltration rates that have been correlated to soil gradation parameters using the ASTM soil gradation procedure. Table 3.8 can be used to estimate long-term des;gn infltration rates directly from soi] gradation data, subject to the approval of the local jurisdiction. As is true ofTable 3.7, the Iong-term rates provided in Table 3.8 represent average conditions rcgarding site variability,the degree of long-term maintenance and pretreatment for TSS control. The long-term infiltration rates in Table 3.8 may need to be derreased if the site is highly variable, or if maintenance and influent characteristics are not well controlled. The data that forms the basis for Table 3.8 was from soils that would be classified as sands or sandy gravels. No data was available for fincr soils at the time the table was developed.Therefore,Table 3.8 should not be used for soils with a d�o size (10%passing the size listed) ]ess than 0.05 mm (U.S. Standard Sieve). Table 3.8—Alternative Recommended Infiitration Rates based on ASTM Gradation Testin . D�a Size from ASTM D422 Soil Estimated Long-Term(Design) Gradation Test(mm} Infiltration Rate(inJhr) >0.4 9. 0.3 6.5* 0.2 3.5* 0.1 2�*„ 0.05 �8 •Not recommended for treatmcnt •Refer to SSC-4 and SSC-6 for treatment acceptability criteria ---- ; February 2005 Volume ll!—Hydrologic Analysis and Flow Contral BMPs 3-77 � �� '-/