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BETA <br /> ENGINEERING, INC. <br /> 39 MAIN STREET, NO. 1 • JACKSON, CA 95642 • 9ETAC-COEPOT.NET • 209.223.4126 209,223.4146 FAX <br /> January 7, 2003 u u���u v hV <br /> BEI 020482, 020483 <br /> Mr. Mike Huggins JAN 0 8 2003 <br /> San Joaquin County Environmental Health Department ENVIRONivIENT HEALTH <br /> 304 E. Weber Avenue PERMIT/SERVICES <br /> Stockton, CA 95202 <br /> RE: On-site Septic System Design and Installation Information, <br /> San Joaquin County Minor Subdivision # PA-02-3 <br /> 17200 Liberty Road <br /> Mr. Huggins, <br /> At your request, the following narrative has been developed to delineate the field data and design <br /> parameters used to develop the two on-site septic system designs for the subject project. This <br /> narrative addresses the means and methods of gathering the field data and lists the technical <br /> documents utilized in developing the disposal fields. <br /> Soil profile holes were conducted on 11/12/02. Numerous soil profiles were excavated throughout <br /> the parcel in an attempt t located adequate soil depths. Observed soils were evaluated for their <br /> suitability for subsurface disposal. Soil structure and texture were determined utilizing a <br /> standardized USDA soil evaluation methodology. Generally speaking, Beta Engineering, Inc. (BEI) <br /> staff observed useable soil depths ranging from 24 to 32 inches in depth. BEI was advised that 3i „ <br /> Environmental Health Department staff did not need to observe soil profile holes. <br /> Percolation testing was conducted on 11/26/02 in the areas identified as having suitable soils. <br /> One area was tested on each of the two proposed parcels. Percolation testing was conducted at <br /> depths of 18 and 24 inches using a standardized falling head methodology. Average percolation 7 <br /> rates for Parcel 1 (Area 1) are 89 mpi. Average percolation rates for Parcel 3 (Area 2) ar23 mm <br /> (excluding P-1). Percolation rates were calculated by using the slowest (most conservative)�rop <br /> measured within the last 90 minutes for the test. Methods for converting field measurements in <br /> millimeters to mpi are presented in Footnote 1.' <br /> 7� <br /> Based upon the relatively shallow soils, mods narcolati(�n rates and gently slope, it was the <br /> decision of BEI to pursue the development of an at grade bed for the two parcels. This system <br /> involves the construction of one or more gravel beds on the ground surface, thereby ensuring that <br /> the wastewater is applied to the upper, more rapidly permeable soil horizons and maximizing the <br /> available vertical separation. <br /> At grade beds were developed at the University of Wisconsin, Madison in the late 1980's by <br /> Converse and Tyler. A widely used design manual was published in 1990 and revised in 1994. <br /> This design manual was incorporated either verbatim or by reference in several counties, including <br /> Calaveras, Contra Costa and Alameda. BEI staff has successfully designed at grade beds in <br /> these counties for many years. <br /> Convert from mm/30min. (drop) to minutes/inch (rate) as follows : <br /> drop x 762 = rate (762 = 25.4mm/1 inch x 30min.) <br /> CIVIL ENGINEERING LAND DEVELOPMENT WATER WASTEWATER ENVIRONMENTAL '\ <br />