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NEIL O. ANDERSON & ASSOCIATES, INC. GEOTECHNICAL • ENVIRONMENTAL • INSPECTIONS . TESTING • LABORATORY SERVICES SACRAMENTO OFFICE CORPORATE OFFICE 4229 Northgate Boulevard, Suite 3 22 Houston Lane CMCO (530) 891-6304 Sacramento, California 95834 Lodi, California 95240 STOCKTON (209) 472-1091 (916) 929-9267 (209) 367-3701 RANCHO CORDOVA (916)631-4455 FAX: (916) 929-9269 FAX: (209) 333-8303 June 6, 2001 Mike Huggins San Joaquin County Environmental Health P.O. Box 388 Stockton, CA 95201 Subject: Engineered Septic Systems Black Oak Estates Quashnick Rd. Morada, California Our Job Number: S9789 Dear Mike: Introduction/Background The general soil profile which exists within the Black Oak development consist of 6 to 10 feet of stiff clay, underlain by alternating stratums of clay, sandy clay, and clayey sand. Small stratums of sand were encountered within the upper zone of clay, which accounts for the wide range of shallow percolation test results. Our office has performed over 130 shallow percolation tests within the subject development. Test results range from 7.5 minutes per inch to 240+ minutes per inch. Shallow tests were repeated at various locations until a "passing" test (<120 min/in.) was obtained on each of the 57 lots (see our report dated March 2, 1999). The average of the 57 "passing" tests is 29 min./in. In addition to the shallow percolation tests our office has performed 33 deep pit percolation tests within the development. These tests were performed using a modified Sacramento County deep pit percolation test procedure as indicated in our report dated August 24, 1998. The Sacramento County procedure utilizes a "column" of water throughout the depth of the hole so that the entire exposed soil stratum is tested at once. The clear water percolation rate determined by the test is then multiplied by a "sewage factor" in order to obtain the allowable sewage application rate per pit. Results of these test produced computed clear water rates (for 36 inch diameter dry wells) ranging from a low of 446 gal/day to a high of 17,928 gal/day with an average of 3375 gal/day. The typical sewage factor is 4%, which would produce an average application rate of 135 gal/day for 36 inch diameter by 25 foot deep pits. Our office was requested to see if we could produce an on-site sewage disposal septic system design which we felt, in our engineering design and judgement, would be suitable to be used and located anywhere on the individual lots, within the subject development. To this end we have completed a design.