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-1 TO: Stan Phialippe FROM: Frank McDermott LIQ` MEMO RAN DUMLill MAY G 1981 5AN n'rQUIN LOC,4L HEALTH D STRII;T 4 Play 1981 SUBJECT: SANTOS RANCH SUBDIVISION, SAN JOAQUIN COUNTY On 26 March 1981, we mailed our comments to the San Joaquin County Planning Depart- ment regarding the application for a 55 unit Santos Ranch Residential Subdivision. We were concerned with high ground water conditions in the Santos Ranch area and requested denial of the application until further information was compiled and submitted to interested agencies for review and comment. On 8 April 1981, Bob Fujii, Regional Board; Carl Borgman, San Joaquin County Super- vising Sanitarian, Karen Moroz, San Joaquin County Sanitarian, and I inspected the area, which includes the Currier Estates Subdivision and the Santos Ranch Subdivision. Currier Estates, which is adjacent to and southeast of the planned Santos Ranch Subdivision, was a planned community of 200 homes, of which 30 are completed. Santos Ranch Subdivision is a planned community of 135 homes. Santos Ranch Units 1 and 2 are completed. Unit 3, which has a proposed 55 homes, is under construc- tion, and Unit 4 will be built in the future. We sounded two individual domestic wells in Currier Estates to determine the static head. One well indicated an approximate static head at 5 feet and the other an approximate 10 feet static head. We then sounded a newly constructed well in the Santos Ranch area and determined the static head at approximately 7 feet. While in the Santos Ranch area, we observed a backhoe in operation and measured first ground water at 6 feet. Well logs for domestic wells in the area indicated alter- nating clay -sand layers to a depth of 100 feet level for local water supply. Percolation test observed by County Sanitarians in nine test holes showed a wide variation of percolation rates ranging from 23 minutes/inch to 80 minutes/inch, indicating good to bad`soil adsorption and percolation rates. Regional Board "Guidelines for Waste Disposal from Land Developments" states in part: "Percolation rates shall not be slower than 60 minutes/inch, soil depth below the bottom of a leaching trench shall not be less than 5 feet, and depth to anticipated highest level of ground water below the bottom of a leaching trench shall not be less than 5 feet." The limited information suggests that the percolation rates in some areas are too slow and that the bottom of leaching trenches do not have the required 5 foot separation from high ground water.