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New Hope Soil Suitability • June 26,2008 File No.2836-001.01 Page 4 6.0 PERCOLATION TEST INFORMATION • The locations of each percolation test site are shown on the attached Plate 2. As can be seen, there is one test hole on each proposed property; each hole is approximately 200 feet westerly of the easterly boundary of each property. Each percolation test hole was six inches in diameter and 36 inches deep. All holes were "scratched" with a wire brush to remove smeared surfaces. The bottom two inches of each test hole was covered with 3/8`h-inch pea gravel. The holes were • drilled by hand auger on March 25, 2008, and were pre-saturated at the time of drilling. Testing was performed on March 26 and again on March 27, as requested by the County. All holes were uniform and without significant sloughing and raveling following the pre-saturation and the two test intervals. The tests were performed by the placement of six inches of water over the pea • gravel, with the holes refilled as necessary during the testing. All tests were conducted for four hours with readings on one-half hour intervals. The final readings at each test site were observed by Lisa XA&ma of San Joaquin County. Copies of the actual field tests are attached as Plates 3 through 6,Perc Test Rate Form 1c. As discussed briefly above, it may be necessary to elevate leach fields slightly on the properties created by the proposed subdivision. Other than this, we would expect that conventional waste disposal systems to be appropriate. Although no percolation was measured for percolation test 5 (on Lot 5), because of the sizes of all of the proposed properties, we would expect with proper siting that appropriate permeability rates are obtainable. The size of the proposed properties (and their cost) like + Il ive rise to relatively large dwellings whose owners are able to design and e and effect ive waste disposal systems. .0 CONCLUSIONS The avera surface elevation at the site is on the order of 0 feet, USGS datum. In • addition, the Mokelumne River will form the westerly boundary of each proposed property. All the properties are below the 100 year flood level. Measured free groundwater levels were 7.50 and 5.75 feet below ground surface at the time of our late March 2008 testing, and we would expect significantly higher free groundwater levels during extended high stage conditions on the Mokelumne and/or during heavy irrigation' / f.� 7 y� KC Fnf- Percolation tests 2 (Lot 2), 3 (Lot 3), 4 (Lot 4), 5 (Lot 5) and 8 (Lot 8) resulted in percolation j rates slower than 60 minutes per inch. According to County standards, additional percolation d testing must be performed to find disposal locations with rates faster than 60 minutes per inch, or engineered alternate disposal systems must be used on these lots. Percolation tests 6 (Lot 6) and 7 (Lot 7) resulted in percolation rates of 60 minutes per inch, which are at the limit of what is allowed for non-engineered conventional septic disposal systems. With the results obtained on the other lots, we suggest engineered disposal systems also be considered for these lots. / ` As discussed above, elevating (mounding) of the disposal systems somewhat above the existing Y grades is warranted to provide clearance to groundwater levels. With proper choice and construction of disposal mounds, percolation rates also can be improved. We conclude that on-