SU0000019 SSNL - Laserfiche WebLink

Home Browse Search

SOIL PROFILE AND-PERCOLATION TESTING - The soil from 0 inches to 42 inches is uniform and consists of a light brown very fine sandy silt, with some organic matter and little moisture. There is a small amount of clay in the topsoil (0"- 6") as evidenced by surface cracking in the surrounding soils. The Unified Soil Classification System (USCS) classifies this soil as CL/ML for the topsoil and SM/ML for the remaining soil to a depth of 42 inches. A Log of Boring designating the USCS soil classifications for the -percolation test boring is found near the top right-hand corner of the FIELD PERCOLATION TESTING REPORT. A Well Drillers Log for the Costa's domestic well illustrates alternating thin strata of gravel/rock and thicker clay strata from the surface to the well depth of 200 ft. Percolation testing was conducted on Parcel "A" on the south side of the existing house, directly east of the existing leachfield area. Based upon past experience with this soil type, one shallow (42 inches) perc test was done. Pere testing was not done on the Designated Remainder, in accordance with Environmental Health Department regulations. The boring was drilled, scarified and pre-saturated on July 11,the day before testing. Readings were taken over a four- hour test period to ensure maximum soil saturation under "worst-case scenario" conditions. The pere test exhibited an extremely rapid pore rate throughout the four-hour test period with nearly all six inches of head water seeping away within each 30 minute test period. The final pore rate was 5.2 min/in. This rapid perc rate can be attributed to the porosity of the fine sandy-silty soil structure at the perc test depth. LOCAL GROUNDWATER AND SURFACE WATER INFORMATION The 1992 Lines of Equal Elevation Map published by the San Joaquin County Flood Control District is the only recent groundwater map available that illustrates the groundwater elevation in this area. Since the ground elevation is 100 feet and the equal elevation was approximately 70 feet, the static.water.,table was approximately 30 feet below grade-in 1992. It is our understanding from recent wells installed in this area,that this water table elevation has risen substantially in the past nine years to approximately .15:feet below grade.;. It is unlikely that perched water table conditions exist at higher elevations than the static water table. There is no potential for future septic impact to surface waters,provided applicable distance requirements are followed, and there is no surfacing of effluent from inundated conditions caused by over-irrigation of the beans or tomatoes. Analysis of water drawn from the Costa's domestic well reveals a comparatively high nitrate concentration at 32 ppm nitrate (as NO3). The Maximum Contaminant Level (MCL) for NO3 in drinking water is 45 ppm. The construction details of this domestic well reveal a grout seal to Page -2- 7Ia(ky Ag Research