SU0000048 SSNL - Laserfiche WebLink

Home Browse Search

rr"worst-case scenario' conditions. The deep perc test boring exhibited a rapid perc rate throughout the four-hour test period with all six inches of head water seeping away within each 30 minute test period. The final perc rate was 4.9 min/in. This can be attributed to the sandy soil structure at the 8-9 ft depth referenced above. For the shallow perc test,the four-hour test revealed that the perc rate slowed by approximately 50%over the duration of the test in response to soil saturation. The final perc rate was 15 min/in. [4] LOCAL GROUNDWATER AND SURFACE WATER INFORMATION The 1999 Lines of Equal Depth Map published by the San Joaquin County Flood Control District indicates the depth to groundwater in this area to be approximately 35 feet below grade. The Lines of Equal Elevation Map shows the subject property to be directly south of a groundwater recharge area with a groundwater elevation of-20 ft below mean sea level. The project elevation is approximately 15 feet above sea level;therefore, the groundwater equal elevation maps correlate with the water table depth. Because the site appears to be south of a zone of groundwater recharge, directional flow may be slightly to the north. 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 alfalfa. There is an irrigation ditch to the south of Parcel 1 which cannot influence the existing septic system. Analysis of water drawn from the domestic well on Parcel 1 reveals a very low nitrate concentration of 3 ppm nitrate (NO3). The Maximum Contaminant Level (MCL)for NO3 in drinking water is 45 ppm. The construction details of this domestic well are unknown, including its depth. Considering the site is near an area of groundwater recharge and the fact that there has been a high degree of agricultural production in this locale,a higher nitrate level would have been expected. Therefore,the underlying aquifers have not been significantly affected by nitrate sources and may be protected by intervening clay strata. Nitrate sources may include confined animal facilities, fertilizer applications, and/or surrounding septic systems. The agrichemicals DBCP and EDB were below detection limits (BDL) which is equivalent to non-detect(ND). 3 Vaf(ey Ag Research