SU-2601443_SSNL - Laserfiche WebLink

Home Browse Search

Civil, �i�vlrarrmrnla! R iAlo�cr Resaurees MEMORANDUM FNGINEERING CORP. TO: Kasey Foley,REHS Interim Director, San Joaquin Environmental Health Department FROM: Norman Hantzsche,PE, Questa Engineering Gorporatikl DATE: February 12,2019 UBJECT: OWTS Design Review for 11065 N Alpine Road,Lodi PROJECT OVERVIEW The project is for the construction of a new 4-bedroom single family residence and onsite wastewater treatment system(OWTS)on a 1.5-acre parcel in an agricultural area about 7 miles southeast of the City of Lodi. The property was historically used for agriculture in the 1930s, with residential uses dating back to the 1950s. presently the site is vacant with all prior buildings having been removed_ Plans and supporting documentation For the OWTS are contained in the "Soil Suitability/Nitrate Loading Study" by Terracon Consultants, Inc., dated November 20,2019. Surface soils in the area are mapped as Hollenbeck silty clay with slow permeability. Soil borings and percolation testing to depths of 25 feet showed reported soils predominantly consisting of silty sand,silty clay and clay. Six percolation test were conducted at depths ranging from 3 to 25 feet,showing unsatisfactory results with the exception of one passing test of 27.7 minutes per inch at a depth of 21 feet. Groundwater in the project area is estimated from regional groundwater maps to be about 90 to 100 feet below ground surface. Groundwater from the onsite domestic well was found to have nitrate-nitrogen concentration of I5 mg-NIL. The nitrate leading study by Terracon Consultants utilized a water-nitrogen mass balance analysis following the HantzschelFinnemore methodology. The resultant nitrate-nitrogen concentration impacting the groundwater from the new OWTS was estimated to be 15.9 mg-NIL, which exceeds the 10 tag-NIL drinking water criterion. On the basis of this result Terracon recommended the use of an advanced/supplemental treatment system to mitigate the potential groundwater nitrate impact of the project_ COAC"NTS My review comments pertain specifically to the nitrate loading study and recommendation for supplemental treatment for nitrogen reduction. I agree with the overall approach,methodology and information provided in the Teracon study. However, I believe some of the assumptions used 1 Box 70356. 1220 Brickyard Cove Rd.Suite 206 Pt.Richmond,CA 94807 T.5101236,6114 F.5101235.2423 f:Ouestad Quota Mcom