SR0087834_NITRATE LOADING STUDY ADDENDUM

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Beginning with the repair/replacement area for the existing residential structure, repair leachlines must be installed in-between the exiting leachlines, as illustrated in red. Until the existing system is uncovered, the exact distances of the seepage.pits from the onsite domestic well is unknown. If a 150 ft distance-from the well cannot be achieved,then three 2'W x 121 x 8'D.sumps (max. 8 ft depth)must be installed, as illustrated. Otherwise,25 ft deep seepage pits may be installed. 1 The primary filter bed disposal structure for the ADU is proposed to be constructed in the NWC of the property and consist of 30 ft N-S and 70 ft E-W=2,100 sf filter bed using Infiltrator EZflow 1201-GEO and 1201 P-GEO modules. Four, 48" dia. x 25' deep seepage pits are to be drilled simultaneously directly south of this filter bed. Potential overflow from the ADU filter bed will drain into the westernmost seepage pit, as illustrated. The reserve/replacement area for the'ADU is to consist of a"flag" orientation, with the filter bed composed of 352 sf+ 1,152 sf= 1,504 sf of filter bed floor area. The remaining three seepage pits will contribute an additional 264 sf/seepage pit x 3 pits= 792 sf of infiltrative surface area, for a total of 1,504+ 792 =2,296 sf of infiltrative surface area. Conventional washed drain rock may be used for this reserve/replacement area. OPERATIONS AND MAINTENANCE PLAN Under Section 1.12.1 of the EHD OWTS Standards Manual,"All engineered designed OWTS shall be operated and maintained pursuant to an Operations and Maintenance Plan(OMP) compiled by the designer." The following comprises the OMP: 1. The septic tank should be inspected every three years, and pumped-out if inspection warrants pumping. Pumping will remove excess organic nitrogen. 2. Lawn grass may be planted over the ADU filter bed area and should be mowed periodically; however,the grass clippings must be discarded as solid waste and not mulched back into the lawn grass. Otherwise the nitrogen cycle will be completed and may contribute excess nitrogen to the i soil environment. 3. When the primary filter bed area and the one seepage pit fail for the proposed ADU, the 100% reserve filter bed must be activated and the three remaining seepage pits connected to the reserve/ ireplacement filter bed. Likewise, when the OWTS for the existing residential structure fails, the jnew leachlines and sumps (or seepage pits)must be installed immediately. ' i i I ' CONCLUSIONS i jThe revised nitrate loading calculations now indicate the average concentration of nitrate-nitrogen in effluent recharge water will be under the MCL drinking water standard of 10 mg/L N. i Shallow perc tests were conducted for this Addendum,with failing perc rates. The EHD has accepted the passing shallow perc test conducted by LOGE. The calculated disposal area design for the OWTS ADU is based on the perc test results conducted for this Addendum Report: Page -4- Chesney Engineering, Inc.