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L Deep Percolation (Rainfall Recharge).The Nitrate Loading Study used a value of 17.01 inches per year as the assumed average annual deep percolation(i.e.,rainfall recharge)for use in the water-nitrogen mass balance analysis. On page 5,the report explains that this was determined from average monthly precipitation and evapotranspiration rates for the area. However,this is not reflected in the data and calculations presented in Appendix B. Appendix B presents monthly CIMIS data for the 2018-2019 water year,which was an unusually wet rainfall year,and not indicative of average rainfall conditions.It is also not clear from these data how the value of 17.01 inches deep percolation was calculated. I prepared an independent water balance calculation using average monthly rainfall data for Lodi and published average monthly evapotranspiration(ETo)data for CIMIS Zone 12, which is attached. By my analysis for a"hypothetical'development site in the area,I calculated an average annual rainfall recharge/deep percolation value of 8.79 inches/year, considerably less than the 17.01 inches assumed in the Dillon&Murphy study.Note that in my water balance calculation I include an adjustment for actual evapotranspiration based on typical land surface conditions.This is important,since the published ETo values represent the estimated ET(water demand)for lawns and other uniform turf areas,which are generally much higher than the ET for most types of vegetation,e.g.,trees,shrubs,ground cover, perennials,etc. The ET associated with buildings and paved areas is even less(e.g.,<10%of ETo). Since rural development sites will commonly have a mix of vegetation and landscape features,the water balance-recharge calculations will be more accurate by adjusting the ETo (downward),according to the mix of developed landscape conditions. In my attached example I used hypothetical values,not necessarily those for the 7151 Peltier site,which Dillon&Murphy would be able to estimate more accurately. Substituting my deep percolation value of 8.79 inches/year along with the other Dillon& Murphy assumptions,gives a resultant nitrate-nitrogen estimate of 9.69 mg-N/L for the projected wastewater flow of 1.240 gpd. Using 17.01 inches deep percolation,Dillon& Murphy calculated a resultant value of 9.89 mg-N/L for a potential flow of 2,480 gpd,which underestimates the potential nitrate impact at this artificially higher level of wastewater flow. However,since 2,480 gpd is double the actual wastewater flow projection,this can be ignored. Since my attached calculations and resultant nitrogen value of 9.89 mg N/L are for hypothetical site development-landscape conditions,I recommend that Dillon&Murphy consider these suggested changes to the water balance—deep percolation methodology,and submit revised project calculations for final review. 2. Wastewater Flow and Nitrate Concentration.In the Hantzsche/Finnemore methodology, the values for wastewater flow and nitrogen concentration are meant to approximate long- term average conditions. The wastewater flow assumptions by Dillon&Murphy are representative of maximLun daily flow,commordy used for system design,and over-estimate the average wastewater discharge for the property. On the other hand,the wastewater effluent nitrate concentration assumption of 35 mg-N/L is on the low side. However taken together, the over- and under-estimations cancel each other to produce a reasonable estimate of total wastewater mass nitrogen loading,which is the relevant factor. For future reference,a typical per person mass nitrogen loading rate of 13 to 14 g/person/day can be used as a check 2