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03/14/2006 16:51 FAX fa002/003 On October 14, 2002 a staff geologist with our firm obtained a sample of groundwater using clean procedures from a spigot on a residential home located west of Lot 4. That same day, the water sample was submitted to Sequoia Analytical using chain-of- custody procedures for DBCP and nitrate testing, Copies of the test results and the chain-of-custody are presented on Plate 7. NITRATE LOADING CALCULATIONS We have been requested by Mr. Mike Huggins of the San Joaquin County Public Health Services Department Environmental Health Division (PHS/EHD) to calculate the nitrate loading for the proposed leach field. As you are aware, the drinking water standard for nitrate is 45 milligrams per liter (NO3) and 10 mg/I as Nitrogen (N). In dur evaluation of nitrate loading, we have used the Hantzsche mass balance equation (source: Predicting Ground-Water Nitrate-Nitrogen Impacts, Hantzsche and Finnemore (1992)), which is presented below with an explanation for each factor and the value used in our study. We have calculated the average nitrate (Ne) in groundwater based on two homes per lot and taking into consideration a square mile area around the project site being developed in the future as required by Mr. Huggins with SJCEHD. N< .- AWNw 1..-D).+ (Nt) r AW+ r Where: N, = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources and precipitation - mg/I, as N A - Number of dwelling units per acres on septic tanks (unittacre) _ .49 (estimated based on 157 lots per square mile around the project site, assuming 2 homes per lot (314 homes total), divided by 640 acres) W - Annual wastewater loading per dwelling unit per acre (inches) =r1:37 w4chas (based on 300 gpd/residence) N,„ = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 mg/I typical (Hantzsche and Finnemore (1992)) D - Percent dentrification of leachfield effluent = 0.25 percent (0.1 to 0.25 percent typical per Hantzsche and Finnemore (1992). 0-25 selected given the large depth to groundwater and the presence of interbedded low, permeable clay layers.) r = Annual deep percolation of precipitation (inches) = 9.8 inches (representing 70 percent of the average annual rainfall of 14 inches in project area. Remaining 30 percent of rainfall is assumed to drain off-site into natural or manmade drainages) Nb = Background nitrate concentration of the deep percolating precipitation -- mg/I = 0.5 mg/I (per Technical Memorandum, Hydrologic and Soil Investigation for the Chico Urban Area, page 6, Dames and Moore, April 1996) 23107.0O215T06R149 February 10,2006 copyfight 2006 Klcinf31dcr,Inc Page 4 of 6