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F7Fromthe USIONS AND RECOMMENDATIONS FOR IMPACT MITIGATION water data collected,there are elevated levels of nitrate within the groundwater project site. Test results from the seven wells analyzed reveal significanthe nitrate concentrations, from 10 ppm to 89 ppm. Explanations for this variability may include differing perforation elevations,total depth of each well, grouting depth, immediate and surrounding land use around the wells, or a cracked or missing wellhead or sanitary seal. If the highest and lowest nitrate concentrations were omitted for averaging purposes,the median nitrate concentration from the wells tested would be 33 ppm, which is 73% of the MCL. Two separate scientific methods were used in this study to assess and quantify nitrate loading. The Hantzsche/Finnemore Formula predicts a resultant average concentration in the recharge water from the proposed project to be 24.1 ppm as NO3. The Laak Method estimates the total nitrogen concentration in the top 10 ft of the highest aquifer under the project to be 48.5 ppm NO3. Based upon the Hantzsche/Finnemore Equation, which is in our opinion the closest nitrate loading projection to reality,the nitrate impact from the proposed development is lower than the average nitrate concentration currently in the underlying groundwater(24 ppm NO3 vs. 33 ppm NO3)- With regard to the agrichemical DBCP concentrations, since a percentage of the acreage is, and .. has been in grapes for many years, and DBCP was used on grapes up to 1976, it was detected in three of the seven wells. Only one well had a significant DBCP concentration at 50% of the MCL. Given the intense farming practices that have occurred over the entire subject property, as well as upgradient, and given the sandy soils of the region,higher nitrate concentrations would have been expected. It may be theorized that the nitrate concentrations are in equilibrium and if all factors affecting this concentration remain steady, there may not be a significant increase in nitrate. Additionally,the referenced hardpan layer may be having an attenuation effect on the nitrate concentration. It has been observed by the Environmental Health Department over the years that nitrate concentrations can fluctuate substantially at different times of the year. This is due to factors such as irrigation recharge, rainfall weather patterns and water well usage. It is obvious from the soil analytical test results that Mr. Hams has applied nitrogen in the proposed development area very carefully. This may be one explanation for the low nitrate concentration of 10 ppm NO3 in the downgradient domestic well located at the NWC of North Ripon Road and Highway 120 (14966 North Ripon Road) For each of the new Parcels, it is recommended that test wells be initially drilled to deeper aquifers to test for nitrate and DBCP concentrations. When an aquifer(s) is encountered with low nitrate and no DBCP,the test well may be developed into the domestic well to serve that residence. The grout seal should extend to at least 150 ft. LL— 11 Vaffey Ag Research