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Taking the existing nitrate concentration determined in the on-site well in combination with the <br /> estimated theoretical recharge from the proposed 11 homes, the resultant concentration will <br /> theoretically remain under the MCL. <br /> SSS§ 4.2 Groundwater analyses of the on <br /> domestic well,which has subsequently been destroyed, <br /> indicates a relatively low nitrate concentration of 9 ppm. Considering upgradient potential nitrate <br /> sources,this concentration would have been expected to be higher. As referenced, the Groundwater <br /> Study conducted by EHD in 1994 revealed a very low impact to the domestic wells sampled and tested <br /> in the Morada Area. The primary logical reason for this low nitrate well water concentration must be <br /> attributable to the subsurface soils possessing a high denitrification potential. <br /> Groundwater depth under the site has risen from an approximate depth of 76 feet in 1992 to an <br /> approximate depth of 68 feet as measured in the on-site well for this Study. The groundwater <br /> directional flow has been in a predominate east southeast direction. Only the regional groundwater <br /> directional flow can be ascertained from the information provided in the Lines of Equal Elevation <br /> groundwater maps. It is possible that under localized conditions,the groundwater may flow in a <br /> different direction than that determined as the regional flow. Regardless, it is known that the Morada <br /> area and upgradient land use was, and still is under agricultural production, in addition to other potential <br /> upgradient nitrate sources. <br /> It can be hypothesized that the observed nitrate concentrations within Morada area groundwater is in <br /> equilibrium. Sources contributing nitrate to the underlying groundwater include indigenous soil <br /> concentrations from decomposing organic matter from past farming operations,rainfall, upgradient and <br /> historical agricultural fertilizer inputs, septic systems (particularly sumps and pits), and lawn/landscape <br /> fertilization. The sum total of these sources would suggest the potential for a much higher nitrate <br /> concentration than what was observed in the on-site well and in surrounding domestic wells. <br /> Factors decreasing the groundwater nitrate concentration include denitrification, groundwater <br /> movement(both vertical and horizontal),well pumping and hydraulics, and clean water recharge which <br /> contributes to a dilution effect. Therefore, if each of these sources and attenuating factors could be <br /> quantified on a mass balance basis, it may be that nitrate input is now roughly equivalent to output, or <br /> attenuation. Given that agricultural irrigation recharge is the largest single contributor to groundwater <br /> nitrate concentrations, and since the surrounding land has been farmed for several decades, it would be <br /> assumed that the nitrate concentrations in the underlying groundwater should be much higher than <br /> observed, if the attenuating factors were not significant. This is what was observed with the soil <br /> chemical analyses. The nitrate concentration within the soil environment under the existing leachline <br /> revealed a very high nitrate-nitrogen concentration of 97 ppm directly under the drain rock. <br /> SSS§ 6.7 For the Las Palmas project, it is imperative that: 1.) The architect/engineer/designer of <br /> the residential structures, 2.) The plumber, 3.)The septic system contractor, and 4.) The landscaper <br /> or landscape architect, must coordinate their services simultaneously for each individual Lot. The <br /> architect/engineer/designer must orientate the house on the Lot, taking into consideration the size <br /> of the house and location of the septic system disposal area. He/she must coordinate with the <br /> plumber to bring the influent to the proper location in relation to the septic tank(s) location. The <br /> septic system contractor must connect the system to the plumber's piping and install the disposal <br /> area under EHD guidelines. The landscaper must work with, and around the location of the tanks <br /> and disposal areas. <br /> Page -13- <br /> Chesney Consulting <br />