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III. MASS BALANCE OF NITRATE-NITROGEN LOADING The initial investigative factors of any nitrate source identification procedure involves the assessment of the site to inventory and identify all potential nitrate sources. This Study identifies all on-site sources of nitrate impact which contribute a percentage of the total amount. The _ nitrate loading potential of the subject facility originates from primarily four sources: 1.) The corral areas - open corrals, covered corrals and proposed freestall barns. 2.) The separation basin and wastewater holding pond, 3.) Septic system impact and 4.) Solid manure and wastewater application to cropland. Each of the sources and their potential nitrate nitrogen concentration are discussed below: SPECIFIC NITROGEN SOURCE CONSIDERATIONS 1.) The Corral Areas: Freestall corrals contribute very little nitrogen to the underlying soil due to the concrete-lined flush system which transports wastes from these corrals. In addition, since these corrals will be covered, there is virtually no hydraulic head from rainfall or other sources which would drive the nitrate molecules continually deeper into the soil. Three factors are of significant importance regarding nitrogen contribution and the mitigation of the potential for nitrate impact from the open corrals. The first mitigating factor concerns the sloping of the open corrals to manage rainwater runoff. Each corral should be sloped 4% to 6% from the center to the ends to promote rainwater runoff. This water management technique reduces percolating water through the soil profile by preventing hydraulic head. Since the soil under the open corrals is composed of a clay material, permeability is reduced. When ponding of water does occur in the open corrals, a sump pump is used to transfer water into the separation basin. The second factor reducing nitrate impact to the groundwater is the clay content of the soil. The clay content percentage was determined to be 34% by the hydrometer test, ASTM D422: Particle Size Analysis of Soils. These samples were taken from the home application acreage. In addition to this test, a permeability test was also conducted on a representative sample taken from the open corral area. Test results indicate the indigenous soils possess a hydraulic conductivity, k, of 1.3 X 10-6 cm/sec. By using an average water table, or zone of saturation depth of 4 feet below grade, the following calculation illustrates that it will theoretically take 3 years before a nitrate laden wetting front reaches the saturated zone: 1.3 X 10"6 cm/sec. X 60 sec/1 min X (525,600 min/year- 30.5 cm/ft)= 1.34 ft/year. 4 ft - 1.34 ft/yr= 3 years. The dairy has been in operation for over thirty years, consequently, a higher nitrate concentration in the groundwater would be expected. The third mitigating factor is the soil compaction from the animals. The hooves of the cows act essentially like a "sheepsfoot" soil compactor, creating a high density, low void space soil "cap" in the top six inches of the soil profile. Soil compaction attenuates the downward migration of nitrate molecules by reducing pore water permeability. 5 Valfey Ag Pfsearch