06/17/86 Special Meeting - Laserfiche WebLink

Home

from the USGS report on types of homes and wastewater flows, as well as the age of the homes, well logs of the drinking water wells, septic tank and well spacing, and previous land use in the area was not available. However, based on the findings of the USGS study (referenced in the DEIS) and based on new information derived since the DEIS was produced, some trends are becoming apparent. I l It appears the highest nitrate concentrations are found in shallow aquifers in areas that have irrigated, cultivated, agricultural land use. The lowest nitrate concentrations are found deeper in the drift in non-residential, non-agricultural areas (considered background levels). Nitrate concentrations in residential areas rank third, after cultivated, non-irrigated land use. This was the ranking suggested by the USGS findings and these results are somewhat supported by a study being conducted by the Anoka County Health Department as well as other studies performed in sandy soils. The Anoka County study, still in progress, is examining an area about one mile northeast of Northfork. Some drinking water wells in a residential area about two square blocks in size have elevated nitrate levels ranging from 3.5 to 33 mg-N/l. Wells are about 7B to 8B feet deep. However, the development is only about five years old. Rough calculations (using Brown et. ale and MPCA 1984 as a guide) would indicate that septic tank systems would not be able to produce the high nitrate concentrations at those depths in five years. In this case, previous land use practices may be a factor; this site in Ramsey was previously an irrigated, cultivated agricultural area. The one deep well (155 feet) in the study area nad .nitrate nitrogen concentrations of less than 1.B mg/l. \ Other studies conducted in outwash sands find similar trends. In three cases, where residential onsite systems coincided with various agricultural land use (nursery production, poultry raising, cherry orchards), agricultural land use was the most important source of nitrate contamination. However, deep wells (greater than 3B meters) typically had low nitrate concentrations (Matisoff et. ale no date, Ritter and Chirnside 1984, and USEPA 1982). r . I I Northfork drinking water wells appear to have a moderate risk for nitrate contamination. Eighty acres of corn have been fertilized with 75 Ibs of nitrogen/acre. 2BB acres of soybeans and lsB acres of oats are in production, but have not been fertilized. No irrigation has been used. Prior to 1984, this acreage was owned by General Mills and land was leased for farming. Farming practices are not known for the years prior to 1984. -77- I ...........