The effect of septic systems on groundwater quality in the Prairie Aquigroup and Alexandrian-Maquoketa aquifer, Campton Township, Kane County Illinois

Includes bibliographical references (pages [211]-214)Campton Township is a rapidly growing rural community located in the central portion of Kane County in northeast Illinois. The township consists of large residential areas, small businesses, and farmland which border the western suburbs of Chicago. Since most of the area is beyond the reach of municipal sewer networks, individual septic systems are used extensively throughout the township to dispose of sewage produced by each household. The majority of residential water wells in Campton Township are located in close proximity to the septic absorption fields and obtain water from the Prairie Aquigroup or the Alexandrian-Maquoketa aquifer. The Alexandrian-Maquoketa aquifer is composed predominantly of the Maquoketa Shale Group, which includes relatively impermeable Ordovician age shales, permeable argillaceous dolomites, and minor limestones. Thin, laterally discontinuous Alexandrian units overlie the Maquoketa Shale Group and are made up almost entirely of fine-grained dolomites. Overlying the irregular bedrock surface, the Prairie Aquigroup includes all of the unconsolidated glacial drift, sand and gravel, alluvium, and other Holocene sediments. These locally confined units are recharged by precipitation and are in close hydraulic connection with the bedrock. A basic geochemical and hydrogeologic analysis was focused on these aquifers and used to gain information about the effects of septic systems on groundwater quality. Water samples were taken during two sampling periods, including a short reconnaissance sampling of groundwater and surface water and a second larger sampling of groundwater. ABSTRACT These samples were field screened for pH, Eh, temperature, conductivity, and dissolved oxygen and analyzed in the laboratory for nitrate-nitrogen, nitrite-nitrogen, ammonianitrogen, alkalinity, sulfate, chloride, calcium, magnesium, iron, manganese, strontium, potassium, and sodium. Concentrations of these constituents, along with X-Y plots, geochemical concentration maps, and existing well information were used to make interpretations about the geochemical system. The analysis indicated that the general groundwater flow direction in the township is from west to east and water level elevations display local recharge and dewatering patterns. The Prairie Aquigroup and Alexandrian- Maquoketa aquifer are hydraulically connected through recharge and the groundwater in both aquifer zones is very similar in general composition. Several ion sources, along with localized groundwater flow and preferential flow paths, create differences in chemical concentration patterns between the two aquifer zones. Although plumes of high chemical concentrations in the direction of groundwater flow such as those found in related studies are not strongly defined in spatial plots of the analytes, relatively high concentrations of ammonia-nitrogen in the deeper groundwater indicate that septic systems are a likely contributor to the geochemical system. A limited supply of available oxygen most likely contributes to incomplete aerobic treatment of septic wastewater and agriculturally impacted soil water as it travels into the deeper groundwater system. A limited amount of nitrification occurs to produce relatively high concentrations of nitrate and nitrite in areas of the shallow aquifer zone. Denitrification transforms almost all of the nitrate to ammonium and ammonia under the anoxic conditions found in the deeper groundwater. If inadequate aerobic conditions persist in the shallow groundwater zones, they have the potential to cause severe clogging in septic absorption fields in the area and increasingly poor wastewater treatment over time.M.S. (Master of Science