T169 Urban Geochemistry (Posters)

Tuesday, 6 November 2018
9:00 AM - 6:30 PM
Halls J-K

IMPACTS OF MODERNIZING URBAN WATER SYSTEMS ON NUTRIENT LOADS, HEAVY METALS AND FECAL COLIFORM BACTERIA LEVELS IN A MUNICIPAL WATERSHED

Paper number: T169-6
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The Pleasant Run waterway (PRW) is an urban watershed in Southeastern Indianapolis with combined sewage overflow (CSO) disposal systems, which discharge both storm-drain runoff and raw sewage during rainfall events. The city of Indianapolis is replacing this outdated system, but the PRW will be the last area to be updated. The objective of this study is to assess the baseline geochemistry of this waterway before the CSO intervention occurs to eventually understand how, or if, the intervention changes waterway geochemistry. Our main initial focus is on anthropogenic and sewage-derived elements (e.g., lead, zinc, copper) and on fecal coliform along the PRW. Water and soil samples were taken during three different sampling efforts in summer 2018 from six locations along the waterway. Soil samples were dried, sieved and analyzed via x-ray fluorescence (XRF) for geochemistry. Water samples were filtered through a 0.45 micron filter and analyzed for dissolved geochemistry, and the filter was incubated on an agar plate for microbiological analyses, to include fecal coliform concentrations. For the geochemical analyses, the filtered water samples were tested via inductively coupled plasma optical emission spectrometry (ICP-OES). The dissolved geochemistry revealed high calcium, characteristic of the limestone bedrock in the area. Other metals were low (we plan to analyze these by ICP-MS in the future), although both phosphorus and boron, both related to anthropogenic sources, were detectable and showed high variability in space and time. The stream sediment geochemistry varied significantly, with several hotspots for lead occurring near/downstream of industrial sites. The lead values ranged from a low of 25 ppm, similar to background soil lead values, to 231 ppm. For Pb, a level similar to the elevated values is found in many of the urban soils in the area. Initial results from the microbiological analyses suggest high amounts of sewage entering the waterway, with nearly all of the cultures being above the safe contact level for e. coli. Data will continue to be collected until the CSOs have been replaced in order to paint a more complete picture of the state of the PRW. The initial results of this study indicate that CSOs have a negative impact on water quality, and updating the system is expected to reduce these negative effects.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-323702

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