Concentrations, loads, and yields of selected water-quality constituents during low flow and storm runoff from three watersheds at Fort Leavenworth, Kansas, May 1994 through September 1996

A study of the effects of storm runoff from urban areas on water quality at Fort Leavenworth, Kansas, was conducted from May 1994 through September 1996. The purpose of this report is to present information to assess the current (1994-96) conditions and possible methods for anticipating future water-quality effects from storm runoff and changes in land use. Three sampling sites were established to monitor streamflow and water quality from three watersheds draining the study area. Streamflow was monitored continuously, and water-quality samples were collected during low-flow (12 samples) and storm-runoff (21 samples) conditions to determine mean annual constituent loads.

Constituent concentrations for the most part were smallest during low flow with the exception of major ions, dissolved solids, and some nutrients. Concentrations of suspended solids and total recoverable metals at all three sites were much larger in storm-runoff samples than in low-flow samples--typically an order of magnitude larger than low-flow concentrations. Mean low-flow nutrient concentrations were either larger than or smaller than storm-runoff concentrations depending on the watershed.

Total chloroform and total tetrachloroethylene were the only two volatile organic compounds detected, and acid-base/neutral organic compounds were not detected in any of the samples collected. Eight pesticides were detected in low-flow samples, and 15 pesticides were detected in storm-runoff samples. The only mean concentrations of the selected constituents in this study that exceeded either the U.S. Environmental Protection Agency's Maximum Contaminant Level or the Secondary Maximum Contaminant Level were dissolved solids and total recoverable iron and manganese.

Mean annual loads for 10 selected constituents were estimated for each watershed. Overall, storm runoff contributed more than one-half of the total mean annual loads for 8 of the 10 selected constituents. In fact, more than 70 percent of the mean annual loads for suspended solids and total recoverable copper, lead, and zinc were contributed by storm runoff. More than one-half the mean annual load was contributed during lowflow for dissolved
solids at all watersheds.

Mean annual yields (mass per unit area) of selected constituents from each watershed indicated few differences between watersheds. The lack of variability of yields among the three watersheds indicates that differences in land uses are small enough that few distinctions can be made between watersheds. Overall, storm runoff contributed more than one-half of the mean annual yields for chemical oxygen demand, suspended solids, most of the selected nutrient constituents, and total recoverable copper, lead, and zinc. Large yields of chemical oxygen demand, suspended solids, and total recoverable metals during storm runoff from one of the watersheds are probably related to the erosion of exposed soils at construction sites within the watershed. Low yields of suspended solids and total recoverable copper and zinc from another watershed are probably related to retention-storage effects from lakes upstream from the sampling site.