WATER QUALITY MONITORING OF THE OSAGE CREEK ABOVE THE HIGHWAY 112 BRIDGE NEAR CAVE SPRINGS, ARKANSAS

The City of Rogers is one of the fastest growing communities in Arkansas. Located in Northwest Arkansas, Rogers lies in two primary watersheds; the Illinois River Watershed and Beaver Lake Watershed. The Illinois River Watershed receives municipal wastewater discharge from most of the metropolitan communities in Northwest Arkansas, along with nonpoint source urban and agricultural runoff. The Illinois River originates in Arkansas and flows west into Oklahoma where it is classified as a scenic river. The river has been a source of interstate disputes for a number of years. A federal interstate compact commission was established to mediate these disputes, especially concerning high levels of phosphorus, which is perceived to degrade in-stream water quality as well as to accelerate eutrophication of an Oklahoma reservoir. Recent developments include establishment of instream phosphorus limits of 0.037 mg/l for Oklahoma scenic rivers (current levels at the state line are around 0.4 mg/l) and an EPA request that the Illinois river and Osage creek be included on Arkansas' 303d list as impacted by high levels of phosphorus.A growing concern about sediment and phosphorus loading into the Illinois River led the City of Rogers to submit a proposal for and receive EPA 319 Nonpoint Source grant funding. That funding established a water quality monitoring station on Osage Creek in 2001. Osage Creek is the tributary of the Illinois River which originates in and drains most of the City of Rogers. The monitoring station was established at a USGS gauging station located just below the city limits of Rogers and about a mile below the City's WWTP and 200 acre sludge application area. The monitoring protocol used at the Osage Creek site was identical to that used at five other watersheds in Northwest Arkansas including the Illinois River at the state line. It consisted of taking base-flow grab samples every two weeks and using automatic sampling equipment to sample all storm events from start to finish. All samples were analyzed for nutrients and sediment and some samples were screened for a host of other constituents including metals and bacteria. Sampling was conducted at this site for a period of two years during which time nutrient and sediment loadings and concentrations were determined.In 2001 two additional sampling stations were established on Osage Creek. They were established on the property used by the Rogers WWTP to land apply sludge. One sampler was established above the application area and one in a location that receives most of the overland flow from the waste application area. These sites used the same protocol as the original Osage Creek monitoring station except the stage and rating curve measurements were performed by a water quality engineer and not the USGS. These sites were established to attempt to partition the nutrient and sediment loads between developing urban watershed, WWTP effluent, and contributions from the sludge application area.Results from the two year project indicate that the TSS contribution from this quickly developing urban watershed is greater on a per hectare basis than the other watersheds (except one) studied in Northwest Arkansas, most of which are primarily agricultural. Total phosphorus loads were higher per hectare than two of the watersheds and lower than the other three. About 1/3 of the phosphorus was transported during base-flow conditions and base-flow concentrations averaged 0.2 mg/l.Analysis of the data from the additional sampling sites and discharge records from the WWTP indicates that the predominate source of phosphorus in this watershed is from the urban area and not from the direct discharge by the WWTP or from the sludge application area. The strategy of transferring phosphorus from the wastewater stream to the land applied sludge appears to be an effective strategy for lowering P levels in the Illinois River.