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Water Quality Conditions in Steamboat Creek, Washoe County, NV, with particular emphasis on NPS Loading of N, P, and selected Metals

While there is a currently established and comprehensive water quality monitoring program on the lower portion of the Truckee River downstream of Reno, and nutrient load entering the river from the Reno-Sparks Wastewater Treatment Facility (RSWTF) is well documented, very little is known about the magnitude and importance of nonpoint source (NPS) nutrients from the urban-agricultural watershed south of Reno. Indeed, in many systems, nonpoint source pollution to receiving bodies exceeds point source discharge. In response to this, the Nevada Division of Environmental Protection, in cooperation with the Washoe County Department of Comprehensive Planning has been conducting an extensive water quality monitoring program on Steamboat Creek and its major tributaries in order to (1) determine the relative magnitude of this creek with regard to nitrogen and phosphorus loading to the Truckee River and (2) determine its contribution of metals and its effect on downstream water quality.

In this report, we examine the data base which was collected between 1987 and 1991 when samples were taken bi-monthly from fifteen (15) locations. The purpose of this data evaluation is to: summarize physical, chemical and biological darn taken during the 1987-1991 monitoring of Steamboat Creek and its major tributaries; describe changes in constituent concentration as water flows downstream towards the Truckee River calculate changes in nitrogen and
phosphorus load by reach of stream; describe changes in metals concentrations in the study system and identify sources; use correlational relationships to assist in the interpretation of water quality data; estimate nitrogen and phosphorus loading to the Truckee River via Steamboat Creek and compare this to other regional point and nonpoint sources; provide a preliminary evaluation of recommended N-removal techniques and; recommend future studies.
Throughout the entire period of record, and at all stations, flow ranged from a minimum of 0.0-0.1 cfs to a maximum of 84 cfs; with few exceptions, mean annual flow was uniform between each of the water years. The eight drainage tributaries to Steamboat Creek separated into three categories with respect to magnitude of discharge. Annual average flows were greatest at Steamboat Ditch and Boynton Slough -±11-16 cfs; intermediate to low at Galena Creek, Whites Creek, and Alexander Ditch -±3-5 cfs, and low at Thomas Creek, Rio Poco Drain and Yori Drain -±1-4 cfs. The largest contributor of flow to Steamboat Creek was Boynton Slough with a mean annual discharge typically in the range of 12.0-16.2 cfs. Boynton Slough is a major route for regional agricultural return flows to the Truckee River, consequently, summer flows are very high. Flow at Kimlick Lane (just upstream from RSWTP and the most downstream station) was the largest in the system with a mean annual discharge which ranged from 23.5 to 34.2 cfs.

For nitrogen concentration the following generalizations were apparent;
1) N-concentrations were relatively consistent during each of the four years of monitoring,
2) TN, TKN and N03 was typically lower at the upstream stations SB 3 (Pleasant Valley), -SB 10 (Thomas Creek) as compared to the remaining downstream stations; and concentrations rose significantly between SB 7 (Geiger Grade) and SB 11 (Short Lane),
3) TKN typically dominated TN with the clear exception of Yori Drain and to a lesser extent, Rio Poco and Boynton, and
4) N03 concentrations in the Yori Drain were exceptionally high. TN-load to Steamboat Creek increased significantly between SB 7 and SB 11; this was related to surface and groundwater inputs of both TKN and N03. TN-load was very high from downstream tributaries which drain either agricultural lands, receive groundwater flow with regionally high nitrate, or both.
The project mean of the individual annual mean TN-load values in order of magnitude are Boynton Slough (73.7 lbs/day), Alexander Drain (31.1 lbs/day) Yori Drain (25.3 lbs/day), and in Rio Poco Drain (10.5 lbs/day). Nitrate load was relatively low in Alexander Drain and Rio Poco Drain, but much higher in Boynton Slough and Yori Drain. With the exception of 1991, the sum of N03-load at these latter stations was very similar to that calculated at Kimlick Lane.
TN-load from Steamboat Creek was 50-55% of the TN-load from the RSWTP.

The only tributary which showed a high P-concentration was Alexander Ditch. High flows of low P water in Boynton Slough acted to reduce the concentrations measured at Kimlick Lane. Water entering Steamboat Creek in the upper portion of the drainage (i.e. discharge from Little Washoe Lake and Galena Creek) did not carry significant P-loads relative to the more downstream locations. The increase in mean annual TP-load (3.3 1-8.48 lbs/day) and OP-load
(2.27-6.41 lbs/thy) between Geiger Grade and Short Lane was most likely the result of groundwater flow and irrigation return water with elevated P-concentration. This is supported by the seasonality of the P-spikes and by the fact that OP typically comprised 70-80% of the TI’ at Short Lane. Alexander Ditch and Boynton Slough typically contributed large P-loads to Steamboat Creek, on the order of 5-15 lbs/day. Conversely, Rio Poco Drain and Yori Drain
discharged much less TP; 1-2 lbs/day. The region of the system which showed the greatest P-loading was that segment of the creek between the confluence of Yori Drain and Kimlick Lane. Mean annual TP-loading in this reach ranged from 6.86 to 30.36 lbs/day, with the majority in the particulate-P form. This was in contrast to all the upstream sites which was dominated by OP. TP-load from RSWTF ranged from 37-125 lbs/day over the period of record, with most values between 50-70 lbs/thy; P-load from Steamboat Creek ranged from 7-150 lbs/day; however, values were commonly less in the 20-50 lbs/thy range. Average daily load at Kimlick Lane from Oct-87 to Jun-91 was 43 lbs/day for TP and 18 lbs/day for OP.

The data indicated that the Steamboat Hot Springs were a significant source of arsenic, boron and chloride (plus TDS) to Steamboat Creek. The other measured constituents were not elevated by this nonpoint source. For all the constituents for which water quality standards have been established in the Steamboat Creek study area, only arsenic and boron routinely and significantly exceeded these standards. Given the rich geologic nature of the Steamboat Hot
Springs and its thermal discharge to the creek it is not unexpected to fmd these high downstream concentrations.

Doc 6.1142 WQ in Steamboat Creek.pdf4.53 MB