Rock Creek IA 01-MAQ-3
from unnamed tributary in SW 1/4 NE 1/4 S30 T81N R6E Clinton Co. (upstream from PCS Nitrogen) to unnamed tributary in S23T81NR5E Clinton Co.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
- Trend
- Stable
- Created
- 2/18/2016 2:48:19 PM
- Updated
- 11/17/2016 8:13:34 AM
The presumptive Class A1 (primary contact recreation) uses remain not assessed (IR 3a) due to the lack of information upon which to base an assessment. None of the monitoring conducted in this segment has included analysis for indicator bacteria. The Class B(WW2) aquatic life uses are assessed (monitored) as "fully supported" (IR 2a). Results of water quality monitoring from 2012 through 2014 continue to show generally good water quality in this segment of Rock Creek. The assessment of support of the Class B(WW2) uses as "fully supported" is based on comparison of monitoring data to Iowa water quality standards for ammonia-nitrogen, dissolved oxygen, and pH.
SOURCES OF DATA: Staff of the Upper Mississippi River "Long Term Resource Monitoring Program" at Bellevue, Iowa, continue to monitor the water quality of Rock Creek (two sites) and Shrickers Slough. The LTRMP monitoring station on Rock Creek above PCS-Nitrogen (Site RK03.7M) is located at County Road Z40, approximately 1.5 miles upstream from the former PCS-Nitrogen facility. Although surface water monitoring is also conducted on a weekly basis at seven locations in the Rock Creek watershed by QC Analytical Services of Le Claire, IA, none of the QC Analytical sites is useful for characterizing water quality upstream from the PCS-Nitrogen facility.
EXPLANATION: Results of water quality monitoring conducted by LTRMP staff from January 2012 to November 2014 show no violations of water quality criteria designed to protect Class B(WW2) aquatic life uses, thus suggesting "full support" of these uses. Data for ammonia-nitrogen, dissolved oxygen, and pH were compared to Class B(WW2) criteria.
AMMONIA-NITROGEN: Levels of ammonia-nitrogen in one of 42 samples (2%) collected by LTRMP staff at County Road Z40 between January 2012 and November 2014 violated Class B(WW2) chronic criteria. The maximum ammonia concentration in the LTRMP samples was 12.3 mg/l; (median = 0.03 mg/l). According to the Iowa DNR's assessment methodology, impairment of aquatic life uses is suggested if significantly more than 10% of the samples violate water quality criteria for ammonia. The frequency of violations of ammonia criteria (2%) is well below that impairment threshold. In contrast to the lower segment of Rock Creek, these results suggest that levels of ammonia are not a water quality concern in this segment of the stream.
DISSOLVED OXYGEN: None of the 42 samples collected upstream from the PCS facility at County Road Z40 by LTRMP from January 2012 to November 2014 violated the Class B(WW2) criterion for dissolved oxygen (5.0 mg/l). These results suggest that levels of dissolved oxygen in this segment of Rock Creek are adequate to fully support the Class B(WW2) aquatic life uses.
pH: Levels of pH in one of 42 samples (2%) collected by LTRMP staff at County Road Z40 between January 2012 and November 2014 violated Class B(WW2) criteria for pH. Similar to results for dissolved oxygen, none of the 42 samples collected by the LTRMP at County Road Z40 violated Class B(WW2) water quality criteria for pH. According to the Iowa DNR's assessment methodology, impairment of aquatic life uses is suggested if significantly more than 10% of the samples violate water quality criteria for pH. The frequency of violations of this criterion (2%) is well below that impairment threshold, thus suggesting that pH levels are not causing impairment of aquatic life uses.