Rock Creek IA 01-MAQ-3

Assessment Comments

Assessment is based on monitoring upstream from PCS Nitrogen Co. by LTRMP staff (Bellevue Office) from 2010-2012.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, this segment is now presumptively designated for Class A1 (primary contact recreation) uses.   The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses).   Thus, for the current (2012) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses remain not assessed 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 2010 through 2012 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 2010 to November 2012 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 all 42 samples collected by LTRMP staff at County Road Z40 between January 2010 and November 2012 were well-below Class B(WW2) chronic criteria.   The maximum ammonia concentration in the LTRMP samples was 0.35 mg/l; (median = 0.03 mg/l).   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 (for comparison, see assessment for lower Rock Creek, Waterbody ID:  IA 01-MAQ-0010_1).    

DISSOLVED OXYGEN:  None of the 42 samples collected upstream from the PCS facility at County Road Z40 by LTRMP from January 2010 to November 2012 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:  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.