Assessment Comments
Assessment is based on results of bacteria monitoring from 2004 through 2009 conducted as part of an IDALS/Division of Soil Conservation watershed project.
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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), and due to completion and approval of a use attainability analysis, this segment is now designated for Class A3 (children’s recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2010) assessment, the available water quality monitoring data will be compared to the applicable Class A3 and Class B(WW2) water quality criteria.]
SUMMARY: The Class A3 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria. The Class B(WW2) aquatic life uses remain “not assessed” due to the lack of information on which to base an assessment. The source of information for this assessment is results of bacteria monitoring during recreational seasons of 2004 through 2009 at three stations in this segment of Mad Creek monitored as part of an IDALS/Division of Soil Conservation watershed project: (1) station 50 near the mouth of Mad Creek, (2) station 66 in the city of Muscatine, and (3) station 49 downstream from Hwy 38 north of Muscatine.
EXPLANATION: The Class A3 (children’s recreation) uses are assessed as "not supported" based on levels of indicator bacteria during the recreational seasons of 2004 through 2009 that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) at all three monitoring stations of the IDALS/DSC project exceeded the Iowa water quality criterion to protect children’s recreation uses. The geometric means of E. coli bacteria at these stations were as follow: Station 50 (near mouth): 702 orgs/100ml in 7 samples with 71% of the samples greater than the single sample maximum criterion of 235 orgs/100 ml.; Station 66 (in Muscatine): 601 orgs/100 ml in 10 samples with 70% of the samples greater than the single sample maximum criterion of 235 orgs/100 ml.; Station 49 (north of Muscatine, dstr Hwy 38): 980 orgs/100ml in 11 samples; all 11 samples exceeded the single sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, the Class A3 uses are assessed (monitored) as not supported; this impairment will be added to Iowa’s 2010 Section 303(d) list of impaired waters.
The Class B(WW2) aquatic life uses remain “not assessed” due to the lack of water quality data/information upon which to base an assessment.
