Assessment Comments
Assessment is based on results of monitoring (1) Site 8 of the Upper Iowa River Watershed (UIRW) project from April 2010 through September 2012, (2) IDNR project Site 5 at County Road W14 from April to July of 2011, and (3) IDNR project site 8 at Cresco from April 2011 to July 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 (2014) 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 are assessed (monitored) as "not supported" (IR 5p) due to levels of indicator bacteria that exceeded state water quality criteria. The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported” (IR 2a) based on results of chemical/physical monitoring at three stations during the 2010-2012 period. The sources of data for this assessment include the results of monitoring at three stations: (1) Site 8 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 191910002) from April 2010 through September 2012, (2) IDNR project Site 5 at County Road W14 (STORET station 15960044) from April to July of 2011, and (3) IDNR project site 8 at Cresco (STORET Station 15960010) from April 2011 to July 2012.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria at all three sites monitored during the 2010-2012 period. At site UIRW 8 (STORET station 191910002), the geometric means of indicator bacteria (E. coli) in the 18 samples collected during the recreational seasons of 2010 through 2012 were as follows: the 2010 geometric mean was 706 orgs/100 ml, the 2011 geometric mean was 885 orgs/100 ml and the 2012 geometric mean was 432 orgs/100 ml. All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Sixteen of the 18 samples (89%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.
At site 5 (Co. Rd. W14, STORET station 15960044), the geometric means of indicator bacteria (E. coli) in the 12 samples collected during the recreational seasons of 2011 and 2012 were as follows: the 2011 geometric mean (eight samples) was 249 orgs/100 ml, the 2012 geometric mean (four samples) was 337 orgs/100. Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Six of the 12 samples (50%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.
At site 8 near Cresco (STORET station 15960010), the geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2011 and 2012 were as follows: the 2011 geometric mean (17 samples) was 962 orgs/100 ml, the 2012 geometric mean (five samples) was 1,007 orgs/100. Both geometric means exceed the Class A1 criterion of 126 orgs/100 ml. Eighteen of the 22 samples (82%) exceeded the Class A1 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 a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, due to geometric mean violations at all three monitoring sites in this assessment segment, the Class A1 uses are assessed (monitored) as “not supported”.
Results of chemical/physical water quality monitoring from 2010 to 2012 suggest "full support" of the Class B(WW2) aquatic life uses. Monitoring at stations 191910002, 15960044, and 15960010 showed no violations of Class B(WW2) water quality criteria for ammonia in the combined 41 samples from the three stations analyzed over the 2010-2012 period. One of the 24 samples analyzed for dissolved oxygen violated the Class B(WW2) criterion of 5 mg/l. The sample collected from sation 15960044 on July 27, 2011 contained 4.4 mg/l of dissolved oxygen and thus violated the Class B(WW2) standard. Also, one of the 32 samples measured for pH violated the Class B(WW2) criterion of 6.5. The sample measured on July 6, 2010 at station 191910002 had a pH of 6.4 units, thus slightly violating the criterion of 6.5 pH units. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as pH and dissolved oxygen suggests impairment of aquatic life uses. Based on IDNR’s assessment methodology, however, these results suggest that the frequency of violations is not significantly greater than 10 percent; thus, these results do not suggest impairment of the Class B(WW2) aquatic life uses. Thus, the Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported”.
