Assessment Comments
Assessment based on results of (1) monitoring from May 2011 to November 2012 at station GRA 10 at Fox Road (STORET No. 15330005)and (2) a February 2012 summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) 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 also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses. This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]
SUMMARY The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supporting” (IR 5p) due to levels of indicator bacteria (E. coli) that exceed state water quality criteria. This is a new impairment for this assessment segment. The presumptive Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as "fully supported” (IR 2a). The source of E. coli data and data for chemical/physical parameters for this assessment is monitoring from May 2011 to November 2012 at station GRA 10 at Fox Road (STORET No. 15330005). The Class B(CW1) coldwater aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a) based on the February 2012 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau. Fish consumption uses remain "not assessed."
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the seven monthly samples collected during the recreational season of 2011 (95 orgs/100 ml) was below the Class A1 criterion, but the geometric mean of the eight samples collected during 2012 (267 orgs/100 ml) slightly exceeded the Class A1 criterion of 126 orgs/100 ml. Five of the combined 15 samples (33%) exceeded Iowa’s 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 contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The presumptive Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as "fully supported" based on levels of indicator bacteria that are well below the Class A2 criterion. The geometric means of indicator bacteria (E. coli) in the seven monthly samples collected during 2011 (95 orgs/100 ml), and the geometric mean of the eight samples collected during 2012 (267 orgs/100 ml) are both far below the Class A2 criterion of 630 orgs/100 ml. Only one of the combined 15 samples (7%) exceeded Iowa’s single-sample maximum criterion of 2,880 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 less than 630 orgs/100 ml., the secondary contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
Results of chemical/physical water quality monitoring in 2011 and 2012 do not suggest impairment of the Class B(WW2) aquatic life uses. Monitoring at station GRA 10 (STORET station 15330005) showed no violations of Class B(WW2) water quality criteria for ammonia or temperature in the 15 samples analyzed. Two of the 15 samples (13%) analyzed for dissolved oxygen violated the Class B(CW1) criterion of 7 mg/l. The samples collected on August 1 and September 5 of 2012 both contained 6 mg/l of dissolved oxygen and thus violated the Class B(WW2) standard (note: dissolved oxygen was recorded only to the nearest mg/l). Similarly, one of the 15 samples (7%) analyzed for pH violated the Class B(CW1) criterion of 9.0 pH units: the sample collected on June 1, 2011 contained a pH of 9.5 units, thus violating the water quality criterion. 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 than10 percent; thus, these results do not suggest impairment of the Class B(CW1) aquatic life uses. Thus, the Class B(CW1) aquatic life uses are assessed (monitored) as “fully supported”.
An updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2012 is consistent with the assessment of the Class B(CW1) coldwater aquatic life uses as "fully supported". According to the updated summary, Grannis Creek is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of the listed species without any stocking (a Category I trout stream). This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.
Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.
