Assessment Comments
Assessment based on results of (1) chemical/physical monitoring from May 2011 to November 2012 at station HEW 20 (STORET station 15220013), (2) IDNR/SHL biological sampling in 2013, and (3) a summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in 2012.
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 and the presumptive Class A2 (secondary contact recreation) are assessed as “not supporting” due to levels of indicator bacteria that violate state water quality standards (IR 5p). The Class B(CW1) coldwater aquatic life uses are assessed (monitored) as "partially supported" (IR 5a) due to violation of the Class B(CW1) criterion for temperature. These are all new impairments for this assessment segment. Fish consumption uses remain “not assessed.” The sources of data for this assessment include results of (1) chemical/physical monitoring from May 2011 to November 2012 at station HEW 20 at Crystal Road (STORET station 15220013), (2) IDNR/SHL biological sampling in 2013, and (3) a summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in 2012.
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 (517 orgs/100 ml), and the geometric mean of the eight samples collected during 2012 (655 orgs/100 ml) both exceeded the Class A1 criterion of 126 orgs/100 ml. Twelve of the combined 15 samples (80%) 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 presumptive primary 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 are also 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 2011 (517 orgs/100 ml) is below the Class A2 criterion of 630 orgs/100 ml, but the geometric mean of the eight samples collected during 2012 (655 orgs/100 ml) very slightly exceeds the Class A2 criterion. Only 1 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 greater than 126 orgs/100 ml., the presumptive secondary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Due to the fact that the 2012 geometric mean of 655 orgs/100 ml is likely not statistically different from the Class A2 criterion of 630 orgs/100 ml, this impairment should be considered very slight.
The Class B(CW1) aquatic life uses are assessed (monitored) as “partially supported.” Four of the 15 samples measured for water temperature during the May 2011 to November 2012 period at Station Cox 20 violated the Class B(CW1) criterion of 20C: 21.2C on August 3, 2011, 24.2C on July 2, 2012, 21.6C on August 1, 2012, and 21.3C on September 5, 2012. According to the IDNR assessment/listing methodology, the percentage of violations (27%) is significantly greater than 10% and thus suggests “partial support” of the Class B(CW1) aquatic life uses. Results for the approximately 15 samples collected from May 2011 to November 2012 show no violations of the Class B(CW1) criteria for ammonia and pH. Two of the 15 samples, however, violated the Class B(CW1) criterion for dissolved oxygen of 7.0 mg/l (the samples collected on July 2 and August 1 of 2012 both had 6 mg/l of dissolved oxygen) (note: dissolved oxygen values were reported to the nearest mg/l). According to the IDNR assessment/listing methodology, however, the percentage of violation (13%) is not significantly greater than 10% and thus these violations do not suggest impairment of the Class B(CW1) uses.
The assessment of the Class B(CW1) coldwater aquatic life uses is also based on results of biological monitoring in 2013 conducted as part of the IDNR/SHL coldwater stream sampling project. The results of this monitoring suggested (evaluated) “partial support” (IR 3b-c) of the Class B(CW1) uses. A series of biological metrics which reflect coldwater stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa that were collected in the stream sampling reach. The biological metrics were combined to make a coldwater benthic index (CBI). The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2013 CBI scores were 53 and 66. The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the CBI scores with biological impairment criteria (BIC) established for the 2012 Section 305(b) report. The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011. The CW BIC is 60 and this segment passed the CW BIC 1/2 times in 2013. This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.
IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”. This segment had multiple samples collected in a single year (2013). According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation). Despite this change in assessment methodology and type, this waterbody remains in IR Category 5a and remains on Iowa’s 2012 Section 303(d) list of impaired waters based on the temperature violations.
In addition, this assessment is also based on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2012 which suggests that the Class B(CW1) uses should be assessed as "fully supported". According to the updated summary, Hewitt (Hewett) 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 recent, but inconsistent, reproductive success and are not capable of maintaining a viable population of brown trout at this time (a Category II trout stream).
Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.
