Assessment Comments
Assessment is based on: (1) bacterial monitoring conducted approximately ½ mile downstream from Coffins Grove County Park (STORET station 15280006) as part of the Lake Delhi watershed assessment from April to June, 2006 and (2) biological monitoring conducted by the IDNR Fisheries Bureau in 1998.
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), 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 (2010) 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” due to levels of indicator bacteria that exceed state water quality criteria. This assessment represents a new Section 303(d) impairment for this assessment segment. The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported” based on results of biological monitoring conducted in 1998. The sources of data used for this assessment are (1) bacterial monitoring conducted approximately ½ mile downstream from Coffins Grove County Park (STORET station 15280006) as part of the Lake Delhi watershed assessment from April to June, 2006 and (2) biological monitoring conducted by the IDNR Fisheries Bureau in 1998. This is the same assessment as that developed for the previous (2008) Integrated Report.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric mean of E. coli in the 7 samples collected at the monitoring station on Coffins Creek from April to June, 2006, was 612 orgs/100 ml. Four of the seven samples (57%) 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 of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Although IDNR’s listing methodology requires that a minimum of ten E. coli samples be collected over a three-year period to support a Section 303(d) listing, this segment is being added to Iowa’s 2010 Section 303(d) list based on overwhelming evidence of impairment. That is, even if three additional samples had been collected, and each of these three samples had less than 10 orgs/100 ml (the INDR detection level), the resulting geometric means of E. coli at this station (178 orgs/100 ml) would still exceed Iowa’s Class A1 criterion of 126 orgs/100 ml. Thus, the Class A1 uses of this segment are assessed (“monitored”) as “not supported,” and this impairment is being added to Category 5a of IDNR’s 2010 Integrated Report (Iowa’s Section 303(d) list).
The assessment of the Class B(WW2) aquatic life uses was based on data collected in 1998 as part of an IDNR Fisheries stream sampling project: Manchester research station. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data. The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1998 evaluated FIBI was 61 (good). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The non-riffle site FIBI BIC for this ecoregion is 44. This segment passed the FIBI BIC 1/1 times in 1998.
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 between 2004 and 2008 to be considered “monitored”. This segment had a single sample collected in 1998. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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).
[Note: although data for ammonia nitrogen were collected at STORET station 15280006 as part of the Lake Delhi watershed assessment project, supporting data for pH and temperature were not collected. Thus, INDR was not able to compare the sample ammonia values to the temperature/pH-dependent Class B(WW2) water quality criteria for ammonia.]
