Assessment Comments
Assessment is based on (1) results of water quality monitoring in 2006 by the Lake Delhi Watershed Association at two locations on the Maquoketa River (below Backbone Lake (STORET station 15280001) and approximately 4 miles SE of Dundee (STORET station 15280002)) and (2) biological monitoring in 2001 by the IDNR Fisheries Bureau: FIBI average (n=2) = 45 (fair). Non-riffle FIBI BIC = 44.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this river segment was designated only for Class B(WW) aquatic life uses, including fish consumption 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 the completion of a Use Attainability Analysis in 2007, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (evaluated) as “not supported” due to levels of indicator bacteria that exceeds state water quality criteria. The Class B(WW1) are assessed (evaluated) as “fully supported” based on results of biological (fish) monitoring in 2001 by the IDNR Fisheries Bureau. Fish consumption uses are not assessed due to lack of fish contaminant monitoring in this assessment segment. Sources of data used for this assessment include (1) results of water quality monitoring in 2006 by the Lake Delhi Watershed Association at two locations on the Maquoketa River (below Backbone Lake (STORET station 15280001) and approximately 4 miles SE of Dundee (STORET station 15280002)) and (2) biological monitoring in 2001 by the IDNR Fisheries Bureau.
EXPLANATION: The Class A1 (primary contact recreation) uses were assessed (evaluated) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A1 criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A1 uses for purposes of Section 305(b) assessments and Section 303(d) listings.
The geometric mean of E. coli in the seven samples collected by the Lake Delhi Watershed Association at the monitoring station downriver from Backbone Lake was 1,066 orgs/100 ml; five of the seven samples (71%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. Similarly, the geometric mean of E. coli in the seven samples collected at their monitoring station downriver from Dundee was 2,198 orgs/100 ml; six of the seven samples (86%) 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 the geometric means at both sites were well above the state water quality criterion of 126 orgs/100 ml, too few data points are available do develop a “higher confidence” assessment. According to the IDNR assessment methodology a minimum of ten samples per site is required for a “monitored” (higher confidence) assessment based on levels of indicator bacteria; assessments developed with fewer than 10 samples are considered “evaluated” (lower confidence) and are not typically appropriate for Section 303(d) listing. Because fewer than 10 samples were available for the assessments at these monitoring stations, IDNR considers the assessment of support of the Class A uses as of relatively low confidence (evaluated) and thus not appropriate for Section 303(d) listing.
The Class B(WW1) aquatic life uses remain assessed (evaluated) as “fully supported” based on results of biological monitoring. The evaluated assessment was based on data collected in 2001 as part of a DNR 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 2001 FIBI average (n=2) was 45 (fair). 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 FIBI BIC for this ecoregion is 44.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this assessment segment.
