Assessment Comments
Assessment based on results of (1) IDNR/SHL biological sampling in 2008, 2009 and 2012; (2) an IDNR investigation of a fish kill in August 2005; and (3) results of chemical/physica//bacterial monitoring from May 2011 to November 2012 at station ROB-50 at Dalmatian Avenue (STORET station 15220019).
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 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 “partially supported” due to violations of Iowa water quality criteria for indicator bacteria (IR 5p). This represents a new impairment for this stream segment. The Class B(WW2) aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a) based on (1) results of IDNR/SHL biological sampling in 2008, 2009 and 2012 and (2) based on chemical/physical water quality monitoring in 2011 and 2012. Occurrence of a fish kill in August 2005 due to hog manure suggested impairment of the Class B(WW2) uses of this stream. The party responsible for this kill was identified, and IDNR sought restitution for the value of the fish killed and the costs incurred by IDNR during investigation of the kill. This fish kill-related impairment would be appropriate for Category 4d of Iowa’s Integrated Report. Because more than five years have elapsed since the most recent kill, this 4d impairment was moved to IR Category 3b in Iowa’s 2012 Integrated Report. The source of water quality data for this assessment is the results of monitoring from May 2011 to November 2012 at station ROB-50 at Dalmatian Avenue (STORET station 15220019).
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 (255 orgs/100 ml), and the geometric mean of the eight samples collected during 2012 (259 orgs/100 ml) both slightly exceeded the Class A1 criterion of 126 orgs/100 ml. Eleven of the combined 15 samples (73%) 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 primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW2) aquatic life uses are assessed (monitored) as "fully supporting" based on data collected in 2008, 2009 and 2012 as part of IDNR/SHL stream biological sampling projects. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and 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) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2008 FIBI scores were 43, 52 (fair) and 64 (good) and the BMIBI scores were 61, 66, 69 (all good). The 2009 FIBI score was 55 (good) and the BMIBI score was 67 (good). The 2012 FIBI score was 45 (fair) and the BMIBI score was 49 (fair). The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores 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 1994-2008. The FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This segment passed the FIBI BIC 3/5 times and passed the BMIBI BIC 4/5 times in the last five years.
Results of chemical/physical water quality monitoring conducted between May 2011 and November 2012 also suggest “full support” of the Class B(WW2) aquatic life uses. No violations of Class B(WW2) water quality criteria for ammonia, dissolved oxygen, pH, or temperature occurred in the approximately 15 samples analyzed during this period.
A fish kill occurred in this stream segment on or before August 1, 2005 and was caused by a release of hog manure from an over-full storage pit. According to the IDNR investigation, an outdoor storage pit lacked sufficient capacity to handle the amount of manure delivered to it from an indoor storage pit; thus, an overflow occurred. Approximately 2.25 miles of Roberts Creek were affected by the resulting kill. The kill began in an unnamed tributary to Roberts Creek (waterbody IA 01-TRK-0361-0) in Section 8 of T95N, R6W, Clayton County, and proceeded downstream through Section 9, 15, and 15 of T95N, R6W. An estimated 8,000 fish were killed. Based on IDNR records, the value of the fish killed was estimated at $4,893. Other than a notation that the kill affected “mostly non-game species", no detailed information on species killed is available. The party responsible for the kill was identified. IDNR has sought restitution for the value of the fish killed and the costs incurred by IDNR during investigation of the kill.
According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill during an assessment period indicates "partial support" of the aquatic life uses. If, however, a consent order has been issued to the party responsible for the kill and monetary restitution has been sought for the fish killed, the affected waterbody should be placed in IR Category 4d (impaired but TMDL not required). Thus, this impairment was appropriate for Category 4d of Iowa’s 2008 and 2012 Integrated Reports. IDNR considers IR 4d fish kill waters with no subsequent kills in at least the five years subsequent to the kill as appropriate for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Thus, this fish kill impairment was moved to IR Category 3b for the 2012 Integrated Report.
