Assessment Comments
Assessment is based on results of (1) IDNR/UHL ambient monitoring from 2002-04 upstream from Cedar Rapids, (2) monitoring of the Cedar River for nitrate by the Cedar Rapids Water Department from 2002-04, and (3) USGS ambient monitoring from 2002-04.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses were assessed (monitored) as “partially supported” due to levels of indicator bacteria that exceed state criteria. The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of ambient water quality monitoring. The Class C (drinking water) uses were assessed (monitored) as "fully supported/threatened" (impaired) with a declining water quality trend due to levels of nitrate that occasionally exceed the state drinking water criterion of 10 mg/l (=U.S. EPA’s MCL for nitrate). Fish consumption uses were not assessed due to the lack of fish contaminant monitoring in this river segment. The sources of data for this assessment are (1) the results of monthly monitoring from January 2002 through December 2004 at the IDNR ambient city monitoring station located at County Road E36 east of Palo (STORET station 10570002), (2) the results of ambient monitoring of the Cedar River for nitrate by the Cedar Rapids Water Department from 2002 through 2004, and (3) results of USGS chemical/physical water quality monitoring at Edgewood Road from February 2002 through September 2004.
EXPLANATION: The Class A uses were assessed as "partially supported" based on results of monitoring for indicator bacteria (E. coli). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A 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 A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in the 24 samples collected (75 orgs/100ml) is well below the Iowa Class A water quality criterion of 126 orgs/100ml. Six of the 24 samples (25%), however, exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if levels of E. coli exceed the single-sample maximum value in more than 10% of the samples, the primary contact recreation uses should be assessed as “partially supported” (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, these results suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum value, thus suggesting that the Class A uses should be assessed as “partially supported/impaired”.
The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of water quality monitoring from (1) the IDNR ambient station near Palo and (2) the USGS station at Edgewood Road from 2002 through 2004. Monitoring at these stations showed no violations of Class B(WW) water quality criteria for dissolved oxygen, ammonia-nitrogen, or for toxic metals and toxic organic compounds in the approximately 30 samples analyzed during this assessment period; none of the 7 samples analyzed for pesticides exceeded their respective Class B(WW) criteria. The level of pH, however, in one of the 36 samples from the IDNR/UHL station, and in one of the 24 samples from the USGS station, violated the Class B(WW) criterion of 9.0 pH units. Both samples were collected during the first week of October, 2003. Because these violations are more likely related to natural conditions than to a pollutant, the occurrence of the high level of pH in this river segment is not seen as a water quality impairment. In addition, the frequency of pH violations does not suggest impairment: according to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of less than 10 % for conventional parameters such as pH suggest "full support" of aquatic life uses. Thus, the percentages of violations of the pH criterion at the IDNR and USGS stations (3% and 4%, respectively) do not suggest an impairment of aquatic life uses.
Based on results of ambient monitoring conducted by IDNR and by the Cedar Rapids Water Department, the Class C (drinking water) uses were assessed as "fully supported/threatened" with a declining water quality trend due to violations of the state water quality standard (= U.S. EPA’s MCL) for nitrate. Results of IDNR ambient monthly monitoring at the Palo station show only one violation of the nitrate MCL in the 36 monthly samples (3% violation) collected during the 2002-2004 assessment period (mean=5.5 mg/l; maximum=11.0 mg/l). According to the IDNR assessment methodology, these results do not suggest that the Class C drinking water uses are impaired. Based on DNR's Section 305(b) assessment methodology, if less than 10% of the samples exceed the nitrate MCL, the drinking water uses should be assessed as "fully supported". In addition, two of the 36 samples analyzed for atrazine during the 2002-04 assessment period at the IDNR/UHL station exceeded the Iowa Class C criterion for atrazine of 3 ug/l (=U.S. EPA’s MCL). The average level of atrazine in the 36 samples was 0.6 ug/l (median=0.2 ug/l); these results do not suggest an atrazine-related impairment of the Class C uses.
Monitoring of the Cedar River by the Cedar Rapids Water Department (CRWD) near their water supply intake areas from January 2002 through December 2004, however, suggests that the drinking water uses of this segment of the Cedar River should remain assessed as “impaired”. The CRWD data from two stations show that 101 of the 446 samples collected (23% violation) at the Mohawk Park station, and 8 of the 265 samples collected (3%) at the Black Hawk Park station, exceeded the 10 mg/l water quality standard of 10 mg/l. At the Mohawk Park station, the mean, median, and maximum values were 7.2, 6.5, and 14.7 mg/l, respectively. At the Black Hawk Park station, the mean, median, and maximum values were 4.7, 5.3, and 11.8 mg/l, respectively. Violations tended to occur during the late spring and early summer.
Due to over-sampling by water supply utilities during times of year when nitrate levels tend to be high, the use of a simple percentage violation likely overestimates the percentage of time that nitrate levels actually exceed the MCL. Thus, in order to determine whether the Class C uses are impaired, IDNR staff summarized nitrate data from the Cedar River Water Department and other water utilities as weekly averages and compared these averages to the water quality standard. Thirteen of the 150 weekly average nitrate levels (9%) for the period 2002-2004 exceeded the MCL at the Mohawk Park station. Only one of the 85 weekly average nitrate levels (1%) for the period 2002-2004 exceeded the MCL at the Black Hawk Park station. According to IDNR's assessment guidelines, both the IDNR and CRWD datasets show an MCL violation frequency of less than 10% and thus suggest “full support” of the Class C drinking water uses. Additional information supplied by the Cedar Rapids Water Department, however, shows evidence of increasing nitrate levels over time. This increasing trend in nitrate suggests that less than full support is likely within the next few years. According to IDNR assessment guidelines, waterbodies assessed as "fully supported with a declining water quality trend are considered "impaired" and are candidates for Section 303(d) listing. This assessment is consistent with previous assessment and the Section 303(d) listing history for this segment of the Cedar River.
Fish consumption uses remain “not assessed” due to lack of recent fish tissue monitoring in this river segment.
