Colorado Water Quality FORUM Arsenic Work Group

Transcription

1 Colorado Water Quality FORUM Arsenic Work Group Recommendations for Voluntary Collection of Arsenic Water Quality Data Purpose Collection of additional arsenic data has been identified by the Arsenic Work Group as a priority to help characterize arsenic sources and to evaluate effectiveness of arsenic treatment from various types of treatment technologies. It is critical that samples be analyzed at levels low enough to detect levels of total arsenic in the water. Since the current arsenic fish + water numeric water quality standard is 0.02 ug/l (total arsenic), low detection limits are necessary to determine how the arsenic levels in the sources relate to the standard. Provided below are recommendations for the collection of arsenic data to further support the development of a proposal for the 2016 Basic Standards Hearing. Wastewater Sources to be Sampled Arsenic data from the following sources are recommended. More than one source may apply to each entity collecting data. Municipal/Publically Owned Treatment Works or Private o Mechanical facility (activated sludge, etc.) o Package plants o Lagoon system o Treatment facilities with and without Industrial Pretreatment programs Industrial Wastewater Treatment Facilities o State permitted facility discharging directly to a receiving water o Regulated (Industrial Pretreatment permit) or unregulated facility discharging to a POTW sanitary sewer system Mining Operation Discharges Groundwater Dewatering Discharges (construction dewatering, other) Drinking Water Supplies (raw water source surface water, ground water) 1

2 Sampling Locations Arsenic data from the following sample locations are recommended. Several locations may apply to each entity collecting data. Raw influent to treatment facility Treated effluent from treatment facility Receiving water upstream of treatment facility discharge (may be multiple locations) Receiving water at a fully mixed location downstream of treatment facility (may be multiple locations) Drinking water supply raw source water prior to treatment Treated drinking water Other locations to support arsenic characterization For instance, for a typical domestic wastewater facility, the following locations should be considered: raw influent; treated effluent; treated drinking water; receiving water upstream of the discharge; and a fully mixed location in the receiving water downstream of the outfall. For a mining operation, it may be only possible to sample upstream of the discharge, influent to the plant, treated effluent, and a fully mixed location downstream of the outfall. For construction dewatering, it may be only possible to sample the influent and the effluent. Sampling Protocol It is recommended that samples be collected and managed following procedures which minimize the potential for contamination and ensure the collection of a representative sample. If sampling procedures are not available samples can be collected following procedures outlined in Standard Methods for the Examination of Water and Wastewater, 20 th Edition (section 9060). It is important that the location and volume of sample collected is representative of actual conditions and is not affected by factors such as unmixed conditions in the receiving water. Depending on available time and resources, samples can be collected as composite samples (time or flow weighted composite) or grab samples (single sample from representative location and time). 2

3 Number of Samples to be Collected If possible, the number of samples collected should be sufficient to characterize natural variability or variability due to other factors. For receiving water and drinking water supply samples it is suggested that one sample per month be collected for each month of the year. For treatment facilities (domestic, industrial, groundwater) sufficient data should be collected, if possible, to cover a range of influent concentrations, if influent concentrations are variable. If influent concentrations are fairly consistent, sufficient data should be collected to adequately calculate percent arsenic removal and treated effluent quality. Arsenic Form and Analytical Laboratory Methods. The type of analytical laboratory method will depend on the type of analytical equipment used. Different analytical methods can be used but samples should be analyzed for total arsenic and to the lowest level possible. Form of Arsenic to be Analyzed The fish + water arsenic water quality standard is in the total form and samples should be analyzed for total arsenic. Analytical Laboratory Methods EPA Method 200.7: Used with Inductively Coupled Plasma (ICP) instrument. o May not provide low enough detection level. Method Detection Limit (MDL) is typically 3-5 ug/l; Reporting Limit (RL) typically 10 to 50 µg/l EPA method 200.8: Used with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) Instrument. o Provides lower detection limit than EPA method. o Lower detection level and ability to analyze with matrix interferences can be achieved by using ICP-MS with a Collision Cell. MDL median 0.07 ug/l and mean 0.16 µg/l RL median.55 µg/l and mean.92 µg/l). CDPHE PQL 1.0 µg/l 3

4 EPA Method 200.9: Use with Stabilized Temperature Graphite Furnace Atomic Absorption. o Provides lower detection limit than EPA method. MDL is typically, µg/l, RL is typically 0.2 to 0.4 µg/l Analytical Detection Level There are a number of analytical detection limits that are commonly used. It is important to generate data which has a detectable concentration and avoid below detection (non-detect) results. All analytical results should also include the method detection limit (MDL) to help eliminate non-detect results. The following should be considered when analyzing total arsenic, either with an internal laboratory or a contract laboratory. Instrument Detection Level: Provides results with a stated confidence limit and can be used for regulatory compliance. May be presented as the Detection Limit or Reporting Limit. o The IDL should always be below the method detection limit, and is not used for compliance data reporting, but may be used for statistical data analysis and comparing the attributes of different instruments. Method Detection Limit (MDL): Provides the minimum concentration that can be measured and reported with 99 percent confidence that the concentration is greater than zero, but the exact concentration cannot be reliably quantified. o Although MDL data cannot not be used for regulatory compliance results can be useful for characterizing arsenic concentrations at low levels and can eliminate non-detect data. Reporting Limit (RL): An arbitrary number below which data is not reported. The reporting limit may or may not be statistically determined, or may be an estimate that is based on the experience and judgement of the analyst. This limit is frequently used as the lowest point on the calibration curve. Practical Quantification Limit (PQL): Provides the minimum concentration of an analyte (substance) that can be measured with a high degree of confidence that the analyte is present at or above that concentration. 4

5 o Currently, the PQL for arsenic is in the range of 1 ug/l and may be too high to detect total arsenic. Data Submittal It is anticipated there will be two data deliverables, one submittal in late 2014 to allow the Arsenic Work group to look at preliminary data and a final submittal in spring Possible formats/templates for data submittal, and where to store the data, will be covered at a future Arsenic Work Group meeting. Supplemental Information The following information should be gathered and provided as part of an arsenic data submittal. Type of treatment facility POTW, industrial, type of treatment process, etc. Is an Industrial Pretreatment program in place? Coordinates or specific description of sample locations for receiving waters and drinking water supplies. Total arsenic analytical results including, at a minimum: sample date, sample location, type of sample (receiving water, industrial discharge, etc.) water body name, detection level and type of detection level (DL, RL, etc.), MDL and analytical method. All results above the MDL should be reported. Results between the MDL and RL (or PQL) may be reported with a qualifier. Additional information to help support characterization of arsenic. 5