11 Miss. Code. R. 6-1.2.6
The second step involves the development of permit limits in accordance with accepted state and national water quality criteria for those facilities exhibiting potential toxicity. Permit limits may take the form of chemical specific and/or whole effluent toxicity based limits.
The third step in the process involves additional testing and actual toxicity reduction for those facilities which fail any whole effluent toxicity requirements included in their permits. Permits addressing whole effluent toxicity have specific language requiring the permittee to perform a Toxicity Reduction Evaluation (TRE) upon non-compliance with the whole effluent toxicity limitations contained in the permit.
Where: Kp = Linear Partition Coefficient
Kpo = Regression Coefficient (from table)
TSS = Total Suspended Solids Concentration (site specific 15th percentile)
a = Exponent Constant (from table)
Where: C/CT = Dissolved Fraction of metal
Identify every toxic parameter in the permit and/or application above quantitation levels 1 and set up a table for each outfall, listing for each parameter the following2:
The following calculation conventions shall be utilized when using data reported as non-detect or less than detection:
The Department will not consider an application complete if the concentrations required are reported as "N.D." (Not Detected) unless a
1Where application form data are reported as "less than" (<) compare the method detection limit (MDL) as defined in Appendix B of 40 CFR 136 which is incorporated herein and adopted by reference. MDLs will be utilized in determining the reasonable potential of a given pollutant to violate water quality criteria. If a pollutant is reported as "non-detectable" above the MDLs as defined in Appendix B of 40 CFR 136, the pollutant will be assumed to be present at that reported level of sensitivity.
2Note in some cases parameters limited by the permit may be below the minimum quantitation level. chemical by chemical listing of the quantitation levels used is provided with the application.
Technology/federal guidelines based permit limits are calculated using current facility data and federal guidelines. If existing permit limits are more stringent and are being attained, use existing permit limits.
Appropriate 7Q10 and annual average flows will be calculated in accordance with the methods found in Techniques for Estimating 7-Day, 10-Year Low-Flow Characteristics for Ungaged Sites on Streams in Mississippi (USGS Report 91-4130), and Low-Flow and Flow-Duration Characteristics of Mississippi Streams (USGS Report 90-4087) or the most recent edition, respectively.
Where: IWC = Instream Wastewater Concentration (where facility water supply is not receiving water.)
Qr4 = Receiving water flow at appropriate low flow
Qw = For non-domestic facilities - Maximum 30-day average wastewater flow, if available;
Domestic facilities - design flow; Hydrographic control release facilities - appropriate wastewater to stream flow ratio.
3 For calculation of all instream waste concentrations, and instream pollutant concentrations for chronic toxicity and human health screening, instantaneous complete mixing will be assumed unless addressed otherwise in the regulations. IWC is expressed in a percentage throughout these regulations. For acute screening in streams and rivers, complete mixing will be assumed if the IWC is greater than or equal to 10[CENT]. If the IWC is less than 10[CENT], the Permit Board may evaluate local acute toxic impacts and require application of mixing zones in accordance with the Mississippi Water Quality Standards.
For oceans, bays, estuaries, and lakes, a Mixing Zone evaluation will be completed to determine the appropriate dilution factors for calculating IWC at the edge of the (regulatory) mixing zone and at the edge of the smaller area of discharged-induced mixing zone (ADIM). In the absence of a site specific evaluation, dilution at the edge of the mixing zone will be assumed to be one part effluent to six parts receiving water body. Mixing zones and associated instream calculations shall be performed as described in EPA's "Technical Support Document for Water Quality-Based Toxics Control" (EPA/505/2-90-001) March 1991, which is referenced in the bibliography (Exhibit F to this chapter).
4 Where Qr = (7Q10 for Acute)
= (7Q10 for Chronic)
= (Mean annual flow for Human Health)
If 7Q10 = 0 then Qr = 7Q10 for conditions except for human health and then Qr equals mean annual flow if available.
Where: IWC = Instream Wastewater Concentration (where facility water supply is not receiving water)
Qw = maximum 30-day average wastewater flow, if available
Qr = receiving stream flow
Xr = receiving stream concentration
Xw = historical effluent data
Xwa = permit limits from previous permit or from effluent guidelines
Xta = the calculated instream concentration based on existing permit limits or the calculated limit based on current effluent guidelines
Xt = the calculated instream concentration based on historical effluent data from application
If IWC is < one percent, do not develop the chronic table.
If Qr = 0 then Xt = Xw * IWC/100
NOTE: To calculate Xta substitute Xwa for Xw Xwa = Permit Limit
Where: Number of samples is >12 & 7Q10 is >0 then;
| TABLE | Xw5, 6 | Qr | Xr7 |
| Acute | Maximum Concentration | 7Q10 | Instream Background Concentration |
| Chronic | Long Term Average Concentration | 7Q10 | Instream Background Concentration |
| Human Health | Long Term Average Concentration | Mean Annual | Instream Background Concentration |
The appropriate criteria to use in each table are a s follows:
| IWC | Acute | Chronic | Human Health |
| >1% | Compare Xt and Xta to Acute Water Quality Criterion Value | Compare Xt and Xta to Chronic Water Quality Criterion Value | TSD |
| <1% | Same as above | Do Not Compare | Same as above |
5 from 2C application and/or other appropriate data sources
6 if number of samples is <12 then Xw = (appropriate concentration * 10). The permittee may request utilization of alternative methods for determining reasonable potential set forth in the Technical Support Document for Water Quality-Based Toxics Control (EPA/505/2-90-001) or its amendments (TSD), subject to prior Permit Board review and approval of the method's implementation.
7 if no instream background concentration exists Xr = 0
A parameter fails the screen when the appropriate instream concentration or effluent concentration (as per above) exceeds the appropriate criterion.
MDEQ will use the chronic and acute water quality criteria and/or values as described in State of Mississippi Water Quality Criteria for Intrastate, Interstate, and Coastal Waters. If the permittee's discharge evaluation is based on species not found in Mississippi, the permittee may submit an alternative criterion as per the State's Water Quality Standards. However, said criterion shall conform to EPA's accepted procedures / rationale and is subject to both State and EPA approval.
Chemical specific limits shall be placed in a permittee's permit if any of the parameters evaluated in the toxic screening procedure indicate the reasonable potential for violation of the appropriate criteria (Acute, Chronic, and Human Health). The only exception is when a permittee fails the criteria due only to the application of the variability factor, that is a number of samples less than 12. In the case of the preceding exception, the permittee shall be required to monitor those parameters at a frequency of at least once per month for twelve months with the toxicity screening procedures being reapplied and the permit modified accordingly. The limits for the subject parameters will not be established until the subject data is received.
Toxicity limitations may take two forms;
In the absence of WET testing data, WET monitoring will be required upon failure of the acute or chronic chemical specific criteria screening. Failure of WET testing will be a basis for permit WET limitations. Failure will be defined as follows: an acute test that results in an LC50 < 3 * IWC, or a chronic test that results in an IC25 < IWC. The IC25 refers to the Inhibition Concentration 25, which shall be defined as a point estimate of the effluent concentration that would cause a 25[CENT] reduction in a non-lethal biological measurement of the test organisms, such as reproduction or growth.
The establishment of a WET limit versus WET monitoring shall be in accordance with 40 CFR 122.44(d), which is incorporated herein and adopted by reference. If chronic toxicity is indicated, the permit shall limit toxicity by requiring the IC25 of the effluent to equal or exceed the IWC. When acute toxicity is indicated, the toxicity limit will take the following form:
Effluent 48-hour LC50 > 3 * IWC (not to exceed 100[CENT])
TOXICITY SCREENING MATRIX
IWC | Screening Resu ts | Permit Requirements | ||||
CSSA | CSSC | WET8 | CSL | WETL | WETM | |
All | Pass | Pass | Pass | No | No | No |
<=1% | Pass | Pass | Fail | No | YesA | N/A |
Fail | Pass | Fail | Yes | YesA | N/A | |
Fail | Pass | Pass | Yes | No | No8 | |
>1% | Fail | Fail | Fail | Yes | YesC | N/A |
Fail | Fail | Pass | Yes | No | No8 | |
Pass | Fail | Fail | Yes | YesC | N/A | |
Pass | Fail | Pass | Yes | No | No8 | |
Fail | Pass | Fail | Yes | YesC | N/A | |
Fail | Pass | Pass | Yes | No | No8 | |
Where:
CSSA = Chemical Specific Screening Acute
CSSC = Chemical Specific Screening Chronic
WET = Whole Effluent Toxicity Data
CSL = Chemical Specific Limits= WQS/(IWC/100)
WETL = Whole Effluent Toxicity Limits W/Monitoring
WETM = Whole Effluent Toxicity Monitoring Only
YesA = Yes/Acute WET Limit = LC50 = 3 * IWC
YesC = Yes/Chronic WET Limit = IC25 = IWC
N/A = Not Applicable
YAM = Yes, Acute WET Monitoring Only
YCM = Yes, Chronic Monitoring Only
Pass = Acute: LC50 3 * IWC
= Chronic: IC25 IWC
Fail = Acute: LC50 < 3 * IWC
= Chronic IC25 < IWC
Human health shall be evaluated in accordance with "USEPA, Technical Support Document". When a parameter violates the human health criteria either for "water and organisms" or "organisms only", as appropriate, numerical limitations shall be placed in the permit.
8Where application form data are reported as "less than" (<) compare the method detection limit (MDL) as defined in Appendix B of 40 CFR 136 which is incorporated herein and adopted by reference. MDLs will be utilized in determining the reasonable potential of a given pollutant to violate water quality criteria. If a pollutant is reported as "non-detectable" above the MDLs as defined in Appendix B of 40 CFR 136, the pollutant will be assumed to be present at that reported level of sensitivity.
Calculation:
Where:
SWA = Site Watershed Area
GWA = Gage Watershed Area
For both small watersheds without gaging data and industrial sites, the stream flow and site runoff will be estimated using the Rational Equation, assuming the average storm event intensity over the entire area. The Rational Equation is:
Where:
Q = the flow in cfs,
C = the runoff coefficient,
I = the rainfall intensity in inches/hour, and
A = area in acres.
The conversion factor to cfs is slightly less than 1.01 and is generally ignored. Attached to Rule 1.1.2 collectively as Exhibit "C" and incorporated herein by reference is a table of runoff coefficients and a map showing average storm event intensity over Mississippi. The area is estimated using GIS software applications.
Calculation:
For large watersheds without an applicable gaging station, Best Professional Judgment (BPJ) will be used.
In determining limits for an Individual Storm Water Permit, a distinction is made between conventional pollutants and priority toxic pollutants (i.e., metals, organic chemicals, etc.). For oxygen demanding pollutants the Storm Water Section, after making preliminary determinations for wet weather flows, will request a wasteload allocation determination from the Surface Water Division to establish limits for oxygen demanding pollutants. For toxics, including metals and organic chemicals, MDEQ will calculate limits at wet weather flows in two steps as follows:
Where:
SWA = Site Watershed Area
GWA = Gage Watershed Area
Where:
Qws = flow from the watershed in cfs
Aws = Area in acres
I = average storm event intensity in inches per hour
C = appropriate runoff coefficient
WS = watershed
Where:
PL = Permit Limit
CMC = Criteria Maximum Concentration (Acute)
Q I = Flow from industry
QS = Flow from stream
When the model or calculated limit is higher than the maximum concentration reported on the 2F application, the permit will generally only require monitoring.
When there are no ELG or WQS numeric limitations or standards, BPJ will be used to set permit limits or to require Best Management Practices (BMPs) to protect water quality.
It is recognized that the calculated limits for specific chemicals may be below the analytical minimum quantitation level for the pollutant of concern. However, in this case the permit limit will be this calculated value. In such cases, compliance with the permit limits shall be determined as follows:
http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&tpl=/ecfrbrowse/Title40/40cfr136_main_02.tpl
The following language shall be placed in permits:
If the results for a given sample analysis are such that any parameter (Other than fecal coliform, enterococci, e coli) is not detected at or above the minimum level for the test method used, a value of zero will be used for that sample in calculating an arithmetic mean value for the parameter. If the resulting calculated arithmetic mean value for that reporting period is zero, the permittee shall report "NODI=B" on the DMR. For fecal coliform and other pollutants that are based on calculating a geometric mean, a value of 1.0 shall be used in calculating the geometric mean. If the resulting fecal coliform mean value is 1.0, the permittee shall report "NODI=B" on the DMR. For each quantitative sample value that is not detectable, the test method used and the minimum level for that method for that parameter shall be attached to and submitted with the DMR. The permittee shall then be considered in compliance with the appropriate effluent limitation and/or reporting requirement.
Permits will specify the appropriate analytical method, based on the appropriate sensitivity. Permittees must then report results based on data containing acceptable calibration points at least as low as the MQL.
Exhibit "D", which is attached hereto and incorporated herein by reference, represents the standard bioassay language placed in NPDES permits for chronic and acute bioassays, respectively. The fundamentals of the bioassay monitoring requirements are as follows:
Biomonitoring is for the life of the NPDES permit. Assuming compliance with the toxic limits, monitoring is at a frequency of once per quarter for the first twelve months for industrial and municipal permittees and semi-annually thereafter. The sampling frequency during compliance monitoring shall be at least twice per year unless specified otherwise elsewhere in these regulations, and sampling shall be timed to include the seasonal extremes of the year (hot-dry and cold-wet).
At least two species (one vertebrate and one invertebrate) must be used.
Permittee must use the most current EPA accepted procedures. Procedural references are specified in the bioassay language.
A permitted facility shall be considered in non-compliance when it fails any bioassay subject to a WET limit. Once a permittee fails a WET test, the permittee shall conduct a second WET test. For chronic tests, the second Chronic WET test must be completed within 30 days following completion of the failed test. For acute tests, the second WET test must be completed within two weeks of the completion of the failed test. Results must be submitted to the Department within two weeks of test completion. If the permittee fails the second WET test, then the permittee shall submit a preliminary Toxicity Reduction Evaluation Plan (TREP) within 45 days, following completion of the follow-up test, the first step of which shall be increased monitoring to determine the characteristics of the toxicity. If the permittee passes the second WET test, the permittee shall conduct the next WET test at the regularly scheduled frequency in the permit. Repeated failure of the WET tests may result in the Permit Board increasing the frequency of WET testing. The Commission will determine the appropriate enforcement response in accordance with existing enforcement policy.
A permittee must submit with each WET test result a completed OPC NPDES Whole Effluent Toxicity Testing Report form prescribed by the Commission (included in Exhibit "D").
Whenever a new WQBEL is imposed in a permit, the permittee shall have no more than three years in which to achieve compliance with such limitations. A permittee may apply to the Permit Board for a variance from the compliance schedule.
11 Miss. Code. R. 6-1.2.6