REV13940

• Permit No: M1977342
• IBM Index Class Name: Revision
• Doc Date: 8/4/1995
• Doc Name: RATIONALE FOR PUBLIC NOTICE
• Type & Sequence: AM2
• Media Type: D
• Archive: No

yCOLORADO DEPAR77LIENT OF PUBLJ,IEALTH AND THE ENVIRONMENT, Wat~uality Control Division
Rationale -Page 8, Permit No. CO-00041467
i
While the overall level of toxicity appears to have been reduced 6y the hydrologic and
treatment modifications that have been performed, some level ojtoxiciry likely remains.
Also, it is not yet clear what range of Jlows will be discharged, or what the treatment
capacity is. For these reasons, the Division believes that there is a reasonable potential
for the discharge ro interfere with attainment of applicable water quality classifications or
standards. Pursuant to section 6.9.2. (S) of the Re,~lations for State Discharge Permit
Svstem (5 CCR 1002-21. a chronic limit should be incorporated into the permit. However,
due to the relatively limited amount of chronic monitoring that has occurred to-date, the
limit will not become effective immediately. Since this permit will expire September 30,
1997, the imposition ojthe limit will be delayed umil the renewal permit is issued.
Prior to the chronic limit becoming effective, the permittee is required to conduct routine
monitoring. The results of the resring are to be reported on Division approved forms.
The perminee will be required to conduct two types of statistical derivations on the data,
one looking jot any statistically significant difference in toxicity between the control and
the eJJluent concentrations and the second identifying the IC,s, should one exist. Both sets
of calculations will look at the full range of toxicity (lethality, growth and reproduction).
If a level of chronic toxicity occurs, such that there is a statistically significant difference
in the lethality (at the 95'% confidence level) between the control and any e,~luent
cncemration less than or equal to the Instream Waste Concentration (!WC) and if the
lethality /Cx, < the IWC, the permittee will be required to follow the automatic
compliance schedule identified in Part I.B. of the permit, if the observed toxicity is due to
organism lethality. Once the chronic lethality limitation becomes effective, only
exceedance of the limitation that will be specified in Part I.A. will trigger the requirement
jot conducting the automatic compliance schedule identified in Part /.B. of the permit.
Prior to and after the limitation becomes effective, if the Toxicity is due to differences in
the growth of the jathead minnows or the reproduction of the Ceriodaphnia, no immediate
action on the part of the permittee will be required. However, this incident, along with
other WET data, will be evaluated by the Division and may form the basis for reopening
the permit and including additional WET limits or other requirements.
Also, until additional chronic Wt:7'tesNng results are available for review, the permittee's
request for a reduction in test species will not be granted.
d) General Information: The permiltee should read the WET testing sections of Part /.A. and
I.B. of the permit carejully. The permit outlines the test requirements and the required
follow-up actions the permittee must take to resolve a toxicity incident. The permittee
should read, along with the documems listed in Pan I.B ojthe permit, the Colorado
Water OualiN Control Division Biomanitoring Guidance Document. dated July I, 1993.
This document outlines the criteria used by the Division in such areas as granring relief
from WET testing, modifying test methods and changing test species. The permittee
should be aware that some of the conditions outlined above may be subject to change ij
the jaciliry experiences a change in discharge, as outlined in Part I/.A.1 of the pernut.
Such changes shall be reported to the Division immediately.
In order to incorporate the new WET conditions, pages Ic(iii), lc(vii), !g(i), and 1(h)
thru I (L) will be revised.
Rich Horstmann
July 20, 1995