62-610.860. Limited Wet Weather Discharge

(1) The Department encourages implementation of reuse of reclaimed water programs. Demand for reclaimed waters normally declines during wet weather periods. During such wet weather periods, surface water stream flows normally increase. Allowing limited wet weather discharge of excess reclaimed waters during such wet weather periods will facilitate implementation of reuse projects. Therefore, persons implementing reuse projects are authorized to seek approval for limited wet weather discharges as described below.

(2) An applicant requesting a permit for a limited wet weather discharge shall include the following information in the engineering report:

(a) A map showing the locations of the point of discharge and of the proposed receiving stream.

(b) Descriptions and locations of downstream lakes, estuaries, reservoirs, Outstanding Florida Waters, or Class I waters.

(c) An analysis of the historic records for daily rainfall for a period of record covering at least the most recent 20 years, using climatic data that are available from, or are representative of, the area involved. This shall include calculation of the average annual rainfall.

(d) An analysis of the historic records for stream flow in the proposed receiving stream.

(e) Estimates of time of travel from the proposed point of limited wet weather discharge to downstream lakes, estuaries, reservoirs, Outstanding Florida Waters, or Class I waters during periods when limited wet weather discharge would occur.

(f) Analysis of the proposed operation of the reuse, storage, and limited wet weather discharge systems including identification of the proposed operating schedule, frequency of limited wet weather discharge, duration of limited wet weather discharge, quantity of reclaimed water to be discharged, quality of the reclaimed water to be discharged, and the flow in the receiving stream during limited wet weather discharge periods. The analysis shall be conducted for a year from the historic record which had rainfall that was within 10 percent of the average annual rainfall (referred to as “the average rainfall year”).

(g) Calculation of the required minimum stream dilution factor as follows:

SDF	=	P(0.085 CBOD5 + 0.272 TKN - 0.484)
Where:
SDF	=	minimum required stream dilution factor (dimensionless),
P	=	percent of the days of the year that limited wet weather discharge will occur during an average rainfall year (e.g. if discharge will occur on 73 days; P = 100% × (73/365) = 20; if P is less than 1, use P = 1),
CBOD5	=	the treatment facility’s design monthly maximum limitation for CBOD5 in mg/L,
TKN	=	the treatment facility’s design monthly maximum limitation for TKN expressed in mg/L of nitrogen.

(h) Documentation required by the antidegradation policy in Rules 62-4.242 and 62-302.300, F.A.C., if the limited wet weather discharge will be a new or expanded surface water discharge.

(i) If the minimum stream dilution factor calculated in paragraph 62-610.860(2)(g), F.A.C., is less than 1.0, the minimum stream dilution factor shall be set equal to 1.0.

(3) Limited wet weather discharge for a reuse project shall be permitted without the need for a WQBEL or other water quality analyses only if all of the following requirements are met:

(a) The anticipated frequency of limited wet weather discharge (P) during the average rainfall year shall not exceed 25 percent which is equivalent to 91 days during the year;

(b) The actual stream dilution ratio during periods when the limited wet weather discharge is activated shall be equal to or greater than the minimum required stream dilution factor;

(c) The receiving water body is a Class III, IV, or V stream with a downstream travel time during periods of limited wet weather discharge that is at least 24 hours to any lake, estuary, reservoir, Outstanding Florida Water, or Class I water. If this minimum travel time requirement is not met, a limited wet weather discharge shall be permitted if the stream flow is at least the minimum required stream dilution factor times the limited wet weather discharge flow multiplied by a factor equal to 24 hours divided by the travel time in hours. If the minimum travel time requirement is not met, the stream dilution factor multiplied by a factor equal to 24 hours divided by the travel time will be referred to as “the adjusted stream dilution factor;”

(d) The receiving water body at the immediate point of discharge shall not be a lake, estuary, reservoir, Outstanding Florida Water, or Class I water; and,

(e) The reuse system is a slow-rate land application system regulated by Part II or III of this chapter.

(4) If the conditions described in subsection 62-610.860(3), F.A.C., are not met, a WQBEL analysis pursuant to Chapter 62-650, F.A.C., shall be required for a surface water discharge that serves as a backup disposal method for a reuse system.

(5) A limited wet weather discharge into a controlled canal system is allowed if the canal system is flowing during the periods of discharge and all other requirements of this rule, including the minimum dilution requirements, are met during all periods of discharge.

(6) Dechlorination requirements apply to limited wet weather discharges. Discharged flows which have been retained in a storage system for a minimum of three days shall be presumed to meet the total chlorine residual limitation for dechlorination, as long as additional chlorination has not been provided after the storage facility.

(7) A stream gauging station shall be furnished at a point upstream of the discharge point. In cases where stream gauging is not possible, the applicant shall provide an affirmative demonstration that alternative means of measuring or estimating flows and dilution provide reasonable assurances that the dilution requirements in Rule 62-610.860, F.A.C., will be met during periods of discharge.

(8) The permit for a limited wet weather discharge shall include the following:

(a) Maximum monthly average limitations for CBOD5 and TKN in the effluent discharged;

(b) Minimum stream dilution factor, or adjusted minimum stream dilution factor, if required by paragraph 62-610.860(3)(c), F.A.C.;

(c) The expected frequency (P) of discharge during an average rainfall year, expressed as a percentage; and,

(d) The average annual rainfall.

(9) A reuse system having a permit for a limited wet weather discharge shall report the following to the Department monthly:

(a) A list of days on which limited wet weather discharge to the surface receiving water body occurred;

(b) The stream flow in the receiving water body upstream of the limited wet weather discharge on the days of discharge;

(c) The flow rate of the limited wet weather discharge on the days of discharge;

(d) The resulting stream dilution ratio (stream flow divided by limited wet weather discharge flow) for each day of discharge;

(e) The CBOD5 and TKN concentrations of the effluent being discharged;

(f) An explanation of any factors contributing to the limited wet weather discharge;

(g) The cumulative number of days during the calendar year during which the limited wet weather discharge was activated; and,

(h) The month’s rainfall and the cumulative rainfall during the calendar year during which the limited wet weather discharge was activated.

(10) The minimum stream dilution factor, or adjusted minimum stream dilution factor, as required by paragraph 62-610.860(3)(c), F.A.C., shall be an enforceable permit condition and shall apply on each day during which the limited wet weather discharge is activated. The permittee may discharge a volume greater than the permitted capacity of the reuse or treatment facility if the stream dilution ratio during the period of discharge equals or exceeds the minimum stream dilution factor, or adjusted minimum stream dilution factor, as required by paragraph 62-610.860(3)(c), F.A.C., whichever is greater.

(11) The permit limits for CBOD5 and TKN shall apply as maximum monthly average limits for each month during which the limited wet weather discharge was activated. Only CBOD5 and TKN values obtained during days on which the limited wet weather discharge was activated shall be used to calculate the monthly average CBOD5 and TKN in the effluent.

(12) The expected frequency of discharge (P) is not an enforceable permit limit. It is expected that during years having rainfall greater than average the frequency of discharge may be greater than P. During years having rainfall less than average, the frequency of discharge normally will be less than P. However, under no circumstances shall the limited wet weather discharge be activated on more than 150 days during any one calendar year.

(13) The Department may revoke the permit for the limited wet weather discharge if the permittee discharges when the stream dilution ratio is less than the minimum required stream dilution factor or minimum adjusted stream dilution factor, whichever is greater, justified in the engineering report or if the limited wet weather discharge results in a significant adverse effect on the receiving stream.

(14) A limited wet weather discharge is not an emergency discharge pursuant to this chapter.

(15) Form 62-620.910(2) shall be used to apply for a permit to construct or operate a limited wet weather discharge. The permit application may be combined with an application for a reuse/land application system or for a treatment plant.

Rulemaking Authority 403.051, 403.061, 403.087 FS. Law Implemented 403.021, 403.051, 403.061, 403.062, 403.085, 403.086, 403.087, 403.088 FS. History–New 4-2-90, Formerly 17-610.860, Amended 1-9-96, 4-1-21.