COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT WATER QUALITY CONTROL DIVISION TELEPHONE: (303) 692-3500

AMENDMENT 1 -- RATIONALE Colorado Discharge Permit System (CDPS) General Permit for Domestic Wastewater Treatment Works With Land Treatment of Effluent Permit COX-632000

I. Purpose of Amendment 1: The Water Quality Control Division (“the Division”) is providing modifications to General Permit 632000 for Domestic Wastewater Treatment Works with Land Treatment of Effluent in order to clarify and refine the permit requirements and to address comments and concerns raised after the General Permit was issued on March 30, 2007. II. Amendment 1 Changes: •

Section I.A.2. References to Regulation 84 – Reclaimed Water Control Regulation were deleted from the permit applicability section. Recent regulatory changes to Regulation 84 no longer allow reuse facilities to apply reuse water at above-agronomic rates.

•

Section V.A.5. Text was added indicating that wastewater treatment works (WWTWs) subject to Colorado Watershed Protection Control Regulations (Regulation Nos. 71 through 75) may be required to install and monitor lysimeters. This change was made because the Watershed Protection Control Regulations include requirements for using lysimeters to demonstrate compliance with phosphorus loading limitations. This modification adds flexibility to the general permit monitoring requirements and expands the applicability of the general permit to WWTWs within watershed protected areas.

•

Section VI.C.1. This section was added to summarize the general permit monitoring requirements and to indicate that on a case-by-case basis, the Division may increase or decrease the number of ground water monitoring wells required at the site in order to achieve: representative sampling of effluent from the treatment system, representative sampling of ambient ground water quality, and the determination of ground water flow direction. The Division may also require lysimeters in addition to, or in lieu of ground water monitoring wells. This modification was made to give the Division more flexibility in determining the total number of ground water wells and/or lysimeters necessary to ensure the protection of human health and the environment. In some cases, such as for very small WWTWs with well-defined ground water flow direction, fewer than three monitoring wells may be adequate to achieve ground water monitoring objectives. In other cases, more than three wells may be necessary to achieve monitoring objects. Where ground water monitoring is not feasible, lysimeters may provide the best monitoring approach. Monitoring locations and any modifications from the monitoring requirements provided in the general permit will be defined in the Certification.

Page 1 of 3

AMENDMENT 1 -- RATIONALE Permit COX-632000 •

Section VI.C.2. Text was modified to clarify the monitoring locations that must be proposed in the permit application.

•

Section VI.E.3. A redundant paragraph regarding modification of flow requirements was removed.

III. Public Notice Changes: •

Subsequent to public notice, the Division wanted to further clarify the applicability of the effluent limitations for BOD5, TSS, pH, and oil and grease (i.e., secondary treatment standards provided in Regulation No. 62, Regulations for Effluent Limitations) to land treatment systems. For facilities designed to provide secondary treatment through land application of effluent (such as through irrigation), the appropriate point of compliance for secondary treatment standards may be located subsequent to the land application area. Furthermore, monitoring for secondary standards subsequent to the land application area in some cases may be impracticable. Section V.A.6 of the general permit has been modified to include the following text: V.A.6

Where a facility is specifically designed to provide secondary treatment through the land application of effluent, the Division may waive monitoring requirements for secondary standards and instead employ permit-required practice-based measures and/or the submission of an annual report to ensure that the WWTW provides adequate treatment to comply with the secondary standards at an appropriate point of compliance.

Note that an unlined impoundment does not represent a Division-approved land treatment design for providing secondary treatment and requested modifications to secondary treatment standards prior to an unlined impoundment will not be granted.

The treatment system Scenarios 3 and 4 provided in the Rationale for General Permit COX-632000 are clarified as follows:

Scenario 3: WWTW discharges to a lined pond(s). Reg. 41 GW standards cannot be met prior to the land treatment site. Effluent applied for land treatment.

Up MW WW Flow

300I

WWTW

Lined Pond

001A

Land Treatment Site

002A

Regulatory Applicability: • • • •

300I: Influent flow, BOD, TSS 001A: Effluent flow (if required) 001A or 002A: Reg. 62 parameters. MW: Reg. 41 GW parameters. (Monitoring wells are required down-gradient of the land treatment site.)

AMENDMENT 1 -- RATIONALE --- Page 2 of 3

MW

AMENDMENT 1 -- RATIONALE Permit COX-632000 Scenario 4: WWTW discharges directly to land treatment site. Reg. 41 GW standards cannot be met prior to land treatment site. Effluent applied for land treatment.

WWTW WW Flow

300I

001A

Land Treatment Site

002A

MW

Regulatory Applicability: • • • •

300I: Influent flow, BOD, TSS 001A: Effluent flow (if required) 001A or 002A: Reg. 62 parameters. MW: Reg. 41 GW parameters. (Monitoring wells are required down-gradient of the land treatment site.)

Permit Writer: Margo Griffin January 10, 2008

AMENDMENT 1 -- RATIONALE --- Page 3 of 3