City of Crystal Lake, IL Article VI Performance Standards

§ 595-25 Soil erosion and sediment control.

Table 3. Applicability of Soil Erosion and Sediment Control Performance Standards** [Amended 9-6-2016 by Ord. No. 7290]
Type of Development	Basic Requirements (Subsection A)	Requirements for Development Disturbing 1 Acre or More (Subsection B)	Channel Requirements (Subsection C)	Inspections and Maintenance Requirements (Subsection D)	Notification Requirements (Subsection E)	Special Precautions (Subsection F)
General permit	Waived*	N/A	Waived*	Waived*	Waived*	Waived*
Minor	X	N/A	If channel construction included	X	X	X
Intermediate	X	N/A	If channel construction included	X	X	X
Major	X	X	If channel construction included	X	X	X
Public road	X	If development greater than 1 acre	If channel construction included	X	X	X
Mining	X5	If development greater than 1 acre	If channel construction included	X	X	X
Flood hazard area	X	If development greater than 1 acre	If channel construction included	X	X	X
Wetland	X	If development greater than 1 acre	If channel construction included	X	X	X

5	Requirements may be waived by the enforcement officer for portions of the development site that do not drain off site.
*	Refer to the Performance Standards and Terms and Conditions of Specified Development of the specific General Permit.
**	See the Crystal Lake Watershed Design Manual and Crystal Lake Watershed Stormwater Management Program Implementation Plan for Soil Erosion and Sediment Control Performance Standards in the Crystal Lake Watershed

A. Basic requirements. The following requirements apply to all regulated development, except regulated development authorized by a general permit. Specific requirements may be waived by the enforcement officer for portions of the development site that do not drain off site.

(1) Control measures shall meet the minimum standards and specifications of the Illinois Urban Manual unless stated otherwise in this chapter.

[Amended 11-17-2020 by Ord. No. 7671]

(2) Soil disturbance shall be conducted in such a manner as to minimize erosion. Areas of the development site that are not to be disturbed shall be protected from construction traffic or other disturbance until final stabilization is achieved.

(3) Soil stabilization measures shall consider the time of year, development site conditions and the use of temporary or permanent measures.

(4) Stabilization by seeding shall include topsoil placement and fertilization, as necessary.

(5) Native seed mixtures shall include rapid-growing annual grasses or small grains to provide temporary soil stabilization.

(6) Off-site property shall be protected from erosion and sedimentation. Velocity dissipation devices shall be placed at concentrated discharge locations and along the length of any outfall channel, as necessary to prevent erosion.

(7) Sediment control measures shall be installed prior to the disturbance of tributary areas.

(8) Stabilization of disturbed areas shall be initiated immediately whenever any clearing, grading, excavating or other earth-disturbing activities have permanently ceased on any portion of the development site, or temporarily ceased on any portion of the development site and will not resume for a period exceeding 14 calendar days. Stabilization of disturbed areas shall be initiated within one working day of permanent or temporary cessation of earth-disturbing activities and shall be completed as soon as possible, but not later than 14 calendar days from the initiation of stabilization work in an area. Exceptions to these time frames are specified below:

(a) Where the initiation of stabilization measures is precluded by snow cover, stabilization measures shall be initiated as soon as practicable; and

(b) In areas where construction activity has temporarily ceased and will resume after 14 days, a temporary stabilization method may be used.

(9) Disturbance of steep slopes shall be minimized. Areas or embankments having slopes steeper than 3:1 shall be stabilized with staked-in-place sod, erosion control blankets in combination with seeding, or an equivalent control measure.

(10) The interior side slopes of all stormwater management facilities shall be stabilized with staked-in-place sod, erosion control blankets in combination with seeding, or an equivalent control measure. The control measure shall be installed between the design high water level and the bottom of the facility in a dry-bottom stormwater management facility, or between the design high water level and the normal water level for all other stormwater management facilities.

(11) Perimeter control measures shall be provided downslope and perpendicular to the flow of runoff from disturbed areas, where the tributary area is greater than 5,000 square feet, and where runoff will flow in a sheet flow manner. Perimeter erosion control shall also be provided at the base of soil stockpiles. Acceptable perimeter control measures include:

(a) Silt fences meeting the standards and specifications of the Illinois Urban Manual or AASHTO Standard Specification 288-00;

[Amended 11-17-2020 by Ord. No. 7671]

(b) A vegetated filter strip meeting the following standards:

[1] A minimum width of 25 feet perpendicular to the flow of runoff; and

[2] Vegetation consists of native plants, turf grass, or other plants that cover 70% or more of the ground surface; or

(c) An equivalent control measure. The enforcement officer may allow agricultural crops as a perimeter control measure, if such measures are projected to control erosion as well as other typical perimeter controls. The appropriateness of agricultural crops as a perimeter control measure depends on development-site-specific considerations, such as the ground slope, type of crop, and the distance to the nearest channel or adjacent property.

(12) The stormwater management system shall be protected from erosion and sedimentation downslope from disturbed areas. Inlet protection that reduces sediment loading, while allowing runoff to enter the inlet shall be required for all storm sewers. Check dams, or an equivalent control measure, shall be required for all channels. Filter fabric inlet protection and straw bale ditch checks are not acceptable control measures.

(13) If dewatering services are used, discharges shall be routed through an effective sediment control measure (e.g., sediment trap or an equivalent control measure). The enforcement officer shall be notified prior to the commencement of dewatering activities.

(14) All temporary soil erosion and sediment control measures shall be removed within 30 days after final stabilization of the development site is achieved or after the temporary measures are no longer necessary. Trapped sediment shall be removed and disturbed areas shall be permanently stabilized.

(15) Stockpiled soil and materials shall be removed from flood hazard areas at the end of each work day. Soil and materials stockpiled in IWMC or buffer areas shall be placed on timber mats, or an equivalent control measure.

(16) Effective control measures shall be utilized to minimize the discharge of pollutants from the development site. At a minimum, control measures shall be implemented in order to:

(a) Minimize the discharge of pollutants from equipment and vehicle washing, wheel wash water, and other wash water; and

(b) Minimize the exposure of building materials, building products, construction wastes, trash, landscape materials, fertilizers, pesticides, herbicides, detergents, vehicle fluids, sanitary waste, and other materials present on the development site to precipitation and to stormwater.

(17) Adequate receptacles shall be provided for the depositing of all construction material debris generated during the development process. The applicant shall not cause or permit the dumping, depositing, dropping, throwing, discarding or leaving of construction material debris upon or into any development site, channel, or IWMC. The development site shall be maintained free of construction material debris.

(18) Where regulated development is allowed within a buffer area, construction fencing shall be installed a minimum of one foot outside the WOTUS or IWMC and all other regulated development shall be limited to the non-WOTUS or non-IWMC side of the construction fence. This requirement shall not apply to regulated development involving impacts to or enhancement of WOTUS or IWMC.

(19) The enforcement officer may require additional or alternate soil erosion and sediment control measures, based on development-site-specific considerations and the effectiveness of the installed control measures.

B. Requirements for development disturbing one acre or more. In addition to the basic requirements, the following requirements apply to major development, public road development and mining development disturbing one acre or more:

(1) Meet the requirements of IEPA General NPDES Permit No. ILR10, if applicable. This permit must be obtained before a stormwater management permit can be issued.

(2) A stabilized construction entrance shall be located at any point where traffic will be exiting a development site to a public right-of-way, street, alley or parking area. Any sediment or soil reaching an improved public right-of-way, street, alley or parking area shall be removed by scraping or street cleaning as accumulations warrant and transported to a controlled sediment disposal area.

(3) Structural control measures shall be utilized, when necessary, to treat wash water, divert flows from exposed soils, store flows or otherwise limit runoff and the discharge of pollutants from exposed areas of the development site. Such practices may include: earth dikes, drainage swales, sediment traps, check dams, subsurface drains, pipe slope drains, level spreaders, storm drain inlet protection, rock outlet protection, reinforced soil retaining systems, gabions, and sediment basins.

(4) Unless otherwise specified in this chapter or in the Illinois Urban Manual, the structural practices shall be designed for a storm event equal to or greater than a twenty-five-year, twenty-four-hour storm.

[Amended 11-17-2020 by Ord. No. 7671]

(5) Sediment traps and sediment basins shall be appropriately sized and designed to facilitate periodic removal of sediment, and located with regard to the size of the tributary area:

(a) Runoff from disturbed areas with more than one acre but fewer than five acres of tributary area shall be routed to a sediment trap, or an equivalent control measure;

(b) Runoff from disturbed areas with a tributary area of five acres or more shall be routed to a sediment basin with a perforated filtered riser pipe, or an equivalent control measure; and

(c) Sediment basins shall have both a permanent pool (dead storage) and additional volume (live storage). Each volume shall, at a minimum, be equal to the amount of runoff from a two-year, twenty-four-hour storm over the on-site hydrologically disturbed tributary area. The live storage volume may be determined using the Detention Volume vs. Percent Impervious Chart in Appendix 6[1] and the developed condition percent impervious area. The available sediment volume below the normal water level shall be in addition to the dead storage volume and shall be sized for the estimated sediment load generated from the development site over the duration of the construction period. For construction periods exceeding one year, the one-year sediment load may be utilized with an annual sediment removal schedule.

[1] Editor's Note: Appendix 6 is included as an attachment to this chapter.

C. Channel requirements. In addition to other applicable soil erosion and sediment control performance standards of this chapter, the following requirements apply to regulated development below the ordinary high water mark of channels:

(1) Land disturbance in channels shall be avoided, where possible. The following requirements shall be met when land disturbance below the ordinary high water mark of channels cannot be avoided:

(a) Disturbance shall be timed to occur during low-flow or no-flow conditions;

(b) Equipment shall only cross channels at permanent bridges or culverts, except when a temporary channel crossing meets the following criteria:

[1] Fill within the channel shall be composed of nonerosive material, such as rip-rap or gravel; and

[2] The temporary channel crossing, including temporary approach roads, shall be removed within one year after installation, unless the enforcement officer grants an extension of time.

(c) Temporary cofferdams may be required by the enforcement officer and shall be constructed of nonerosive material; and

(d) The disturbed area, including bed and banks, shall be stabilized with staked-in-place sod, erosion control blankets in combination with seeding, or an equivalent control measure no more than 48 hours after disturbance is completed or interrupted.

(2) New or relocated channels shall be constructed in dry conditions. All construction, including stabilization, shall be completed prior to diversion of water into the new or relocated channel.

D. Inspection and maintenance requirements. The following requirements apply to all regulated development, except regulated development authorized by a general permit:

(1) Development plans bearing the approval stamp of the enforcement officer shall be retained at the development site throughout the duration of construction activities and shall be annotated with field changes.

(2) Disturbed areas that have not been finally stabilized and areas used for storage of materials that are exposed to precipitation shall be inspected for evidence of, or the potential for, pollutants entering the drainage system. Structural control measures identified in the plans shall be observed to ensure that they are operating correctly. Discharge locations shall be inspected to evaluate whether soil erosion and sediment control measures are effective in preventing significant impacts to receiving waters. Locations where vehicles enter or exit the development site shall be inspected for evidence of off-site sediment tracking. Such inspections shall be performed at the intervals stated in Subsection D(3) below.

(3) Regulated development disturbing one acre or more.

[Amended 9-6-2016 by Ord. No. 7290]

(a) For regulated development disturbing one acre or more, a qualified inspector (provided by the applicant) shall inspect the development site at the following intervals:

[1] Upon completion of installation of soil erosion and sediment control measures (including perimeter controls and diversions), prior to proceeding with any other earth disturbance or grading;

[2] After stripping and clearing;

[3] After rough grading;

[4] After final grading;

[5] After seeding and landscaping;

[6] After final stabilization and landscaping, prior to removal of sediment controls;

[7] At least once every seven calendar days; and

[8] Within 24 hours of the end of a storm that is a 0.5 inch or greater rain event or a discharge due to snowmelt.

(b) Inspections may be reduced to once per month when construction activities have ceased due to frozen conditions. Weekly inspections will recommence when construction activities are conducted, or if there is a 0.5 inch or greater rain event, or a discharge due to snowmelt occurs.

(4) For regulated development disturbing less than one acre, an inspector (provided by the applicant) shall inspect the development site at intervals (a), (c), (d), (f), (g) and (h) of the above list.

(5) Inspections may be reduced to once per month when construction activities have ceased due to frozen ground conditions. Weekly inspections shall resume when construction activities resume, within 24 hours of the end of a storm that is 0.5 inch or greater, or when snowmelt results in a discharge from the development site.

(6) Inspection reports shall be retained at the development site throughout the duration of construction activities, and made available to the enforcement officer upon request. The reports shall include:

(a) The scope of the inspection;

(b) The name and signature of the inspector;

(c) Qualifications of the qualified inspector, if required;

(d) The date of the inspection;

(e) Observations relating to the conditions and effectiveness of control measures; and

(f) Corrective actions taken to address deficiencies.

(7) All temporary and permanent erosion and sediment control measures shall be maintained in an effective working condition throughout the duration of construction activities. Deficiencies shall be identified through regular inspections, summarized in inspection reports, and repaired or replaced immediately. The enforcement officer shall be notified of any incidence of noncompliance filed with the IEPA and whenever an ineffective control measure needs to be replaced with an alternative control measure.

E. Notification requirements. The following requirements apply to all regulated development, except regulated development authorized by a general permit. To facilitate inspections by the enforcement officer and to ensure compliance with the stormwater management permit, and this chapter, the applicant shall notify the enforcement officer within two working days of the construction stages specified below:

(1) For regulated development disturbing one acre or more:

(a) Prior to the start of construction;

(b) Upon completion of installation of soil erosion and sediment control measures (including perimeter controls and diversions), prior to proceeding with any other earth disturbance or grading;

(c) After stripping and clearing;

(d) After rough grading;

(e) After final grading;

(f) After seeding and landscaping; and

(g) After final stabilization and landscaping, prior to removal of sediment controls.

(h) If stripping, clearing, grading and/or landscaping are to be done in phases or areas, the applicant shall give notice at the completion of each of the above work stages in each phase or area.

(2) For regulated development disturbing less than one acre, notifications are required at stages (a), (b), (d) and (g) of the above list.

F. Special precautions.

(1) If, at any stage of the construction, the enforcement officer determines that the nature of the regulated development is such that further work authorized by an issued stormwater management permit is likely to imperil any property, public way, IWMC, WOTUS, buffer area, or stormwater management system, the enforcement officer may require, as a condition of allowing the work to be continued, that reasonable special precautions be taken to avoid the likelihood of such peril. Special precautions may include, but shall not be limited to: constructing a more level exposed slope; constructing additional drainage facilities, berms, or terraces; compaction, or cribbing; temporary or permanent stabilization; or hiring a professional consultant to recommend corrective actions.

(2) Where it appears that damage may occur due to incomplete grading at the development site, work may be stopped and the applicant required to install temporary structures, or take such other measures as may be required to protect adjoining property or the public safety prior to the advent of seasonal rains or winter shut-down. For regulated development disturbing one acre or more, or where unusual site conditions prevail, the enforcement officer may require that the operations be conducted in specific stages, so as to ensure the completion of protective measures or devices.

§ 595-26 Runoff control.

A. Basic requirements. The following requirements apply to all regulated development, except regulated development authorized by a general permit:

(1) All concentrated stormwater discharges from a development site shall be conveyed into an existing channel, storm sewer, or overland flow path with adequate downstream stormwater capacity and shall not result in flood damage.

[Amended 11-17-2020 by Ord. No. 7671]

(2) The diversion of stormwater runoff shall be prohibited unless no reasonable alternative exists, as determined by the enforcement officer. The diversion of stormwater runoff shall not result in flood damage at the development site, upstream of the development site, or on downstream adjoining properties.

(3) Within a development site, streets, blocks, lots, deed or plat restrictions, parks and other public grounds shall be located in such a manner as to preserve natural streams and channels.

(4) Stormwater management facilities within subdivisions, planned unit developments, and manufactured home parks with five or more parcels platted after December 1, 2015, shall be located within an outlot.

(5) The development plans and plats for subdivisions, planned unit developments, and manufactured home parks shall show the BFE, as well as the limits of flood hazard areas, public bodies of water, WOTUS, IWMC, and buffer areas.

(6) The plats for subdivisions, planned unit developments, and manufactured home parks shall include a signed statement by a licensed professional engineer that accounts for changes in the drainage of surface water in accordance with the Plat Act (765 ILCS 205/2).

(7) The plats for subdivisions, planned unit developments, and manufactured home parks shall specify the minimum low opening elevation for each lot adjacent to an overland flow path, the minimum lowest adjacent grade for each lot adjacent to a flood hazard area, and the maximum impervious area allowed on each lot for the provided stormwater storage volume.

(8) The stormwater management system for a regulated development shall be functional prior to the issuance of a certificate of occupancy or a certificate of completion for any building which is part of the regulated development.

(9) The City shall not approve any preliminary planned unit development or plat of subdivision unless the planned unit development or plat is subject to meeting the minimum standards of this chapter.

(10) The City shall not approve any final planned unit development or plat of subdivision unless the planned unit development or plat meets the minimum standards of this chapter.

(11) A final planned unit development or plat of subdivision with an area greater than five acres platted after December 1, 2015, shall state the maximum impervious area allowed for each lot or parcel of land based on the design of the stormwater management system.

(12) Pursuant to state law, a property owner of a parcel being subdivided adjacent to a state or county right-of-way shall notify the highway authority of the proposed subdivision in writing, and request that the highway authority provide, at the cost of the highway authority or otherwise provided by law, the amount of additional capacity in any stormwater detention facility to be constructed in the subdivision for the future availability of the highway authority for meeting stormwater detention requirements of any future public construction on the highway.

(13) A maintenance plan shall be recorded for the stormwater management system. The enforcement officer may waive this requirement for minor and intermediate development.

B. Overland flow paths. In addition to other applicable runoff control performance standards, the following requirements apply to all regulated development, except regulated development authorized by a general permit:

(1) An overland flow path shall be provided for all areas of a development site. The overland flow path shall convey floodwaters for all storm events up to and including the base flood event without flood damage at the development site or upstream of the development site. Where the tributary area is less than 20 acres, the storm sewers and inlets may be sized for the base flood event in lieu of providing an overland flow path.

(2) An overland flow path serving more than one property shall be protected from obstructions, such as fencing, landscaping, or storage sheds, through a deed or plat restriction. The enforcement officer may waive the requirement for a deed or plat restriction where an increase in flood heights on upstream adjoining properties is unlikely to result from obstruction of the overland flow path.

(3) The overland flow path shall be designed to:

(a) Ensure the freeboard requirement of this chapter is met;

(b) Prevent an increase flood heights on upstream adjoining properties; and

(c) Prevent flood damage at the development site.

(4) The overland flow path shall be designed using a model or technique identified in Appendix 5 of this chapter[1] or otherwise approved by the City, based on the flow rate for:

(a) The base flood event, considering all on-site and off-site tributary areas; or

(b) Conveyance of a minimum of one cfs per acre of tributary area.

[1] Editor's Note: Appendix 5 is included as an attachment to this chapter.

(5) The minimum low opening elevation for a new building that is located adjacent to an overland flow path and has not been wet floodproofed according to the building protection standards of this chapter shall meet the following freeboard requirement:

(a) At least 0.5 foot above the BFE where the tributary area is 20 acres or less; or

(b) At least 1.0 foot above the BFE where the tributary area is between 20 acres and 100 acres; or

(c) At least 2.0 feet above the BFE where the tributary area is 100 acres or more.

(6) Modification of an existing overland flow path shall not result in increased flood heights on upstream adjoining properties or flood damage at the development site.

C. Drain tiles. In addition to other applicable runoff control performance standards, the following requirements apply to all regulated development, except regulated development authorized by a general permit:

(1) Drain tiles disturbed during regulated development shall be reconnected by those responsible for their disturbance, unless the development plans specify abandonment of the drain tiles.

(2) All abandoned drain tiles within disturbed areas shall be removed in their entirety.

(3) Drain tiles within the disturbed area of a development site shall be replaced, bypassed around the development site or intercepted and connected to the stormwater management system for the development site. The size of the replaced or bypassed drain tile shall be equivalent to the existing drain tile.

(4) Existing drain tiles shall be protected from an adverse tailwater condition due to a new stormwater management system.

(5) Observation wells, or similar structures for inspecting and maintaining drain tiles, shall be installed at any point where an existing drain tile flows into or out of a development site. Maintenance access shall be provided to the observation well through a deed or plat restriction for regulated development disturbing five acres or more.

(6) A drain tile survey shall locate existing farm and storm drain tiles by means of slit trenching or other appropriate methods performed by an experienced subsurface drainage consultant. A drain tile survey shall include the following, as applicable, on a topographic map:[2]

(a) The location of each slit trench identified to correspond with the tile investigation report and field-staked at no less than fifty-foot intervals;

(b) The location of each drain tile with a flow direction arrow, tile size and any connection to adjoining properties;

(c) A summary of the tile investigation report showing trench identification number, tile size, material and quality, percentage of the tile filled with water, percentage of restrictions caused by sediment; depth of ground cover and tile system classification; and

(d) The name, address and phone number of the person or consultant responsible for the drain tile survey.

[2] Editor's Note: Former Subsection C(6), regarding connection of concentrated discharges from a development site to a drain tile, was repealed 11-17-2020 by Ord. No. 7671. This ordinance also redesignated former Subsection C(7) and (8) as Subsection C(6) and (7), respectively.

(7) The enforcement officer may accept a drain tile map prepared by a drainage district or other reliable source in lieu of a drain tile survey. The drain tile survey requirement shall be waived for any minor development and the enforcement officer may waive the drain tile survey requirement for an intermediate development, major development, public road development or mining development, provided the applicant submits a narrative and supporting evidence indicating to the satisfaction of the enforcement officer that drain tiles are not likely to be present within the development site. This evidence may consist of:

(a) Soil maps;

(b) Historic aerial photographs;

(c) Historic topographic maps; and

(d) Wetland maps.

D. Storm sewers. In addition to other applicable runoff control performance standards, the following requirements apply to all regulated development, except regulated development authorized by a general permit:

(1) Storm sewers shall not connect to sanitary sewers.

(2) Energy-dissipation devices shall be provided at the outlets of all storm sewer systems to minimize erosion.

(3) New storm sewers serving new regulated development shall be designed by a licensed professional engineer for the ten-year critical duration storm as a minimum. The storm sewer design shall be based on full flow conditions, unless detailed calculations demonstrate the hydraulic grade line would not exceed the ground elevation. The enforcement officer may waive this requirement when storm sewers are not necessary for the development site to meet the requirements of this chapter.

(4) New inlets shall be designed to prevent ponding in streets from exceeding 0.5 foot during the one-hundred-year storm and to prevent ponding in parking lots from exceeding nine inches during the one-hundred-year storm. Ponding depth shall be measured at the inlet. The enforcement officer may waive this requirement when storm sewers are not necessary for the development site to meet the requirements of this chapter.

(5) The minimum full flow velocity for new storm sewers serving new regulated development shall be 2.5 feet per second. The maximum full flow velocity for new storm sewers serving new regulated development shall be 8.0 feet per second. The enforcement officer may waive this requirement when storm sewers are not necessary for the development site to meet the requirements of this chapter.

(6) The minimum storm sewer size shall be 12 inches for storm sewers serving more than one property. The enforcement officer may waive this requirement when storm sewers are not necessary for the development site to meet the requirements of this chapter.

(7) New storm sewers serving more than one property shall be located in a deed or plat restriction of sufficient size to maintain and reconstruct the storm sewer. The enforcement officer may waive the requirement for a deed or plat restriction where an increase in flood heights on upstream adjoining properties is unlikely to result from the lack of maintenance of the storm sewer.

E. Runoff rate reduction. In addition to other applicable runoff control performance standards, the following requirements apply to all regulated development required to provide stormwater storage:

(1) Stormwater storage requirements.

(a) Stormwater storage shall be required for a regulated development that creates 20,000 square feet or more of new impervious area, unless the conditions of Subsection E(1)(a)[1], [2] or [3] are met:

[1] One acre or less of new impervious area is created; and:

[a] The total impervious area, including the proposed development, would not exceed 10% of the contiguous property; and

[b] The applicant demonstrates to the satisfaction of the enforcement officer that there is adequate downstream stormwater capacity and the development shall not result in flood damage; or

[Amended 11-17-2020 by Ord. No. 7671]

[2] The total impervious area, including the proposed development, would not exceed 5% of the contiguous property; and:

[a] An agricultural conservation easement or other conservation easement is recorded over sufficient undeveloped area that the total impervious area may not exceed 5% of the contiguous property. The easement shall be granted to the City. The easement may be temporary, but the term of the easement shall run until the stormwater storage waiver is no longer necessary, for reasons such as the removal of new impervious area or the installation of a stormwater management facility; and

[b] The applicant demonstrates to the satisfaction of the enforcement officer that there is adequate downstream stormwater capacity and the development shall not result in flood damage; or

[Amended 11-17-2020 by Ord. No. 7671]

[3] The regulated development is a public road development and less than 1.5 acres of new impervious area are created.

(b) Linear impervious areas, such as a widened road, driveways and public recreational trails, which are less than 12.4 feet wide (1.5 acres per lineal mile) may be excluded when calculating the new impervious area to determine whether stormwater storage is required. This exclusion shall apply only when determining whether stormwater storage is required and not to the design of a stormwater management facility in cases where stormwater storage is required.

(c) The enforcement officer may require additional evaluation and detention for projects with less than 20,000 square feet of new impervious area:

[1] Where potential downstream drainage impacts may occur;

[2] Where the project is located partially or completely in the Crystal Lake Watershed;

[3] At the discretion of the enforcement officer.

(2) Allowable release rates.

(a) The allowable release rates for a development site shall be calculated based on the hydrologically disturbed area of the regulated development, except that the allowable release rate for a public road development involving an existing linear impervious surface shall be based on the new impervious area, rather than the hydrologically disturbed area.

(b) Release rates for a detention facility shall not exceed the lesser of the following:

[1] Four hundredths cubic foot per second per acre for the two-year, twenty-four-hour storm and 0.15 cubic foot per second per acre for the one-hundred-year, twenty-four-hour storm;

[2] More restrictive release for the two-year and one-hundred-year storm rates, if adopted by the City; or

[3] The existing conditions peak runoff rate.

(c) The allowable release rates for a detention facility shall be utilized for the design of an infiltration facility, unless the enforcement officer approves a design based on the infiltration rate of the underlying soil, as determined by a qualified professional. In such a case, the enforcement officer may add special conditions to the approval, such as a performance guarantee or a design factor of safety.

(3) Runoff rates and storage volume.

(a) The required stormwater storage volume may be determined by:

[1] The Detention Volume vs. Percent Impervious Chart in Appendix 6[3] for stormwater management facilities with a tributary area less than 10 acres, provided that the allowable release rates are 0.04 cubic foot per second per acre for the two-year storm and 0.15 cubic foot per second per acre for the one-hundred-year storm; or

[3] Editor's Note: Appendix 6 is included as an attachment to this chapter.

[2] A licensed professional engineer using a model or technique identified in Appendix 5 of this chapter[4] or otherwise approved by the City or IDNR/OWR.

[4] Editor's Note: Appendix 5 is included as an attachment to this chapter.

(b) Runoff calculations for all off-site tributary areas may be based on either the anticipated future land use conditions or existing land use conditions. Anticipated future land use conditions shall be based on future land use and existing off-site stormwater management facilities. Existing land use conditions shall be based on existing land use and existing off-site stormwater management facilities.

(c) Compensatory storage for flood storage volume lost in a depressional storage area may either be:

[1] Added to the required two-year stormwater storage volume; or

[2] Replaced as a new depressional storage area.

(d) The enforcement officer may waive the requirement to add compensatory storage volume to the required detention storage volume if accessing the compensatory storage volume would:

[1] Require a control structure with a diameter smaller than the minimum diameter; or

[2] Result in a dewatering time that exceeds the maximum dewatering time.

(e) Any regulated development that results in impervious area exceeding the design parameters of an existing detention or infiltration facility shall either expand the existing stormwater management facility, or include a control measure designed to reduce the additional volume of runoff from the regulated development, such as a rain garden or the replacement of existing impervious pavement with permeable pavement.

(4) Stormwater management facilities.

[Amended 9-15-2020 by Ord. No. 7653; 11-17-2020 by Ord. No. 7671]

(a) Basic requirements. The following requirements apply to the stormwater management facilities for all regulated development required to meet the stormwater storage requirements of this chapter:

[1] Off-site runoff may be bypassed around a proposed stormwater management facility.

[2] Stormwater management facilities shall be sized for the runoff from any public road improvements required as part of the regulated development.

[3] Stormwater management facilities shall be designed to dewater within 72 hours following the end of the design storm.

[4] A stable overflow shall be provided for each stormwater management facility. The overflow shall be capable of passing the unattenuated inflow from the 100-year critical duration storm from the entire tributary area without increasing flood heights on upstream adjoining properties or resulting in flood damage at the development site, based on runoff calculations meeting the runoff rates and storage volume standards of this chapter. The overflow elevation shall be at or above the 100-year design high water elevation.

[5] A minimum freeboard of one foot shall be provided above the design high water surface elevation of the 100-year flow through the overflow.

[6] Stormwater management facilities serving more than one property shall be located in a deed or plat restriction with access to the stormwater management facility from the public right-of-way. The enforcement officer may waive the requirement for a deed or plat restriction where an increase in flood heights on upstream properties is unlikely to result from the lack of maintenance of the stormwater management facility.

[7] The applicant shall notify adjoining downstream property owner(s) via certified mail return receipt of any proposed stormwater management facility outlet location and design. Notification shall occur prior to preliminary planned unit development or plat of subdivision or shall be provided at the first permit application submittal, whichever is earlier.

[8] The applicant shall notify any drainage district within the watershed where the development site is located via certified mail return receipt of any proposed stormwater management facility outlet location and design. Notification shall occur prior to preliminary planned unit development or plat of subdivision or shall be provided at the first permit application submittal, whichever is earlier.

[9] Concentrated discharges from a development site shall be connected to an existing drain tile, where possible; however, the primary outlet from the development site should be a surface discharge and the drain tile connection shall be designed as a secondary, low flow outlet. When no reasonable alternative exists, the enforcement officer may approve the connection of a concentrated discharge from a development site to an existing drain tile as the primary outlet, provided the existing drain tile has adequate hydraulic capacity and structural integrity and is located within a recorded deed or plat restriction to the point it discharges into a channel. The deed or plat restriction must be approved by the enforcement officer prior to issuance of a stormwater management permit.

[10] Stormwater management facility discharges onto adjoining properties shall be designed to release as sheet flow using a level spreader, or other energy dissipation device, approved by the enforcement officer.

[11] An off-site outfall shall be constructed to convey the release from a stormwater management facility if an analysis demonstrates that adequate downstream stormwater capacity cannot be achieved or if land damage to an agricultural swale may occur.

[a] The off-site outfall shall be evaluated to the nearest open channel. If the outfall is located within a publicly owned storm drainage system, it shall be evaluated to the downstream location directed by the Enforcement Officer.

[b] Stormwater management facility discharges to downstream agricultural surface drainage systems with no base flow must be conveyed 100% underground within 48 hours after a storm event up to and including the 100-year, twenty-four-hour storm event.

[c] Off-site outfalls shall be located within a public right-of-way or deed or plat restricted area and marked on the as-built plans. The deed or plat restriction language shall clearly define the individual or entity responsible for perpetual maintenance.

[d] If an off-site outfall is required to be constructed and the downstream property owner(s) refuse(s) to grant access across his or her property, and construction within a right-of-way or alternative route is not feasible or reasonable, the applicant shall provide the enforcement officer a two-year post-development security for the engineer's estimate of probable construction cost for the off-site outfall plus a 10% contingency. If the downstream property owner has not granted access for construction of the improvements within two years following completion of the development, the enforcement officer shall release the security.

(b) Detention facilities. In addition to other applicable stormwater management facility standards, the following requirements apply to detention facilities for all regulated development required to meet the stormwater storage requirements of this chapter.

[1] Single-pipe outlets shall have a minimum inside diameter of 12 inches. Control structures such as orifices, weirs, and perforated risers may be used to meet the allowable release rates. Outlet pipes and control structures shall be designed to minimize the need for maintenance and prevent tampering.

[2] Control structures shall have a minimum diameter of four inches when a single-pipe outlet or an orifice plate is used to restrict the outflow from a detention facility. If a smaller diameter is necessary to meet the allowable release rates, the control structure shall be designed to prevent clogging.

[3] Detention facilities shall be designed with appropriate tailwater conditions, as approved by the enforcement officer.

[4] Inlets to the detention facility shall be located as far from the outlet as possible. Paved low-flow channels shall not be allowed between inlets and the outlet.

[5] The side slopes at the shoreline of wet bottom and wetland detention facilities (from at least six inches below to at least six inches above normal water level) shall be no steeper than 10:1 to prevent shoreline erosion due to wave action and fluctuating water levels. Above shoreline areas, or in dry detention facilities, the maximum side slope shall be 4:1.

[6] Wet bottom detention facilities with a permanent pool depth greater than three feet shall include a safety shelf with a minimum eight-foot width that is no more than one foot below normal water level.

(c) Online detention. In addition to other applicable stormwater management facility standards, the following requirements apply to online detention facilities for all regulated development required to meet the stormwater storage requirements of this chapter:

[1] Online detention shall not be allowed on perennial streams.

[2] Online detention shall not be allowed in HQAR.

[3] Online detention shall not be allowed where the off-site to on-site tributary area ratio is greater than 10:1, except for regulated development that provides a watershed benefit. Online detention shall not be allowed where the tributary area is greater than 640 acres, except for regulated development that provides a watershed benefit.

[4] The release rates shall be 0.04 cubic foot per second per acre of the total tributary area at the elevation created by impoundment of the required two-year stormwater storage volume, and 0.15 cubic foot per second per acre of the total tributary area at the elevation created by impoundment of the required 100-year stormwater storage volume. The release rate and required stormwater storage volume shall be calculated using the twenty-four-hour storm. These standards may be modified by the enforcement officer to prevent an increase in the existing condition peak discharge rate or to prevent frequent overflow from the online detention facility.

[5] Compensatory storage shall be provided for the volume of flood storage lost due to fill and stormwater storage within a flood hazard area. The compensatory storage volume shall be in addition to the required detention volume.

[6] Meet IDNR/OWR and USACE requirements for modifications to a channel to accommodate online detention, if applicable.

[7] An impoundment of a channel shall be designed to allow the migration and movement of present or potentially present indigenous species that require access upstream and downstream of the impoundment as part of their life cycle.

(d) Detention within WOTUS and IWMC. In addition to other applicable stormwater management facility standards, the following requirements apply to detention facilities located within WOTUS or IWMC.

[1] Detention within WOTUS shall meet the requirements of the USACE, if applicable.

[2] Detention within IWMC shall require IWMC mitigation, unless the detention facility is vegetated according to the standards of the Native Plant Guide for Streams and Stormwater Facilities in Northeastern Illinois (NRCS, et al.) and the pre-development IWMC is comprised of:

[a] Farmed wetlands;

[b] Non-farmed wetlands that are not HQAR covered by at least 85% of one or more of the following species:

[i] Reed canary grass (Phalaris arundinacea)

[ii] Purple loosestrife (Lythrum salicaria);

[iii] Common reed (Phragmites australis)

[iv] Buckthorn (Rhamnus spp.);

[c] Non-farmed wetlands that are not HQAR with a FQI of 7 or less; or

[d] Open water that is not HQAR.

(e) Infiltration facilities. In addition to other applicable stormwater management facility standards, the following requirements apply to infiltration facilities for all regulated development required to meet the stormwater storage requirements of this chapter.

[1] The underlying soils shall have an infiltration rate of at least 0.5 inch per hour. The development site specific infiltration rate shall be determined by a qualified professional and approved by the enforcement officer. Column drains may be used to access more permeable substrate, at the discretion of the enforcement officer, if designed by a geotechnical engineer in a sealed opinion.

[2] The bottom of the infiltration facility shall be at least four feet above the seasonal high groundwater elevation. The development site specific seasonal high groundwater elevation shall be determined by a qualified professional and approved by the enforcement officer.

[3] The design high water level of the facility shall be at least 200 feet from water supply wells and on-site waste disposal systems.

[4] The design high water level of the facility shall be at least 10 feet from any building foundation.

[5] Direct infiltration (i.e., column drain) must be at least 200 feet away from any water supply wells and 1,000 feet away from a public water supply well. Direct infiltration structures must be at least 25 feet away from a building foundation unless a suitable design is produced by a licensed engineer and approved by the enforcement officer.

[6] Pre-treatment shall be provided to prevent obstruction of the infiltration facility.

[7] Runoff from the following areas shall not be routed to an infiltration facility:

[a] Areas subject to frequent winter deicing; and

[b] Other areas where precipitation will be exposed to potential contaminants.

[8] The maximum side slope shall be 4:1. However, side slopes as steep as 3:1 may be permitted at the discretion of the enforcement officer when 4:1 is not practical or possible. Stabilization of areas with 3:1 side slopes with erosion control blanket and standard IDOT Class 3 seeding or equivalent is required.

F. Runoff volume reduction hierarchy. In addition to other applicable runoff control performance standards, the following requirements apply to major development, public road development and mining development disturbing one acre or more. The applicant shall choose one or more strategies from the following hierarchy to minimize the increase in runoff volume from the development site:

(1) Preservation of natural features of the development site (e.g., natural storage and infiltration characteristics, floodplains, wetlands, prairies and woodlands);

(2) Preservation of the existing natural streams, channels and drainageways;

(3) Minimization of impervious surfaces created at the development site (e.g., narrowing road width, minimizing driveway length and width, clustering homes and shared driveways);

(4) Conveyance of stormwater in open vegetated channels;

(5) Natural landscaping as an alternative to turf grass;

(6) Structural measures that provide water quality and quantity control;

(7) Structural measures that provide only quantity control.

G. Water quality protection. In addition to other applicable runoff control performance standards, the following requirements apply to all regulated development, except regulated development authorized by a general permit:

(1) Water quality treatment shall be provided for stormwater runoff from increased impervious areas.

(a) The development shall provide water quality treatment for runoff from increased impervious areas to minimize impacts of post-construction stormwater runoff on water quality. The site development plan shall include a description of the water quality protection measures incorporated into the site design. The following treatment methods shall be evaluated and incorporated in the following order to reduce pollution and stormwater volumes to the maximum extent practicable:

[1] Sedimentation facilities (basins and traps), followed by infiltration basins followed by column drains, if necessary.

[2] If infiltration is infeasible, then use wetland detention facilities.

(b) On highly impervious development sites, such as multifamily residential and nonresidential developments, water quality treatment devices shall be designed to remove both floatable and settleable pollutants from as much of the stormwater runoff from increased impervious areas as possible. This requirement may be met by directing as much stormwater runoff from increased impervious areas as possible through a hydrodynamic separator, or into a catch basin fitted with a hooded outlet cover. Alternate treatment methods providing a similar or higher level of water quality treatment may be approved by the enforcement officer.

(c) In public road developments, the stormwater management system shall be designed to direct as much stormwater runoff from increased impervious areas as possible through a vegetated swale, across a vegetated filter strip, or into a catch basin before being discharged from the development site. Alternate treatment methods providing a similar or higher level of water quality treatment may be approved by the enforcement officer.

(2) Appropriate pretreatment shall be provided for stormwater runoff directed to new or existing Class V injection well.

(3) Appropriate pretreatment shall be provided for stormwater runoff directed to infiltration based practices in areas designated as High or Moderately High Potential for Aquifer Recharge/Contamination on the McHenry County Sensitive Aquifer Recharge Areas Map.

H. Watershed-specific requirements. In addition to other applicable runoff control performance standards, the following requirements apply to watershed-specific area development, except regulated development authorized by a general permit:

(1) Crystal Lake Watershed specific requirements.

(a) The boundary of the Crystal Lake Watershed is generally depicted in Appendix 9[5] and in the Crystal Lake Watershed Design Manual. Any area of land along the watershed boundary that can be shown to be outside of the Crystal Lake Watershed shall not be subject to the Crystal Lake Watershed specific requirements.

[5] Editor's Note: Appendix 9 is included as an attachment to this chapter.

(b) Areas located within the Crystal Lake Watershed boundaries shall follow the requirements outlined in Chapter 630, Watershed, and the latest versions of the Crystal Lake Watershed Design Manual and Crystal Lake Watershed Stormwater Management Program Implementation Plan, as necessary.

(2) McHenry County Watershed Plans are listed in Appendix 10 for reference only.[6]

[6] Editor's Note: Appendix 10 is included as an attachment to this chapter.

§ 595-27 Flood hazard areas.

A. A development is located in a flood hazard area if any of the following criteria are met:

(1) If any portion of the development site is within a mapped flood of record area on the USGS-Hydrologic Investigation Atlas Flood of Record Map;

(2) If any portion of the development site is within a closed contour of a depressional storage area;

(3) If any portion of the development site is within a channel that has a tributary area greater than 100 acres;

(4) If any portion of the development site is within a mapped Zone AE, A, AH or AO floodplain on the FEMA FIRM;

(5) If any portion of the development site is outside a mapped Zone AE, but is below the BFE; or

(6) If any portion of the development site is below the BFE determined by the simplified methods for estimating the BFE described in the FEMA publication "Managing Floodplain Development in Approximate Zone A Areas."

B. Determining the BFE and limits of a flood-prone area.

(1) The BFE shall be determined utilizing one of the following methodologies:

(a) Adding three feet to the flood of record indicated on the USGS-Hydrologic Investigation Atlas;

(b) Adding 0.5 foot to the surface overflow of a depressional storage area. Where a smaller depressional storage area exists within a larger depressional storage area, the BFE shall be based on the highest surface overflow; or

(2) The BFE may be determined by a licensed professional engineer using a model or technique identified in Appendix 5 of this chapter[1] or otherwise approved by MCSC or IDNR/OWR.

[1] Editor's Note: Appendix 5 is included as an attachment to this chapter.

(3) The limits of a flood-prone area shall be the projection of the BFE onto the development site topography.

C. Determining the BFE and limits of a Zone AE floodplain.

(1) The BFE shall be determined utilizing the following hierarchy as it applies to the development site:

(a) The one-percent annual chance elevation from the summary of stillwater elevations table in the FIS (for non-riverine flood sources);

(b) The regulatory one-percent annual chance floodwater surface elevation from the floodway data table in the FIS (for a development site located at a cross-section);

(c) The one-percent annual chance flood elevation at the development site scaled onto the flood profile in the FIS; or

(d) The BFE may be determined by a licensed professional engineer using a model or technique identified in Appendix 5 of this chapter[2] or otherwise approved by MCSC or IDNR/OWR.

[2] Editor's Note: Appendix 5 is included as an attachment to this chapter.

(2) The limits of a Zone AE floodplain shall be the projection of the BFE onto the development site topography. The building protection standards for flood hazard areas of this chapter apply to a building within a mapped Zone AE floodplain until a LOMC is obtained from FEMA.

D. Determining the BFE and limits of a Zone A floodplain.

(1) The BFE shall be determined utilizing one of the following methodologies:

(a) For regulated developments less than 50 lots and five acres, the enforcement officer may approve the use of the simplified methods for estimating the BFE described in the FEMA publication "Managing Floodplain Development in Approximate Zone A Areas"; or

(b) The BFE shall be determined by a licensed professional engineer using a model or technique identified in Appendix 5[3] or otherwise approved by MCSC or IDNR/OWR.

[3] Editor's Note: Appendix 5 is included as an attachment to this chapter.

(2) The limits of a Zone A floodplain shall be the projection of the BFE onto the development site topography. The building protection standards for flood hazard areas of this chapter apply to a building within a mapped Zone A floodplain until a LOMC is obtained from FEMA.

E. Determining the BFE and limits of a Zone AH floodplain.

(1) The BFE shall be determined utilizing one of the following methodologies:

(a) The elevation noted on the FIRM; or

(b) The BFE may be determined by a licensed professional engineer using a model or technique identified in Appendix 5 of this chapter[4] or otherwise approved by MCSC or IDNR/OWR.

[4] Editor's Note: Appendix 5 is included as an attachment to this chapter.

(2) The limits of a Zone AH floodplain shall be the projection of the BFE onto the development site topography. The building protection standards for flood hazard areas of this chapter apply to a building within a mapped Zone AH floodplain until a LOMC is obtained from FEMA.

F. Determining the BFE and limits of a Zone AO floodplain.

(1) The BFE shall be determined utilizing one of the following methodologies:

(a) The depth noted on the FIRM plus the highest adjacent grade;

(b) At least two feet above the highest adjacent grade if no depth is noted on the FIRM; or

(c) The BFE may be determined by a licensed professional engineer using a model or technique identified in Appendix 5 of this chapter[5] or otherwise approved by MCSC or IDNR/OWR.

[5] Editor's Note: Appendix 5 is included as an attachment to this chapter.

(2) The limits of a Zone AO floodplain shall be the projection of the BFE onto the development site topography. The building protection standards for flood hazard areas of this chapter apply to a building within a mapped Zone AO floodplain until a LOMC is obtained from FEMA.

G. Determining the limits of floodways.

(1) The designated floodway boundary shall be as depicted on the FIRM. The nondesignated floodway boundary shall match the floodplain boundary as depicted on the FIRM. The location of the floodway boundary shall be scaled onto the development plan using references common to both the FIRM and the development plan. IDNR/OWR shall determine the exact location of the floodway boundary wherever an interpretation is needed, including nondesignated floodways not depicted on the FIRM.

(2) Any area of land that can be shown to be higher than the BFE and is located within the boundary of a designated or nondesignated floodway is considered a floodway until a LOMR has been obtained from FEMA to revise the floodway boundary.

H. Basic requirements. The following requirements apply to all regulated development in a flood hazard area, except regulated development authorized by a general permit, and where these requirements are modified in the public flood control project standards of this chapter:

(1) Regulated development within a flood hazard area, including both permanent and temporary measures, shall meet the following criteria:

(a) Regulated development shall not result in increased flood damage at the development site or upstream of the development site.

(b) Any water surface profile increase shall:

[1] Be contained within the banks of the water body; or

[2] Be contained within the development site, property in which the applicant has an ownership interest, or a deed or plat restriction; or

[3] Not exceed 0.1 foot upstream flood height increase for the base flood event, except as allowed by the bridge and culvert standards of this chapter.

[Amended 9-6-2016 by Ord. No. 7290]

(c) Any increase in average channel velocity shall:

[1] Not exceed the scour velocity of the predominant soil type of the channel; or

[2] Provide stabilization measures to prevent increased scour and erosion.

(2) Any regulated development involving a channel modification, fill, stream maintenance, or a levee shall not decrease the flood-carrying capacity of the flood hazard area.

(3) All regulated development in a flood hazard area shall meet IDNR/OWR requirements for floodway construction, dam safety, and public bodies of water, if applicable.

(4) A LOMC from FEMA shall be required, with concurrence from IDNR/OWR, for any regulated development that:

(a) Increases the water surface profile by 0.1 foot or more in a floodplain for the base flood event;

(b) Increases the water surface profile by more than 0.0 foot in a floodway for the base flood event;

(c) Revises the boundary of a floodplain for a future building by the placement of fill;

(d) Revises the boundary of a floodway; or

(e) Establishes the BFE for a regulated development equal to or exceeding 50 lots or five acres.

(5) A CLOMR is required prior to issuance of a stormwater management permit when a regulated development within a floodplain would increase flood heights more than 0.1 foot, or when a regulated development within a floodway would increase flood heights more than 0.0 foot. Once a CLOMR has been issued by FEMA, with concurrence from IDNR/OWR, the enforcement officer may allow filling, the construction or reconstruction of bridges and culverts, and similar regulated development within the floodplain necessary to obtain the LOMR.

I. Additional standards for designated floodways.

[Amended 9-6-2016 by Ord. No. 7290]

(1) The only development in a designated floodway which will be allowed is an appropriate use which will not cause a rise in the BFE, and which will not create a damaging or potentially damaging increase in flood heights or velocity or be a threat to public health and safety and welfare or impair the natural hydrologic and hydraulic functions of the floodway or channel, or permanently impair existing water quality or aquatic habitat. Construction impacts shall be minimized by appropriate mitigation methods as called for in this chapter. Only those appropriate uses listed in 17 Ill. Adm. Code Part 3708 will be allowed. The approved appropriate uses are as follows:

(a) Flood control structures, dikes, dams and other public works or private improvements relating to the control of drainage, flooding, erosion or water quality or habitat for fish and wildlife.

(b) Structures or facilities relating to the use of, or requiring access to, the water or shoreline, such as pumping and treatment facilities, and facilities and improvements related to recreational boating, commercial shipping and other functionally water-dependent uses.

(c) Storm and sanitary sewer relief outfalls.

(d) Underground and overhead utilities.

(e) Recreational facilities such as playing fields and trail systems, including any related fencing (at least 50% open when viewed from any one direction) built parallel to the direction of flood flows, and including open-air pavilions and toilet facilities (four-stall maximum) that will not block flood flows nor reduce floodway storage.

(f) Detached garages, storage sheds, or other nonhabitable accessory buildings that will not block flood flows nor reduce floodway storage.

(g) Bridges, culverts, roadways, sidewalks, railways, runways and taxiways and any modification thereto.

(h) Parking lots built at or below existing grade where either:

[1] The depth of flooding at the base flood event will not exceed 1.0 foot; or

[2] The depth of flooding can be greater than 1.0 foot for parking lots used for short-term outdoor recreational use facilities, provided the applicant agrees to restrict access during overbank flooding events and agrees to accept liability for all damage caused by vehicular access during all overbank flooding events.

(i) Designated floodway regrading, without fill, to create a positive nonerosive slope toward a channel.

(j) Floodproofing activities to protect previously existing lawful buildings, including the construction of watertight window wells, elevating buildings, or construction of floodwalls around residential, commercial or industrial principal buildings where the outside toe of the floodwall shall be no more than 10 feet away from the exterior wall of the existing building, and which are not considered substantial improvements to the building.

(k) The replacement, reconstruction, or repair of a damaged building, provided that the outside dimensions are not increased, and provided that the building protection standards are met if the replacement, reconstruction, or repair is a substantial improvement or if the building is considered substantially damaged.

(l) Modifications to an existing building that would not increase the enclosed floor area of the building below the BFE, and which will not block flood flows, including, but not limited to, fireplaces, bay windows, decks, patios and second-story additions. Substantial improvements shall meet the building protection standards.

(2) Appropriate uses do not include the construction or placement of any new buildings, fill, building additions, buildings on stilts, excavation or channel modifications done to accommodate otherwise nonappropriate uses in the floodway, fencing (including landscaping or planting designed to act as a fence) and storage of materials except as specifically defined above as an appropriate use.

(3) Development of an appropriate use will be considered permissible, provided that the development meets the following criteria:

(a) All effective designated floodway conveyance lost due to the development will be replaced for all flood events up to and including the base flood event. In calculating effective designated floodway conveyance, the following factors shall be taken into consideration:

[1] K = (1.486/n)(AR^2/3)

where "n" is Manning's roughness factor, "A" is the effective flow area of the cross-section, and "R" is the ratio of the area to the wetted perimeter.

[2] The same Manning's "n" value shall be used for both existing and proposed conditions unless a recorded maintenance agreement with a federal, state, or local unit of government can assure the proposed conditions will be maintained or the land cover is changing from a vegetative to a nonvegetative land cover.

[3] Transition sections shall be provided and used in calculations of effective designated floodway conveyance. The following expansion and contraction ratios shall be used (unless alternate ratios are approved by IDNR/OWR) for excavations in the designated floodway, between cross-sections with rapid expansions and contractions, and when matching the designated floodway boundary on an adjoining property:

[a] Water will expand no faster than at a rate of one horizontal foot for every four feet of the flooded stream's length.

[b] Water will contract no faster than at a rate of one horizontal foot for every one foot of the flooded stream's length.

[c] Water will not expand or contract faster than one vertical foot for every 10 feet of the flooded stream's length.

[d] All cross-sections used in the calculations shall be located perpendicular to the flood flows.

[e] In the design of excavations in the designated floodway, erosion or scour protection shall be provided on land upstream and downstream of proposed transition sections.

J. Public health protection standards. The following requirements apply to all regulated development in a flood hazard area, except regulated development authorized by a general permit:

Table 4. Minimum Elevation Standards for Public Health Protection
Type of Flood Hazard Area	Storage of Materials Outside a Building Subsection J(1)	Water Supply Systems Subsection J(2)	Sanitary Sewers Subsection J(2)	Wells Subsection J(3)	New On-Site Waste Disposal Systems Subsection J(4)	Replacement On-Site Waste Disposal Systems Subsection J(5)	Wastewater Treatment Plants Subsection J(5)
Flood-prone area	Waived	Waived	Waived	Waived	Waived	Waived	FPE
Floodplain: flood fringe and floodway	BFE	FPE	FPE	FPE	N/A	Waived	FPE

(1) No regulated development in a floodplain shall include the outside storage of chemicals, explosives, buoyant materials, fertilizers, flammable liquids, pollutants, or other hazardous or toxic materials below the BFE.

(2) New and replacement water supply systems and sanitary sewer lines in a floodplain shall consist of watertight construction below the FPE.

(3) The wellhead for new wells in a floodplain shall be elevated to the FPE to prevent floodwaters from entering the well. The enforcement officer may provide an approximate BFE for the purpose of well protection.

(4) New on-site waste disposal systems, such as septic systems, shall not be installed in the floodplain. Replacement on-site waste disposal systems may be installed in the flood hazard area below the BFE if no reasonable alternative exists, as determined by the enforcement officer, and provided that the system has a watertight holding tank and all mechanical and electrical components and aboveground openings of the system below the BFE are watertight.

(5) Wastewater treatment plants in a flood hazard area shall be equipped with watertight openings below the FPE. These facilities shall be located to avoid impairment to the facility or contamination of floodwaters during the base flood.

K. Building protection standards for flood hazard areas. The following requirements apply to: all new buildings, building additions, and substantial improvements located within a floodplain; and to all new buildings and building additions in a flood-prone area after December 1, 2015, that increase total enclosed area below the BFE by more than 600 square feet. These requirements apply to a building within a mapped floodplain until a LOMC is obtained from FEMA.

(1) Basic requirements.

(a) A building may be constructed in a flood hazard area, provided that it meets the FPE and lowest floor elevation requirements listed in Table 5 by utilizing an acceptable protection measure listed in Table 6. Lowest floor elevation requirements do not apply to buildings utilizing dry floodproofing as the flood protection measure.

(b) All building protection measures shall meet the standards for flood protection measures in this chapter.

(c) An elevation certificate or a floodproofing certificate shall be required for any building, building addition, or substantial improvements to a building within a floodplain. The elevation certificate or a floodproofing certificate shall be prepared on forms published by FEMA; except for small accessory buildings, the enforcement officer may allow alternate documentation that the constructed building complies with the building protection standards for flood hazard areas of this chapter.

Table 5. Building Protection Standards for Flood Hazard Areas
Type of Building	Type of Flood Hazard Area	Flood Protection Elevation (feet above BFE)	Lowest Floor Elevation (feet above BFE)6
Residential	Flood-prone area	2	2
	Floodplain	2	2
Attached garage	Flood-prone area	0.5	0.5
	Floodplain	0.5	0.5
Accessory	Flood-prone area	2	<BFE
	Floodplain	2	0.5
Small accessory	Flood-prone area	0.5	<BFE
	Floodplain	0.5	<BFE
Nonresidential	Flood-prone area	2	2
	Floodplain	2	2
Agricultural	Flood-prone area	2	<BFE
	Floodplain	2	<BFE

6	This requirement does not apply to dry floodproofed buildings.

Table 6. Acceptable Measures for Flood Protection
Type of Building	Type of Flood Hazard Area	Construction on Permanent Fill Subsection K(2)(a)	Elevation on Crawl Space, Stilts, Piles, Walls, etc. Subsection K(2)(b)	Dry Flood- proofing Subsection K(2)(c)	Wet Flood- proofing Subsection K(2)(d)
Residential	Flood-prone area	YES	NO	YES	NO
	Floodplain	YES	NO	NO	NO
Attached garage	Flood-prone area	YES	NO	YES	NO
	Floodplain	YES	NO	NO	NO
Accessory	Flood-prone area	YES	NO	YES	YES
	Floodplain	YES	NO	YES	NO
Small accessory	Flood-prone area	YES	NO	YES	YES
	Floodplain	YES	NO	YES	YES
Nonresidential	Flood-prone area	YES	NO	YES	NO
	Floodplain	YES	NO	YES	NO
Agricultural	Flood-prone area	YES	NO	YES	YES
	Floodplain	YES	NO	YES	YES

(2) Standards for flood protection measures.

(a) Elevation on permanent fill. A building elevated on fill shall meet the following criteria:

[1] The lowest floor (including basement) shall be at or above the lowest floor elevation shown in Table 5, based on the type of building and the type of flood hazard area;

[2] Fill shall be placed following the FEMA guidelines for ensuring that buildings placed on fill (FEMA Technical Bulletin 10-01, or current guidelines) are reasonably safe from flooding, except where the requirements of this chapter exceed FEMA guidelines;

[3] All building components shall be constructed of flood-damage-resistant materials up to the FPE shown in Table 5, based on the type of building and the type of flood hazard area;

[4] Manufactured homes, recreational vehicles, or travel trailers installed on a site for more than 180 consecutive days shall be elevated to or above the FPE; and shall be anchored to resist flotation, collapse, or lateral movement by being tied down in accordance with the Rules and Regulations for the Illinois Mobile Home Tie-Down Act issued pursuant to 77 Ill. Admin. Code Part 870; and recreational vehicles or travel trailers shall be required to meet the elevation and anchoring requirements above unless:

[a] They are on site for fewer than 180 consecutive days; and

[b] They are fully licensed and ready for highway use. A recreational vehicle or travel trailer is ready for highway use if it is on its wheels or jacking system, is attached to the site only by quick-disconnect-type utility and service devices, and has no permanently attached additions.

FIGURE 1

How to Elevate Your Floodplain Building*

(IDNR Floodplain Management in Illinois Quick Guide, 2001)

*Note: The Crystal Lake Stormwater Ordinance recognizes elevation on fill only and does not allow elevation by crawl space, piles, stilts, walls, etc.

FIGURE 2

Enclosures Below the BFE

(IDNR Floodplain Management in Illinois Quick Guide, 2001)

(b) Dry floodproofing. A building that is dry floodproofed shall meet the following criteria:

[1] Dry floodproofing shall be provided to the FPE shown in Table 5.

[2] Dry floodproofing shall follow current FEMA guidelines, except where the requirements of this chapter exceed FEMA guidelines; and

(c) Wet floodproofing. A building that is wet floodproofed shall meet the following criteria:

[1] The building shall not be used for human habitation;

[2] All building components below the FPE shown in Table 5 shall be constructed with flood-damage-resistant materials;

[3] The building shall be anchored to prevent flotation, collapse, or lateral movement;

[4] All electrical, heating, ventilating, plumbing, and air-conditioning equipment and utility meters shall be located at or above the FPE shown in Table 5;

[5] Water and sewer pipes, electrical and telephone lines, submersible pumps, and other waterproofed service facilities may be located below the FPE shown in Table 5; and

[6] The permanent openings shall meet all of the following criteria:

[a] The bottom of the permanent openings shall be no more than one foot above the lowest adjacent grade;

[b] The total net area shall be provided below the BFE and consist of a minimum of two openings for each enclosed area, with each opening of an enclosed area on a different exterior wall;

[c] Any louvers, screens, or other opening covers shall not block or impede the automatic flow of floodwaters into and out of the enclosed area; and

[d] The openings shall have a total net area of not less than one square inch for every one square foot of enclosed area subject to flooding below the BFE, unless the building is equipped with engineered openings meeting the FEMA guidelines for openings in foundation walls and walls of enclosures (FEMA Technical Bulletin 1-08, or current guidelines), except where the requirements of this chapter exceed FEMA guidelines.

FIGURE 3

Accessory Structures

(IDNR Floodplain Management in Illinois Quick Guide, 2001)

L. Substantial improvement standards. In addition to other applicable flood hazard area performance standards, the following requirements apply to any repair, reconstruction, rehabilitation, addition, or other activity to a building within a floodplain:

(1) Determining substantial improvement. The repair or improvement of a building shall be considered a substantial improvement if either of the following criteria is met:

(a) The cost of a single project or the value of damage caused by a single event equals or exceeds 50% of the market value of the building before the improvement or repair is started; or

(b) The cumulative cost of two or more projects requiring a building permit or a stormwater management permit over a ten-year period equals or exceeds 50% of the market value of the building tracked on a percentage basis for each project.

(2) Determining the cost.

(a) A detailed and complete cost estimate shall be prepared by the applicant on a form provided by McHenry County. The cost estimate may exclude items not considered a permanent part of the building (i.e., plans, surveys, or permits), but shall include the cost of:

[1] Damages of any origin, regardless of the actual repair work; and

[2] Maintenance of existing buildings that was or will be part of a larger project requiring a building permit or a stormwater management permit.

(b) The cost estimate shall be based on pre-damage costs, if applicable.

(c) The cost of all materials shall be equal to the actual or estimated fair market value of the materials. Where materials or servicing equipment are donated or discounted below normal market value, the cost shall be adjusted to fair market value.

(d) The cost of all labor shall be equal to the actual or estimated fair market value of the labor. Where volunteer or discounted labor is involved, the cost of the labor shall be adjusted to fair market value.

(3) Determining the market value.

(a) A signed and notarized market value determination shall be prepared on a form provided by McHenry County. The market value may be determined by:

[1] Multiplying the current tax-assessed value of the building by three. The current tax-assessed value shall exclude:

[a] The value of the land; and

[b] The value of any other buildings or exterior improvements on the land; or

[2] A certified appraisal prepared by a state-licensed appraiser, completed within the previous two years, and based on the comparable sales method;

[3] An estimate prepared and sealed by a licensed architect; or

[4] An alternate approach, approved by the enforcement officer, provided that the building does not have a tax-assessed value and the cost estimate is clearly less than 50% of the market value.

(b) The market value shall be based on the value prior to any construction or damages, if applicable.

(4) Determining the cumulative percentage.

(a) The percentage for each individual project shall be determined by dividing the cost of the project (at the time the project was completed, including the full cost of any damage, if applicable) by the value of the structure (at the time the project was completed, or prior to any damage, if applicable); and

(b) Adding the percentages of each individual project.

(5) Substantial improvements to buildings shall meet the building protection standards for flood hazard areas of this chapter.

M. Compensatory storage volume standards. The following requirements apply to all regulated development resulting in flood storage volume lost or displaced due to the placement of fill, materials, or structures in a flood hazard area, or due to draining a depressional storage area, except regulated development authorized by a general permit or specifically exempted below.

Table 7. Compensatory Storage Exemptions
Type of Flood Hazard Area	Fill Less than 5 Cubic Yards Subsection M(1)(a)	Replacement Septic Systems and Wells Subsection M(1)(b)	Floodproofing Habitable Buildings Subsection M(1)(c)	Artificially Created Storage Subsection M(1)(d)	All Other Regulated Development Subsection M(2)
Flood-prone area	Exempt	Exempt	Exempt	Exempt	Not exempt
Floodplain: flood fringe	Exempt	Exempt	Exempt	Exempt	Not exempt
Floodplain: designated or nondesignated floodway	Not exempt	Not exempt	Exempt	Exempt	Not exempt

(1) Compensatory storage exemptions.

(a) Compensatory storage may be waived through a written waiver by the enforcement officer for up to five cubic yards of fill within the flood fringe or a flood-prone area. This waiver may only be exercised one time per parcel. The enforcement officer may deny the waiver for reasons including, but not limited to:

[1] A determination that the fill would create a damaging or potentially damaging increase in flood heights or velocity; or

[2] That a parcel has been subdivided to qualify for more than one waiver.

(b) Compensatory storage shall not be required for replacement on-site waste disposal systems within the flood fringe or a flood-prone area. The applicant shall demonstrate to the satisfaction of the enforcement officer that no reasonable alternative location exists outside of the flood hazard area and that the fill volume is the minimum necessary.

(c) Compensatory storage shall not be required for the floodproofing of existing lawful habitable residential or commercial buildings within 10 feet of the outside face of the building.

(d) Compensatory storage shall not be required to replace the loss of artificially created storage due to a reduction in upstream head loss caused by a bridge, culvert, storm sewer, or constructed embankment.

	Table 8. Required Compensatory Storage Ratios
	Type of Flood Hazard Area	Regulated Development without As-Builts7	Regulated Development with As-Builts	Public Road Development
	Riverine floodplain	1.5:1	1.2:1	Minimum 1:1
	Riverine flood-prone area	1.5:1	1.2:1	Minimum 1:1
	Non-riverine floodplain	1:1	1:1	1:1
	Non-riverine flood-prone area	1:1	1:1	1:1

7

As-built plans shall be required for any regulated development resulting in 100 cubic yards or more of fill in a flood hazard area.

(2) Compensatory storage requirements.

(a) Compensatory storage volume shall be provided below the BFE and above the normal water level.

(b) As-built plans shall be required for any regulated development resulting in 100 cubic yards or more of fill in a flood hazard area. The enforcement officer may require as-built plans for regulated development resulting in smaller amounts of fill in a flood hazard area based on development-site-specific considerations.

(c) For regulated development in a riverine flood hazard area:

[Amended 9-6-2016 by Ord. No. 7290]

[1] Hydraulically equivalent compensatory storage volume shall be provided at ratios at least equal to:

[a] One and five-tenths times the flood storage volume lost or displaced; or

[b] One and two-tenths times the flood storage volume lost or displaced, provided that as-built plans are submitted.

[2] For a public road development that cannot reasonably provide the compensatory storage volume required by this chapter:

[a] The hydraulically equivalent compensatory storage volume required at a minimum 1:1 ratio may be waived by the enforcement officer as long as the total compensatory storage ratio is at least equal to 1:1. The waiver shall be the minimum necessary to afford relief. Any compensatory storage within a designated floodway shall be approved by IDNR/OWR.

[b] The additional compensatory storage volume required beyond a 1:1 ratio may be waived by the enforcement officer. The waiver shall be the minimum necessary to afford relief.

[3] Any additional compensatory storage volume required beyond a 1:1 ratio may be provided above or below the ten-year flood elevation.

[4] The compensatory storage area shall be located in close proximity to the fill area and shall drain freely and openly to the channel.

(d) For regulated development in a nonriverine flood hazard area:

[1] The compensatory storage volume shall be at least equal to the flood storage volume lost or displaced; and

[2] The compensatory storage volume lost by filling or draining a depressional storage area shall be based on the critical duration storm.

N. Public flood control project standards. The flood hazard area performance standards of this chapter shall be considered met for any public flood control project that meets all the following criteria:

(1) Flood heights shall not be increased outside a deed or plat restriction for all flood events up to and including the base flood event.

(2) The improvements shall be owned and maintained by a public agency. A land stewardship corporation, or similar entity, may own and maintain the improvements, provided that a public agency executes an agreement with the corporation to take over ownership, operation, and maintenance if the corporation dissolves or fails to meet its obligations.

(3) A CLOMR and a LOMC from FEMA shall be required, with approval from IDNR/OWR, for any regulated development that:

(a) Increases the water surface profile by 0.1 foot or more in a floodplain for any storm event up to and including the base flood event;

(b) Revises the boundary of a floodplain by the placement of fill; or

(c) Revises the boundary of a floodway.

O. Standards for on-stream structures built for the purpose of backing up water.

[Added 9-6-2016 by Ord. No. 7290]

(1) Any water surface profile increase shall:

(a) Be contained within the banks of the water body; or

(b) Be contained within the development site, property in which the applicant has an ownership interest, or a deed or plat restriction; or

(c) Not exceed 0.1 foot upstream flood height increase for all events up to and including the base flood event.

(2) All dams and impoundment structures shall meet the applicable requirements of 17 Ill. Adm. Code Part 3702 (Construction and Maintenance of Dams).

(3) If the proposed activity involves a modification of the channel or floodway to accommodate an impoundment, it shall be demonstrated that:

(a) The impoundment is determined to be in the public interest by providing flood control, public recreation, or regional stormwater detention;

(b) The impoundment will not prevent the migration of indigenous fish species which require access to upstream areas as part of their life cycle, such as for spawning;

(c) The impoundment will not cause or contribute to degraded water quality or habitat conditions. Impoundment design should include gradual bank slopes, appropriate bank stabilization measure, and a pre-sedimentation basin; and

(d) A nonpoint source control plan has been implemented in the upstream watershed to control the effects of sediment runoff as well as minimize the input of nutrients, oil and grease, metals and other pollutants. If there is more than one municipality in the upstream watershed, the municipality in which the impoundment is constructed should coordinate with upstream municipalities to ensure comprehensive watershed control.

P. Bridge and culvert standards.

[Added 9-6-2016 by Ord. No. 7290]

(1) Designated floodways.

(a) New bridges and culverts.

[1] Any water surface profile increase shall:

[a] Be contained within the banks of the water body; or

[b] Be contained within the development site, property in which the applicant has an ownership interest, or a deed or plat restriction; or

[2] The proposed structure shall not result in an increase of upstream flood stages greater than 0.1 foot for all flood events up to and including the base flood event; and

[3] If the proposed construction will increase upstream flood stages greater than 0.1 foot within a designated floodway, the applicant shall contact IDNR/OWR to obtain a permit for a dam or waiver.

(b) Reconstruction or modification of existing bridges, culverts and approach roads.

[1] The bridge or culvert and roadway approach reconstruction or modification shall be constructed with no more than 0.1 foot increase in backwater over the existing flood profile for all flood frequencies up to and including the base flood event, if the existing bridge or culvert is not a source of flood damage.

[2] If the existing bridge or culvert and roadway approach is a source of flood damage to buildings in the upstream floodplain, the applicant's engineer shall evaluate the feasibility of redesigning the structure to reduce the existing backwater, taking into consideration the effects on flood stages on upstream and downstream properties.

[3] The determination as to whether or not the existing crossing is a source of flood damage and should be redesigned must be prepared in accordance with 17 Ill. Adm. Code Part 3708 (Floodway Construction in Northeastern Illinois) and submitted to IDNR/OWR for review and concurrence before a permit is issued.

(2) Non-designated floodways and flood-prone areas.

(a) New bridges and culverts.

[1] Documentation must be provided that the proposed crossing will not cause demonstrable flood damage; and

[2] Any water surface profile increase shall:

[a] Be contained within the banks of the water body; or

[b] Be contained within the development site, property in which the applicant has an ownership interest, or a deed or plat restriction; or

[3] In urban areas, the water surface profile increase would not exceed 0.5 foot at the structure, nor 0.1 foot at a point 1,000 feet upstream of the structure, for all flood events up to and including the base flood event, as determined by the horizontal projection of the increase and the slope of the hydraulic grade line for the existing and proposed conditions hydraulic models; or

[4] In rural areas, the water surface profile increase would not exceed 1.0 foot at the structure, nor 0.5 foot at a point 1,000 feet upstream of the structure, for all flood events up to and including the base flood event, as determined by the horizontal projection of the increase and the slope of the hydraulic grade line for the existing and proposed conditions hydraulic models; and

[5] Any increase in the average channel velocity would not be beyond the scour velocity of the predominant soil type of the channel; or

[6] Increased scour, erosion and sedimentation would be prevented by the use of rip-rap or other design measures.

(b) Reconstruction or modification of existing bridges, culverts and approach roads.

[1] The reconstruction (including approach roads) shall be no more restrictive to normal and flood flows than the existing bridge or culvert crossing; and

[2] Documentation must be provided that the existing crossing has not caused demonstrable flood damage. In the case of public projects, certification by a District Engineer of the Department of Transportation's Division of Highways, a county engineer (if a licensed professional engineer), or a municipal engineer (if a licensed professional engineer) that the existing crossing has not caused demonstrable flood damage will be adequate documentation.

[Amended 11-17-2020 by Ord. No. 7671]

§ 595-28 Wetlands and waters.

A. Minimization of impacts. All reasonable measures shall be taken to avoid and minimize impacts to wetlands, streams, ponds and lakes.

B. Jurisdictional determination.

(1) The applicant shall obtain a jurisdictional determination from the USACE for any regulated development that impacts wetlands or waters or is adjacent to wetlands or waters. This requirement may be waived by the enforcement officer when the USACE issues a letter of no objection for the regulated development.

(2) Impacts to WOTUS shall be mitigated according to the requirements of the USACE.

(3) Impacts to IWMC shall be mitigated according to the requirements of this chapter. No IWMC impacts shall be allowed without a clear purpose and need for the regulated development and without demonstrating the measures taken to avoid and minimize IWMC impacts to the satisfaction of the enforcement officer.

C. Boundary determination requirements. The following requirements apply to all regulated development within or adjacent to IWMC, except regulated development authorized by a general permit:

(1) A letter of no impact prepared by a wetland specialist may be accepted by the enforcement officer, in lieu of a wetland determination report, when a field investigation by the wetland specialist reveals the closest wetland or water to a regulated development is clearly beyond the limits of the required buffer. A letter of no impact shall include:

(a) The date of the field investigation;

(b) A written description of the development site closest to the IWMC;

(c) Color photographs representative of the development site closest to the IWMC;

(d) A grading plan showing the limits of development site and the approximate boundary of the IWMC closest to the development site; and

(e) An aerial photograph showing the limits of development site and the approximate boundary of the IWMC closest to the development site.

(2) The presence and boundary of waters shall be determined by a wetland specialist. Waters shall include the entire area inundated at the ordinary high water mark.

(3) The presence and boundary of farmed wetlands on agricultural land within or adjacent to a development site shall be determined by the NRCS or a wetland specialist, in accordance with the current NRCS or USACE wetland delineation methodology.

[Amended 11-17-2020 by Ord. No. 7671]

(4) The presence, boundary, and quality of non-farmed wetlands within or adjacent to a development site shall be determined by a wetland delineation conducted in accordance with the current USACE wetland delineation methodology. The findings of this determination shall be documented in a wetland determination report prepared by a wetland specialist.

(5) A wetland determination report shall be prepared by a wetland specialist and shall include:

(a) A plan showing the location and extent of all wetlands and waters within or adjacent to the development site. The boundaries of these wetlands and waters shall be flagged in the field and surveyed. The approximate location and extent of off-site wetlands and waters within 100 feet of the development site shall also be shown. The approximate off-site boundaries shall be established using the best available information, as approved by the enforcement officer. The best available information may include:

[1] Aerial photography;

[2] A previously approved wetland determination report, even if the report was prepared more than five years ago;

[3] The ADID map or other wetland map; and

[4] McHenry County Soil Survey;

(b) An aerial photograph delineating all wetlands and waters within or adjacent to the development site, as well as the approximate location and extent of wetlands and waters within 100 feet of the development site;

(c) The most recent version of the following maps, delineating the limits of the development site:

[1] USGS Quadrangle Map;

[2] NRCS Wetland Inventory Map;

[3] FEMA FIRM;

[4] McHenry County Soil Survey;

[5] USGS Hydrologic Investigations Atlas; and

[6] ADID Map;

(d) USACE data sheets with color photographs provided for representative upland and wetland data points; and

(e) A narrative description of the wetlands, including a floristic quality assessment, as determined by the methodology described in Plants of the Chicago Region (Swink, F. and G. Wilhelm, 1994, 4th Edition, Indianapolis: Indiana Academy of Science). Floristic quality assessments shall be conducted during the local growing season, generally between May 15 and October 1. Non-growing-season assessments may require additional sampling during the growing season prior to approval.

(6) Approval of a wetland determination report shall remain valid for five years.

D. Hydrology requirement. The following requirement applies to all regulated development within or adjacent to IWMC, except regulated development authorized by a general permit:

(1) The regulated development shall maintain 80% to 150% of the existing condition runoff volume from the development site to each IWMC for the two-year, twenty-four-hour storm event; otherwise, the IWMC shall be considered impacted and shall be subject to the mitigation requirements of this chapter.

E. Mitigation requirements. The following requirements apply to all regulated development resulting in an IWMC impact, except regulated development authorized by a general permit:

(1) IWMC mitigation is required for regulated development resulting in IWMC impacts greater than or equal to 0.10 acre to IWMC. The enforcement officer may require mitigation for IWMC impacts less than 0.10 acre for reasons including, but not limited to:

(a) The proposed regulated development would result in a cumulative IWMC impact greater than or equal to 0.10 acre, due to a prior unmitigated impact to the same IWMC; or

(b) A prior unmitigated impact to another IWMC within the contiguous property.

Table 9. IWMC Mitigation Ratios
Category	IWMC Quality	Impact Area (acres)	Regulated Develop- ment Type	Sub- section E(1)	Sub- section E(3)(a)	Sub- section E(3)(b)	Sub- section E(3)(c)	Sub- section E(3)(d)	Sub- section E(3)(e)
I	Any	<0.10	Any	Exempt
I	Standard8	0.1-1.0	Any		1.5:1 or 1:1
II	Standard8	1.0-2.0	Any		1.5:1 or 1:1
III	Standard8	>2.0	Any		1.5:1 or 1:1
III	HFVW	Any	Any			3:19
III	HQAR or HQHS	Any	Any				5:19
Impacts prior to permit issuance								5:19
IV	Any	Any	Restoration, creation, and enhance- ment						1:1
V	Any	Any	Temporary impact						1:1

8	"Standard" means any IWMC that is not a HFVW, HQAR, or HQHS.
9	May be reduced to 1:1. Refer to Subsection D(5)(c)[6].

(2) IWMC impacts shall be categorized as follows:

(a) Category I: IWMC impacts with a cumulative impact area less than or equal to one acre and not impacting HQAR, HFVW, or HQHS;

(b) Category II: IWMC impacts with a cumulative impact area greater than one acre and less than or equal to two acres and not impacting HQAR, HFVW, or HQHS;

(c) Category III: IWMC impacts with a cumulative impact area greater than two acres or impacting HQAR, HFVW, or HQHS;

(d) Category IV: IWMC impacts necessary for wetland restoration, wetland creation and/or wetland enhancement, including streambank and shoreline stabilization projects that utilize appropriate bioengineered practices; or

(e) Category V: temporary IWMC impacts.

(3) IWMC mitigation shall replace the area of IWMC impacted by regulated development at the following proportional rates (i.e., creation acreage to IWMC impact acreage):

(a) For IWMC impacts under Categories I, II and III that are not designated as HQAR, HQHS, or HFVW: 1.5:1 ratio; or a minimum 1:1 ratio for USACE-certified wetland mitigation bank credits;

(b) For IWMC impacts that are designated as HFVW: 3:1 ratio is required;

(c) For IWMC impacts that are designated as HQHS or HQAR: 5:1 ratio is required;

(d) For IWMC impacts prior to issuance of a stormwater management permit, if the enforcement officer determines that IWMC mitigation is an acceptable alternative to wetland restoration: 5:1 ratio is required; and

(e) For IWMC impacts under Categories IV and V: 1:1 ratio is required; or

(f) For IWMC impacts under Categories I, II and III, including HQAR, HQHS, and HFVW: 1:1 ratio may be allowed, provided that IWMC mitigation occurs on-site according to the requirements of this chapter.

(4) A mitigation plan shall be prepared by a wetland specialist for any regulated development that requires IWMC mitigation. A mitigation plan shall include:

(a) A statement of the purpose and need for the project;

(b) A statement of the area, type, and category of the IWMC impact;

(c) A statement of the selected mitigation option;

(d) A narrative describing the alternative measures taken to avoid, minimize, or mitigate IWMC impacts;

(e) A narrative describing any benefits to the aquatic environment;

(f) A narrative describing how the selected mitigation alternative is consistent with the mitigation hierarchy of this chapter; and

(g) A narrative describing the monitoring and maintenance tasks necessary to ensure the long-term success of the mitigation.

F. Mitigation options. The following requirements apply to all regulated development resulting in an IWMC impact requiring IWMC mitigation:

(1) IWMC mitigation shall be designed to duplicate or improve the hydrologic, biologic, botanic, and wildlife features of the IWMC.

(2) On-site IWMC mitigation.

(a) On-site IWMC mitigation includes mitigation on a parcel adjacent to the development site, even if the adjacent parcel has a different owner.

(b) On-site IWMC mitigation shall only be allowed for IWMC impacts in Categories IV and V, or if the mitigation area is 1.5 acres or larger and:

[1] The IWMC mitigation area is located within a conservation easement managed by a conservation agency; or

[2] The applicant establishes performance standards approved by the enforcement officer, and provides a performance guarantee payable to the MCSC Wetland Restoration Fund in the event the performance standards are not met.

(c) Temporary IWMC impacts shall be restored in place. The disturbed area shall:

[1] Be returned to its original contour and general soil profile;

[2] Be restored to a comparable IWMC community type; and

[3] Exhibit an FQI no lower than that of the IWMC prior to disturbance.

(d) The buffer area performance standards of this chapter shall apply to IWMC mitigation areas, except mitigation for IWMC impacts in Categories IV and V.

(e) The area of wetland restoration shall not be less than the area of IWMC impact. The additional mitigation area may consist of wetland enhancement; however, only 0.25 acre of mitigation shall be credited for each acre of wetland enhancement.

(f) Wetland creation shall not be credited for mitigation of IWMC impacts.

(3) Wetland mitigation banking.

(a) Wetland mitigation banking shall be required if the IWMC mitigation area is less than 1.5 acres.

(b) Mitigation credit may be obtained by payment into a wetland bank or the MCSC Wetland Restoration Fund. A receipt for payment into a wetland bank or the MCSC Wetland Restoration Fund shall be provided prior to issuance of a stormwater management permit.

(c) To provide credit for mitigation, a wetland bank must be certified by the USACE and comply with the Interagency Coordination Agreement on Wetland Mitigation Banking within the Regulatory Boundaries of Chicago District, dated January, 1997, or current version.

(d) Payment into the MCSC Wetland Restoration Fund shall not be allowed if the IWMC impact is in the same watershed as a wetland bank in existence at the time the MCSC Wetland Restoration Fund was established, provided the wetland bank has mitigation credits available. The following wetland banks were in existence at the time the MCSC Wetland Restoration Fund was established:

[1] Sybaquay Girl Scout Camp (Kishwaukee River Watershed);

[2] Kishwaukee Bottoms (Kishwaukee River Watershed);

[3] Marengo (Kishwaukee River Watershed); and

[4] Slough Creek (Nippersink Creek Watershed).

(e) A stormwater management permit will not be issued until a copy of the receipt of payment is provided.

G. Mitigation hierarchy. In addition to other applicable wetland and waters performance standards, the following requirements apply to all regulated development requiring IWMC mitigation:

(1) IWMC mitigation shall be provided as close to the IWMC impact site as possible, with respect to the following hierarchy:

(a) On site, provided the criteria for on-site mitigation are met;

(b) Wetland mitigation banking within the same sub-watershed;

(c) Wetland mitigation banking within an adjacent sub-watershed and within the same watershed;

(d) Wetland mitigation banking within the same watershed;

(e) Wetland mitigation banking within an adjacent watershed; or

(f) Wetland mitigation banking within McHenry County.

(2) Any funds paid into the MCSC Wetland Restoration Fund shall only be used to fund wetland restoration activities located fully within McHenry County.

H. Requirements for underground utilities. The following requirements apply to all regulated development involving the installation of underground utilities, except regulated development authorized by a general permit:

(1) In the case of underground stream crossings, the top of the pipe or encasement shall be buried a minimum of three feet below the existing stream bed.

(2) In IWMC, any excavation shall be backfilled with soil excavated from the trench in the same stratification in which it was removed.

(3) A contingency plan for frac-out shall be required for any utility proposed to be installed by directional boring.

§ 595-29 Buffer areas.

A. Buffer requirements. The following requirements apply to all regulated development adjacent to WOTUS or IWMC, except regulated development authorized by a general permit. These requirements are minimum standards and may be superseded by more restrictive USACE requirements.

Table 10. Buffer Widths
Buffer Type	Criteria	Subsection A(2)(a)	Subsection A(2)(b)	Subsection A(3)(a)	Subsection A(3)(b)	Subsection A(3)(c)
Linear	Tributary area > 20 acres	50 feet
Linear	HFVW, HQHS, or HQAR		100 feet
Nonlinear	0.25 acre < surface area < 0.50 acre			30 feet
Nonlinear	0.50 acre < surface area				50 feet
Nonlinear	HFVW, HQHS, or HQAR					100 feet

(1) Roadside drainage ditches, detention facilities, borrow pits, quarries, and improvements to public roads shall be exempt from these buffer requirements.

(2) Buffers shall be designated along both sides of linear WOTUS and IWMC using the following widths:

(a) Fifty feet on each side of linear WOTUS and IWMC having a tributary area greater than 20 acres; or

(b) One hundred feet on each side of linear WOTUS and IWMC that are HFVW, HQHS, or HQAR.

(3) Buffers shall encompass all nonlinear WOTUS and IWMC using the following widths:

(a) Thirty feet for all nonlinear WOTUS and IWMC with a surface area of at least 0.25 acre but less than 0.50 acre;

(b) Fifty feet for all nonlinear WOTUS and IWMC with a surface area of at least 0.50 acre; or

(c) One hundred feet for all nonlinear WOTUS and IWMC that are HFVW, HQHS, or HQAR. Crystal Lake falls under this section.

(4) Buffer areas for wetlands shall extend landward from the wetland boundary.

(5) Buffer areas for water bodies which are WOTUS or IWMC shall extend landward from the ordinary high water mark.

(6) A property may contain a buffer area originating from WOTUS or IWMC on another property.

(7) Buffer widths may be increased by the enforcement officer where state or federal threatened and endangered species may be present or for Illinois Natural Area Inventory sites following consultation with IDNR and USFWS.

(8) Buffer areas within subdivisions, planned unit developments, and manufactured home parks with five or more parcels platted after December 1, 2015, shall be located within an outlot with adjacent stormwater management facilities, WOTUS, and/or IWMC.

(9) Buffer areas within regulated development disturbing five acres or more shall be located within a deed or plat restriction with adjacent stormwater management facilities, WOTUS, and/or IWMC.

(10) A maintenance plan shall be prepared for the buffer areas. The enforcement officer may waive this requirement for minor and intermediate development.

(11) Filling WOTUS or IWMC to meet these buffer requirements or any other regulatory program shall not be allowed.

B. Buffer use. The following requirements apply to all regulated development within buffer areas for WOTUS or IWMC, except regulated development authorized by a general permit. These requirements may be superseded by more restrictive USACE requirements.

(1) Buffer areas shall be maintained free from development, including disturbance of the soil, dumping or filling, erection of buildings and placement of impervious areas, except as follows:

(a) Buildings, trails, water-dependent facilities, other new impervious areas occupying a maximum of 20% of the buffer area, provided that the stormwater runoff from the new impervious areas is not concentrated;

(b) Grading or filling, provided that the hydrologically disturbed area is revegetated according to the Native Plant Guide for Streams and Stormwater Facilities in Northeastern Illinois, NRCS et al. (as amended);

(c) Redevelopment within the footprint of legal nonconforming development in existence within a buffer area prior to the effective date of this chapter;

(d) BMPs;

(e) Stormwater management facilities; and

(f) Utilities, including wastewater wetlands, but not including septic leach fields.

(2) Regulated development within buffer areas which does not conform to the allowable uses shall be mitigated by:

(a) Varying the buffer width to a minimum of 1/2 the prescribed buffer width, provided that the total area of the buffer adjacent to WOTUS or IWMC is not reduced and that the buffer is located within a deed or plat restriction; or

(b) Replacing the impacted buffer area with BMPs, such as a rain garden or replacement of existing turf grass with native vegetation, at a 1:1 proportional rate.

(c) The consultation of the USACE, IDNR, or USFWS may preclude the use of either mitigation approach.

C. In the event the implementation of these buffer requirements precludes an otherwise legally buildable parcel from being developed, the enforcement officer may allow the minimal amount of relief from the buffer area performance standards in order to restore the parcel to a buildable condition.