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Home My WebLink About20252323.tiff i Weld CountyDrinage Code _CertIcate of Compliancetr „, _ . .4. 4 ealai ` I - " Weld County Case Number : PU DF24 - 0001 _ _ � r N Parcel Number : 121308000014 , 121317100016 and 121309000026 Legal Description , Section / Township / Range : Part of Sections 8 , 9 and 17 , T3N , R65W Date : May 7 , 2025 I Todd A . Johnson , Consultant Engineer for Terra Forma Solutions , Inc . ( Applicant ) , understand and acknowledge that the applicant is seeking land use approval of the case and parcel in the description above . I have designed or reviewed the design for the proposed land use set for in the application . I hereby certify , on behalf of the applicant , that the design will meet all applicable drainage requirements of the Weld County Code with the exception of the variances ) described on the attached exhibits . This certification is not a guarantee or warranty either expressed or implied . Engineer ' s Stamp : epofin �e�ll�ltit � l � � � � �1�/�� , •, ,, rs- : A® .; �� : • .e • me • + %0, �• 5 / 7 / 2 5 4.00 * Ss/ � • • • • • • . . . . • . • • . • . . G Variance Request Of Applicable ) • • • . a • ;. 4,ONAL 1 . Describe the hardship for which the variance is being requested . 2 . List the design criteria of the Weld County Code of which a variance is being requested . 3 . Describe the proposed alternative with engineering rationale which supports the intent of the Weld County Code . Demonstrate that granting of the variance will still adequately protect public health , safety , and general welfare and that there are no adverse impacts from stormwater runoff to the public rights - of - way and / or offsite properties as a result of the project . Retention ponds are not permitted per Section 8 - 11 - 40 - E of the Weld County Code . Additionally , Section 5 . 10 . 1 of the Weld County Engineering and Construction Criteria states : " Stormwater retention facilities ( stormwater infiltration facilities ) normally are not allowed in Weld County but shall be considered for special circumstances with the issuance of a variance . Variance requests shall only be considered in situations where there is a proven hardship on the proposed site . A hardship would be considered where there is not adequate topography to physically drain a pond ( sump in basin ) , refusal of an irrigation ditch to accept additional drainage , or some other physical site constraint . " The proposed project site meets both hardship criteria . The site includes several historic low points that are infeasible to drain by gravity without extreme excavation ( > 50 feet ) or the use of mechanical pumping . Given the presence of Type A sandy soils , these areas currently allow stormwater to infiltrate naturally . The proposed design seeks to minimize disturbance and preserve existing drainage patterns by placing retention ponds in the general area of these larger depressions . Due to the topography , there is no feasible way to drain the proposed ponds using a typical gravity outlet structure . Therefore , runoff entering these ponds will infiltrate into the ground as it does under existing conditions . Furthermore , the Farmers Reservoir and Irrigation Company ( FRICO ) , which owns and operates the downstream Milton reservoir , does not permit stormwater discharges into their system . As a result , all developed runoff will be captured by the proposed retention ponds and infiltrated on site , with no negative impacts to surrounding areas . We are proposing retention ponds due to these historic site constraints . The ponds will be sized for 1 . 5 times the total inflow volume from the 24 - hour , 100 - year event and will include 1 foot of freeboard to the spillway , in accordance with Section 5 . 10 . 1 of the Weld County Engineering and Construction Criteria . The site is composed of highly sandy soils , making it unlikely that water will be retained in the ponds for any longer duration than occurs under current conditions . This proposed condition is also consistent with existing conditions in Filing No . 1 , and the associated maintenance requirements will be similar for the Metropolitan District . Public Works Director/ Designee Review ( If Applicable ) Mike McRoberts , P . E . � ' y� � ; itta - Public Works Director / Designee Name Signature July 16 , 2025 Date of Signature .— Approved ❑ Denied Comments : Department of Public Works Development Review 1111 H Street , Greeley , CO 80631 I Ph : 970 - 304 - 6496 1 www . weldgov . com / departments / public_ works / development _ review 08 / 02 / 2019 i Weld CountyDrinage Code _CertIcate of Compliance it Weld County Case Number : PU DF24 - 0001 _ _ � r N Parcel Number : 121308000014 , 121317100016 and 121309000026 Legal Description , Section / Township / Range : Part of Sections 8 , 9 and 17 , T3N , R65W Date : May 71 2025 I Todd A . Johnson , Consultant Engineer for Terra Forma Solutions , Inc . ( Applicant ) , understand and acknowledge that the applicant is seeking land use approval of the case and parcel in the description above . I have designed or reviewed the design for the proposed land use set for in the application . I hereby certify , on behalf of the applicant , that the design will meet all applicable drainage requirements of the Weld County Code with the exception of the variances ) described on the attached exhibits . This certification is not a guarantee or warranty either expressed or implied . Engineer ' s Stamp : 410.9. . . .1!9/ 5/0 Q • I • � ` , j • • r • � �0, 5 / 7 / 2 5 . � _ ��i Cam . • • • • • • . . . . • • • ' • • . G ~�. Variance Request Of Applicable ) cfr,,�ss�� • • • • �NAL ��`` 1 . Describe the hardship for which the variance is being requested . 2 . List the design criteria of the Weld County Code of which a variance is being requested . 3 . Describe the proposed alternative with engineering rationale which supports the intent of the Weld County Code . Demonstrate that granting of the variance will still adequately protect public health , safety , and general welfare and that there are no adverse impacts from stormwater runoff to the public rights - of - way and / or offsite properties as a result of the project . Per Section 5 . 10 . 1 of the Weld County Engineering and Construction Criteria , an emergency spil way is required for all retention ponds . Retention Pond W3 is located within a deep natural depression . When the required volume 1 . 5 times the 100 - year , 24 - hour runoff is calculated , the corresponding storage elevation is approximately five feet below the natural overflow point , which discharges off - site to the east . Due t0 the topography and existing site constraints , it is not feasible to raise the pond elevation without creating a low point directly over an existing Oil & Gas facmlity . As a result , there is no practical way to construct a concrete emergency spillway within the reasonable limits of the pond area that would provide positive drainage . However , there should be no adverse impacts to any proposed lots by omitting the spillway . The pond will infiltrate all runoff and will provide significantly more storage capacity than required , including the necessary freeboard . Public Works Director/ Designee Review ( If Applicable ) Mike McRoberts , P . E . _ � __—/t t dsals - Public Works Director / Designee Name Signature July 16 , 2025 Date of Signature Approved ❑ Denied Comments : Department of Public Works 1 Development Review 1111 H Street , Greeley , CO 80631 I Ph : 970 - 304 - 6496 1 www . weldgov . com / departments / public_ works / development _ review 08 / 02 / 2019 i Weld CountyDrinage Code _CertIcate of Compliance it Weld County Case Number : PU DF24 - 0001 _ _ � r N Parcel Number : 121308000014 , 121317100016 and 121309000026 Legal Description , Section / Township / Range : Part of Sections 8 , 9 and 17 , T3N , R65W Date : May 71 2025 I Todd A . Johnson , Consultant Engineer for Terra Forma Solutions , Inc . ( Applicant ) , understand and acknowledge that the applicant is seeking land use approval of the case and parcel in the description above . I have designed or reviewed the design for the proposed land use set for in the application . I hereby certify , on behalf of the applicant , that the design will meet all applicable drainage requirements of the Weld County Code with the exception of the variances ) described on the attached exhibits . This certification is not a guarantee or warranty either expressed or implied . Engineer ' s Stamp : 410.9. . . .1!9/ 5/0 Q • I • � ` , j • • r • � �0, 5 / 7 / 2 5 . � _ ��i Cam . • • • • • • . . . . • • • ' • • . G ~�. Variance Request Of Applicable ) '/�i,,ss�o • • • � �NAL \��` 1 . Describe the hardship for which the variance is being requested . 2 . List the design criteria of the Weld County Code of which a variance is being requested . 3 . Describe the proposed alternative with engineering rationale which supports the intent of the Weld County Code . Demonstrate that granting of the variance will still adequately protect public health , safety , and general welfare and that there are no adverse impacts from stormwater runoff to the public rights - of - way and / or offsite properties as a result of the project . Per Section 5 . 10 . 1 of the Weld County Engineering and Construction Criteria , an emergency spil way is required for all retention ponds . Retention Pond W3 is located within a deep natural depression . When the required volume 1 . 5 times the 100 - year , 24 - hour runoff is calculated , the corresponding storage elevation is approximately five feet below the natural overflow point , which discharges off - site to the east . Due t0 the topography and existing site constraints , it is not feasible to raise the pond elevation without creating a low point directly over an existing Oil & Gas facmlity . As a result , there is no practical way to construct a concrete emergency spillway within the reasonable limits of the pond area that would provide positive drainage . However , there should be no adverse impacts to any proposed lots by omitting the spillway . The pond will infiltrate all runoff and will provide significantly more storage capacity than required , including the necessary freeboard . Public Works Director/ Designee Review ( If Applicable ) Public Works Director / Designee Name Signature Date of Signature f 1 Approved ❑ Denied Comments : Department of Public Works 1 Development Review 1111 H Street , Greeley , CO 80631 I Ph : 970 - 304 - 6496 www . weldgov . com / departments / public_ works / development _ review 08 / 02 / 2019 1ea TERRA FORMA SOLUTIONS ( AKA BEEBE DRAZZ ( t ! 2 FINAL DRAINAGE REPORT JANUARY 2025 REVISED MAY 2025 For : RE I Limited Liability Co P . O . BOX 156 Red Feather Lakes , CO 80545 By : Terra Forma Solutions , Inc . Todd Johnson , P . E . Todd@terraformas . com 303 . 257 . 7653 Weld County Case Number PUDF24 - 0001 PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 1 Of 21 PROFESSIONAL ENGINEER ' S CERTIFICATION I hereby certify that this report for the Final Drainage Study for the Pelican Lake Ranch Filing No . 2, was prepared by me ( or under my direct supervision ) in accordance with the provisions of the Weld County Engineering and Construction Criteria Manual for the owners thereof . Jaya ti . e tt • 376611 G41/ / Qat \ \* Il00 ‘ 5 / 8 / 25 Todd Johnson , P . E . Date State of Colorado No . 37660 For and on behalf of Terra Forma Solutions , Inc . PELICAN LAKE RANCH FILING NO . 2 FINAL DRAINAGE REPORT Page 2of21 TABLE OF CONTENTS 1 . GENERAL LOCATION AND PROJECT DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 A . Project Location 3 B . Project Plan 3 C . Site Features , Existing Land Use & Constraints . 4 D . Floodplains & Wetland Areas 4 E . Soils & Groundwater 4 11 . DRAINAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 A . Existing Onsite Conditions 5 B . Existing Offsite Condition 5 C . Historic Conditions EPA - SWMM Results 5 111 . DRAINAGE FACILITY DESIGN - PROPOSED CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 A . Developed Onsite Condition 7 B . On - Site Retention - Infiltration 7 C . Erosion Control 8 D . Drainage Facility Design 8 V . VARIANCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 V . SUMMARY & CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 VI . GENERAL DRAINAGE MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 VI1 . LIST OF REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 3of21 1 . G NERAL LOCATION AND PROJ CT DESCRI PT ON A . Project Location The Overall Project Site is located in the Sections 3 , 4 , 5 , 8 , 9 , 10 , 15 , and 17 of Township 3 North , Range 65 West of the 6th P . M . , and is currently within Weld County , Colorado . The Second Filing is located west of Milton Reservoir and State Own Land with a total area of approximately 854 . 2 acres . The Second Filing is bounded on the east by the State own land , on the north by the First Filing of Beebe Draw , on the south by County Road 32 and on the west by County Road 39 . A Project Vicinity map and Drainage Plan are included within this Report . This site is in a non - urbanizing area . According to Weld County ' s online GIS database , no portion of this project area is located within any Weld County MS4 areas and therefore this project is not subject to the requirements of the County ' s MS4 program . B . Project Plan In 1989 , a Zone Change was approved that included this proposed development . Also in 1989 , a portion of the approved PUD was platted ( Corrected First Filing of Beebe Draw Farms and Equestrian Center ) . The First Filing is located near the center of the PUD , and it is adjacent to WCR 39 . The First Filing also included outlots that are east of the Platte Valley Canal . In 1998 , A Phase III Drainage Report for Filing 1 was approved by Weld County . Subsequentially , additional drainage letters / calculations were approved by the County as different phases of Filing 1 were constructed . The proposed Second Filing consists of two areas of development with a total of 283 residential lots and associated infrastructure and open space . The area that is located between the First Filing eastern boundary and Milton Reservoir is called the East Area of Filing 2 and consists of 31 lots . The area that is located south of Filing 1 boundary , between WCR 39 and the State Land , is the main area and remainder of Filing 2 consisting of 252 lots . The minimum lot size is 1 acre . The Developer intends to utilize the natural grade and terrain as much as possible to facilitate adequate drainage of stormwater to the proposed retention / infiltration basins . All of the area within Filing 2 drains toward Milton Reservoir . The Farmers Reservoir and Irrigation Company has been contacted and they do not allow stormwater to discharge into their system . Infiltration basins will be used to eliminate , as much as possible , the storm runoff from the development . The development will have private maintained streets with borrow ditches on both sides . The roadway network will connect to the ex ' sting roadways that are located within Beebe Draw Farms & Equestrian Center First Filing . In addition , there will be two new accesses off of County Road 32 and 39 . The total area of Pelican Lake Ranch Filing Number 2 is 854 . 2 acres , of which approximately 723 . 5 acres will be developed . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 4of21 C . Site Features , Existing Land Use & Constraints . The site can be characterized as relatively flat to gently rolling . There is approximately 96 feet of vertical elevation drop across the site . Numerous gas / oil wells are located throughout the site . The remainder of the site is currently being used as grazing land or dry farmland . The exiting runoff generally drains to the southeast and into the Milton Reservoir . There are several low areas on the development that don ' t have an outfall , however , the soils in these areas are sandy and any runoff to these low areas currently infiltrates into the ground . D . Floodplains & Wetland Areas Based on the FEMA - Weld County , Colorado Flood Insurance Rate Map ( FIRM ) Community Panel Number 08123C1935E ( 1 / 20 / 2016 ) , the flood plain for Milton Reservoir does not encroach into this development . The proposed construction within Filing 2 will not impact the any FEMA flood plain . E . Soils & Groundwater Per the Geotechnical Due Diligence Study for Pelican Lakes , Filing 2 , prepared by AGW and dated April 29 , 2025 , the subsurface conditions in the project area consist of topsoil , clay , sand , and gravel overlying sedimentary bedrock . According to the USDA MRCS Web Soil Survey , the surface soils are primarily a mix of Valent sand and Vona loamy sand . These soils are classified as Hydrologic Soil Group A , indicating low runoff potential and high infiltration capacity . All soil types are considered suitable for residential development . Groundwater was generally encountered at depths ranging from 16 to over 40 feet below existing grade and is expected to fluctuate seasonally and with future irrigation . Notably , groundwater levels are more than 15 feet below proposed finished grades across most of the site , with the exception of Pond E1 , where groundwater was observed in the worst case around 4 feet below the proposed excavated pond bottom . 11 . DRAINAGE This section discusses historic , existing , and proposed , drainage basin hydrology . Since there are basins that will be larger than 160 acres , EPA - SWMM computer program was u sed , in addition to the rational method , to calculate the Historic and Developed Runoff for retention pond sizing , as well as the peak flows for several channels and culverts where the tributary areas exceeded 160 acres . The calculation conforms with the appropriate sections of the " Weld County Engineering and Construction Guidelines " u pdated January 2021 and the Weld County Code , as well as Mile High Flood District ' s Drainage Criteria Manuals . The site is located in a non - urban area and therefore , the 10 - year storm was utilized for the minor storm event . The Rational Method was used to determine runoff to the proposed culverts and drainage swales . The on - site swales were sized to pass the 100 - year event . Per the Weld County Engineering and Construction Guidelines , the culverts n eed to be sized to convey the 10 - year runoff with no more than 6 inches overtopping the roadway and convey the 100 - year runoff with no more than 18 inches overtopping the roadway . In addition , the maximum headwater to depth ratio ( HW / D ) shall not exceed 2 . 0 for culverts under 36 " in diameter , and 1 . 7 for culverts 36 " to 60 " in diameter . This criteria was used as a minimum design standard . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 5of21 The Rational Method utilized the one - hour storm event . Using the NOAA Atlas 14 Volume S version 2 maps , point precipitation values were obtained to develop rainfall intensity calculations . One - hour rainfall depths of 1 . 39 inches and 2 . 69 inches were determined for the 10 - year and 100 - year event , respectively . The EPA SWMM computer model was used to calculate the major runoff , retention volume and release rates . The SCS Type II — 24 Hour hydrograph was used as the model storm in the SWMM program . The 100 - year , 24 - hour rainfall is 4 . 64 inches . The infiltration ponds will be sized assuming no infiltration rates . The infiltration rate that was used in the Filing 1 calculations was approximately 1 inch per hour . The SCS Soil map has predominately 2 types of sandy soil located in Filing 2 . One type ( Vona Loamy Sand ) has published infiltration rates between 2 and 6 inches per hour . While the second type ( Valent Sand ) has published infiltration rates between 6 and 40 inches per hour . Given a 24 - hour design storm , there will be infiltration occurring at the ponds and the assumption of no infiltration results in higher calculated volumes . The water quality capture volumes are designed within the pond to infiltrate into the soil . A . Existing Onsite Conditions The Site is in unincorporated Weld County . There are numerous gravel / dirt access roads located throughout the site that provides access to the existing gas / oil wells and tank batteries . The remainder of the site is pervious with the ground cover consisting of grasses and sage brush . There are several depressions that infiltrate the tributary runoff . The existing soil is capable of infiltrating runoff . The site drains toward the southeast and eventually into the Milton Reservoir . B . Existing Offsite Condition Approximately 1 , 956 acres of offsite tributary area historically drain towards / thru this site to the outfall into Milton Reservoir . While the roadside swales that are adjacent to the County Roads ( WCR 39 ) will intercept some of the runoff , it is not anticipated that they will be able to convey a significant amount . Therefore , it was assumed that the runoff from the offsite tributary areas will drain across the county roads . The offsite runoff will be conveyed to the proposed retention / infiltration ponds via open swales . In addition , the bottom of the proposed retention ponds will have native vegetation and sandy bottoms which will infiltrate all of the runoff . Where necessary , swales and pipes will be constructed to convey the runoff around lots and under streets . C . Historic Conditions EPA - SWMM Results The EPA SWMM model was set up for the historic conditions . Historic Conditions estimates the expected runoff prior to Filing 1 construction . The Horton ' s Equation for infiltration loss were used to model infiltration losses for the basins . The SCS Type II — 24 Hour hydrograph was multiplied by the NOAA 100 - year value for the 24 - hour storm and was used as the rain gage . The following table shows the results of the SWMM model for the historic conditions : PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 6 of 21 Historic Conditions 1.11 Sub - Design Basin Area Basin 100 r Combined Combined Total g Y Total Trib Basin Point ( Ac ) Runoff ( cfs ) Area ( Ac ) 100yr Runoff ( cfs ) OFFSITE ON1 DP ON1 307 234 OW1 DP OW1 48 41 OW2 DP OW2 182 93 OW3 DP OW3 66 45 OW4 DP OW4 81 42 OW5 DP OW5 591 284 OW6 DP OW6 174 93 0S1 DP 0S1 187 140 0S2 DP 0S2 23 8 ONSITE H 1 DP H 1 666 521 1107 541 H2 DP H2 63 47 H3 DP H3 35 43 H4 DP H4 258 210 H5 DP H5 30 33 H6 DP H6 39 47 H7 DP H7 5 5 H8 DP H8 272 128 750 189 H9 DP H9 99 42 861 290 H10 DP H10 90 98 681 277 H 11 DP H 11 39 33 900 269 H12 DP H12 81 23 981 238 H13 DP H13 26 37 H14 DP H14 51 29 H15 DP H15 1475 625 2127 765 H16 DP H16 28 16 H17 DP H17 22 28 H18 DP H18 111 24 H19 DP H19 134 122 PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 7of21 1 I . DRA NAGE FACILITY DESIGN PROPOSED CONDITIONS Due to the large size lots being proposed , the existing drainage patterns will remain as much as possible , with the exception of the flows to the existing sumps . The existing sumps will either have a retention pond constructed in their location , be filled with dirt , or be drained via swales . Some of the smaller existing sumps within the lots will be filled at the time of individual lot development . A . Developed Onsite Condition All roads will be paved and maintained by the metro district . The minimum lot size will be 1 acre and there will be a 150 feet setback from all existing ( active ) gas wells . With the setbacks from the wells and the access to the wells , areas of open space will be created . It is anticipated that approximately 15 to 20 percent of the land will be impervious due to streets , houses , paved driveways and auxiliary buildings . Per Mile High Flood District Table 6 - 3 , for residential lots from 0 . 75 to 2 . 5 acres , a 20 % imperviousness is recommended . Therefore , a 20 % imperviousness was used for developed area in Filing 2 . The runoff coefficient for the developed condition incorporates the anticipated impervious areas . Filing 1 lots sizes were 2 to 4 acres in size . A half dozen lots that have been built out were selected at random and their percent imperviousness was calculated including the area of the street adjacent to their lot . These lots imperviousness varied between 10 . 4 to 13 . 8 percent with the average being 12 . 1 % . In addition to lots , there is a significant amount of open space in Filing 1 that was not included in the 12 . 1 % calculations . A 12 . 1 % imperviousness rate was utilized for Filing 1 area that drains onto Filing 2 . B . On - Site Retention - Infiltration In order to reduce / eliminate the total volume of runoff from the site , infiltration basins will be utilized . The infiltration basins will be sized to infiltrate 1 . 5 times the 100 year 24 - hour storm event for the tributary area including onsite and offsite tributary runoff . A conservative infiltration rate of 1 inch per hour has been used to demonstrate appropriate drain times in accordance with Colorado Revised Statute 37 - 92 - 602 ( 8 ) . Overflow swales will be provided at infiltration basins that will safely convey runoff in excess of the retention pond volumes . The retention ponds will provide for stormwater quality treatment in accordance with Mile High Flood District criteria . The Water Quality Capture Volume ( WQCV ) will be captured in the lower stages of the retention ponds and allowed to infiltrate . The swales leading to and from the proposed ponds will be grass lined with slopes as flat as 0 . 2 % . With the sandy soil , these swales will encourage the storm runoff to infiltrate and thereby reducing the volume of the runoff to the ponds . For calculations purposes , the swales were assumed not to have infiltration . Once the location of the infiltration ponds are finalized , infiltration tests will be conducted in accordance with Mile High Flood District criteria and an infiltration rate for each pond will be determined . Per Mile High Flood District criteria , the infiltration rate that is used in the design will be 50 % of the measured rate . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 8of21 C . Erosion Control Erosion control will be provided and will be consistent with the Final Phasing P lan . More specifically , BMPs will be installed as appropriate to minimize erosion due to wind and surface runoff affects . BMPs during construction may include sediment traps , tracking pads , silt fencing , inlet protection , rock - lined rundowns , revegetation , and contour roughening . Post - Construction BMPs may include infiltration basins , vegetation , and proper maintenance of open areas . D . Drainage Facility Design General Concept The majority of the onsite areas will drain to the proposed infiltration ponds . The infiltration ponds were sized to hold and infiltrate 1 . 5 times the 100 - year developed runoff . The emergency spillway was sized for the developed onsite and historic offsite 100 - year runoff . No developed runoff from the West Area will be release into the Milton Reservoir during the 100 - year storm event with the exception of about 5 . 6 acres that drains easterly onto the State Land . This area is comprised of the very rear portions of several lots and the downstream end of the Pond 4 Spillway and therefore will have little to no imperviousness and should not result in any adverse downstream impacts . S pecific Details The onsite grading will convey the 100 - year storm event to the infiltration ponds . Offs ite Basins : Sub - Basin ON1 , 307 - acres , 2 % impervious , undeveloped offsite area that drains onto future phases on this development and will drain to the proposed Retention P ond UP1 that is located north of the Beebe Draw Farms Parkway . This basin ground cover consists of open range . Sub - Basin OW1 , 48 - acres , 2 % impervious , undeveloped offsite area that drains onto future phases on this development and will drain to the existing Retention P ond 9 that is located south of the Beebe Draw Farms Parkway . This basin ground cover consists of open range . Sub - Basin OW2 , 181 . 8 - acres , 2 % impervious , undeveloped offsite area that drains onto the First Filing and into the existing retention ponds . This basin ground cover consists of open range . Sub - Basin OW3 , 66 . 4 - acres , 2 % impervious , undeveloped offsite area that drains onto the First Filing and into the existing retention ponds . This basin ground cover consists of open range . Sub - Basin OW4 , 80 . 7 - acres , 2 % impervious , undeveloped offsite area that drains onto this site and combines with onsite Sub - basin W2 to drain to Pond W1 . This basin ground cover consists of open range . Sub - Basin OW5 , 590 . 74 - acres , 2 % impervious , undeveloped offsite area that drains onto this site and combines with onsite Sub - basin W1 to drain to Pond W1 . This basin ground cover consists of open range . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 9of21 Sub - Basin OW6 , 173 . 92 - acres , 2 % impervious , undeveloped offsite area that drains onto this site and combines with onsite Sub - basin S1 to drain to Pond S1 . This basin ground cover consists of open range . Sub - Basin 0S1 , 1876- acres , 2 % impervious , undeveloped offsite area that drains onto future phases of this development . This basin ground cover consists of open range . Sub - Basin 0S2 , 23 - acres , 2 % impervious , undeveloped offsite area that drains onto future phases of this development at the southeast corner of future development . This basin ground cover consists of open range . Rational Method Calculations : Main Area Basins : Sub - Basin W1 , 11 . 3 - acres , 20 % impervious , onsite area within Filing 2 . This sub - basin combines with basin OW5 and drains to a culvert under Fairbanks Road to basin W - la and then continues to Pond W1 . Sub - Basin W1 a , 10 . 26 - acres , 20 % impervious , onsite area within Filing 2 . This sub - basin combines with Basins W - 1 and OW5 and drains via a grass - lined channel to Pond W1 . Sub - Basin W1b , 8 . 6 - acres , 20 % impervious , onsite area within Filing 2 . This sub - basin combines with Basins W1 , W1 a , and OW5 immediately before Pond W1 and drains via a grass - lined channel to Pond W1 . Sub - Basin W2 , 32 . 2 - acres , 7 . 3 % impervious , consisting of a small area of Filing 2 , and larger areas on Filing 1 and open space . This sub - basin combines with Basin OW4 and drains to a culvert under Fairbanks Road to basin W2a then continues to a grass - lined channel to Pond W1 . Sub - Basin W2a , 4 . 4 - acres , 13 . 8 % impervious , consisting of onsite area within Filing 2 as well as open space . This sub - basin combines with Basins W2 and OW4 and drains via a grass - lined channel to Pond W1 . Sub - Basin W3 , 15 . 6 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located south of Morning Dove Lane and drains via a culvert to Basin W3a then continues to a grass - lined channel to Pond W1 . Sub - Basin W3a , 26 . 6 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin combines with Basins W3 and W3b and drains via a grass - lined channel to Pond W1 . Sub - Basin W3b , 1 . 0 - acres , 20 % impervious , consisting of onsite area within Filing 2 southeast of Morning Dove Lane and Falcon Way . This sub - basin drains via a culvert to Basin W3a and eventually to Pond W1 . Sub - Basin W4 , 46 . 8 - acres , 9 . 5 % impervious , consisting of onsite area within Filing 2 as well as area within Filing 1 and open space . This sub - basin drains directly into Pond W1 . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 10 of 21 Sub - Basin W5 , 37 . 2 - acres , 14 . 5 % impervious , consisting of onsite area within Filing 2 as well as open space associated with gas well production . This sub - basin is located south of Morning Dove Lane and drains via a culvert to Basin W6b then continues to the storm sewer system that discharges to Pond 4 . Sub - Basin W6a , 23 . 2 - acres , 10 . 5 % impervious , consisting of onsite area within Filing 2 as well as area within Filing 1 and open space . This sub - basin drains to Basin 6b then continues to the storm sewer system that discharges to Pond 4 . Sub - Basin W6b , 6 . 54- acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin drains directly into the storm sewer system that discharges to Pond 4 after combining with Basin W5 and Basin W6a . Sub - Basin W6 , 9 . 7- acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin drains via a culvert to Basin W10 , then continues into the storm sewer system that discharges to Pond 4 . Sub - Basin W8a , 1 . 1 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin drains via a culvert to Basin W8 and into Pond W3 . Sub - Basin W8 , 23 . 34- acres , 20 % impervious , consisting of onsite area within Filing 2 as well as open space associated with gas well production . This sub - basin drains directly into Pond W3 . Sub - Basin W10 , 18 . 2 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located between Morning Dove Lane and Ledyard Road and combines with Basins W7 , W9 , W11 , and W12 and drains directly into the storm sewer system and outfall channel which drains to Pond 4 . Sub - Basin W11 , 1 . 44 - acres , 12 . 1 % impervious , consisting of onsite area within Filing 1 . This sub - basin is located north of Ledyard Road and drains to Pond 4 via the Pond W1 outfall channel . Sub - Basin W12 , 8 . 1 - acres , 19 . 4 % impervious , consisting of onsite area within Filing 2 as well as a small area within Filing 1 . This sub - basin is located north of Ledyard Road and drains via a culvert to Basin W10 , then continues into the storm sewer system that discharges to Pond 4 . Sub - Basin W13 , 13 . 7 - acres , 10 . 4 % impervious , consisting of area within State Land ( which is considered open space ) , open space and lot area within Filing 2 as well as a small area within Filing 1 . This sub - basin directly drains to the Pond W1 outfall channel and into Pond 4 . Sub - Basin W14 , 179 . 2 - acres , 9 . 2 % impervious , consisting of 125 . 5 acres of residential area within Filing 1 and 51 . 18 acres of open space within Filing 1 . This sub - basin directly drains to Pond 4 . Sub - Basin W15 , 4 . 7 - acres , 2 . 0 % impervious , consisting of area within State Land ( which is considered open space ) . This sub - basin directly drains to Pond 4 . Sub - Basin W16 , 2 . 4 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located northeast of the intersection of Fairbanks Road and Morning Dove Lane . This Basin drains via a culvert into Basin S2 and continues into Pond S1 . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 11 of 21 Sub - Basin S1 , 27 . 7- acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located between County Road 39 and Fairbanks Road and drains directly into a culvert under Fairbanks Road which drains directly into P ond S1 . Sub - Basin S2 , 22 . 0 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located east of Fairbanks Road and drains directly into Pond S 1 . Sub - Basin S3 , 6 . 1 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located northeast of the intersection of Falcone Drive and P elican Lake Lane , and drains directly into a culvert under Falcon Drive into Basin S4 . Sub - Basin S4 , 21 . 1 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located west of the intersection of Falcon Drive and Pelican Lake Lane , and drains directly into a culvert under Pelican Lake Lane which drains directly into Pond S2 . Sub - Basin S5 , 8 . 6 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located east of the intersection of Pelican Lake Lane and Falcon Drive , and drains directly into a culvert under Falcon Drive which drains directly into Pond S2 . Sub - Basin S6 , 26 . 2 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located south of the intersection of Pelican Lake Lane and Falcon Drive , and drains directly into Pond S2 . Sub - Basin S8 , 1 . 9 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located northwest of the intersection of Falcon Drive and Nuthatch Way , and drains to a culvert under Nuthatch Way into Basin S9 . Sub - Basin S9 , 10 . 4 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located north of Falcon Drive , and drains southerly toward the culvert under Falcon Drive into Basin S10 . Sub - Basin S10 , 12 . 9 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located north of Meadowlark Lane , and drains southerly toward a culvert under Meadowlark ane into Basin S13 . Sub - Basin S11 , 11 . 2 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located northwest of the intersection of Meadowlark P lace and Nighthawk Way and drains easterly to a culvert under Nighthawk Way and into Basin S12 . Sub - Basin S12 , 18 . 2 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located north of Meadowlark Lane and drains southerly toward a culvert under Meadowlark Lane into Basin S13 . Sub - Basin S13 , 72 . 8 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located between Nighthawk Drive and Meadowlark Lane and drains easterly to a culvert under Nighthawk Drive directly into Pond S 4 . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 12 of 21 Sub - Basin S14 , 22 . 8 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located northwest of the intersection of Pelican Lake P lace and Fairbanks Drive and drains southeasterly to a culvert under Pelican Lake Place directly into Pond S3 . Sub - Basin S15 , 23 . 3 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located between Fairbanks Drive and County Road 39 and drains southeasterly to a culvert under Sora Way into Basin S16 . Sub - Basin S16 , 2 . 9 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located southwest of the intersection of Fairbanks Drive and Bunting Way and drains easterly to a culvert under Bunting Way into Basin S17 Sub - Basin S17 , 29 . 2 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located south of Fairbanks Drive and west of Pelican Lake Drive and drains easterly to a culvert under Pelican Lake Drive directly into P ond S3 . Sub - Basin S18 , 12 . 2 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located west of Fairbanks Drive and east of County Road 39 and drains easterly to a culvert under Fairbanks Drive into Basin S19 . Sub - Basin S19a , 2 . 2 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located northeast of the intersection of Fairbanks Drive and Pelican Lake Lane and drains to a culvert under Pelican Lake Lane into Basin S19 . Sub - Basin S19 , 67 . 4 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located between Fairbanks Drive and Nighthawk Drive and drains southeasterly to a culvert under Fairbanks Drive into Basin S20 . Sub - Basin S20 , 60 . 2 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located south of Fairbanks Drive and south of Nighthawk Drive and drains easterly into Pond S4 . Sub - Basin S21 , 7 . 1 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located northeast of the intersection of Meadowlark Way and Nighthawk Drive and drains southerly into a culvert under Meadowlark Way into Basin S22 . Sub - Basin S22 , 17 . 1 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located south of Meadowlark Way and east of Nighthawk Drive and drains southerly into Pond S4 . Sub - Basin S23 , 7 . 0 - acres , 20 % impervious , consisting of onsite area within Filing 2 . This sub - basin is located along the eastern boundary and drains southerly into P ond S4 . Sub - Basin U1 , 5 . 4 - acres , 2 % impervious , consisting of the rear portion of residential lots and open tract area . This Basin is anticipated to be almost entirely undeveloped and drains onto the State Land , following existing drainage patterns . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 13 of 21 Sub - Basin U2 , 2 . 8 - acres , 20 % impervious , consisting of the rear portion of residential lots . This Basin is anticipated to be mostly undeveloped and drains onto the County Road 32 and 29 ROWs , following existing drainage patterns . Sub - Basin U3 , 2 . 6 - acres , 2 % impervious , consisting of the downstream side of the Pond 4 spillway . This Basin will remain undeveloped and drains onto the State Land , following existing drainage patterns . East Area Basin : North Basins Sub - Basin H4 , 255 . 4 - acres , 2 % impervious , consists of an area that is north of the existing Beebe Draw Farms Parkway and will be a part of future development of Pelican Lakes . This sub - basin drains Pond 9 . Sub - Basin H4 was used in the EPASWMM model , and the Rational Method runoff was not calculated for this sub - basin . Sub - Basin EN1 , 3 . 9 - acres , 20 % impervious , onsite area within Filing 2 . This sub - basin drains to a culvert under Egret Road into Basin EN6 and then continues along the south side of Beebe Draw Farms Parkway and eventually to Pond E2 . Sub - Basin EN2 , 2 . 1 acres , 20 % impervious , onsite area within Filing 2 . This sub - basin drains to a culvert under Blue Huron Street at the northern intersection with Egret Road and then continues to Basin EN6 along the south side of Beebe Draw Farms Parkway and eventually to Pond E2 . Sub - Basin EN3 , 2 . 2 - acres , 20 % impervious , onsite area within Filing 2 . This sub - basin drains along the southwest side of Egret Road to a culvert into Basin EN4 and eventually to Pond E2 . Sub - Basin EN4 , 10 . 8 - acres , 20 % impervious , onsite area within Filing 2 . This sub - basin drains to a culvert under Blue Heron Street and then continues north to toward Beebe Draw Farms Parkway and eventually to Pond E2 . Sub - Basin EN5 , 3 . 7 - acres , 20 % impervious , onsite area within Filing 2 . This sub - basin drains north to toward Egret Road to a culvert into Basin EN6 and eventually to Pond 2 . Sub - Basin EN - 6 , 12 . 1 - acres , 20 % impervious , onsite area within Filing 2 . This sub - basin drains toward Beebe Draw Farms Parkway and eventually to Pond E2 . Sub - Basin EN7, 18 . 5 - acres , 20 % impervious , onsite area within Filing 2 . This sub - basin drains towards Beebe Draw Farms Parkway and eventually to Pond E2 . Sub - Basin E9 , 8 . 3 - acres , 20 % impervious , onsite area within Filing 2 containing the existing Pond 9 from Filing 1 , as well as the rear portion of several lots . This sub - basin drains directly into Pond 9 , following existing drainage patterns . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 14 of 21 S outh Basins Sub - Basin Fl , 12 . 3 - acres , 12 . 1 % impervious , consisting of offsite residential area within Filing 1 . This sub - basin drains to the overflow swale for Pond 9 and eventually to Pond El . Sub - Basin F2 , 6 . 9 - acres , 12 . 1 % impervious , consisting of offsite residential area within Filing 1 . This sub - basin drains to the overflow swale for Pond 9 and eventually to Pond El . Sub - Basin ESI , 24 . 9 - acres , 20 % impervious , consisting of open space areas and residential areas . This sub - basin drains to the overflow swale for Pond 9 and eventually to Pond El . Sub - Basin ES2 , 8 . 8 - acres , 20 % impervious , consisting of residential areas . This sub - basin drains to a culvert under Blue Heron Street , continuing to the overflow swale for Pond 9 and eventually to Pond El . Sub - Basin ES3 , 27 . 7 - acres , 20 % impervious , consisting of open space areas and residential areas . This sub - basin drains to the overflow swale for Pond 9 which drains to Pond El . Sub - Basin EU1 , 14 . 8 - acres , 2 % impervious , onsite area within Filing 2 . This area will remain undeveloped and will drain to the southeast , following existing drainage patterns . Retention Ponds : S ince the tributary areas to most of the Ponds are greater than 160 acres , the EPASWMM Computer Model was utilized to model the ponds . In addition , since the irrigation company who owns / operate the downstream reservoir doesn ' t permit storm water to drain into their facilities , the 100 - year runoff must be retained onsite and infiltrated in the sandy soil . The ponds in the EPASWMM model have no infiltration . Upon review of the SCS soil map descriptions , the expected infiltration rate will be between 2 inches per hour and 40 inches per hour . Therefore , the assumption of no infiltration is very conservative . Upon construction of the ponds , infiltration tests will be performed to confirm drain down times . S ince the ponds will retain stormwater and infiltrate it into the soil , the 100 - year , 24 - hour storm was used to size the ponds . The 100 - year , 24 - hour rainfall is 4 . 64 inches . U pstream of Filing 2 are the existing retention ponds located within the First Filing . The 1998 Drainage Report for the First Filing has a table listing the volumes for each retention pond . In order to determine the runoff from Filing 1 that is tributary to Filing 2 , the Filing 1 retention ponds were modeled within the EPASWMM model for Filing 2 . With the exception of one small pond , the EPASWMM model shows that all of the existing Filing 1 ponds will retain 100 percent of the 100 - year runoff . Upon additional examination , Pond 9 , as constructed , will retain the 100 - year historic runoff but does not provide the additional required volume ( 1 . 5 times the 100 - yr volume ) plus the one - foot freeboard , and therefore will be expanded with the development of Filing 2 . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 15 of 21 P onds for West Area Pond WI , tributary area of 828 . 00 acres , of which 671 . 44 acres is offsite area from west of CR 39 and 42 . 01 acres consists of Filing 1 residential area . Per the EPA S WMM model , the peak 100 - year flow into Pond W1 is 355 . 07 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 40 . 96 ac - ft . The bottom of the retention pond is at an elevation of 4884 . 5 and the 100 - year water surface is 4890 . 09 . Multiplying the 100 - year volume by 1 . 5 gives a required volume of 61 . 44 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4892 . 58 . The elevation of the spillway is 4894 . Per the calculations in the Appendix , the length of the spillway will need to be 365 feet long . The 100 - year water depth is approximately 5 . 59 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 67 . 1 hours . Pond 4 , tributary area of 301 . 88 acres , of which 133 . 6 acres is offsite area from Filing 1 residential area . Pond 4 is an existing infiltration pond that was constructed with Filing 1 but will be expanded with developed tributary area from Filing 2 . Per the EPA SWMM model , the peak 100 - year flow into Pond 4 is 97 . 31 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 16 . 63 ac - ft . The bottom of the detention pond is at an elevation of 4831 and the 100 - year water surface is 4835 . 10 . Multiplying the 100 - year volume by 1 . 5 gives a required volume of 24 . 95 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4836 . 65 . The existing elevation of the spillway is 4839 . 08 . The length of the existing spillway is approximately 128 feet long . Per the calculations in the Appendix , the length of the existing spillway is sufficient to pass the 100 - year developed flow at a flow depth of 0 . 5 ' and therefore no changes to the existing spillway are necessary . The 100 - year water depth is approximately 4 . 10 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 49 . 1 hours . Pond W3 , tributary area of 24 . 36 acres . Pond W3 is a natural depression / sump that will be utilized as a retention pond for this Filing . Per the EPASWMM model , the peak 100 - year flow into Pond W3 is 34 . 79 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 2 . 24 ac - ft . The bottom of the detention pond is at an elevation of 4891 and the 100 - year water surface is 4894 . 04 . Multiplying the 100 - year volume by 1 . 5 gives a required volume of 3 . 36 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4895 . 20 . Since this pond is located in an existing natural depression , no feasible overflow path exists and it will be allowed to pond several feet above the required volume . Therefore , no adverse impacts are anticipated to any proposed lots . A variance request has been included for the absence of a spillway on this pond . The 100 - year water depth is approximately 3 . 04 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 36 . 4 hours . Pond Si , tributary area of 225 . 93 acres of which only 52 . 01 acres are within Filing 2 . P ond S1 is situated on land that is planned for Open Space . Per the EPA SWMM model , the peak 100 - year flow into Pond S1 is 107 . 38 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 12 . 46 ac - ft . The bottom of the detention pond is at an elevation of 4915 and the 100 - PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 16 of 21 year water surface is 4918 . 06 . Multiplying the 100 - year volume by 1 . 5 gives a required volume of 18 . 69 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4919 . 43 . The elevation of the spillway is 4921 . Per the calculations in the Appendix , the length of the spillway will need to be 105 feet long . The 100 - year water depth is approximately 3 . 06 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 36 . 8 hours . Pond S2 , tributary area of 62 . 06 acres . Pond S2 is situated on land that is planned for Open Space . Per the EPA SWMM model , the peak 100 - year flow into Pond S2 is 88 . 66 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 5 . 66 ac - ft . The bottom of the detention pond is at an elevation of 4887 and the 100 - year water surface is 4891 . 98 . Multiplying the 100 - year volume by 1 . 5 gives a required volume of 8 . 49 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4893 . 76 . The elevation of the spillway is 4895 . 0 . Per the calculations in the Appendix , the length of the spillway will need to be 81 feet long . The 100 - year water depth is approximately 4 . 99 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 59 . 8 hours . Pond S3 , tributary area of 78 . 17 acres . Pond S3 is situated on land that is planned for Open Space . Per the EPA SWMM model , the peak 100 - year flow into Pond S3 is 87 . 22 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 6 . 93 ac - ft . The bottom of the detention pond is at an elevation of 4889 and the 100 - year water surface is 4893 . 45 . Multiplying the 100 - year volume by 1 . 5 gives a required volume of 10 . 39 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4894 . 88 . The elevation of the spillway is 4896 . 00 . Per the calculations in the Appendix , the length of the spillway will need to be 55 feet long . The 100 - year water depth is approximately 4 . 45 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 53 . 5 hours . Pond S4 , tributary area of 304 . 48 acres . Pond S4 is situated on land that is planned for Open Space . Per the EPA SWMM model , the peak 100 - year flow into Pond S4 is 286 . 84 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 26 . 99 ac - ft . The bottom of the detention pond is at an approximate elevation of 4854 and the 100 - year water surface is 4857 . 89 . Multiplying the 100 - year volume by 1 . 5 gives a required volume of 40 . 49 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4859 . 64 . The elevation of the spillway is 4861 . 0 . Per the calculations in the Appendix , the length of the spillway will need to be 275 feet long . The 100 - year water depth is approximately 3 . 89 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 46 . 7 hours . Ponds For East Areas Pond 9 , tributary area of 366 . 6 acres , of which 48 . 0 acres is offsite area from west of CR 39 . All of the tributary area to Pond 9 is undeveloped therefore , 2 percent imperviousness was used in determining the runoff to Pond 9 . The existing pond encroaches onto existing lots within Filing 1 and the existing pond doesn ' t have the County requirement of 1 . 5 times the 100 - year volume for retention ponds . Therefore , Pond 9 will be enlarged to provide the 1 . 5 times the 100 - year volume plus a PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 17 of 21 minimum of one foot freeboard above the water surface associated with the 1 . 5 times the 100 - year volume . Per the EPASWMM model , the peak flow into Pond 9 is 210 . 52 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 28 . 28 ac - ft . The bottom of the retention pond is at an approximate elevation of 4829 and the 100 - year water surface is 4834 . 73 . Multiplying the 100 - year volume by 1 . 5 give the required volume of 42 . 43 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4837 . 05 . The existing elevation of the overflow is 4838 . 66 and is 194 . 4 feet long . Per the calculations in the Appendix , the length of the existing spillway is sufficient to pass the 100 - year developed flow at a flow depth of 0 . 55 ' and therefore no changes to the existing spillway are necessary . The 100 - year water depth is approximately 5 . 73 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 68 . 8 hours . The enlargement of Pond 9 will lower the 100 - year water surface thereby reducing the impacts on the existing residential lots on Filing 1 . With future development on the northside of Beebe Draw Farms Parkway , it is anticipated that would reduce the runoff to Pond 9 . Pond El , tributary area of 80 . 52 acres , of which 19 . 2 acres consists of Filing 1 residential area . Per the EPA SWMM model , the peak flow into Pond E1 is 101 . 80 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 7 . 05 ac - ft . The bottom of the retention pond is at an elevation of 4815 and the 100 - year water surface is 4819 . 87 . Multiplying the 100 - year volume by 1 . 5 gives a required volume of 10 . 57 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4821 . 65 . Since Pond E1 is a temporary pond , no overflow is provided . The 100 - year water depth is approximately 4 . 87 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 58 . 4 hours . Pond E2 , tributary area of 53 . 32 acres . Per the Rational Method model , the peak flow into Pond E2 is 82 . 26 cfs . The County requires 1 . 5 times the 100 - year volume for retention ponds . The 100 - year retention volume is 5 . 06 ac - ft . The bottom of the retention pond is at an elevation of 4803 . 5 and the 100 - year water surface is 4807 . 19 . Multiplying the 100 - year volume by 1 . 5 gives a required volume of 7 . 59 ac - ft of storage . The corresponding water surface for the 1 . 5 times the 100 - year volume is 4808 . 90 . Since Pond E2 is a temporary pond , no overflow is provided . The 100 - year water depth is approximately 3 . 69 feet deep . Using an infiltration rate of 1 inch per hour , the 100 - year volume will drain in approximately 44 . 3 hours . V . VARIANCES The following variances from the Weld County Engineering and Construction Criteria are proposed as a part of this project : 1 . Allowing Retention Ponds • Per section 5 . 10 . 1 " Stormwater retention facilities ( stormwater infiltration facilities ) normally are not allowed in Weld County but shall be considered for special circumstances with the issuance of a variance . Variance requests shall only be considered in situations where there is a proven hardship on the proposed site . A hardship would be considered where there is not adequate PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 18 of 21 topography to physically drain a pond ( sump in basin ) , refusal of an irrigation ditch to accept additional drainage , or some other physical site constraint . " • The proposed project conditions have both hardships . There are multiple large existing depressional areas throughout the development that do not surface drain . With the presence of Type A sandy soils , these areas currently infiltrate into the ground . The proposed design is attempting to minimize disturbance and maintain existing drainage patterns as much as possible by placing retention ponds in the general area of the larger depressions . By doing so , there is no feasible way to drain these ponds with a typical gravity outlet structure , and therefore , runoff entering these ponds will infiltrate into the ground , as is occurring in the existing condition . In addition , The Farmers Reservoir and Irrigation Company who owns and operates the downstream reservoir , does not allow stormwater to discharge into their system . Therefore , all developed runoff is proposed to be captured by retention ponds and infiltrated into the ground with no negative impacts to surrounding areas . 2 . Emergency Spillway • Per section 5 . 10 . 1 , an emergency spillway is required for retention ponds . • Retention Pond W3 is located within a deep natural depression . When the required volume 1 . 5 times the 100 - year , 24 - hour runoff is calculated , the corresponding storage elevation is approximately five feet below the natural overflow point , which discharges off- site to the east . Due to the topography and existing site constraints , it is not feasible to raise the pond elevation without creating a low point directly over an existing oil & Gas facility . As a result , there is no practical way to construct a concrete emergency spillway within the reasonable limits of the pond area that would provide positive drainage . However , there should be no adverse impacts to any proposed lots by omitting the spillway . The pond will infiltrate all runoff and will provide significantly more storage capacity than required , including the necessary freeboard . V . SUMMARY & CONCLUSIONS In summary , the Pelican Lakes project will make use of existing grades to the greatest extent possible , minimize impacts to on - site environmental amenities , provide conveyance of on - and off - site storm flows through the site , and provide storm retention in manner consistent with Best Management Practices . Under the Plan , no adverse impacts to the local community or environment are expected . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 19 of 21 V1 . G NERAL DRAINAGE MAIN ENANC The following is the drainage / site maintenance plan for the project : 1 . At all times , any erosion that may occur shall be corrected as soon as possible to mitigate the chance of sediment leaving the site . 2 . All outlet structures , storm pipes and swales shall be inspected regularly and cleaned if necessary . 3 . Any seeded areas that are not covered with vegetation shall be re - seeded and irrigated as necessary to establish permanent vegetation . 4 . Snow should not be piled in swales or near the detention pond . 5 . Any necessary repairs shall be made as soon as possible . Repairs to privately owned stormwater facilities shall not be the responsibility of Weld County . Retention / Infiltration Pond Maintenance : The following description was taken from the Mile High Flood District Urban Storm Drainage Criteria Manual volume 3 ( November 2010 ) and modified for this specific situation : Inspection Inspect the infiltrating surface at least twice annually following precipitation events to determine if the retention area is providing acceptable infiltration . Retention / Infiltration facilities are designed with a maximum depth for the WQCV of one foot and soils that will typically drain the WQCV over approximately 12 hours . If standing water persists for more than 24 hours after runoff has ceased , clogging should be further investigated and remedied . Additionally , check for erosion and repair as necessary . Debris and Litter Removal Remove debris and litter from the infiltrating surface to minimize clogging of the media . Mowing and Plant Care All vegetation : Maintain healthy , weed - free vegetation . Weeds should be removed before they flower . The frequency of weeding will depend on the planting scheme and cover . When the growing media is covered with mulch or densely vegetated , less frequent weeding will be required . Grasses : When started from seed , allow time for germination and establishment of grass prior to mowing . If mowing is required during this period for weed control , it should be accomplished with hand - held string trimmers to minimize disturbance to the seedbed . After established , mow as desired or as needed for weed control . Following this period , mowing of native / drought tolerant grasses may stop or be reduced to maintain a length of no less than 6 inches . Mowing of manicured grasses may vary from as frequently as weekly during the summer , to no mowing during the winter . Irrigation Scheduling and Maintenance Adjust irrigation throughout the growing season to provide the proper irrigation application rate to maintain healthy vegetation . Less irrigation is typically needed in early summer and fall , while more irrigation is needed during the peak summer months . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 20 of 21 Native grasses and other drought tolerant plantings should not typically require routine irrigation after establishment , except during prolonged dry periods . Sediment Removal and Growing Media Replacement If ponded water is observed in a retention pond for more than 24 hours after the end of a runoff event , maintenance is needed . Maintenance activities to restore infiltration capacity of infiltration facilities will vary with the degree and nature of the clogging . If clogging is primarily related to sediment accumulation on the surface , infiltration may be improved by removing excess accumulated sediment and scarifying the surface with a rake . If the clogging is due to migration of sediments deeper into the pore spaces of the soil , removal , and replacement of a portion of the underlying may be required . The frequency of media replacement will depend on site - specific pollutant loading characteristics . Based on experience to date in the metro Denver area , the required frequency of media replacement is not known . Although surface clogging of the media is expected over time , established root systems promote infiltration . This means that mature vegetation that covers the filter surface should increase the life span of the growing media , serving to promote infiltration even as the media surface clogs . VI LIST OF REFERENCES 1 . Geotechnical Due Diligence Study , Pelican Lakes , Filing 2 , AGW , Project Number 247117 , April 29 , 2025 . 2 . FEMA Flood Insurance Rate Map , Weld County , Colorado Unincorporated Area , Community Panel Number 08123C1935E , January 20 , 2016 . 3 . Weld County Engineering and Construction Criteria , Updated January 2021 . 4 . Weld County Code , Chapter 8 , Article XI — Storm Drainage Criteria 5 . Mile High Flood District , Urban Storm Drainage Design Criteria Manual , V . 1 - 3 , 2001 , latest additions . 6 . Phase III Drainage Report for Beebe Draw Farms Filing 1 , June 1 , 1998 , by Milestone Engineering . 7 . Drainage Letter Beebe Draw Farms and Equestrian Center Filing 1 — Phase 5 , December 29 , 2017 , by Crestone Consultants , LLC . PELICAN LAKE RANCH F ING NO . 2 FINAL DRAINAG REPORT Page 21 of 21 APPENDICES APPENDIX A — Referenced Material APPENDIX B — Hydrologic Calculations APPENDIX C — Hydraulic Calculations APPENDIX D — SWMM Calculations APPENDIX - — Drainage Plans APPENDIXA - RE RENCED ATERIAL i Weld CountyDrinage Code _ - � ► Erg CertIcate of Compliance ealai ` I - " Weld County Case Number : PU DF24 - 0001 _ _ � r N Parcel Number : 121308000014 , 121317100016 and 121309000026 Legal Description , Section / Township / Range : Part of Sections 8 , 9 and 17 , T3N , R65W Date : May 7 , 2025 I Todd A . Johnson , Consultant Engineer for Terra Forma Solutions , Inc . ( Applicant ) , understand and acknowledge that the applicant is seeking land use approval of the case and parcel in the description above . I have designed or reviewed the design for the proposed land use set for in the application . I hereby certify , on behalf of the applicant , that the design will meet all applicable drainage requirements of the Weld County Code with the exception of the variances ) described on the attached exhibits . This certification is not a guarantee or warranty either expressed or implied . Engineer ' s Stamp : epofin �e�ll�ltit � l � � � � �1�/�� , •, ,, rs- : A® .; �� : • .e • me • + %0, �• 5 / 7 / 2 5 4.00 * Ss/ � • • • • • • . . . . • . • • . • . . �� •Variance Request Of Applicable ) / • . . . . t\' \ck��®��,iNAL 1 . Describe the hardship for which the variance is being requested . 2 . List the design criteria of the Weld County Code of which a variance is being requested . 3 . Describe the proposed alternative with engineering rationale which supports the intent of the Weld County Code . Demonstrate that granting of the variance will still adequately protect public health , safety , and general welfare and that there are no adverse impacts from stormwater runoff to the public rights - of - way and / or offsite properties as a result of the project . Retention ponds are not permitted per Section 8 - 11 - 40 - E of the Weld County Code . Additionally , Section 5 . 10 . 1 of the Weld County Engineering and Construction Criteria states : " Stormwater retention facilities ( stormwater infiltration facilities ) normally are not allowed in Weld County but shall be considered for special circumstances with the issuance of a variance . Variance requests shall only be considered in situations where there is a proven hardship on the proposed site . A hardship would be considered where there is not adequate topography to physically drain a pond ( sump in basin ) , refusal of an irrigation ditch to accept additional drainage , or some other physical site constraint . " The proposed project site meets both hardship criteria . The site includes several historic low points that are infeasible to drain by gravity without extreme excavation ( > 50 feet ) or the use of mechanical pumping . Given the presence of Type A sandy soils , these areas currently allow stormwater to infiltrate naturally . The proposed design seeks to minimize disturbance and preserve existing drainage patterns by placing retention ponds in the general area of these larger depressions . Due to the topography , there is no feasible way to drain the proposed ponds using a typical gravity outlet structure . Therefore , runoff entering these ponds will infiltrate into the ground as it does under existing conditions . Furthermore , the Farmers Reservoir and Irrigation Company ( FRICO ) , which owns and operates the downstream Milton reservoir , does not permit stormwater discharges into their system . As a result , all developed runoff will be captured by the proposed retention ponds and infiltrated on site , with no negative impacts to surrounding areas . We are proposing retention ponds due to these historic site constraints . The ponds will be sized for 1 . 5 times the total inflow volume from the 24 - hour , 100 - year event and will include 1 foot of freeboard to the spillway , in accordance with Section 5 . 10 . 1 of the Weld County Engineering and Construction Criteria . The site is composed of highly sandy soils , making it unlikely that water will be retained in the ponds for any longer duration than occurs under current conditions . This proposed condition is also consistent with existing conditions in Filing No . 1 , and the associated maintenance requirements will be similar for the Metropolitan District . Public Works Director/ Designee Review ( If Applicable ) Public Works Director / Designee Name Signature Date of Signature f 1 Approved ❑ Denied Comments : Department of Public Works Development Review 1111 H Street , Greeley , CO 80631 I Ph : 970 - 304 - 6496 www . weldgov . com / departments / public_ works / development _ review 08 / 02 / 2019 i Weld CountyDrinage Code _CertIcate of Compliance it Weld County Case Number : PU DF24 - 0001 _ _ � r N Parcel Number : 121308000014 , 121317100016 and 121309000026 Legal Description , Section / Township / Range : Part of Sections 8 , 9 and 17 , T3N , R65W Date : May 71 2025 I Todd A . Johnson , Consultant Engineer for Terra Forma Solutions , Inc . ( Applicant ) , understand and acknowledge that the applicant is seeking land use approval of the case and parcel in the description above . I have designed or reviewed the design for the proposed land use set for in the application . I hereby certify , on behalf of the applicant , that the design will meet all applicable drainage requirements of the Weld County Code with the exception of the variances ) described on the attached exhibits . This certification is not a guarantee or warranty either expressed or implied . Engineer ' s Stamp : 410.9. . . .1!9/ 5/0 Q • I • � ` , j • • r • � �0, 5 / 7 / 2 5 . � _ ��i Cam . • • • • • • . . . . • • • ' • • . G ~�. Variance Request Of Applicable ) '/�i,,ss�o • • • � �NAL \��` 1 . Describe the hardship for which the variance is being requested . 2 . List the design criteria of the Weld County Code of which a variance is being requested . 3 . Describe the proposed alternative with engineering rationale which supports the intent of the Weld County Code . Demonstrate that granting of the variance will still adequately protect public health , safety , and general welfare and that there are no adverse impacts from stormwater runoff to the public rights - of - way and / or offsite properties as a result of the project . Per Section 5 . 10 . 1 of the Weld County Engineering and Construction Criteria , an emergency spil way is required for all retention ponds . Retention Pond W3 is located within a deep natural depression . When the required volume 1 . 5 times the 100 - year , 24 - hour runoff is calculated , the corresponding storage elevation is approximately five feet below the natural overflow point , which discharges off - site to the east . Due t0 the topography and existing site constraints , it is not feasible to raise the pond elevation without creating a low point directly over an existing Oil & Gas facmlity . As a result , there is no practical way to construct a concrete emergency spillway within the reasonable limits of the pond area that would provide positive drainage . However , there should be no adverse impacts to any proposed lots by omitting the spillway . The pond will infiltrate all runoff and will provide significantly more storage capacity than required , including the necessary freeboard . Public Works Director/ Designee Review ( If Applicable ) Public Works Director / Designee Name Signature Date of Signature f 1 Approved ❑ Denied Comments : Department of Public Works 1 Development Review 1111 H Street , Greeley , CO 80631 I Ph : 970 - 304 - 6496 www . weldgov . com / departments / public_ works / development _ review 08 / 02 / 2019 Hello