The URL can be used to link to this page

Browse Search

Home My WebLink About20081217.tiff • J&T Consulting, Inc. id I October 19, 2007 Weld County Public Works Department Attn: Mr. David Bauer 1111 H Street, P.O. Box 758 Greeley, Colorado 80632 RE: Northern Colorado Constructors, Inc. — USR 1394 Amendment- NCCI Pit#1 Drainage Plan & Report Mr. Bauer: We have prepared this report to address the requirements of the Weld County Use by Special Review permit regarding storm drainage for Northern Colorado Constructors, Inc. (NCC) NCCI Pit #1. In the paragraphs to follow please find descriptions of the drainage basins and direct runoff that affects the NCCI Pit #1 site. The 2-year (minor) storm event, along with the 5-year, 10-year, and 100-year(major) storm events were analyzed. Site Location • The proposed project is located in the southeast and northeast quarters of Section 24, Township 6 North, Range 67 West of the 6'h P.M., Weld County, Colorado (See Vicinity Map / Drainage Basins Map on the following page). The property is bounded by private pasture land on the west, by private irrigated agricultural land on the north, by County Road 25 on the east, and by County Road 18 on the south. U.S. Highway 85 is approximately one-half mile east of the project site. Site Description The site generally slopes at one percent or less from south to north. There is an existing gravel mining operation being conducted in the southern portion of the property. Little Dry Creek runs along the western boundary of the property and an irrigation ditch runs along a portion of the east property boundary. A wetland area is present on the west side of the property adjacent to Little Dry Creek. The soils on the site are identified as Aquolls and Aquents, and Bankard sandy loam per the Soil Survey of Weld County (See soils information in Appendix B). The existing vegetation within the site consists of mainly noxious weeds with poor grasses interspersed. A few existing trees are located in the extreme north portion of the property. Existing Drainage Facilities Offsite flows enter the west side of the property and are conveyed either through the site to the to north property boundary or into the existing gravel pit where they are discharged via the pit dewatering activities either into recharge ditches and back into the groundwater aquifer, or into Little Dry Creek, to its historic point of discharge. There is no existing storm sewer adjacent to or entering the site. Little Dry Creek is the only means of conveyance for stormwater runoff in the areas surrounding the subject property. • V 1400 W 122nd Avenue—Suite 120•Westminster CO 80234•Ph: 303-457-0735• Fax:303-920-0343 2008-1217 i • `J ' . ') ` R67W r R66W. ,_/_____:(f.. a ! •85, 0 , (I.c ri j . i r\LL,>. .. .;',.. ' (AA11VoIsmar. e3'►;II :! . \\: ., . A mm a5a sef► 5 277 • - ._ r • Al �' y Y • Y ;.,. . • :+K 5 203 A D ME - - -� A , AREA .• 5 74 +A k'. I 1 k Ni • f• 3 I L 4.4v 19 • 41960 • ( ' ri_ •'. ' c... .c ' Z 0 a 9 •— T 2 N 644 I .eSphai - — Flume Q.B.18 • I >•es o Said Ha! •• 1 • i"../O1•1 t „ 1..i • MCCI PIT #i 8 --, 5 273 • o'..a. I o •, - o c •. k ... • ((( J • � '26 5 3O•/ a . CA r _ • i/ �. a. ti 1 T Ne. •; i,•. O p LEGEND: p i BASIN DELINEATION 0 co • BASIN PATH o il /A\ DESIGN POINT m co io o A DRAINAGE BASIN DESIGNATION 2000 1000 0 2000 c BASIN PERCENT 5 74 BASIN AREA P m IMPERVIOUS SCALE IN FEET O ilkDote: 9/10/07 o © glair Consulting,Inc. Northern Colorado Constructors, Inc. Job No: 06109 ch NCCI Pit #1 Drown: TPY o 1400 W 122nd Avenue-Suite 120 o o Westminster.CO 80234 Vicinity Map / Drainage Basins Map Sc°1e: 1 = 20O L 303-457-0735 Sheet: 1 Of: 1 Mr. Bauer RE: Northern Colorado Constructors, Inc. — USR 1394 Amendment- NCCI Pit#1 • Drainage Plan & Report Page 3 General Concept The proposed operation will be an expansion of the gravel mine at the NCC pit site. The runoff entering and from the site will be directed into the pit during the mining of the site. Dewatering of the pit will be necessary to mine the sand and gravel. Storm discharges that enter the pit will be removed by dewatering operations, which will consist of either pumping from the pit to recharge ditches along the perimeter of the pit and back into the groundwater aquifer, or pumping from the pit into Little Dry Creek to its historic points of discharge. The net affect that this will have on the storm flows during mining will be to increasingly attenuate the peak discharge rate as the extents of the pit are enlarged and as the pit is deepened, providing more incidental storage for stormwater collection. The water that is collected in the pit will be dewatered at a rate of 10 to 20 cfs. Method of Analysis The Colorado Urban Hydrograph Procedure and the UDSWM Hydrograph Routing Procedure were used to model the stormwater flows generated by the basins as permitted in the Urban Storm Drainage Criteria Manual. The report analyzes the 2-year (minor), 5 year, 10 year, and 100-year (major) storm events for the proposed land uses associated with the NCC pit. Drainage Basins According to the FEMA Flood Insurance Rate Map (FIRM) Community Panel Nos. 080266- 0868C and 0866C, revised September 28, 1982, the entire project site lies within Zone A, which • is within the 100-year floodplain. The storm runoff comes from the west and through the NCC pit site. The runoff comes from Basins A, Al, and B, which include the project site, as shown on the Vicinity Map / Drainage Basins Map. The historic and proposed basins are the same. Because there are few developed sites within the basin areas the percent impervious was estimated to be 5% and the initial infiltration rate was calculated to be 4" using a weighted average based on the hydrologic soil groupings for the existing soils for each basin. The proposed use will not change the percent impervious or the infiltration rates of the basins. The basins are all located in agricultural or pasture land use types. The impervious areas are mainly paved roads, houses, and outbuildings so the estimated 5% impervious area is conservative. The individual basin descriptions are detailed below. Calculations for the runoff generated for each basin and for each event are included in Appendix A. Basin A is located west of County Road 23 and just north of Sand Hill Lake. This area consists of 74 acres. The runoff sheet flows through pastures/fields before concentrating and crossing County Road 23 into Basin Al. Basin Al is just east of Basin A on the east side of County Road 23, includes a portion of the project site, and covers an area of 203 acres. The runoff sheet flows through pastures/fields before concentrating and moving north into Little Dry Creek, its historic point of discharge. Basin B is just east of Sand Hill Lake, north of County road 18, west of County Road 25, and contains the remainder of the project site. This area consists of • 273 acres. The runoff sheet flows through irrigated pastures/fields before N 1400 W 122n°Avenue—Suite 120•Westminster CO 80234•Ph: 303-457-0735•Fax:303-920-0343 Mr. Bauer RE: Northern Colorado Constructors, Inc. — USR 1394 Amendment- NCCI Pit#1 Drainage Plan & Report • Page 4 concentrating and moving east into the County Road 25 borrow ditch, its historic point of discharge. Runoff Summary Peak Flow Peak Flow Peak Flow Peak Flow Basin Area Q(2) Q(5) Q(10) Q(100) Basin (Acres) (cfs) (cfs) (cfs) (cfs) A 74 3 28 44 127 Al 203 8 69 107 318 B 273 9 76 120 364 Contributing Peak Flow Peak Flow Peak Flow Peak Flow Design Area Q(2) Q(5) Q(10) Q(100) Point (Acres) (cfs) (cfs) (cfs) (cfs) Al 277 9 71 113 346 • B 273 9 76 120 364 Compliance with Standards This Drainage Report is in compliance with the Weld County Storm Drainage Criteria. Future Designs Future design will be required when the mining operation is reclaimed. Runoff will have to be conveyed through the site and discharged at historic rates as well as the historic points of discharge. Please feel free to contact us if you need any additional information or have any questions or comments. Sincerely, Mr. J.C. York,!P.E. Enclosures: • Appendix A Appendix B ►/I 1400 W 122nd Avenue—Suite 120•Westminster CO 80234•Ph:303-457-0735• Fax: 303-920-0343 • Appendix A • • • N N N Y) C Y 2 0 0 0 0 • LL ¢¢R -. C C ...... CO CO CO CO o M c ,`m c O O O O gE 0 .. 0 000 a m c r U To m L v v a e c am' c m N N It) N C C , 0 0 0 O Q — 0 00 0 0 S. E a G U) N0 N) E Cr) M M m 0000 E 5 o i1 — m to a m m a s o To g$ u) LO N in E > m W £ c c a m m• D a' m a O v c m n E o m ▪ v co Co g m v e o S. ro � > E. o o o o o o o o co y — • o a c m �, y r oo Ar v C E as t c m ... C) E m m ° J mm m 0)d .� 0) 0) V N U d V N .m.. E O No O O a W• e m.. 0 a 3 p O 0 E c l'" _ NM ED ., a• C cu LO m CI) of OU O E ',co m Z' c. CD t-- COr ca Er E E E m „^ - ro as O V S E E 2 E o 0 0 0 O m= 0 N Co t 0 N a r c m o a L° m0) Cucm mco QCO to CO CO n Cu — R CD N N N N Y ID E N N N ID m N 0 0 r r r r co L m Cmg ▪ E m v 0 m N m 0 f t m g E c r co m .C a` c v n m u9 m o 0 j L CO 0 To m • m = r c > z m N m L m C m m E m m _ Qi m t y c o L a a ¢ m c in D E a m c c c c m y 0 = m ~m b b Y) N co :c F vmmmm o al A= • m m 0 a E ., E .3` N N 10.1 O e > • 170P0 €• y 2 0. 5 LL 000 • 0,-00 0 6 • _ 0 0 A N •U U 0 N m m W 0. ✓ 6970000 Ia t 0 0 0 0 W K W �C P3 y �p • 00 E c a a a)o it gun; N A o m U rN N N N N N Jig O 6 co co y 044 f 0 • w 5 A E y E•• K m.-n ea, '- 0 0 A 0 I m g 0 0 0 A E 0 2 0 : N N I r a• U L E Y N M W 2 Pau N- 0 of • o m 6 • C � 0 0 0 0 O = b C N 10 Y Y E 0 m onunn N m N- 01010101 U0000 0 m ry r 0000 0 U 0 U v c E s a` E t CO 0 U 7 'e s m E m E E U m e 0. 2222 0000 0(000 (0wøø 45 KLLKK .= N N N N 0 • w E • P 7 E i E E t << Cm co 0 m m m m .. N In in in • . C 2 n 0 0 0 0 LL C P C a c 0 0 0 0 EF >,3 Y 0 0 0 0 0 0 t _ S n O A y L O O C V C K Z y) in N u() ill C C 0 0 0 0 O C - 0 0 0 0 0 1 a � 0iinin a ; 0000 z _ a 2 pi 0. as , o > a Nn u) in E > m a on c .c c c a v a 8 O a o 6 a a 0t0 r0 O C a O E U Oq C O O m _ m < 0 0 N La _ �6 a a a a - v 6 6 6 6 a a € 0 a � c t y • N N N0. o a ~ t c cc E o o a a y a Ol d w O) O) V N mm a W E b nl M X a 0 on E 6 0 0 0 w ri a 8 a a o a o E c = a E Scm q m CO c j a 0 a >.L m r r CO�p f` CO C- 0 EE QEo000 as a m > > 0 '» U (nm n o `- en C9 ~ c a a) ° m E t c g E g g a s 2 o 0 0 0 n a >` r >` i c E In u) in In a E ° 2 m c n a c n E a 2 a m m ) m 0) o f t a m E c m .co c mYE - a v n a o a r o a a ` $ La E a a E • o La a e > Z Lame a a C N a E 3 a a Q M L c C O L a a Q co . 0 = E a 2 z a a 0 a W -a m 'a m m FL- F o ii-- 0 mmmm L • V m p- m a - E - n m m nn ; n N N N • CCCT _ N m R.r Y v• 6 LL Ir 0 n N rl 6 • -.▪ r P ro C4 C K N-N N N a • nnnn 3 2 e • t o c o 0 w $ w p • m3vo E e a a a o j N"n'om E n n 0) S -N N N s d mm S . n. P N'n z9FuE u I-- m C 7n� 3'0 • PIA r�m • •Sm a E £' n"mn E n I0 N N N d s E co co P N N n Qeam ��oa a; a a •-• C a n m ro C = C N l't Y 0 3E m CO CO in n NNN N j U o 0 0 0 g n a•a•s �aaa p 5 0000 U a C c w E o a` E L m E c m E E o C • a. t n fl @ 0000 �I-NN m m m m O IX WC(IC = in n in n • • E C m E t i c m • G E taaam • • `m `m N U m m m m 2 ! { 6666 • . | t , 22 [ o cola s; 6 ; crek | co lf) 10 in in E 'Ea aiin in LO 10 � | f � S228 f ! ve| © ° ` ° 2 0 3c2) i ! ! t ! k § ) co ; ; w Co a -( 0666 g • u \ g � B8 r glaar `- ° E em 48 8 ® {/ k { , O 0 0 -LLI j § ! { � ) §CU f f \{ E 2EE ! \ j § § § a. ) 0) EEEE | ! 0000 - ce 03 (0 03 CO / k , ! § ` 2 2 c7,wane co a. $ ) T § 11 I" • A; E$ \ � co ! aaam _ ! ! [ E _cccc _ _ _ j / 3 ! ! 4200 ! L m ww n m a— a -, m o a n g a z p 22,2 Y J • T = y e O 0 e N • a O M LL N m m i noa� q u am0f N C N " nbb a W I . ; 2222 • s o 0 0 0 la g W � ;3W8 m 4 P O m O U m-mh O m O m N NO m m • N N N Y • flm Q Y .. a R m • c A iii E W n'-nn y ebe O w mmmn • b C 2 c r N N • S E L aCO 0 m NMN eg � � .dn"a a3aa _T • '_ C C m a ba CO m C = L'. N 17 Y Y 0 3E m cmi mNN N N N N 00 0000 0 mvyn ta m q 5 0 0 0 J u m U v c N E N • E L m9 0 U • m E • E N U m O a J L K W W W A OOOO 0000 KKKK a` >>>> 0000 O • c N i c m m Q E L C C CSitt mC J • m m m m f/1 U mmmm Q O 6 00 2 c 0 • it K L.---.- 03 m c0 O • C T m C 0000 p Y m — 0 0000 otg , y L Y NI-41- V 0 in in in 1n C C 0 0 0 0 0 0 - 0 6 6 6 6 a u) o m E in E u) u) G a In m mM J 0 0 0 0 0 0 W 0 - f a 0 0 ▪ J o > a in Ina in E E > m m a c .c 9 m U o n m a 2 o 0 g c m E a 0 c Jo $ _ maeo D 0 > S. O O O O 0 = a O O O d m Fs v m 0 • N n 0 9L f0 L .. R hOO � � E 00 - - L m m ▪ N 0 0 J u E m a _ m ' m m e .-. O a, N O. 0 0 r N 6 CO m E 0000 m w E a-- uv • c m v c 5 0 m 2 E D = a c w m y c j m V J E 0 • L C (0 !.- cn n RI 0EL L co E 0 „^ rmov $ E 0000 co a co J J a • w' 0m co L• N com•- c 0 0 m 0 € € € € O 0 0 0 0 0 0 EL 0 0 m 0 to m - Y Y Y >- o. 0 0 0 0 0 O E a a m m g rn 2 m 1° m 1° d 0 a E 0 m 0 N C m O) o f m m m E c £ m 'c — m m c `a � -0 n c m N m J L 0 0 CD 0 III) € JE co co To co E • 0 J T >cic Z c- E '` a m 3 c L ' E a o c c c c m a m J 0 't 'W m 'V) 'N co H F u H 0 m m m m 0004-10 = e a m m at E — o N b ` - u m m N g1- j :Ebb • - N- Am ZC amv s a G m LL n n bm • m.--en a W t-mN V d0 4 n b N O C d b b a • a 1 �ebbm • • • x t W W • m1iaE - n m N d d m O • V m ▪ - N P O W h m d 2- ‘- N NN • • • a erne* 211- E r-nn- a b nr eue ea, u s m a • E mNbn E b2 "5"NN ays s E G • co e dNn6 o� Q i vin o rz a• _T • C a b b b O J wa C 0 0 0 0 L 3E m v..- (pm.. NNNN O U 6000 0 mon O N-••••p 6 6 6 6 6 U C m m E N O a` r CO • C V o m 7 'Q s m E m E u m a ssss WiteCX 0000 00 0 0 FFFF mm bb ≥≥≥i 9 0000 0000 0 • e E 5 z m • E r a a • m E E s • 'a'i'm /1 o mmmm • Appendix B • • Ill00* 001 0091444 00S:Pitt 00Z III 0060vty 00904•r4 N o O CNI CU O (a i y V _. f f a V NC.) * I1 '7 e a° • "III""IIIIIS 5Z oa O0 . tit S i ,s if l" ' A ' 1, 4'1 S - (l O CO Ott' t -c I 1' • _ 1 } . . .Ait 0 a O --- e rn O CD N _ fd ..%). Ill y NO aip 2 Bottom Bch a 2 o ii T, oC) ♦J _ y! O � 4 _ _ o . _ N....ed. r_) _ 0-4-.--- 0 o U 03 0 76 ....) . _ .,- - O `i --�r� �' 11 O Z O) /. O O r. f _ 8 M� 1y if) lt is INi CZ 08 03 cNi 2-.. ' a 10 6 o t • f 0 . t 4 ' r ti Nor 0 ` 8 $-..... ; . \the r _ tom+ N \O o Q t O 8_cts ct 0 ,,,, 1 $ oo (n `' U '" lit"i " VO o o v0i O If i lb -. ¢ ii M a co O Z < ZU ill 1 ` 1 ' 1 ' I 1 A'�, OOv 4v4 0G: 744 00R1444 0051444 00Z 1444 0060444 00 0: v: /rS • N . o . C) a) %O O C N 4 To a 0) aN- o o as a) O o n o a) O 'C �, E > ca r l (.) O V co O O V O Q) M - n 0) a) Q) .C - tea) a) N Cl) c rn co, E w DL � c � It �_ cri oc0aE Z a > a O O c0 O O) co ,O o Iii >, E u `c Cl) o rn a) 0 O co > UCL u) t` r _c y n3 N Z a o O E o) a a) a.) C O co N O Q E > C o Cl) O O L (13 E a 0 U ._ Z r a ` y c y o o c a) et 2 ° a� °) O c m ° t Q . O 3 00 ) C ) 2, -) o co -Clawaai LL io c°n 3 ° 3 L E a co ° a) U � a) a ►v EN OC a a) 0E � Z a) N .O (r t 2 a) 0 o a) vs .O a) Wc r m L ? 0 > a`) n. a) E a a - a) 3 m Q E .CO � -; 1-7) cn 0 � cuca) 'ac °>, Z _ — O O N O (U a C E C N L = D - Zcc2eE . a�iN 0) 0 af°ic'vo .E OO -6 >• D Oa, cc) a) a > >. Nco > 0 a) o 0 co 0 O (n v co m L c a sa —_ al o � dcn 2_ COa) t5 co >' 2 a`) am -- � � _ men 0 'o c o 'in a Q f° .C AI a c CC ME E EWE Q > c) ate) oa0 m • om ° — 9 a) ac`f � a) .� cao oa) o •tea) 'OO co � ocoE C O5 o f cn5U I— -.E. cnv) 0 F- o .E o 45 O 0 U) 0 Cl N N a) O ` >. 1 O Q > U a) O CI) (/) 2 C C O • O 0 U a)r- i O) - a) a LU : U ' o to N coV Z N al O O O � ( c�pp m o U t Y o.) _, O -5 a Vo > Z I 11J W J a) 3 a m Q . Cu TO c Cu 5 v -6 N 3 IA f� n O U . >. ,a2 - c �, .co) co m c `O l0 c ± c ¢) Cu m m O o m Q m (3 = N ' v) Nc E O "y, N O a 0 0 0 O j m +.. -e 0 U CD C 'E 2 m 1�0 t_ 1 a) Q U) p) C a m m U U O Z +' U D E O if) w a C D cn O m C m m .. r r CO . to in o ❑ ❑ ❑ ❑ ❑ ❑ ❑ m L o c re m c o v b + cc ° Q v) a. I— v' z 17 Hydrologic Soil Group—Weld County,Colorado,Southern Part NCCI Pit#1 Drainage Area • Hydrologic Soil Group Hydrologic Soil Group—Summary by Map Unit—Weld County,Colorado,Southern Part Map unit symbol Map unit name Rating Acres In AOI Percent of AOI 3 Aquolls and Aquents, D 193.4 36.9% gravelly substratum 10 Bankard sandy loam,o to A 52.9 10.1% 3 percent slopes 69 Valent sand,0 to 3 A 197.4 37.7% percent slopes 70 Valent sand,3 to 9 A 57.1 10.9% percent slopes 72 Vona loamy sand,0 to 3 B 12.6 2.4% percent slopes 73 Vona loamy sand,3 to 5 B 0.3 0.1% percent slopes 74._.._.__... Vona loamy sand,5 to 9 B 10.2 1.9% percent slopes Totals for Area of Interest(AOI) 523.9 100.0% • 4slm Natural Resources Web Soil Survey 2.0 10/17/2007 Conservation Service National Cooperative Soil Survey Page 3 of 4 Hydrologic Soil Group—Weld County,Colorado,Southern Part NCCI Pit#1 Drainage Area • Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D)and three dual classes(A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate(low runoff potential)when thoroughly wet. These consist mainly of deep,well drained to excessively drained sands or gravelly sands.These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet.These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture.These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture.These soils have a slow rate of water transmission. • Group D. Soils having a very slow infiltration rate(high runoff potential)when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (ND, B/D, or C/D),the first letter is for drained areas and the second is for undrained areas.Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff- None Specified Tie-break Rule: Lower • USDA Natural Resources Web Soil Survey 2.0 10/17/2007 Conservation Service National Cooperative Soil Survey Page 4 of 4 Hello