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Home My WebLink AboutOffsite Sewer-Revised Alignment km ENGINEERING 9233 WEST STATE STREET I BOISE,ID 83714 I 208.639.6939 I FAX 208.639.6930 October 22,2014 Project No.: 14-031 Ms.Dinae Edwards City of Meridian 33 E.Broadway Avenue Meridian, Idaho 83642 RE: Hill's Century Farm Offsite Sewer—Revised Alignment Dear Ms. Edwards: Please find included with this letter the latest plans for the Hills Century Farm Offsite Sewer. This letter is to explain the revisions we made to the sewer plans. The Ada County Highway District reviewed the plans and we worked with them to adjust the sewer main alignment near the intersection of W.Amity Road and S.Eagle Road. The proposed sewer main alignment has been moved south of the storm retention pond at said intersection to avoid multiple utility conflicts, trenching within the 5-year pavement cut moratorium, and potential conflicts due to the future widening of the round-about. Should you have questions on this material or need further information,please feel free to call. Sincerely, KM Engineering,LLP rte- MA- Kevin McCarthy,P.E. Principal Engineer cc: Steve Hart,Brighton Corp. Jim Pickard,ACHD Tim Nicholson,ACHD ENGINEERS I SURVEYORS PLANNERS www.kmengllp.com GATEWAY tr%MB J lJ BCOMPANIESI LANODON MAPPIN GasouP - INC. J•U•B ENGINEERS,INC. Technical Memorandum DATE: September 5, 2014 vr CAL *{ . TO: Clint Dolsby, P.E.; Emily Skoro, P.E.FROM: Phil Krichbaum, P.E.; Chris Webb, P.E. %SUBJECT: Master Plan Trunkshed Modification—Hill's Century Farm �� I. Background The City recently reviewed the Hill's Century Farm development application. City policy dictates that new developments extend sewer to and through their property. The application shows a preliminary sewer layout throughout the development with stubs out to the development boundaries, per City policy. Proposed inverts on the southern boundary of the development appear adequate to serve additional master plan service areas not designated in the 2010 Master Plan. A large portion of this development falls within the southeastern most service area of the South Ten Mile Trunk. The South Ten Mile Trunk is composed of two branches, one on each side of the Ten Mile Creek. This analysis looks at the impacts of modifying which service areas flow to each branch of the trunkline. II. Service Area Routing Alternatives Two alternatives were evaluated as described below and shown in Figure 1: 1. Lake Hazel Road Alternative—Blue highlighted area in Figure 1 2. Eagle Road Alternative— Blue and purple highlighted areas in Figure 1 Lake Hazel Road Alternative The 2010 Master Plan shows the area to the south of Lake Hazel Road being served by the west branch of the South Ten Mile Trunk. The service area to the south of Lake Hazel Road flows into master plan manhole MP-874, which has an invert of 2690.04. The stub on the southern edge of the proposed development abutting Lake Hazel Road shows an invert of 2688.82, lower than master plan invert located 430 feet to the west. This stub could serve the master plan service area on the south side of Lake Hazel Road. A small section of the development is located on the west side of Ten Mile Creek. The stub on the southern edge of this part of the development has a preliminary invert of 2681.69, lower than the nearest master plan invert (MP-868 = 2684.14). This stub could provide service for the master plan service area on the northeast corner of Lake Hazel Road and Eagle Road. a 250 South Beechwood Avenue Suite 201,Boise,ID 83709 p 208-376-7330 f 208-323-9336 w www.jub.com Page 2 I.2681.69 ..,',4*. ..- -:-..";7, �ref �.� �. 't` ,218 x:. � � r. x e1 ��.z�. dd ,"' ::al., >�_`. � ...�_-. .�.,.. ' .::,rl� ;1:,,,.t..•.. Y .._.......ten ` p! {: Master Pian Invert *C x i % 1 2684.14 \ r k' I'3Li,i a tb9"ly 1 '� ..,i 'r4 tee..,.,t,e, Proposed Invert 2688.82 trNtie 4+a Master Pian Invert 4 2690.64 rs 1 � 41, Yd Q 'M "^A'i " II,. y 4 t f �i iC, �M'` t. FIGURE 1 —SERVICE AREA ROUTING ALTERNATIVES Eagle Road Alternative This alternative modifies the Lake Hazel Road Alternative by including additional master plan service areas. The master planned 10-inch line in Eagle Road to the south of Lake Hazel Road can be routed to the southern edge of the portion of the development on the west side of Ten Mile Creek. Master plan manhole MP-856 has[ an invert of 2686.66.,A r connection is easily made to the stub described above . 4 with a proposed invert of 2681.69. " Change#1u III. Service Area Modifications t Three minor service area changes were made to `:w accommodate the proposed development and satisfy , *_ �." the Master Plan. Change#1 —A portion of the service area to the south of ill Lake Hazel Road was combined with the service area on the northeast corner of Lake Hazel Road and Eagle Road. y www.jub.com J U B ENGINEERS,Inc. Page 3 r Change#2—The proposed development includes about 27 � `°':nt;. acres on the west of Ten Mile Creek that was originally Change #2 master planned to go to the west branch of the South Ten , t r� , � ` Mile Trunk. �: Change#3—40 acres to the north of the proposed development was originally master planned to be served ` IF1 `''� ' from the general area of the proposed development. The 1. „,,,,,,...1.4:,,,,;,,,,,.,-,,,,,t4t topography is such that it can be served from Eagle Road to .,? r „,,:t.,_.,1:., ' :; R the north of the proposed development. @@� �� , ... A previous analysis for the Nesting Swan development looked at modifications to the service area to the north of Amity Road. These modifications were also included d� in this analysis. �� r Ivo IV. Impacts to Master Plan Pipe Sizes ' � } Lake Hazel Road Alternative 9: . t, t' ; In order to provide meet the design parameters for t .w ., � master planned pipes for the east branch of the South \::,...c, g Ten Mile Trunk, the 15-inch trunk needs to be I Change#3 { extended another 750 feet down Eagle Road. The 12- inch trunk should be extended another 700 feet to receive w i„.:60. " a .,,ii,z,,,,,„:3,-.7-2:,,,, ' flow from the portion of the ` - development on the west side ,„ : ' :., E ..- ft: d xt L.9.'. of Ten Mile Creek. The 10-inch - ! , ttom . trunk serving the southern r ,o- n a s: portion of the development , , 1 ,, o .t. ;1 i; , ;. can be shortened by about 650 ®` ,. �.� �'t ;M ,.s.:), feet and still provide sufficient �� capacity and service depth forN.4.,,,,,,,i,,,,t,,,:0,,,, ” . ,o �' . the expanded southernPlan J. ,a�,�n t' - .. �f The 10-inch trunk serving the northeast portion of the tips t" development and the future "� ,# �M elementary school could be � 3 reduced to an 8-inch line, but it ., 10-inch would be more difficult to serve the future service area to the east. The check line to the l ' future service area to the east _ __ . ; ' .e<, only has 3 feet of cover if the FIGURE 2—LAKE HAZEL ROAD ALTERNATIVE PIPE SIZES line is reduced to 8-inch. If a www.jub.com 1-U-B ENGINEERS,Inc. Page 4 10-inch line is installed, it may '� require a more frequent "`i cleaning cycle due to the <� possibility of low flows. �' The reduction in flows to t . 4 he ` west branch of the South Ten Mile Trunk results in reduced ' ®` z ti pipes sizes as well. An 18-inch trunk is no longer needed for the northern % mile of this t wn �3 branch. A 15-inch trunk is now 'a " ", sufficient. Figure 2 shows the 3; t necessarypipe sizes for this � �� ` alternative. Eagle Road Alternative This alternative further reduces the trunk line size ;on the western branch of the South Ten Mile Trunk to a 12- FIGURE 3—EAGLE ROAD ALTERNATIVE PIPE SIZES inch. The eastern branch would need upsized through the final Messina Meadows phase to an 18-inch trunk. The 15-inch trunk would also need to be extended well into the proposed development as shown in Figure 3. V. Impacts to Other Developments Nearby Several nearby developments are impacted by the alternatives evaluated above, including Whitebark (on-site), Southern Highlands, Messina Meadows and Nesting Swan. The sewer for most of these has been designed and some are currently under construction. Sewer that has already been installed may drive the decision for the current alternative evaluation. Record drawings, if available, should be obtained and reviewed to determine the size and inverts of constructed pipes. VI. Summary The proposed sewer has sufficient depth to serve a significant area beyond the current master plan. Serving the additional area would require changes to master plan pipe sizes downstream. The South Ten Mile trunkshed is served by two branches, one on each side of Ten Mile Creek. Changing which trunk serves the most southeasterly service areas affects pipe sizes on both branches. After review,the City has selected the Lake Hazel Road Alternative as the preferred option. This alternative (see Figure 2) will serve as the Master Plan for the South Ten Mile Trunk going forward. www.jub.com 1-U-B ENGINEERS,Inc.