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Last modified
8/16/2009 3:13:51 PM
Creation date
10/4/2006 7:12:56 AM
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Board Meetings
Board Meeting Date
7/23/2001
Description
CF Section - Changes to Existing Loans - City of Idaho Springs, Idaho Springs Reservoir Rehabilitation Project
Board Meetings - Doc Type
Memo
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<br />. <br /> <br />e <br /> <br />e <br /> <br />. <br /> <br />DISCUSSION <br /> <br />The Idaho Springs Reservoir, located on Chicago Creek, provides storage for the reliable <br />raw water supply to the City of Idaho Springs and the City's service area. The Office of the State <br />Engineer, Dam Safety Branch, has progressively restricted the capacity of the reservoir due to the <br />deteriorated condition of the dam, evidence of seepage, and structural damage of the spillway. <br />Current restriction on the reservoir limits its storage to 120 acre-feet. The reservoir capacity is 270 <br />acre-feet at the crest of the spillway. <br /> <br />Parson's Engineering Science, Inc. of Denver, Colorado completed the feasibility study for <br />the project, in November of 1997. The estimated project cost to address embankment seepage and <br />to repair the spillway area was $1,100,000. <br /> <br />Below is a brief summary of the major project elements and their estimated cost as <br />presented in the original cost estimate: <br /> <br />Planning and Design <br />Dam Rehabilitation <br />Spillway Rehabilitation <br />Construction Insp./Contigencies <br />Total: <br /> <br />= $95,825 <br />= $523,250 <br />= $350,000 <br />= $130.925 <br />= $1,100,000 <br /> <br />The dam and spillway rehabilitation work was bid for construction in the fall of 2000, and <br />was awarded to Harrison Westem Constructiorl Company of Lakewood, Colorado, in August of <br />2000, at a bid price of $1,010,263. The Contractor mobilized on-site in August of 2000 and is <br />currently 50% complete with the project. Prior to and during construction the Contractor has <br />encountered cost overruns. These additional costs can be summarized as follows; cost overruns <br />due to unforeseen changes encountered in the ficeld, design changes incorporated into the project at <br />the time of construction, and changes instituted by the State Engineer's Office not included in the <br />original proj ect cost estimate. <br /> <br />Dam Embankment - Additional costs due to unforeseen chanf!es encountered in the field: <br /> <br />The awarded bid for the dam and spillway rehabilitation work was $137,013 over the <br />project costs presented in the original cost estimate. The original concept for addressing seepage in <br />the dam embankment was to seal the borrow pit area and other apparent seeps with gunite or <br />concrete, perform hot asphalt injection grouting along the dam face, and to install a free draining <br />rock berm along the toe of the dam. Upon uncovering the dam face, however, significant voids, <br />piping, and organics were discovered within the existing embankment area, that required an <br />a1temate design be developed to adequately address the existing seepage. <br /> <br />The modified design, reviewed and approved by the State Engineer's Office, was the <br />placement of a Bentomat CL T Liner, placed in conjunction with various soil zones above and below <br />the liner, extended along the dam face to the existing spillway abutment and past the existing outlet <br />structure. Additionally, the existing rip rap layer over the existing dam face was removed, screened, <br />and reset at a uniform 3-foot thickness across the dam face. This modified dam embankment <br />design is reflected in the Harrison Western's additional construction cost of $137,013. <br />Additionally, the City ofIdaho Springs incurred an additional design cost of $35,000 to address the <br />actual field conditions encountered in the dam face. <br />
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