Item 1: PH on Ordinance Amending Metro Plan (Delta Sand and Gravel)

Home Browse Search

Regarding ground water and the construction of a low permeability barrier, Mr. Cornacchia said several citizens had raised concern that the barrier would raise ground water levels and cause flooding., He stressed that surface and ground water were two different things and, in fact, ground water would move sidewayso.nce it reached the low permeability barrier and would continue to move sideways until it found an open way elsewhere. He reiterated that the water level would not be raised. In response to a question from Lane County Planning Commission member Jozef Zdzienicki regarding the requested variance, Mr. Cornacchia said the request for variance on the west side of the property had been withdrawn but the request for the variance for remaining sides was still valid. In response to a question from Lane County Commission member John Sullivan regarding the letters received and where it was stated that a Traffic Impact Analysis was not required, Ms. Schulz said the written material she had just distributed had an e-mail memorandum where that statement from Lane County Transportation Staff was shown. . Shane Hughes, Principal Engineer for EGR and Associates, noted thatthere had been concern on the part of the opposition about the.low permeability barrier and whether it would cause flooding. Regarding surface ,water aspects, he said anything below the ground did not have anything to do with surface water. He said that during a flooding event it was assumed that the ground was saturated or of low enough permeability that there was no penetration. He called attention to pages 3-5 of his report regarding flood impacts as well as page 18 of the staff report ,'He said there were references to an adjustment to a vertical datum that had been transposed and noted that the actual number was 3.57 feet. He said there were planes of reference that surveyors took their measurements from.including flood elevations. He noted that there were more than one datum and said that the two that were in use for the proceedings were NGVD 29 and NA VD 88. He said all of the site data was on the 88 datum and ~11 of the flood data was on the 29 datum. He said, in order to make the numbers make sense when they were compared with one another they would have to be put on the same plane of reference. He stressed that this had nothing to do with altering flood elevations or FEMA mapping. He also stressed that all of the proposed activity for the proj ect would be done below grade and excavation with no filling above grade or above grade sound berms so there would be nothing to impede flood waters and, In fact, the excavation would buffer against a flood should one occur. In response to a question from Eugene Planning Commission member 'John Belcher regarding whether the low permeability barrier would cause the ground around it to be saturated faster, Mr. Hughes said the measurement of flood in?pacts did not include whether the ground was saturated. He said other experts would testify to the ground water level. He said the commissioners should also consider the excavation volume of the gravel pit itself. In response to a question from Lane County Planning Commission member Steve Dignam regarding whether it was his contention that there was no increased risk of flooding as a result of the project, Mr. Hughes stressed that there was zero chance of increased flooding. Ii1 response to a question from Mr. Zdzienicki regarding whether it was his contention that there would be no risk of flooding because of the installation of the low permeability barrier, Mr. Hughes said the low permeability barrier surrounding certain sides of the pit was designed to not allow ground water tables to be drawn down. He reiterated that this activity would have nothing to do with surface waterflooding or the analysis of surface water. Mr. Zdzienicki said the reason for the low permeability barrier was to prevent ground water from adjoining properties to seep into the pit. MINUTES-La~e' County Planning Commission Eugene Planning Commission January 17, 2006 3