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Home My WebLink AboutSDP000000003 Assessment - Groundwater 1977-11-14 NIY OF ALeEj�,�q GO Fv p AL6 �<� JZ y� * hf ®Ti Office of County Engineer 414 EAST MARKET STREET CHARLOTTESVILLE, VIRGINIA 22901 J. HARVEY BAILEY J.ASHLEY WILLIAMS COUNTY ENGINEER ASSISTANT COUNTY ENGINEER MEMORANDUM MARK F.OSBORNE ASSISTANT COUNTY ENGINEER DATE: November 14, 1977 TO: Mary Joy Scala FROM: J. Harvey Bailey1 SUBJECT: Review of Site Plan Application - Rivanna Water and Sewer Authority - A.W.T. Plant Attached hereto are my comments on the captioned subject . George Williams talked with Mr. Krebs , the consultant , today. He says the final clarifiers can be relocated. This leaves the holding ponds as the only real obstruction to the floodway. There is no way to relocate these on the site and have them function. I re- commend approval . cc : George Williams ADVANCED WASTE WATER TREATMENT PLAN Site Plan The County Engineer has received a request from the County Planner and County Zoning Administrator to review the plans which have been submitted by the Rivanna Water and Sewer Authority, for the purpose of determining his opinion on the following matters: 1. Are any structures of the ANT plant located within the floodway of Moores Creek? 2. Is a Landfill permit required? red? A special permit for an ANT plant at this site was granted the Rivanna Water and Sewer Authority by the County in 1974. .This approval required that all structures should be located at or above ground elevation 330, as shown on a drawing prepared by Paul B. Krebs and Associates, Consulting Engineers, entitled "Existing Moores Cree W.W.T.P. Site and Property South of Moores Creek." The design of the facility has now been completed, reviewed and approved by the regulatory agencies, state and federal and the Rivanna Authority has made application to the County for approval of the site plan. A drawing entitled "Moores Creek A.W.T. Plant Overall Layout Appendix," prepared by Paul B. Krebs and Associates, Consulting Engineers, was submitted with the application. This plan shows that during design, the number and size of units which make up the facility were greatly expanded so that the design plan shows several structures located on ground elevations which are below the 330 elevation cited in the special permit of 1974. This will require an amendment to the permit. Because certain structures are located below the 330 elevation, it becomes necessary to determine whether or not any are within the floodway. The Zoning Ordinance defines the floodway of any flood plain as, "the area needed to transmit and discharge the flood water or flood flows of any river or stream." The general flood zone for Moores Creek has been established by the U. S. Corps of Engineers. The division of the flood plain into flood fringe and flood way is to be determined by engineering principals and is site-particular. -2- The County Engineer requested the Rivanna Water and Sewer Authority to prepare a study to show the effect the A.W.T. plant will have on the flooding of Moores Creek and to ascertain the properties that would be thereby effected. This study has been delivered to this office and has been reviewed by the Engineer. A copy of the Rivanna Water and Sewer Authority report was given the Planning Department. The report states that the gas storage sphere and chlorine storage building can be relocated to an elevation above 330. Also since the report was delivered, the Rivanna Authority has been assured by its consultant, Mr. Paul B. Krebs, that the future final clarifies can be removed from the flood plain. There remains the pump stations and the holding ponds that cannot be relocated. Pump stations must be located at the end of the interceptors they are designed to serve. In this instance one pump station is located at the end of the Moores Creek Interceptor, and the other at the outfall line from the Moores Creek Plant, both of which are now in use. This second station makes possible the use of the existing Moores Creek Plant as a part of the future A.W.T. plant. The holding ponds are a requirement of the State Health Department. Their purpose is to prevent the discharge of raw sewage into the receiving stream in the event of a power failure or some other untoward happening. This requires that they be placed at an elevation that allows flows by gravity from the treatment plant. The holding ponds are the major factors to be considered in assessing flood conditions that are altered. Certain structures which are water related are now permitted within the floodway, under the provisions of the Flood Plain Ordinance. At its meeting on November 9, the Board of Supervisors passed a resolution of intent to include pump stations and holding ponds in the category of structures that are permitted in the floodway. If and when this amendment is adopted, the Rivanna Authority will be free to act. Rivanna Water and Sewer Authority calculations indicate that the presence of the holding pond in the flood plain will cause the predicted inteunediate flood elevation to rise 3.68 feet immediately upstream and the corresponding backwater curve will extend approximately 2680 feet upstream. The results of this backwater were -3- plotted on the planographic map of the City of Charlottesville to show the areas and buildings effected. Fran this map study, it appears that an many as nine buildings would experience some degree of flooding that would not occur in the absence of the holding ponds. The Rivanna Water and Sewer Authority should acquire flooding easements from the parties effected in order to compensate the landholder for the additional risk of flooding to which they may be subjected. It is my opinion that: 1. Same of the A.W.T. structures are located within the floodway of Moores Creek. However, they are located as they are in order to fulfill their function respective to the operation of the A.W.T. plant. They should be permitted. 2. A landfill permit is required, particularly for the dikes which faun the holding ponds. This can be reviewed when application for a building permit is made. 3. The Rivanna Water and Sewer Authority should be required to obtain flood ease- ments over those properties that are subject to additional flooding by reason of the construction of the stilling basins, that is, over the area lying between the intermediate flood line, as predicted by the U. S. Corps of Engineers and the intermediate flood line above the stilling basins, as calculated by the Rivanna Water and Sewer Authority. 4. The gas storage sphere, chlorine storage building and final clarifiers shall be located above the 330 elevation, as required in the approved special permit. All other structures shall be allowed to remain in their respective locations, as shown on the plan which accompanies the Rivanna Water and Sewer Authority's site plan application. • 8 SEA 22P 4 9G RIVANNA WATER & SEWER AUTHORITY P. O. BOX 18 • CHARLOTTESVILLE. VIRGINIA 22902 • (804) 977-2970 �OlTESV1UE' • November 10, 1977 Mr. Harvey Bailey _ County Engineering Department Albemarle County 414 E. Market St. Charlottesville, Va. 22902 Re: SP-373 Amendment, AWT Plant Site Plan approval Dear Mr . Bailey: At this time the Rivanna Water Sewer Authority has an application for amendment to SP-373 before the Albemarle Co . Planning Commission, also accompanying this is application for site plan approval for the AWT Plant. The purpose of this letter is to (1) comment on possible effects due to filling in the Moores Creek flood plain for proposed treat- ment units ; (2) comment on the location of the miscellaneous structures also located in the flood plain. Article 9-A, Flood Plain Districts , of the Zoning Ordinances , in paragraph 9-A- 5 and 9-A- 5-6 calls for studies to be submitted to the County Engineer for his approval . I . Emergency Holding Ponds : The original site plan as submitted with SP-373 showed no emergency holding ponds . In the interim between the filing of SP- 373 and the review by the Va . State Health Dept. , of the final plans of the AWT Plant, Va. State wastewater treat- ment plant regulations were amended so that emergency hold- ing ponds became a required treatment facility. Due to space restrictions at the proposed treatment plant site, the ponds were designed to be located below elev. 330. The construction of these holding ponds could possibly cause damage upstream to certain property owners as the flood plain would be constricted at the ponds . To determine the full extent of any possible damage calculations were done to find the changed backwater profile, new backwaters have been plotted on topographical maps and a preliminary reconaisance of the affected area was made. (The topographic maps and calculations are also delivered with this letter) . November 10 , 1977 Page 2 II . Miscellaneous Structures in Flood Plain: 1 . Influent Pump Sta. : This pump station location was deter- mined by the existing influent sewer connection to the original plant. The pump station operating floor elevation will be above 331. 00 (there will be no openings below 331. 00) . Therefore, the station will be immune to damage from the 100 yr. frequency flood. 2 . Gas Storage Sphere : This above ground tank holds methane gas from the digesters . The consultant will move the sphere to an elevation above 331 . 00, thus out of the 100 yr. flood plain. 3 . Effluent Pumping Sta. : This pump station pumps "grey water" to the plants non- potable water system and its location was determined from the existing plant outfall line which will be utilized in the new treatment plant. The consultant has designed this station so that all openings are above the 100 yr . flood elev. 4. Cl2 Storage Building: This structure originally located below elev. 331 . 00 will be moved to a location above the 100 yr. flood plain. 5 . Future Final Clarifer #4 : In discussing the location of this unit with the consultant it is apparent that this location is the only one suitable because of the piping arrangement around the originally planned clarifiers and because of the space limitations of the site. The structure would be situated so that its top walls will be above 331. 00 . Attached to this letter is a stream cross-section which shows the flood plain before and after the building of the proposed clarifer. Summary: It is the Authority' s opinion that the increase in elevation of flood waters caused by the construction of the proposed emergency holding ponds is minimal. The treatment plant structures which are below the 100 year flood plain elev. are protected from the flood and their locations were dictated by existing conditions . (except the future final clarifer #4) . November 10, 1977 Page 3 Please find enclosed the AWT Plant Site Plan on a 1" = 50 ' scale . This map is also to be used by the Planning Dept., and for presentation to the Planning Commission on November 22, 1977 . Thank you for your cooperation in this matter, please call if you have any questions. Sincerely, t“.A6166;it Miflt(64aW(.- hael McGovern Sanitary Engineer MM/rc , Enclosures _,_,t__... ,.. • 5Td 4-0 0 t . . . . „ , . • , . . • ; . . 1 , , , : • , . . . , : , , . . i , . . . • -• : ,, ii : : : . 1 . 1 , ; : : i : I . ' : • :, :_ . .:i , , . : . , , ; ; 1 I • , . .. 1 • I 1 , 1 4 . 1 ' ,O L./.,A././.-- 1,f- . ) ,-...--65 P",t 1 tO(:),% t/V 7 Z./I.IL.1! /G. .4..Vi A( . . . . i • JI • .. .....$.1 ,O. r ,t Lt. tf.E.P,,,e:-... r-ii,' Li Qtj - 1 4)4 4 0 4-1- . • 1 -- 4 - . 1t , . ., I1 , i • . • . ; ' , ' . ' -• ' ' ' 1 ' , 71h : , - ' 11 1 ,,'-' : 1 ' , Ai /1 -fT.(1'5'. c:': h':,::. 11'0.1'7 F. if 1 )92'2.- -cr--1 ,- • . : . 4 • 4 4i,44.-4 4. • 4, : 4 .i --*-t-'-f-1----- ---- , • r i . 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