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Home My WebLink AboutStormwater Site Plan for COM2003-00197 - PLN General - 12/26/2003 MASON COUNTY PUBLIC WORKS DIRECTORICOUNTY ROAD ENGINEER Shehoq Washington 98584 DATE: December 261h, 2003 INTER-DEPARTMENTAL COMMUNICATIONS TO: Rick Mraz, DCD-Planner FROM: Alan A. Tahja, P/W- Co. Hydr. Engr. WON PLG-03 SUBJ: Stormwater Site Plan (SSP) NAME: Cady Office Bldg - Belfair COM2003-00197 Rick, The Stormwater Site Plan(SSP)prepared for the proposed commercial development/redevelopment of the Cady Family/Reid Realty property in Belfair,has been received and reviewed by Public Works. Total infiltration of storm events through a 100 year 24 hour event is promoted as the main destination for collected stormwater runoff. The proposed infiltration gallery is proposed to be preceded by a water quality treatment swale sized to provide treatment for Ecology's Water Quality Design Storm event. The engineer who developed the stormwater site plan has indicated that offsite analysis and mitigation is not necessary due to the intended infiltration of collected stormwater runoff. Normally offsite impacts are not anticipated from sites which are able to infiltrate their stormwater runoff,but the urbanized area of Belfair in which the subject property is located in, has existing problems with a high groundwater table, and wet surface conditions in the down- gradient properties from the Cady property. These existing problems raise the need to ascertain potential surface and sub-surface flows and impacts. Since the high groundwater table problems have been brought to the County Engineer's attention, stormwater features in the general urban Belfair area have been required to employ detention facilities instead of or in concert with retention facilities. Since the Cady property has no apparent surface discharge location, other than sheet flow to neighboring properties or infiltration, it seems apparent that infiltration is almost the only method available short of developing a storm sewer route to an acceptable disposal location. Since infiltration appears to be the most practical and financially appealing stormwater disposal practice, limiting the infiltration rate seems a logical solution to diminishing down-gradient property groundwater problems. If an infiltration facility is pursued as part of the final design, soil exploration information File: H: \WP\St=wtr\Reviews\Cady-Reid Realty.doc reporting, and infiltration rates will need to be determined in accordance with Ecology's Technical Manual procedures (See the Puget Sound Water Quality Authority's Stormwater Management Manual for the Puget Sound Basin version 1992, Chapter III-3). I've discussed these issues with the project engineer(Marley Young,P.E.),and with Jerry Hauth, the County Engineer, and can only report at this time that Public Works cannot recommend acceptance of the currently proposed stormwater site plan. Detaining runoff from the developed site and infiltrating it onsite at a prescribed rate currently appears to be a likely approach to disposing of site developed runoff. Infiltrating stormwater runoff at a downstream erosion control discharge rate has been discussed as a potential infiltration rate,but determining potential impacts from a detention-infiltration facility is expected to be addressed in the Stormwater Site Plan as a potential offsite impact. Please feel free to contact me at County extension 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Si cerely, na.-t—J-2Z z A Ian A. Tahja File: H: \WP\Strmwtr\Reviews\Cady-Reid Realty.doc MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton,Washington 98584 INTER-DEPARTMENTAL COMMUNICATIONS DATE: February 61h, 2004 TO: Rick Mraz, DCD - Planner FROM: Alan A. Tahja, P/W - Co. Hydr. Engr. WO# PLG-04 SUBJ: Stormwater Site Plan (SSP) NAME: Cady/Reid Realty Office Bldg - Belfair COM2003-00197 The revised Stormwater Site Plan (SSP) prepared for the proposed redevelopment of the commercial Cady Family/Reid Realty property in Belfair, has been received and reviewed by Public Works. I've had several discussions with Marley Young, P.E., regarding design approaches, and have discussed the current plan with Jerry Hauth, and feel I can recommend acceptance of the revised stormwater site plan subject to a couple of minor revisions/additions to the proposal. The infiltration pond proposed in the design is located less than 50 feet from a steep (> 15%) slope. Since the proposed location is less than Ecology's minimum setback distance from the slope, a geotechnical report addressing the potential impact of a wet pond on a steep slope should be required to be prepared and submitted to the County for review and comments. The second issue raised by Public Works' review is the need to incorporate an emergency overflow feature on the retention pond. I've discussed these two issues with Mr. Young, who felt both could be addressed to the County's satisfaction. Included in Mr. Young's SSP narrative is a copy of an Operation and Maintenance (O&M) Covenant Form (blank). The Covenant form needs to be appropriately filled out, recorded with the County Auditor's Office, and a copy of the recorded instrument delivered to Public Works for monitoring and administration. I've requested that when the O&M Covenant is prepared for recording, that a copy of the Permanent Stormwater Control Plan(Sheet C2) be recorded with the covenant. Subject to the issues relating to a pond overflow, geotechnical investigation, and inclusion of a portion of the SSP into the O&M Covenant, Public Works considers the proposed Stormwater Site Plan to be acceptable and appropriate for the redevelopment of the subject property. Please feel free to contact me at County extension 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. File: H: \WP\Strmvtr\Reviews\Cady-Reid Realty-2.doc rrvlxrx vRuCK - r'UtJLIIU VVURKS DEPT. (a Date: r)/ (E) Work Order PERMIT 0: �,m �,I _06I S-7 Number: k,, ,�._.•: Requested by:. c� 2- Authorized by: Date: Type of Work: vt E-CHAR�a��C'�.,- der:t ;r 'NXME AGENCY/COMPANY /h V \j cc�T BILLING ADDRESS K rrr, PHONE —7 FRS 4&y.w8w Nison In Cha e: :X•Y:o•,rYvc<aa ...:.�:oK-::kF !+RccY:Y.�xt^:c%>. .. .`Y%vY<'Nl:Y?C>:iv..w:ry.x..:.;;.;.h:Y;Y.hi:4:•^:.:-R.\.Yi-:i:•;vv..•., (c) Project Time Line: (from—.to dates) _ cr c, TO Pro}edt Stet date: _`1-f=`� Esfta(ed Fk4sh DsW: ApR'0°ftage hours: 3 ES711AATEDTOTAL COST ESTIMATE (D) Employ« 112M Syb( FrIpoe% TOTAL$ ! I Em TOTAL n EQUIPMENT USED., MATERIAL USED: NOR- (F) Actual Cost GARS: PROJ P DATE emloy" Q Nww Flours stjmgw FJinat% TOTAL$ EQUIPMENT USED: 14 Vit at TOTAL S'S MATERIAL USED: TOTAL ALL (0) BILLED DATE INV 1 PAID DATE REC.M CKX � l P( E MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton,Washington 98584 INTER-DEPARTMENTAL COMMUNICATIONS DATE: March 8 h, 2004 TO: Rick Mraz, DCD - Planner Michael, Grohs, Bldg Dept.—Bldg Inspector FROM: Alan A. Tahja, P/W- Co. Hydr. Engr. WO#PLC-04 SUBJ: Stormwater Site Plan (SSP) NAME: Cady/Reid Realty Office Bldg - Belfair COM2003-00197 The most recent revised Stormwater Site Plan(SSP dated Feb. 23, 2004)prepared for the proposed redevelopment of the commercial Cady Family/Reid Realty property in Belfair,has been received and reviewed by Public Works. The revised plan addresses issues raised by this department's review dated February 6 h, 2004, and includes geotechnical information relating to the integrity of the proposed retention pond and design infiltration rates. A copy of the recorded Operation and Maintenance (O&M) Covenant(County Auditor's file #1805726)has been received by this office, and is considered complete and acceptable. The retention pond design includes a fine sand filter layer covering the pond floor, and is intended to control the rate at which stormwater runoff is allowed to be percolated into the underlying soils. The project engineer Mr. Marley Young,has been contacted regarding this feature to discuss approaches to ensuring the proposed features perform as designed. This question has also been discussed with and considered by the County Engineer/Public Works Director, Jerry Hauth, and a monitoring plan is requested to be developed by Mr. Young which will be expected to be concluded with a minimum of two reports on the monitored performance of the infiltration feature. The two reports would be expected to cover roughly two 6 month periods of observations with a report of observed or measured performance. If the constructed facilities do not perform within reasonable design perimeters,the infiltration features or elements of the permanent water quality protection plan may need to be re-designed or reconstructed. Please feel free to contact me at County extension 461 if you have any questions regarding these comments, or if you feel additional concerns need further attention. Si ely, r XI An A. Tahja File: H: \WP\St=wtr\Reviews\Cady-Reid Realty-3.doc