HomeMy WebLinkAboutACHD Comments 7.17.03.~ ~~~~
Sherry R.
37th Sfmw4
Susan S. Eastlake, 1st Vice President
Dave Bivens, 2nd Vice President
David E. Wynkoop, Commissioner
John S. Franden, Commissioner
Garden City ID 83714-6499
Phone (208) 387-6100
FAX (208) 387-6391
E-mail: tellusna.ACHD.ada.id.us
July 17, 2003
The Honorable Mayor Robert Corrie, and
Members of the City Council
City of Meridian
33 E Idaho Avenue
Meridian, ID 83642
Subject: Proposed Clearbrook Estates Subdivision
PP 03-007 and VAR 03-072
Dear Mayor and Council Members:
& Development Services
RECEIVED
JUL 2 1 1003
City Of Meridian
City Clerk Office
ACHD has been asked to respond to various drainage issues involving the subject subdivision. Although
many of them are normally addressed during the review of construction drawings as part of final plat
approval, the following is provided to inform the Council of our requirements.
General Drainage Policies
Groundwater separation
ACHD requires a 3-foot separation from the bottom of a detention pond or seepage bed to the high seasonal
groundwater table. To be less than 3 feet, the pond must be lined with an impervious material, such as
bentonite clay.
DEQ requires various levels of separation, depending on which Best Management Practice is used to treat
the stormwater before entering the pond or seepage bed.
Detention ponds
A dry pond has the outlet set at the same elevation as the bottom of the pond. ACHD allows wet ponds
(where the outlet elevation is higher than the pond bottom) when dry ponds are not feasible, with the
requirement that wet ponds must circulate or aerate the water. All ponds, wet or dry, require an outlet for
stormwater. If no outlet is available, and no other remedies are possible (such as seepage beds) due to high
groundwater, the development may be rejected.
Mosquito abatement
ACHD has no requirements related to mosquito abatement, except that ponds must have an outlet to keep
water circulating through it. We are not aware of CC&R's that have addressed this issue.
Ada County Highway District
stormwater treatment
Pollutants are removed from stormwater through accepted Best Management Practices, such as wet ponds,
sand & grease traps, running stormwater through grass-lined swales, etc.
II. Clearbrook Estates Subdivision
Nampa & Meridian Irrigation District
The applicant has applied to discharge their pre-development rate of stormwater runoff into the South
Slough. Based on prior experience, they will likely grant the applicant's request, especially if the adjacent
slough is carrying off excess water, as opposed to delivering it. However, there has been no requirement
previously that ACHD must enter into a third party agreement with NMID and the developer.
Swales for drainage
ACHD has allowed roadside Swales with sand filter bottoms in certain high groundwater situations. Our
policy allows these facilities in subdivisions with lots exceeding one acre in size, but they have also been
problematic, as builders, landscapers or homeowners have occasionally filled in the Swales. We have
allowed a couple of newer subs with lots about 3/ acre in size to utilize Swales, positioned between the
sidewalk and roadway, with an expanded right-of-way, as test cases. To date the developments have not
built out, so no data is available. This option would not be feasible for Clearbrook Estates, due to the depth
and size of the lots, and due to the fact that it has an option to outlet into the South Slough.
Hopefully this information is useful to the City of Meridian in determining how to proceed with the application
for Clearbrook Estates Subdivision. I will be in attendance at your July 22 meeting if clarification is required.
Sincerely,
Bruce G. Mills, P.E., Manager
Righf-of--Way & Development Services
C: Anna Powell
Richard Cook
Gary Inselman
bgm/