在緬因州的波特蘭市,建築物的停車場或屋頂等非滲透性鋪面若佔地超過1英畝(0.4公頃),現在開始必須根據清淨水源法案申請許可,才能將雨水逕流排放到波特蘭市區周圍的隆溪(Long Creek)流域。
隆溪流域一帶是緬因州成長最快速的區域,近來的各種開發建設包括緬因商城(Maine Mall),州際公路、工業廠房,辦公園區、旅館等,造成非滲透性鋪面增加,更多污染物被雨水沖刷流入隆溪。
非滲透性鋪面的擴增讓雨水逕流的總量及頻率上升,使得隆溪水質惡化,不符合衡量表水健康程度的緬因州水質標準。
美國環保署與緬因州環保部門在12月5日宣佈,要更嚴格管制排放進入隆溪的污染雨水逕流
建物的非滲透性鋪面若超過1英畝,許可制度要求產權擁有者必須透過各種方式減少污染,包括讓雨水能滲入土壤、更頻繁並更徹底清掃街道、在建物內儲存石油、油漆等污染物質更為謹慎,以及進行雨水逕流的其他管理或是溪流復育行動等。
當車輛每次經過或停放在大型停車場與道路,污染物就會累積,包括輪胎磨損殘留的鋅,柴油燃燒產生的鉛,煞車磨損產生的銅等等。污染物質堆積在硬質的表面,之後就被雨水沖刷,不像自然情形下能夠滲入土壤中。
在購物商場、停車場等擁有大範圍鋪面的地點,雨水逕流會將高濃度的沉積物、營養鹽、與有毒金屬帶入附近的水域。每當波特蘭出現明顯降雨的時候,綜合污水下水道便會將雨水與未處理過的廢水一併送進卡司寇 灣(Casco Bay) 。
緬因環境部在1998年確認隆溪周圍出現水質惡化,原因是購物中心、商圈的快速發展。環境部早早便進行許多科學研究,增加對隆溪流域物理、生物與水文特徵的了解。
研究分析結果顯示,影響隆溪的除了雨水從非滲透性鋪面沖刷下來的污染物,該區域雨水逕流的總量也是因素之一。
本次代表保育法律基金會(Conservation Law Foundation),請求環保署針對隆溪污染排放執行許可管制的律師辛屈曼(Steve Hinchman)表示,「雨水逕流已經成為新英格蘭地區水污染的首要原因,如不加以控管,受污染的雨水逕流將摧毀緬因海岸寶貴的海灣與沙灘。」
Properties with more than one acre of impervious area, such as parking lots and large roofs, must from now on apply for a Clean Water Act permit for stormwater discharges to Long Creek, which drains a watershed in the Portland metropolitan area.
Many of the impervious surfaces causing polluted stormwater runoff to Long Creek are the result of recent development in the watershed, one of the fastest growing areas in Maine, including construction of the Maine Mall, Interstate highways and interchanges, industrial facilities, office parks and hotels.
This expansion of impervious cover has caused an increase in volume and frequency of stormwater runoff, a decline in Long Creek water quality, and violations of Maine’s water quality standards, which are measures of the health of surface waters.
The U.S. EPA and the Maine Dept. of Environmental Protection on Friday announced stricter controls on polluted stormwater discharging into Long Creek.
The permits will require that owners of properties with more than one acre of impervious area reduce pollution by allowing stormwater to percolate into soils, by conducting more frequent and thorough street sweeping, by being more careful in storing polluting materials, such as oils and paints, on their property, or by conducting other stormwater management and stream restoration activities.
Stormwater runoff at sites with large paved areas, including shopping malls and parking areas, can deposit concentrated amounts of sediment, nutrients and toxic metals into surrounding waters. In Portland, every time there is measurable rainfall, combined sewer overflows send a mix of rain water and raw sewage into Casco Bay.
Large parking lots and roads collect pollution every time a vehicle drives across them or parks on them. Pollutants include zinc from the wear of automobile tires, lead from diesel fuel combustion, copper from auto brake pad wear and oil from auto engines. Pollutants accumulate on these hard surfaces, and are washed off by rainfall that would otherwise percolate into the soil under natural conditions.
In 1998, DEP identified Long Creek area as an urban watershed suffering water quality degradation caused by rapid development, including malls and commercial sites. Since then, DEP has conducted numerous scientific studies of Long Creek to better understand the physical, biological and hydrological characteristics of the watershed.
This analysis indicates that Long Creek is being harmed not only by the pollutants contained in stormwater from impervious areas, but also by the volume of stormwater these areas generate.
"Stormwater has become a leading source of water pollution in New England," said Steve Hinchman, attorney for the Conservation Law Foundation, which petitioned the EPA to require permits limiting polluted discharges into Long Creek. "Left unchecked, polluted stormwater could destroy the bays and beaches that are the jewels of the Maine Coast."