Montana Water Quality Use Class

Montana’s surface-water-use classification system bases class assignments primarily on water temperature, fish, and associated aquatic life. Each class has an associated beneficial use. A waterbody supports its beneficial uses when it meets the Water Quality Standards (WQS) established to protect those uses. A waterbody is impaired when any one of its WQS are violated. Determining whether or not a specific use is supported is independent of all other designated uses. For example, a waterbody may partially support aquatic life because of excess nutrients, not support drinking water because of arsenic, but fully support agriculture and industrial uses. Classes A, B, and C are the three most common. Class I is a temporary category assigned to three streams that were grossly impaired when the system was established. Classes A-Closed and A-1 are considered high quality, the principal beneficial use of which is public water supply. The A-Closed class may invoke watershed protection and use restrictions to protect drinking water. Classes B and C each have subsections according to whether they support coldwater or warmwater aquatic life. B-1, B-2, C-1, and C-2 support coldwater aquatic life; B-3 and C-3 support warmwater aquatic life. B and C waters have nearly identical use classifications, but B waters specify drinking water as a beneficial use whereas C waters do not. C-3 streams are suitable for warmwater aquatic life and recreation. Because these streams often contain naturally high total dissolved solids (salinity), their quality is marginal for drinking and agricultural and industrial uses. In August 2003 Montana added four additional classes: D, E, F, and G. The classes include ephemeral streams (E-1, E-2), ditches (D-1, D-2), seasonal or semi-permanent lakes and ponds (E-3, E-4, E-5), and waters with low or sporadic flow (F-1). G-1 waters must be maintained for watering wildlife and livestock and supporting secondary contact recreation and aquatic life, not including fish. These waters are marginally suitable for irrigation after treatment or with mitigation measures and includes “holding water” from coal bed methane development. Note: The classification system designated uses for waterbodies as present at the time of classification in 1955. Waterbodies may now have other realized uses that are not officially designated. In such cases, a waterbody may be reclassified to officially recognize these other uses. Conversely, designated uses cannot be removed from a waterbody without a formal Use Attainability Analysis and approval under rulemaking by the Montana Board of Environmental Review. Streams forming the boundary of Indian Reservations are coded as State of Montana (SOM) waters for practical reasons related to enforcing Federal and Montana water quality standards. In some cases meanders, canals, and ditches that transect the boundary and then reconnect with a border stream are also coded as SOM waters even when they are located in part or entirely within the Indian Reservation. As a result of this coding protocol, if you use the "select by location" procedure to identify streams that are completely within one of the reservations, the resulting selected records may include a small number of streams coded as SOM in the "Authority Entity" field. This is not a mistake and needs to be kept in mind when interpreting selection results. Streams that are not parallel to or located on a border but that cross into and are entirely within an Indian Reservation retain the use class as designated by the ARM description for the watershed they are part of but they are designated as "Not State Jurisdiction" or NSJ in the event table's "Jurisdiction" field and the name of the tribe is recorded in the "Authority Entity" field. The name of the reservation is recorded in the "Area Name" field. Streams that are not parallel to or located on a border but that cross into and are entirely within national parks, wilderness areas or primitive areas are assigned a use class of A-1 as specified by ARM Title 17 Chapter 30 Sub-Chapter 614 (https://deq.mt.gov/files/DEQAdmin/DIR/Documents/legal/Chapters/CH30-06.pdf). The name of the park, primitive area, or wilderness area is recorded in the "Area Name" field of the event table. As a consequence, a stream crossing a border will likely have different use classes on either side of the border.蒙大拿州地表水使用分类系统主要依据水温、鱼类及相关水生生物划定水体类别，每一类水体均对应特定的有益用途。当水体达到为保护该类有益用途而制定的水质标准（Water Quality Standards, WQS）时，即可支持其对应的有益用途；若任一水质标准被违反，则该水体即被认定为受损水体。某一特定有益用途是否可被支持，与其他指定用途相互独立。例如，某水体可能因营养盐过剩而部分支持水生生物用途，因砷含量超标而无法支持饮用水用途，但可完全满足农业与工业用途。 A、B、C三类是最常见的水体类别。I类为临时类别，仅用于系统建立时存在严重受损的三条溪流。A-Closed与A-1类属于高品质水体，其核心有益用途为公共供水；A-Closed类可通过流域保护与使用限制措施保护饮用水源。 B、C两类均根据其支持冷水性还是暖水性水生生物划分亚类：B-1、B-2、C-1、C-2支持冷水性水生生物，B-3与C-3则支持暖水性水生生物。B、C两类的用途分类框架基本一致，但B类将饮用水列为明确的有益用途，而C类未作此规定。C-3类溪流适宜暖水性水生生物生存及休闲活动，由于这类水体通常天然总溶解固体（盐度）含量较高，其水质在饮用水、农业与工业用途方面仅处于边际合格水平。 2003年8月，蒙大拿州新增D、E、F、G四类水体：其中包括暂时性溪流（E-1、E-2）、沟渠（D-1、D-2）、季节性或半永久性湖泊与池塘（E-3、E-4、E-5），以及低流量或间歇性水流水体（F-1）。G-1类水体需维持其功能，用于野生动物与牲畜饮水，同时支持二级接触式休闲活动及非鱼类水生生物；经处理或采取缓解措施后，这类水体可勉强用于灌溉，其中还包括煤层气开发产生的“滞留水”。 注：本分类系统所指定的水体用途，以1955年分类时的现状为准。当前部分水体可能已具备其他未被正式指定的实际用途，此时可对水体重新分类以正式认可这些新增用途。反之，若未经蒙大拿州环境审查委员会（Montana Board of Environmental Review）通过规则制定程序开展正式的用途可达性分析（Use Attainability Analysis）并获得审批，不得移除水体已有的指定用途。 出于执行联邦与蒙大拿州水质标准的实际需求，构成印第安保留地边界的溪流被编码为蒙大拿州（State of Montana, SOM）水体。部分穿越保留地边界并与边界溪流重新连通的河曲、运河及沟渠，即便部分或全部位于印第安保留地内，同样会被编码为SOM水体。按照此编码规则，若通过按位置选择（select by location）流程识别完全位于某一保留地内的溪流，最终选中的记录中可能包含少量在“主管实体”字段中被编码为SOM的溪流——这并非错误，在解读选择结果时需注意这一点。 未沿边界分布或未位于边界之上，但完全穿越并位于印第安保留地内的溪流，仍保留其所属流域的《蒙大拿州行政规章汇编》（Administrative Rules of Montana, ARM）所指定的用途类别，但在事件表的“管辖权限”字段中会被标记为“非州管辖”（Not State Jurisdiction, NSJ），且“主管实体”字段将记录对应部落的名称，“区域名称”字段则记录保留地的名称。 未沿边界分布或未位于边界之上，但完全穿越并位于国家公园、荒野区域或原始区域内的溪流，其用途类别将被指定为符合《蒙大拿州行政规章汇编》第17章第30节第614小节（ARM Title 17 Chapter 30 Sub-Chapter 614，https://deq.mt.gov/files/DEQAdmin/DIR/Documents/legal/Chapters/CH30-06.pdf）规定的A-1类，事件表的“区域名称”字段将记录该公园、原始区域或荒野区域的名称。 因此，穿越边界的溪流在边界两侧可能被赋予不同的用途类别。