Economic Causes of Non-Point Pollution in the Boise River By Roger B. Long and Jinghua Zhang oth point pollutants and non-point pollutants series of drains returns unused and excess water Bare responsible for water pollution. While the to the river near Parma, which is a short distance former can easily be traced to a source, such as a from where the Boise River empties into the Snake manufacturing plant, the latter cannot. Non-point River. By comparing measurements of nitrogen pollution creates a perplexing problem, since it is and phosphorus at Lucky Peak Dam (above Boise) difficult to relate it to specific causes. Although with similar measurements at Parma, an estimate agriculture is believed to be the major cause of of pollution from both urban and rural sources surface-water pollution in the nation today along the river can be made. Contamination (Crutchfiled 1995), urban activity also contributes concentrations vary greatly with the level of to the problem. Exactly who is responsible for stream flow because of the dilution effect. Stream non-point pollution and to what degree are largely flow varies greatly from year to year and within unanswered questions that need to be addressed the year, depending upon the amount of runoff by research. available from snowfall in the mountains. This The Boise River of southern Idaho offers a complicates the analysis of the causes of non-point unique opportunity to study non-point pollution. pollution, because high flows carry more pollut- The river has a relatively pure source of water ants (loads) but also have the effect of diluting from snow melt and is only 60 miles long down- pollution concentrations. stream from the city of Boise. It has two major potential sources of water pollution: urban activity Previous Studies and irrigated agriculture. Boise is located along Long (1976) and Fitzsimmons (1978) studied the river and has been steadily growing over the the impacts of irrigation on water quality and past 20 years. Downstream from Boise is a long- quantified the economic losses that resulted from established irrigated area (primarily flood irri- irrigating land in the Boise Valley nearly 20 years gated) producing up to 60 commercial crops on ago. The impacts on water quality were deter- about 150,000 acres. Along with irrigation are mined by studying and comparing water quality well-established livestock and food-processing parameters associated with irrigation above Boise activities that are supported by irrigated crops. before the water was used for irrigation and at Consequently, upstream pollution primarily Notus, where the Boise River enters the Snake comes from urban activities, while downstream River. The parameters measured were specific pollution is primarily related to agricultural conductivity (an indicator of salts and suspended activities. State and federal environmental agen- solids), three forms of nitrogen, and phosphorus. cies have done much to control point sources of Results showed that the average yearly specific pollution over the past 20 years. Additional sew- conductivity (the ability to conduct electricity) age treatment plants have been constructed in reading at Notus was much higher than at Boise, major urban areas as population has grown. Non- indicating increased concentrations of salts in the point pollution, however, is still a problem. Refer to the map and chart of Boise River Diversions Water is taken from the Boise River above and Drains, 1995 on pages 6 and 7 (centerfold) to Boise and distributed to irrigators downriver. A locate mileage references contained in the text. Cooperative Extension System • Agricultural Experiment Station BUL 783 Boise River at Notus. Nitrogen, phosphorus, and costs were calculated for six crop rotations on six sediment levels were also compared. Results land classes for a representative 320-acre farm. showed that they were much higher near Caldwell Crop budgets were compiled using the “Okla- than below Lucky Peak Dam, implying that homa State Budget Generator.” Costs for sedi- irrigation did impact water quality at that time. ment retention structures were obtained from a Clark and Bauer (1983) established a water construction firm local to the LQ drain. Capital quality monitoring program on the irrigation and ownership costs of long-term investments drainage system in the lower Boise River Valley as were calculated using engineering economics. part of a “208 project” to develop a pollution Sediment reduction resulting from BMPs imple- abatement plan for agricultural lands. The 208- mentation on crop rotations and land classes was project area encompassed irrigated lands along the determined by monitoring studies. Calkins deter- Boise River from Caldwell to the Snake River. The mined the cost-effectiveness of best management area was divided into the following groups based practices in reducing sediment for each crop on watersheds: Conway Drain and Sand Hollow rotation and land class combination by comparing Drain on the north side; Dixie Drain; Ross East the implementation costs to the reduction effi- End Drain; and South Boise Drain on the south ciency of each practice. Cost-effective practices side. Suspended sediment loads (materials in the included vegetative filter strips, mini-basins, river) were calculated on an annual and irrigation buried drain runoff control systems, and sediment season basis. Annual suspended sediment loads basins. Vegetative filter strips on land with 0-2 for the major drains were: Sand Hollow Drain, percent slope showed an increased net income of 11,040 tons; Dixie Drain, 11,900 tons; Ross East 75 percent. For total control of sediment, tailwater Drain, 4,100 tons; and South Boise Drain, 3,260 recovery-pumpback and side-roll sprinklers were tons. It was also found that concentrations of total cost-effective. Practices not cost-effective on all phosphorus and inorganic nitrogen exceeded land classes included semi-automated gated pipe, accepted in-stream criteria in most drains through- gravity-improved management and I-slot sedi- out the year. Calculated total phosphorus loads ment structures. A linear programming model was showed that the drains contribute large quantities used in this study to simulate the least-cost mix of of phosphorus to the Boise and Snake rivers. BMPs achieving varied reductions of sediment in Annual mean concentrations of inorganic nitrogen the entire LQ watershed. Results showed that ranged from 2.20 to 4.80 milligrams per liter (mg/l). simultaneous consideration of crop rotations and Fish were analyzed for pesticide residues in this land classes was possible. Sediment delivery study. Results showed that of the 18 pesticides or reductions of up to 54 percent from the watershed other trace organic factors analyzed, only two, resulted in a modest income penalty of less than 1 DDT and toxaphene, were consistently above percent. Greater sediment control became progres- minimum detection limits. A comparison of total sively more costly with mini-basins and sediment phosphorus concentrations during the irrigation basins being implemented on 0-2 percent-sloped season and the non-irrigation season showed that land. Total sediment control on relatively level there was a slight increase in total phosphorus land (0-2% slope) and side-roll sprinklers on concentrations during the irrigation season. steeper land (2+% slope) decreased income by Therefore, Clark and Bauer concluded that in- nearly 20 percent. creases in phosphorus loads during the irrigation As the above studies indicate, stream pollu- season were due primarily to increased drain tion problems and the means of their solutions discharges during this period. have been studied for almost 20 years. It is also Calkins (1980) provided an economic evalua- known from Idaho Department of Health and tion of best management practices (BMPs) for Welfare sources that additional sewage treatment controlling sedimentation in irrigation return and better farm management practices have been flows. His study area was the LQ drain, a 3,300- adopted over this period. Data, however, are not acre watershed in the Magic Valley of southcentral available regarding the extent of these efforts. The Idaho and the site of a project demonstrating focus of this study is to better establish the rela- sediment control practices. The additional costs of tionships between urban and rural activities BMPs implementated above baseline management associated with pollution in the Boise River. 2 Glade Walker Boise Project, Arrowrock Division, Anderson Ranch Dam. Located on the South Fork of the Boise River, 20 miles northeast of Mountain Home, this earthfill structure is 456 feet high and has a storage capacity of 493,200 acre-feet. Historical Pollution Trends concentrations (mg/l) and total load of pollutants Data on pollution levels have been collected (lb/day). Each method has advantages and disad- by several government agencies at different points vantages. Pollutant concentrations are inversely along the Boise River for the past 40 years. These related to stream flow. When stream flow is high, data help one understand how pollution increases pollutant concentrations are low, and when stream as the river flows from Lucky Peak Dam to Parma. flows are low concentrations are high. On the Pollution indicators that are high near Boise, but other hand, total load (pounds of pollutants) is decline toward Parma, are likely to be caused by directly related to stream flows, that is, larger urban sources. On the other hand, sudden in- volumes of water at low concentration levels carry creases in pollution levels near Parma are more more pollutants. Depending on how one defines likely to be associated with agricultural activities. pollution, the measurement used may influence As is true for much of the United States, even the results. Because the Boise River had relatively common water-quality data have not been col- low flows in the late 1980s and early 1990s, it was lected in a systematic way or for the same periods felt that concentration measurements (mg/l) best of time in the Boise River.